Wild boar versus domestic pig-Deciphering of crown growth in porcine second molars

First insights into the life history of the early Miocene deer Procervulus ginsburgi from Spain

The small-sized cervid Procervulus is considered as the most basal member of the Cervidae and one of the earliest ruminants bearing antler-like appendages. The Iberian Miocene record of this stem-cervid is extensively documented and largely overlaps with the Miocene Climatic Optimum (MCO), a transient period of global warming of particular interest when comparing present and near future conditions. Despite receiving a substantial amount of attention, histological studies on Procervulus are very scarce and only limited to postcranial remains of Procervulus praelucidus from Germany (MN3). Here we focus for the first time on the dental histology of Procervulus ginsburgi from the Early Miocene Iberian site of Artesilla (MN4, 16.49 Ma), and examine its daily enamel secretion rate (DSR), enamel extension rate (EER) and crown formation time (CFT). Results reveal a brief CTF and high DSR and EER for P. ginsburgi and suggest a fast development at least early in its ontogeny. In addition, the pronounced growth rate of P. ginsburgi emerges as higher than that of the roe deer C. capreolus-documented as an r-strategist and here examined as a possible extant analog. Overall, our findings point toward a fast life history strategy for P. ginsburgi, which unexpectedly contrasts with that of the 2 million-year-older P. praelucidus from Wintershof-West, with a marked slower growth and maturation. When these results are analyzed together with other evidence, the somewhat drier and more open conditions of Artesilla as a result of the effects of the MCO seem to be the explanation for the different life history and ecology between these Procervulus species. More generally, this study illustrates that life histories within a single genus evolve in response not only to internal constraints but also to the environments, as predicted by the Life History Theory.

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.

Human-like enamel growth in Homo naledi

OBJECTIVES

A modern pattern (rate and duration) of dental development occurs relatively recently during human evolution. Given the temporal overlap of Homo naledi with the first appearance of fossil Homo sapiens in Africa, this small-bodied and small-brained hominin presents an opportunity to elucidate the evolution of enamel growth in the hominin clade. Here we conduct the first histological study of two permanent mandibular canines and one permanent maxillary first molar, representing three individuals attributed to H. naledi. We reconstruct the rate and duration of enamel growth and compare these findings to those reported for other fossil hominins and recent humans.

MATERIALS AND METHODS

Thin sections of each tooth were produced using standard histological methods. Daily and longer period incremental markings were measured to reconstruct enamel secretion and extension rates, Retzius periodicity, canine crown and molar cusp formation time.

RESULTS

Daily enamel secretion rates overlapped with those from recent hominins. Canine crown formation time is similar to that observed in recent Europeans but is longer than canine formation times reported for most other hominins including Australopithecus and H. neanderthalensis. The extended period of canine formation appears to be due to a relatively tall enamel crown and a sustained slow rate of enamel extension in the cervical portion of the crown. A Retzius periodicity of 11 days for the canines, and nine days for the molar, in H. naledi parallel results found in recent humans. An 11-day periodicity has not been reported for Late Pleistocene Homo (H. erectus, H. neanderthalensis) and is rarely found in Australopithecus and Paranthropus species.

DISCUSSION

Enamel growth of H. naledi is most similar to recent humans though comparative data are limited for most fossil hominin species. The high Retzius periodicity values do not follow expectations for a small-brained hominin.

Proteomic Analyses Discern the Developmental Inclusion of Albumin in Pig Enamel: A New Model for Human Enamel Hypomineralization

Excess albumin in enamel is a characteristic of the prevalent developmental dental defect known as chalky teeth or molar hypomineralization (MH). This study uses proteomic analyses of pig teeth to discern between developmental origin and post-eruptive contamination and to assess the similarity to hypomineralized human enamel. Here, the objective is to address the urgent need for an animal model to uncover the etiology of MH and to improve treatment. Porcine enamel is chalky and soft at eruption; yet, it hardens quickly to form a hard surface and then resembles human teeth with demarcated enamel opacities. Proteomic analyses of enamel from erupted teeth, serum, and saliva from pigs aged 4 (n = 3) and 8 weeks (n = 2) and human (n = 4) molars with demarcated enamel opacities show alpha-fetoprotein (AFP). AFP expression is limited to pre- and perinatal development and its presence in enamel indicates pre- or perinatal inclusion. In contrast, albumin is expressed after birth, indicating postnatal inclusion into enamel. Peptides were extracted from enamel and analyzed by nano-liquid chromatography-tandem mass spectrometry (nanoLC-MS/MS) after tryptic digestion. The mean total protein number was 337 in the enamel of all teeth with 13 different unique tryptic peptides of porcine AFP in all enamel samples but none in saliva samples. Similarities in the composition, micro-hardness, and microstructure underscore the usefulness of the porcine model to uncover the MH etiology, cellular mechanisms of albumin inclusion, and treatment for demarcated opacities.