Researchers describe new fossil species that represents ancient pioneers of most modern reptiles

Reconstruction of Taytalura’s life in its natural habitat by the extinct conifer Rhexoxylon of the Upper Triassic Ischigualast (Argentina), hiding from the primitive dinosaur Eodromaeus (background) in the skull of the mammal ancestor Credit: scientific illustrator Jorge Blanco

Lizards and snakes are important components of most terrestrial ecosystems on Earth today. Scaled reptiles (all lizards and snakes), along with the charismatic New Zealand tuatara (“living fossils” represented by a single living species), constitute the lepidosauria. By far the largest modern group of reptiles. Squamata and Tuatara both have a very long evolutionary history. Their lineage is older than the divergent dinosaurs that were born from each other around 260 million years ago. However, the early stages of Lepidosauria evolution 260 to 150 million years ago are characterized by highly fragmented fossils and do not provide much useful data for understanding early evolution. Without providing, the origins of this very diverse group of animals have been shrouded in mystery for decades.

In a study published on August 25 Nature An international team of researchers describes a new species that represents the most primitive members of lepidosauria. Taytalura alcoberiFound in Upper Triassic deposits in Argentina. Discovered by lead author Dr. Ricardo N. Martinez, curator at the National University of San Juan in Argentina and at the Museum of Natural Sciences. Taytalura It is the first fossil of early lepidosauria preserved in three dimensions. This allows scientists to confidently deduce that they are located in the evolutionary reptile tree, helping to bridge the gap in knowledge of their origin. Early development of lepidosauria.

Martinez and co-authors Dr. Sebastián Apesteguía, Universidad Maimónides, Buenos Aires, Argentina, Taytalura He provided confirmation that he was related to ancient lizards. Then I reached out to co-author Dr Tiago R. Simes, a postdoctoral researcher in the Department of Bioevolutionary Biology at Harvard University, to help me identify and analyze the fossils. Simões specializes in the study of these creatures and in 2018 published the largest dataset available to understand the evolution of major groups of reptiles (living and extinct). Nature..

“I knew the age and origin of the fossil, and by examining some of its external characteristics, I was able to discover that it was closely related to the lizard, but that it was better than the real lizard. It also looks primitive and it’s very special, ”said Simões.

The researchers then contacted Dr Gabriella Sobral, co-author of the paleontology department at the National Museum in Stuttgart, Germany, to process the data from the CT scan. Sobral, a specialist in CT data processing, created a color mosaic of each bone in the skull. This allows the team to understand the anatomy of fossils in high resolution at a scale of a few micrometers, roughly the same thickness as human hair. ..

Using data from Sobral, Simões was able to apply evolutionary Bayesian analysis to determine the correct placement of fossils in the reptile dataset. Simões recently applied the Bayesian method, which applies the method initially developed in epidemiology to study the evolution of viruses like COVID-19. Time and speed of anatomical evolution during the ascent of the tetrapod. Statistical analysis confirmed their suspicions Taytalura In fact, it was the most primitive member of the line that ultimately produced all of the lizards and snakes. “It’s not even an evolutionary arboreal lizard, but it’s the next thing that exists among true lizards and tuatara, and all other reptiles,” Simes said.

“This beautifully preserved 3D fossil is a really important find. It is the most complete fossil that represents the early stages in the evolution of lepidosauria to date. All other known fossils are too incomplete and are certain. Difficult to classify, but the complete and clear nature of Taytalura We are going to make this relationship more secure. “

Reconstruction of Taytalura’s skull based on high-resolution CT scans (left) and placement of reptiles in the evolutionary tree (right). Credits: Left) Gabriella Sobral, Jorge Blanco, Ricardo Martinez. Right) Tiago Simes

Simes agreed, “Taytalura This is the main point of the reptile tree of life that was previously missing. These fossils are so small that they are very difficult to keep in their fossil record. And the candidate fossils that we have are very fragmented and poorly preserved, so there isn’t a lot of useful data for analysis. “

Taytalura The skull reveals that the early Lepidosaurus look much more like tuatara than scaled reptiles, so the scaled reptiles represent a major deviation from this ancestral pattern. In addition, it has a unique dentition, unlike teeth found in living or extinct groups of the epidosauria. “Our analysis shows that in addition to other anatomical features found in the skull, at least in the skull, this tuatara body shape is an ancestor model of lepidosauria. It’s more like a lepidosauria. “

“”Taytalura It retains a composition of features not found in these early fossils. For example, you will see some features that you thought were exclusive to the tuatara group. On the other hand, we will wonder if some characteristics of lizards are really “primitive” and scientists will reconsider certain points in the evolution of this group, ”Sobral said. Said.

“Almost completely preserved Taytalura The skull details how a very successful group of animals were born, including more than 10,000 species of snakes, lizards and tuatara. Save some of the most primitive dinosaurs known in the world. The extraordinary quality of conservation of the fossils here has allowed small specimens as fragile as this specimen to be preserved for 231 million years. “

“Unlike almost all Triassic lepidosauria fossils found in Europe, this is the first early lepidosauria found in South America, and lepidosauria dates from the early history of evolution. This suggests that we were able to travel to a very remote geographic area, ”Simões agreed.

“We are used to accepting that the Mesozoic was an era of giant reptiles, giant proto-mammals and giant trees. Therefore, we are usually fossils visible at human height just by walking. Find out, ”Apestegia said. “But most of the components of the old ecosystem were as small as they are today. The world of fauna slipped between the feet of the biggest, claws or hooves. Taytalura Not only looking for large animals, but as the evidence has been substantiated so far, thinking that the origin of lizards is only in the northern hemisphere tells us that there is a lack of important information. “

waiting for Taytalura This is a primary lepidosauria and not the oldest. The fossils are 231 million years old, but there are also real 11 million year old lizard fossils. The team then plans to explore older sites in hopes of finding similar or different species of the same strain that diverge just before their true origin. Lizards ..


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For more information:
Lepidosauria with a Triassic stem shed light on the origin of reptiles such as lizards. Nature (2021). DOI: 10.1038 / s41586-021-03834-3, www.nature.com/articles/s41586-021-03834-3

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Researchers describe new fossil species that represents ancient pioneers of most modern reptiles

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