Abstract
The phylogenetic position of the giant panda, Ailuropoda melanoleuca (Carnivora: Ursidae: Ailuropodinae), has been one of the most hotly debated topics by mammalian biologists and paleontologists during the last century. Based on molecular data, it is currently recognized as a true ursid, sister-taxon of the remaining extant bears, from which it would have diverged by the Early Miocene. However, from a paleobiogeographic and chronological perspective, the origin of the giant panda lineage has remained elusive due to the scarcity of the available Miocene fossil record. Until recently, the genus Ailurarctos from the Late Miocene of China (ca. 8–7 mya) was recognized as the oldest undoubted member of the Ailuropodinae, suggesting that the panda lineage might have originated from an Ursavus ancestor. The role of the purported ailuropodine Agriarctos, from the Miocene of Europe, in the origins of this clade has been generally dismissed due to the paucity of the available material. Here, we describe a new ailuropodine genus, Kretzoiarctos gen. nov., based on remains from two Middle Miocene (ca. 12–11 Ma) Spanish localities. A cladistic analysis of fossil and extant members of the Ursoidea confirms the inclusion of the new genus into the Ailuropodinae. Moreover, Kretzoiarctos precedes in time the previously-known, Late Miocene members of the giant panda clade from Eurasia (Agriarctos and Ailurarctos). The former can be therefore considered the oldest recorded member of the giant panda lineage, which has significant implications for understanding the origins of this clade from a paleobiogeographic viewpoint.
Highlights
The Fossil Record of the Giant Panda Lineage The extant giant panda from central Asia, Ailuropoda melanoleuca [1], differs from other living ursids by the presence of several craniodental adaptations to durophagy [1,2,3,4]
Cladistic Analysis A cladistic analysis based on a morphologic data matrix for living and fossil ursids recovered a single most parsimonious tree of 157 steps (Figure 3)
The analysis recovers the monophyly of the Ursidae, represented by three consecutive members of its stem lineage (Ballusia elmensis, Ursavus primaevus and Ursavus brevirhinus, the latter suggesting that the genus Ursavus is paraphyletic), and two major clades: the Ailuropodinae, including the extant giant panda (Ailuropoda); and the Ursinae + Tremarctinae, including all the extand ursids except Ailuropoda
Summary
The Fossil Record of the Giant Panda Lineage The extant giant panda from central Asia, Ailuropoda melanoleuca [1], differs from other living ursids by the presence of several craniodental adaptations to durophagy (i.e., feeding tough plant material, mainly bamboo) [1,2,3,4]. These adaptations are already present, to a large extent, in the Plio-Pleistocene relatives of A. melanoleuca (Ailuropoda microta and Ailuropoda wulingshanensis) [2,4], which displayed a larger distribution, from northern China to Southeast Asia [5,6,7], than the living giant panda. Ailurarctos has been considered to be descended from an unidentified Miocene species of Ursavus [4,5,6,7,14], no formal cladistic analysis had been far provided to substantiate such phylogenetic hypothesis
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