This study site was used by researchers to examine a portion of the Oman–United Arab Emirates ophiolite’s metamorphic sole. Credit: Tyler Ambrose
When two of Earth’s tectonic plates collide, the heavier plate is forced underneath and back into the mantle in a process called subduction. During the early stages of newly initiated subduction zones, the uppermost part of the downward traveling plate can detach and accrete to the base of the overriding (upper) plate. Later, these slices can be exposed at Earth’s surface and are known as metamorphic soles.
Soles provide direct evidence of conditions in the subduction zone; however, their interpretation is clouded by uncertainties surrounding how the sole accretes to the base of the upper plate and the process by which it is then exhumed from within the subduction zone. Ambrose et al. attempt to trace this sequence of events by mapping the evolution of the sole’s texture, the arrangement and orientation of a rock’s component minerals. They do so in a region of well-exposed oceanic crust in the United Arab Emirates.
The authors extracted 16 thin sections distributed across a 250-meter exposed section of the sole. The scientists then performed extensive laboratory testing on 10 of the samples. Using the observed mineral distribution and composition, they deduced a gradient in temperature but not pressure across the sole. This gradient implies that the sole attached to the upper plate in layers as the region cooled but that the entire accretion of the sole occurred at depths of 30–40 kilometers.
The study concludes by outlining a three-step sequence for the evolution of the metamorphic sole. At the onset of subduction, the oceanic crust sinks to a depth of 30–40 kilometers and is heated to temperatures of 700°C–900°C. Then, during peak metamorphic conditions, increased viscosity during the formation of a granulite facies (a kind of metamorphic rock that contains minerals) assemblage causes the subduction plate boundary to migrate deeper into the slab, leaving behind the high-temperature portion of the sole. Finally, as the region cools, the sole grows with layers at similar pressures but increasingly lower temperatures.
Reference:
T. K. Ambrose et al, Burial, Accretion, and Exhumation of the Metamorphic Sole of the Oman‐UAE Ophiolite, Tectonics (2021). DOI: 10.1029/2020TC006392
Note: The above post is reprinted from materials provided by Eos, hosted by the American Geophysical Union.
Early lineages of mammal like this large Gobiconodon from Mongolia, outcompeted the ancestors of modern mammals in the time of dinosaurs. Credit: Corbin Rainbolt
A new study led by researchers from the Oxford University Museum of Natural History, University of Oxford and the University of Birmingham for Current Biology has used new methods to analyse the variability of mammal fossils, revealing extraordinary results: it was not dinosaurs, but possibly other mammals, that were the main competitors of modern mammals before and after the mass extinction of dinosaurs.
The study challenges old assumptions about why mammals only seemed to diversify, becoming larger and exploring new diets, locomotion and ways of life, after the extinction of the non-bird dinosaurs. It points to a more complex story of competition between distinct mammal groups. The new research also highlights the importance of testing old and established ideas about evolution using the latest statistical tools.
“There were lots of exciting types of mammals in the time of dinosaurs that included gliding, swimming and burrowing species, but none of these mammals belonged to modern groups, they all come from earlier branches in the mammal tree.” said Dr Elsa Panciroli, a researcher from the Oxford University Museum of Natural History and a co-author of the study. “These other kinds of mammals mostly became extinct at the same time as the non-avian dinosaurs, at which point modern mammals start to become larger, explore new diets and ways of life. From our research it looks like before the extinction it was the earlier radiations of mammals that kept the modern mammals out of these exciting ecological roles by outcompeting them.”
Most of the mammal species alive today trace their origins to groups that expanded explosively 66 million years ago, when a mass extinction killed all non-bird dinosaurs. It was traditionally thought that, before the extinction, mammals lived in the shadow of the dinosaurs. They were supposedly prevented from occupying the niches that were already occupied by the giant reptiles, keeping the mammals relatively small and unspecialised in terms of diet and lifestyle. It appeared that they were only able to flourish after the dinosaurs’ disappearance left these niches vacant.
However, new statistical methods were used to analyse how constrained different groups of mammals were in their evolution before and after the mass extinction. These methods identified the point where evolution stopped producing new traits and started producing features that had already evolved in other lineages. This allowed the researchers to identify the evolutionary “limits” placed on different groups of mammals, showing where they were being excluded from different niches by competition with other animals. The results suggest that it may not have been the dinosaurs that were placing the biggest constraints on the ancestors of modern mammals, but their closest relatives.
The study looked at the anatomy of all the different kinds of mammals living alongside dinosaurs, including the ancestors of modern groups, also known as therians. By measuring how frequently new features appeared, such as changes in the size and shape of their teeth and bones, and the pattern and timing of their appearance before and after the mass extinction, the researchers determined that the modern mammals were more constrained during the time of the dinosaurs than their close relatives. This meant that while their relatives were exploring larger body sizes, different diets, and novel ways of life such as climbing and gliding, they were excluding modern mammals from these lifestyles, keeping them small and generalist in their habits.
“This result makes very little sense if you assume that it was the dinosaurs constraining the therians” said Dr Neil Brocklehurst of the University of Oxford, who led the research. “There is no reason why the dinosaurs would be selectively competing with just these mammals and allowing others to prosper. It instead appears that the therians were being held back by these other groups of mammals.”
The researchers suggest the extinction of other mammal groups was more important in paving the way for modern mammal success. As further evidence for this, the researchers looked at body size in different mammal groups. They discovered that both the smallest and largest mammals showed the same release from constraints following the dinosaur extinction, suggesting that size made little difference to their success.
Co-author Dr Gemma Benevento of the University of Birmingham said, “Most of the mammals that lived alongside the dinosaurs were less than 100g in body mass — that’s smaller than any non-bird dinosaur. Therefore, these smallest mammals would probably not have been directly competing with dinosaurs. Despite this, small mammals show diversity increases after the extinction which are just as profound as those seen in larger mammals.”
Dr Brocklehurst added, “Palaeontology is undergoing a revolution. We have greatly expanded the toolkit available to analyse large datasets and directly test our ideas about evolution. Most studies of the mammal radiation have focused on how fast they evolved, but analysing what limits there were on the evolution provides new perspectives. We have had to rethink many of our theories using these state-of-the-art approaches.”
Reference:
Neil Brocklehurst, Elsa Panciroli, Gemma Louise Benevento, Roger B.J. Benson. Mammaliaform extinctions as a driver of the morphological radiation of Cenozoic mammals. Current Biology, 2021; DOI: 10.1016/j.cub.2021.04.044
A cross-section of an 18.5 million-year-old fossil of Ampelorhiza heteroxylon. Credit: Nathan Jud/Provided
An 18.5 million-year-old fossil found in Panama provides evidence of a new species and is the oldest reliable example of a climbing woody vine known as a liana from the soapberry family. The discovery sheds light on the evolution of climbing plants.
The new species, named Ampelorhiza heteroxylon, belongs to a diverse group of tropical lianas called Paullinieae, within the soapberry family (Sapindaceae). More than 475 species of Paullinieae live in the tropics today.
Researchers identified the species from fossilized roots that revealed features known to be unique to the wood of modern climbing vines, adaptations that allow them to twist, grow and climb.
The study, “Climbing Since the Early Miocene: The Fossil Record of Paullinieae (Sapindaceae),” was published April 7 in the journal PLOS ONE.
“This is evidence that lianas have been creating unusual wood, even in their roots, as far back as 18 million years ago,” said wood anatomist Joyce Chery ’13, assistant research professor in the School of Integrative Plant Science, Plant Biology Section, in the College of Agriculture and Life Sciences, and a corresponding author of the paper.
“Before this discovery, we knew almost nothing about when or where these lianas evolved or how rapidly they diversified,” said first author Nathan Jud, assistant professor of plant biology at William Jewell College and a former Cornell postdoctoral researcher.
Panama was a peninsula 18.5 to 19 million years ago, a volcanic landscape covered with tropical forest in North America and separated from South America by a Central American seaway. While these forests contained North American animals, the plants mostly descended from South American tropical plants that had dispersed across the seaway, Jud said.
“The fossil we described is the oldest macrofossil of these vines,” he said, “and they were among the plants that made it to North America long before the Great American Biotic Interchange when large animals moved between the continents some 3 million years ago.”
In the study, the researchers made thin slices of the fossil, examined the arrangements and dimensions of tissues and water conducting vessels under a microscope and created a database of all the features. They then studied the literature to see how these features matched up with the living and fossil records of plants.
“We were able to say, it really does look like it’s a fossil from the Paullinieae group, given the anatomical characteristics that are similar to species that live today,” Chery said.
During their analyses, the researchers identified features that are characteristic of lianas. Most trees and shrubs have water-conducting tissues (which transport water and minerals from roots to leaves) that are all roughly the same size when viewed in a cross-section; in vines, these conduits come in two sizes, big and small, which is exactly what the researchers discovered in the fossil.
“This is a feature that is pretty specific to vines across all sorts of families,” Chery said.
The two vessel sizes provide insurance for a twisting and curving plant, as large vessels provide ample water flow, but are also vulnerable to collapse and develop cavities that disrupt flow. The series of smaller vessels offers a less vulnerable backup water transport system, Chery said.
Also, cross-sections of the wood in trees and shrubs are circular, but in the fossil, and in many living vines, such cross-sections are instead irregular and lobed.
Thirdly, on the walls of those vascular vessels, they found long horizontal perforations that allow for water to flow in lateral directions. That is a distinguishing feature of lianas in the soapberry family, Chery said.
In future work, now that they can place the lianas of Sapindaceae to 18.5 million years ago, the researchers intend to continue their investigation of the evolutionary history and diversification of this family. Chery also plans to investigate how wood has evolved in this group of vines, including identifying the genes that contribute to lobe-shaped stems.
The study was partly funded by the National Science Foundation.
Reference:
Nathan A. Jud, Sarah E. Allen, Chris W. Nelson, Carolina L. Bastos, Joyce G. Chery. Climbing since the early Miocene: The fossil record of Paullinieae (Sapindaceae). PLOS ONE, 2021; 16 (4): e0248369 DOI: 10.1371/journal.pone.0248369
Note: The above post is reprinted from materials provided by Cornell University. Original written by Krishna Ramanujan.
The Earth has a layered internal structure with the crust, upper mantle, mantle transition zone, lower mantle, outer core, and inner core from the surface to the center. In the Earth’s formation stage at approximately 4.6 billion years ago, the heavy metal components were separated from silicates and sank in the magma ocean, and a core formed at the center of the Earth. In this core-mantle separation process, partitioning of noble gases between the core and mantle occurred. Credit: Taku Tsuchiya, Ehime University
Noble gases, including helium, neon, and argon, are characterized by high chemical inertness which causes low reactivity with other materials and high volatility. Among them, 3He, 20Ne, and 36Ar are particular isotopes which were components of the primordial solar nebula existing in space before the Earth had formed. 3He is also known to have been produced by the Big Bang and a substantial amount is contained in ocean island basalts, e.g., Loihi Seamount, Hawaii (e.g., Dixon et al., 2000). Such basalts are hot spot rocks which originated in the Earth’s deep interior, indicating that 3He was stored somewhere in the deep Earth. It is surprising that such primordial helium has been confined in the Earth’s interior for 4.6 billion years, from the time of the Earth’s formation to now, even though noble gases are highly volatile. Considering the vigorous mantle convection throughout the geological time scale (e.g., Van der Hilst et al., 1997; Wang et al., 2015), it would seem unlikely that noble gases would be trapped inside the Earth so long. Although it has been suggested that the candidates for the location of the reservoir of primordial helium are the deepest mantle and the core (image 1), its location remains unclear. This is one of the biggest mysteries in deep Earth science and still under intense debate.
The outer core, composed mainly of liquid iron, is a candidate for the reservoir of primordial helium, and there is a possibility that helium is supplied from this area to the mantle. Such noble gases could be carried up to the surface with upwelling mantle plumes. This seems a reasonable scenario to explain the fact that rocks collected in the active hot spot areas, such as in Loihi Seamount and Iceland, contain high concentrations of primordial noble gases. If the outer core is the reservoir of noble gases, the necessary amounts would have to be dissolved in liquid iron under high pressure. However, previous experimental studies reported that at relatively low pressures from 1 atm to 20 GPa, noble gases generally prefer silicates (the mantle) to metals (the core) (e.g., Bouhifd et al., 2013). (The property by which a particular solute is dissolved into different coexisting solvents in different amounts is called element partitioning.) On the other hand, there exists no study so far which has investigated the property of metal/silicate partitioning of noble gases at pressures of 10 GPa to 100 GPa, corresponding to the conditions where the Earth’s proto core reacted with the magma ocean in the early stage of the Earth’s formation. Therefore, it is hard to exclude the possibility that the core is a reservoir of noble gases. If noble gases change to prefer metals with increasing pressure (a property called siderophile), more could be dissolved into the core, and it is important to clarify the partitioning properties of noble gases.
Precise experimental measurements of elements partitioning under high pressure are quite difficult, so in this study, by means of the quantum mechanical computer simulation technology called the ab initio method, the partitioning properties of helium and argon between liquid iron and molten silicate (magma) were investigated in the wide pressure range of 20 GPa to 135 GPa. Computer simulations of element partitioning were conducted by calculating the reaction energies when noble gases are dissolved into liquid iron and molten silicate. By comparing these reaction energies, the relative differences in the equilibrium of the noble gas concentrations in coexisting liquid iron and molten silicate could be estimated. Based on the fundamental principle of thermodynamics, noble gases are dissolved more into a solvent with a smaller reaction energy, and thus larger differences in the reaction energies more greatly enhance the contrast in the noble gas concentrations in liquid iron and molten silicate. Special techniques are required to compute the reaction energies of noble gases with liquids such as liquid iron and molten silicate. In this study, this was conducted by combining a method called the thermodynamic integration method, authorized by statistical mechanics, with the ab initio molecular dynamics method.
The calculations of the partitioning properties of noble gases between liquid iron and molten silicate obtained by these original techniques indicate for the first time in the world that noble gases remain, preferring molten silicate to liquid iron up to the core-mantle boundary pressure (135 GPa), and there is no distinct increase in their siderophility. The amount of helium dissolved in the core in the early stage of the Earth’s formation is considered to be approximately 1/100 of the amount dissolved in the mantle. (In contrast, argon is found to become more siderophile with increasing pressure. The different high-pressure behaviors are caused by the different atomic sizes of helium and argon.) This result, showing no considerable pressure effects, suggests that the core is unsuitable as the primordial reservoir, but the estimated total amount of 3He stored in the core is, even if only 1/100, enough to explain the 3He flux measured in the present hot spots.
Even though 100 times more helium was dissolved into the magma ocean, most of it would have evaporated into the air while it solidified and only marginal amounts would be left due to its high volatility. In contrast, helium dissolved in the core during the proto core formation in the magma ocean was confined to the core after the magma ocean solidified. It is considered that such helium has been gradually seeping into the mantle across the core-mantle boundary and ascending to the surface with upwelling plumes over a long period of time. It can be measured in the hot spot rocks even now. These results provide conclusive support showing that the 3He reservoir is at the core. This is an important insight for the location of the primordial reservoir, one of the long-standing mysteries in geoscience.
Reference:
Zhihua Xiong et al. Helium and Argon Partitioning Between Liquid Iron and Silicate Melt at High Pressure, Geophysical Research Letters (2020). DOI: 10.1029/2020GL090769
Note: The above post is reprinted from materials provided by Ehime University .
Hesperornis image provided by the Yale Peabody Museum of Natural History. (Photo: Robert Lorenz)
If paleontologists had a wish list, it would almost certainly include insights into two particular phenomena: how dinosaurs interacted with each other and how they began to fly.
The problem is, using fossils to deduce such behavior is a tricky business. But a new, Yale-led study offers a promising entry point — the inner ear of an ancient reptile.
According to the study, the shape of the inner ear offers reliable signs as to whether an animal soared gracefully through the air, flew only fitfully, walked on the ground, or sometimes went swimming. In some cases, the inner ear even indicates whether a species did its parenting by listening to the high-pitched cries of its babies.
“Of all the structures that one can reconstruct from fossils, the inner ear is perhaps that which is most similar to a mechanical device,” said Yale paleontologist Bhart-Anjan Bhullar, senior author of the new study, published in the journal Science.
“It’s so entirely dedicated to a particular set of functions. If you are able to reconstruct its shape, you can reasonably draw conclusions about the actual behavior of extinct animals in a way that is almost unprecedented,” said Bhullar, who is an assistant professor of earth and planetary sciences and an assistant curator at the Yale Peabody Museum of Natural History.
Working with colleagues at the American Museum of Natural History, Bhullar and first author Michael Hanson of Yale compiled a matrix of inner ear data for 128 species, including modern-day animals such as birds and crocodiles, along with dinosaurs such as Hesperornis, Velociraptor, and the pterosaur Anhanguera.
Hesperornis, an 85-million-year-old bird-like species that had both teeth and a beak, was the inspiration for the research. The Yale Peabody Museum of Natural History has the world’s only three-dimensional fossil that preserves a Hesperornis inner ear.
“I was aware of literature associating cochlear dimensions with hearing capability, and semicircular canal structure with locomotion in reptiles and birds, so I became curious as to how Hesperornis would fit into the picture,” said Hanson, a graduate student at Yale.
Hanson and Bhullar analyzed the Hesperornis inner ear with CT scanning technology to determine its three-dimensional shape.
Next, the researchers conducted the same analysis with a variety of other fossils — and current species — to determine whether the inner ear provided strong indications of behavior. In many cases, the researchers created 3D models from crushed or partially-crushed skull fossils.
After assembling the data, the researchers found clusters of species with similar inner ear traits. The clusters, they said, correspond with the species’ similar ways of moving through and perceiving the world.
Several clusters were the result of the structure of the top portion of the inner ear, called the vestibular system. This, said Bhullar, is “the three-dimensional structure that tells you about the maneuverability of the animal. The form of the vestibular system is a window into understanding bodies in motion.”
One vestibular cluster corresponded with “sophisticated” fliers, species with a high level of aerial maneuverability. This included birds of prey and many songbirds.
Another cluster centered around “simple” fliers like modern fowl, which fly in quick, straight bursts, and soaring seabirds and vultures. Most significantly, the inner ears of birdlike dinosaurs called troodontids, pterosaurs, Hesperornis, and the “dino-bird” Archaeopteryx fall within this cluster.
The researchers also identified a cluster of species which had a similar elongation of the lower portion of the inner ear — the cochlear system — that has to do with hearing range. This cluster featured a fairly large group of species, including all modern birds and crocodiles, which together form a group called archosaurs, the “ruling reptiles.”
Bhullar said the data suggest that the cochlear shape’s transformation in ancestral reptiles coincided with the development of high-pitched location, danger, and hatching calls in juveniles.
It implies that adults used their new inner ear feature to parent their young, the researchers said.
“All archosaurs sing to each other and have very complex vocal repertoires,” Bhullar said. “We can reasonably infer that the common ancestors of crocodiles and birds also sang. But what we didn’t know was when that occurred in the evolutionary line leading to them. We’ve discovered a transitional cochlea in the stem archosaur Euparkeria, suggesting that archosaur ancestors began to sing when they were swift little predators a bit like reptilian foxes.”
Co-authors of the study are Mark Norell and Eva Hoffman of the American Museum of Natural History.
The Yale Department of Earth & Planetary Sciences, the Yale Institute for Biospheric Studies, the American Museum of Natural History, and the National Science Foundation funded the research.
Reference:
Michael Hanson, Eva A. Hoffman, Mark A. Norell, Bhart-Anjan S. Bhullar. The early origin of a birdlike inner ear and the evolution of dinosaurian movement and vocalization. Science, 2021; 372 (6542): 601 DOI: 10.1126/science.abb4305
Note: The above post is reprinted from materials provided by Yale University. Original written by Jim Shelton.
In the 150 years since Charles Darwin speculated that humans originated in Africa, the number of species in the human family tree has exploded, but so has the level of dispute concerning early human evolution. Fossil apes are often at the center of the debate, with some scientists dismissing their importance to the origins of the human lineage (the “hominins”), and others conferring them starring evolutionary roles. A new review out on May 7 in the journal Science looks at the major discoveries in hominin origins since Darwin’s works and argues that fossil apes can inform us about essential aspects of ape and human evolution, including the nature of our last common ancestor.
Humans diverged from apes — specifically, the chimpanzee lineage — at some point between about 9.3 million and 6.5 million years ago, towards the end of the Miocene epoch. To understand hominin origins, paleoanthropologists aim to reconstruct the physical characteristics, behavior, and environment of the last common ancestor of humans and chimps.
“When you look at the narrative for hominin origins, it’s just a big mess — there’s no consensus whatsoever,” said Sergio Almécija, a senior research scientist in the American Museum of Natural History’s Division of Anthropology and the lead author of the review. “People are working under completely different paradigms, and that’s something that I don’t see happening in other fields of science.”
There are two major approaches to resolving the human origins problem: “Top-down,” which relies on analysis of living apes, especially chimpanzees; and “bottom-up,” which puts importance on the larger tree of mostly extinct apes. For example, some scientists assume that hominins originated from a chimp-like knuckle-walking ancestor. Others argue that the human lineage originated from an ancestor more closely resembling, in some features, some of the strange Miocene apes.
In reviewing the studies surrounding these diverging approaches, Almécija and colleagues with expertise ranging from paleontology to functional morphology and phylogenetics discuss the limitations of relying exclusively on one of these opposing approaches to the hominin origins problem. “Top-down” studies sometimes ignore the reality that living apes (humans, chimpanzees, gorillas, orangutans, and hylobatids) are just the survivors of a much larger, and now mostly extinct, group. On the other hand, studies based on the “bottom-up”approach are prone to giving individual fossil apes an important evolutionary role that fits a preexisting narrative.
“In The Descent of Man in 1871, Darwin speculated that humans originated in Africa from an ancestor different from any living species. However, he remained cautious given the scarcity of fossils at the time,” Almécija said. “One hundred fifty years later, possible hominins — approaching the time of the human-chimpanzee divergence — have been found in eastern and central Africa, and some claim even in Europe. In addition, more than 50 fossil ape genera are now documented across Africa and Eurasia. However, many of these fossils show mosaic combinations of features that do not match expectations for ancient representatives of the modern ape and human lineages. As a consequence, there is no scientific consensus on the evolutionary role played by these fossil apes.”
Overall, the researchers found that most stories of human origins are not compatible with the fossils that we have today.
“Living ape species are specialized species, relicts of a much larger group of now extinct apes. When we consider all evidence — that is, both living and fossil apes and hominins — it is clear that a human evolutionary story based on the few ape species currently alive is missing much of the bigger picture,” said study co-author Ashley Hammond, an assistant curator in the Museum’s Division of Anthropology.
Kelsey Pugh, a Museum postdoctoral fellow and study co-author adds, “The unique and sometimes unexpected features and combinations of features observed among fossil apes, which often differ from those of living apes, are necessary to untangle which features hominins inherited from our ape ancestors and which are unique to our lineage.”
Living apes alone, the authors conclude, offer insufficient evidence. “Current disparate theories regarding ape and human evolution would be much more informed if, together with early hominins and living apes, Miocene apes were also included in the equation,” says Almécija. “In other words, fossil apes are essential to reconstruct the ‘starting point’ from which humans and chimpanzees evolved.”
Reference:
Sergio Almécija, Ashley S. Hammond, Nathan E. Thompson, Kelsey D. Pugh, Salvador Moyà-Solà, David M. Alba. Fossil apes and human evolution. Science, 2021; 372 (6542): eabb4363 DOI: 10.1126/science.abb4363
An enhanced image of Bicellum showing an outer wall of sausage-shaped cells enclosing an inner cell mass. Credit: Boston College
The billion-year-old fossil of an organism, exquisitely preserved in the Scottish Highlands, reveals features of multicellularity nearly 400 million years before the biological trait emerged in the first animals, according to a new report in the journal Current Biology by an international team of researchers, including Boston College paleobotanist Paul K. Strother.
The discovery could be the “missing link” in the evolution of animals, according to the team, which included scientists from the U.S., United Kingdom, and Australia. The microfossil, discovered at Loch Torridon, contains two distinct cell types and could be the earliest example of complex multicellularity ever recorded, according to the researchers.
The fossil offers new insight into the transition of single celled organisms to complex, multicellular animals. Modern single-celled holozoa include the most basal living animals and the fossil discovered shows an organism which lies somewhere between single cell and multicellular animals, or metazoa.
“Our findings show that the genetic underpinnings of cell-to-cell cohesion and segregation — the ability for different cells to sort themselves into separate regions within a multicellular mass — existed in unicellular organisms a billion years ago, some 400 million years before such capabilities were incorporated into the first animals,” said Strother, a research professor in the Department of Earth and Environmental Sciences at Boston College.
The fossil’s discovery in an inland lake shifts the focus on the first forms of early life from the ocean to freshwater.
Animals, or etazoa, are one of only five groups of organisms that have evolved complex multicellularity — organisms that grow from a single cell that develops into a myriad of different cells and tissues. Animals probably evolved from unicellular ancestors that went through multicellular stages during their life cycles, said Strother, an expert in paleobotany and palynology, the study of fossil spores and pollen. Land plants, too, achieved complex multicellularity when they evolved from simpler algal ancestors some time during the early Paleozoic from about 500 to 400 million years ago..
“We describe here a new fossil that is similar to living unicellular relatives of animals, belonging to the group Ichthyosporea,” said Strother. “Our fossil shows life-cycle stages with two different kinds of cells, which could be the first step toward the evolution of complex multicellularity in the evolutionary lineage leading to the Metazoa.”
The study was based on populations of cells preserved in the mineral phosphate that were collected from billion-year-old lake deposits found in the northwest Scottish Highlands, Strother said. Samples are prepared in rock thin sections which allow microfossils to be seen under the light microscope or with a focused ion beam microscope.
The microfossils were discovered as part of an ongoing project to describe life living in freshwater lakes one billion years ago, using samples collected in Scotland and Michigan by Strother beginning in 2008, with support from NASA and the National Geographic Society, and now the Natural Environment Research Council in the UK.
The new fossil has been described and formally named Bicellum brasieri in the new report.
Strother said the discovery has the potential to change the way scientists look at the earliest forms of life on Earth.
“Our study of life in billion-year-old lakes is challenged by our ability to determine which kinds of organisms are represented in these deposits,” he said. “Previously we have assumed that most of what we see in these deposits are various kinds of extinct algae, but the morphological features of Bicellum really are more like those of modern-day unicellular relatives of animals. This is causing us to broaden our approach to reconstructing the diversity and ecology of life on Earth one billion years ago.”
The discovery will allow researchers to expand upon a more thorough reconstruction of the life-cycle of Bicellum, Strother said.
“Armed with comparative morphology with modern day Ichthyosporeans, we may be able to recognize additional morphogenic stages and determine how a single generative cell divides to become a multicellular cell mass,” he said.
Reference:
Paul K. Strother, Martin D. Brasier, David Wacey, Leslie Timpe, Martin Saunders, Charles H. Wellman. A possible billion-year-old holozoan with differentiated multicellularity. Current Biology, 2021; DOI: 10.1016/j.cub.2021.03.051
Note: The above post is reprinted from materials provided by Boston College. Original written by Ed Hayward.
Researchers also want to encourage the locals to develop practical evacuation plans to help them feel less pessimistic about their survival odds. Credit: Katsushika Hokusai
A new study found overlooked tsunami hazards related to undersea, near-shore strike-slip faults, especially for coastal cities adjacent to faults that traverse inland bays. Several areas around the world may fall into this category, including the San Francisco Bay area, Izmit Bay in Turkey and the Gulf of Al-Aqaba in Egypt.
The study led by University of Illinois Urbana-Champaign civil and environmental engineering professor Ahmed Elbanna and professor Ares Rosakis of the California Institute of Technology used the Blue Waters supercomputer at the National Center for Supercomputing Applications to model tsunami hazards related to strike-slip faults around the globe. The results are published in the Proceedings of the National Academy of Sciences.
“Whenever we saw large tsunamis triggered by earthquakes along strike-slip faults, people assumed that perhaps the earthquake had caused an undersea landslide, displacing water that way,” Rosakis said.
The researchers said that a strike-slip fault exists when two blocks of rock on the fault line slide horizontally past one another. The San Andreas Fault is an example of a strike-slip fault.
In September 2018, a moderate 7.5 magnitude earthquake and unexpectedly powerful tsunami swept through Palu, a city situated on the inland side of Palu Bay on the Indonesian island of Sulawesi. The quake occurred along a northwest-southeast trending strike-slip fault that runs through the city and plunges below the bay along Palu’s northwest shore.
“It looked like a bulldozer had come in and leveled the town,” said co-author Costas Synolakis, the president of Athens College and a professor of civil engineering at the University of Southern California, who surveyed the area following the devastating event. “This is why it is so important that we try to understand what really happened.”
Studies exploring connections between strike-slip faulting and tsunamis exist. However, they focus on specific fault systems or geographic locations, obscuring the complex details of the fault geometry and bathymetry, the study reports.
“What is unique about our study is that instead of considering a location-specific event, we focused on the fundamentals of a strike-slip fault system interacting within the boundaries of a narrow bay,” Elbanna said. “We opted to simulate a very basic planar fault passing through a very simplified smooth-bottomed bay, similar to a bathtub. Having this simplified baseline model allows us to generalize to any place on the planet that may be at risk.”
Intersonic earthquakes are fault ruptures that happen so quickly that their movement outpaces the seismic shear waves they generate — like a sonic boom, but with the shock wave moving through the earth’s crust. The simulations found that intersonic earthquakes can provide enough energy and large enough horizontal displacements to trigger large tsunami waves.
When such earthquakes occur within a narrow bay, the researchers reported three distinct phases that can lead to a tsunami: the initial fault movement and shockwave causing almost instantaneous shaking of the coastal land; the displacement of water while the earthquake is occurring; and gravity-driven motion of the tsunami wave after the ground motion has subsided that carries the wave to shore.
“Each of these phases will have a different effect depending on the unique geography of the surrounding land and bathymetry of the bay,” Elbanna said. “And, unlike the earthquakes and subsequent water displacement that occur many miles offshore, an earthquake and tsunami that occurs within the narrow confines of a bay will allow for very little warning time for the coast.”
Elbanna compares the effect of horizontal strike-slip fault displacements to holding a water cup in your hand and shaking it horizontally.
“The sloshing motion is a result of the horizontal shaking. When an earthquake occurs along a strike-slip fault in a narrow bay, the horizontal ground motion pushes and pulls the boundaries of the bay leading to displacement of water in the vertical direction and initiation of the tsunami,” he said.
“The physics-based model used in this study provides critical insight about the hazard associated with strike-slip faulting, particularly, the need to account for such risk to mitigate future damage to other bays traversed by strike-slip faults,” said Illinois graduate student Mohamed Abdelmeguid, who conducted the simulations along with former graduate student Xiao Ma, currently a senior research scientist at Exxon Mobil.
The at-risk regions identified by the team — Northern California, Turkey and Egypt — have experienced intersonic earthquakes in the past, and the researchers recommend revisiting the tsunami hazard rating of underwater strike-slip faults, particularly those traversing narrow bays.
“It may not look like the tsunami scene from Dwayne Johnson’s ‘San Andreas’ movie, but the tsunami risk for Northern California and several places worldwide need to be seriously revisited,” Elbanna said.
Reference:
Ahmed Elbanna et al. Anatomy of strike-slip fault tsunami-genesis. PNAS, 2021 DOI: 10.1073/pnas.2025632118
A close-up image of bladed barite crystals in the Mapepe Formation in the Barberton Greenstone Belt of South Africa. Credit: Desiree Roerdink
The first emergence and persistence of continental crust on Earth during the Archaean (4 billion to 2.5 billion years ago) has important implications for plate tectonics, ocean chemistry, and biological evolution, and it happened about half a billion years earlier than previously thought, according to new research being presented at the EGU General Assembly 2021.
Once land becomes established through dynamic processes like plate tectonics, it begins to weather and add crucial minerals and nutrients to the ocean. A record of these nutrients is preserved in the ancient rock record. Previous research used strontium isotopes in marine carbonates, but these rocks are usually scarce or altered in rocks older than 3 billion years.
Now, researchers are presenting a new approach to trace the first emergence of old rocks using a different mineral: “barite.”
Barite forms from a combination of sulfate coming from ocean water mixing with barium from hydrothermal vents. Barite holds a robust record of ocean chemistry within its structure, useful for reconstructing ancient environments. “The composition of the piece of barite we pick up in the field now that has been on Earth for three and a half billion years, is exactly the same as it was when it when it actually precipitated,” says Desiree Roerdink, a geochemist at University of Bergen, Norway, and team leader of the new research. “So in essence, it is really a great recorder to look at processes on the early Earth.”
Roerdink and her team tested six different deposits on three different continents, ranging from about 3.2 billion to 3.5 billion years old. They calculated the ratio of strontium isotopes in the barite, and from there, inferred the time where the weathered continental rock made its way to the ocean and incorporated itself into the barite. Based on the data captured in the barite, they found that weathering started about 3.7 billion years ago — about 500 million years earlier than previously thought.
“That is a huge time period,” Roerdink says. “It essentially has implications for the way that we think about how life evolved.” She added that scientists usually think about life starting in deep sea, hydrothermal settings, but the biosphere is complex. “We don’t really know if it is possible that life could have developed at the same time on land,” she noted, adding “but then that land has to be there.”
Lastly, the emergence of land says something about plate tectonics and the early emergence of a geodynamic Earth. “To get land, you need processes operating to form that continental crust, and form a crust that is chemically different from the oceanic crust,” Roerdink says.
Two of the most destructive forces of nature — earthquakes and tsunamis — might actually be more of a threat than current estimates according to new research conducted by scientists at The University of New Mexico and the Nanyang Technological University published today in Nature Geoscience.
The researchers developed a new method to assess earthquake and tsunami hazards represented by the most distant part of offshore subduction zones and found that the hazard might have been systematically underestimated in some areas, meaning that tsunami risk assessments should be redone given the new results. The findings have important implications for the mitigation of risk in affected areas worldwide, including Southeast Asia and the Pacific Rim, in the event of future earthquakes and tsunamis.
Megathrust earthquakes are among the most powerful earthquakes experienced worldwide and occur in subduction zones, where two tectonic plates converge, and one slides under the other. The plates move toward each other continuously, but if the interface, or fault, between them is stuck, then a slip deficit builds up over time. Like a debt, this slip deficit has to be paid off eventually, and for tectonic plates pay day is earthquake day. When these earthquakes affect the shallowest part of the fault near the seafloor, they have the potential to shift the seafloor upward and create devastating tsunamis as well.
Understanding the potential rupture behavior of megathrusts, particularly in the shallow offshore part of the fault where most destructive tsunamis are generated, is therefore a critical task for geoscientists forecasting seismic and tsunami inundation hazards. The likelihood of seismic behavior is often assumed to be somewhat low in the shallow part of the fault, based on laboratory studies of recovered fault zone material.
The fault’s rate of slip deficit buildup can also be measured through the use of geodetic observations that track how the earth’s surface moves over time, for example by using highly precise GPS sensors installed on land, together with a model that relates how slip on the fault affects the movement of these stations. However, it is hard for scientists to use this technique to “see” what is going on in the shallowest part of the fault, because it is far from land, below kilometers of water, where traditional GPS instruments cannot operate.
Now, scientists at The University of New Mexico and the Nanyang Technological University (NTU) in Singapore have developed a new geodetic method for inferring this value that accounts for the interaction between different parts of the fault, resulting in a much more physically accurate result. Lindsey’s team noted that previous models have failed to take into account the fact that if the deep part of the fault is stuck between earthquakes, the shallow part can’t move either — it is in what they term a ‘stress shadow’ and there is no buildup of energy available to cause it to slip. By taking this effect into account, the team developed a technique that uses the same land-based data but results in a vast improvement in their ability to “see” the fault slip in the areas that are farthest from shore, allowing researchers to reassess the hazard presented by the offshore parts of subduction zones most prone to tsunami generation.
“We applied this technique to the Cascadia and Japan subduction zones and found that wherever deeper locked patches are present, the shallow fault must also have a high slip deficit — regardless of its own frictional properties,” said Eric Lindsey, an assistant professor in the UNM Department of Earth and Planetary Sciences who conducted the research while at the Earth Observatory of Singapore at NTU. “If these areas can slip seismically, global tsunami hazard could be higher than currently recognized. Our method identifies critical locations where seafloor observations could yield information about frictional properties of these faults in order to better understand their slip behavior.”
This study is important because it calls for a reassessment of previous models of tsunami hazard on megathrusts worldwide. Because this can be done with existing data, the reassessment can be done comparatively quickly as well. Hopefully, this will lead to better preparedness among coastal communities for future events.
Reference:
Eric O. Lindsey, Rishav Mallick, Judith A. Hubbard, Kyle E. Bradley, Rafael V. Almeida, James D. P. Moore, Roland Bürgmann, Emma M. Hill. Slip rate deficit and earthquake potential on shallow megathrusts. Nature Geoscience, 2021; DOI: 10.1038/s41561-021-00736-x
Hydraulic fracturing to extract trapped fossil fuels can trigger earthquakes. Most are so small or far from homes and infrastructure that they may go unnoticed; others can rattle windows, sway light fixtures and jolt people from sleep; some have damaged buildings.
Stanford University geophysicists have simulated and mapped the risk of noticeable shaking and possible building damage from earthquakes caused by hydraulic fracturing at all potential fracking sites across the Eagle Ford shale formation in Texas, which has hosted some of the largest fracking-triggered earthquakes in the United States.
Published April 29 in Science, the results show the most densely populated areas — particularly a narrow section of the Eagle Ford nestled between San Antonio and Houston — face the greatest risk of experiencing shaking strong enough to damage buildings or be felt by people. “We found that risks from nuisance or damage varies greatly across space, depending mostly on population density,” said lead study author Ryan Schultz, a PhD student in geophysics at Stanford.
Social license
Tens of thousands of wells drilled in the vast formation over the past decade helped to fuel the U.S. shale boom and contributed to a dramatic increase in earthquakes in the central and eastern U.S. starting around 2009. Although damaging earthquakes are rare, the authors write, “the perceived risks of hydraulic fracturing have both caused public concern and impeded industry development.”
In sparsely populated areas within the southwestern portion of the Eagle Ford, the researchers found damage is unlikely even if fracking causes earthquakes as large as magnitude 5.0. Allowing such powerful quakes, however, could jeopardize the “social license to operate,” they write. The phrase, which emerged within the mining industry in the 1990s and has since been adopted by climate activists, refers to the unofficial acceptance by local community members and broader civil society that oil, gas and mining operations need to do business without costly conflicts.
“Seismicity is part of the social license for hydraulic fracturing, but far from the only issue,” said study co-author Bill Ellsworth, a geophysics research professor at Stanford’s School of Earth, Energy & Environmental Sciences (Stanford Earth). “Eliminating hydraulic fracturing seismicity altogether wouldn’t change any of the other concerns.”
Among those concerns are health threats from living near oil and gas wells and greenhouse gas emissions from fossil fuel production and use. California’s recent announcement of plans to stop issuing new permits for hydraulic fracturing by 2024, for example, comes as part of an effort to phase out oil extraction and reduce greenhouse gas emissions.
Starting with risk
The researchers say their goal is to make it easier for operators, regulators, local residents and property owners to discuss the risks that are important to them without technical expertise. “The approach we’ve developed provides the risk of nuisance or damage as a shared frame of reference and tools to evaluate it,” said study co-author and geophysics professor Greg Beroza, co-director of the Stanford Center for Induced and Triggered Seismicity (SCITS).
The new risk analysis applies a technique first published last year for considering where people and structures are located as well as forecasts for maximum earthquake magnitude and geological factors that can amplify or dampen tremors as they travel underground. The approach makes it possible to start out with some level of risk — such as a 50 percent chance of 30 households experiencing shaking that feels exciting but not frightening, based on community questionnaires — and calculate the largest earthquake magnitude that would keep risk at or below that level.
The authors propose using this type of analysis as a starting point for managing earthquake risk caused by fracking using a system known as a traffic-light protocol. Adopted in states including Ohio and Oklahoma to manage seismic hazards related to oil, gas and some geothermal energy development, traffic-light protocols give operators a green light to proceed as long as quakes remain relatively small. Larger earthquakes may require an operator to adjust or halt fluid injections, knowing that shaking may continue and even intensify after the pumps shut down.
“If the goal is to treat everyone equally in terms of risk, our analysis shows action should be taken at lower magnitudes for drill sites near the cities in the north of the Eagle Ford than for those in rural areas in the south,” explained Ellsworth, who is also a co-director of SCITS.
According to the researchers, it’s “unfair” to set a uniform threshold for the amount of shaking allowed across a large formation like the Eagle Ford. “Single valued thresholds can allow for thresholds that are too permissive in urban regions or too restrictive in rural regions,” said Beroza, the Wayne Loel Professor at Stanford Earth. “Instead, if you start with a tolerance to risk, you can set thresholds that vary according to changes in the risk.”
Beroza is also co-director of the Southern California Earthquake Center (SCEC).
This research was supported by SCITS.
Reference:
Ryan Schultz, Gregory C. Beroza, William L. Ellsworth. A risk-based approach for managing hydraulic fracturing–induced seismicity. Science, 2021; 372 (6541): 504 DOI: 10.1126/science.abg5451
Note: The above post is reprinted from materials provided by Stanford University. Original written by Josie Garthwaite.
“Hollywood” specimen, same species as Teratophoneus, discovered approximately two miles north of the “Rainbows and Unicorns Quarry” on Grand Staircase-Escalante National Monument. Credit: U.S. Bureau of Land Management
The fearsome tyrannosaur dinosaurs that ruled the northern hemisphere during the Late Cretaceous period (66-100 million years ago) may not have been solitary predators as popularly envisioned, but social carnivores similar to wolves, according to a new study.
The finding, based on research at a unique fossil bone site inside Utah’s Grand Staircase-Escalante National Monument containing the remains of several dinosaurs of the same species, was made by a team of scientists including Celina Suarez, University of Arkansas associate professor of geosciences.
“This supports our hypothesis that these tyrannosaurs died in this site and were all fossilized together; they all died together, and this information is key to our interpretation that the animals were likely gregarious in their behavior,” Suarez said.
The research team also include scientists from the U.S. Bureau of Land Management, Denver Museum of Nature and Science, Colby College of Maine and James Cook University in Australia. The study examines a unique fossil bone site inside Grand Staircase-Escalante National Monument called the “Rainbows and Unicorns Quarry” that they say exceeded the expectations raised even from the site’s lofty nickname.
“Localities [like Rainbows and Unicorns Quarry] that produce insights into the possible behavior of extinct animals are especially rare, and difficult to interpret,” said tyrannosaur expert Philip Currie in a press release from the BLM. “Traditional excavation techniques, supplemented by the analysis of rare earth elements, stable isotopes and charcoal concentrations convincingly show a synchronous death event at the Rainbows site of four or five tyrannosaurids. Undoubtedly, this group died together, which adds to a growing body of evidence that tyrannosaurids were capable of interacting as gregarious packs.”
In 2014, BLM paleontologist Alan Titus discovered the Rainbows and Unicorns Quarry site in Grand Staircase-Escalante National Monument and led the subsequent research on the site, which is the first tyrannosaur mass death site found in the southern United States. Researchers ran a battery of tests and analyses on the vestiges of the original site, now preserved as small rock fragments and fossils in their final resting place, and sandbar deposits from the ancient river.
“We realized right away this site could potentially be used to test the social tyrannosaur idea. Unfortunately, the site’s ancient history is complicated,” Titus said. “With bones appearing to have been exhumed and reburied by the action of a river, the original context within which they lay has been destroyed. However, all has not been lost.” As the details of the site’s history emerged, the research team concluded that the tyrannosaurs died together during a seasonal flooding event that washed their carcasses into a lake, where they sat, largely undisturbed until the river later churned its way through the bone bed.
“We used a truly multidisciplinary approach (physical and chemical evidence) to piece the history of the site together, with the end-result being that the tyrannosaurs died together during a seasonal flooding event,” said Suarez.
Using analysis of stable carbon and oxygen isotopes and concentrations of rare earth elements within the bones and rock, Suarez and her then-doctoral student, Daigo Yamamura, were able to provide a chemical fingerprint of the site. Based on the geochemical work, they were able to conclusively determine that the remains from the site all fossilized in the same environment and were not the result of an attritional assemblage of fossils washed in from a variety of areas.
“None of the physical evidence conclusively suggested that these organisms came to be fossilized together, so we turned to geochemistry to see if that could help us. The similarity of rare earth element patterns is highly suggestive that these organisms died and were fossilized together,” said Suarez.
Excavation of the quarry site has been ongoing since its discovery in 2014 and due to the size of the site and volume of bones found there the excavation will probably continue into the foreseeable future. In addition to tyrannosaurs, the site has also yielded seven species of turtles, multiple fish and ray species, two other kinds of dinosaurs, and a nearly complete skeleton of a juvenile (12-foot-long) Deinosuchus alligator, although they do not appear to have all died together like the tyrannosaurs.
“The new Utah site adds to the growing body of evidence showing that tyrannosaurs were complex, large predators capable of social behaviors common in many of their living relatives, the birds,” said project contributor, Joe Sertich, curator of dinosaurs at the Denver Museum of Nature & Science. “This discovery should be the tipping point for reconsidering how these top carnivores behaved and hunted across the northern hemisphere during the Cretaceous.”
Future research plans for the Rainbows and Unicorns Quarry fossils include additional trace element and isotopic analysis of the tyrannosaur bones, which paleontologists hope will determine with a greater degree of certainty the mystery of Teratophoneus’ social behavior.
In stark contrast to the social interaction between humans and among many species of animals, paleontologists have long debated whether tyrannosaurs lived and hunted alone or in groups.
Based on findings at a site in Alberta, Canada, with over 12 individuals, the idea that tyrannosaurs were social with complex hunting strategies was first formulated by Philip Currie over 20 years ago. This idea has been widely debated, with many scientists doubting the giant killing machines had the brainpower to organize into anything more complex than what is observed in modern crocodiles. Because the Canadian site appeared to be an isolated case, skeptics claimed it represented unusual circumstances that did not reflect normal tyrannosaur behavior. Discovery of a second tyrannosaur mass death site in Montana again raised the possibility of social tyrannosaurs, but this site was still not widely accepted by the scientific community as evidence for social behavior. The researcher’s findings at the Unicorns and Rainbows Quarry provides even more compelling evidence that tyrannosaurs may have habitually lived in groups.
Reference:
Alan L. Titus, Katja Knoll, Joseph J.W. Sertich, Daigo Yamamura, Celina A. Suarez, Ian J. Glasspool, Jonathan E. Ginouves, Abigail K. Lukacic, Eric M. Roberts. Geology and taphonomy of a unique tyrannosaurid bonebed from the upper Campanian Kaiparowits Formation of southern Utah: implications for tyrannosaurid gregariousness. PeerJ, 2021; 9: e11013 DOI: 10.7717/peerj.11013
Rats, by and large, aren’t terribly popular animals. But while you don’t want an infestation of common black rats living in your house, their distant cousins in the Philippines are downright cuddly. These “giant cloud rats” live in the treetops of misty mountain forests, and they fill an ecological role occupied by squirrels in the US. And, it turns out, we have new evidence that they’ve been living in the Philippines for a long time — scientists have discovered the fossils of three new species of giant cloud rats that lived alongside ancient humans.
“Our previous studies have demonstrated that the Philippines has the greatest concentration of unique species of mammals of any country, most of which are small animals, less than half a pound, that live in the tropical forest,” Larry Heaney, the Neguanee Curator of Mammals at Chicago’s Field Museum and an author of a study in the Journal of Mammalogy describing the new species. “These recently extinct fossil species not only show that biodiversity was even greater in the very recent past, but that the two that became extinct just a few thousand years ago were giants among rodents, both weighing more than two pounds. Their abrupt disappearance just a few thousand years ago leaves us to wonder if they were big enough that it might have been worthwhile to hunt and eat them.”
“We have had evidence of extinct large mammals on the Philippine island of Luzon for a long time, but there has been virtually no information about fossils of smaller-sized mammals. The reason is probably that research had focused on open-air sites where the large fossil mammal faunas were known to have been preserved, rather than the careful sieving of cave deposits that preserve a broader size-range of vertebrates including the teeth and bones of rodents,” says Janine Ochoa, an Assistant Professor of Archaeology at the University of the Philippines — Diliman and the study’s lead author.
At the outset of the study, Ochoa was examining the fossil assemblages from caves in the Callao limestone formation, where a couple of years ago, scientists discovered the remains of an ancient species of humans, Homo luzonensis. “We were looking at the fossil assemblages associated with that hominin, and we found teeth and fragments of bone that ended up belonging to these new species of cloud rats,” says Ochoa.
The fossil fragments discovered by the excavation team in Callao Cave aren’t the only traces of the cloud rats, though — they were able to add to them some other fossils in the collections of the National Museum of the Philippines. “Some of these fossils were actually excavated decades ago, in the 1970s and 1980s, and they were in the museum, waiting for someone to have time to do a detailed study. When we began to analyze the fossil material, we were expecting fossil records for known living species. To our surprise, we found that we were dealing with not just one but three buot, or giant cloud rat species that were previously unknown,” said Marian Reyes, a zooarcheologist at the National Museum of the Philippines, one of the study’s authors.
The researchers didn’t have a ton of material to work with, though — just fifty or so fragments. “Normally, when we’re looking at fossil assemblages, we’re dealing with thousands and thousands of fragments before you find something rare and really nice,” says Ochoa. “It’s crazy that in these fifty fragments, we found three new species that haven’t been recorded before.”
The fragments that the researchers found were mostly teeth, which are covered in a hard enamel substance that makes them hardier than bone. From just a few dozen teeth and bits of bone, though, the researchers were able to put together a picture of what these animals were like in life, thanks to, in Heaney’s words, “days and days and days staring through a microscope”
By comparing the fossils to the 18 living species of giant cloud rats, the researchers have a decent idea of what these three new fossil species would have looked like.
“The bigger ones would have looked almost like a woodchuck with a squirrel tail,” says Heaney. “Cloud rats eat plants, and they’ve got great big pot bellies that allow them to ferment the plants that they eat, kind of like cows. They have big fluffy or furry tails. They’re really quite cute.”
The newly recorded fossil species came from Callao Cave, where Homo luzonensis was discovered in 2019, and several adjacent smaller caves in Penablanca, Cagayan Province. Some specimens of all three of the new fossil rodents occurred in the same deep layer in the cave where Homo luzonensis was found, which has been dated at about 67,000 years ago. One of the new fossil rodents is known from only two specimens from that ancient layer, but the other two are represented by specimens from that early date all the way up to about 2000 years ago or later, which means that they were resilient and persistent for at least 60,000 years. “Our records demonstrate that these giant rodents were able to survive the profound climatic changes from the Ice Age to current humid tropics that have impacted the earth over tens of millennia. The question is what might have caused their final extinction?” adds Philip Piper, a coauthor based at the Australian National University.
Two of these giant rodents apparently disappeared about two thousand years ago, or soon after. “That seems significant, because that is roughly the same time that pottery and Neolithic stone tools first appear in the archeological record, and when dogs, domestic pigs, and probably monkeys were introduced to the Philippines, probably from Borneo. While we can’t say for certain based on our current information, this implies that humans likely played some role in their extinction,” says Armand Mijares, Professor in the Archaeological Studies Program at the University of the Philippines — Diliman, who headed the excavations of Callao Cave.
“Our discoveries suggest that future studies that look specifically for fossils of small mammals may be very productive, and may tell us a great deal about how environmental changes and human activities have impacted the really exceptionally distinctive biodiversity of the Philippines,” according to Ochoa. And such studies may also tell us a lot specifically about the impact of human activities, perhaps specifically including over-hunting, on biodiversity, notes Heaney. “This is something we need to understand if we are going to be effective in preventing extinction in the future.”
Reference:
Janine Ochoa, Armand S B Mijares, Philip J Piper, Marian C Reyes, Lawrence R Heaney. Three new extinct species from the endemic Philippine cloud rat radiation (Rodentia, Muridae, Phloeomyini). Journal of Mammalogy, 2021; DOI: 10.1093/jmammal/gyab023
Rafinesquina, seen in this close-up shot, was an ancient genus of brachiopod belonging to order Strophomenida. This order survived two mass extinction events, but the second represented a ‘death sentence’ from which they were unable to recover diversity, persisting for another hundred million years as a ‘dead clade walking’ before their eventual extinction. IMAGE: Provided by Benjamin Barnes
Mass extinctions are known as times of global upheaval, causing rapid losses in biodiversity that wipe out entire animal groups. Some of the doomed groups linger on before going extinct, and a team of scientists found these “dead clades walking” (DCW) are more common and long-lasting than expected.
“Dead clades walking are a pattern in the fossil record where some animal groups make it past the extinction event, but they also can’t succeed in the aftermath,” said Benjamin Barnes, a doctoral student in geosciences at Penn State. “It paints the pictures of a group consigned to an eventual extinction.”
The scientists found 70 of the 134 orders of ancient sea-dwelling invertebrates they examined could be identified as DCW in a new statistical analysis of the fossil record.
“What really fascinated us was that over half of all the orders we looked at have this phenomenon and that it can look like many different things,” said Barnes, who led a group of graduate students and a postdoctoral researcher on the study. “In some cases, you have a group that has a sudden drop in diversity and lasts for a few more million years before disappearing from the record. But we also found many orders straggled along sometimes for tens or hundreds of millions of years.”
The findings, published in the journal Proceedings of the National Academy of Sciences, challenge the view of extinction as a sudden disappearance and suggest that the full impact of mass extinctions lag behind the events themselves longer than previously expected, the scientists said.
“I think it raises questions about how the so-called kill mechanism operates,” Barnes said. “We think of mass extinctions as being these selective forces that cause large groups of animals to go extinct, but our results really show there are a lot of instances where it’s not so sudden. It raises questions about why that’s such a long delay.”
Paleontologist David Jablonski first coined the term DCW more than 20 years ago, and since then it has been associated almost exclusively with mass extinctions. Using a wealth of new fossil record data made available over the last two decades, the study found DCW are also common around smaller, more localized background extinction stages, the scientists said.
“Our results suggest that rather than representing a rare, brief fossil pattern in the wake of mass extinction events, DCWs are actually a really diverse phenomenon and that there might be a lot of drivers that produce this pattern in the fossil record,” Barnes said. “These DCWs may represent a major macroevolutionary pattern.”
The scientists used a statistical technique called a Bayesian change point algorithm to analyze fossil records from the Paleobiology Database, a public record of paleontological data maintained by international scientists.
The method allowed the researchers to search time series data for significant points where the data deviated from the pattern. They were able to identify negative jagged shifts in diversity and rule out that the organism went extinct immediately but instead persisted.
“So you might be looking in the fossil record and you’ll find tons of a type of brachiopod,” Barnes said. “Each order has a handful of families and dozens of genera within those families. Then you might see a drop in diversity, and the majority of those genera disappear and perhaps there’s only one family that continues to survive.”
Those survivors can continue in their niche for millions of years, even into the present. But their lack of diversity makes them more susceptible to future environmental challenges or extinction events, the scientists said.
“I think these findings cause you to reexamine how you measure success,” Barnes said. “It’s quite possible for an animal group not to produce new families and new genera at a rate like it did before, but if it continues to survive for many millions of years, that’s still some form of success. I think it raises a lot of questions about what it means to be successful as a fossil organism and what ultimately are the controls of origination.”
Reference:
B. Davis Barnes, Judith A. Sclafani, Andrew Zaffos. Dead clades walking are a pervasive macroevolutionary pattern. Proceedings of the National Academy of Sciences, 2021; 118 (15): e2019208118 DOI: 10.1073/pnas.2019208118
Bathymetric chart of a part of the Red Sea. Source GEOMAR.
The Red Sea is a fascinating and still puzzling area of investigation for geoscientists. Controversial questions include its age and whether it represents a special case in ocean basin formation or if it has evolved similarly to other, larger ocean basins. Researchers have now published a new tectonic model that suggests that the Red Sea is not only a typical ocean, but more mature than thought before.
It is 2,250 kilometers long, but only 355 kilometers wide at its widest point — on a world map, the Red Sea hardly resembles an ocean. But this is deceptive. A new, albeit still narrow, ocean basin is actually forming between Africa and the Arabian Peninsula. Exactly how young it is and whether it can really be compared with other young oceans in Earth’s history has been a matter of dispute in the geosciences for decades. The problem is that the newly formed oceanic crust along the narrow, north-south aligned rift is widely buried under a thick blanket of salt and sediments. This complicates direct investigations.
In the international journal Nature Communications, scientists from GEOMAR Helmholtz Centre for Ocean Research Kiel, King Abdullah University for Science and Technology in Thuwal (Saudi Arabia) and the University of Iceland have now published a study that makes a good case for the Red Sea being quite mature and having an almost classical oceanic evolution. “Using a combination of different methods, we can show for the first time that the structures in the Red Sea are typical for a young but already fully developed ocean basin.” says Dr. Nico Augustin from GEOMAR, lead author of the study.
In addition to information from high-resolution seafloor maps and chemical investigations of rock samples, the team primarily used gravity and earthquake data to develop a new tectonic model of the Red Sea basin. Gravity anomalies have already helped to detect hidden seafloor structures such as rift axes, transform faults and deep-sea mountains in other regions, for example in the Gulf of Mexico, the Labrador Sea or the Andaman Sea.
The authors of the current study compared gravity patterns of the Red Sea axis with comparable mid-ocean ridges and found more similarities than differences. For example, they identified positive gravity anomalies running perpendicular to the rift axis, which are caused by variations in crustal thickness running along the axis. “These so-called ‘off-axis segmentation trails’ are very typical features of oceanic crust originating from magmatically more active, thicker and thus, heavier areas along the axis. However, this observation is new for the Red Sea,” says Dr. Nico Augustin.
Bathymetric maps as well as earthquake data also support the idea of an almost continuous rift valley throughout the Red Sea basin. This is also confirmed by geochemical analyses of rock samples from the few areas that are not overlain by salt masses. “All the samples we have from the Red Sea rift have geochemical fingerprints of normal oceanic crust,” says Dr. Froukje van der Zwan, co-author of the study.
With this new analysis of gravity and earthquake data, the team constrains the onset of ocean expansion in the Red Sea to about 13 million years ago. “That’s more than twice the generally accepted age,” Dr. Augustin says. That means the Red Sea is no longer a baby ocean, but a young adult with a structure similar to the young southern Atlantic some 120 million years ago.
The model now presented is, of course, still being debated in the scientific community, says the lead author, “but it is the most straightforward interpretation of what we observe in the Red Sea. Many details in salt- and sediment-covered areas that were previously difficult to explain suddenly make sense with our model.” While it has thus been able to answer some questions about the Red Sea, the model also raises many new ones that inspire further research in the Red Sea from a whole new scientific perspective.
Reference:
Nico Augustin, Froukje M. van der Zwan, Colin W. Devey, Bryndís Brandsdóttir. 13 million years of seafloor spreading throughout the Red Sea Basin. Nature Communications, 2021; 12 (1) DOI: 10.1038/s41467-021-22586-2
It seems like a smooth slab of stainless steel, but look a little closer, and you’ll see a simplified cross-section of the Los Angeles sedimentary basin.
Caltech researcher Sunyoung Park and her colleagues are printing 3D models like the metal Los Angeles proxy to provide a novel platform for seismic experiments. By printing a model that replicates a basin’s edge or the rise and fall of a topographic feature and directing laser light at it, Park can simulate and record how seismic waves might pass through the real Earth.
In her presentation at the Seismological Society of America (SSA)’s 2021 Annual Meeting, Park explained why these physical models can address some of the drawbacks of numerical modeling of ground motion in some cases.
Small-scale, complex structures in a landscape can amplify and alter ground motion after an earthquake, but seismologists have a difficult time modeling these impacts, said Park. “Even though we know that these things are very important to ground shaking, the effects of topography, interfaces and edges are hard problems to study numerically.”
Incorporating these features in ground motion simulations requires a lot of computational power, and it can be hard to verify these numerical calculations, she added.
To address these challenges, Park began creating 3D models of simple topographical and basin features to explore these effects on ground shaking. Metal is her preferred printing material, “because it can be as rigid as the conditions at the Earth’s lower crust,” she said.
By controlling the printing parameters, Park can also control the density of the metal as it is laid down by the printer, creating a material with different seismic velocities. The result, in the case of the Los Angeles basin example that she showed at the meeting, is a 20 by 4-centimeter model that represents a 50-kilometer cross-section through the basin.
At a scale of about 1:250,000 for the printed landscape, Park needed to scale down the wavelengths that she used to simulate seismic waves as well, which is where the laser-based source and receiver system comes in. A laser shot at the model mimics a seismic source event, and laser doppler receivers sense the resulting vibrations as the seismic waves interact with the model’s features.
Experiments with the models have yielded some intriguing findings. With a shallow basin cross-section, for instance, Park found that some of the high-frequency waves were blocked from traveling across the basin.
“We know that basins are usually amplifying ground motions,” she said, “but this suggests we should be thinking about that in terms of different frequency contents as well.”
Park said the models might also be useful for studying wave propagation through other seismologically complex features, such as highly damaged rock near a fault, rock layers injected with fluids and gases during oil and gas extraction or carbon sequestration, and features in the deep Earth.
Park will join the Department of Geophysical Sciences at The University of Chicago in June 2021.
From left, University of Wyoming students Shane Scoggin, Adam Trzinski and Jessie Shields are part of new research investigating crustal melting in western North America. Here, they examine igneous rocks in the Snake Range of Nevada. Credit: Jay Chapman
A group of University of Wyoming professors and students has identified an unusual belt of igneous rocks that stretches for over 2,000 miles from British Columbia, Canada, to Sonora, Mexico.
The rock belt runs through Idaho, Montana, Nevada, southeast California and Arizona. “Geoscientists usually associate long belts of igneous rocks with chains of volcanoes at subduction zones, like Mount Shasta, Mount Hood, Mount St. Helens and Mount Rainer,” says Jay Chapman, an assistant professor in UW’s Department of Geology and Geophysics. “What makes this finding so interesting and mysterious is that this belt of igneous rocks is located much farther inland, away from the edge of the continent, and doesn’t contain any evidence for producing volcanoes. In fact, all of the melting to generate the igneous rocks originally took place deep underground, five to 10 miles beneath the surface.”
Chapman is lead author of a paper, titled “The North American Cordilleran Anatectic Belt,” which was published online in February in the journal Earth-Science Reviews. The print version will be published this month.
The paper is a result of a special course taught by Simone Runyon, an assistant professor in UW’s Department of Geology and Geophysics, and Chapman. Runyon, six UW graduate students and one undergraduate student, who took part in the course, are co-authors of the paper.
“It was really fascinating to start with a scientific question in a classroom, then collect and analyze data, and eventually publish our results,” says Cody Pridmore, a UW graduate student from Orange, Calif., and co-author of the paper. “It’s a process most college students don’t get to experience.”
One clue to the origin of the belt of igneous rocks is that the rocks chiefly formed 80 million to 50 million years ago, during a mountain-building event called the Laramide orogeny.
“The Laramide orogeny created most of the major mountain ranges we have in Wyoming, and the name actually comes from the Laramie Range,” Chapman says. “Although there are no igneous rocks of this type and age present in those mountains, we suspect that the tectonic processes that created the mountains also contributed to melting Earth’s crust.”
The researchers have several working hypotheses about what caused the rocks to melt. One hypothesis is that water infiltrated the deep crust.
“The geochemistry of these rocks indicates that melting may have occurred at relatively low temperatures, below 800 degrees Celsius,” says Jessie Shields, a Ph.D. student at UW from Minneapolis, Minn., who is working to solve this mystery. “That is still very hot, but not hot enough to produce very large volumes of magma. Water lowers the melting point of rocks, similar to how salt lowers the melting point of ice, and could increase the amount of magma generated.”
This work has implications for what causes rocks to melt and where specific types of magmas can be found.
“Many of the igneous systems in the study area contain economically important ore deposits,” says Runyon, who specializes in ore deposits. “Understanding the large-scale igneous processes that form these provinces helps us to better understand how ore deposits form and to better explore for natural resources.”
Reference:
James B. Chapman, Simone E. Runyon, Jessie E. Shields, Brandi L. Lawler, Cody J. Pridmore, Shane H. Scoggin, Nathan T. Swaim, Adam E. Trzinski, Hannah N. Wiley, Andrew P. Barth, Gordon B. Haxel. The North American Cordilleran Anatectic Belt. Earth-Science Reviews, 2021; 215: 103576 DOI: 10.1016/j.earscirev.2021.103576
West Mato Volcano erupting in 2009, courtesy of the National Oceanic and Atmospheric Administration.
Volcanic eruptions deep in our oceans are capable of extremely powerful releases of energy, at a rate high enough to power the whole of the United States, according to research published today.
Eruptions from deep-sea volcanoes were long-thought to be relatively uninteresting compared with those on land. While terrestrial volcanoes often produce spectacular eruptions, dispersing volcanic ash into the environment, it was thought that deep marine eruptions only produced slow moving lava flows.
But data gathered by remotely operated vehicles deep in the North East Pacific and analysed by scientists at the University of Leeds, has revealed a link between the way ash is dispersed during submarine eruptions and the creation of large and powerful columns of heated water rising from the ocean floor, known as megaplumes.
These megaplumes contain hot chemical-rich water and act in the same way as the atmospheric plumes seen from land-based volcanoes, spreading first upwards and then outwards, carrying volcanic ash with them. The size of megaplumes is immense, with the volumes of water equivalent to forty million Olympic-sized swimming pools. They have been detected above various submarine volcanoes but their origin has remained unknown. The results of this new research show that they form rapidly during the eruption of lava.
The research was carried out by Sam Pegler, from the School of Mathematics and David Ferguson, from the School of Earth and Environment and is being published today in the journal Nature Communications.
Together they developed a mathematical model which shows how ash from these submarine eruptions spreads several kilometres from the volcano. They used the ash pattern deposited by a historic submarine eruption to reconstruct its dynamics. This showed that the rate of energy released and required to carry ash to the observed distances is extremely high — equivalent to the power used by the whole of the USA.
David Ferguson said: “The majority of Earth’s volcanic activity occurs underwater, mostly at depths of several kilometres in the deep ocean but, in contrast to terrestrial volcanoes, even detecting that an eruption has occurred on the seafloor is extremely challenging. Consequently, there remains much for scientists to learn about submarine volcanism and its effects on the marine environment.”
The research shows that submarine eruptions cause megaplumes to form but the release of energy is so rapid that it cannot be supplied from the erupted molten lava alone. Instead, the research concludes that submarine volcanic eruptions lead to the rapid emptying of reservoirs of hot fluids within the earth’s crust. As the magma forces its way upwards towards the seafloor, it drives this hot fluid with it.
Sam Pegler added: “Our work provides evidence that megaplumes are directly linked to the eruption of lava and are responsible for transporting volcanic ash in the deep ocean. It also shows that plumes must have formed in a matter of hours, creating an immense rate of energy release.
David Ferguson adds: “Observing a submarine eruption in person remains extremely difficult but the development of instruments based on the seafloor means data can be streamed live as the activity occurs.
Efforts like these, in concert with continued mapping and sampling of the ocean floor means the volcanic character of our oceans is slowly being revealed.”
Reference:
Samuel S. Pegler, David J. Ferguson. Rapid heat discharge during deep-sea eruptions generates megaplumes and disperses tephra. Nature Communications, 2021; 12 (1) DOI: 10.1038/s41467-021-22439-y
Over approximately 2.5 million years, North America likely hosted 2.5 billion Tyrannosaurus rexes, a minuscule proportion of which have been dug up and studied by paleontologists, according to a UC Berkeley study. (Image by Julius Csotonyi, courtesy of Science magazine)
How many Tyrannosaurus rexes roamed North America during the Cretaceous period?
That’s a question Charles Marshall pestered his paleontologist colleagues with for years until he finally teamed up with his students to find an answer.
What the team found, to be published this week in the journal Science, is that about 20,000 adult T. rexes probably lived at any one time, give or take a factor of 10, which is in the ballpark of what most of his colleagues guessed.
What few paleontologists had fully grasped, he said, including himself, is that this means that some 2.5 billion lived and died over the approximately 2 1/2 million years the dinosaur walked the earth.
Until now, no one has been able to compute population numbers for long-extinct animals, and George Gaylord Simpson, one of the most influential paleontologists of the last century, felt that it couldn’t be done.
Marshall, director of the University of California Museum of Paleontology, the Philip Sandford Boone Chair in Paleontology and a UC Berkeley professor of integrative biology and of earth and planetary science, was also surprised that such a calculation was possible.
“The project just started off as a lark, in a way,” he said. “When I hold a fossil in my hand, I can’t help wondering at the improbability that this very beast was alive millions of years ago, and here I am holding part of its skeleton — it seems so improbable. The question just kept popping into my head, ‘Just how improbable is it? Is it one in a thousand, one in a million, one in a billion?’ And then I began to realize that maybe we can actually estimate how many were alive, and thus, that I could answer that question.”
Marshall is quick to point out that the uncertainties in the estimates are large. While the population of T. rexes was most likely 20,000 adults at any give time, the 95% confidence range — the population range within which there’s a 95% chance that the real number lies — is from 1,300 to 328,000 individuals. Thus, the total number of individuals that existed over the lifetime of the species could have been anywhere from 140 million to 42 billion.
“As Simpson observed, it is very hard to make quantitative estimates with the fossil record,” he said. “In our study, we focused in developing robust constraints on the variables we needed to make our calculations, rather than on focusing on making best estimates, per se.”
He and his team then used Monte Carlo computer simulation to determine how the uncertainties in the data translated into uncertainties in the results.
The greatest uncertainty in these numbers, Marshall said, centers around questions about the exact nature of the dinosaur’s ecology, including how warm-blooded T. rex was. The study relies on data published by John Damuth of UC Santa Barbara that relates body mass to population density for living animals, a relationship known as Damuth’s Law. While the relationship is strong, he said, ecological differences result in large variations in population densities for animals with the same physiology and ecological niche. For example, jaguars and hyenas are about the same size, but hyenas are found in their habitat at a density 50 times greater than the density of jaguars in their habitat.
“Our calculations depend on this relationship for living animals between their body mass and their population density, but the uncertainty in the relationship spans about two orders of magnitude,” Marshall said. “Surprisingly, then, the uncertainty in our estimates is dominated by this ecological variability and not from the uncertainty in the paleontological data we used.”
As part of the calculations, Marshall chose to treat T. rex as a predator with energy requirements halfway between those of a lion and a Komodo dragon, the largest lizard on Earth.
The issue of T. rex’s place in the ecosystem led Marshall and his team to ignore juvenile T. rexes, which are underrepresented in the fossil record and may, in fact, have lived apart from adults and pursued different prey. As T. rex crossed into maturity, its jaws became stronger by an order of magnitude, enabling it to crush bone. This suggests that juveniles and adults ate different prey and were almost like different predator species.
This possibility is supported by a recent study, led by evolutionary biologist Felicia Smith of the University of New Mexico, which hypothesized that the absence of medium-size predators alongside the massive predatory T. rex during the late Cretaceous was because juvenile T. rex filled that ecological niche.
What the fossils tell us
The UC Berkeley scientists mined the scientific literature and the expertise of colleagues for data they used to estimate that the likely age at sexual maturity of a T. rex was 15.5 years; its maximum lifespan was probably into its late 20s; and its average body mass as an adult — its so-called ecological body mass, — was about 5,200 kilograms, or 5.2 tons. They also used data on how quickly T. rexes grew over their life span: They had a growth spurt around sexual maturity and could grow to weigh about 7,000 kilograms, or 7 tons.
From these estimates, they also calculated that each generation lasted about 19 years, and that the average population density was about one dinosaur for every 100 square kilometers.
Then, estimating that the total geographic range of T. rex was about 2.3 million square kilometers, and that the species survived for roughly 2 1/2 million years, they calculated a standing population size of 20,000. Over a total of about 127,000 generations that the species lived, that translates to about 2.5 billion individuals overall.
With such a large number of post-juvenile dinosaurs over the history of the species, not to mention the juveniles that were presumably more numerous, where did all those bones go? What proportion of these individuals have been discovered by paleontologists? To date, fewer than 100 T. rex individuals have been found, many represented by a single fossilized bone.
“There are about 32 relatively well-preserved, post-juvenile T. rexes in public museums today,” he said. “Of all the post-juvenile adults that ever lived, this means we have about one in 80 million of them.”
“If we restrict our analysis of the fossil recovery rate to where T. rex fossils are most common, a portion of the famous Hell Creek Formation in Montana, we estimate we have recovered about one in 16,000 of the T. rexes that lived in that region over that time interval that the rocks were deposited,” he added. “We were surprised by this number; this fossil record has a much higher representation of the living than I first guessed. It could be as good as one in a 1,000, if hardly any lived there, or it could be as low as one in a quarter million, given the uncertainties in the estimated population densities of the beast.”
Marshall expects his colleagues will quibble with many, if not most, of the numbers, but he believes that his calculational framework for estimating extinct populations will stand and be useful for estimating populations of other fossilized creatures.
“In some ways, this has been a paleontological exercise in how much we can know, and how we go about knowing it,” he said. “It’s surprising how much we actually know about these dinosaurs and, from that, how much more we can compute. Our knowledge of T. rex has expanded so greatly in the past few decades thanks to more fossils, more ways of analyzing them and better ways of integrating information over the multiple fossils known.”
The framework, which the researchers have made available as computer code, also lays the foundation for estimating how many species paleontologists might have missed when excavating for fossils, he said.
“With these numbers, we can start to estimate how many short-lived, geographically specialized species we might be missing in the fossil record,” he said. “This may be a way of beginning to quantify what we don’t know.”
Reference:
Charles R. Marshall, Daniel V. Latorre, Connor J. Wilson, Tanner M. Frank, Katherine M. Magoulick, Joshua B. Zimmt, Ashley W. Poust. Absolute abundance and preservation rate of Tyrannosaurus rex. Science, 2021 DOI: 10.1126/science.abc8300
The world’s smallest stegosaur footprint (less than 6 cm long), Xingjiang, China. Photo credit – Lida Xing.
A single footprint left by a cat-sized dinosaur around 100 million years ago has been discovered in China by an international team of palaeontologists.
University of Queensland researcher Dr Anthony Romilio was part of the team that investigated the track, originally found by Associate Professor Lida Xing from the China University of Geosciences (Beijing).
“This footprint was made by a herbivorous, armoured dinosaur known broadly as a stegosaur — the family of dinosaurs that includes the famed stegosaurus,” Dr Romilio said.
“Like the stegosaurus, this little dinosaur probably had spikes on its tail and bony plates along its back as an adult.
“With a footprint of less than six centimetres, this is the smallest stegosaur footprint known in the world.
“It’s in strong contrast with other stegosaur prints found at the Chinese track site which measured up to 30 centimetres, and prints found in places like Broome in Western Australia where they can be up to 80 centimetres.”
The tiny footprint has similar characteristics of other stegosaur footprints with three short, wide, round toe impressions.
However researchers found the print wasn’t elongated like larger counterpart prints discovered at the track sites, which suggests the young stegosaur had a different behaviour.
“Stegosaurs typically walked with their heels on the ground, much like humans do, but on all fours which creates long footprints,” Dr Romilio said.
“The tiny track shows that this dinosaur had been moving with its heel lifted off the ground, much like a bird or cat does today.
“We’ve only previously seen shortened tracks like this when dinosaurs walked on two legs.”
Associate Professor Xing said that it was plausible young stegosaurs were toe-walkers.
“This could be possible as this is the ancestral condition and a posture of most dinosaurs, but the stegosaur could also have transitioned to heel-walking as it got older,” Dr Xing said.
“A complete set of tracks of these tiny footprints would provide us with the answer to this question, but unfortunately we only have a single footprint.”
Finding the tiny tracks on crowded track sites will be challenging for the researchers.
“The footprints made by tiny armoured dinosaur are much rarer than those formed by other groups of dinosaurs,” Associate Professor Xing said.
“Now that our study has identified nine different dinosaur track sites from this locality, we will look even closer to see if we can find more of these tiny tracks.”
Reference:
Lida Xing, Martin G. Lockley, W. Scott Persons, Hendrik Klein, Anthony Romilio, Donghao Wang, Miaoyan Wang. Stegosaur Track Assemblage from Xinjiang, China, Featuring the Smallest Known Stegosaur Record. PALAIOS, 2021; 36 (2): 68 DOI: 10.2110/palo.2020.036
