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More notoungulates leave this extinct clade.

Saturday, October 1, 2016 18:43
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(Before It's News)

Some of the taxa I met this weekend, and you’ll meet shortly,
I’ve never heard of before. Even so, here’s another paleo story waiting to be told.

When I added
Protypotherium (Fig. 1) and Miocochilius (Fig. 2) to the large reptile tree (now 828 taxa, but not yet updated), I learned that they were both considered members of the Interatheridae, which Wikipedia considers,  “an extinct family of notoungulate mammals from South America.”

Figure 1. Protypotherium nests with Miocochilius and Homalodotherium in the LRT between mesonychids and paenungulates.

Figure 1. Protypotherium nests with Miocochilius and Homalodotherium in the LRT between mesonychids and paenungulates.

Earlier we learned
that all tested members of the Notoungulata do nest not with each other, but with a variety of established clades within the Theria. Some members of the invalid Notoungulata nested with wombats, others with various placentals. And today this issue keeps dragging on…

Figure 2. Miocochilius has reduced it imprint to just two functional toes.

Figure 2. Miocochilius has reduced it imprint to just two functional fingers and toes. Look at those long horse-like teeth exposed by erosion of the bone.

So where there’s an Interatheridae…
there should be an Interatherium. And there is one (Fig. 3). Trouble is, the Interatherium skull with that crooked diastema did not look like the straight jawed full set of teeth found in Protypotherium and Miocochilius. So I added Interatherium to the LRT to find out.

Turns out, like many notoungulates before, 
that Interatherium nests with wombats, between Vombatus and Toxodon even though Interatherium is much smaller, longer, and leaner than its sisters. It also lacks digit 1 on all four extremities. Apparently there is a wide range of wombat/marsupial morphologies that we’re just now beginning to appreciate and identify. For instance, that notch and descending maxillary palate in Interatherium (Fig. 3) resemble those of the bizarre marsupial beaver-mimic wombat, Vintana, which also nests nearby.

Figure 3. Interatherium does not nest with notoungulates or other purported interotheres. Rather cat-sized Interatherium nests with wombats, between Vombatus and the giant Toxodon.

Figure 3. Interatherium does not nest with notoungulates or other purported interotheres. Rather cat-sized Interatherium nests with wombats, between Vombatus and the giant Toxodon.

If Interatherium is a marsupial, 
the two placentals, Protypotherium and Miocochilius, cannot be interatheres. Or if they were defined as interatheres, that definition should be modified. Best to just call Protypotherium and Miocochilius typotheres — unless Typotherium turns out to be unrelated to these two, too.

Now,
as I look up “Typotherium,” I see it is better known by its senior synonym, Mesotherium, originally named, according to Wikipedia, in the belief that it was a transitional taxon between rodents and pachyderms. I have not tested Mesotherium (Fig. 4) yet, but with that diastema, it looks more like Interatherium, the wombat, than Protypotherium and Miocochilius, the condylarths. Only testing will tell, though…

Figure 4. Mesotherium. What is it, if not the long lost link between rodents and elephants? : )

Figure 4. Mesotherium. What is it, if not the long lost link between rodents and elephants?  Just kidding! I don’t see scale bars for this taxon, but Wiki reports it was the size of a small sheep at 55 kilograms (121 pounds. So it probably had a skull the size of a small sheep.

But wait, there’s more…
There was, indeed, a larger member of the Protypotherium and Miocochilius clade. Seems that the  clawed browser, Homalodotherium (Fig. 5), which I earlier nested with the clawed ungulate, Chalicotherium, now nests with Protypotherium and Miocochilius given the opportunity to do so (taxon exclusion rises again!). These three form a clade nesting between mesonychids (including hippos and Paleoparadoxia) and paenungulates (elephants, hyraxes and sea cows) where big front teeth rule, but tusks are not yet present in these three (yet-to-be-named clade) taxa.

Figure 6. Bear-sized Homalodotherium nests with cat-sized Protypotherium and Miocochilius. They all have a full arcade (11x4) of relatively flat teeth.

Figure 6. Bear-sized Homalodotherium nests with cat-sized Protypotherium and Miocochilius. They all have a full arcade (11×4) of relatively flat teeth. Note the resemblance to Chalicotherium here, by convergence.

I’m catching up
but still behind in updating the pertinent web page at ReptileEvolution.com. It’s not easy, but I’m getting there.

References
Ameghino F 1882. Ungulata, Typotheria, Interatheridae. Catalog de la Prov. de Buenos Aires en la Expedicion Cont. Sud-America. March 1882. Boletino Instituto Geologia Argentino, June 1882. Cont. Conocimenient Mamif. Fosil. Repub. Argentina, in Accd. Nac. Cien., Cordoba 6:474-480. 1889.
Croft DA 2007. The Middle Miocene (Laventan) Quebrada Honda wildlife, southern Bolivia and a description of ITS Notoungulates. Palaeontology 50(1):277-303.
Huxley TH 1870. Anniversary address of the President of the Geological Society. Quarterly Journal of the Geological Society of London 26:42-64.
Stirton RA 1953. A new genus of interatheres from the Miocene of Colombia. University of California Publications in Geological Sciences 29: 265-348

wiki/Homalodotherium
wiki/Protypotherium
wiki/Miocochilius

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