Faster growth corresponds with shallower linear hypoplastic defects in great ape canines

3D enamel profilometry reveals faster growth but similar stress severity in Neanderthal versus Homo sapiens teeth

“…The extent to which faster anterior tooth growth rates relate to other aspects of life history is yet to be fully understood, but recent evidence suggests that the tempo and mode of brain ontogeny, and possibly skeletal growth, differs between the two species 6 . Among extant apes, faster-growing species like mountain gorillas have shallower LEH defects, faster enamel growth (extension) rates, accelerated brain and somatic growth, and faster life history schedules [17][18][19]32,33 . However, more comparative data from extant and fossil hominoids are needed in order to further assess the relationships among these variables in hominins.…”

“…Defect and perikymata depths also follow the predicted pattern based on documented differences in enamel growth rates between different tooth positions, including when comparing matched defects across the same dentitions (Table S2). Shallower features occur in teeth with faster average enamel extension rates and thinner enamel 18 , such as in incisors vs. canines 29,34 . This inter-tooth difference is understood to be a consequence of growth-related variation in underlying enamel geometry, namely the angles that striae of Retzius make as they meet the outer enamel surface 18 .…”

“…Shallower features occur in teeth with faster average enamel extension rates and thinner enamel 18 , such as in incisors vs. canines 29,34 . This inter-tooth difference is understood to be a consequence of growth-related variation in underlying enamel geometry, namely the angles that striae of Retzius make as they meet the outer enamel surface 18 . Faster enamel extension rates are also associated with less tightly packed perikymata on the tooth surface 35 , as exhibited by Neanderthals compared to modern humans, particularly in the cervical crown 36 .…”

Molar crown formation times of fossil orangutan molars from Guangxi, China

“…The range (9–10 days) of long period line periodicity in fossil orangutans from Guangxi was narrower than the values for extant orangutans reported by Schwartz et al (2001; 8–11 days), Kelley and Schwartz (2010; 9 and 11 days), and McGrath et al (2019; 12 days in males and 9–10 days in females), and also narrower than the values for fossil orangutans reported by Smith (2016; 9–12 days, n = 15) but was same as the value for extant orangutans reported by Smith (2016; 9–10 days). The average values of long period line periodicity of fossil orangutans in this article were smaller than the values for extant and fossil orangutans reported by Smith in 2016 (extant orangutans: 9.5 days, n = 12; fossil orangutans: 10.1 days, n = 15).…”

“…Smith (2016) studied the dental development in extant and fossil orangutan, and found that the molar crown formation times of fossil and extant orangutans were longer than African apes and other fossil apes, and fossil orangutans possess larger crowns, fast daily secretion rate, and longer crown formation time than living orangutans, but show similarities in periodicities. Number of canine long period lines and crown formation times of extant orangutan in McGrath's study (McGrath et al, 2019) were in the variation range of fossil orangutans from Guangxi in the study of Hu et al (2012). Therefore, it is still not clear what and how is the difference in the extant and Pleistocene fossil orangutan and other fossil great apes due to small sample size.…”