The “lost” quadratojugal and supratemporal of Wumengosaurus

In basal enaliosaurs, the quadratojugal tends to be ignored or misidentified. Claudiosaurus is one such example. That’s because the qj generally shifts during taphonomy.  Wumengosaurus is another such taxon based on several specimens (Fig. 1). There is also a misidentified supratemporal here.

Figure 1. The unidentified supratemporal (in yellow/green) and quadratojugal (in lavender) in two Wumengosaurus specimens. Postorbital in violet. Squamosal in magenta. this is the ichthyosaur temporal region pattern, losing the lateral temporal fenestra, but gaining a secondary lateral temporal fenestra by the raising of the quadratojugal.

Figure 1. The unidentified supratemporal (in yellow/green) and quadratojugal (in lavender) in two Wumengosaurus specimens. Postorbital in violet. Squamosal in magenta. this is the ichthyosaur temporal region pattern, losing the lateral temporal fenestra, but gaining a secondary lateral temporal fenestra by the raising of the quadratojugal.

Why look for a bone that’s not identified?
Because sister taxa (Stereosternum, Mesosaurus, ichthyosaurs)  have a supratemporal and quadratojugal.

The fact that the lateral temporal fenestra disappears between the quadratojugal and squamosal in ichthyosaurs, yet both are arched posterior to the jugal means ichthyosaurs have a secondary lateral temporal fenestra, convergent with the typical lateral temporal fenestra of basal diapsids and protorosaurs + archosauriforms. And that’s how ichthyosaurs need to be scored in phylogenetic analysis.

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.
Maisch MW 2010. Phylogeny, systematics, and origin of the Ichthyosauria – the state of the art. Palaeodiversity 3: 151-214.
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.

wiki/Wumengosaurus

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