A histological reconstruction of dental development in the common chimpanzee,Pan troglodytes

doi:10.1006/jhev.1998.0248

Journal of Human Evolution

Volume 35, Issues 4–5, October 1998, Pages 427-448

https://doi.org/10.1006/jhev.1998.0248 Get rights and content

Abstract

Much is known about the dental development ofPancompared with that for other extant great apes. The majority of information available has concentrated either on the emergence times of teeth or on the sequence of mineralization stages of the teeth as revealed from radiographs. However, the problems of defining stages of tooth formation sufficiently accurately on radiographs are only now becoming recognized. All of the data available to date suggest the presence of a more variable picture for the timing of mineralization stages in chimpanzees than for the timing of tooth emergence. In particular, arguments persist in the literature over the time of initial mineraliz-ation and the time it takes to form each anterior tooth crown in chimpanzees. Therefore we attempt to provide a more precise chronological time scale for dental development in our closest living relative. Furthermore, we examine the sequence of molar cusp formation relative to enamel formation times related specifically to those cusps and to try to tie these data in with information from functional studies of molar crowns. Histological sections of 14 maxillary and 28 mandibular teeth from four chimpanzee (Pan troglodytes) individuals and three molar teeth from three chimpanzees of unknown origin were prepared in accordance with a well-established protocol. By combining data on short-period and long-period incremental lines (including daily secretion rates, periodicity, prism lengths and enamel thickness) in both enamel and dentine, we reconstruct times for the onset and duration of crown formation as well as construct a schedule for the pattern and timing of dental development in this one hominoid species. Interestingly, our histologically-derived data confirms that the data from radiographic studies underestimate crown formation times by the following amounts for each tooth type: I₁2·5 years, I₂3·1 years, C 1·6 years, P₃1·9 years, P₄0·1 years, M₁0·8 years, M₂1·1 years and M₃0·3 years. When combined with data on gingival emergence, it seems that chimpanzee teeth have a greatly reduced time for root growth before emergence occurs and that the major differences betweenHomo sapiensandPanlie in the first part of the root formation rather than in the total period of crown formation. Maxillary and mandibular molar functional cusps take longer to complete enamel formation to the cervix than any other cusp in that same tooth, which makes sense as these cusps are thick enamelled. These results suggest that new links can be made between developmental aspects, occlusal morphology and tooth function.

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The underlying cause for metric differences in antimeric tooth pairs is an important question for understanding dental variation. We hypothesize that localized variation in crown dimensions will be reflected in localized variation in daily enamel secretion rate.
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Patterns of permanent incisor, canine and molar development in modern humans, great apes and early fossil hominins
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Citation Excerpt :
Radiographic studies of tooth development in great apes have provided further information about the sequence of crown and root formation stages both prior to and after gingival emergence (Anemone et al., 1991; Boughner et al., 2012; Boughner et al., 2015; Dean & Wood, 1981; Winkler et al., 1991) and when the chronological age of individuals has been known it has been possible to put a time scale to radiographically defined stages of tooth development in great apes (Anemone et al., 1996; Kralick et al., 2017; Kuykendall, 1996). Besides these radiographic studies, histological studies have provided yet more evidence for the chronology of crown and root formation stages in developing great ape dentitions (Beynon et al., 1991; Dean, 2010; Kelley & Schwartz, 2010; Reid et al., 1998; Schwartz & Dean, 2001; Schwartz et al., 2006; Smith, 2016; Smith et al., 2007). An unresolved issue arising from radiographic and histological comparisons of modern human and great ape dentitions is to what degree there is overlap in the development of M1 and M2 crown formation and of M2 and M3 crown formation and whether this relates simply to differential tooth size, space in the jaws and/or jaw growth (Boughner & Dean, 2004; Simpson et al., 1992; Tompkins, 1996a, 1996b).
The objectives of this study were to quantify the variation in coincident stages of incisor, canine and molar eruption and tooth formation in modern humans and great apes and then to ask if any early fossil hominins showed a dental development pattern beyond the human range and/or clearly typical of great apes.
Four stages of eruption and 18 stages of tooth development were defined and then scored for each developing tooth on radiographs of 159 once-free-living subadult great apes and on orthopantomographs of 4091 dental patients aged 1–23 years. From original observations, and from published images of eleven early fossil hominins, we then scored formation stages of permanent incisors when M1 was at root formation stage R¼-R½ and R¾-RC.
Incisor and canine eruption/development was delayed in great apes relative to molar development when compared with humans but there was overlap in almost all anterior tooth stages observed. Molar crown initiation was generally advanced in great apes and delayed in humans but again, we observed overlap in all stages in both samples. Only two fossil hominin specimens (L.H.–3 from Laetoli, Tanzania and KNM-KP 34725 from Kanapoi, Kenya) showed delayed incisor development relative to M1 beyond any individuals observed in the human sample.
For certain tooth types, the distribution of formation stages in our samples showed evidence of generally advanced or delayed development between taxa. However, it would rarely if ever be possible to allocate an individual to one taxon or another on this basis.
Distinguishing primate taxa with enamel incremental variables
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Citation Excerpt :
Counts of Retzius lines and their periodicity can be used to determine the duration of imbricational enamel growth (Reid et al., 1998a). The duration of cuspal enamel growth can be quantified by dividing the enamel thickness by the mean cuspal DSR (Reid et al., 1998a; Smith, 2008), and the time taken to form the cuspal enamel can be combined with the imbricational enamel to estimate the duration of cusp-specific formation (e.g., protoconid, metaconid). The timing of initiation, duration, and crown completion differ across cusps, therefore calculating time for each cusp is necessary (Smith et al., 2007a; Antoine et al., 2009).
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Reconstructing diets from stable carbon isotopic signals in enamel bioapatite requires the application of a δ¹³C enamel-diet enrichment factor, or the isotopic offset between diet and enamel, which has not been empirically determined for any primate. In this study, an enamel-diet enrichment factor (ε∗_enamel-diet) of 11.8 ± 0.3‰ is calculated for chimpanzees (Pan troglodytes) at Ngogo in Kibale National Park, Uganda, based on a comprehensive isotopic assessment of previously analyzed dietary plant data and new isotopic analyses of enamel apatite. Different enamel sampling methods are evaluated to determine the potential influence of weaning on isotopic enamel values and dietary interpretations. The new chimpanzee enrichment factor and a sampling strategy that excludes teeth that formed before weaning completion are applied to all known chimpanzee δ¹³C_enamel data, either previously published or newly derived in this study, resulting in a dietary range of almost 6‰ across all chimpanzees sampled. This new chimpanzee enamel-diet enrichment factor is then used to reassess dietary reconstructions of 12 fossil hominin species whose isotopic enamel signatures have been determined. Results reveal hominin diets that are isotopically more positive than previously reconstructed, highlighting the widespread contribution of ¹³C-enriched C₄/crassulacean acid metabolism (CAM) resources in fossil hominin diets and emphasizing the broad use of these resources during human evolution. These findings stress the importance of ascertaining and employing an appropriate enrichment factor for dietary reconstructions of specific taxa as well as standardizing the sampling protocol for tooth enamel in isotopic paleodietary reconstructions.
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^☆: J. Moggi-Cecchi

^f1: Address correspondence to: Dr Gary T. Schwartz, Evolutionary Anatomy Unit, Department of Anatomy & Developmental Biology, University College London, Rockefeller Building, University Street, London WC1E 6JJ, U.K. Tel.: +11-44-171-209-6155; Fax: +11-44-171-209-0346; E-mail:[email protected]

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Regular ArticleA histological reconstruction of dental development in the common chimpanzee,Pan troglodytes☆

Abstract

Regular Article
A histological reconstruction of dental development in the common chimpanzee,Pan troglodytes☆