The exquisite transitional fossil Tetrapodophis – interpreted as a stem-snake with four small legs from the Lower Cretaceous of Brazil – has been widely considered a burrowing animal, consistent with recent studies arguing that snakes had fossorial ancestors. We reevaluate the ecomorphology of this important taxon using a multivariate morphometric analysis and a reexamination of the limb anatomy. Our analysis shows that the body proportions are unusual and similar to both burrowing and surface-active squamates. We also show that it exhibits striking and compelling features of limb anatomy, including enlarged first metapodials and reduced tarsal/carpal ossification – that conversely are highly suggestive of aquatic habits, and are found in marine squamates. The morphology and inferred ecology of Tetrapodophis therefore does not clearly favour fossorial over aquatic origins of snakes.
Keywords: Squamata; Ophidia; Serpentes; Evolution; Cretaceous; Paleoecology
Tetrapodophis does not clearly fall into any of the known ecological categories, but the presence of the limb features discussed above is difficult to explain as anything but holdovers from a more aquatically-adapted ancestor. Tetrapodophis therefore represents a truly enigmatic animal, combining the body proportions of an elongate squamate with the limbs of a swimmer (or former swimmer). The precise ecology of this iconic fossil will thus continue to be debated. Perhaps the reality lies in between, and Tetrapodophis may have been both fossorial and aquatic, a lifestyle exhibited by some living snakes such as neotropical pipesnakes (Anilius) (e.g. Murphy, 2010).
Michael S.Y. Lee, Alessandro Palci, Marc E.H. Jones, Michael W. Caldwell, James D. Holmes and Robert R. Reisz. 2016. Aquatic Adaptations in the Four Limbs of the Snake-like Reptile Tetrapodophis from the Lower Cretaceous of Brazil. Cretaceous Research.
Did snakes evolve from ancient sea serpents? http://phy.so/385370720 via @physorg_com