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| Tetrapodophis amplectus Martill, Tischlinger & Longrich, 2015 in Caldwell, Simões, Palci, et al., 2021. |
Abstract
The origin of snakes remains one of the most contentious evolutionary transitions in vertebrate evolution. The discovery of snake fossils with well-formed hind limbs provided new insights into the phylogenetic and ecological origin of snakes. In 2015, a fossil from the Early Cretaceous Crato Formation of Brazil was described as the first known snake with fore- and hind limbs (Tetrapodophis amplectus), and was proposed to be fossorial, to exhibit large gape feeding adaptations (macrostomy) and to possess morphologies suggesting constriction behaviours. First-hand examination of T. amplectus, including its undescribed counterpart, provides new evidence refuting it as a snake. We find: a long rostrum; straight mandible; teeth not hooked zygosphenes/zygantra absent; neural arch and spines present and tall with apical epiphyses; rib heads not tubercular; synapophyses simple; and lymphapophyses absent. Claimed traits not preserved include: braincase/descensus parietalis; ‘L’-shaped nasals; intramandibular joint; replacement tooth crowns; haemal keels; tracheal rings; and large ventral scales. New observations include: elongate retroarticular process; apex of splenial terminating below posterior extent of tooth row; >10 cervicals with hypapophyses and articulating intercentra; haemapophyses with articulating arches; reduced articular surfaces on appendicular elements; rows of small body scales; and reduced mesopodial ossification. The axial skeleton is uniquely elongate and the tail with >100 vertebrae is not short as previously claimed, although overall the animal is small (∼195 mm total length). We assessed the relationships of Tetrapodophis using a revised version of the original morphological dataset, an independent morphological dataset, and these two datasets combined with molecular data. All four were analysed under parsimony and Bayesian inference and unambiguously recover Tetrapodophis as a dolichosaur. We find that Tetrapodophis shows aquatic adaptations and there is no evidence to support constricting behaviour or macrostomy.
Keywords: Tetrapodophis amplectus, lizards, snakes, mosasauroids, pythonomorphs, phylogeny, fossils, character evolution, Cretaceous, Brazil, Crato Formation
Systematic palaeontology
Squamata Oppel, 1811
Pythonomorpha Cope, 1869
Dolichosauridae Gervais, 1852
Tetrapodophis amplectus Martill, Tischlinger & Longrich, 2015
Etymology: No etymology was given by Martill et al. (2015), the genus and species were presented as Tetrapodophis amplectus gen. et sp. nov. We note that ‘tetra’, ‘pod’ and ‘ophis’ are Greek words for four, foot and snake respectively, and that ‘amplectus’ or ‘amplexus’, is Latin for ‘to embrace’, and media interviews by the original authors support this interpretation (e.g. Watson 2015).
Michael W. Caldwell, Tiago R. Simões, Alessandro Palci, Fernando F. Garberoglio, Robert R. Reisz, Michael S. Y. Lee and Randall L. Nydam. 2021. Tetrapodophis amplectus is not a Snake: Re-assessment of the Osteology, Phylogeny and Functional Morphology of An Early Cretaceous Dolichosaurid Lizard. Journal of Systematic Palaeontology. DOI: 10.1080/14772019.2021.1983044
