Latest Research and Press Resources
Silhouette credits from Phylopic.com: Gallimimus, Silesaurus- Scott Hartman; Desmatosuchus- Steven Traver; Effigia- Sarah Werning; Smilosuchus- Robert Gay; Gavialis- Evan Boucher; Lesothosaurus- Jaime Headden, modified by T. Michael Keesey; Ankylosaurus- Andrew Farke
We describe an exciting new species of extinct reptile (closely related to dinosaurs and crocodylians), Triopticus primus, as part of a diverse reptilian fauna from ~230 million years ago in Texas. This single group of reptiles preserves an extensive range of skeletal shapes and structures that each are re-evolved by dinosaurs and crocodylians millions of years later, presenting a striking example of convergent evolution among vertebrates.
A Dome-Headed Stem Archosaur Exemplifies Convergence among Dinosaurs and Their Distant Relatives
Michelle R. Stocker, Sterling J. Nesbitt, Katharine E. Criswell, William G. Parker, Lawrence M. Witmer, Timothy B. Rowe, Ryan Ridgely, and Matthew A. Brown
- Triassic-aged (~230 million years ago) Triopticus evolved a bony dome-head 140 million years before the more famous Cretaceous-aged (~90 million years ago) pachycephalosaur dinosaurs
- After the end-Permian extinction, the biggest extinction of all time, the early archosauromorph cousins of dinosaurs and crocodylians evolved explosively into extreme body plans that were much later re-evolved by dinosaurs and crocs.
- Dinosaurs re-evolved the common and bizarre body plans present in their Triassic-aged relatives that were once thought to be unique to dinosaurs
- The early evolution of body plans may constrain later body plans in the same group
The skull of Triopticus primus in side view. Scale bar = 1 cm. Photo by Matthew Brown
Helpful Facts/Background for press articles:
- The Triassic Period lasted from ~250 million years ago to ~200 million years ago.
- These fossils were collected by the Works Progress Administration (WPA) in West Texas in the late 1930s and early 1940s.
- The skull of Triopticus was found by Stocker, Nesbitt, Criswell, Parker, and Rowe in a drawer in the Texas Vertebrate Paleontology Collections (essentially a fossil library) of The University of Texas at Austin completely surrounded in rock as part of a seminar course in 2010. Nesbitt initially noticed the intact braincase attached to the dome of the skull.
- The Mesozoic Era includes the Triassic, Jurassic and Cretaceous Periods
- The earliest dinosaurs that lived at the same time as Triopticus were small (~9 feet long) and looked like small bipedal carnivores. Later after the Triassic Period, dinosaurs evolved into their much more familiar and larger shapes.
- Triopticus is represented by a single partial skull.
- Not much is known about the skeleton of Triopticus, but it was no bigger than a lion.
- Crocodylians and birds are each other's closest living relatives and are part of the reptile group Archosauria. All dinosaurs are archosaurs.
- The end of the Permian Period (~250 million years ago) experienced the largest extinction of all time where 80% - 95% of all life went extinct. Similarly, a mass extinction also occurred at the end of the Triassic Period (~200 million years ago) where many vertebrates went extinct.
- The reoccurring body plans of dinosaurs mostly occurred over tens of millions of years after the extinction of the reptiles in the Triassic Period. Some body plans were repeated within a few million years after the end-Triassic extinction, whereas others evolved up to 100 million years later.
- The world was much hotter in the Triassic Period than it is now.
- The Triopticus skull and other fossils of reptiles found at the same fossil locality were buried in a large river system similar to the current Mississippi River.
- Triopticus was found in West Texas near the city of Big Spring, Texas.
Quotes available for press articles:
-Michelle Stocker, Virginia Tech: [statements about Otis Chalk and convergence/diversification of Triassic fauna …] “The Otis Chalk fauna is an amazing single snapshot of geologic time where you have this extraordinary range of animal body plans all present at the same time living together. This fauna is one of the earliest records of Late Triassic life in the American West, and we are able to discover so much about it today because of work done by the WPA over 70 years ago.”
“Among the animals preserved in the Otis Chalk fauna, Triopticus exemplifies this phenomenon of body shape convergence because its skull shape was repeated by very distantly-related dome-headed dinosaurs more than 100 million years later.”
“Triopticus is an extraordinary example of evolutionary convergence between the relatives of dinosaurs and crocodylians and later dinosaurs that is much more common than anyone ever expected. What we thought were unique body shapes in many dinosaurs actually evolved millions of years before in the Triassic Period.”
-Sterling Nesbitt, Virginia Tech: “After the enormous end-Permian mass extinction, the group that includes the living crocodylians and birds and their close relatives exploded onto the scene and diversified into many different sizes and shapes. These early body shapes were later mimicked by dinosaurs.”
-Katharine Criswell, University of Chicago: [statements about disparity and convergence…] : “It is amazing to think that many of the iconic dinosaur features that we know and love, such as long snouts, toothless beaks, armor plates, and thickened dome skulls were arrived at completely independently up to 100 million years earlier in these distant reptilian cousins.”
“This project started out as part of a paleontology class that many of us took when we were graduate students at the University of Texas at Austin. Triopticus was collected by the Works Progress Administration in the 1940s, and had been sitting in a drawer in the paleontology collections for almost 70 years when we discovered it. With a combination of CT scans and fossil comparisons we were able to give this old fossil new life.”
-William Parker, Petrified Forest National Park: [statements about Triassic fauna…] “Triopticus reveals insight in the window of hidden diversity in the Triassic faunal assemblages.”
-Lawrence Witmer and Ryan Ridgely, Ohio University: [statements about CT/brain evolution and convergence…]
Witmer: “This project combines both old-school and hi-tech approaches. Careful excavation and cleaning of the fossils showed the team that we had something special in Triopticus, but being able to peer inside the skull with X-ray CT scanning was a game-changer. It showed us that the similarity of Triopticus with the much later dome-headed pachycephalosaur dinosaurs was more than skin deep, extending to the structure of the bone and even the brain.”
-Matthew Brown and Timothy Rowe, The University of Texas at Austin: [statements about importance of natural history collections…] Brown: “Triopticus was dug up 76 years ago along with thousands of other fossils from Texas. We can gain new insights into the history of life because specimens like Triopticus have been curated into museum collections like the one at The University of Texas at Austin. These collections are the foundation of natural history research, and this new animal illustrates how exciting discoveries are continually made thanks to the forethought and investment of past generations. It will be fascinating to see what the students of tomorrow find next.”
“This Triassic radiation of archosaurs and their close relatives delimited the majority of the possible shapes that non-avian dinosaurs were able to take on later, but it took hundreds of millions of years for dinosaurs to achieve that full range of body shapes.” Michelle Stocker, Virginia Tech
1. YouTube video of Triopticus braincase & brain endocast with labels: https://www.youtube.com/watch?v=TbnEZABTCjk
2. Sketchfab animation of Triopticus braincase with labels: https://skfb.ly/QFLx
3. Sketchfab animation of transparent Triopticus braincase revealing brain endocast: https://skfb.ly/QFKG
Lead author Dr. Michelle R. Stocker, Departement of Geosciences, Virginia Tech. Photo by Sterling Nesbitt.
Photograph from the Works Progress Administration, showing excavation in the general area from which Triopticus primus was collected in 1940 near Big Spring, Texas. Original photo on file in the Vertebrate Paleontology Collections of The University of Texas at Austin.
The skull of Triopticus primus in side view showing the reconstructed brain. Scale bar = 1 cm.
The origin and early evolution of dinosaurs has been a topic of great scientific interest since their discovery. Dinosaurs and their evolutionary descendants, the birds, belong to a larger group of fossil reptiles called archosaurs (which also includes pterosaurs as well as crocodylians and their relatives). The closest relatives of dinosaurs are non-dinosaur members of the evolutionary lineage of archosaurs that gave rise to pterosaurs, dinosaurs and birds: Avemetatarsalia, known as 'bird-line archosaurs'. However, the early evolution of bird-line archosaurs is poorly understood, and this has obscured understanding of how dinosaurs acquired their characteristic anatomical, ecological, and biological features. For many years, the closest relatives of dinosaurs were known from only a few fragmentary fossils. Recently, however, important new species were discovered from around the world.
In this paper, we integrate all of this recent information with an extremely important fossil discovery from the Middle Triassic (ca. ~245 million years ago) of Tanzania. We describe a new species (Teleocrater rhadinus) that is the oldest member of the bird-line archosaurs. This species provides new information that allows us to recognise an entirely new group of enigmatic reptiles (which we name Aphanosauria) at the base of bird-line archosaurs, prior to the split between the pterosaur and dinosaur lineages. Members of Aphanosauria have transitional morphologies, combining features present in the last common ancestor of birds and crocodylians (e.g., a crocodylian-like ankle joint) with some classic dinosaur characters (e.g., depressions for enlarged dinosaur-like jaw musculature on the roof of the skull). Furthermore, we also show that species that have traditionally been used as models for understanding dinosaur origins (e.g., Lagerpeton, Marasuchus), are actually highly specialised, and do not represent the ancestral condition for bird-line archosaurs.
The earliest bird-line archosaurs and the assembly of the dinosaur body plan
Sterling J. Nesbitt, Richard J. Butler, Martin D. Ezcurra, Paul M. Barrett, Michelle R. Stocker, Kenneth D. Angielczyk, Roger M. H. Smith, Christian A. Sidor, Grzegorz Niedzwiedzki, Andrey G. Sennikov, and Alan J. Charig.
· The discovery of Teleocrater fills in a critical gap in the fossil record of dinosaur cousins and it shows that some features thought to characterize dinosaurs evolved much earlier than previously thought.
· The Triassic Period has long been known as the 'age of crocodile relatives' because these animals were diverse, abundant, and widespread. However, it is now clear that close relatives of dinosaurs were also diverse at this time and just as widespread.
· Teleocrater and other animals closely related to dinosaurs indicate that the bird-like ankle of dinosaurs evolved from a crocodile-like ankle after the split between the crocodile and dinosaur-bird lineages. Moreover, a bird-like ankle may have evolved on as many as four independent occasions in Triassic members of the bird-dinosaur lineage.
· Teleocrater and its closest relatives (which form a group that we name Aphanosauria in this paper) are found across the world in Russia, India, Tanzania, and Brazil.
· Several groups of close dinosaur relatives, like the group containing Teleocrater, spread independently across Pangaea.
· Cross-sections of the bones of Teleocrater indicate that it grew more like a dinosaur (with fast growth early in life) than a crocodylian relative.
“The discovery of Teleocrater fundamentally changes what our idea about the earliest history of dinosaur relatives also raises far more questions that it answers.” Sterling Nesbitt, Virginia Tech
Life reconstruction of Teleocrater rhadinus feasting on a deep relative of mammals, Cynognathus. The large dicynodont Dolichuranus is seen in the background. Credit: Natural History Museum, London, artwork by Mark Witton.
Life reconstruction of the new species Teleocrater rhadinus, a close relative of dinosaurs. Credit: Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" (Buenos Aires, Argentina), artwork by Gabriel Lio.
The relationships of Teleocrater rhadinus, a close relative of dinosaurs. Teleocrater is more closely related to pterosaurs and dinosaurs (inlcuding birds) than to crocodylians. Teleocrater is the first branch of the Archosauria lineage that leads to birds. Credit: Sterling Nesbitt
Reconstruction of the skeleton of Teleocrater rhadinus. Scale = 25 cm. Credit: Scott Hartman. Scott's webpage: http://www.skeletaldrawing.com/
Excavating the remains of Teleocrater rhadinus and other animals in southern Tanzania in 2015. Christian Sidor (left), Sterling Nesbitt (middle left), Kenneth Angielczyk (upper right), Michelle Stocker (lower right). Credit: Roger Smith.
The important upper leg bone of Teleocrater rhadinus found in 2015. Credit: Michelle Stocker.
“Dinosaurs were amazingly successful animals. It's natural to want to know where they came from, and how they became so dominant. Teleocrater is hugely exciting because it blows holes in many of our classic ideas of dinosaur origins.” Richard J. Butler, University of Birmingham
Helpful Facts/Background for press articles:
· 'Teleocrater' is derived from ancient Greek roots and refers to its closed hip socket ('Teleos', finished or complete and 'krater', bowl or basin), and 'rhadinos' (slender) refers to the slender body plan.
· We estimate that Teleocrater was ~2–3 meters long, with a long tail and was about 0.5–0.75 meters tall at the hip.
· 10–30 kilograms in weight (20–65 pounds).
· Crocodylians and birds are each other's closest living relatives and are part of the reptile group Archosauria. All dinosaurs are archosaurs.
· Teleocrater is more closely related to dinosaurs and birds than to crocodiles, belonging to the 'bird-line' of archosaur evolution.
· 'Bird-line archosaurs', 'avian-line archosaurs', 'avemetatarsalians' are three different terms used for the same group of reptiles, which includes pterosaurs, non-avian dinosaurs, birds, Teleocrater, and other species.
· Teleocrater and its relatives split off from other bird-line archosaurs before the evolutionary split between pterosaurs (flying reptiles) and dinosaurs.
· Aphanosauria/aphanosaurs = a group of long-necked, slender-limbed, and carnivorous reptiles that lived in the Middle Triassic across Pangaea.
· Teleocrater likely stood on all four legs with its limbs positioned directly underneath its body.
· Teleocrater had a relatively long neck like other relatives of dinosaurs.
· Teleocrater had sharp, recurved, and serrated teeth, suggesting that it had a carnivorous diet.
· Much of the skeleton of Teleocrater is represented, but the skull, hands, feet, and tail are largely unknown.
Age & Geography
· The Mesozoic Era includes the Triassic, Jurassic, and Cretaceous periods.
· The Triassic Period lasted from 252–201 million years ago, and the following animals arose during this time: dinosaurs, crocodile relatives, mammals, pterosaurs, turtles, frogs, and lizards.
· Teleocrater is from the Anisian (Middle Triassic, ~245 million years old) and predates the first true dinosaurs by ~10 million years.
· Teleocrater fossils were excavated from the Manda Beds of southern Tanzania.
· During the Triassic, the continents were coalesced into a single landmass named Pangaea. Tanzania was located ~50° south of the equator (i.e., much farther south than today).
· The southern portion of Pangaea is called Gondwana, and included what is now South America, Africa, Madagascar, Antarctica, Australia, and India.
· The world was much hotter in the Triassic Period than it is today.
Discovery and history of the specimens
· The first fossils of Telocrater were collected in 1933 by F. Rex Parrington, a famous paleontologist based at the University of Cambridge (UK).
· Alan J. Charig (1927–1997), completed the initial work on Parrington's specimens in 1956, but his findings were never published.
· Charig was the Curator of Fossil Reptiles, Amphibians and Birds at the Natural History Museum in London.
· Charig went to Tanzania in search of more fossil reptiles in 1963.
· Other remains of Teleocrater were collected by an international team including many of the authors in 2015.
· All specimens of Teleocrater are from a rock unit called the Manda Beds, in the Ruhuhu Basin of southern Tanzania, Africa.
· Teleocrater was found with other reptiles and early relatives of mammals in the Manda Beds, which represent Triassic-aged river deposits.
· The oldest unambiguous dinosaurs are about 231 million years old and are found in Argentina, Brazil, Zimbabwe, and India.
· Crocodylia is the group that includes living crocodiles, like the American alligator and the Nile crocodile as well as their extinct relatives.
· Most previously known dinosaur relatives were rather small (under 1 meter in length) and include animals named Marasuchus, Lagerpeton, Dromomeron, and Silesaurus (~2 meters long).
Excavating the remains of Teleocrater rhadinus and other animals in southern Tanzania in 2015. Credit: Christian Sidor.
Excavating the remains of Teleocrater rhadinus and other animals in southern Tanzania in 2015. Sterling Nesbitt (left) and Christian Sidor (right). Credit: Roger Smith.
Quotes available for press articles:
-Dr. Sterling J. Nesbitt, Virginia Tech:
“The discovery of Teleocrater fundamentally changes our ideas about the earliest history of dinosaur relatives. It also raises far more questions that it answers”.
“The discovery of such an important new species is a once in a lifetime discovery”.
“Teleocrater is to early dinosaur origins as Tiktaalik is to the origin of animals with four distinct limbs (tetrapods)”.
- Dr. Richard J. Butler, University of Birmingham:
“Dinosaurs were amazingly successful animals. It's natural to want to know where they came from, and how they became so dominant. Teleocrater is hugely exciting because it blows holes in many of our classic ideas of dinosaur origins.”
“It's astonishing to think that it's taken more than 80 years for the true scientific importance of these fossils to be understood and published”.
“Teleocrater fundamentally challenges our models of what dinosaur relatives would have looked like”.
- Dr. Martín D. Ezcurra, Museo Argentino de Ciencias Naturales, Buenos Aires, Argentina:
“Teleocrater and its close relatives show that the overall body plan that once was thought to characterize crocodile-line reptiles was also present in the first members of the lineage that lead to dinosaurs”.
“The discovery of new fossils and reinterpretations of previously known specimens collected in several continents allowed us to change a paradigm in a so debated topic like the origin of dinosaurs”.
“Teleocrater and its close relatives shed light on one of the most successful evolutionary radiations of vertebrate animals, which was part of the reshaping of ecosystems after the deadliest mass extinction in the history of life”.
- Prof. Paul M. Barrett, Natural History Museum, London:
“Our discovery shows the value of maintaining and re-assessing historical collections: many new discoveries, like this one, can be made by looking through museum collections with fresh eyes”.
“ My colleague Alan Charig would have been thrilled to see one of 'his' animals finally being named and occupying such an interesting position in the Tree of Life”.
- Dr. Michelle R. Stocker, Virginia Tech:
“It's so exciting to solve puzzles like Teleocrater, where we can finally tease apart some of these tricky mixed assemblages of fossils and shed some light on broader anatomical and biogeographic trends in an iconic group of animals.”
Protecting the remains of Teleocrater rhadinus with plaster bandages in 2015. Michelle Stocker (left) and Sterling Nesbitt (right). Credit: Roger Smith.
Labeling the plaster jackets containing the bones of Teleocrater rhadinus at night in 2015. Credit: Roger Smith.
-National Science Foundation
-National Geographic Society
-Marie Curie Career Integration Grant
-National Geographic Society Young Explorers grant
-Russian Government Program of Competitive Growth of Kazan Federal University
The upper jaw of Teleocrater on top a complete skull reconstruction. Credit: Michelle Stocker.
We reevaluate an exquisitely preserved specimen of extinct reptile (closely related to dinosaurs and crocodylians), Diandongosuchus fuyuanensis, as the earliest known member of Phytosauria. This specimen fills in temporal and morphological gap in our knowledge of phytosaur evolution, showing that the features we most easily associate with phytosaurs (long rostrum, large body size) appeared much later in the evolution of the group.
A Short-Snouted, Middle Triassic Phytosaur and its Implications for the Morphological Evolution and Biogeography of Phytosauria
Michelle R. Stocker, Li-Jun Zhao, Sterling J. Nesbitt,, Xiao-Chun Wu, and Chun Li.
The skull of Diandongosuchus fuyuanensis in side view. Credit: Michelle Stocker
The skeleton of Diandongosuchus fuyuanensis in side view. This is one of the most complete skeletons of a phytosaur ever discovered! Credit: Michelle Stocker
· Diandongosuchus represents the oldest known phytosaur specimen, the only short-snouted phytosaur, and the only phytosaur known from China.
· An Early Triassic (~249 million years ago) divergence time had been predicted for phytosaurs despite most specimens being known from rocks that are ~228-200 million years old, and Diandongosuchus fills in ~10 million years of that missing record.
· Some features of the skulls of large, derived phytosaurs are already present in Diandongosuchus, and these may be associated with the early evolution of features associated with enhanced prey capture.
· Diandongosuchus supports that phytosaurs were present across Pangea, suggesting early ecosystem exploration for archosaur relatives through nearshore environments and leading to ease of dispersal across the Tethys.
“So much of our study of the fossil record is about filling in the gaps in our knowledge of how animals came to look as they do or live where they are, and Diandongosuchus does that for phytosaurs. We're never done filling in those gaps.” Michelle Stocker, Virginia Tech
· Diandongosuchus lived ~240 million years ago in the Middle Triassic.
· The Triassic Period lasted from ~250 million years ago to ~200 million years ago.
· The Mesozoic Era includes the Triassic, Jurassic and Cretaceous Periods.
· The majority of confirmed phytosaurs are ~225-205 million years old.
· Diandongosuchus was collected from the lower part of the Falang Formation of Yunnan Province, China.
· Diandongosuchus was published in 2012 as a poposauroid (a group more closely related to crocodylians).
· Much of the skeleton is represented, but parts of the hands, feet, and tail are still unknown.
· Diandongosuchus was ~2 meters long including its tail.
· Most previously known phytosaurs were rather big (~ 5-7 meters in length) and include animals named Parasuchus, Leptosuchus, Smilosuchus, and Machaeroprosopus.
· Phytosaurs are sometimes compared to living crocodylians because they share the same general body shape, were carnivorous, and may have had a similar semi-aquatic ecology.
· Crocodylia is the group that includes the American alligator and the Nile crocodile - Crocodylians and birds are each other's closest living relatives and are part of the reptile group Archosauria. All dinosaurs are archosaurs.
· The world was much hotter in the Triassic Period than it is now.
· Diandongosuchus was found with other reptiles in the same set of rocks (possibly representing near-shore marine deposits).
The front portion of the tail of Diandongosuchus fuyuanensis in side view. Credit: Michelle Stocker
Michelle Stocker studying the skeleton of Diandongosuchus fuyuanensis in China. Credit: Sterling Nesbitt
Sterling Nesbitt rearticulated the head of Diandongosuchus fuyuanensis with the body. Credit: Michelle Stocker
Quotes available for press articles:
- Dr. Michelle Stocker, Virginia Tech:
“So much of our study of the fossil record is about filling in the gaps in our knowledge of how animals came to look as they do or live where they are, and Diandongosuchus does that for phytosaurs. We're never done filling in those gaps.”
-Dr. Sterling Nesbitt, Virginia Tech:
“Early members of these Triassic reptile lineages are appearing where they've been predicted for years. Now we have the fossils.”
-Dr. Xiao-Chun Wu, Canadian Museum of Nature:
“In 1951, Dr. C.C. Young, the founder of the vertebrate paleontology of China, reported the discovery of a phytosaur (Pachysuchus imperfectus) in China based on a fragmentary specimen from Yunnan province, but the phytosaur status of that specimen was doubted and often considered as indeterminable. Therefore, Diandongosuchus is the first true phytosaur found in China, which, with its basal-most position within the Phytosauria, not only expanded the biogeographic range of the lineage, but also enriched our knowledge on the origin and early radiation of the Phytosauria.”