Bone-cracking hyenas (carnivora, hyaenidae) from the european neogene and quaternarytaxonomy, paleobiology and evolution

Resumen

The family Hyaenidae (Mammalia, Carnivora) include four extant species restricted to Africa and Asia: the bone-cracking hyenas (Crocuta crocuta, Hyaena hyaena, Parahyaena brunnea) and the myrmecophagous aardwolf (Proteles cristata). During the Neogene and Quaternary, hyaenids were more diverse and widely distributed throughout the Old World and even North America, although their diversity and ecomorphological disparity progressively declined since the late Miocene onwards. Many controversies remain about the origin and diversification of hyaenids. This dissertation aims to address some of these topics based on new remains and innovative techniques. It includes a compendium of published articles, organized in two blocks: the first consists of five papers about extinct hyaenids (Hyaenictis, Pliocrocuta and Pachycrocuta), mostly devoted to the morphological description and morphometric comparison of previously unpublished fossils and related taxonomic issues, with emphasis on dental adaptations to durophagy; the second block relies on 3D imaging techniques applied to computed tomography (CT) scans to study the internal cranial anatomy of extinct hyaenids (Pliocrocuta, Crocuta), with emphasis on brain morphology and proportions to derive paleoneurological inferences on social behavior. The main conclusions of the dissertation may be grouped as follows: 1. Taxonomy: The unpublished material from Ronda Oest de Sabadell (late Miocene), La Puebla de Valverde and Villarroya (Late Pliocene-Early Pleistocene), and Cueva Victoria (Late Early Pleistocene) is attributed, respectively, to Hyaenictis aff. almerai, Pliocrocuta perrieri, and Pachycrocuta brevirostris. The authorship of the latter is corrected from “Aymard, 1846” to “Gervais, 1850”. Differences in brain morphology support the distinction of both Crocuta spelaea and Crocuta ultima from Crocuta crocuta at the species rank. 2. Paleobiology: The taphonomic study of the large herbivore remains from the Vallparadís Section (Late Early Pleistocene) indicates that Pachycrocuta brevirostris was the main bone modificator agent in the site. In turn, the developed frontal sinuses of Pliocrocuta perrieri, related to improved skull resistance against bite stresses, support a durophagous diet for this species, and the same holds for the zig-zag enamel microstructural pattern of both Pliocrocuta perrieri and Hyaenictis aff. almerai, which enable to reassign the latter to the transitional bone-cracking ecomorphotype 5. With regard to brain morphology, Pliocrocuta perrieri, Crocuta spelaea and Crocuta ultima resemble extant hyaenines, although their frontal lobe is less developed than in Crocuta crocuta, suggesting a less complex social behavior than in the latter species (comparable to that of Hyaena and Parahyaena). Currently available paleoneurological evidence indicates that the hyaenid brain evolved towards greater relative size and complexity throughout the Miocene and that Proteles probably displays the most plesiomorphic brain among extant hyaenids. 3. Evolutionary history: Based on the new morphofunctional and paleoneurological evidence presented, new hypotheses for the evolution of bone-cracking hyaenids are proposed, such as the origin of hyaenines from Hyaenictis. Some of these hypotheses differ from those supported by morphology-based cladistic analyses but are in greater agreement with molecular evidence. The results highlight the potential of cranial internal morphology as a source of phylogenetically informative data that, in the future, might hopefully enable more comprehensive and better resolved phylogenetic analyses that could settle some of the current debates about the evolutionary history of hyaenids.