Paleontologists don’t like to think of Scleromochlus (Woodward 1907) as a bipedal crocodylomorph. Not sure why not. It’s in good company (Fig. 1). They’d rather see it as pterosaur closest cousin (Benton 1999, Bennett 1996, Hone and Benton 2008, Senter 2003, Sereno 1991). Unlikely, considering those tiny hands.
There are quite a few bipedal basal crocs and protoarchosaurs. You can see them all here to scale.
Another fairly well known bipedal croc is Terrestrisuchus (Fig. 1). Funny thing, you almost never see these two taxa mentioned together in the same sentence or see them on the same phylogenetic analysis. But you can see them together here and here and in figure 1.
Focus on the hand
Crush (1984) introduced us to the complete skeleton of a basal bipedal crocodylomorph, Terrestrisuchus (Late Triassic) and did a great job! The elements came from a fissure fill, so had to be reassembled as if they were puzzle pieces. Some were easy. Others were difficult. Crush (Fig. 2) put the hand together with a small thumb, similar to a human hand. However, reassembling the pieces to more closely mimic or echo sister taxa provides a revised reconstruction (Fig. 2) with continuous PILs. I did this with Photoshop to maintain precision and avoid freehand unconscious bias.
The revised hand (Fig. 2) aligns metacarpals 1-3 as in sister taxa. Metacarpal 4 is slightly shorter than mc3. Metacarpal 5 was probably very short as in Erpetosuchus and Hesperosuchus. The digits are easy. They taper distally and are shorter distally terminating in tiny unguals. The proximal phalanges are subequal.
Basal croc hands, as you can see, are notoriously incomplete. So we have to glean clues from all of them, despite their morphological disparity and wonderful variety.
Once again, phylogenetic bracketing saves the day!
And yes those incredibly long wrist bones are proximal carpals, the radiale and ulnare. Modern crocs retain those.
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Crush PJ 1984. A late upper Triassic sphenosuchid crocodilian from Wales. Palaeontology 27: 131-157.
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