Kretzoiarctos gen. nov., the oldest member of the giant panda clade

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.

Figure 1. Dentognathic material of Kretzoiarctos gen. nov. beatrix.

1, Right mandible with canine and p2–m3 IPS46473 from ACM/C6-Camí in labial (a), lingual (b) and occlusal (c) views; 2, Broken P4 IPS46473 in labial (a) and occlusal (b) views; 3, Left P4 NV-2-42 (holotype) in labial (a), occlusal (b) and lingual (c) views; 4, Right M1 NV-2-42 (paratype) in labial (a), occlusal (b) and lingual (c) views from Nombrevilla 2.

Figure 2. Drawing of the new material of Kretzoiarctos gen. nov. beatrix from ACM/C6-Camí.

a, labial; b, occlusal; c, lingual. Artwork by Marta Palmero.

Figure 3. Single most parsimonious cladogram recovered by the cladistic analysis using the branch-and-bound method.

See the data matrix employed in Table S1. Agriarctos spp. includes A. gaali, A. vighi and A. depereti. Numbers above each clade indicate bootstrap support over 50%. The cladogram further incorporates the known stratigraphic range for each taxon. Cladogram metrics: tree length, 159 steps; Consistency Index, 0.553; Retention Index, 0.710; Homoplasy Index, 0.447.