First cranial remains of Cheirogaster richardi (Testudines: Testudinidae) from the Late Miocene of Ecoparc de Can Mata (Vallès-Penedès Basin, NE Iberian Peninsula): taxonomic and phylogenetic implications

Although skulls of extinct Testudinidae are generally much scarcer than shell remains, when available they provide important data for resolving taxonomic and phylogenetic problems, as illustrated here by two well-preserved giant tortoise skulls from the early Vallesian (MN9, Late Miocene) of Ecoparc de Can Mata (ECM; els Hostalets de Pierola, Valles-Penedes Basin, NE Iberian Peninsula). These specimens, referable to the extinct genus Cheirogaster, differ significantly from C. bolivari and are assigned to C. richardi, whose cranial morphology was previously unknown. This nominal taxon had been considered a junior subjective synonym of C. bolivari, due to a previous neotype designation for the former, based on shell remains, that did not meet the requirements of the International Code of Zoological Nomenclature. This designation is here considered invalid because it was based on material from a different geographical area, even though remains from the original type locality area were available. Given that the holotype of C. richardi (from the early Vallesian of els Hostalets de Pierola) has been destroyed, to clarify the taxonomic status of this taxon we here designate one of the two ECM skulls as the neotype of the species. On this basis, an emended diagnosis is provided, which leads us to conclude that two different species are recorded from the Iberian Miocene: C. bolivari, from the middle Aragonian of the inner Iberian basins; and C. richardi, from the latest Aragonian and Vallesian of the Valles-Penedes Basin. Additional cranial material of Cheirogaster from inner Iberia would be required to clarify whether these species display distinct geographical distributions and/or different chronostratigraphical ranges. A cladistic analysis of Testudinidae based on cranial morphology supports a sister-taxon relationship between Cheirogaster and Centrochelys. Overall, our results highlight the significance of cranial morphology for attaining a better understanding of turtle taxonomy and phylogenetic relationships.