Anterior ossicone variability in Decennatherium rex Ríos, et al. 2017 (Late Miocene, Iberian Peninsula)

Abstract

The recovery of a new partial cranium of Decennatherium rex Ríos et al. 2017 bearing two anterior and two posterior ossicones from the Late Miocene deposits of the site Batallones-10 (MN-10, Cerro de los Batallones, Madrid Basin) sheds light on the complex variability of the cranial appendages of these extinct giraffids. The special features of the anterior ossicones of BAT10’18-C6-40, each formed by two bosses and separated by a septum increase the range of morphological variability found in the anterior ossicones of giraffids. Posterior ossicone variability has already been described in several sivatherine taxa as Sivatherium maurusium (Harris, 1974) but anterior ossicone variability has never been discussed for four-ossicone taxa. This new specimen accounts for the third morphotype found in D. rex anterior ossicones. BAT10’18-C6-40 is identified as an adult D. rex male on the basis of the development of the posterior ossicones. These are large and already show the first large bump which in this taxon is always located on the middle of the dorsal surface at a similar height on the right and left ossicones which agrees with Solounias (1988) who stated that these small irregular protuberances have a somewhat fixed position, suggesting a genetic basis. This new specimen represents a new example of cranial variability in D. rex, and makes it the extinct giraffid with the largest anterior ossicone variability found so far.