In the present paper, we describe the craniodental remains of three individuals of an amphicyonid previously determined as Thaumastocyon sp. from the late Miocene (c. 9.1 Ma) pseudokarstic site of Batallones-3. Dentognathic differences in relation to other Thaumastocyoninae enable a new taxon, Ammitocyon kainos gen. et sp. nov., to be defined; it is both the most recent and the most complete member of this subfamily known in the fossil record. The results of our phylogenetic analysis demonstrate that this new form reached the maximum degree of specialization within Thaumastocyoninae, a group that includes the most hypercarnivorous amphicyonid species of the Miocene. The masticatory apparatus of A. kainos is extremely derived, with the loss of the mesial premolars (P3 / P2 and p1–p3) and the third molars (M3 / m3). The robustness of the chin and muzzle is in contrast with the slender and highly sectorial postcanine dentition (p4 / m2 and P4 / M2), features that are consistent with the values provided by an analysis of the bending resistance of the mandible performed for these specimens. All the anatomical features combined, both cranial and postcranial, reveal the complexity of the body plan of A. kainos. This species combines a derived hypercarnivorous dentition with one of the most robust postcranial skeletons recorded for all large caniform carnivorans, outlining an enigmatic taxon that possesses unique ecological adaptations.

The present study was supported by the Spanish Ministerio de Economía y Competitividad (Research Projects PGC2018-094122-B100 and CGL2016-76431-P) (AEI/FEDER, UE), the Research Groups CSIC 64 1538 and CAM-UCM 910607, the Generalitat de Catalunya (CERCA Programme, and Beatriu de Pinós contract 2017 BP 00223 from AGAUR to JA), and Gobierno de Aragón (E33_17R). Additionally, our research received funding from the SYNTHESYS Project http://www.synthesys.info/, which is financed by European Community Research Infrastructure Action under the FP7 ‘Capacities’ Program under the grant agreement (SYNTHESYS; CZ-TAF-3329) with JA. The ‘Juan de la Cierva Formación’ program (FJC2018-036669-I), from the Spanish Ministry of Science, Innovation, and Universities also funded AV.

Peer reviewed