Eomaia needs a makeover

With the recent nesting
of Eomaia (Ji et al. 2002) closer to Thylacinus (Fig. 1) than to eutherians (click here). Thylacinus is the longn-legged marsupial wolf AND it’s a basal marsupial with an unspecialized dentition. So maybe that slinky rat-like appearance originally given to Eomaia (Fig. 1) needs an update. I mean, look at those long legs! (Then again, the proximal sister, Didelphis, (Fig. 2) also has long legs, but you’d never know it the way it slinks around.

Maybe the carriage of Eomaia was a bit more upright,
like Thylacinus, despite the great size difference. The morphology was similar enough to nest the two together to the exclusion of all other 783 taxa. The metacarpals and metatarsals appear to trend toward digitigrade, as in so many marsupials, not flat-footed as originally reconstructed. The PILs align either way.

Let’s see what happens
when we let the bones and phylogenetic bracketing tell another tale.

Figure 1. Eomaia in situ, as originally reconstructed, as reconstructed here and compared to Thylacinus. This is what this blog and ReptileEvolution.com do best. Show sister taxa together to scale and not to scale to drive home their similarities with a strong visual impression. You can always ask for the data matrix later.

Figure 1. Eomaia in situ, as originally reconstructed, as reconstructed here and compared to Thylacinus. This is what this blog and ReptileEvolution.com really do best. Show sister taxa together to scale and not to scale to drive home their similarities with a strong visual impression. You can always ask for the data matrix later.

 

I note
long neural spines in Eomaia around the shoulders. The tibia and fibula appear to be able to be closely appressed, despite their disturbance post-mortem. The slender cervicals are unlike those of Didelphis (Fig.2). The lumbar region appears to be more supple, like Thylacinus, built for galloping.

Figure 2. Didelphis, the extant opossum, a slinky marsupial more primitive than Eomaia.

Figure 2. Didelphis, the extant opossum, a slinky marsupial more primitive than Eomaia.

I’d like to see original data
for the reflected process of the dentary on Eomaia. Sister taxa don’t have a ventral protrusion, but they do have a sharp little ascending curl of bone, and I don’t see it in the fossil.

References
Ji et al 2002. The earliest known eutherian mammal, Nature 416:816-822.m online here.

wiki/Eomaia

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