Tetrapodophis

Hindlimbs

Tetrapodophis possesses small yet well-developed fore- and hindlimbs, a feature found in no living species of snake. Nevertheless, it shares many characteristics with modern snakes, including an elongate body, short tail, broad belly scales, a skull with a short snout and long braincase, curved jaws, and sharp hooked teeth. BMMS BK 2-2 contains bones of another animal in its gut, indicating that Tetrapodophis was carnivorous like most snakes. Other features such as short neural spines suggest that Tetrapodophis was adapted to burrowing, lending support to the hypothesis that snakes evolved in terrestrial environments (another hypothesis posits that they evolved in aquatic environments).[2] The high number of vertebrae (upwards of 150) in Tetrapodophis and snakes is not seen in other burrowing reptiles with elongate bodies and reduced or absent limbs, meaning that it is most likely not an adaptation for a serpentine form of locomotion[1] Dolichosaurids are thought to be phyogenetically close to snakes as members of Ophidiomorpha, which explains some of the morphological similarities.

The type species, Tetrapodophis amplectus, was named in 2015 on the basis of a complete skeleton (BMMS BK 2-2) preserved on a limestone slab in the Bürgermeister Müller Museum in Solnhofen, Germany, which was labeled as "unknown fossil" until its importance was recognized by paleontologist David Martill, and illegally exported from Brazil,[3] since the country's laws do not allow the removal of fossils from its territory, nor that studies on them be conducted without the participation of at least one Brazilian scientist. The specimen was later determined to come from the Early Cretaceous Crato Formation in Ceará, Brazil. When asked why he didn't have a Brazilian scientist in the describing team, as required by Brazilian law, Martill responded:[4]

But what difference would it make? I mean, do you want me also to have a black person on the team for ethnicity reasons, and a cripple and a woman, and maybe a homosexual too just for a bit of all round balance? … If you invite people because they are Brazilian then people will think that every Brazilian author on a scientific paper is there because he is Brazilian and not because he is a clever scientist

A phylogenetic analysis published alongside the original 2015 description of Tetrapodophis places it as a close relative of other early snakes such as Coniophis, Dinilysia, and Najash, but outside the crown group Serpentes, meaning that it branched off before the most recent common ancestor of all living snakes. Below is a cladogram from that analysis:[1]

The interpretation of Tetrapodophis amplectus as an early fossorial snake was challenged by Caldwell et al. (2016), who considered it more likely to be a dolichosaurid squamate.[5][6] A position corroborated by later analysis.[7]

• Media related to Tetrapodophis at Wikimedia Commons
• Tetrapodophis as it may have been in life
• Scientists Discover Four-Legged Snake Fossil. On: SciTechDaily, Source: University of Portsmouth. August 2, 2015
• Susan Evans: “Four legs too many?,” In: Science Vol. 349 no. 6246 pp. 374–375. 24 July 2015; doi:10.1126/science.aac5672