A neomorphic ossification connecting the braincase, squamosal, and quadrate in choristoderan reptiles: insights from µCT data

Choristoderes are extinct semi-aquatic to aquatic diapsid reptiles, occupying a similar niche as modern crocodilians from the Jurassic Miocene. Distinct other diapsids, choristoderes have neomorphic ossification between braincase, squamosal, and quadrate. This bone is described thin plate-like in long-snouted (Neochoristodera), yet little known about its presence morphology short-snouted non-neochoristoderes that sister groups Neochoristodera. Using X-ray micro-CT scanning, this study describes detail neomorph of two non-neochoristoderes, Coeruleodraco jurassicus Philydrosaurus proseilus . The both species found parietal, quadrate, squamosal. shape resembles pyramid three-dimensions, with triangular dorsal surface prominent ventral process. confirms shared among early late branching choristoderes; therefore, potential synapomorphy Choristodera. In addition, pterygoquadrate foramen identified for first time, located quadrate C. holotype P. , were dislocated, but possible bones. Although been suggested be homologous stapes stapedial Champsosaurus more evidences required confirm homology because 1) long neochoristoderes, pyramid-shaped non-neochoristoderes; 2) situated lateral prootic opisthotic; articulation (or opisthotic) cannot confirmed due damage braincase during preservation. To understand origin neomorph, intact specimens needed assess contact relationships otic region non-neochoristoderes.