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 t he long bone diaphyses, especially of the front limbs, possess abnorma lly thickened multilayered ''pachyostotic'' bone deposits, all adult i ndividuals being affected (MNI = 24). These remains are identified as belonging to a new genus and species of giraffoid Lorancameryx pachyos toticus, close to Teruelia adroveri, another lower Miocene giraffoid f rom Spain without pachyostosis. In searching for an explanation for th e phenomenon of pachyostosis in the Loranca giraffoid, the authors hav e developed an hypothesis about the evolution of ''abnormal'' bony dep osits in artiodactyls, including the appearance of frontal appendages in several Miocene to Recent lineages (Cervidae, Climacoceratidae, Lag omerycidae, Bovidae, Giraffidae, Antilocapridae, Hoplitomerycidae, Pal aeomerycidae, Suidae) and of pachyostotic mandibles and maxillae in so me Pleistocene Cervidae. The hypothesis is that all these ''abnormal'' bony deposits are simply different strategies for maintaining body/sk eletal relations relatively constant in species which undergo marked s easonal body weight fluctuations. The onset of marked seasonality towa rds the end of the lower Miocene period appears to have been the ''tri gger'' for the independent evolution of bony cranial appendages in at least 7 lineages of ruminants and of pachyostotic limb bones in the Lo ranca giraffoid. Once such appendages had evolved they secondarily too k on behavioural significance. The authors also discuss the reasons fo r the onset of marked seasonality towards the end of the lower Miocene .