At the end of the Cretaceous, the duck-billed hadrosaurs were the most advanced herbivores on Earth. New research has revealed just how voracious these dinosaurs were, with their average tooth worn away in less than two months as they consumed enormous amounts of plants. Some of Earth’s most successful herbivores may have had hundreds of thousands of teeth in their lifetime.

The ornithopods are a group of dinosaurs that include Iguanodon, Hypsilophodon and their relatives, including the rare rhabdodontids. Ornithopods first appeared in the Middle Jurassic but were most prominent in the Cretaceous, when they became the dominant herbivores across large parts of the world.

This journey took them from small generalists to becoming large and specialized “plant-eating machines” which rival modern cows and sheep. The research, led by Dr. Attila Ősi from Eötvös Loránd University in Hungary, shows that the dinosaurs achieved this following the evolution of vast numbers of replacement teeth, which allowed them to eat even the toughest of plants in large quantities.

“The teeth and jaws of the ornithopods changed drastically during their evolution,” Attila says. “Earlier members of the group, like Iguanodon, took more than 200 days to form their teeth and at least that long to wear them down by chewing. But by the end of the Cretaceous, hadrosaurs would wear through their teeth in as little as 50 days.”

“We think this is because the later ornithopods must have been feeding on tough plants that rapidly eroded their teeth. As they wore away at a huge rate, these dinosaurs would have needed to build up banks of teeth in their skulls to stop themselves from starving.”

The findings of the study are published in the journal Nature Communications.

Becoming the top dinosaur herbivores

While herbivory is one of the most common ways of life for animals, it’s surprisingly difficult to eat plants. Unlike meat, which is easily broken down in the gut, plants are generally made up of tough fibers and complex carbohydrates which are hard to digest.

Teeth are on the front line of this dietary battle, breaking open plants and cutting them into smaller pieces so that gut bacteria can break them down more efficiently. However, as co-author Professor Paul Barrett explains, this takes its toll on the teeth.

“Across a herbivore’s life, its teeth gradually wear down,” Paul says. “This puts an upper limit on the life of some mammals, like elephants or cows. Once their teeth are gone, the animal can no longer feed, and so it dies.”

“This isn’t a problem for reptiles. They are able to continually make new teeth, with a replacement ready to surface from beneath as soon as its predecessor wears out. As a result, dinosaur teeth are common fossils, making them a valuable way to investigate how these animals evolved.”

The team were particularly interested in investigating the teeth and jaws of the ornithopods, which eventually became some of the most advanced herbivores to have ever lived on our planet. By examining well-preserved skulls, they were able to track how the dinosaurs’ skulls developed into increasingly complex forms that were better suited to eating plants.

“We can see a sequential increase in the complexity of their adaptations for herbivory as they evolve,” Paul explains. “At the start, they had single rows of fairly simple teeth with limited wear, probably because these dinosaurs focused on fruits and softer plants.”

“By the time the hadrosaurs evolved, they had vastly more teeth which developed a large blade-like edge on one side and a series of ridges behind it. This structure is unique to these dinosaurs, and kept the upper and lower teeth sharp as they ground against each other.”

Later ornithopods also moved their jaws in new ways, being able to slide them back and forth and side to side, allowing them to grind plants down even further. Their bodies also grew much bigger, allowing them to accommodate larger guts that can more effectively release the nutrients inside plants.

Different dinosaurs took different approaches to herbivory. But the team noticed that a few groups of ornithopods, like the tenontosaurids and their more advanced iguanodontian relatives, all follow a strikingly similar evolutionary path. They believe this is an example of convergent evolution.

“About 110 million years ago, these ornithopods rapidly evolved a series of similar characteristics,” Paul explains. “Their teeth increase in number, their jaws interlock more tightly and they build up more replacement teeth, making them more effective herbivores.”

“We also see this happen in the horned dinosaurs, which include species like Triceratops. It’s tempting to speculate that these changes happened for similar reasons.”

Could flowers be responsible?

While the evidence that the environment changed in the Early Cretaceous is strong, finding out exactly what happened is challenging. To try and reveal potential causes, the team examined worn areas of dinosaur teeth, known as wear facets, for signs of microscopic changes.

“Before the Early Cretaceous, ornithopod teeth had a lot of large pits,” Attila says. “This suggests that they were eating a large amount of plant seeds, as well as potentially consuming a lot of dust and soil by feeding close to the ground.”

“Later forms have fewer pits, with many more scratches instead. This suggests that they were now eating harder plants, or feeding in a different way.”

Rather than the dinosaurs actively changing what they ate, one possible explanation could be that certain plants became more common. It’s possible that the rise of flowers could be responsible, but it doesn’t quite fit the available evidence.

“While it is suspicious that the flowering plants start to diversify around this time, they were still pretty uncommon at the time,” Paul says. “In fact, until the Late Cretaceous, horsetails, ferns and conifers would be much more common for dinosaurs looking for something to eat.”

“As it’s very difficult to disentangle the plant and dinosaur fossil records, it’s unlikely we’ll ever have enough detailed evidence to prove there is a link, even if it is a very interesting idea.”

Having finished their work on the ornithopods, the team hope to gradually widen their research to other herbivorous dinosaurs, like the ankylosaurs or the horned dinosaurs. This could give us a better idea of why these reptiles were so successful, and how evolution shaped the diet of the different groups.

“We’d like to be able to sample other dinosaurs to see if the trend of increasing body size, tooth number and the change in teeth wear we found in the ornithopods is more widespread,” Attila says. “If we can find out what changes herbivores were going through at the time, it will give us a much better chance of understanding the place of these dinosaurs in the ecosystems of the Mesozoic Era.”

Reference:
Attila Ősi et al, Trophic evolution in ornithopod dinosaurs revealed by dental wear, Nature Communications (2024). DOI: 10.1038/s41467-024-51697-9

Note: The above post is reprinted from materials provided by Natural History Museum.

Some species of pterosaurs flew by flapping their wings while others soared like vultures, demonstrates a new study published in the peer-reviewed Journal of Vertebrate Paleontology.

It has long been debated whether the largest pterosaurs could fly at all.

However, “remarkable” and “rare” three-dimensional fossils of two different large-bodied azhdarchoid pterosaur species — including one new-to-science — have enabled scientists to hypothesize that not only could the largest pterosaurs take to the air, but their flight styles could differ too.

The new findings are led by experts from the University of Michigan, in the US, the Natural Resources Authority and Yarmouk University, in Jordan, and the Saudi Geological Survey, in Saudi Arabia.

Their paper details how these fossils — which date back to the latest Cretaceous period (approximately 72 to 66 million years ago) — were remarkably three-dimensionally preserved within the two different sites that preserve a nearshore environment on the margin of Afro-Arabia, an ancient landmass that included both Africa and the Arabian Peninsula. The research team used high-resolution computed tomography (CT) scans to then analyze the internal structure of the wing bones.

“The dig team was extremely surprised to find three-dimensionally preserved pterosaur bones, this is a very rare occurrence,” explains lead author Dr Kierstin Rosenbach, from the Department of Earth and Environmental Sciences of the University of Michigan.

“Since pterosaur bones are hollow, they are very fragile and are more likely to be found flattened like a pancake, if they are preserved at all.

“With 3D preservation being so rare, we do not have a lot of information about what pterosaur bones look like on the inside, so I wanted to CT scan them.

“It was entirely possible that nothing was preserved inside, or that CT scanners were not sensitive enough to differentiate fossil bone tissue from the surrounding matrix.”

Luckily, though, what the team uncovered was “remarkable,” via “exciting internal structures not only preserved, but visible in the CT scanner.”

CT scans reveal one soars; one flaps!

Newly collected specimens of the already-known giant pterosaur, Arambourgiania philadelphiae, confirm its 10-meter wingspan and provide the first details of its bone structure. CT images revealed that the interior of its humerus, which is hollow, contains a series of ridges that spiral up and down the bone.

This resembles structures in the interior of wing bones of vultures. The spiral ridges are hypothesized to resist the torsional loadings associated with soaring (sustained powered flight that requires launch and maintenance flapping).

The other specimen analyzed was the new-to-science Inabtanin alarabia, which had a five-meter wingspan. The team named it after the place where it was excavated — near a large grape-colored hill, called Tal Inab. The generic name combines the Arabic words “inab,” for grape, and “tanin” for dragon. ‘Alarabia’ refers to the Arabian Peninsula.

Inabtanin is one of the most complete pterosaurs ever recovered from Afro-Arabia, and the CT scans revealed the structure of its flight bones was completely different from that of Arambourgiania.

The interior of the flight bones were crisscrossed by arrangement with struts that match those found in the wing bones of modern flapping birds.

This indicates it was adapted to resist bending loads associated with flapping flight, and so it is likely that Inabtanin flew this way — although this does not preclude occasional use of other flight styles too.

“The struts found in Inabtanin were cool to see, though not unusual,” says Dr Rosenbach.

“The ridges in Arambourgiania were completely unexpected, we weren’t sure what we were seeing at first!

“Being able to see the full 3D model of Arambourgiania’s humerus lined with helical ridges was just so exciting.”

What explains this difference?

The discovery of diverse flight styles in differently-sized pterosaurs is “exciting,” the experts state, because it opens a window into how these animals lived. It also poses interesting questions, like to what extent flight style is correlated with body size and which flight style is more common among pterosaurs.

“There is such limited information on the internal bone structure of pterosaurs across time, it is difficult to say with certainty which flight style came first,” Dr Rosenbach adds.

“If we look to other flying vertebrate groups, birds and bats, we can see that flapping is by far the most common flight behavior.

“Even birds that soar or glide require some flapping to get in the air and maintain flight.

“This leads me to believe that flapping flight is the default condition, and that the behavior of soaring would perhaps evolve later if it were advantageous for the pterosaur population in a specific environment; in this case the open ocean.”

Co-author Professor Jeff Wilson Mantilla, Curator at Michigan’s Museum of Paleontology, and Dr Iyad Zalmout, from the Saudi Geological Survey, found these specimens in 2007 at sites in the north and south of Jordan.

Professor Jeff Wilson Mantilla says the “variations likely reflect responses to mechanical forces applied on the pterosaurs’ wings during flight.”

Enabling further study of vertebrate flight

Concluding, Dr Rosenbach states: “Pterosaurs were the earliest and largest vertebrates to evolve powered flight, but they are the only major volant group that has gone extinct.

“Attempts to-date to understand their flight mechanics have relied on aerodynamic principles and analogy with extant birds and bats.

“This study provides a framework for further investigation of the correlation between internal bone structure and flight capacity and behavior, and will hopefully lead to broader sampling of flight bone structure in pterosaur specimens.”

Journal Reference:
Kierstin L. Rosenbach, Danielle M. Goodvin, Mohammed G. Albshysh, Hassan A. Azzam, Ahmad A. Smadi, Hakam A. Mustafa, Iyad S. A. Zalmout, Jeffrey A. Wilson Mantilla. New pterosaur remains from the Late Cretaceous of Afro-Arabia provide insight into flight capacity of large pterosaurs. Journal of Vertebrate Paleontology, 2024; DOI: 10.1080/02724634.2024.2385068

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

An international team of researchers led by SMU paleontologist Louis L. Jacobs has found matching sets of Early Cretaceous dinosaur footprints on what are now two different continents.

More than 260 footprints were discovered in Brazil and in Cameroon, showing where land-dwelling dinosaurs were last able to freely cross between South America and Africa millions of years ago before the two continents split apart.

“We determined that in terms of age, these footprints were similar,” Jacobs said. “In their geological and plate tectonic contexts, they were also similar. In terms of their shapes, they are almost identical.”

The footprints, impressed into mud and silt along ancient rivers and lakes, were found more than 3,700 miles, or 6,000 kilometers, away from each other. Dinosaurs made the tracks 120 million years ago on a single supercontinent known as Gondwana — which broke off from the larger landmass of Pangea, Jacobs said.

“One of the youngest and narrowest geological connections between Africa and South America was the elbow of northeastern Brazil nestled against what is now the coast of Cameroon along the Gulf of Guinea,” Jacobs explained. “The two continents were continuous along that narrow stretch, so that animals on either side of that connection could potentially move across it.”

Most of the dinosaur fossils were created by three-toed theropod dinosaurs.. A few were also likely made by sauropods or ornithischians, said Diana P. Vineyard, who is a research associate at SMU and co-author of the study.

Other co-authors of the study were Lawrence J. Flynn in the Department of Human Evolutionary Biology at Harvard University, Christopher R. Scotese in the Department of Earth and Planetary Sciences at Northwestern University and Ismar de Souza Carvalho at the Universidade Federal do Rio de Janeiro and Centro de Geociências.

The study was published by New Mexico Museum of Natural History & Science in a tribute to the late paleontologist Martin Lockley, who spent much of his career studying dinosaurs tracks and footprints.

Dinosaur footprints tell the whole story

Africa and South America started to split around 140 million years ago, causing gashes in Earth’s crust called rifts to open up along pre-existing weaknesses. As the tectonic plates beneath South America and Africa moved apart, magma from the Earth’s mantle rose to the surface, creating new oceanic crust as the continents moved away from each other. And eventually, the South Atlantic Ocean filled the void between these two newly-shaped continents.

Signs of some of those major events were evident between both locations where the dinosaur footprints were found — at the Borborema region in the northeast part of Brazil and the Koum Basin in northern Cameroon. Half-graben basins — geologic structures formed during rifting as the Earth’s crust pulls apart and faults form — are found in both areas and contain ancient river and lake sediments. Along with dinosaur tracks, these sediments contain fossil pollen that indicate an age of 120 million years.

Before the continental connection between Africa and South America was severed, “rivers flowed and lakes formed in the basins” Jacobs said. “Plants fed the herbivores and supported a food chain. Muddy sediments left by the rivers and lakes contain dinosaur footprints, including those of meat-eaters, documenting that these river valleys could provide specific avenues for life to travel across the continents 120 million years ago.”

Note: The above post is reprinted from materials provided by Southern Methodist University.