|ARCHOSAUROMORPHA - Archosauromorpha, Archosauria (clade), Thecodontia (grade)|
o Sauria |--Lepidosauromorpha `--o Archosauromorpha |?--Choristodera `--+--Rhynchosauria `--+--Trilophosauridae `--+--Prolacertiformes `--o--Proterosuchidae `--+--Erythrosuchidae `--+--Euparkeriidae `--o--Proterochampsidae `--o Archosauria |--o Ornithodira | |--Pterosauria | `--Dinosauromorpha `--Crurotarsi
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Discussion: If the tendency to gigantism was represented by Erythrosuchus, then the opposite, tendency towards the small light agile bird-like form was expressed by its cat-sized relative Euparkeria, which at 65 centimeters (26 inches) from snout to tail-tip was only an eighth the linear dimensions. This was a small, long-legged, and agile, with a more erect stance, and capable of bipedal gait. Something similar to Euparkeria, in turn, gave rise to two evolutionary branches: the psuedosuchians and crocodiles on the one hand, and ornithodires and dinosaurs on the other. Both began as small agile forms, but the pseudosuchians quickly reverted to the standard lizard-like form, although these were lizards of great size, e.g. the phytosaurs, Aetosauridae, and Crocodylia, all of which reached 3 metres or more in length. Most interesting of all were the great rauisuchians, which although roughly lizard/crocodile-like in form had a fully erect dinosaurian and mammalian posture. MAK991018.
Characters: Small (0.5+ m); slender; facultative bipeds (?); large skull; maxillary and mandibular fenestrae present; no parietal (pineal) foramen or fossa [P93]; for braincase, see essay; foramina for internal carotids posterior to basipterygoid process [P93]; palatal teeth present [P93]; teeth laterally compressed, serrated, thecodont; vertebral intercentra present [P93]; posterior limbs 1.5x anterior, but joint surfaces etc. not specialized as biped; fourth trochanter present; mesotarsal joint (like dinosaurs) between proximal & distal tarsals (compare croc crurotarsal joint between astragalus & calcaneum) [P93]; astragalar facets for tibia and fibula separated by flat, non-articular surface [S91]; calcaneum with hemi-cylindrical facet for astragalus [P93]; calcaneal tuber convex on both sides [P93]; calcaneal tuber with some posterior deviation from lateral projection [P93]; calcaneal tuber taller than broad [P93]; calcaneal facet for fibula continuous with facet for distal tarsal IV [P93]; foot symmetrical, with elongated digit III.; dorsal row of dermal ossicles on vertebral column & tail [P93].
References: Gower (2002) [G02], Gower & Sennikov (2000) [GS00], Gower & Weber (1998) [GW98], Parrish (1993) [P93], Sereno (1991) [S91]. ATW030825.
- Introduction to Euparkeria
- Lecture 8 - Tetrapods (skeletal anatomy)
- Triassico (Italian)
- Archosauria: More on Morphology
- Archosaurs - A new wave of Invadors
- 1 Meeting of the EAVP (see Borsuk-Bialynicka abstract -- new Polish form)
- Euparkeria capensis (images of fossil)
- Dino Web - How dinosaurs moved