• Tetrapodophis is not a snake

    From Pandora@21:1/5 to All on Fri Nov 19 15:50:13 2021
    Tetrapodophis amplectus is not a snake: re-assessment of the
    osteology, phylogeny and functional morphology of an Early Cretaceous dolichosaurid lizard

    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.

    Open access:
    https://www.tandfonline.com/doi/full/10.1080/14772019.2021.1983044

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