Reptiles are a species-rich class of vertebrates: they include such fascinating creatures as snakes, crocodiles and lizards. Paleontologists have now discovered an early representative of the reptiles near Vellberg in Baden-Württemberg. There they dug the 240 million year old fossil of a mini lizard. The special feature: It is a hitherto completely unknown species, which is similar to today’s lizards and snakes and is one of the oldest representatives of the so-called scale lizards. The fossil thus makes a valuable contribution to better understanding the evolution of reptiles.
The Triassic period was a phase of dramatic changes on Earth: At the transition to this age, the greatest mass extinction in the history of our planet occurred – more than 90 percent of all animal and plant species in the ocean and 70 percent of all land inhabitants were wiped out at the time. After that, life on earth had to be rearranged. The ancestors of today’s lizards, turtles and crocodiles were created in the course of this process. The dinosaurs from which the birds later emerged also developed at that time. How exactly the evolution of these animals went is only partially known. Because from the middle Triassic period 247 to 237 million years ago there are no fossils of terrestrial organisms. “This limits our understanding of the early diversification of lineages, which today represent some of the world’s most species-rich fauna – for example the lepidosauromorpha,” explains Gabriela Sobral from the State Museum of Natural History in Stuttgart and her colleagues. This taxon includes scaled lizards such as snakes and lizards.
Similarity to lizards and snakes
This makes the fossil that the scientists found at Vellberg in the Schwäbisch-Hall district all the more exciting: they dug the 240 million year old tiny skull of a lizard there. The animal was only ten centimeters long during its lifetime and probably not yet fully grown. As Sobral’s team reports, the anatomical features of this mini-lizard are very similar to modern lizards and snakes. According to this, the fossil resembles, among other things, in terms of its teeth and lower jaw bones, a mosaic of the properties of early scaly reptiles (Squamata) and Rhynchocephalia – an animal group that only exists today in the form of the bridge lizards (Tuatara) native to some New Zealand islands.
This means that the mini-lizard may be a common ancestor of these two groups of animals. It could belong to the lineage from which the Squamata and Rhynchocephalia split off. According to the researchers, this makes them a stem lepidosauromorph and thus one of the oldest representatives of the scaly lizards. You assign the reptile to a previously unknown species: Vellbergia bartholomaei. The new species is not only interesting because of its unique combination of anatomical properties. Their age also implies a surprising coexistence. Because this lizard lived in Central Europe at a time when the first representatives of the Squamata and Rhynchocephalia emerged from their lineage. “This suggests that stem lepidosauromorphs survived up to the middle Triassic,” Sobral and her colleagues explain.
Small thanks to the Liliput effect?
The small size of Vellbergia bartholomaei is also striking. Even if the reptile was still a young animal, it would also have been rather small when fully grown – like many other land vertebrate fossils discovered at the site near Vellberg. “This coincides with what we see in part in the fauna of the early Triassic. This could have resulted in a long-lasting Liliput effect in these animals, ”the scientists suspect. This effect describes the reduction in body size of organisms, which is commonly assumed to occur frequently during or after mass extinctions.
All in all, the mini lizard provides valuable new insights into the evolution of reptiles. In addition, their discovery shows once again that the site at Vellberg hides a real fossil treasure – especially with regard to the period shortly before the creation of the dinosaurs. Paleontologists have already found amphibians and crocodile relatives there. In 2015, they also discovered the 240 million year old fossil of Poppochely’s great turtle. A real missing link: this animal did not yet have a complete shell, but its ribs were already widened. It thus forms a perfect link between early lizards and turtles, as the Stuttgart research team reported at the time.
Source: Gabriela Sobral (State Museum of Natural History Stuttgart) et al., Scientific Reports, doi: 10.1038 / s41598-020-58883-x