PACHYOSTOSIS IN A LOWER MIOCENE GIRAFFOID FROM SPAIN, LORANCAMERYX-PACHYOSTOTICUS NOV GEN NOV-SP AND ITS BEARING ON THE EVOLUTION OF BONY APPENDAGES IN ARTIODACTYLS

At the lower Miocene locality of Loranca, Spain, numerous skeletal and dental remains of a peculiar Giraffoid have been collected. Many of the long bone diaphyses, especially of the front limbs, possess abnormally thickened multilayered ''pachyostotic'' bone deposits, all adult individuals being affected (MNI = 24). These remains are identified as belonging to a new genus and species of giraffoid Lorancameryx pachyostoticus, close to Teruelia adroveri, another lower Miocene giraffoid from Spain without pachyostosis. In searching for an explanation for the phenomenon of pachyostosis in the Loranca giraffoid, the authors have developed an hypothesis about the evolution of ''abnormal'' bony deposits in artiodactyls, including the appearance of frontal appendages in several Miocene to Recent lineages (Cervidae, Climacoceratidae, Lagomerycidae, Bovidae, Giraffidae, Antilocapridae, Hoplitomerycidae, Palaeomerycidae, Suidae) and of pachyostotic mandibles and maxillae in some Pleistocene Cervidae. The hypothesis is that all these ''abnormal'' bony deposits are simply different strategies for maintaining body/skeletal relations relatively constant in species which undergo marked seasonal body weight fluctuations. The onset of marked seasonality towards the end of the lower Miocene period appears to have been the ''trigger'' for the independent evolution of bony cranial appendages in at least 7 lineages of ruminants and of pachyostotic limb bones in the Loranca giraffoid. Once such appendages had evolved they secondarily took on behavioural significance. The authors also discuss the reasons for the onset of marked seasonality towards the end of the lower Miocene.