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. The crown of the tooth is triangular and contains six cusps, connected by low crests, that surround two prominent, low-lying fossae (basins) and a third, smaller fossa. Because of the complexity of the crown, Goin and colleagues interpreted it as a molar; because of the number of roots, the arrangement of the cusps, and the shape of the tooth, as an upper molar; and because it tapers towards the end, as a last molar. One side, the longest, is flat and low compared to the others, suggesting it is the labial (outer) face. This would imply that the tooth is from the left jaw. Under this interpretation, the length of the tooth is 2.65 mm, width is 2.20 mm, height at the labial side is 1.05 mm, and height at the lingual side is 1.30 mm. For convenience, Goin and colleagues designated the six cusps as A through F: A on the front labial corner of the tooth; B on the labial face; C on the back corner; D on the lingual (inner) face; E on the front lingual corner; and F on the front face. The large front fossa is located between cusps A, B, D, E, and F; the smaller intermediate fossa is between cusps B and D; and the much smaller back fossa is just in front of cusp C. All three are nearly round. Cusp A, the largest cusp, is triangular in shape and is separated from the smaller, rounded B by a deep valley; a low crest connects the two cusps further lingually, separating the valley from the front fossa. 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