Intriguing fossil reptile offers clues to the origin of snakes and lizards

The reptile.

Twenty years after its discovery in Argentina, the 231.4 million year old Lepidosaurus fossil has been described in detail by paleontologists. This animal has characteristics that place it before the split between lizards, snakes and sphenodonts (a branch of reptiles that today only includes the strange tuatara). The fossilized skull recently underwent a CT scan and an interdisciplinary team of researchers published their analysis of the specimen this week in Nature.

The animal is Taytalura alcoberi. To the untrained eye, it looks a lot like a lizard (a rusty gecko, to this writer). But the animal’s anatomy is much older, which the research team found when they were able to examine the fossil in detail. None of the animal’s bodies have been preserved, but the skull – which is about an inch and a half long – is the most complete evolutionary fossil of Lepidosaurus ever known, said the co-author of the study Gabriela Sobral, who supervised the CT scan, in a Harvard Press release. Viewing the skull in three dimensions has provided new information on how the skulls of modern day snakes, chameleons, geckos, tuatara, and others were derived.

“The almost perfectly preserved Taytalura skull shows us details of how a very successful group of animals, which includes nearly 11,000 species, including snakes, lizards and tuataras, are native, ”said Ricardo Martínez, lead author of the study and paleontologist at the National University of San Juan in Argentina.

Taytalura shows some features that we thought were exclusive to the tuatara group, ”Martínez wrote in an email to Gizmodo. “The skull of Taytalura shows that the first Lepidosaurus looked more like the tuataras than the squamates, and therefore, that the squamates represent a major deviation from the ancestral model. Squamates are the group of reptiles made up of snakes, lizards, and worm lizards.

Discovered in Argentina in 2001 (“I just found it on the surface and picked it up,” Martínez said), T. alcoberi is what researchers call a “stem species», A term designating the animals which branched out from the evolutionary tree before the lines which persist to this day. In other words, they are species with a previous evolution that do not have living descendants. T. alcoberi is an evolutionary branch that indicates what life was like before Lepidosaurs divided into two groups: squamates and sphenodonts. Although T. alcoberi is younger than some lizards – the earliest fossils of squamates and sphenodonts date back to 242 million and 238 million years ago, respectively – its morphology is older. Dating from the Triassic, the reptile precedes Tyrannosaurus Rex by more than 150 million years.

Taytalura from the bones.

T. alcoberi had certain characteristics that indicated to Tiago Simões, an evolutionary biologist at Harvard University and co-author of the article, that he was special. It lacked a muzzle opening common in archosaurs, the evolutionary lineage that includes crocodilians and dinosaurs. Its square bone, which connects the skull to the lower jaw, had a peculiar shape. But the CT scan really got things done at home: the animal had bones mutually exclusive to both squamates and sphenodonts.

The tuatara, a reptile endemic to New Zealand, was the only sphenodont living on Earth for some 60 million years. For its relatively unchanged anatomy through the ages, the tuatara is often referred to as a “living fossil”. And T. alcoberi corroborates this label, the fossil animal resembling the tuatara more than chameleons, legless lizards and snakes.

Simões applied Bayesian analysis to place the fossil in the evolutionary tree. The modeling allowed the research team to estimate when specific adaptations developed in lepidosaurs and how quickly they changed. The Bayesian method confirmed to the team that T. alcoberi is the most primitive known member of the reptilian lineage from which all lizards and snakes emerged.

“In science, we never look for real answers or proofs because the fundamental premises of science prohibit the existence of real answers… on principle, these trees are never correct and they change frequently over time. But if after future analyzes, and perhaps new data, the placement of Taytalura remains the same, it may cement our ideas in this article as a new theory of the origin of lepidosaurus, ”Simões said in an email to Gizmodo.

An evolutionary tree showing where the new species fits.

The fossil is a big step towards understanding today’s reptiles; in other words, those who didn’t fall with the dinosaurs. With the exception of crocodilians, many of these animals were smaller, living in the shadow of giants for millions of years.

“We’re used to accepting that the Mesozoic era was a time of gigantic reptiles, huge proto-mammals, and huge trees, so we commonly look for fossils that are visible at human height just by walking. However, most of the components of the ancient ecosystem were small, like today. There was a universe of fauna slipping through larger paws, claws or hooves, ”said co-author Sebastián Apesteguía, paleontologist at Maimónides University in Buenos Aires, in a report. Press release.

It’s always cool to see a newly discovered twig on the Tree of Life, but maybe even cooler to see clues as to how whole branches sprouted to begin with. T. alcoberi is exactly that; a pint-sized remnant of a large rift between reptiles.

Correction: A sentence in this article incorrectly referred to the tuatara as a “lizard”. While tuataras certainly resemble lizards, they are sphenodonts. I apologize to the readers and the tuataras for this error.

More: This Ancient Reptile Developed A Weird Bird-Like Head 100 Million Years Before Birds Did

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