The first skull of the earliest giant panda

Abstract

Fossils of the giant panda Ailuropoda (Order Carnivora, Family Ursidae) are largely isolated teeth, mandibles, and a few rare skulls, known from the late Pliocene to late Pleistocene in China and Southeast Asia. Much of this material represents a Pleistocene chronospecies, Ailuropoda baconi, an animal larger than the living giant panda, Ailuropoda melanoleuca. The earliest certain record of Ailuropoda is the late Pliocene chronospecies, Ailuropoda microta, smaller than either A. baconi or A. melanoleuca, and previously known only from teeth and a few mandibles from karst caves in south China. Here, we report the discovery of the first skull of A. microta, establishing its cranial anatomy and demonstrating that the specialized cranial and dental adaptations of Ailuropoda for durophagous feeding behavior centered on bamboo were already evident in this late Pliocene species. The skull from Jinyin cave (Guangxi) and dental remains from other karst localities in southeastern China show that Ailuropoda microta occupied south China from approximately 2 to 2.4 Myr ago after a marked global climatic deterioration. Dental and basicranial anatomy indicate a less specialized morphology early in the history of the lineage and support derivation of the giant panda from the Miocene Asian ursid Ailurarctos.

Fig. 1.

Comparison of the skull and upper dentition of fossil and extant giant pandas. (A and D) Ailuropoda microta (IVPP V14564), late Pliocene, Jinyin cave, China. (B and E) A. baconi, Pleistocene, Liujiang, Guangxi, China. (C and F) Living A. melanoleuca, China.

Fig. 2.

Geographic distribution and craniodental dimensions of fossil and living giant pandas. (A) Localities yielding A. microta and A. wulingshanensis in southeastern China relative to the geographic range of the giant panda in the Pleistocene. Present-day range of the giant panda is from Loucks et al. (28). The southernmost range of the giant panda is defined by fossil discoveries at Mogok, Burma (5), Chaiyaphum, Thailand (14), and Lang Trang, Vietnam (29). (B) Condylobasal length of skull (in millimeters) for the living giant panda A. melanoleuca relative to the Jinyin cave A. microta skull (IVPP V14564). Range, 1 SD and the mean are indicated; sample size noted within each SD bar. The four upper samples represent subpopulations of the living giant panda (11); the lower three samples are 18 skulls of A. melanoleuca measured in North American museums (22). These 18 skulls are then separated by sex to demonstrate dimorphism. No skulls of A. wulingshanensis are known, and the few skulls of A. baconi fall in the upper part of the range of the living giant panda. (C and D) Distribution of dental measurements (in millimeters) for the four species of giant panda Ailuropoda (late Pliocene–Recent); M₁, M₂ lengths (C); P⁴, M¹, M² lengths (D). Sample size is indicated within each range bar.

Fig. 3.

Stereoimages of the skull of Ailuropoda microta, Jinyin cave, China. Teeth, skull, and basicranial anatomy of IVPP V14564 show detail clearly comparable with these features in the living giant panda, indicating the appearance of these specialized traits in the lineage by the late Pliocene (≈2 to 2.4 Myr). bs, basisphenoid; bo, basioccipital; eam, osseous external auditory meatus; e1, anterior caudal entotympanic; e2, posterior caudal entotympanic; ic, entrance of internal carotid artery; m, mastoid; pg, postglenoid process of squamosal; pp, paroccipital process; t, ectotympanic; C, canine, P^2–4, premolars; M^1–2, molars.

Fig. 4.

CT scanned image and 3D reconstruction of A. microta skull, Jinyin cave, China. (A–D) Transverse CT sections through the dorsal paranasal sinuses (dps), cerebral fossa (crf), cerebellar fossa (cbf), and olfactory fossa (of). (E) Note greatly inflated dorsal paranasal sinus complex. m, maxillary sinus; nc, nasal cavity; s, sphenoid sinus; te, tentorium.

Fig. 5.

Late Cenozoic temporal distribution of species of the giant panda Ailuropoda in southeastern Asia (, , , , , –32); time scale (33).