title: Craniofacial modularity, character analysis, and the evolution of the premaxilla in early African hominins.
abstract: Phylogenetic analyses require evolutionarily independent characters, but there is no consensus, nor has there been a clear methodology presented on how to define character independence in a phylogenetic context, particularly within a complex morphological structure such as the skull. Following from studies of craniofacial development, we hypothesize that the premaxilla is an independent evolutionary module with two integrated characters that have traditionally been treated as independent. We test this hypothesis on a large sample of primate skulls and find evidence supporting the premaxilla as an independent module within the larger module of the palate. Additionally, our data indicate that the convexity of the nasoalveolar clivus and the contour of the alveolus are integrated within the premaxilla. We show that the palate itself is composed of two distinct modules: the FNP-derived premaxillae and the mxBA1-derived maxillae and palatines. Application of our data to early African hominin facial morphology suggests that at least three separate transitions contributed to robust facial morphology: 1) an increase in the size of the post-canine dentition housed within the maxillae and palatines, 2) modification of the premaxilla generating a concave clivus and reduced incisor alveolus, and 3) modification of the zygomatic, shifting the zygomatic root and lateral face anteriorly. These data lend support to the monophyly of Paranthropus boisei and Paranthropus robustus, and provide mounting evidence in favor of a Paranthropus clade. This study also highlights the utility of applying developmental evidence to studies of morphological evolution.
authors.affiliation: Center for the Advanced Study of Hominid Paleobiology, Department of Anthropology, George Washington University, 2110 G Street, NW, Washington DC 20052, USA; Department of Anthropology, University College London, 14 Taviton Street, London WC1H 0BW, United Kingdom. Electronic address: bav@gwu.edu.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Villmoare
authors.affiliation: Department of Anthropology, University College London, 14 Taviton Street, London WC1H 0BW, United Kingdom.
authors.forename: Christopher
authors.initials: C
authors.lastname: Dunmore
authors.affiliation: Department of Anthropology, University College London, 14 Taviton Street, London WC1H 0BW, United Kingdom.
authors.forename: Shaun
authors.initials: S
authors.lastname: Kilpatrick
authors.affiliation: Department of Anthropology, University College London, 14 Taviton Street, London WC1H 0BW, United Kingdom.
authors.forename: Nadja
authors.initials: N
authors.lastname: Oertelt
authors.affiliation: Department of Orthopaedic Surgery, UCSF, 2550 24th Street, SFGH Bldg 9, Room 346, San Francisco, CA 94110, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Depew
authors.affiliation: Department of Orthopaedic Surgery, UCSF, 2550 24th Street, SFGH Bldg 9, Room 346, San Francisco, CA 94110, USA. Electronic address: jennifer.fish@ucsf.edu.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Fish
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005145:Face / Q000033:anatomy & histology*; D005580:Fossils; D015186:Hominidae; D008437:Maxilla / Q000033:anatomy & histology*; D012886:Skull / Q000033:anatomy & histology*
keywords: Africa; Character independence; Craniofacial development; Geometric morphometrics; Hominin phylogeny; Morphological integration; Paranthropus; Plio-Pleistocene