Life history, enamel formation, and linear enamel hypoplasia in the Ceboidea

Abstract

Linear enamel hypoplasia (LEH), a developmental defect of enamel, increases in frequency from prosimian to monkey to lesser ape to great ape grades (Guatelli-Steinberg 2000 Am. J. Phys. Anthropol. 112:395-410, [2001] Evol. Anthropol. 10:138-151; Newell 1998 Ph.D. dissertation, Temple University). This taxonomic pattern in the distribution of LEH is closely related to maturation length across the primate order (Newell 1998 Ph.D. dissertation, Temple University, 2000 Am. J. Phys. Anthropol. [Suppl.] 30:236). Longer maturation periods are associated with higher LEH frequencies; they appear to provide greater opportunity for defects to form. The present study explores the relationship between maturation length and LEH frequency within the Ceboidea. Because of its prolonged period of growth, Cebus is predicted to manifest LEH at a higher frequency than the more rapidly maturing ceboid genera. To test this hypothesis, two separate researchers (E.A.N. and D.G.-S.) examined LEH in nonoverlapping museum series of ceboids. The results support the hypothesis: in 13 genera (n = 1,276), E.A.N. found that LEH frequencies ranged from 0% in Callicebus, Cebuella, and Saimiri to 20% in Cebus. D.G.-S. found similar frequencies among five genera (n = 107), from 0% in Saimiri to 32% in Cebus. Thus, the broad pattern of LEH distribution evident across major taxonomic groups of primates is repeated within the Ceboidea. We also examined a related hypothesis linking the spacing of perikymata, which is influenced by enamel extension rates (Shellis 1998 J. Hum. Evol. 35:387-400), to LEH. The most likely areas of tooth crowns to exhibit LEH in human teeth are those in which perikymata are most closely spaced (Hillson and Bond 1997 Am. J. Phys. Anthropol. 104:89-103). We hypothesized that the longer-maturing Cebus, with its elevated LEH frequency, will also exhibit more closely spaced perikymata than other ceboids. Analysis of a small microscopic subsample (n = 8) lends limited support to this second hypothesis.

Frequency and developmental timing of linear enamel hypoplasia defects in Early Archaic Texan hunter-gatherers

“…Perhaps the developmental timing of most LEH defects has less to do with extreme stress from weaning and more with the more with the acute angles formed by the Striae of Retzius relative to the enamel surface to enamel formation. It has been suggested that these acute angles make even small disruptions in enamel production are more pronounced and visible in the intermediate and occlusal thirds of the tooth (Blakey, Leslie & Reidy, 1994; Newell et al.,  2006). …”

Sex differences in anthropoid mandibular canine lateral enamel formation

“…Anthropoid species were selected on the basis of perikymata visibility. For example, perikymata are rarely preserved on the teeth of Alouatta (Newell et al, 2006) as a result of their folivorous diets, which abrade tooth surfaces. One mandibular canine from the antimeric pair of each individual was included in the study.…”

Linear enamel hypoplasia as an indicator of physiological stress in great apes: Reviewing the evidence in light of enamel growth variation

“…It is not currently known if the angles that striae of Retzius make at the enamel surface are more acute in the more folivorous primate species. Newell et al (2006) found that in folivores in particular, perikymata are often completely worn away from the enamel surface, even when most of the crown height is present. Thus, shorter periods of enamel formation do not necessarily imply more rapid rates of enamel formation and more acute Retzius angles at the enamel surface.…”

“…Previous studies, including that of Hannibal and Guatelli-Steinberg (2005), have not controlled for surface abrasion, which can obliterate minor LEH defects consisting of only a few perikymata. Newell et al (2006) found that in folivores in particular, perikymata are often completely worn away from the enamel surface, even when most of the crown height is present.…”