Leaping lizards in the Late Triassic

Lockley 2006
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’.

Figure 1. Gwyneddichnium tracks (note the acceleration). Along with a to scale Tanytrachelos and Tanytrachelos pes. Note digit 1 does not impress.

Figure 1. Gwyneddichnium tracks CU 159.10 (note the acceleration). Along with a to scale Tanytrachelos and Tanytrachelos pes. Note digit 1 does not impress. As in Cosesaurus, digit 1 impressed only rarely and then only as a point.

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.

Figure 1. Tanytrachelos hopping to match Gwyneddichnium tracks (see figure 2).

Figure 2. Tanytrachelos hopping to match Gwyneddichnium tracks (see figure 1).

Running and arm flapping in Cosesaurus
led to flapping flight in pterosaurs (Fig. 3).

Figure 1. Cosesaurus flapping - fast. There should be a difference in the two speeds. If not, apologies. Also, there should be some bounce in the tail and neck, but that would involve more effort and physics.

Figure 3. Click to enlarge and animate. Cosesaurus flapping – fast. There should be a difference in the two speeds. If not, apologies. Also, there should be some bounce in the tail and neck, but that would involve more effort and physics.

Gwyneddichnium and Rotodactylus tracks
are from trackmakers (Fig. 4)in the same clade of Tritosauria.

Cosesaurus matched to Rotodactylus from Peters 2000.

Figuure 4. Cosesaurus matched to Rotodactylus from Peters 2000.

Another relative of Tanytrachelos, Langobardisaurus,
(Fig. 5) has been considered bipedal by prior authors (Renesto, et al. 2002).

Figure 4. Langobardisaurus bipedal.

Figure 5. Langobardisaurus bipedal.

References
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.

 

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