Ever wonder about Galepus?

As opposed to the wildly popular bird-like dromaesaurs, the squirrel-like dromasaurs (lacking the “e” in the middle), like Galepus (Fig. 1, Broom 1910) are rarely studied. Brinkman (1981) made an important contribution. These less popular anomodonts are cousins to the hippo-like dicynodonts (Fig. 2). Both were herbivores of the Late Permian, nesting within the Therapsida and Synapsida.

I’ve seen a century-old reconstruction of the skull of Galepus, but I’ve never seen the whole body reconstructed (Fig. 10. That seems a shame as it is represented by a nicely curled nearly complete skeleton at the American Museum of Natural History (hirez color images kindly provided by their staff). And it’s been known for some time now. Much of the skull and skeleton is represented by impressions of missing bone in coarse sandstone.

Figure 1. Galepus, the dromasaur, anomodont, therapsid, reconstructed from the complete skeleton at the AMNH.

Figure 1. Galepus, the dromasaur, anomodont, therapsid, synapsid reconstructed from the complete skeleton #5541 at the AMNH. Wrist and ankle are reconstructed according to patterns seen in Galechirus and Suminia (Fig. 2, wrist and ankle inserts copied above). Note the oversized clavicle here. I’m wondering if I made a misidentification here, or is this taxon just odd that way? The hands are indeed robust with great symmetry, like a mammalian burrower, the mole, also known for its strong forelimbs.

The skull is only a cast of the internal surface of the roofing bones. Well marked, but odd.

Galepus has been nested (ref) with Galechirus close to Galeops at the transition to Eodicynodon (Fig. 3) between dromasaurs + kin and dicynodonts + kin.

Figure 2. Two other dromasaurs, Suminia and Galechirus.

Figure 2. Two other dromasaurs, Suminia and Galechirus. Galepus was close in size. Note the small clavicles here. Those go along with smaller forelimbs and a more asymmetric manus.

However,
The large reptile tree found a different relationship, with dromasaurs + dicynodonts splitting from the other therapsids at the base of that clade. Earlier we looked at differences and similarities between Galeops and Eodicynodon (Fig. 3). While they share many traits, phylogenetic analysis finds more parsimonious relationships when more taxa are introduced. Earlier we also looked at the base of the Anomodontia and the new taxa now nesting there.

Figure 1. Eodicynodon the basal dicynodont and Galeops the derived dromasaur. Did dicynodonts arise from dromasaurs? Not likely according to the large reptile tree which nests Stenocybus as their last common ancestor.

Figure 3. Click to enlarge. Eodicynodon the basal dicynodont and Galeops the derived dromasaur. Did dicynodonts arise from dromasaurs? Despite several convergent traits, not likely according to the large reptile tree which nests Stenocybus as their last common ancestor and recovers other taxa closer to both.

Earlier we looked at Stenocybus nesting at the base of the Anomodontia. Here’s the new synapsid tree (Fig. 4).

Figure 4. Therapsid family tree. Note anomodonts are separate from the other therapsids.

Figure 4. Therapsid family tree. Note anomodonts are separate from the other therapsids. And dromasaurs are distinct from dicynodonts. Stenocybus is their common ancestor. Here sister taxa are more parsimoniously nested. IOW they look more like each other and share more traits.

References
Brinkman D 1981. The Structure and Relationships of the Dromasaurs (Reptilia: Therapsida). Brevioria, 465: 1-34.
Broom R 1910. A comparison of the Permian reptiles of North America with those of South Africa. Bulletin of the American Museum of Natural History 28: 197-234.

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