Evolution of the Pterosaur Palate – part 2: Dimorphodontoidea, Anurognathidae

Not much attention has been paid to the anurognathid palate.
Earlier we looked at the evolution of the pterosaur palate from ancestral taxa to basal pterosaurs. Here we’ll look at another clade of basal pterosaurs, the lineage of the anurognathids beginning with an outgroup taxon, Dimorphodon.

Earlier Mistakes
In this clade the unique wiry medial processes of the maxilla, have been traditionally (Wellnhofer 1991, Bakhurina 1988) considered the palatines. Since the skull of anurognathids is more gracile and wider than that of other pterosaurs, the palate is more often better exposed, typically beneath the skull roofing elements. With all the crushing and shifting of these extremely thin elements, only DGS (digital graphic segregation) makes order out of chaos, as here in Batrachognathus.

Anurognathid palate

Figure 1. Anurognathid palates in phylogenetic order. All of these specimens are badly crushed so picking out details is difficult at best. Some autapomorphies (like the maxillary process origin in Jeholopterus) likely represent errors due to taphonomic shifting. Nevertheless this is the first publication of several anurognathid palates all in one place.

The Trend
The trend in the lineage of anurognathids is toward a wider, shorter skull (approaching a circle in palatal view) with relatively larger palatal elements, especially the ectopalatine (=ectopterygoid + palatine now fused). The vomers and pterygoids also become more robust. Considering the fragility of the rest of the skull, much of its strength is here in the palate.  Note the placement of the ectopalatine in Jeholopterus, ready to transmit impact/compression forces from the roots of the fangs back toward the quadrate and the sides of the skull. The other anurognathids don’t have that trait to this degree. The enlargement of elements to create a more solid and substantial palate is convergent with what happened with other, longer snouted pterosaurs, but employing different bones to do so.

Transitional Taxon
The IVPP embryo appears to bridge the gap between ancestral dimorphodontids with small ectopalatines and the much smaller anurognathids with much larger ectopalatines.

Skull Connections
As is typical of other pterosaurs, the ectopterygoid always intersects the cheek where the maxilla meets the jugal and the palatine typically points to the base of the ascending process of the maxilla.

Maxilla Palatal Rods
The branching slender rods of the maxilla palatal process appear (to me at least) to be sensitive to slight vibrations, like the tiny bones of the middle ear. Perhaps they automatically snap the trap of the jaws when they are touched by prey entering the mouth in anurognathids that have them. Perhaps they and other soft tissues help tie the palatal elements together for strength. The in situ placement in Jeholopterus is autapomorphic. The other rods emerge from near the first maxillary tooth. Perhaps the one that is visible in Jeholopterus broke off and drifted posteriorly to emerge below the ascending process of the maxilla where it was preserved. So I moved it back to emerge from behind the first tooth, the fang.

The wide variation in anurognathid palates means that many intermediates were present, and we’re all looking forward to seeing these as they become known.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again. If anyone comes up with any better interpretations of these palates, please share them.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

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