Vancleavea campi (Nesbitt et al. 2009) Late Triassic,~210 mya, ~1.2 meters in length, was originally considered a very weird archosauriform close to Doswellia, Turfanosuchus, Chanaresuchus and Erythrosuchus, but that's because the authors did not compare it to Helveticosaurus and Miodentosaurus, with which Vanclevea now nests. It turns out that Vanclevea was a not-so-weird thalattosaur and a prime example of what happens when the gamut of the inclusion set is decided prior to the analysis. Derived from a sister to Helveticosaurus, Vancleavea was the last in its lineage.
Distinct from Helveticosaurus, the skull of Vancleavea had a shorter rostrum and a longer postorbital portion. The jugal was robust and the orbit was smaller. The teeth were much larger in proportion to the skull. Both had a taller than wide skull. The mandible was deeper especially posteriorly.
I think Nesbitt et al. (2009) estimated too few dorsal vertebrae (in grey above) and reconstructed too short of a torso.The actual number appears to have been 35 or so, similar to Miodentosaurus. The number of cervicals was likely ~10, as in Miodentosaurus and Helveticosaurus. The tail was deeper in Vancleavea and further deepened by elongated osteoderms on top. Since the vertebrae are largely covered by ossified scales these determinations are guesses.
The pectoral girdle and forelimb were smaller, but otherwise similar to Helveticosaurus.
The pelvis wasn't deep. It was ventrally wide and the two sacrals would have set it lower than the vertebral column. The hind limb was longer than the forelimb, but the pes was probably no larger than the manus.
Unlike other thalattosauriforms, Vancleavea was armored with a variety of ossified scales covering the body.
A family tree of the Enaliosauria is here. A more complete tree of the Reptilia is here.
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