Tag Archives: #reptiles

New Jurassic Flying Reptile Reveals the Oldest Opposed Thumb (Paleontology)

A new 160-million-year-old arboreal pterosaur species, dubbed ‘Monkeydactyl’, has the oldest true opposed thumb – a novel structure previously not known in pterosaurs.

An international team of researchers from China, Brazil, UK, Denmark and Japan have described a new Jurassic pterosaur Kunpengopterus antipollicatus, which was discovered in the Tiaojishan Formation of Liaoning, China.

It is a small-bodied darwinopteran pterosaur, with an estimated wingspan of 85 cm. Most importantly, the specimen was preserved with an opposed pollex (“thumb”) on both hands.

The species name ‘antipollicatus’ means ‘opposite thumbed’ in ancient Greek, in light of the opposed thumb of the new species. This is the first discovery of a pterosaur with an opposed thumb. It also represents the earliest record of a true opposed thumb in Earth’s history. The researchers published their discovery today in the journal Current Biology.

A true opposed pollex is mostly present in mammals (e.g. primates) and some tree frogs, but extremely rare among extant reptiles except for chameleons. This discovery adds to the list that darwinopteran pterosaurs such as K. antipollicatus also evolved an opposed thumb.

The research team scanned the fossil of K. antipollicatus using micro-computed tomography (micro-CT), a technique making use of X-ray to image an object. By studying its forelimb morphology and musculature, they suggest that K. antipollicatus could have used its hand for grasping, which is likely an adaptation for arboreal life.

In order to test the arboreal interpretation, the team analysed K. antipollicatus and other pterosaurs using a set of anatomical characters related to arboreal adaptation. The results support K. antipollicatus as an arboreal species, but not the other pterosaurs from the same ecosystem. This suggests niche-partitioning among these pterosaurs and provides the first quantitative evidence that at least some darwinopteran pterosaurs were arboreal.

Fion Waisum Ma, co-author of the study and PhD researcher at the University of Birmingham, said: “The fingers of ‘Monkeydactyl’ are tiny and partly embedded in the slab. Thanks to micro-CT scanning, we could see through the rocks, create digital models and tell how the opposed thumb articulates with the other finger bones.

“This is an interesting discovery. It provides the earliest evidence of a true opposed thumb, and it is from a pterosaur – which wasn’t known for having an opposed thumb.”

Xuanyu Zhou from China University of Geosciences who led the study commented: “Tiaojishan palaeoforest is home to many organisms, including three genera of darwinopteran pterosaurs. Our results show that K. antipollicatus has occupied a different niche from Darwinopterus and Wukongopterus, which has likely minimized competition among these pterosaurs.”

Rodrigo V. Pêgas from Federal University of ABC, in Sao Bernardo, Brazil, said: “Darwinopterans are a group of pterosaurs from the Jurassic of China and Europe, named after Darwin due to their unique transitional anatomy that has revealed how evolution affected the anatomy of pterosaurs throughout time.

“On top of that, a particular darwinopteran fossil has been preserved with two associated eggs, revealing clues to pterosaur reproduction. They’ve always been considered precious fossils for these reasons and it is impressive that new darwinopteran species continue to surprise us!”

Featured image: Life reconstruction of K. antipollicatus (Image credit: Chuang Zhao)

Reference: “A new darwinopteran pterosaur reveals arborealism and an opposed thumb” by Xuanyu Zhou, Rodrigo V. Pêgas, Waisum Ma, Gang Han, Xingsheng Jin, Maria E.C. Leal, Niels Bonde, Yoshitsugu Kobayashi, Stephan Lautenschlager, Xuefang Wei, Caizhi Shen and Shu’an Ji, 12 April 2021, Current Biology.
DOI: 10.1016/j.cub.2021.03.030

Provided by University of Birmingham

Pterosaurs Undergo Dental Examination To Reveal Clues About Diets And Lifestyles (Paleontology)

Researchers at the University of Leicester’s Centre for Palaeobiology Research and the University of Birmingham used dental microwear analysis to look at the wear patterns still visible on the teeth of 17 different species of pterosaur. They compared these with similar patterns on the teeth of modern reptiles, including monitor lizards and crocodilians, where much more is known about their diet.

Microscopic analysis of the teeth of pterosaurs has revealed new insights into the diets and behaviours of Earth’s earliest flying reptiles. © University Of Birmingham.

The team was able to show for the first time how the technique can be used to not only tell us what these animals ate, but also to challenge ideas about their lifestyles and evolution. Their results are published in Nature Communications.

“Most existing ideas about what pterosaurs ate come from comparisons of the shapes of their teeth with those of living animals,” explains lead author Dr Jordan Bestwick, of the University of Birmingham’s School of Geography, Earth and Environmental Sciences. “For example, if the animal had conical teeth like a crocodile, we might assume it ate fish. But this approach has obvious shortcomings – the teeth of pandas and polar bears, for example, are similar, but comparing them wouldn’t give us an accurate picture of their diets.”

The analysis showed that modern reptiles with rougher wear on their tooth surfaces are more likely to have eaten crunchy things, such as shelled invertebrates – beetles or crabs – whereas reptiles which eat mainly soft items, such as fish, have smoother tooth surfaces. By applying the technique to pterosaurs the team was able to determine the diet of each species.

Dr Bestwick says: “Our analysis has yielded some fascinating insights into individual species, but also into some of the bigger questions around how these pterosaurs evolved and whether their lifestyles were more similar to those of modern day birds or reptiles. Evidence from dental microwear analysis can shed new light on this debate.”

Professor Mark Purnell, Professor of Palaeobiology at the University of Leicester said: “This is the first time this technique has been applied in this way to ancient reptiles, and it’s great to find it works so well. Often, palaeontologists have very little to go on when trying to understand what extinct animals ate. This approach gives us a new tool, allowing us to move from what are sometimes little more than educated guesses, into the realms of solid science.”

In one example, the team examined the teeth of Rhamphorhynchus, a long-tailed pterosaur from the Jurassic period. Researchers found that juvenile Rhamphorhynchus had insect-based diets, whereas their adult counterparts – about the size of a large seagull – were more likely to have eaten fish. This suggests a species in which the adults took little care of their young – a behaviour that is common in reptiles and is not exhibited by birds.

The team also investigated whether their analysis could shed light on how different species of pterosaurs evolved. Pterosaurs lived between 210 and 66 million years ago, eventually dying out at the same time as dinosaurs. In that time, according to the dental microwear analysis, there was a general shift in diet from invertebrates such as insects, towards a more meat or fish-based diet.

“We found that the earliest forms of pterosaurs ate mainly crunchy invertebrates,” says Dr Bestwick. “The shift towards eating fish or meat coincides with the evolution of birds. We think it’s possible, therefore, that competition with birds could explain the decline of smaller-bodied pterosaurs and a rise in larger, carnivorous species.”

Natalia Jagielska, a PhD researcher in pterosaur palaeontology at the University of Edinburgh, (not involved in this study) says the research adds much-needed clarity to the behaviour and ecological role of pterosaurs in ancient food webs.

“Pterosaurs are a fascinating group of Mesozoic reptiles with astounding diversity in tooth morphology,” she says. “This study is important for contributing to the idea that young Rhamphorhynchus were independent invertebrate hunters before becoming fish consumers, rather than being fed and nurtured by parents, like birds. Or that in pterosaur-rich environments, like the Late Jurassic Bavarian lagoons, pterosaur species have partitioned to occupy variations of dietary niches.”

The research team anticipate their methods will set a new benchmark for robust interpretation of extinct reptile diets, paving the way for an enhanced understanding of ancient ecosystems.

The research was carried out in the University of Leicester’s Centre for Palaeobiology Research and was funded by the Natural Environment Research Council and the University of Leicester, with additional support from the Paleontological Association.

Read the article titled “Dietary diversity and evolution of the earliest flying vertebrates revealed by dental microwear texture analysis. Nature Communications.”

References: Bestwick, J., Unwin, D.M., Butler, R.J. et al. Dietary diversity and evolution of the earliest flying vertebrates revealed by dental microwear texture analysis. Nat Commun 11, 5293 (2020). https://doi.org/10.1038/s41467-020-19022-2 https://www.nature.com/articles/s41467-020-19022-2

Provided by Birmingham University

New Pterosaur Species Unearthed in China (Paleontology)

A new genus and species of dsungaripterid pterosaur that lived during the Early Cretaceous epoch has been identified from the incomplete lower jaws found in China.

Life reconstruction of Ordosipterus planignathus. Image credit: Chuang Zhao.

Pterosaurs are highly successful flying reptiles that lived at the same time as dinosaurs, between 210 million and 65 million years ago.

They were Earth’s first flying vertebrates, with birds and bats making their appearances much later.

Some pterosaurs, such as the giant azhdarchids, were the largest flying animals of all time, with wingspans exceeding 9 m (30 feet) and standing heights comparable to modern giraffes.

The newly-identified species, dubbed Ordosipterus planignathus, lived between 120 and 110 million years ago during the Cretaceous period.

This flying reptile belongs to Dsungaripteridae, a family of robust pterosaurs that includes several genera and species from Asia and South America.

“As a member of the Dsungaripteridae family, Ordosipterus planignathus enlarges the geographical distribution of the dsungaripterid pterosaurs from the northwestern China — with western Mongolia — to central North China,” said Dr. Shu-an Ji, a paleontologist in the Institute of Geology at the Chinese Academy of Geological Sciences and the Key Laboratory of Stratigraphy and Palaeontology at China’s Ministry of Natural Resources.

Incomplete articulated lower jaws of Ordosipterus planignathus: (a) dorsal view, (b) left lateral view, (c) ventral view. Image credit: Shu-an Ji, doi: 10.31035/cg2020007.

The fossilized remains of Ordosipterus planignathus were found in the Luohandong Formation near Xinzhao village in Inner Mongolia, China.

“The specimen consists of the anterior portion of articulated lower jaws, with a partial tooth and several alveoli,” Dr. Ji said.

“The rostral tip of the mandibular symphysis is missing.”

“The preserved segments of the left and right dentaries measure 7.7 cm (3 inches) and 4.5 cm (1.8 inches) long, respectively.”

Ordosipterus planignathus represents the first convincible pterosaur from the Ordos Region in Inner Mongolia, and the second pterosaur species from the Ordos Basin after Huanhepterus quingyangensis in Gansu Province,” he concluded.

“This fossil further strengthens the opinion that the northern China and Mongolia belong to a unique and endemic dinosaur biogeographic realm featured by the presence of Psittacosaurus and pterosaurs during the Early Cretaceous period.”

The discovery of Ordosipterus planignathus is described in a paper published in the journal China Geology.

References: Shu-an Ji. 2020. First record of Early Cretaceous pterosaur from the Ordos Region, Inner Mongolia, China. China Geology 3 (1): 1-7; doi: 10.31035/cg2020007

This article is republished here from sci news under common creative licenses.

Bat-winged Dinosaurs That Could Glide (Paleontology)

Despite having bat-like wings, two small dinosaurs, Yi and Ambopteryx, struggled to fly, only managing to glide clumsily between the trees where they lived, according to a new study led by an international team of researchers, including McGill University Professor Hans Larsson. Unable to compete with other tree-dwelling dinosaurs and early birds, they went extinct after just a few million years. The findings, published in iScience, support that dinosaurs evolved flight in several different ways before modern birds evolved.

Life reconstruction of the bat-winged scansoriopterygid dinosaur Ambopteryx in a glide. Image credit: Gabriel Ugueto.

“We know some dinosaurs could fly before they evolved into birds,” says Professor Larsson, Director of McGill’s Redpath Museum. “What this shows us is that at least one lineage of dinosaurs experimented with a completely different mode of aerial locomotion. Gliding evolved countless times in arboreal amphibians, mammals, lizards, and even snakes – and now we have an example of dinosaurs.”

Yi and Ambopteryx were small animals from the Late Jurassic of China, living about 160 million years ago. Weighing in at about half a kilogram, they are unusual theropod dinosaurs. Theropods are carnivorous dinosaurs that include all birds alive today. Most theropods were ground-loving carnivores, but Yi and Ambopteryx were at home in the trees and lived on a diet of insects, seeds, and plants.

Map of the skeleton and preserved soft tissues of Yi. Image credit: Dececchi et al. 2020.

“Once birds got into the air, these two species were so poorly capable of being in the air that they just got squeezed out,” says lead author Thomas Dececchi, an assistant professor of biology at Mount Marty University. “Maybe you can survive a few million years underperforming, but you have predators from the top, competition from the bottom, and even some small mammals adding into that, squeezing them out until they disappeared.”

Little creatures could glide, not fly

Curious about how these animals could have flown, the researchers, scanned fossils using Laser-Stimulated Fluorescence (LSF), a technique that uses laser light to pick up soft tissue details of their wing membranes that can’t be seen with standard white light. Later, the team used mathematical models to predict how they might have flown, testing different variables like weight, wingspan, wing shape, and muscle placement.

“The results are clear these animals were not able to fly like birds,” says Larsson. “They didn’t have adaptations to even get close to the physical thresholds for powered flight, but their weird membranous wings do give them enough of an aerofoil to have glided. They are not comparable to living gliding squirrels or lizards but seem to have come up with a really novel way of getting a large enough wing membrane.”

Graphical summary of the major findings of the new study. Image credit: Dececchi et al. 2020.

Although gliding is not an efficient form of flight since it can only be done if the animal has already climbed to a high point, it probably did help Yi and Ambopteryx stay out of danger while they were still alive.

“Living gliders don’t travel long distances through the air,” says Dececchi. “It’s not efficient, but it can be used as an escape hatch. It’s not a great thing to do, but sometimes it’s a choice between losing a bit of energy and being eaten. Once they were put under pressure, they just lost their space. They couldn’t win on the ground. They couldn’t win in the air. They were done.”

The researchers are now looking more closely at the musculoskeletal anatomy of these bat-winged and other feathered dinosaurs that evolved around the origin of birds. “The diversity of dinosaurs just before the origin of birds amazes me,” Larsson says. “We used to think of birds evolving as a linear trend from their ground-dwelling dinosaur ancestry. We can know revise this textbook scenario to one that had an explosive diversity of experimentation, with dinosaurs evolving powered flight several times independently from birds, many having fully feathered wings but with bodies too heavy or wings too small to have gotten off the ground, and now, a weird bat-winged group of dinosaurs that were not only the first arboreal dinosaurs, but ones that glided! I feel like we are still just scratching the surface.”

References: “Aerodynamics show membranous-winged theropods were a poor gliding dead-end” by T. Alexander Dececchi, Arindam Roy, Michael Pittman, Thomas G. Kaye, Xing Xu, Michael B. Habib, Hans C.E. Larsson, Xiaoli Wang, and Xiaoting Zheng is published in iScience. DOI: http://dx.doi.org/10.1016/j.isci.2020.101574

Provided by McGill University

World’s Greatest Mass Extinction Triggered Switch To Warm-Bloodedness (Paleontology)

Mammals and birds today are warm-blooded, and this is often taken as the reason for their great success.

University of Bristol palaeontologist Professor Mike Benton, identifies in the journal Gondwana Research that the ancestors of both mammals and birds became warm-blooded at the same time, some 250 million years ago, in the time when life was recovering from the greatest mass extinction of all time.

The origin of endothermy in synapsids, including the ancestors of mammals. The diagram shows the evolution of main groups through the Triassic, and the scale from blue to red is a measure of the degree of warm-bloodedness reconstructed based on different indicators of bone structure and anatomy. Credit: Mike Benton, University of Bristol. Animal images are by Nobu Tamura, Wikimedia.

The Permian-Triassic mass extinction killed as much as 95 per cent of life, and the very few survivors faced a turbulent world, repeatedly hit by global warming and ocean acidification crises. Two main groups of tetrapods survived, the synapsids and archosaurs, including ancestors of mammals and birds respectively.

Palaeontologists had identified indications of warm-bloodedness, or technically endothermy, in these Triassic survivors, including evidence for a diaphragm and possible whiskers in the synapsids.

More recently, similar evidence for early origin of feathers in dinosaur and bird ancestors has come to light. In both synapsids and archosaurs of the Triassic, the bone structure shows characteristics of warm-bloodedness. The evidence that mammal ancestors had hair from the beginning of the Triassic has been suspected for a long time, but the suggestion that archosaurs had feathers from 250 million years ago is new.

Posture shift at the end of the Permian, 252 million years ago. Before the crisis, most reptiles had sprawling posture; afterwards they walked upright. This may have been the first sign of a new pace of life in the Triassic. Credit: animal drawings by Jim Robins, University of Bristol.

But a strong hint for this sudden origin of warm-bloodedness in both synapsids and archosaurs at exactly the time of the Permian-Triassic mass extinction was found in 2009. Tai Kubo, then a student studying the Masters in Palaeobiology degree at Bristol and Professor Benton identified that all medium-sized and large tetrapods switched from sprawling to erect posture right at the Permian-Triassic boundary.

Their study was based on fossilised footprints. They looked at a sample of hundreds of fossil trackways, and Kubo and Benton were surprised to see the posture shift happened instantly, not strung out over tens of millions of years, as had been suggested. It also happened in all groups, not just the mammal ancestors or bird ancestors.

Professor Benton said: “Modern amphibians and reptiles are sprawlers, holding their limbs partly sideways.

“Birds and mammals have erect postures, with the limbs immediately below their bodies. This allows them to run faster, and especially further. There are great advantages in erect posture and warm-bloodedness, but the cost is that endotherms have to eat much more than cold-blooded animals just to fuel their inner temperature control.”

The evidence from posture change and from early origin of hair and feathers, all happening at the same time, suggested this was the beginning of a kind of ‘arms race’. In ecology, arms races occur when predators and prey have to compete with each other, and where there may be an escalation of adaptations. The lion evolves to run faster, but the wildebeest also evolves to run faster or twist and turn to escape.

Something like this happened in the Triassic, from 250 to 200 million years ago. Today, warm-blooded animals can live all over the Earth, even in cold areas, and they remain active at night. They also show intensive parental care, feeding their babies and teaching them complex and smart behaviour. These adaptations gave birds and mammals the edge over amphibians and reptiles and in the present cool world allowed them to dominate in more parts of the world.

Professor Benton added: “The Triassic was a remarkable time in the history of life on Earth. You see birds and mammals everywhere on land today, whereas amphibians and reptiles are often quite hidden.

“This revolution in ecosystems was triggered by the independent origins of endothermy in birds and mammals, but until recently we didn’t realise that these two events might have been coordinated.

“That happened because only a tiny number of species survived the Permian-Triassic mass extinction – who survived depended on intense competition in a tough world. Because a few of the survivors were already endothermic in a primitive way, all the others had to become endothermic to survive in the new fast-paced world.”

References: Michael Benton, “The origin of endothermy in synapsids and archosaurs and arms races in the Triassic”, Gondwana Research, 2020. Doi: https://doi.org/10.1016/j.gr.2020.08.003 link: https://www.sciencedirect.com/science/article/pii/S1342937X20302252

Provided by University Of Bristol

Ancient Tiny Teeth Reveal First Mammals Lived More Like Reptiles (Paleontology)

Pioneering analysis of 200 million-year-old teeth belonging to the earliest mammals suggests they functioned like their cold-blooded counterparts – reptiles, leading less active but much longer lives.

Long: Scientists count fossilised growth rings in teeth like tree-rings to find out how long the earliest mammals lived. From left to right: reconstruction of Morganucodon; Morganucodon tooth with cementum, the structure that locks tooth roots to the gum, highlighted in green; as it grows non-stop throughout life, cementum deposits every year like tree rings, highlighted using coloured arrows; These were turned into 3D models to count 14 years of life in the shrew- sized Morganucodon. Short: Scientists count fossilised growth rings in teeth like tree-rings to find out how long the earliest mammals lived. ©Graphics: Nuria Melisa Morales Garcia. Morganucodon based on Bob Nicholls/ Palaeocreations 2018 model

The research, led by the University of Bristol, UK and University of Helsinki, Finland, published today in Nature Communications, is the first time palaeontologists have been able to study the physiologies of early fossil mammals directly, and turns on its head what was previously believed about our earliest ancestors.

Fossils of teeth, the size of a pinhead, from two of the earliest mammals, Morganucodon and Kuehneotherium, were scanned for the first time using powerful X-rays, shedding new light on the lifespan and evolution of these small mammals, which roamed the earth alongside early dinosaurs and were believed to be warm-blooded by many scientists. This allowed the team to study growth rings in their tooth sockets, deposited every year like tree rings, which could be counted to tell us how long these animals lived. The results indicated a maximum lifespan of up to 14 years – much older than their similarly sized furry successors such as mice and shrews, which tend to only survive a year or two in the wild.

“We made some amazing and very surprising discoveries. It was thought the key characteristics of mammals, including their warm-bloodedness, evolved at around the same time,” said lead author Dr Elis Newham, Research Associate at the University of Bristol, and previously PhD student at the University of Southampton during the time when this study was conducted.

“By contrast, our findings clearly show that, although they had bigger brains and more advanced behaviour, they didn’t live fast and die young but led a slower-paced, longer life akin to those of small reptiles, like lizards.”

Using advanced imaging technology in this way was the brainchild of Dr Newham’s supervisor Dr Pam Gill, Senior Research Associate at the University of Bristol and Scientific Associate at the Natural History Museum London, who was determined to get to the root of its potential.

“A colleague, one of the co-authors, had a tooth removed and told me they wanted to get it X-rayed, because it can tell all sorts of things about your life history. That got me wondering whether we could do the same to learn more about ancient mammals,” Dr Gill said.

By scanning the fossilised cementum, the material which locks the tooth roots into their socket in the gum and continues growing throughout life, Dr Gill hoped the preservation would be clear enough to determine the mammal’s lifespan.

To test the theory, an ancient tooth specimen belonging to Morganucodon was sent to Dr Ian Corfe, from the University of Helsinki and the Geological Survey of Finland, who scanned it using high-powered Synchrotron X-ray radiation.

“To our delight, although the cementum is only a fraction of a millimetre thick, the image from the scan was so clear the rings could literally be counted,” Dr Corfe said.

It marked the start of a six-year international study, which focused on these first mammals, Morganucodon and Kuehneotherium, known from Jurassic rocks in South Wales, UK, dating back nearly 200 million years.

“The little mammals fell into caves and holes in the rock, where their skeletons, including their teeth, fossilised. Thanks to the incredible preservation of these tiny fragments, we were able to examine hundreds of individuals of a species, giving greater confidence in the results than might be expected from fossils so old,” Dr Corfe added.

The journey saw the researchers take some 200 teeth specimens, provided by the Natural History Museum London and University Museum of Zoology Cambridge, to be scanned at the European Synchrotron Radiation Facility and the Swiss Light Source, among the world’s brightest X-ray light sources, in France and Switzerland, respectively.

In search of an exciting project, Dr Newham took this up for the MSc in Palaeobiology at the University of Bristol, and then a PhD at the University of Southampton.

“I was looking for something big to get my teeth into and this more than fitted the bill. The scanning alone took over a week and we ran 24-hour shifts to get it all done. It was an extraordinary experience, and when the images started coming through, we knew we were onto something,” Dr Newham said.

Dr Newham was the first to analyse the cementum layers and pick up on their huge significance.

“We digitally reconstructed the tooth roots in 3-D and these showed that Morganucodon lived for up to 14 years, and Kuehneotherium for up to nine years. I was dumbfounded as these lifespans were much longer than the one to three years we anticipated for tiny mammals of the same size,” Dr Newham said.

“They were otherwise quite mammal-like in their skeletons, skulls and teeth. They had specialised chewing teeth, relatively large brains and probably had hair, but their long lifespan shows they were living life at more of a reptilian pace than a mammalian one. There is good evidence that the ancestors of mammals began to become increasingly warm-blooded from the Late Permian, more than 270 million years ago, but, even 70 million years later, our ancestors were still functioning more like modern reptiles than mammals”

While their pace-of-life remained reptilian, evidence for an intermediate ability for sustained exercise was found in the bone tissue of these early mammals. As a living tissue, bone contains fat and blood vessels. The diameter of these blood vessels can reveal the maximum possible blood flow available to an animal, critical for activities such as foraging and hunting.

Dr Newham said: “We found that in the thigh bones of Morganucodon, the blood vessels had flow rates a little higher than in lizards of the same size, but much lower than in modern mammals. This suggests these early mammals were active for longer than small reptiles but could not live the energetic lifestyles of living mammals.”

References: Elis Newham, Pamela G. Gill, Philippa Brewer, Michael J. Benton, Vincent Fernandez, Neil J. Gostling, David Haberthür, Jukka Jernvall, Tuomas Kankanpää, Aki Kallonen, Charles Navarro, Alexandra Pacureanu, Berit Zeller-Plumhoff, Kelly Richards, Kate Robson-Brown, Philipp Schneider, Heikki Suhonen, Paul Tafforeau, Katherine Williams, Ian J. Corfe, “Reptile-like physiology in Early Jurassic stem-mammals”, BioRxiv, doi: https://doi.org/10.1101/785360 link: https://www.biorxiv.org/content/10.1101/785360v1

Provided by University Of Bristol

Harvard Researchers Rebuts 75-Year-Old Belief In Reptile Evolution (Paleontology)

Challenging a 75-year-old notion about how and when reptiles evolved during the past 300 million-plus years involves a lot of camerawork, loads of CT scanning, and, most of all, thousands of miles of travel. Just check the stamps in Tiago R. Simões ‘ passport.

Animals sampled in the analysis. ©Tiago R. Simões

Simões is the Alexander Agassiz Postdoctoral Fellow in the lab of Harvard paleontologist Stephanie Pierce. From 2013 to 2018, he traveled to more than 20 countries and more than 50 different museums to take CT scans and photos of nearly 1,000 reptilian fossils, some hundreds of millions of years old. It amounted to about 400 days of active collection, helping form what is believed to be the largest available timeline on the evolution of major living and extinct reptile groups.

Now, a statistical analysis of that vast database is helping scientists better understand the evolution of these cold-blooded vertebrates by contradicting a widely held theory that major transitions in evolution always happened in big, quick (geologically speaking) bursts, triggered by major environmental shifts. The findings are described in a recently published paper in Nature Communications.

In it, researchers show that the evolution of extinct lineages of reptiles from more than 250 million years ago took place through many small bursts of morphological changes, such as developing armored body plans or wings for gliding, over a period of 50 million years instead of during a single major evolutionary event, as previously thought. They also show that the early evolution of most lizard lineages was a continuously slower and more incremental process than previously understood.

“It wasn’t a sudden jump that kind of established the wide diversity that we see today in reptiles,” Simões said. “There was an initial jump, but relatively small, and then a sustained increase over time of those rates [of evolution] and different diversity values.”

Evidence of this has been seen in other types of animals, but this is the first time it’s been seen in reptiles — one of the most diverse animals on the planet, with more than 10,000 different species and a dizzying variety of abilities and traits. Consider how some lizard species can freeze solid overnight then thaw the next morning, or how turtles grow protective armor.

The findings run contrary to the evolutionary theory of adaptive radiation that Harvard paleontologist George G. Simpson popularized in the 1940s, which sought to explain the origins of the planet’s biological diversity. Adaptive radiation has been the focus of intense investigation for decades, but wasn’t until recent years that the technology, methods, and data have existed to precisely measure rapid rates of evolution in the fossil record in terms of different animal species, morphologies, and at the molecular level using DNA.

Researchers of this study also included Pierce, the Thomas D. Cabot Associate Professor of Organismic and Evolutionary Biology and curator of vertebrate paleontology in the Museum of Comparative Zoology; Oksana Vernygora, a graduate student from the University of Alberta in Canada; and Professor Michael Wayne Caldwell at Alberta.

Simões traveled to almost all of the world’s major natural history museums to collect the data for the study, including the national natural history museums in London, Paris, Berlin, Ottawa, Beijing, and Tokyo. In the U.S., he visited the Smithsonian National Museum of Natural History, the Carnegie Museum of Natural History, and Harvard’s Museum of Comparative Zoology.

The scientists believe that by understanding how animals evolve over longer periods of time, they can glean a number of lessons on ecology and how organisms are affected by environmental changes. Using the database, researchers can determine when major reptile lineages or morphologies originated, see how those changes affected reptile DNA, and learn important lessons about how species were impacted by historical events.

Reptiles, for instance, have survived three major mass extinction events. The biggest was the Permian-Triassic mass extinction about 250 million years ago that killed about 90 percent of the planet’s species, earning it the moniker the Great Dying. It’s believed to have been caused by a buildup of natural greenhouse gases.

The timeline researchers created found that the rates at which reptiles were evolving and the anatomical differences among them before the Great Dying were nearly as high as after the event. However, it was only much after the Great Dying that reptiles became dominant in many ecosystems and extremely diverse in terms of the number of different species.

That finding cemented that fast rates of anatomical change don’t need to coincide with genetic diversity or an abundance of species (called taxonomic diversity), and further rebutted adaptive radiation as the only explanation for the origin of new animal groups and body plans. The researchers also note that it took reptiles almost 10 million years to recover to previous levels of anatomical diversity.

“That kind of tells you on the broad scheme of things and on a global scale how much impact, throughout the history of life, sudden environmental changes may have,” Simões said.

Further evidence that contradicted adaptive radiation included similar but surprising findings on the origins of snakes, which achieved the major aspects of their skinny, elongated body plans early in their evolution about 170 million years ago (but didn’t fully lose their limbs for another 105 million years). They also underwent rapid changes to their skulls about 170 to 165 million years ago that led to such powerful and flexible mouths that today they can swallow whole prey many times their size. But while snakes experienced the fastest rates of anatomical change in the history of reptile evolution, these changes did not coincide with increases in taxonomic diversity or high rates of molecular evolution as predicted by adaptive radiations, the researchers said.

The scientists weren’t able to pinpoint why this mismatch happens, and suggested more research is needed. In particular they want to understand how body plans evolve and how changes in DNA relate to it.

“We can see better now what are the big changes in the history of life and especially in the history of reptile life on Earth,” Simões said. “We will keep digging.”

References: Simões, T.R., Vernygora, O., Caldwell, M.W. et al. Megaevolutionary dynamics and the timing of evolutionary innovation in reptiles. Nat Commun 11, 3322 (2020). Doi: https://doi.org/10.1038/s41467-020-17190-9 link: https://www.nature.com/articles/s41467-020-17190-9

Provided by Harvard University

How Reptiles Divided Up The Spoils In Ancient Seas? (Paleontology)

While dinosaurs ruled the land in the Mesozoic, the oceans were filled by predators such as crocodiles and giant lizards, but also entirely extinct groups such as ichthyosaurs and plesiosaurs.

Duria Antiquior – a more ancient Dorset. Watercolour of a Mesozoic marine ecosystem by geologist Henry De la Beche, painted in 1830. Ancient oceans have fascinated natural historians since the 1800s. Credit: Tom Stubbs, University of Bristol

Now for the first time, researchers at the University of Bristol have modelled the changing ecologies of these great sea dragons.

Mesozoic oceans were unique in hosting diverse groups of fossil reptiles, many of them over 10 metres long.

These toothy monsters fed on a variety of fishes, molluscs, and even on each other. Yet most had disappeared by the end of the Cretaceous, 66 million years ago, when the dinosaurs also died out. There are still some marine crocodiles, snakes and turtles today, but sharks, seals, and whales took over these ecological roles.

In a new study, completed when she was studying for the MSc in Palaeobiology at the University of Bristol’s School of Earth Sciences, Jane Reeves, now a PhD student at the University of Manchester, used modern computational methods to explore how all these marine reptiles divided up the spoils.

Jane said: “It’s difficult to work out the ecology and function of fossil animals but we decided to focus mainly on their feeding and swimming styles. I tracked down information on 371 of the best-known Mesozoic marine tetrapods, and coded each one for 35 ecological traits, including body size, diet, likely hunting style, tooth type, presence or absence of armour, limb shape and habitat.”

The numerical analysis showed that all these marine reptiles could be divided into just six ecological categories linking how they moved, where they lived, and how they fed: pursuit predators that chased their prey, ambush predators that lurked and waited for the prey to swim past (two groups, one in deep water, one in shallow), a fourth group of reptiles that could still walk on land, shallow-water shell-crushers and foragers, and marine turtles with a variety of life modes.

Professor Mike Benton, who co-supervised the study, said: “A problem with studies of form and function of fossils is that we have to be careful in reconstructing the behaviour of ancient animals. But in Jane’s study, she used ecological characters from the start where their function had already been established. For example, sharp pointy teeth mean fish-eating, whereas broad, flat teeth mean shell crushing.”

Mesozoic marine tetrapod ecospace. Animals in each group share ecological characteristics. They came in many shapes and sizes and had great variation in feeding apparatus. Credit: Tom Stubbs, University of Bristol

Dr Ben Moon, another co-supervisor, said: “We knew that the different marine reptile groups came and went through the 186 million years of the Mesozoic.

“I’m especially interested in ichthyosaurs, and we wanted to test an idea that they had migrated through ecospace during the Mesozoic. Jane’s study shows definite movement through time from being semi-terrestrial at the beginning of the Triassic to a wide range of ecologies, including ambush hunting, and finally pursuit predation in the Jurassic and Cretaceous.”

Dr Tom Stubbs, another co-supervisor, said: “We also wanted to test whether all these animals were competing with each other. But in fact, they seem to have avoided competition.

“For example, after a substantial extinction of marine reptiles around the end of the Triassic, the surviving ichthyosaurs and plesiosaurs showed considerable conservatism. They didn’t expand their ecological roles at all, and many niches were left empty until new groups of crocodiles and turtles emerged later in the Jurassic to take over these roles.”

Jane Reeves added: “It was a great experience being able to study a large variety of creatures, and to then reconstruct the ecological lifestyles of extinct animals from just their fossils.

“You do have to be very careful in doing these kinds of studies, not to make any unfounded assumptions. We know animals can be opportunistic, and don’t always behave exactly how we think they should, but we’re confident that the data we collected reflects the most common, day-to-day, behaviours of each animal. These results give us a great insight into what was really happening under the surface of the Mesozoic seas.”

This research was part funded by the Natural Environment Research Council (NERC) and the European Research Council (ERC).

References: Jane C. Reeves, Benjamin C. Moon, Michael J. Benton, Thomas L. Stubbs, “Evolution of ecospace occupancy by Mesozoic marine tetrapods”, Online Wiley Library, Paleontology, 2020

Provided by University of Bristol

Peterosaurs Had No ProtoFeathers (Paleontology)

The debate about when dinosaurs developed feathers has taken a new turn with a paper refuting earlier claims that feathers were also found on dinosaurs’ relatives, the flying reptiles called pterosaurs.

Pterosaur expert Dr David Unwin from the University of Leicester’s Centre for Palaeobiology Research, and Professor David Martill, of the University of Portsmouth have examined the evidence that these creatures had feathers and believe they were in fact bald.

They have responded to a suggestion by a group of his colleagues led by Zixiao Yang that some pterosaur fossils show evidence of feather-like branching filaments, ‘protofeathers’, on the animal’s skin.

Dr Yang, from Nanjing University, and colleagues presented their argument in a 2018 paper in the journal Nature Ecology and Evolution. Now Unwin and Martill, have offered an alternative, non-feather explanation for the fossil evidence in the same journal.

While this may seem like academic minutiae, it actually has huge palaeontological implications. Feathered pterosaurs would mean that the very earliest feathers first appeared on an ancestor shared by both pterosaurs and dinosaurs, since it is unlikely that something so complex developed separately in two different groups of animals.

This would mean that the very first feather-like elements evolved at least 80 million years earlier than currently thought. It would also suggest that all dinosaurs started out with feathers, or protofeathers but some groups, such as sauropods, subsequently lost them again – the complete opposite of currently accepted theory.

The evidence rests on tiny, hair-like filaments, less than one tenth of a millimetre in diameter, which have been identified in about 30 pterosaur fossils. Among these, Yang and colleagues were only able to find just three specimens on which these filaments seem to exhibit a ‘branching structure’ typical of protofeathers.

Unwin and Martill propose that these are not protofeathers at all but tough fibres which form part of the internal structure of the pterosaur’s wing membrane, and that the ‘branching’ effect may simply be the result of these fibres decaying and unravelling.

Dr Unwin said: “The idea of feathered pterosaurs goes back to the nineteenth century but the fossil evidence was then, and still is, very weak. Exceptional claims require exceptional evidence – we have the former, but not the latter.”

Professor Martill noted that either way, palaeontologists will have to carefully reappraise ideas about the ecology of these ancient flying reptiles. He said, “If they really did have feathers, how did that make them look, and did they exhibit the same fantastic variety of colours exhibited by birds. And if they didn’t have feathers, then how did they keep warm at night, what limits did this have on their geographic range, did they stay away from colder northern climes as most reptiles do today. And how did they thermoregulate? The clues are so cryptic, that we are still a long way from working out just how these amazing animals worked.

References: Unwin, D.M., Martill, D.M. No protofeathers on pterosaurs. Nat Ecol Evol (2020). https://doi.org/10.1038/s41559-020-01308-9 link: https://www.nature.com/articles/s41559-020-01308-9

Provided by University of Portsmouth