Lingual incisor traits in modern hominoids and an assessment of their utility for fossil hominoid taxonomy

Abstract

The morphology of the anterior dentition has received scant attention for purposes of taxonomic discrimination. Recently, however, lingual incisor morphology was used in differentiating several Miocene ape species and genera. This paper assesses the utility of this morphology for taxonomic discrimination by examining the nature and patterns of variation in lingual incisor morphology in extensive samples of modern chimpanzees, gorillas, orangutans, and gibbons. This paper documents discrete morphological traits on the lingual side of incisors. Trait frequencies are used in univariate and multivariate analyses to examine the apportionment of variation in species, subspecies, and populations. A correlation between lingual incisor traits, tooth dimensions, and sex attempts to determine if such factors affect the manifestation of traits. Finally, the findings are applied to understanding patterns of variation in the Miocene hominids. The study demonstrates that: 1) lingual incisor morphology differs substantially between the hylobatids and great apes; 2) variation in incisor traits is high within species, and most of it is found within local populations; and 3) incisor traits do not correlate significantly with incisor dimensions or sex. Species and to some extent subspecies of extant hominoids can be differentiated statistically using lingual incisor traits, but the frequency of traits such as continuous or discontinuous cingulum, or the presence or absence of pillars, differentiates them. Given this pattern of variation, I argue that it is necessary to assume and document similar patterns of variation in Miocene apes before incisor morphology is used for differentiating taxa.

Early evidence of the genus Homo in East Asia

“…2), have previously been described and attributed to Homo (Sinanthropus) erectus yuanmouensis (Hu,1973;Wu and Poirier,1995). These incisors lack a cervical cingulum, large expansion of the cervical half of the lingual surface, and the overall splaying or rounded arch typical of the I 1 crowns of extant great apes (Pilbrow, 2006). Their dimensions also fall outside the 95% confidence intervals determined from the large sample of I 1 crowns known for Lufengpithecus, a late Miocene ape from southwest China, including older sediments in the Yuanmou Basin (Wood and Xu, 1991;Liu et al, 2000).…”

A unique Middle Miocene European hominoid and the origins of the great ape and human clade

“…Furthermore, Pierolapithecus catalaunicus shares with G. alpani the highly distinctive spatulate central incisor with a lingual pillar continuous with the lingual cingulum. This is a feature shared with later, more derived, Eurasian hominoids (26)(27). This contradictory evidence makes it difficult to determine which of the 2 kenyapithecin genera is more closely related to hominids, while it clearly stresses the role of homoplasy in hominoid evolution.…”

Upper incisor morphology of the Late Miocene hominoid <i>Ouranopithecus macedoniensis</i> from Axios Valley (Macedonia, Greece)

“…The studied modern hominoids belong to Gorilla gorilla (3 individuals), Pan troglodytes (7 individuals), and Pongo pygmeaus (5 individuals) and are all mentioned in the text with their generic name. The nomenclature for the lingual traits of incisors 122 120 131 126 -----% H/MD 91 88 82 77 -- follows that of Pilbrow (2006) (Figure 1). Following this author, the incisors preserving lingual traits are divided in three dental wear stages: 1, a thin dentine strip exposed along the incisal margin; 2, a thick dentine strip exposed along the incisal margin; and 3, dentine starts to extend onto the lingual surface.…”

“…Begun et al, 1990;Begun, 1992;Andrews et al, 1996;Ward et al, 1999), although they were some doubts regarding their taxonomic and/or phylogenetic significance (Harrison, 1991;Ribot et al, 1996). On the other hand the incisor's lingual morphology in the modern great apes shows great variation (Kelley et al, 1995;Benefit and McCrossin, 2000;Pilbrow, 2006). According to the last author the incisors of the extant great apes (gorillas, chimpanzees, orang-utans) have a high variation in their lingual morphology within the species and local populations, though it is possible in some populations to separate statistically species or subspecies based on the frequency of the lingual incisor traits (Pilbrow, 2006).…”

“…On the other hand the incisor's lingual morphology in the modern great apes shows great variation (Kelley et al, 1995;Benefit and McCrossin, 2000;Pilbrow, 2006). According to the last author the incisors of the extant great apes (gorillas, chimpanzees, orang-utans) have a high variation in their lingual morphology within the species and local populations, though it is possible in some populations to separate statistically species or subspecies based on the frequency of the lingual incisor traits (Pilbrow, 2006). In some recent publications, the incisor's lingual morphology has been used for taxonomic separation of some Miocene hominoid samples (e.g.…”