Wumengosaurus and mesosaurs: how can these two NOT be related?

Figure 1. Wumengosaurus specimens from Wu et al. scaled to show size variety.

Wumengosaurus, the basal enaliosaur, is known from several sizes (Fig 1). Sometimes that’s not readily apparent when all the images are published at the same size, not to the same scale.

What happens to the skull of Wumengosaurus as it matures (Fig. 2)?

Figure 2. Wumengosaurus in small and large varieties along with Stereosternum and Mesosaurus to scale.

The rostrum doesn’t get relatively longer. The skull becomes relatively smaller.

The relatively small Stereosternum is a sister to Wumengosaurus in the large reptile tree. Their skulls document their similarities, overlooked by Wu et al. (2011) and Jiang et al. (2008). So what if the temporal fenestra disappear in certain (not all) Mesosaurus? That’s just a small number of characters out of a suite of synapomorphies.

References
Jiang D-Y, Rieppel O, Motani R, Hao W-C, Sun Y-I, Schmitz L and Sun Z-Y. 2008. A new middle Triassic eosauropterygian (Reptilia, Sauropterygia) from southwestern China. Journal of Vertebrate Paleontology 28:1055–1062.
Wu X-C, Cheng Y-N, Li C, Zhao L-J and Sato T 2011. New Information onWumengosaurus delicatomandibularis Jiang et al., 2008, (Diapsida: Sauropterygia), with a Revision of the Osteology and Phylogeny of the Taxon. Journal of Vertebrate Paleontology 31(1):70–83.

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