El patrón de cambios en la masa corporal de los Hipparionini (Perissodactyla, Equidae) de la península ibérica durante el Mioceno Superior-Plioceno Superior

Abstract

The objectives of this study were: 1) to infer the body mass of Hipparionini of the Iberian Peninsula; and 2) to provide the setting for the pattern of changes in body mass within the climatic-environmental evolution of the Iberian Peninsula during the interval of time between the upper Miocene to the upper Pliocene. Body mass was estimated from the width of the articular surface of the first phalange of the central digit using a regression equation. Once body mass was estimated, it was correlated with two paleoecological indicators – the gracility index (IG) and the hypsodonty index (IH). Using Mammal-ages (ELMAs) and Mein zones (MN) as chronological units, the pattern of body mass change over time was analyzed. Results showed that: 1) a majority of fossils (32%) reached a mass that placed them in the 100 Kg. to 200 Kg. interval; followed by those whose mass fell in the 100 to 149 Kg. range (26%). Extreme sizes (i.e., 0-49; 300-349 and 350-399 Kg.) were reported much less frequently (5%), with each of these ranges being represented by a single taxon; 2) throughout their biochron, Hipparionini remained fundamentally within the 100 to 200 Kg. range; 3) the forms with the largest body mass were recorded in MNs 10 and 16, while those of least body mass were recorded in MN 13; 4) there was minimal correlation between body mass and the gracility and hypsodonty indices (r = 0.1465 for the IG and r = -0.2338 for the IH). Through these results, the extrapolation of a relation model between body mass and the climatic-environmental variables (i.e., climate, vegetation type) developed for the Equini, and the bibliographic information regarding the prevailing climatic-environmental conditions on the Iberian Peninsula during the upper Miocene-upper Pliocene interval, it was possible to infer that Hipparionini of least body mass (e.g., H. gromovae; H. periafricanum; H. primigenium) inhabited relatively closed environments (e.g., open forest-thicket), under relatively warm and humid conditions; while forms of greater body mass (i.e., Hipparion from the La Roma 2 site; H. rocinantis) inhabited more open environments (e.g. savanna), under climatic conditions that were relatively colder and drier.