Scientists describe new Brazilian fossil frog – 11/28/2023 – Science

Researchers have described a new species of fossil frog for the Late Cretaceous (about 90 million to 66 million years ago).

baptized by Mariliabatrachus navai (the genus name means “marília frog”, and the specific epithet pays homage to paleontologist William Nava, who found the material), the fossil was found in rocks of the Adamantina Formation, Bauru Basin, in the municipality of Marília (435 km from capital). Fossils of crocodiles, turtles and other reptiles have been found in the same location.

The article describing the find was published on the 15th in the specialized journal Zoological Journal of the Linnean Society. The article is signed by Rodolfo dos Santos, a doctoral student at the London Natural History Museum (NHL) and the USP Zoology Museum, Alberto Carvalho, responsible for the Computed Tomography Laboratory at the same institution, and Hussam Zaher, professor of vertebrate zoology at USP and curator of the Herpetology and Paleontology collections.

Found in 2001 by Nava, the frog had already been the subject of study in Carvalho’s doctoral thesis, but at the time it was difficult to define a new species. “I wrote the description [definição da anatomia do animal, que pode ajudar na sua classificação na árvore evolutiva]but they had many characters that were difficult to see due to their position in the rock, covered by sediment”, he explains.

There was, however, an aggravating factor: the material, although associated (found in the same location and from a probable individual), had disconnected bones, making it difficult to define the animal’s morphology, except for two plates that were more or less a continuity.

“But when we tried to connect one to the other, it wouldn’t connect. It was as if the rock had broken in such a way that we couldn’t put the puzzle together”, he recalls.

Twenty years later, and with the technological revolution offered by the computerized tomography tool, which uses high-intensity X-rays to “see” the preserved hard parts through the sediment, the technique has finally made it possible to virtually “join” the two parts.

“With this, we were able to access information in much more detail,” he says.

Using the virtually reconstituted skeleton, Santos compared the anatomy of the Mariliabatrachus with that of current representatives of anurans, as the group that includes toads, frogs and tree frogs is called. “But it’s difficult because there are more than 8,000 species, and we have limited knowledge of the anatomy of most of these species,” he says.

Evolutionary analysis indicated that the fossil is part of the group known as Neobatrachia, which represents the lineage of amphibians that later diversified into current groups.

“I started by trying to understand which family [grupo] Among current frogs it fits, today I think it is different and I believe it is part of a lineage that is also present in the Cretaceous of Morocco and that did not survive the great extinction at the end of the period”, he says.

It is worth remembering that the extinction at the end of the Cretaceous, famous for having wiped out most dinosaurs, pterosaurs and other giant reptiles, also affected other animals, such as fish, turtles, crocodylomorphs and amphibians.

“In this macroevolutionary context, an interesting thing is that the lineage became extinct precisely at a key moment for anurans, because it was at the end of the Cretaceous that all groups living to date emerged, the neobatrachians. So they appear at the end of the Cretaceous, but diversified from the Paleocene onwards [de 65 a 56 milhões de anos].”

The skeleton of Mariliabatrachus is similar to that of a pepper frog (genus Leptodactylus) or a cane toad (genus Snort). “Frogs have a very conservative morphology, which has not changed much in the 200 million years of their evolution,” says Carvalho.

Differently, ornamentations (holes) in the skull bones and the fusion of the frontal and parietal bones, an extremely variable aspect among known frog species, are more difficult to indicate any major evolutionary change.

There are still some uncertainties, such as in which paleoecological context the frog lived, as other fossils found in the region indicate a semi-arid environment. “The climate was very hot, but it certainly had some bodies of water. It may be that they had the habit of burying themselves in the driest period and emerging from the earth in humid moments, the so-called aestivation, known for some African species”, he concludes. Oak.