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. Yesterday was bite one.
Nesbitt Characters for Erythrosuchus + Archosauria
Sterling Nesbitt (SN) reported, (1) Absence of a large anteriorly opening foramen on the anterolateral surface of the maxilla (31-0). Also absent in basal pterosaurs.
Note: Absent also in basal fenestrasaurs.
(2) Basipterygoid processes directed anteriorly or ventrally at their distal tips (93-1). Not known in basal pterosaurs.
Note: The same holds true for lepidosaurs, fenestrasaurs and all pterosaurs.
(3) Absence of a ridge on lateral surface of inferior anterior process of the prootic ventral to the trigeminal foramen (94-1). Not known in basal pterosaurs.
Crushing makes this ephemeral detail difficult to observe.
(4) Verticalized parabasisphenoid (97-1). Not known in basal pterosaurs.
Note: This conjoined bone is never vertical in lepidosaurs, fenestrasaurs or pterosaurs.
(5) Absence of supratemporals (145-1). Supratemporals are absent in pterosaurs (Bennett, 1996).
Note: Also absent in fenestrasaurs.
(6) Posteroventral portion of the dentary laterally overlaps the anteroventral portion of the angular (164-1). Present in Dimorphodon and a specimen referred to Eudimorphodon (BPS 1994 I 51).
Note: The purported angular in Dimorphodon is actually a displaced pterygoid. Even so, the lepidosaur Tanystropheus unambiguously shares this trait.
(7) Thecodont tooth implantation (174-1). Present in basal pterosaurs.
Note: also present in tritosaurs including fenestrasaurs.
(8) Second primordial sacral rib is not bifurcated (203-1). Not known in basal pterosaurs, but the second primordial sacral rib is not bifurcated in Campylognathoides (BSP 1985 I 87).
Note: also present in lepidosaurs including fenestrasaurs.
(9) Entire anterior margin of the scapula is concave (217-1). Difficult to score with confidence in the highly modified scapulae of pterosaurs.
This is a bogus excuse. The entire anterior margin of the scapula is convex in fenestrasaurs including basal pterosaurs.
(10) Acromion process of the scapula distinctly raised above the ventral edge of the scapula (220-1). Difficult to score with confidence in the highly modified scapulae of pterosaurs.
This is a bogus excuse. There is no acromion process on the strap-like scapula of fenestrasaurs and pterosaurs.
(11) Distinct notch between the scapula and coracoid on the anterior margin (221-0).
Note: Also present in lepidosaurs, fenestrasaurs and pterosaurs.
Tomorrow: Vancleavea + 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.