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.
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.
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