Fossils of small plesiosaurs, long-necked marine reptiles from the age of dinosaurs, have been found in a 100-million year old river system that is now Morocco’s Sahara Desert. This discovery suggests some species of plesiosaur, traditionally thought to be sea creatures, may have lived in freshwater.

Plesiosaurs, first found in 1823 by fossil hunter Mary Anning, were prehistoric reptiles with small heads, long necks, and four long flippers. They inspired reconstructions of the Loch Ness Monster, but unlike the monster of Lake Loch Ness, plesiosaurs were marine animals — or were widely thought to be.

Now, scientists from the University of Bath and University of Portsmouth in the UK, and Université Hassan II in Morocco, have reported small plesiosaurs from a Cretaceous-aged river in Africa.

The fossils include bones and teeth from three-metre long adults and an arm bone from a 1.5 metre long baby. They hint that these creatures routinely lived and fed in freshwater, alongside frogs, crocodiles, turtles, fish, and the huge aquatic dinosaur Spinosaurus.

These fossils suggest the plesiosaurs were adapted to tolerate freshwater, possibly even spending their lives there, like today’s river dolphins.

The new paper was headed by University of Bath Student Georgina Bunker, along with Nick Longrich from the University of Bath’s Milner Centre for Evolution, David Martill and Roy Smith from the University of Portsmouth, and Samir Zouhri from the Universite Hassan II.

The fossils include vertebrae from the neck, back, and tail, shed teeth, and an arm bone from a young juvenile.

“It’s scrappy stuff, but isolated bones actually tell us a lot about ancient ecosystems and animals in them. They’re so much more common than skeletons, they give you more information to work with” said Dr. Nick Longrich, corresponding author on the paper.

“The bones and teeth were found scattered and in different localities, not as a skeleton. So each bone and each tooth is a different animal. We have over a dozen animals in this collection.”

Whilst bones provide information on where animals died, the teeth are interesting because they were lost while the animal was alive — so they show where the animals lived.

What’s more, the teeth show heavy wear, like those fish-eating dinosaur Spinosaurus found in the same beds.

The scientists say that implies the plesiosaurs were eating the same food- chipping their teeth on the armored fish that lived in the river. This hints they spent a lot of time in the river, rather than being occasional visitors.

While marine animals like whales and dolphins wander up rivers, either to feed or because they’re lost, the number of plesiosaur fossils in the river suggest that’s unlikely.

A more likely possibility is that the plesiosaurs were able to tolerate fresh and salt water, like some whales, such as the beluga whale.

It’s even possible that the plesiosaurs were permanent residents of the river, like modern river dolphins. The plesiosaurs’ small size would have let them hunt in shallow rivers, and the fossils show an incredibly rich fish fauna.

Dr Longrich said: “We don’t really know why the plesiosaurs are in freshwater.

“It’s a bit controversial, but who’s to say that because we paleontologists have always called them ‘marine reptiles’, they had to live in the sea? Lots of marine lineages invaded freshwater.”

Freshwater dolphins evolved at least four times — in the Ganges River, the Yangtze River, and twice in the Amazon. A species of freshwater seal inhabits Lake Baikal, in Siberia, so it’s possible plesiosaurs adapted to freshwater as well.

The plesiosaurs belong to the family Leptocleididae- a family of small plesiosaurs often found in brackish or freshwater elsewhere in England, Africa, and Australia. And other plesiosaurs, including the long-necked elasmosaurs, turn up in brackish or fresh waters in North America and China.

Plesiosaurs were a diverse and adaptable group, and were around for more than 100 million years. Based on what they’ve found in Africa — and what other scientists have found elsewhere — the authors suggest they might have repeatedly invaded freshwater to different degrees.

“We don’t really know, honestly. That’s how paleontology works. People ask, how can paleontologists know anything for certain about the lives of animals that went extinct millions of years ago? The reality is, we can’t always. All we can do is make educated guesses based on the information we have. We’ll find more fossils. Maybe they’ll confirm those guesses. Maybe not.”

“It’s been really interesting to see the direction this project has gone in,” said lead author Georgina Bunker. The study initially began as an undergraduate project involving a single bone, but over time, more plesiosaur fossils started turning up, slowly providing a clearer picture of the animal.

The new discovery also expands the diversity of Morocco’s Cretaceous. Said Dr. Samir Zouhri, “This is another sensational discovery that adds to the many discoveries we have made in the Kem Kem over the past fifteen years of work in this region of Morocco. Kem Kem was truly an incredible biodiversity hotspot in the Cretaceous.”

“What amazes me” said coauthor Dave Martill, “is that the ancient Moroccan river contained so many carnivores all living alongside each other. This was no place to go for a swim.”

But what does this all mean for the plausibility of something like a Loch Ness Monster? On one level, it’s plausible. Plesiosaurs weren’t confined to the seas, they did inhabit freshwater. But the fossil record also suggests that after almost a hundred and fifty million years, the last plesiosaurs finally died out at the same time as the dinosaurs, 66 million years ago.

Reference:
Georgina Bunker, David M. Martill, Roy Smith, Samir Zourhi, Nick Longrich. Plesiosaurs from the fluvial Kem Kem Group (mid-Cretaceous) of eastern Morocco and a review of non-marine plesiosaurs. Cretaceous Research, 2022; 105310 DOI: 10.1016/j.cretres.2022.105310

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

A new study refutes a provocative claim made earlier this year that fossils classified as the dinosaur Tyrannosaurus rex represent three separate species. The rebuttal, published today in the journal Evolutionary Biology and led by paleontologists at the American Museum of Natural History and Carthage College, finds that the earlier proposal lacks sufficient evidence to split up the iconic species.

“Tyrannosaurus rex remains the one true king of the dinosaurs,” said study co-author Steve Brusatte, a paleontologist at the University of Edinburgh who conducted his Ph.D. work at the Museum. “Recently, a bold theory was announced to much fanfare: what we call T. rex was actually multiple species. It is true that the fossils we have are somewhat variable in size and shape, but as we show in our new study, that variation is minor and cannot be used to neatly separate the fossils into easily defined clusters. Based on all the fossil evidence we currently have, T. rex stands alone as the single giant apex predator from the end of the Age of Dinosaurs in North America.”

In March 2022, authors of the controversial study, also published in Evolutionary Biology, made the case that T. rex should be reclassified as three species: the standard T. rex, the bulkier “T. imperator,” and the slimmer “T. regina.” The study was based on analysis of the leg bones and teeth of 38 T. rex specimens.

The authors of the new study revisited the data presented in the earlier paper and also added data points from 112 species of living dinosaurs — birds — and from four non-avian theropod dinosaurs. They found that the multiple species argument was based on a limited comparative sample, non-comparable measurements, and improper statistical techniques.

“Their study claimed that the variation in T. rex specimens was so high that they were probably from multiple closely related species of giant meat-eating dinosaur,” said James Napoli, co-lead author of the rebuttal study and a graduating doctoral student in the Museum’s Richard Gilder Graduate School. “But this claim was based on a very small comparative sample. When compared to data from hundreds of living birds, we actually found that T. rex is less variable than most living theropod dinosaurs. This line of evidence for proposed multiple species doesn’t hold up.”

“Pinning down variation in long-extinct animals is a major challenge for paleontologists,” said co-lead author Thomas Carr from Carthage College. “Our study shows that rigorous statistical analyses that are grounded in our knowledge of living animals is the best way to clarify the boundaries of extinct species. In practical terms, the three-species model is so poorly defined that many excellent specimens can’t be identified. That’s a clear warning sign of a hypothesis that doesn’t map onto the real world.”

The original paper asserted that variation in the size of the second tooth in the lower jaw, in addition to robustness of the femur, indicated the presence of multiple species. But the authors of the new study could not replicate the tooth findings, and they recovered different results from their own measurements of the same specimens. In addition, the authors of the new study took issue with how the “breakpoints” for each species using these traits were statistically determined. The statistical analysis in the original study defined the number of groups before the test was run, so it is not useful for testing the hypothesis, according to the authors of the new study. In the latest study, a different statistical technique was used to determine how many clusters exist within the data without any advanced assumptions, finding that they are best considered as a single group — in other words, one species — T. rex.

“The boundaries of even living species are very hard to define: for instance, zoologists disagree over the number of living species of giraffe,” said co-author Thomas Holtz, from the University of Maryland and the National Museum of Natural History. “It becomes much more difficult when the species involved are ancient and only known from a fairly small number of specimens. Other sources of variation — changes with growth, with region, with sex, and with good old-fashioned individual differences — have to be rejected before one accepts the hypothesis that two sets of specimens are in fact separate species. In our view, that hypothesis is not yet the best explanation.”

“T. rex is an iconic species and an incredibly important one for both paleontological research and communicating to the public about science, so it’s important that we get this right,” said co-author David Hone, from Queen Mary University of London. “There is still a good chance that there is more than one species of Tyrannosaurus out there, but we need strong evidence to make that kind of decision.”

Reference:
Thomas D. Carr, James G. Napoli, Stephen L. Brusatte, Thomas R. Holtz, David W. E. Hone, Thomas E. Williamson, Lindsay E. Zanno. Insufficient Evidence for Multiple Species of Tyrannosaurus in the Latest Cretaceous of North America: A Comment on “The Tyrant Lizard King, Queen and Emperor: Multiple Lines of Morphological and Stratigraphic Evidence Support Subtle Evolution and P. Evolutionary Biology, 2022; DOI: 10.1007/s11692-022-09573-1

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

A team co-led by University of Minnesota Twin Cities researcher Peter Makovicky and Argentinean colleagues Juan Canale and Sebastian Apesteguía has discovered a new huge, meat-eating dinosaur, dubbed Meraxes gigas. The new dinosaur provides clues about the evolution and biology of dinosaurs such as the Carcharodontosaurus and Tyrannosaurus rex — specifically, why these animals had such big skulls and tiny arms.

The study is published in Current Biology, a peer-reviewed scientific biology journal.

The researchers initially discovered Meraxes in Patagonia in 2012 and have spent the last several years extracting, preparing, and analyzing the specimen. The dinosaur is part of the Carcharodontosauridae family, a group of giant carnivorous theropods that also includes Giganotosaurus, one of the largest known meat-eating dinosaurs and one of the reptilian stars of the recently released “Jurassic World: Dominion” movie.

Though not the largest among carcharodontosaurids, Meraxes was still an imposing animal measuring around 36 feet from snout to tail tip and weighing approximately 9,000 pounds. The researchers recovered the Meraxes from rocks that are around 90-95 million years old, alongside other dinosaurs including several long-necked sauropod specimens.

Meraxes is among the most complete carcharodontosaurid skeleton paleontologists have found yet in the southern hemisphere and includes nearly the entirety of the animal’s skull, hips, and both left and right arms and legs.

“The neat thing is that we found the body plan is surprisingly similar to tyrannosaurs like T. rex,” said Peter Makovicky, one of the principal authors of the study and a professor in the University of Minnesota N.H. Winchell School of Earth and Environmental Sciences. “But, they’re not particularly closely related to T. rex. They’re from very different branches of the meat-eating dinosaur family tree. So, having this new discovery allowed us to probe the question of, ‘Why do these meat-eating dinosaurs get so big and have these dinky little arms?'”

“The discovery of this new carcharodontosaurid, the most complete up to now, gives us an outstanding opportunity to learn about their systematics, paleobiology, and true size like never before,” said Sebastian Apesteguía, a co-author of the study and a researcher at Maimónides University in Argentina.

With the statistical data that Meraxes provided, the researchers found that large, mega-predatory dinosaurs in all three families of therapods grew in similar ways. As they evolved, their skulls grew larger and their arms progressively shortened.

The possible uses of the tiny forelimbs in T. rex and other large carnivorous dinosaurs have been the topic of much speculation and debate.

“What we’re suggesting is that there’s a different take on this,” Makovicky said. “We shouldn’t worry so much about what the arms are being used for, because the arms are actually being reduced as a consequence of the skulls becoming massive. Whatever the arms may or may not have been used for, they’re taking on a secondary function since the skull is being optimized to handle larger prey.”

The researchers also found that carcharodontosaurids including species from Patagonia evolved very quickly, but then disappeared suddenly from the fossil record very soon after.

“Usually when animals are on the verge of extinction, it’s because they’re evolutionary rates are quite slow, meaning they aren’t adapting very quickly to their environment,” explained Juan Canale, the study’s lead author and a researcher at the National University of Río Negro. “Here, we have evidence that Meraxes and its relatives were evolving quite fast and yet within a few million years of being around, they disappeared, and we don’t know why. It’s one of these finds where you answer some questions, but it generates more questions for the future.”

The research was funded by the National Geographic Society, Municipalidad de Villa El Chocón, Fundación “Félix de Azara,” and the Field Museum in Chicago.

In addition to Makovicky, Apesteguía, and Canale, the research team included National University of Río Negro researcher Alejandro Haluza; Maimónides University researcher Pablo Gallina; West Virginia Institute of Technology Assistant Professor Jonathan Mitchell; Natural History Museum of Los Angeles County researcher Nathan Smith; Carleton University researchers Thomas Cullen; Akiko Shinya of the Field Museum in Chicago; and National University of San Luis researcher Federico Gianechini.

Reference:
Juan I. Canale, Sebastián Apesteguía, Pablo A. Gallina, Jonathan Mitchell, Nathan D. Smith, Thomas M. Cullen, Akiko Shinya, Alejandro Haluza, Federico A. Gianechini, Peter J. Makovicky. New giant carnivorous dinosaur reveals convergent evolutionary trends in theropod arm reduction. Current Biology, 2022; DOI: 10.1016/j.cub.2022.05.057

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

Research led by palaeontologists at the University of Southampton has identified the remains of one of Europe’s largest ever land-based hunters: a dinosaur that measured over 10m long and lived around 125 million years ago.

Several prehistoric bones, uncovered on the Isle of Wight, on the south coast of England, and housed at Dinosaur Isle Museum in Sandown, belonged to a type of two-legged, crocodile-faced predatory dinosaur known as spinosaurids. Dubbed the ‘White Rock spinosaurid’ — after the geological layer in which it was found — it was a predator of impressive proportions.

“This was a huge animal, exceeding 10 m in length and probably several tonnes in weight. Judging from some of the dimensions, it appears to represent one of the largest predatory dinosaur ever found in Europe — maybe even the biggest yet known,” said PhD student Chris Barker, who led the study. “It’s a shame it’s only known from a small amount of material, but these are enough to show it was an immense creature.”

The discovery follows previous work on spinosaurids by the University of Southampton team, which published a study on the discovery of two new species in 2021.

The bones of the ‘White Rock spinosaurid’, which include huge pelvic and tail vertebrae, amongst other pieces, were discovered near Compton Chine, on the southwest coast of the Isle of Wight. The Cretaceous rocks are famous for their dinosaurs, but little appreciated is the fact that the Island’s fossil record preserves dinosaurs from more than one section of history — and some of those sections, even today, are poorly known.

“Unusually, this specimen eroded out of the Vectis Formation, which is notoriously poor in dinosaur fossils,” said corresponding author Dr Neil Gostling, who teaches evolution and palaeobiology at the University of Southampton. “It’s likely to be the youngest spinosaur material yet known from the UK.”

The 125 million year old Vectis Formation preserves the beginning of a period of rising sea levels, where the ‘White Rock spinosaurid’ stalked lagoonal waters and sandflats in search of food.

“Because it’s only known from fragments at the moment, we haven’t given it a formal scientific name” said co-author Darren Naish. He added: “We hope that additional remains will turn up in time.

“This new animal bolsters our previous argument — published last year — that spinosaurid dinosaurs originated and diversified in western Europe before becoming more widespread.”

Marks on the bone also showed how, even after death, the body of this giant probably supported a range of scavengers and decomposers.

“Most of these amazing fossils were found by Nick Chase, one of Britain’s most skilled dinosaur hunters, who sadly died just before the Covid epidemic,” said co-author Jeremy Lockwood, a PhD student at the University of Portsmouth and Natural History Museum. “I was searching for remains of this dinosaur with Nick and found a lump of pelvis with tunnels bored into it, each about the size of my index finger. We think they were caused by bone eating larvae of a type of scavenging beetle. It’s an interesting thought that this giant killer wound up becoming a meal for a host of insects.”

The researchers hope to generate thin sections of the material to look at the microscopic internal properties of the bones in the near future, which may provide information about its growth rate and possible age.

Reference:
Chris T. Barker, Jeremy A.F. Lockwood, Darren Naish, Sophie Brown, Amy Hart, Ethan Tulloch, Neil J. Gostling. A European giant: a large spinosaurid (Dinosauria: Theropoda) from the Vectis Formation (Wealden Group, Early Cretaceous), UK. PeerJ, 2022; 10: e13543 DOI: 10.7717/peerj.13543

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

For decades, paleontologists have debated whether dinosaurs were warm-blooded, like modern mammals and birds, or cold-blooded, like modern reptiles. Knowing whether dinosaurs were warm- or cold-blooded could give us hints about how active they were and what their everyday lives were like, but the methods to determine their warm- or cold-bloodedness — how quickly their metabolisms could turn oxygen into energy — were inconclusive. But in a new paper in Nature, scientists are unveiling a new method for studying dinosaurs’ metabolic rates, using clues in their bones that indicated how much the individual animals breathed in their last hour of life.

“This is really exciting for us as paleontologists — the question of whether dinosaurs were warm- or cold-blooded is one of the oldest questions in paleontology, and now we think we have a consensus, that most dinosaurs were warm-blooded,” says Jasmina Wiemann, the paper’s lead author and a postdoctoral researcher at the California Institute of Technology.

“The new proxy developed by Jasmina Wiemann allows us to directly infer metabolism in extinct organisms, something that we were only dreaming about just a few years ago. We also found different metabolic rates characterizing different groups, which was previously suggested based on other methods, but never directly tested,” says Matteo Fabbri, a postdoctoral researcher at the Field Museum in Chicago and one of the study’s authors.

People sometimes talk about metabolism in terms of how easy it is for someone to stay in shape, but at its core, “metabolism is how effectively we convert the oxygen that we breathe into chemical energy that fuels our body,” says Wiemann, who is affiliated with Yale University and the Natural History Museum of Los Angeles County.

Animals with a high metabolic rate are endothermic, or warm-blooded; warm-blooded animals like birds and mammals take in lots of oxygen and have to burn a lot of calories in order to maintain their body temperature and stay active. Cold-blooded, or ectothermic, animals like reptiles breathe less and eat less. Their lifestyle is less energetically expensive than a hot-blooded animal’s, but it comes at a price: cold-blooded animals are reliant on the outside world to keep their bodies at the right temperature to function (like a lizard basking in the sun), and they tend to be less active than warm-blooded creatures.

With birds being warm-blooded and reptiles being cold-blooded, dinosaurs were caught in the middle of a debate. Birds are the only dinosaurs that survived the mass extinction at the end of the Cretaceous, but dinosaurs (and by extension, birds) are technically reptiles — outside of birds, their closest living relatives are crocodiles and alligators. So would that make dinosaurs warm-blooded, or cold-blooded?

Scientists have tried to glean dinosaurs’ metabolic rates from chemical and osteohistological analyses of their bones. “In the past, people have looked at dinosaur bones with isotope geochemistry that basically works like a paleo-thermometer,” says Wiemann — researchers examine the minerals in a fossil and determine what temperatures those minerals would form in. “It’s a really cool approach and it was really revolutionary when it came out, and it continues to provide very exciting insights into the physiology of extinct animals. But we’ve realized that we don’t really understand yet how fossilization processes change the isotope signals that we pick up, so it is hard to unambiguously compare the data from fossils to modern animals.”

Another method for studying metabolism is growth rate. “If you look at a cross section of dinosaur bone tissue, you can see a series of lines, like tree rings, that correspond to years of growth,” says Fabbri. “You can count the lines of growth and the space between them to see how fast the dinosaur grew. The limit relies on how you transform growth rate estimates into metabolism: growing faster or slower can have more to do with the animal’s stage in life than with its metabolism, like how we grow faster when we’re young and slower when we’re older.”

The new method proposed by Wiemann, Fabbri, and their colleagues doesn’t look at the minerals present in bone or how quickly the dinosaur grew. Instead, they look at one of the most basic hallmarks of metabolism: oxygen use. When animals breathe, side products form that react with proteins, sugars, and lipids, leaving behind molecular “waste.” This waste is extremely stable and water-insoluble, so it’s preserved during the fossilization process. It leaves behind a record of how much oxygen a dinosaur was breathing in, and thus, its metabolic rate.

The researchers looked for these bits of molecular waste in dark-colored fossil femurs, because those dark colors indicate that lots of organic matter are preserved. They examined the fossils using Raman and Fourier-transform infrared spectroscopy — “these methods work like laser microscopes, we can basically quantify the abundance of these molecular markers that tell us about the metabolic rate,” says Wiemann. “It is a particularly attractive method to paleontologists, because it is non-destructive.”

The team analyzed the femurs of 55 different groups of animals, including dinosaurs, their flying cousins the pterosaurs, their more distant marine relatives the plesiosaurs, and modern birds, mammals, and lizards. They compared the amount of breathing-related molecular byproducts with the known metabolic rates of the living animals and used those data to infer the metabolic rates of the extinct ones.

The team found that dinosaurs’ metabolic rates were generally high. There are two big groups of dinosaurs, the saurischians and the ornithischians — lizard hips and bird hips. The bird-hipped dinosaurs, like Triceratops and Stegosaurus, had low metabolic rates comparable to those of cold-blooded modern animals. The lizard-hipped dinosaurs, including theropods and the sauropods — the two-legged, more bird-like predatory dinosaurs like Velociraptor and T. rex and the giant, long-necked herbivores like Brachiosaurus — were warm- or even hot-blooded. The researchers were surprised to find that some of these dinosaurs weren’t just warm-blooded — they had metabolic rates comparable to modern birds, much higher than mammals. These results complement previous independent observations that hinted at such trends but could not provide direct evidence, because of the lack of a direct proxy to infer metabolism.

These findings, the researchers say, can give us fundamentally new insights into what dinosaurs’ lives were like.

“Dinosaurs with lower metabolic rates would have been, to some extent, dependent on external temperatures,” says Wiemann. “Lizards and turtles sit in the sun and bask, and we may have to consider similar ‘behavioral’ thermoregulation in ornithischians with exceptionally low metabolic rates. Cold-blooded dinosaurs also might have had to migrate to warmer climates during the cold season, and climate may have been a selective factor for where some of these dinosaurs could live.”

On the other hand, she says, the hot-blooded dinosaurs would have been more active and would have needed to eat a lot. “The hot-blooded giant sauropods were herbivores, and it would take a lot of plant matter to feed this metabolic system. They had very efficient digestive systems, and since they were so big, it probably was more of a problem for them to cool down than to heat up.” Meanwhile, the theropod dinosaurs — the group that contains birds — developed high metabolisms even before some of their members evolved flight.

“Reconstructing the biology and physiology of extinct animals is one of the hardest things to do in paleontology. This new study adds a fundamental piece of the puzzle in understanding the evolution of physiology in deep time and complements previous proxies used to investigate these questions. We can now infer body temperature through isotopes, growth strategies through osteohistology, and metabolic rates through chemical proxies,” says Fabbri.

In addition to giving us insights into what dinosaurs were like, this study also helps us better understand the world around us today. Dinosaurs, with the exception of birds, died out in a mass extinction 65 million years ago when an asteroid struck the Earth. “Having a high metabolic rate has generally been suggested as one of the key advantages when it comes to surviving mass extinctions and successfully radiating afterwards,” says Wiemann — some scientists have proposed that birds survived while the non-avian dinosaurs died because of the birds’ increased metabolic capacity. But this study, Wiemann says, helps to show that this isn’t true: many dinosaurs with bird-like, exceptional metabolic capacities went extinct.

“We are living in the sixth mass extinction,” says Wiemann, “so it is important for us to understand how modern and extinct animals physiologically responded to previous climate change and environmental perturbations, so that the past can inform biodiversity conservation in the present and inform our future actions.”

Reference:
Jasmina Wiemann, Iris Menéndez, Jason M. Crawford, Matteo Fabbri, Jacques A. Gauthier, Pincelli M. Hull, Mark A. Norell, Derek E. G. Briggs. Fossil biomolecules reveal an avian metabolism in the ancestral dinosaur. Nature, 2022; DOI: 10.1038/s41586-022-04770-6

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

Plesiosaurs, which lived about 210 million years ago, adapted to life underwater in a unique way: their front and hind legs evolved in the course of evolution to form four uniform, wing-like flippers. In her thesis supervised at Ruhr-Universität Bochum and the University of Bonn, Dr. Anna Krahl investigated how they used these to move through the water. Partly by using the finite element method, which is widely used in engineering, she was able to show that it was necessary to twist the flippers in order to travel forward. She was able to reconstruct the movement sequence using bones, models and reconstructions of the muscles.

Plesiosaurs belong to a group of saurians called Sauropterygia, or paddle lizards, that re-adapted to living in the oceans. They evolved in the late Triassic 210 million years ago, lived at the same time as the dinosaurs, and became extinct at the end of the Cretaceous period. Plesiosaurs are characterized by an often extremely elongated neck with a small head — the elasmosaurs even have the longest neck of all vertebrates. But there were also large predatory forms with a rather short neck and huge skulls. In all plesiosaurs, the neck is attached to a teardrop-shaped, hydrodynamically well adapted body with a markedly shortened tail.

Researchers have puzzled for 120 years how plesiosaurs swam

The second feature that makes plesiosaurs so unusual are their four uniform wing-like flippers. “Having the front legs transformed into wing-like flippers is relatively common in evolution, for instance in sea turtles. Never again, however, did the hind legs evolve into an almost identical-looking airfoil-like wing,” explains Anna Krahl, whose doctoral thesis was supervised by Professor P. Martin Sander (Bonn) and Professor Ulrich Witzel (Bochum). Sea turtles and penguins, for example, have webbed feet. For more than 120 years, researchers in vertebrate paleontology have puzzled over how plesiosaurs might have swum with these four wings. Did they row like freshwater turtles or ducks? Did they fly underwater like sea turtles and penguins? Or did they combine underwater flight and rowing like modern-day sea lions or the pig-nosed turtle? It is also unclear whether the front and rear flippers were flapped in unison, in opposition, or out of phase.

Anna Krahl has been studying the body structure of plesiosaurs for several years. She examined the bones of the shoulder and pelvic girdle, the front and hind flippers, and the shoulder joint surfaces of the plesiosaur Cryptoclidus eurymerus from the Middle Jurassic period (about 160 million years ago) on a complete skeleton displayed in the Goldfuß Museum of the University of Bonn. Plesiosaurs have stiffened elbow, knee, hand, and ankle joints, but functioning shoulder, hip, and finger joints. “Analysis comparing them to modern-day sea turtles, and based on what is known about their swimming process, indicated that plesiosaurs were probably not able to rotate their flippers as much as would be necessary for rowing,” concludes Krahl, summarizing one of her preliminary papers. Rowing is primarily a back-and-forth motion that uses water resistance to move forward. The preferred direction of flipper movement in plesiosaurs, on the other hand, was up-and-down, as used by underwater fliers to generate propulsion.

The question remained how plesiosaurs could ultimately twist their flippers to place them in a hydrodynamically favorable position and produce lift without rotating the upper arm and thigh around the longitudinal axis. “This could work by means of twisting the flippers around their long axis,” says Anna Krahl. “Other vertebrates, such as the leatherback turtle, have also been shown to use this movement to generate propulsion through lift.” Twisting, for example, involves bending the first finger far downward and the last finger far upward. The remaining fingers bridge these extreme positions so that the flipper tip is almost vertical without requiring any real rotation in the shoulder or wrist.

A reconstruction of the muscles of the fore- and hind flippers for Cryptoclidus using reptiles alive today showed that plesiosaurs could actively enable such flipper twisting. In addition to classical models, the researchers also made computer tomographies of the humerus and femur of Cryptoclidus and used them to create virtual 3D models. “These digital models were the basis for calculating the forces using a method we borrowed from engineering: the finite element method, or FE,” explains Anna Krahl. All the muscles and their angles of attachment on the humerus and femur were virtually reproduced in an FE computer program that can simulate physiological functional loads, for example on construction components but also on prostheses. Based on muscle force assumptions from a similar study on sea turtles, the team was able to calculate and visualize the loading on each bone.

Twisting of the flippers can be proven indirectly

During a movement cycle, the limb bones are loaded by compression, tension, bending and torsion. “The FE analyses showed that the humerus and femur in the flippers are functionally loaded mainly by compression and to a much lesser extent by tensile stress,” Anna Krahl explains. “This means that the plesiosaur built its bones by using as little material as necessary.” This natural state can only be maintained if the muscles that twist the flippers and the muscles that wrap around the bone are included. “We can therefore indirectly prove that plesiosaurs twisted their flippers in order to swim efficiently,” Anna Krahl sums up.

The team was also able to calculate forces for the individual muscles that generated the upstroke and downstroke. For instance, it transpired that the downstroke of both pairs of flippers was more powerful than the upstroke. This is comparable to our sea turtles today and different from today’s penguins, which move forward the same distance with the upstroke as with the downstroke. “Plesiosaurs adapted to life in water in a very different way than whales, for example,” notes Anna Krahl, who now works at the Eberhard Karls University in Tübingen, Germany. “This unique path of evolution exemplifies the importance of paleontological research because it’s the only way we can appreciate the full range of what evolution can bring about.”

Reference:
Anna Krahl, Andreas Lipphaus, P. Martin Sander, Ulrich Witzel. Determination of muscle strength and function in plesiosaur limbs: finite element structural analyses of Cryptoclidus eurymerus humerus and femur. PeerJ, 2022; 10: e13342 DOI: 10.7717/peerj.13342

Note: The above post is reprinted from materials provided by Ruhr-University Bochum. Original written by Meike Drießen.

Proteins extracted from fragments of prehistoric eggshell found in the Australian sands confirm that the continent’s earliest humans consumed the eggs of a two-metre tall bird that disappeared into extinction over 47,000 years ago.

Burn marks discovered on scraps of ancient shell several years ago suggested the first Australians cooked and ate large eggs from a long-extinct bird – leading to fierce debate over the species that laid them.

Now, an international team led by scientists from the universities of Cambridge and Turin have placed the animal on the evolutionary tree by comparing the protein sequences from powdered egg fossils to those encoded in the genomes of living avian species.

“Time, temperature and the chemistry of a fossil all dictate how much information we can glean,” said senior co-author Prof Matthew Collins from the University of Cambridge’s Department of Archaeology.

“Eggshells are made of mineral crystals that can tightly trap some proteins, preserving this biological data in the harshest of environments – potentially for millions of years.”

According to findings published in the journal Proceedings of the National Academy of Sciences, the ancient eggs came from Genyornis: a huge flightless “mihirung” – or ‘Thunder Bird’ – with tiny wings and massive legs that roamed prehistoric Australia, possibly in flocks.

Fossil records show that Genyornis stood over two metres tall, weighed between 220-240 kilograms, and laid melon-sized eggs of around 1.5 kg. It was among the Australian “mega-fauna” to vanish a few thousand years after humans arrived, suggesting people played a role in its extinction.

The earliest “robust” date for the arrival of humans to Australia is some 65,000 years ago. Burnt eggshells from the previously unconfirmed species all date to around 50 to 55 thousand years ago – not long before Genyornis is thought to have gone extinct – by which time humans had spread across most of the continent.

“There is no evidence of Genyornis butchery in the archaeological record. However, eggshell fragments with unique burn patterns consistent with human activity have been found at different places across the continent,” said senior co-author Prof Gifford Miller from the University of Colorado.

“This implies that the first humans did not necessarily hunt these enormous birds, but did routinely raid nests and steal their giant eggs for food,” he said. “Overexploitation of the eggs by humans may well have contributed to Genyornis extinction.”

While Genyornis was always a contender for the mystery egg-layer, some scientists argued that – due to shell shape and thickness – a more likely candidate was the Progura or ‘giant malleefowl’: another extinct bird, much smaller, weighing around 5-7 kg and akin to a large turkey.

The initial ambition was to put the debate to bed by pulling ancient DNA from pieces of shell, but genetic material had not sufficiently survived the hot Australian climate.

Miller turned to researchers at Cambridge and Turin to explore a relatively new technique for extracting a different type of “biomolecule”: protein.

While not as rich in hereditary data, the scientists were able to compare the sequences in ancient proteins to those of living species using a vast new database of biological material: the Bird 10,000 Genomes (B10K) project.

“The Progura was related to today’s megapodes, a group of birds in the galliform lineage, which also contains ground-feeders such as chickens and turkeys,” said study first author Prof Beatrice Demarchi from the University of Turin.

“We found that the bird responsible for the mystery eggs emerged prior to the galliform lineage, enabling us to rule out the Progura hypothesis. This supports the implication that the eggs eaten by early Australians were laid by Genyornis.”

The 50,000-year-old eggshell tested for the study came from the archaeological site of Wood Point in South Australia, but Prof Miller has previously shown that similar burnt shells can be found at hundreds of sites on the far western Ningaloo coast.

The researchers point out that the Genyornis egg exploitation behaviour of the first Australians likely mirrors that of early humans with ostrich eggs, the shells of which have been unearthed at archaeological sites across Africa dating back at least 100,000 years.

Prof Collins added: “While ostriches and humans have co-existed throughout prehistory, the levels of exploitation of Genyornis eggs by early Australians may have ultimately proved more than the reproductive strategies of these extraordinary birds could bear.”

Reference:
Beatrice Demarchi, Josefin Stiller, Alicia Grealy, Meaghan Mackie, Yuan Deng, Tom Gilbert, Julia Clarke, Lucas J. Legendre, Rosa Boano, Thomas Sicheritz-Pontén, John Magee, Guojie Zhang, Michael Bunce, Matthew James Collins, Gifford Miller. Ancient proteins resolve controversy over the identity of Genyornis eggshell. Proceedings of the National Academy of Sciences, 2022; DOI: 10.1073/pnas.2109326119

Note: The above post is reprinted from materials provided by University of Cambridge. Original written by Fred Lewsey.