There must have been something in the water. Four bipedal lines from distinctly different heritages appeared in the Early to Mid Triassic.
Cosesaurus is a bipedal lizard, close to other bipeds Langobardisaurus, Sharovipteryx and Longisquama. Sister left occassionally bipedal tracks, known as Rotodactylus, distinctive for their asymmetrical digitigrade impressions that elevate the proximal phalanges and imprint just a hint of digit 5 posterior to the others. The femur does not have a strongly inturned head until you get to basal pterosaurs.
Marasuchus, a basal theropod dinosaur (all of which are bipeds) may have inherited its bipedal abilities from a common ancestor with Scleromochlus. Distinctly digit 3 was likely longer than 4 (incomplete preservation makes this a good guess at this point). Again, no digit 5.
Tropidosuchus is closely related to another likely biped, Lagerpeton, which is often wrongly associated with basal dinosaurs. Both have a strongly asymmetric pes (unlike basal dinos but like Rotodactylus trackmakers), and little to no digit 5 (unlike Rotodactylus trackmakers).
Recent work by Brusatte et al. (2012) and Lovelace and Lovelace (2012) considered Rotodactylus tracks to be made by basal dinosauromorphs, but Rotodactylus includes a digit 5 impression, something basal dinosauromorphs would find it impossible to make.
Long hind limbs, an anteriorly extended ilium (with added sacrals) and a relatively short torso are bipedal landmarks. A slender tail is common to all. Note that only Cosesaurus has a distinct pectoral girdle shared with flapping taxa (birds, bats and pterosaurs).
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.
Brusatte SL Niedźwiedzki G and Butler RJ 2011. Footprints pull origin and diversification of dinosaur stem-lineage deep into Early Triassic. Proceedings of the Royal Society of London, Series B, 278, 1107-1113.
Lovelace DM and Lovelace SD 2012. Paleoenvironments and paleoecology of a Lower Triassic invertebrate andvertebrate ichnoassemblage from the Red Peak Formation (Chugwater Group). Palaios 27:636-657. doi: 10.2110/palo.2012.p12-011r