Intra-specific variation of stylohyoid bones in Palaeoloxodon: A case study of Neumark-Nord 1 (Geiseltal, Sachsen-Anhalt, Germany) straight-tusked elephants

摘要

The stylohyoideum is part of the hyoid apparatus, which is situated deep in the throat of extant and extinct proboscideans, and has been regarded as a key structure in their evolution. This delicate bone has rarely been found or collected, and the stylohyoidea of the European straight-tusked elephants are little known and have been reported from very few sites. Recent findings of a quite rich sample of stylohyoidea in the Pleistocene (MIS 7 or MIS 5e) deposits of Neumark-Nord 1 (northern margin of Geiseltal, Sachsen-Anhalt, Germany) provide outstanding information on the morphology and variability of this bone. The comparison with the stylohyoideum from the late Middle Pleistocene (MIS 9) site of La Polledrara di Cecanibbio (Rome, central Italy) highlights the morphological variability of this bone in straight-tusked elephants. The shape of superior ramus ranges from very short and stout, to moderately elongated and slender. The inferior ramus, albeit generally slender, gently curved backwards, is differently angled with respect to both the superior and posterior ramus. The posterior ramus, although shorter than the inferior, is proportionally longer in the Neumark-Nord 1 specimens than in the stylohyoideum from La Polledrara. Conversely to the Japanese palaeoloxodonts, stylohyoidea of European straight-tusked elephants, including dwarf species, lack the depression on the superior-posterior rami, which appears to be exclusive to Palaeoloxodon naumanni. Despite some intra-population variability, the styloihyoidea from Neumark-Nord 1 show advanced features not only with respect to the La Polledrara specimen, but also in comparison with extant elephants and Mammuthus representatives. The variability observed in stylohyoidea of Palaeoloxodon and Mammuthus, suggests that, although the stylohyoid bone can be regarded as a key structure in the evolution of proboscideans, its taxonomical value within the Elephantini tribe needs to be more deeply scrutinized.