Euparkeriidae

From Palaeos

o Sauria
|--Lepidosauromorpha
`--o Archosauromorpha
   |?--Choristodera
   `--+--Rhynchosauria
      `--+--Trilophosauridae
         `--+--Prolacertiformes
            `--o--Proterosuchidae 
               `--+--Erythrosuchidae
                  `--+--Euparkeriidae
                     `--o--Proterochampsidae
                        `--o Archosauria
                           |--o Ornithodira
                           |  |--Pterosauria
                           |  `--Dinosauromorpha
                           `--Crurotarsi

Range: Early Triassic of South Africa; Middle Triassic (Anisian) of Russia.

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.

[edit] Links

Links: </strong><a href="http://www.ucmp.berkeley.edu/diapsids/euparkeria.html">Introduction to Euparkeria</a>; <a href="http://rainbow.ldeo.columbia.edu/courses/v1001/8.html">Lecture 8 - Tetrapods</a> (skeletal anatomy); <a href="http://users.iol.it/ram640k/preistoria/triassico.htm">Triassico</a> (Italian); <a href="http://www.ne.jp/asahi/dinosaur/araki/im/92.htm">???????</a>; <a href="http://www.ucmp.berkeley.edu/diapsids/archomm.html">Archosauria: More on Morphology</a>; <a href="http://www.museums.org.za/sam/resource/palaeo/cluver/archosau.htm">Archosaurs - A new wave of Invadors</a>; <a href="http://eavp.alettra.de/abstracts/1stWEAVPabstracts.pdf">1 Meeting of the EAVP</a> (see Borsuk-Bialynicka abstract -- new Polish form); <a href="http://www.dinooption.com/din04/archosaur005.htm">ｿ｡ｿ・ﾄｸ｣ﾄﾉｸｮｾﾆ(Euparkeria)</a>; <a href="http://www.scientific-art.com/portfolio%20palaeontology%20pages/Euparker.html">Euparkeria</a>; <a href="http://gatito.valdosta.edu/fossil_pages/fossils_tri/r20.html">Euparkeria capensis</a> (images of fossil); <a href="http://www.gly.bris.ac.uk/www/news/resnews/palaeo/Report10/news10.html">Title</a>; <a href="http://www.dino-web.com/movement.html">Dino Web - How dinosaurs moved</a> ATW030825.

[edit] Credits

ATW030825 Palaeos