A new look at Laccopithecus robustus from the Late Miocene of China: Anatomy, systematics, and paleobiology

Laccopithecus robustus, from the Late Miocene of Shihuiba in Yunnan Province of southwestern China, is one of the best known pliopithecoids. Dating to ∼7-6 Ma, it is the last-known surviving pliopithecoid in Eurasia. Preliminary reports of the craniodental material of Laccopithecus have been published, but no detailed accounts of the morphology are available. The current study presents a fuller description of the cranium, mandible, and dentition of Laccopithecus; provides comparisons with other pliopithecoids; and highlights the distinguishing features of the genus. Laccopithecus is a relatively large pliopithecoid, with an estimated body mass of 10-11 kg, similar in size to the extant siamang, Symphalangus syndactylus. A suite of dental synapomorphies links Laccopithecus with other crouzeliid pliopithecoids, and among these, Laccopithecus is inferred to be most closely related to the specialized anapithecine crouzeliids (i.e., Egarapithecus and Anapithecus). Comparisons of the Laccopithecus cranium highlight the remarkable similarity in the cranial bauplan among pliopithecoids, even though Laccopithecus combines these general features with several unique specializations (i.e., relatively small orbits, weakly developed supraorbital rims, deep lower face, a single infraorbital foramen, and marked temporal lines that probably converged relatively anteriorly). Sexual dimorphism of canine size in Laccopithecus is moderately high compared with that in extant catarrhines, and this occurs in conjunction with relatively low levels of estimated body mass dimorphism. A similar pattern is seen in some extant colobines, and possibly also in Anapithecus. In terms of dietary behavior, based on relative shearing crest development, Laccopithecus, like the majority of pliopithecoids, appears to have been predominantly frugivorous. An isolated partial manual phalanx, previously attributed to Laccopithecus, may possibly belong instead to the contemporary sivaladapid, Sinoadapis carnosus.