[N] 2006 Possible record of the South American mammal order Litopterna in Mexico
Ferrusquia-Villafranca, I. & Maldivo-Arriaga, R. (2006) A possible record of the South American mammal order Litopterna in Mexico. JVP 26(3) Abstracts pp.60-61
A fortuitous find of fossil material during the construction of a warehouse in eastern Mexico City might be the possible first record of the South American order Litopterna not only in Mexico but in North America as well. The fossils were found in a ditch excavated on late Pleistocene strata of volcarenitic, poorly consolidated clastics.
The material belonged to a ~bull-sized mammal, it includes an atlas, a thoracic vertebra, a sacrum fragment, and a lower molar; it is large [92 mm high, 58 mm long and 20 mm wide], inward curved, hypsodont, rootless, and thickly enameled.
The occlusal pattern consists of two subequal lobes, the anterior is roughly L-shaped with the short arm wide and antero-lingually directed; the long arm tapers rearwardly (thus becoming wedge-like) and is set parallel to the molar medium plane; it shows a little bulge in the medial part, from where narrow ribs (stylids?) emerge on the labial and lingual sides.
The posterior lobe is a bit smaller, slightly postero-labially set with respect to the medium plane, and placed a little more labially than the anterior lobe; this displacement significantly increases downward; its outline is seleniform (more so downward), with a median concavity that corresponds to a shallow sulcus on the labial side. The tooth has growth lines (~12 to 14 per 1 cm), set as numerous fine striae alternating with a few thicker ones.
This molar built is unlike that of the perissodactyls and artiodactyls, but resembles that of the South American Pleistocene macrauchenid litopterns in being simple, hypsodont, and formed by two, relatively narrow, semilunate lobes; however, the Mexican specimen is more thickly-enameled and more hypsodont than any macrauchenid. This taxon is well known in the late Pleistocene of South America, from Argentina to Venezuela, but has not been recorded in Central America.
If this specimen is indeed a litoptern, it would be the first record of this order in North America; its presence in Mexico would add to the recent discovery in Michoacan, Central Mexico, of another previously unrecorded South American mammal order, represented by a toxodont notungulate.