Life history data derived from the dental histological analysis of Giraffa camelopardalis: Implications for the palaeohistology of extinct giraffids

The analysis of incremental marks in the enamel, dentine and cementum of extant and extinct species provides important information about the rate and pattern of tooth growth, which permits inferences about key life history traits. Traditionally, such research has mainly focused on primates, while other mammalian groups have remained relatively unexplored. In some cases, this has led to the misidentification of incremental markings and the miscalculation of dental growth parameters in non-primate taxa, which has highlighted the importance of obtaining more reliable comparative frameworks. Here, we partially fill this gap by providing a detailed analysis of the dental microstructure in the extant giraffe Giraffa camelopardalis. We specifically studied the histology of the different cusps (i.e. protoconid, metaconid, hypoconid, entoconid and hypoconulid) of two first lower molars and two third lower molars with different degree of wear to identify the different incremental markings and to calculate dental growth parameters such as daily secretion rate and enamel formation front angle for each cusp and tooth. Our results show that incremental markings in enamel were more apparent as compared to those in dentine and/or cementum and have permitted a deeper analysis of the former tissue. Enamel laminations, which had a daily periodicity, were the most common incremental lines in all teeth. Supradaily Retzius lines and subdaily cross-striations and laminations were also recognised in dental enamel, revealing multiple secretory pulses of the ameloblasts in the giraffe. Generally, values of enamel growth parameters (i.e. daily secretion rate and enamel formation front angle) obtained for the first lower molar were comparable to those reported for closely related taxa, while those calculated for the third lower molar present a higher degree of variation that may be linked to differences in general somatic rates of growth. Nevertheless, enamel growth parameters were highly variable within each tooth, suggesting caution when making general (palaeo)biological inferences from dental histology. The giraffe dentine and cementum also register incremental lines. In the dentine, most of these features were classified as daily von Ebner's lines and their counting and measurement revealed values of secretion rates that agree with those previously reported in other artiodactyls. The age calculated from the incremental lines in the dental cementum matches that deduced from dental wear, suggesting that the counting of yearly lines in this tissue is a reliable tool to estimate individual age in giraffids. This study further suggests ways to refine future analyses of dentine and cementum and sets the stage for dental palaeohistology of extinct giraffids and closely related ungulates for which life history information is still unknown.

A labeling study of dentin formation rates during crown and root growth of porcine mandibular first molars

We used fluorochrome labeling to study spatiotemporal variation of dentin apposition (DAR) and extension (DER) rates during crown and root formation of mandibular first molars from wild boar and domestic pigs. DAR was reconstructed along the course of dentinal tubules in four zones of the crown and in the upper root area. In all five zones, mean DAR increased during the first 30% to 40% of apposition, reaching highest values (22-23 μm/day) in the upper-lateral crown zone. Lowest values were recorded near the dentin-pulp interface (DPI). Typically, DARs in contemporaneously formed dentin areas were higher in more cuspally compared to more cervically/apically located zones. DER was high (>200 μm/day) in early postnatal crown dentin and then decreased markedly in cervical direction, with lowest values in the cervical crown zone. After this nadir, DER sharply increased in the upper 30% to 40% of the root extension, reaching values equaling (wild boar) or even surpassing (domestic pigs) those recorded in the upper lateral crown. After this peak, DER again decreased. While DAR did not differ markedly between wild boar and domestic pigs, the DER showed marked differences, both regarding maximum values (208.1 μm/day in wild boar, 272.2 μm/day in domestic pigs) and the timing of the root growth spurt, which occurred earlier in the domestic pigs. We consider the more rapid recruitment of secretory odontoblasts in domestic pigs (reflected by higher DER) a side effect of selection for rapid body growth during pig domestication.

Characterization of short-period and long-period incremental markings in porcine enamel and dentine-Results of a fluorochrome labelling study in wild boar and domestic pigs

Mammalian dental hard tissues exhibit incremental markings that reflect the periodic variation of appositional growth rates. In order to use these markings to characterize dental growth processes and to infer life‐history traits, an unequivocal identification of their periodicities is required. We performed a fluorochrome labelling study on forming enamel and dentine in molar teeth of wild boar and domestic pigs to establish the periodicity and temporal correspondence of incremental markings in enamel and dentine. The dominant incremental markings in enamel (laminations) and dentine (von Ebner lines) recorded in the pig teeth are of a daily nature. In addition, long‐period incremental markings with a periodicity of 2 days were recorded in enamel (striae of Retzius) and dentine (Andresen lines). The 2‐day growth rhythm was also expressed at the lateral crown surface, as evidenced by the pattern of perikymata. In enamel, also markings with a sub‐daily periodicity, representing an ultradian growth rhythm, were observed. Our study provides experimental evidence for the periodicity of incremental markings in porcine enamel and dentine. The findings correct previous misconceptions on incremental markings in dental hard tissues of pigs and other ungulates that had led to erroneous conclusions regarding crown formation parameters.

Assessment of physiological disturbances during pre- and early postnatal development based on microscopic analysis of human deciduous teeth from the Late Epipaleolithic site of Shubayqa 1 (Jordan)

OBJECTIVES

To study pre- and early postnatal tooth formation and to analyze the effects of physiological disturbances on enamel and dentin formation in deciduous teeth of infants from the Late Epipaleolithic (Natufian) site Shubayqa 1.

MATERIALS AND METHODS

Ten deciduous teeth from six infants (ages at death between 21 and 239 days) were analyzed by light and scanning electron microscopy.

RESULTS

Marked prism cross-striations and an abnormal wavy course of the prisms were recorded in pre- and postnatal enamel of all analyzed teeth. Single or multiple accentuated incremental lines were observed in prenatal enamel of nine teeth and in postnatal enamel of eight teeth. Accentuated Andresen lines and broader zones exhibiting an enhanced calcospheritic pattern were recorded in the pre- and postnatally formed dentin of nine teeth.

DISCUSSION

The structural abnormalities in the pre- and postnatally formed enamel of the infants are considered indicative of chronic stress that negatively affected the activity of secretory ameloblasts. The structural aberrations in pre- and postnatal dentin denote that odontoblasts were also affected by this stress. The presence of single or multiple accentuated incremental lines in pre- and postnatal enamel is interpreted as reflecting (short-term) impacts of higher intensity superimposed on the chronic stress. Our findings suggest compromised maternal health affecting the late fetus and compromised health in newborns. Although limited by the small number of analyzed individuals, the present study contributes to the knowledge of maternal and early infant health conditions in Late Epipaleolithic populations.