Ctenochasma porocristatum Needs a Nose Job

Another Heretical Paradigm Buster
Ctenochasma porocristata [ammended to porocristatumSos 2179 (Buisonjé 1981, Fig. 1), Late Jurassic, ~150mya, ~26 cm skull length, was originally considered a species of Ctenochasma due to its many teeth and long flattened skull. However, those teeth were not elongated and laterally oriented, as in Ctenochasma. Unfortunately, there is no evidence in Figure 1 (click to enlarge it) for the elongated teeth that Buisonjé imagined (Fig 3, second from bottom). Contra Bennett (2007), the teeth weren’t all broken off, although a few were. This was no typical ctenochasmatid. The teeth were short, sharp and interlocking creating a seive.

The bump on top of the skull was considered a crest of sorts with “vertical striae in the flanks of the crest, placed at regular intervals of .12mm,” but other ctenochasmatids have a narrow comb-like crest (when present), not a thick bump.

Ctenochasma? porocristatum.

Figure 1. Ctenochasma? porocristatum. Click to enlarge.

The True Identity of “The Bump”
On closer examination, the “bump” turned out to be the missing anterior rostrum, broken off and displaced during taphonomy. Short sharp teeth (misinterpreted “regular striae”?) surround it. Graphically moved to the anterior it becomes a good fit (Fig. 2). Even if the anterior rostrum did not migrate during taphonomy to the mid rostrum, extending the lines of the larger piece anteriorly produces much the same reconstruction, distinct from all other known taxa.

Reconstructing Sos 2179.

Figure 2. Reconstructing Sos 2179.

If Not Ctenochasma, What is Sos 2179?
Phylogenetic analysis nested Sos 2179 with another long jawed oddball also mislabeled “Pterodactylus,” Sos 2428, the flightless pterosaur. Like Sos 2179, Sos 2428 had a very long, flat skull filled with fewer teeth. Sos 2428 was smaller overall with relatively smaller jaws filled with fewer teeth. So it was more primitive. Sos 2179 was larger, toothier and probably just as flightless. Sure would be nice to find the rest of it now. Other members of the clade that includes Sos 2179 and Sos 2428 feature several Pterodactylus lookalikes including n42, n44 and Huanhepterus. As a clade these were all  sisters to the azhdarchid branch.

A selection of valid Ctenochasma skulls

Figure 3. A selection of valid Ctenochasma skulls together with the two interpretations of Sos 2179 (in gray below).

Sos 2179 in Vivo
Given the extremely long flat snout filled with hundreds of short sharp interlocking teeth in Sos 2179, together with comparisons to its flightless, big-bellied sister Sos 2428, we can imagine Sos 2179 was an even larger flightless pterosaur. The big belly in Sos 2428 suggests herbivory, so, if similar, Sos 2179 probably sieved floating algae. A hasty getaway would have involved running with its impressive thighs and flapping its presumably small wings for added thrust.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

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

Bennett SC 2007. A review of the pterosaur Ctenochasma: taxonomy and ontogeny. Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen, 245(1): 23-31.
Buisonjé de PH 1981.
 Ctenochasma porocristata nov. sp. from the Solnhofen Limestone, with some remarks on other Ctenochasmatidae. Proceedings of the Koninklijke Nederlandse Akademie van Wetenchappen, B, 84 (4): 411-436.

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