I never thought it would get this far
and so deep when I started ReptileEvolution.com. I keep thinking I”m coming to the end. But there’s more to be found in the metaphorical and literal leaf litter here than I ever imagined five or so years ago when this all began…
Earlier we nested the extant short-eared elephant shrew, Macroscelides (Fig. 1), with the tree shrew, Tupaia and the golden mole, Chrysochloris. Today we nest the gold-rumped elephant shrew, Rhynchocyon (Fig. 2) with the mesonychid-like tenrec, Sinonyx.
How can that be?
They’re both elephant shrews!!
Once you see them together,
(Figs. 1, 2) you’ll see the many differences that separate them. And that’s the way they also test in the large reptile tree. These two putative elephant shrews are not closely related because several non-elephant shrews phylogenetically separate them. And that’s why these two are diphyletic. Macroscelides arises from within Glires, the rodent and rabbit clade. Rhynchocyon arises from within Tenreccetacea, or tenrecs + whales.
Not sure how the others will line up. We’ll save those for later…
Figure 1. Macroscelides proboscideus skull. Note the several basic differences between the this skull and that of Ryhncocyon and you’ll be as surprised as I was that these were not noticed in prior studies. If so, please bring them to my attention. Imarge from Digimorph.org and used with permission.
The canines on Rhynchocyon
(Fig. 2) were the first clue that not all elephant shrews were sisters. Few skull traits unite Rhynchocyon and Macroscelides, but both do have an elongate flexible nose and long slender legs poking out from fur ball bodies.
Perhaps you’ll be as surprised as I was
that these differences were not noticed in prior studies. If so, please bring them to my attention. A Google search reveals relatively little literature on this/these clade(s) and none (so far) pertinent to the present discussion.
Figure 2. Rhynchocyon skull with select bones colored. Note the large canines, angled rostrum and just the genesis of the high cranial crest seen in the much larger Sinonyx.
there are no skeletons of Rhynchocyon on the net or in published literature that comes up in a Google search.
Figure 3. Skeleton of Macroscelides proboscides from Digimorph.org and used with permission. Note the high sacral spines and elongate metatarsals here.
(Fig. 4) you can see how earlier workers could have allied these two taxa. And you can see how traits they have in common could be plesiomorphic and/or could be homoplastic (a result of convergence).
Figure 4. Rhynchocyon (above) and Macroscelides (below) compared. Though both are considered elephant shrews, they nest in separate major mammal clades in the LRT. Note how the lips cover the fangs in Rhynchocyon.
On a lighter note…
This little movie character has not gone unnoticed in this discussion. This is Scrat, the sabertooth ?squirrel from the Ice Age movie franchise. Perhaps a close cousin to Rhynchocyon ~ after the nose job and lip tuck.
Figure 5. Scrat, the sabertooth squirrel, from the Ice Age movie franchise, has fangs, a long rostrum and short cranium are like Rhynchocyon — by convergence, no doubt. Different nose.