title: Larger mammals have longer faces because of size-related constraints on skull form.
abstract: Facial length is one of the best known examples of heterochrony. Changes in the timing of facial growth have been invoked as a mechanism for the origin of our short human face from our long-faced extinct relatives. Such heterochronic changes arguably permit great evolutionary flexibility, allowing the mammalian face to be remodelled simply by modifying postnatal growth. Here we present new data that show that this mechanism is significantly constrained by adult size. Small mammals are more brachycephalic (short faced) than large ones, despite the putative independence between adult size and facial length. This pattern holds across four phenotypic lineages: antelopes, fruit bats, tree squirrels and mongooses. Despite the apparent flexibility of facial heterochrony, growth of the face is linked to absolute size and introduces what seems to be a loose but clade-wide mammalian constraint on head shape.
authors.affiliation: 1] Dipartimento di Scienze Chimiche e Geologiche, Università di Modena e Reggio Emilia, l.go S. Eufemia 19, 41121 Modena, Italy [2] Centre for Anatomical and Human Sciences, University of Hull, Cottingham Road, Hull HU6 7RX, UK [3] Center for Anatomical and Human Sciences, University of York, Heslington, York YO10 5DD, UK [4] Centre for Forensic Science, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
authors.forename: Andrea
authors.initials: A
authors.lastname: Cardini
authors.forename: P David
authors.initials: PD
authors.lastname: Polly
mesh_terms: D000818:Animals; D000866:Antelopes / Q000033:anatomy & histology / Q000502:physiology; D005075:Biological Evolution; D049628:Body Size; D002685:Chiroptera / Q000033:anatomy & histology / Q000502:physiology; D005145:Face / Q000033:anatomy & histology* / Q000502:physiology; D005260:Female; D008988:Herpestidae / Q000033:anatomy & histology / Q000502:physiology; D006801:Humans; D008297:Male; D015233:Models, Statistical; D012589:Sciuridae / Q000033:anatomy & histology / Q000502:physiology; D012886:Skull / Q000033:anatomy & histology* / Q000502:physiology; D013045:Species Specificity