49 - The Levator Process: Identification of a Novel Neanderthal Autapomorphy

Poster Board Number: 49
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Abstract Body : The Neanderthal cranium has long been studied for distinct phylogenetic traits. However, relatively few have focused on the region of the temporal bone surrounding the osseous Eustachian tube orifice (OEO) and origins of soft palate muscles. Here, we describe a novel osseous structure, the levator process (LP), that likely acted as an attachment for the levator veli palatini muscle (LVP). Our sample consisted of three Neanderthal adults (La Chapelle aux Saints 1, Grotta Guattari 1, Forbes Quarry 1), one pre-Neanderthal adult (Atapuerca 4) and one juvenile Neanderthal specimen (Pech de l’Azé 1) as they exhibited the least amount of temporal bone damage. These were contrasted against a contemporary human growth series (n=417), one mid-Pleistocene African hominin (Kabwe 1), one Asian Homo erectus (Ngandong 7) and one gracile australopith (Sterkfontein 5). La Chapelle aux Saints 1 exhibited the best-preserved LP, including a prominent fossa on its anteromedial surface serving as an LVP origin. Guattari 1 exhibited apical damage to the LP but it could still be visualized whereas Forbes Quarry 1 exhibited the most damage with the process still remaining recognizable. Being a gracile female, it also possessed the smallest relative LP, suggesting a less hypertrophied LVP. Presence of the LP in Pech de l’Azé 1 (a young child) suggests that this trait appears early in Neanderthal development. Its LP also appears too damaged to distinguish the fossa of LVP origin but the process is still clearly present as in Forbes Quarry 1. The same condition is also exhibited in Atapuerca 4 which, despite some apical damage, still has a relatively intact LP. Among modern humans, there is no LP but instead a phlange of bone spanning between the sphenoid spine and inferior lip of the OEO which is sometimes bulbous. This appears to result from an absence of a large entoglenoid process and the presence of an enlarged sphenoid spine whose junction with the petrous temporal is in close proximity to the OEO. A similar condition can be found in Kabwe 1 which has a bulbous inferior lip of the OEO continuing in a thick ridge toward the carotid foramen rim, but no identifiable LP. Neanderthals, by contrast, all possess an enlarged entoglenoid tubercle and a sphenopetrous junction well anterior to the position of the OEO. Thus, the development of a LP among Neanderthals may be related functionally to the evolution of their distinct entoglenoid tubercle morphology. This overall anatomical configuration would have increased the area of LVP attachment, potentially necessitated by the anterior tilt of their hard palate and choanae. Results suggest that both anatomically modern humans and Neanderthals exhibited an autapomorphic suite of features as both differed from earlier fossils (Ngandong 7 and Sterkfontein 5) in their lack of a large infratubal process. This latter feature suggests an ape-like configuration of a lateral origin of the tensor veli palatini muscle relative to the LVP. Thus, the common ancestor of anatomically modern humans and Neanderthals was probably characterized by a loss of the infratubal process but possessed neither the sphenoid spine of humans nor the enlarged entoglenoid tubercle of Neanderthals. Improved understanding of morphological differences such as these among modern humans and Neanderthals may assist in reconstruction of both our phylogeny and the evolution of speech and respiratory abilities among humans and Neanderthals.