Nesbitt (2011) and His Characters – Part 6 Ornithodira

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, 3, 4 and 5.

Nesbitt Characters for Ornithodira
Sterling Nesbitt (SN) reported, (1) Distal end of neural spines of the cervical vertebrae unexpanded (191-0). The neural spines of the cervical vertebrae are unexpanded in pterosaurs.
Note: This trait is also found in lepidosaurs, including fenestrasaurs.

(2) Distal expansion of neural spines of the dorsal vertebrae absent (197-0). The expansion of neural spines of the dorsal vertebrae is absent in pterosaurs.
Note: This trait is also found in lepidosaurs, including fenestrasaurs.

(3) Second phalanx of manual digit II (= 2.2) longer than first phalanx (255-1). This character is present in basal pterosaurs and in dinosaurs.
Note: While present in basal pterosaurs, this trait is not present in the dinosaurs, Herrerasaurus, Thecodontosaurus or Scelidosaurus.

(4) Trenchant unguals on manual digits I–III (257-1). Present in basal pterosaurs.
Note: Also present on the fenestrasaur, Longisquama. Not present in quadrupedal dinosaurs.

(5) Tibia longer than the femur (299-1). Present in basal pterosaurs.
Note: Also present in the fenestrasaurs, Sharovipteryx and Longisquama. Not present in quadrupedal dinosaurs. 

(6) Distal tarsal 4 transverse width subequal to that of distal tarsal 3 (347-1). Present in basal pterosaurs.
Note: In pterosaurs distal tarsal 3 is very tiny, never as large as distal tarsal 4. However the centrale, which is typically confused with distal tarsal 3 in character matrices, is usually just as large. 

(7) Size of articular facet for metatarsal V less than half the width of lateral surface of distal tarsal 4 (348-1). Present in basal pterosaurs.
Note: Also present on basal fenestrasaurs. However, the articular facet for mt5 is usually the majority of the lateral surface of distal tarsal 4 in pterosaurs. 

(8) Anterior hollow of the astragalus reduced to a foramen or absent (357-1). Present in basal pterosaurs.
Note: This trait is also present in all tritosaurs, including fenestrasaurs. 

(9) Anteromedial corner of the astragalus acute (361-1). Clearly present in Dimorphodon (fig. 46).
Note: Nesbitt confused the distal tarsals with the proximal tarsals, which are fused to the tibia. 

(10) Compact metatarsus, metatarsals II–IV tightly bunched (at least half of the length) (382-1). Present in pterosaurs.
Note: Also present in most tritosaurs, including the fenestrasaurs (sans Sharovipteryx). 

(11) Osteoderms absent (401-0). Pterosaurs lack osteoderms.
Note: Also absent in tritosaurs, including fenestrasaurs. Osteoderms are present in Scelidosaurus.

(12) Gastralia well separated (412-1). The gastralia of the holotype of Eudimorphodon are well separated as they are in dinosaurs. In contrast, the gastralia of most non-ornithodiran archosauriforms form an extensive, interlocking basket.
Note: The gastralia are also well separated in lepidosaurs, including fenestrasaurs.

Note: The large reptile tree does not recover a monophyletic Ornithodira, but finds pterosaurs and traditional archosaurs separated, evolving several traits by convergence.

Nesbitt (2011) reported, “The character states supporting pterosaurs as members of Archosauria and Ornithodira are not restricted to character states related to locomotion as suggested by Bennett (1996). As demonstrated in the list above, the character states cover features present all over the body, not just in the hind limb.” Unfortunately, Nesbitt (2011), like so many paleontologists before and since, did not even look at the competing candidates within the fenestrasauria, but force fit those square pegs into those round holes. Not sure why everyone is so afraid to let a large tree recover more parsimonious nestings.

Perhaps now you see why there is something terribly wrong with our current pterosaur studies. It’s an Alice-in-Wonderland world out there.

Tomorrow: Lagerpetidae

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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