Earlier discussions about the pes of Lagerpeton and the ichnite it would have produced inspired these tests. Here a cardboard model of the Lagerpeton pes has been raised to low (Fig. 1) and high (Fig. 2) digitigrade configurations.
These models emphasize the impossibility that anything like Lagerpeton could have produced Prorotodactylus or Rotodactylus ichnites (contra Brusatte et al. 2013). Better matches can be found in Cosesaurus, Tanystropheus and kin as shown earlier.
The Ascending Process
On dinosaurs the ascending process of the astragalus is in front of the ankle. It advances upwards and ultimately covers the lower tibia.
By contrast, in Lagerpeton the ascending process is in back. This is a key difference that goes unrecognized by those who promote a dinosauromorph nesting for Lagerpeton. A small posterior ascending process can also be found in the chanaresuchid, Tropidosuchus.
In the absence of 3D and wire modeling (which I used for Pteranodon), cardboard feet make quick models for difficult subjects. I’ve used them earlier (Peters 2000, 2011) to model various pterosaur feet. Here (Figs. 1, 2) the model pes of Lagerpeton can be raised or lowered to test a variety of possible configurations. You can even split the metatarsals if appropriate. That enables one to arc the metatarsals, like teepee tent poles. In every configuration the PILs (parallel interphalangeal lines) can be drawn on the base/substrate. Those that are the most continuous typically reflect the actual pedal configuration. Here (Fig. 1) the more upright two-digit implant configuration, produces an ostrich-like pes with PILs at right angles to the proposed direction of movement, reflecting that stage in the step-cycle. My guess is this is the more likely candidate.
The evolution of a longer pedal digit 4 in chanaresuchids
In ancestral quadrupedal taxa, like Chanaresuchus (Fig. 3) and Tropidosuchus (Fig. 4) pedal digit 4 is so slender as to appear vestigial.
In derived taxa, like the other purported Tropidosuchus (Fig. 5), the pes does not appear to be so derived.
This apparent reversal to a more primitive condition appears to coincide with the reduction of the forelimb, and, in Lagerpeton to the elongation of the hind limb relative to the size of the pelvis.
Besides, the foot mismatch, Lagerpeton is a pretty large animal, at least twice the size of Tropidosuchus and a maginitude larger than the Rotodactylus trackmaker.
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, Niedz´wiedzki G and Butler RJ 2011. Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic. Proceedings of the Royal Society B, 278, 1107–1113.
Niedzwiedzki G, Brusatte SL and Butler RJ 2013. Prorotodactylus and Rotodactylus tracks: an ichnological record of dinosauromorphs from the Early–Middle Triassic of Poland. Geological Society, London, Special Publications, first published April 23, 2013. doi 10.1144/SP379.12.