Gobiatherium and Uintatherium directly compared

Here
(Fig 1) a two-frame GIF movie shows how the near-circular nasal of Mongolian Late Eocene Gobiatherium is similar to the raised nasal horns of North American Uintatherium.

Perhaps that’s a clue to the origin of this unique narial character.

In Uintatherium
the four small horns and main body of the nasal remain as distinct processes.  And there is no central bone separating the left and right naris.

In Gobiatherium
the four horns of the nasal appear to coalesce with the raised main body of the nasal to frame a large circular naris. These were separated left and right by a central anterior bone. The premaxilla remained essentially unchanged at the lower border of the naris.

In this hypothesis the typical ascending process of the premaxilla is instead a descending process of the anterior nasal. Or it is a new bone.

Otherwise these two disparate taxa share just enough traits to link them together in the LRT. Osborn and Granger 1932 recognized this interrelationship in their original paper. That’s to their credit, but they always struggled with that bulbous nose.

Osborn and Granger wrote of Gobiatherium,
“Of all distinctive features, however, the extremely elevated and arched nasals, rising above the level of the cranial vertex and supported by a median fully ossified septum resting on the slender premaxillaries, are not only surprising but unique. Similar to the typical uintatheridae is the edentulous premaxillary, and in great contrast is the absence of canines, with the exception of one specimen which exhibits an extremely vestigial canine on one side only.”

Don’t overlook the laterally indented cranium. That key trait is shared with other clade members, like Coryphodon and Bathyopsis, but is not scored in the LRT because no other tested taxa share a laterally indented skull.

Sometimes key traits are not needed if a sufficient number of other traits enable the software to lump and separate included taxa.

Osborn and Granger continue,
“Two characters are surprising: the wide transverse extension of the zygomatic arches, reminding us of similar prominences in Entelodon, and the relatively low, flat, backwardly extended temporal fossa and occiput doubtless correlated with the feeble development of the muscles of mastication in adaptation to the relativelv long and slender mandible. The absence of the downward flange in the slender anterior rostrum of the mandible may possibly be a sexual character, because in the female uintatheres with small tusks, the mandibular flange is much less prominent than in the males with their great tusks. However, in the seven specimens present there is no trace of a flange.”

Convergence is rampant in the Chordata
and perhaps more so in the Mammalia. Two taxa may be quite different and share certain traits with unrelated taxa. The only question the software asks is: are they more alike than different. 200+ multistate characters is an appropriate number.

Gobiatherium mirificum
(Osborn and Granger 1932; middle Eocene) is widely considered a distinct type of uintathere, like Uintatherium. Gobiatherium has a long wide skull and no horns – unless the nearly circular nasal is actually a set of merged nasal processes and horns, as shown here  (Fig 1). Note the indented braincase shared with clade members. Osborn and Granger noted, “feeble development of the muscles of mastication in adaptation to the relativelv long and slender mandible” lacking a “downard flange.” 

Note the spoonbill mandible. Perhaps this indicates a pond or river environment, perhaps filled with grasses and lilies for this herbivore. If so, Gobiatherium may have been a hippo analog with dorsal eyes and a raised naris above the surface. The term ‘hippo’ is not found in the Osborn and Granger text so this analogy might be a fresh idea.

References
Osborn HF and Granger W 1932. Coryphodonts and uintatheres from the Mondolian expedition of 1930. American Museum Novitates 5521–16.

wiki/Gobiatherium

Source: https://pterosaurheresies.wordpress.com/2024/11/01/gobiatherium-and-uintatherium-directly-compared/