Nesbitt (2011) and His Characters – Part 4 – Crurotarsi

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. Earlier we considered more basal clades in parts 1, 2 and 3. Today we take on the Crurotarsi.

Nesbitt Characters for Crurotarsi (Phytosauria + Crocodylomorpha)
Sterling Nesbitt (SN) reported, (1) Parabasisphenoid plate absent (96-2). Not known in basal pterosaurs.
Note: Also absent in lepidosaurs and fenestrasaurs.

(2) Semilunar depression on the lateral surface of the basal tubera of the parabasisphenoidabsent (98-1). Not known in basal pterosaurs.
Note: Also absent in lepidosaurs and fenestrasaurs.

(3) Absence of teeth on palatal process of the pterygoid (175-1). Eudimorphodon is the only pterosaur reported with pterygoid teeth (Wild, 1978). The pterygoid teeth are present on the palatal process of the pterygoid.
Note: I have not been able to confirm Wild’s (1978) observation. This absence is also found in tritosaurs and fenestrasaurs. 

(4) Cervical ribs short and stout (196-1). The cervical ribs are short in basal pterosaurs.
Note: This trait is also present in the basal fenestrasaur, Longisquama. By short and stout apparently Nesbitt means these ribs extend the length of two cervicals. If so, that also includes all fenestrasaurs. 

(5) Ventral articular surface of the astragalus calcaneum concavoconvex, with concavity on calcaneum (368-1). Not known in basal pterosaurs.
Note: Actually the ventral surface of the proximal tarsals are straight to convex in tritosaurs, including fenestrasaurs and pterosaurs. 

(6) Ventral articular surface for distal tarsal 4 and the distal end of the tuber of the calcaneum separated by a clear gap (371-1). Not known in basal pterosaurs.
Note: There is no calcaneal tuber on tritosaurs including fenestrasaurs and pterosaurs.

(7) Articular surfaces for fibula and distal tarsal IV on the calcaneum continuous (380-1). The articular surfaces for fibula and distal tarsal IV on the calcaneum are continuous in Dimorphodon (Padian, 1983; Sereno, 1991a).
Note: This trait is shared by tritosaurs including fenestrasaurs and pterosaurs.

Note: Nesbitt (2011) reported: ORIGINAL DEFINITION: Ornithosuchidae, Parasuchia, Aetosauria, Rauisuchia, Crocodylomorpha, and all extinct descendants that are most closely related to these taxa (Sereno and Arcucci, 1990).

REVISED DEFINITION: Node: The least inclusive clade containing Rutiodon carolinensis Emmons, 1856, and Crocodylus niloticus Laurenti, 1768 (new).

The large reptile tree does not recover a monophyletic Crurotarsi, but finds phtyosaurs and proterochampsids separate from the other traditional archosauriforms, evolving several traits by convergence.

Tomorrow: 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.


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