Tetrapodophis
Tetrapodophis (greek meaning "four-footed snake") is an extinct genus of lizard from the Early Cretaceous. Tetrapodophis was previously thought to be one of the oldest members of Ophidia (Snakes and their extinct relatives).[1][2] However, this classification has been disputed by Caldwell et al. (2016),[3] Paparella et al. (2018)[4] and Caldwell et al. (2021),[5] who identify Tetrapodophis as a dolichosaurid (more closely related to the Ophidia than to mosasaurs, but lie in the greater clade, Ophidiomorpha). This species existed in the Cretaceous Period about 120 million years ago, located in modern day Brazil. This four legged animal is around 19.5 cm (7.7 in) long.[5]
Tetrapodophis possesses small yet well-developed fore- and Hindlimbs like a lizard and a long body similar to a 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 but it turns out to be a lizard. 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 movement.[1] Dolichosaurids are thought to be phylogenetically 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,[6] 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:[7]
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 lizards, but outside the crown group Serpentes, meaning that tetrapodophis 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.[3][9] A position corroborated by later analysis in 2018[4] and in 2021.[5]
