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