Lagerpeton: foot configurations modeled in cardboard

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.

Lagerpeton model pes raised to a low digitigrade configuration in which pedal digit 2 would have impressed in line with the metacarpophalangeal joints of 3 and 4.

Figure 1. Lagerpeton model right pes raised to a low digitigrade configuration in which pedal digit 2 would have impressed in line with the metacarpophalangeal joints of 3 and 4. Digit 4 completely impresses and digit 3 is slightly raised proximally.

Lagerpeton raised to a high digitigrade configuration. Here only two digits would have impressed with raised proximal phalanges.

Figure 2. Lagerpeton raised to a high digitigrade configuration. Here only two digits would have impressed with raised proximal phalanges. Either both of these configurations were part of the step cycle or just this one was. We have no Lagerpeton ichnites at present. Rotodactylus and Prorotodactylus ichnites impress five digits. These one likely impressed just two.

Niedwickski et al. (2013) in their quest for a trackmaker to fit Rotodactylus published this image of Lagerpeton, which is an obvious mismatch that doesn't even have a pedal digit 5. Plenty of other taxa are better matches (Figs. 3,4) but those weren't published, tested or promoted.

Figure 3. Click to enlarge. Niedwickski et al. (2013) in their quest for a trackmaker to fit Rotodactylus published this image of Lagerpeton, which is an obvious mismatch that doesn’t even have a pedal digit 5. Plenty of other taxa are better matches (Figs. 3,4) but those weren’t published, tested or promoted.

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.

Cardboard models
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.

Chanaresuchus a quadrupedal ancestor to Tropidosuchus and Lagerpeton and the third taxon.

Figure 4. Chanaresuchus a quadrupedal ancestor to Tropidosuchus and Lagerpeton and the third Tropidosuchus-like taxon.

In derived taxa, like the other purported Tropidosuchus (Fig. 5), the pes does not appear to be so derived.

Tropidosuchus in its two variants. In the holotype (above) the humerus is more robust and pedal digit 4 is gracile, as in Chanaresuchus (Fig. 3). In the referred specimen of Tropidosuchus (below) the humerus is smaller and pedal digit 4 is longer than 3, as in Lagerpeton. The rise to a bipedal configuration appears to coincide with the change in pedal proportions.

Figure 5. Tropidosuchus in its two variants. In the holotype (above) the humerus is more robust and pedal digit 4 is gracile, as in Chanaresuchus (Fig. 3). In the referred specimen of Tropidosuchus (below) the humerus is smaller and pedal digit 4 is longer than 3, as in Lagerpeton. The rise to a bipedal configuration appears to coincide with the change in pedal proportions. This is reptile evolution at work.

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.

Figure 3. The closest kin of Tropidosuchus are the much larger Chanaresuchus (matching Nesbitt 2011) and the smaller Lagerpeton.

Figure 6 The closest kin of Tropidosuchus are the much larger Chanaresuchus (matching Nesbitt 2011) and the larger and taller Lagerpeton.

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.

References
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.

wiki/Lagerpeton

3 thoughts on “Lagerpeton: foot configurations modeled in cardboard

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.