LACM 149371

LACM 149371 was discovered in 1998 at the Santa Rosa fossil site in the Ucayali Region of Peru. The fauna was published in a volume of the Science Series of the Natural History Museum of Los Angeles County in 2004, which included a paper by Francisco Goin and colleagues that described and discussed LACM 149371. The age of the Santa Rosa fauna remains highly uncertain, as the outcrop where the fossils were found cannot easily be placed in a known stratigraphical unit, and the fossils are so distinct from other known fossil faunas that biostratigraphy cannot provide a precise estimate. In a summary of the 2004 volume, Kenneth Campbell tentatively referred Santa Rosa to the Mustersan South American Land Mammal Age (SALMA), which he placed near the Eocene–Oligocene boundary, around 35 million years ago. However, Mario Vucetich and colleagues suggested in 2010 that the Santa Rosa fauna may be substantially later—perhaps as young as the Deseadan SALMA (late Oligocene, around 25 million years ago). According to Campbell, the Santa Rosa mammals likely lived in a savanna habitat that contained rivers. ==Description==

LACM 149371 is a poorly preserved molar-like tooth that largely lacks a recognizable enamel surface and shows many small grooves and holes on the crown surface. This suggests the tooth may have been chemically degraded, perhaps by acidic water or because it passed through the digestive tract of a predator. The roots are broken off, but remaining pulp cavities suggest the presence of four main roots, which are partially joined into two pairs. A smaller pulp cavity between those roots suggests the likely presence of a fifth root and a slight depression in the tooth may represent another root. All three are nearly round. At its back, B connects to a long crest that reaches the back fossa and behind it the small cusp C, which has a groove on its labial side. A valley separates it from cusp D. D itself is crest-shaped and forms the lingual wall of the intermediate fossa; it is described as "very odd", and may in fact consist of two fused, triangular cusps. A crest issuing from D separates the back from the intermediate fossa, and another, larger crest separates the front from the back fossa and nearly reaches cusp B. Cusp E is triangular and separated from cusps F and D by valleys, which are bordered internally by crests connecting the cusps. F is rounded. The microstructure of the tooth enamel is not clearly recognizable, evidently because the tooth is degraded, though structures resembling enamel prisms (bundles of hydroxyapatite crystals) and Hunter-Schreger bands are recognizable. ==Identity==

Because of the complexity of the crown, Goin and colleagues identified the tooth as a mammal; although some non-mammalian groups, like crocodylians, may have complex teeth, none approach the level of complexity seen in LACM 149371. They did see some general resemblances to the upper premolars of the early South American ungulates, but the cusp arrangement is different from that of any ungulate. There are also some resemblances to the early rodents Ivanantonia from Asia and Nonomys from North America, but Ivanantonia has a central groove and lacks fossae, and Nonomys has a prominent cingulum (shelf) at the edges of the tooth and also lacks the fossae of LACM 149371. The tooth resembles multituberculates—a large group of extinct mammals with many-cusped teeth—in the shapes of the valleys and crests, but multituberculates lack fossae and usually have quadrangular teeth with two longitudinal rows of cusps separated by a central valley. In the same features, LACM 149371 resembles gondwanatheres, a small and enigmatic group of mammals from the Cretaceous through Eocene of the southern (Gondwanan) continents that may be related to multituberculates. In particular, Ferugliotherium from the late Cretaceous of Argentina has similarly formed cusps and also has crests that connect the cusps to the center of the tooth. However, the upper molars are unknown, and the low-crowned teeth of Ferugliotherium lack deep fossae. Members of the higher-crowned gondwanathere family Sudamericidae do have fossae. Goin and colleagues conclude that LACM 149371 most likely represents a member of the gondwanathere family Ferugliotheriidae; if so, it would be among the youngest known gondwanatheres. ==References==