Caracterización ecomorfológica del esqueleto postcraneal en rumiantes (Artiodactyla, Mammalia)aplicación en la inferencia de las adaptaciones ecológicas de los rumiantes del plio-pleistoceno de España

Resumen

Recent and extinct ruminants have diversified into numerous niches over time. Their functional morphology has been widely used in paleoenvironmental reconstructions, since its members have been considered sensitive indicators of climate and landscapes changes. Most studies have focused on dentition and cranial features, pushing the postcranial skeleton into the background. However, skeletal structure provides extremely useful information about locomotor system, which can likewise offer clues about environment. In other words, locomotor adaptations seem to be related to specific patterns of predator avoidance and food search strategies that are habitat specific. To expand the knowledge that we have so far about such relations, and subsequently, to infer them in fossils, the present work examines in detail the autopod of a number of extant and Plio-Pleistocene ruminants from three Mediterranean localities (Villarroya, La Puebla de Valverde and Saint-Vallier). The number of morphological characters considered by other authors to date has been enlarged and enhanced, as well as the habitat range. Phylogeny has also been taken into account in a first approach. Results show that two main groups may be established based on locomotion: gallop-stotting (type I) and bounding gallop-zigzagging (type II). The first is mainly used by species living in open and clear environments, which principally are bovids (except Cephalophines). The latter is primarily practiced by moschids, tragulids and cephalophines living in dense habitats. Another important conclusion to be drawn is that metatarsal III-IV can be considered the best ecological indicator among autopod bones, while the rest of the elements provide more limited information. It can be summarized that those bones with strong insertion marks and traits limiting the movement in a parasagittal plane, belong to species with type I locomotion. In contrast, weaker marks and morphologies allowing lateromedial swings are characteristic for those species with type II locomotion. These ecomorphological characters, defined by extant taxa morphology, have been applied to fossil species, finding that both Metacervoceros rhenanus as Eucladoceros senezensis lived in forests with well-developed understories and close to wetlands. In contrast, Gazella borbonica and Gazellospira torticornis inhabited more arid, open and clear environments, probably with abundant sandy and/or stony substrates. The ecotonal habitat between these two landscapes would be occupied by Croizetoceros ramosus and Leptobos elatus, which seem to have more ubiquitous lifestyles. Croizetoceros prefered denser areas, while Leptobos inhabited more open spaces. The caprines, Hesperidoceras merlae and Gallogoral meneghinii, probably occupied steep terrains and adjacent plains in the vicinity of the fossil sites. The less rough zones of these areas could have been inhabited, at least seasonally, by Gazella and Gazellospira. In this work, we have also relied on analogies with extant communities, developing a new paleoecological method to infer bioclimatic conditions from the locomotor spectrum of fossil communities. Bioclimatic analyses show that it is possible to discriminate tropical/subtropical vs. temperate, arid vs. humid, and forest vs. non forest biomes (with 70%, 68% and 70% of correct classification respectively). Based on all this information, we propose a mosaic environment for the fossil localities, with a predominance of arid plains, but dotted with forest patches and steep landscapes. Bioclimatic analyses provide temperate and non forest regional conditions for the three localities. However, regional climate would be more arid in Villarroya and Saint-Vallier than in La Puebla de Valverde.