Nesbitt (2011) and his Characters – part 1

Following remarks from fellow paleontologists asking for my study to include more Nesbitt (2011) characters in the large reptile study, I thought we should dive right into them, taking a few days to digest them all — a bite at a time — then use the ones that make sense to use (will be readily visible across a long list of taxa).

Nesbitt Characters for Archosauriforms
Sterling Nesbitt (SN) reported, “My analysis finds pterosaurs well nested within archosauriforms as the sister taxon to Dinosauromorpha; this is a result obtained by all recent numerical analyses.”
Note: none of these included lepidosaurs including fenestrasaurs.

SN: “Therefore, I present a list of characters that unambiguously support archosauriform clades and indicate whether the character is present in (basal) pterosaurs:”

1) Absence of a parietal foramen (63-1). Basal pterosaurs lack a parietal foramen.
Note: As in certain lepidosaurs, including all fenestrasaurs.

(2) Jugal-quadratojugal contact present (70-1). Present in basal pterosaurs.
Note: As in certain lepidosaurs, including all fenestrasaurs.

(3) Ectopterygoid forms all of the lateral edge of the lateral pterygoid flange (88-1). Not known in basal pterosaurs.
Note: Actually this trait is known. This condition does not occur in any pterosaur. The ectopterygoid is fused to the palatine to form the ectopalatine and the pterygoid does not have a lateral flange.

(4) Ossified laterosphenoid present (92-1). Present in pterosaurs (Bennett, 1996).
Note: Bennett (1991, 2001) identified an indistinct portion of the entirely fused braincase of Pteranodon as the laterosphenoid. Cosesaurus has that same structure. Due to lack of sutures, this trait in pterosaurs has not been definitively determined. And if so, then it has to be applied also to Cosesaurus. 

(5) Antorbital fenestra present (136-1). Present in basal pterosaurs.
Note: As in all fenestrasaurs.

(6) Lateral mandibular fenestra present (138-1). Present in Dimorphodon and a specimen refered to Eudimorphodon (BPS 1994 I 51).
Note: These are bogus identifications both due to a slipped surangular. No other pterosaurs have this trait.

(7) Presence of tooth serrations (168-1). Present in Dimorphodon.
Note: This was claimed for only the third premaxillary tooth in one specimen, but was not visible in the evidential photograph. No other pterosaur but the two specimens of Austriadatylus have serrations, but several have multiple cusps, like those found in higher fenestrasaurs. Here is why we should score characters at the genus level. Choosing Austriadactylus as our “pterosaur” would yield one score. Any other pterosaur would yield the other. 

So far, not a strong case, and a case that makes sense to Nesbitt (2011) only by keeping a blind eye to competing candidates among the fenestrasaurs.

Tomorrow: Erythrosuchus + Archosauria

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.

Nesbitt SJ 2011.
 The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.