Arthropods have been among the most successful animals on Earth since the Cambrian Period, about 520 million years ago. They are the most familiar and ubiquitous, and constitute nearly 80% of all animal species today, far more than any other animals.

But how did arthropods evolve, and what did their ancestors look like? These have been a major conundrum in animal evolution puzzling generations of scientists for more than a century.

Now, researchers from the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences (NIGPAS) have discovered a shrimp-like fossil with five eyes, which has provided important insights into the early evolutionary history of arthropods. The study was published in Nature on Nov. 4.

The fossil species, Kylinxia, was collected from the Chengjiang fauna in southwest China’s Yunnan Province. The fauna documents the most complete early animal fossils in the Cambrian time.

Prof. Huang Diying, corresponding author for the study from NIGPAS, said, “Kylinxia is a very rare chimeric species. It combines morphological features from different animals, which is analogous to ‘kylin,’ a chimeric creature in traditional Chinese mythology.”

“Owing to very special taphonomic conditions, the Kylinxia fossils exhibit exquisite anatomical structures. For example, nervous tissue, eyes and digestive system—these are soft body parts we usually cannot see in conventional fossils,” said Prof. Zhao Fangchen, co-corresponding author of the study.

Kylinxia shows distinctive features of true arthropods, such as a hardened cuticle, a segmented trunk and jointed legs. However, it also integrates the morphological characteristics present in very ancestral forms, including the bizarre five eyes of Opabinia, known as the Cambrian “weird wonder,” as well as the iconic raptorial appendages of Anomalocaris, the giant apex predator in the Cambrian ocean.

Among the Chengjiang fauna, Anomalocaris is a top predator that can reach two meters in body length, and has been regarded as an ancestral form of arthropod. But huge morphological differences exist between Anomalocaris and true arthropods. There is a great evolutionary gap between the two that can hardly be bridged. This gap has become a crucial “missing link” in the origin of arthropods.

The research team conducted detailed anatomical examinations of the fossils of Kylinxia. They demonstrated that the first appendages in Anomalocaris and true arthropods were homologous. The phylogenetic analyses suggested that there was affinity between the front appendages of Kylinxia, small predatory appendages in front of the mouth of Chelicerata (a group that includes spiders and scorpions) and the antennae of Mandibulata (a subdivision of arthropods including insects such as ants and bees).

“Our results indicate that the evolutionary placement of Kylinxia is right between Anomalocaris and the true arthropods. Therefore, our finding reached the evolutionary root of the true arthropods,” said Prof. Zhu Maoyan, a co-author of the study.

“Kylinxia represents a crucial transitional fossil predicted by Darwin’s evolutionary theory. It bridges the evolutionary gap from Anomalocaris to true arthropods and forms a key “missing link” in the origin of arthropods, contributing strong fossil evidence for the evolutionary theory of life,” said Dr. Zeng Han, first author of the study.

Reference:
An early Cambrian euarthropod with radiodont-like raptorial appendages, Nature (2020). DOI: 10.1038/s41586-020-2883-7

Note: The above post is reprinted from materials provided by Chinese Academy of Sciences.

Pterodactyls and other related winged reptiles that lived alongside the dinosaurs steadily improved their ability to fly to become the deadly masters of the sky over the course of millions of years.

A new study published in the journal Nature has shown that pterosaurs — a group of creatures that became Earth’s first flying vertebrates — evolved to improve their flight performance over their 150 million-year existence, before they went extinct at the same time as the dinosaurs 66 million years ago.

Scientists from the Universities of Reading, Lincoln and Bristol carried out the most detailed study yet into how animals evolve to become better suited to their environments over time. They combined fossil records with a new model of flight based on today’s living birds to measure their flight efficiency and fill in the gaps in our knowledge of their evolutionary story.

This allowed the scientists to track the gradual evolution of pterosaurs and demonstrate that they became twice as good at flying over the course of their history. It also showed that their evolution was caused by consistent small improvements over a long period, rather than sudden evolutionary bursts as had been previously suggested.

Professor Chris Venditti, an evolutionary biologist at the University of Reading and lead author of the study, funded by the Leverhulme Trust, said: “Pterosaurs were a diverse group of winged lizards, with some the size of sparrows and others with the wingspan of a light aircraft. Fans of the movie Jurassic World will have seen a dramatisation of just how huge and lethal these creatures would have been. Their diet consisted mostly of other animals, from insects to smaller dinosaurs.

“Despite their eventual prowess in the air being well-known, the question of whether pterosaurs got better at flying and whether this gave them an advantage over their ancestors has puzzled scientists for decades. There are many examples of how natural selection works on relatively short time scales, but until now it has been very difficult to demonstrate whether plants or animals adapt to become more efficient over a long period.

“Our new method has allowed us to study long-term evolution in a completely new way, and answer this question at last by comparing the creatures at different stages of their evolutionary sequence over many millions of years.”

Pterosaurs evolved from land-based animals and first emerged as flyers in the Early Triassic period, around 245 million years ago. The first fossils are from 25 million years later.

The scientists monitored changes to pterosaur flight efficiency by using fossils to measure their wingspan and body size at different stages. Their new model based on living birds was applied to the data for 75 pterosaur species, which showed that pterosaurs gradually got better at flying over millions of years.

The models showed that pterosaurs adapted their body shape and size to use 50% less energy when flying over their 150 million-year history. They showed that the creatures increased in mass by 10 times, some to eventually weigh more than 300kg.

The new method also revealed that one group of pterosaurs — azhdarchoids — was an exception to the rule. Scientists have disagreed over how well these animals flew, but the new study showed that they did not get any better throughout their existence.

The enlarged size of azhdarchoids appeared to provide their survival advantage instead, with one animal — Quetzlcoatlus — growing to the height of a giraffe.

Dr Joanna Baker, evolutionary biologist and co-author at the University of Reading said: “This is unique evidence that although these animals were competent fliers, they probably spent much of their time on the ground. Highly efficient flight probably didn’t offer them much of an advantage, and our finding that they had smaller wings for their body size is in line with fossil evidence for their reduced reliance on flight.”

Professor Stuart Humphries, biophysicist and author from the University of Lincoln said: “One of the few things that haven’t changed over the last 300 million years are the laws of physics, so it has been great to use those laws to understand the evolution of flight in these amazing animals.”

Professor Mike Benton at the University of Bristol said, “Until recently, paleontologists could describe the anatomy of creatures based on their fossils and work out their functions. It’s really exciting now to be able to calculate the operational efficiency of extinct animals, and then to compare them through their evolution to see how efficiency has changed. We don’t just have to look at the fossils with amazement, but can really get to grips with what they tell us.”

Reference:
Chris Venditti, Joanna Baker, Michael J. Benton, Andrew Meade, Stuart Humphries. 150 million years of sustained increase in pterosaur flight efficiency. Nature, 2020; DOI: 10.1038/s41586-020-2858-8

Note: The above post is reprinted from materials provided by University of Reading.

About 240 million years ago, when reptiles ruled the ocean, a small lizard-like predator floated near the bottom of the edges in shallow water, picking off prey with fang-like teeth. A short and flat tail, used for balance, helps identify it as a new species, according to research published in the Journal of Vertebrate Paleontology.

Paleontologists at the Chinese Academy of Scientists and Canadian Museum of Nature have analysed two skeletons from a thin layer of limestone in two quarries in southwest China. They identified the skeletons as nothosaurs, Triassic marine reptiles with a small head, fangs, flipper-like limbs, a long neck, and normally an even longer tail, probably used for propulsion. However, in the new species, the tail is short and flat.

“Our analysis of two well-preserved skeletons reveals a reptile with a broad, pachyostotic body (denser boned) and a very short, flattened tail. A long tail can be used to flick through the water, generating thrust, but the new species we’ve identified was probably better suited to hanging out near the bottom in shallow sea, using its short, flattened tail for balance, like an underwater float, allowing it to preserve energy while searching for prey,” says Dr Qing-Hua Shang from the Chinese Academy of Sciences, in Beijing.

The scientists have named the new species Brevicaudosaurus jiyangshanensis, from the Latin ‘brevi’ for ‘short,’ ‘caudo’ for ‘tail,’ and the Greek ‘sauros’ for ‘lizard.’ The most complete skeleton of the two was found in Jiyangshan quarry, giving the specimen its species name. It’s just under 60cm long.

The skeleton gives further clues to its lifestyle. The forelimbs are more strongly developed than the hind limbs, suggesting they played a role in helping the reptile to swim. However, the bones in the front feet are short compared to other species, limiting the power with which it could pull through the water. Most of its bones, including the vertebrae and ribs, are thick and dense, further contributing to the stocky, stout appearance of the reptile, and limiting its ability to swim quickly but increasing stability underwater.

However, thick, high-mass bones act as ballast. What the reptile lost in speed, it gained in stability. Dense bones, known as pachyostosis, may have made it neutrally buoyant in shallow water. Together with the flat tail, this would have helped the predator to float motionless underwater, requiring little energy to stay horizontal. Neutral buoyancy should also have enabled it to walk on the seabed searching for slow-moving prey.

Highly dense ribs may also suggest the reptile had large lungs. As suggested by the lack of firm support of the body weight, nothosaurs were oceanic nut they needed to come to the water surface for oxygen. They have nostrils on the snout through which they breathed. Large lungs would have increased the time the species could spend under water.

The new species features a bar-shaped bone in the middle ear called the stapes, used for sound transmission. The stapes was generally lost in other nothosaurs or marine reptiles during preservation. Scientists had predicted that if a stapes was found in a nothosaur, it would be thin and slender like in other species of this branch of the reptilian family tree. However, in B. jiyangshanensis it is thick and elongate, suggesting it had good hearing underwater.

“Perhaps this small, slow-swimming marine reptile had to be vigilante for large predators as it floated in the shallows, as well as being a predator itself,” says co-author Dr. Xiao-Chun Wu from the Canadian Museum of Nature.

Reference:
Qing-Hua Shang, Xiao-Chun Wu, Chun Li. A New Ladinian Nothosauroid (Sauropterygia) from Fuyuan, Yunnan Province, China. Journal of Vertebrate Paleontology, 2020; e1789651 DOI: 10.1080/02724634.2020.1789651

Note: The above post is reprinted from materials provided by Taylor & Francis Group.

A new study of coprolites, fossil poop, shows the detail of food webs in the ancient shallow seas around Bristol in south-west England. One hungry fish ate part of the head of another fish before snipping off the tail of a passing reptile.

Marie Cueille, a visiting student at the University of Bristol’s School of Earth Sciences, was working on a collection of hundreds of fish poops from the Rhaetian bone bed near Chipping Sodbury in South Gloucestershire, dated at 205 million years ago.

She applied new scanning technology to look inside these coprolites and found an amazing array of food remains.

Marie said: “The ancient fishes and sharks of the Rhaetian seas were nearly all carnivores. Their coprolites contain scales, teeth, and bones, and these tell us who was eating whom. In fact, all the fish seem to have been snapping at each other, although the general rule of the sea probably applied: if it’s smaller than you, eat it.”

The CT scans of one tiny coprolite, measuring only a centimeter or so in length, contained only three bones, one a highly tuberculated skull bone of another fish, and two vertebrae from the tail of a small marine reptile called Pachystropheus.

Dr. Chris Duffin, who collaborated on the project added: “This shark probably snapped at another fish or scavenged some flesh from the head region of a dead fish. But it didn’t just strip off the flesh but swallowed great chunks of bone at the same time. Then it snapped at a Pachystropheus swimming by and had a chunk of its tail.”

Professor Mike Benton, who co-supervised the study, said: “What amazed us was that the bones and scales inside the coprolites were almost completely undamaged. Today, most predators that swallow their prey whole, such as sharks, crocodiles or killer whales, have powerful stomach acids that dissolve the bone away. These ancient fishes must have had a painful time passing their feces which were absolutely bristling with relatively large chunks of bone.”

The researchers also identified for the first time some coprolites of crabs and lobsters, so this completes the food web. The marine reptiles and sharks were feeding on smaller fishes, which in turn fed on even smaller fishes and lobsters. Some also had crushing teeth adapted to feeding on oysters and other molluscs.

The study has a classical resonance as well, because Rhaetian coprolites from bonebeds near Bristol were some of those studied by William Buckland (1784–1856) in the 1820s when he invented the name coprolite. Buckland was professor of geology at Oxford University, but also Dean of Christ Church, and known for his unusual eating habits. Possibly his interest in eating exotic animals (he would serve his guests roasted dormice or potted panther but declared that moles and house flies were inedible) gave him an interest in animal diets.

Buckland pioneered the use of coprolites to reconstruct ancient food webs. He also collected specimens from the Jurassic around Lyme Regis, and many were supplied by famous fossil collector Mary Anning (1799–1847). Buckland even had these larger coprolites cut across and set into the top of a table, which was highly polished and doubtless formed a conversation opener during lunch and tea parties in the Dean’s lodgings.

The new work also sheds light on the Mesozoic Marine Revolution, the time when marine ecosystems modernized. The coprolites from Bristol show a complex, modern-style ecosystem with lobsters, bony fishes, sharks and marine reptiles at the top of the food web. Reconstructing the timing of the event is of current interest, and the new work suggests the process began earlier than had been thought.

Reference:
Marie Cueille et al. Fish and crab coprolites from the latest Triassic of the UK: From Buckland to the Mesozoic Marine Revolution, Proceedings of the Geologists’ Association (2020). DOI: 10.1016/j.pgeola.2020.07.011

Note: The above post is reprinted from materials provided by University of Bristol.

Fossilized jaw bone fragments of a rat-like creature found at the Petrified Forest National Park in Arizona last year by a Virginia Tech College of Science Ph.D. candidate are in fact a newly discovered 220-million-year-old species of cynodont or stem-mammal, a precursor of modern-day mammals.

The finding of this new species, Kataigidodon venetus, has been published today in the journal Biology Letters by lead author Ben Kligman, a doctoral student in the Department of Geosciences.

“This discovery sheds light on the geography and environment during the early evolution of mammals,” Kligman said. “It also adds to evidence that humid climates played an important role in the early evolution of mammals and their closest relatives. Kataigidodon was living alongside dinosauromorphs and possibly early dinosaurs related to Coelophysis—a small bipedal predator—and Kataigidodon was possibly prey of these early dinosaurs and other predators like crocodylomorphs, small coyote-like quadrupedal predators related to living crocodiles.”

Kligman added that finding a fossil that is part of Cynodontia, which includes close cousins of mammals, such as Kataigidodon, as well as true mammals, from Triassic rocks is an extremely rare event in North America. Prior to Kligman’s discovery, the only other unambiguous cynodont fossil from the Late Triassic of western North America was the 1990 discovery of a braincase of Adelobasileus cromptoni in Texas. Note that 220 million years ago, modern day Arizona and Texas were located close to the equator, near the center of the supercontinent Pangaea. Kataigidodon would have been living in a lush tropical forest ecosystem.

Kligman made the discovery while working as a seasonal paleontologist at Petrified Forest National Park in 2019. The two fossil lower jaws of Kataigidodon were found in the Upper Triassic Chinle Formation. Because only the lower jaws were discovered and are quite small—half an inch, the size of a medium grain of rice—Kligman only has a semi-picture of how the creature looked, roughly 3.5 inches in total body size, minus the tail.

Along with the jawbone fossils, Kligman found incisor, canine, and complex-postcanine teeth, similar to modern day mammals. Given the pointed shape of its teeth and small body size, it likely fed on a diet of insects, Kligman added. (Why are jaw fossils commonly found, even among small specimens? According to Kligman, the fossil record is “biased” toward only preserving the largest and most robust bones in a skeleton. The other smaller or more fragile bones—ribs, arms, feet—disappear.)

Kligman carried out field work, specimen preparation, CT scanning, conception, and design of the studyand drafting of the manuscript. He added that he and his collaborators only discovered the fossils were of a new species after reviewing the CT scan dataset of the jaws and comparing it to other related species.

“It likely would have looked like a small rat or mouse. If you were to see it in person you would think it is a mammal,” Kligman added. Does it have fur? Kligman and the researchers he worked with to identify and name the creature actually don’t know. “Triassic cynodonts have not been found from geological settings which could preserve fur if it was there, but later nonmammalian cynodonts from the Jurassic had fur, so scientists assume that Triassic ones did also.”

The name Kataigidodon venetus derives from the Greek words for thunderstorm, “kataigidos,” and tooth, “odon,” and the Latin word for blue, “venetus,” all referring to the discovery location of Thunderstorm Ridge, and the blue color of the rocks at this site. Kligman didn’t name the creature, though. That task fell to Hans Dieter-Sues, coauthor and curator of vertebrate paleontology at the Smithsonian National Museum.

Additional collaborators include Adam Marsh, park paleontologist at Petrified Forest National Park, who found the jaw fossils with Kligman, and Christian Sidor, an associate professor at the University of Washington’s Department of Biology. The research was funded by the Petrified Forest Museum Association, the Friends of Petrified Forest National Park, and the Virginia Tech Department of Geosciences.

“This study exemplifies the idea that what we collect determines what we can say,” said Michelle Stocker, an assistant professor of geosciences and Kligman’s doctoral advisor. “Our hypotheses and interpretations of past life on Earth depend on the actual fossil materials that we have, and if our search images for finding fossils only focuses on large-bodied animals, we will miss those important small specimens that are key for understanding the diversification of many groups.”

With Kataigidodon being only the second other unambiguous cynodont fossil from the Late Triassic found in western North America, could there be more new species out there waiting to be found?

Kligman said most likely. “We have preliminary evidence that more species of cynodonts are present in the same site as Kataigidodon, but we are hoping to find better fossils of them,” he added.

Reference:
A new non-mammalian eucynodont from the Chinle Formation (Triassic: Norian), and implications for the early Mesozoic equatorial cynodont record, Biology Letters (2020). royalsocietypublishing.org/doi … .1098/rsbl.2020.0631

Note: The above post is reprinted from materials provided by Virginia Tech.

In 2017, while browsing the fossil collections of Yale’s Peabody Museum of Natural History, University of Texas at Austin graduate student Simon Scarpetta came across a small lizard skull, just under an inch long.

The skull was beautifully preserved, with a mouth full of sharp teeth — including some with a distinctive curve.

Much to Scarpetta’s surprise, no one had studied it. Since being discovered in 1971 on a museum fossil hunting trip to Wyoming, the 52 million-year-old skull had sat in the specimen drawer.

“Lizards are small and prone to breaking apart, so you mostly get these individual, isolated fragmented bones,” said Scarpetta, who is studying paleontology at the UT Jackson School of Geosciences. “Anytime you find a skull, especially when you’re trying to figure out how things are related to each other, it’s always an exciting find.”

Scarpetta decided to bring the skull back to the Jackson School for a closer look. And on September 2020, the journal Scientific Reports published a study authored by Scarpetta describing the lizard as a new species, which he named Kopidosaurus perplexus.

The first part of the name references the lizard’s distinct teeth; a “kopis” is a curved blade used in ancient Greece. But the second part is a nod to the “perplexing” matter of just where the extinct lizard should be placed on the tree of life. According to an analysis conducted by Scarpetta, the evidence points to a number of plausible spots.

The spots can be divided into two groups of lizards, representing two general hypotheses of where the new species belongs. But adding to the uncertainty is that how those two groups relate to one another can shift depending on the particular evolutionary tree that’s examined. Scarpetta examined three of these trees — each one built by other researchers studying the evolutionary connections of different reptile groups using DNA — and suggests that there could be a forest of possibilities where the ancient lizard could fit.

The case of where exactly to put the perplexing lizard highlights an important lesson for paleontologists: just because a specimen fits in one place doesn’t mean that it won’t fit equally well into another.

“The hypothesis that you have about how different lizards are related to each other is going to influence what you think this one is,” Scarpetta said.

Paleontologists use anatomical details present in bones to discern the evolutionary relationships of long-dead animals. To get a close look at the lizard skull, Scarpetta created a digital scan of it in the Jackson School’s High-Resolution X-Ray CT Lab. However, while certain details helped identify the lizard as a new species, other details overlapped with features from a number of different evolutionary groups.

All of these groups belonged to a larger category known as Iguania, which includes a number of diverse species, including chameleons, anoles and iguanas. To get a better idea of where the new species might fit into the larger Iguania tree, Scarpetta compared the skull data to evolutionary trees for Iguania that were compiled by other researchers based on DNA evidence from living reptiles.

On each tree, the fossil fit equally well into two general spots. What’s more, the lizard groupings in each spot varied from tree to tree. If Scarpetta had just stopped at one spot or one tree, he would have missed alternative explanations that appear just as plausible as the others.

Scarpetta said that Kopidosaurus perplexus is far from the only fossil that could easily fit onto multiple branches on the tree of life. Paleontologist Joshua Lively, a curator at the Utah State University Eastern Prehistoric Museum, agrees and said that this study epitomizes why embracing uncertainty can lead to better, more accurate science.

“Something that I think the broader scientific community should pull from this is that you have to be realistic about your data and acknowledge what we can actually pull from our results and conclude and where there are still uncertainties,” Lively said. “Simon’s approach is the high bar, taking the high road. It’s acknowledging what we don’t know and really embracing that.”

The research was funded by the Jackson School of Geosciences and the Geological Society of America.

Reference:
Simon G. Scarpetta. Effects of phylogenetic uncertainty on fossil identification illustrated by a new and enigmatic Eocene iguanian. Scientific Reports, 2020; 10 (1) DOI: 10.1038/s41598-020-72509-2

Note: The above post is reprinted from materials provided by University of Texas at Austin.