documented paired, digitigrade, four-toed, accelerating, ‘swimming’ tracks (ichnogenus: Gwyneddichnium; Figs. 1, 2) in the Late Triassic. Tanytrachelos (Figs. 1, 2) was and is considered a good match, but hopping through thinly retreating surf seems to be a better solution. Tanytrachelos is a tritosaur lepidosaur, hence, a ‘leaping lizard’.
Like Cosesaurus and other higher tritosaurs,
Tanytrachelos was digitigrade and facultatively bipedal. Hopping through thinly retreating surf is more likely based on matching the body to the tracks. So we don’t have to imagine the front half floating or swimming underwater to make the hind feet simultaneously kick to make side-by-side tracks.
Running and arm flapping in Cosesaurus
led to flapping flight in pterosaurs (Fig. 3).
Gwyneddichnium and Rotodactylus tracks
are from trackmakers (Fig. 4)in the same clade of Tritosauria.
Another relative of Tanytrachelos, Langobardisaurus,
(Fig. 5) has been considered bipedal by prior authors (Renesto, et al. 2002).
Lockley M 2006. Observations on the ichnogenus Gwyneddichnium and Gwyneddichnium-like footprints and trackways from the Upper Triassic of the western United States. New Mexico Museum of Natural History and Science, Bulletin 37:170–175.
Peters D 2000. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos 7:11-41.
Renesto S, Dalla Vecchia FM and Peters D 2002. Morphological evidence for bipedalism in the Late Triassic Prolacertiform reptile Langobardisaurus. Senckembergiana Lethaea 82(1): 95-106.