Biological structure and health implications from tooth size at Mission San Luis de Apalachee

This study analyzes dental metric variation to examine the biological structure of the native population at Mission San Luis de Apalachee, a late 17th century mission located in the Apalachee Province of Spanish colonial Florida. Three topics are addressed: (1) comparison of tooth sizes among adult and subadults, (2) analysis of the bio-spatial structure of skeletons within the church area, and (3) comparison of phenotypic profiles of individuals interred within coffins in the ritual nucleus of the church: the altar region. Analyses indicate that subadults had smaller average tooth sizes than adults for the posterior dentition that was particularly evident in mandibular nonpolar molars and premolars. This disparity, also documented in two other mission populations, likely represents ontogenetic stress and resulting increased mortality among those most at risk for early death. Analysis of the spatial structure of graves failed to document biological structuring by side of the aisle or by burial row, although some gross differences were evident when front, middle, and rear church burials were compared. Individuals buried in coffins within the same row were phenotypically similar to one another. However, inter-row comparisons indicated lack of phenotypic similarity among all coffin interments. These analyses suggest maintenance of kin-structured burial for elites alone within the San Luis community.     

Technical note: Artificial Resynthesis Technology for the experimental formation of dental microwear textures

Dental microwear formation on the posterior dentition is largely attributed to an organism's diet. However, some have suggested that dietary and environmental abrasives contribute more to the formation process than food, calling into question the applicability of dental microwear to the reconstruction of diet in the fossil record. Creating microwear under controlled conditions would benefit this debate, but requires accurately replicating the oral environment. This study tests the applicability of Artificial Resynthesis Technology (ART 5) to create microwear textures while mitigating the challenges of past research. ART 5 is a simulator that replicates the chewing cycle, responds to changes in food texture, and simulates the actions of the oral cavity. Surgically extracted, occluding pairs of third molars (n = 2 pairs) were used in two chewing experiments: one with dried beef and another with sand added to the dried beef. High-resolution molds were taken at 0, 50, 100, 2500, and 5000 simulated chewing cycles, which equates to approximately 1 week of chewing. Preliminary results show that ART 5 produces microwear textures. Meat alone may produce enamel prism rod exposure at 5000 cycles, although attrition cannot be ruled out. Meat with sand accelerates the wear formation process, with enamel prism rods quickly obliterated and “pit-and-scratch” microwear forming at approximately 2500 cycles. Future work with ART 5 will incorporate a more thorough experimental protocol with improved controls, pH of the simulated oral environment, and grit measurements; however, these results indicate the potential of ART 5 in untangling the complex variables of dental microwear formation.     

Dietary constraints of phytosaurian reptiles revealed by dental microwear textural analysis

Phytosaurs are a group of large, semi‐aquatic archosaurian reptiles from the Middle–Late Triassic. They have often been interpreted as carnivorous or piscivorous due to their large size, morphological similarity to extant crocodilians and preservation in fluvial, lacustrine and coastal deposits. However, these dietary hypotheses are difficult to test, meaning that phytosaur ecologies and their roles in Triassic food webs remain incompletely constrained. Here, we apply dental microwear textural analysis to the three‐dimensional sub‐micrometre scale tooth surface textures that form during food consumption to provide the first quantitative dietary constraints for five species of phytosaur. We furthermore explore the impacts of tooth position and cranial robustness on phytosaur microwear textures. We find subtle systematic texture differences between teeth from different positions along phytosaur tooth rows, which we interpret to be the result of different loading pressures experienced during food consumption, rather than functional partitioning of food processing along tooth rows. We find rougher microwear textures in morphologically robust taxa. This may be the result of seizing and processing larger prey items compared to those captured by gracile taxa, rather than dietary differences per se. We reveal relatively low dietary diversity between our study phytosaurs and that individual species show a lack of dietary specialization. Species are predominantly carnivorous and/or piscivorous, with two taxa exhibiting slight preferences for ‘harder’ invertebrates. Our results provide strong evidence for higher degrees of ecological convergence between phytosaurs and extant crocodilians than previously appreciated, furthering our understanding of the functioning and evolution of Triassic ecosystems.     

MicroWeaR: A new R package for dental microwear analysis

Mastication of dietary items with different mechanical properties leaves distinctive microscopic marks on the surface of tooth enamel. The inspection of such marks (dental microwear analysis) is informative about the dietary habitus in fossil as well as in modern species. Dental microwear analysis relies on the morphology, abundance, direction, and distribution of these microscopic marks. We present a new freely available software implementation, MicroWeaR, that, compared to traditional dental microwear tools, allows more rapid, observer error free, and inexpensive quantification and classification of all the microscopic marks (also including for the first time different subtypes of scars). Classification parameters and graphical rendering of the output are fully settable by the user. MicroWeaR includes functions to (a) sample the marks, (b) classify features into categories as pits or scratches and then into their respective subcategories (large pits, coarse scratches, etc.), (c) generate an output table with summary information, and (d) obtain a visual surface‐map where marks are highlighted. We provide a tutorial to reproduce the steps required to perform microwear analysis and to test tool functionalities. Then, we present two case studies to illustrate how MicroWeaR works. The first regards a Miocene great ape obtained from through environmental scanning electron microscope, and other a Pleistocene cervid acquired by a stereomicroscope.     

Testing hypotheses of dietary reconstruction from buccal dental microwear in Australopithecus afarensis

A recent study of occlusal microwear in Australopithecus afarensis described this species as an opportunistic dweller, living in both forested and open environments and greatly relying on fallback resources and using fewer food-processing activities than previously suggested. In the present study, analysis of buccal microwear variability in a sample of A. afarensis specimens (n = 75 teeth) showed no significant correlations with the ecological shift that took place around 3.5 Ma in Africa. These results are consistent with the occlusal microwear data available. In fact, significant correlations between buccal and occlusal microwear variables were found. However, comparison of the buccal microwear patterns showed clear similarities between A. afarensis and those hominoid species living in somewhat open environments, especially the Cameroon gorillas. A diet based mainly on succulent fruits and seasonal fallback resources would be consistent with the buccal microwear patterns observed.     

Dietary change and the effects of food preparation on microwear patterns in the Late Neolithic of abu Hureyra, northern Syria

Comparison of the microwear features created on the occlusal surfaces of molar teeth from different cultural horizons at abu Hureyra, northern Syria, indicates that the hardness of the food eaten changed profoundly after the introduction of domestic cereal grains at the beginning of the Neolithic (Neolithic 2A), and again after the introduction of pottery in Neolithic 2C times. Comparison with the microwear features on the teeth of human groups known to eat cooked food demonstrated the identity of the microwear on the abu Hureyra teeth from the pottery levels with those who had eaten cooked food. It is suggested that the evidence for an increase in the population in Neolithic 2C times is a direct consequence of changes in food preparation techniques.     

Deciduous dental microwear of prehistoric juveniles from the lower Illinois River valley

Scanning electron microscopy was used to study age-related changes in the dental microwear of 36 prehistoric juveniles ranging from 6 to 27 months of age. Juveniles from horticultural (Middle Woodland) and agricultural (Mississippian) groups were studied to allow an investigation of the impact of diet on deciduous microwear. Inclusion of both molars and incisors in the sample permitted identification of age at earliest appearance of wear and comparisons between the age-related microwear characterizing different tooth types. Data on feature frequency and enamel surface characteristics were analyzed. Microwear feature frequencies generally increase with age and/or exposure to wear. Enamel surface characteristics show consistent qualitative changes associated with both age and exposure to wear. Molars and incisors differ for such surface characteristics in a way that make biomechanical sense, given the relative bite forces characterizing these teeth. Dietary reconstruction based on deciduous microwear is complex because of the effects of both age and exposure to wear on feature frequencies and enamel surface characteristics. Nonetheless, the present analyses suggest that 1) diets differed for younger and older juveniles within each cultural group and 2) the Middle Woodland juvenile diet was both harder and more varied in physical consistency than the Mississippian juvenile diet.     

Electron-optical microscopic study of incipient dental microdamage from experimental seed and bone crushing

No living analogue exists for the hypothetical early hominid hard/tough-seed, coarse-root-eating, and bone-crushing masticatory adaptation. To investigate possible microdamage/microwear to dental enamel caused by such usage, puncture-crushing experiments were carried out on single human teeth, using an Instron compression apparatus on the following six test materials: Makapansgat Limeworks chert (e.g., taphonomy), fresh steer longbone, mongongo nuts, Grewia berries, Carob beans, and wild-onion bulbs. Pairs of extracted unworn third molars were utilized, with one tooth acting as the control. The teeth were mounted, ultrasonically cleaned, and two-stage replicas made with a vinyl polysiloxane elastomer and araldite epoxy resin. After Instron loading and materials failure (1.2–395.0 kg) the test items and the crowns were prepared for comparison with scanning electron microscopy and dispersive x-ray elemental analysis and mapping. The results revealed that although grit adhering to food item surfaces caused microscratches (0.1–1.0 μm wide) similar in appearance to those caused by opal phytoliths in grasses, the dicotyledonous seed coats per se were unable to score enamel. This suggests microscratch morphology alone may not provide a reliable indication of food type. In some cases puncture-crushing of bone and hard legumes produced a localized microfracture pattern (crazing with cracks less than or equal to 0.1–1.0 μm wide) that was readily distinguishable from the simulated taphonomic damage caused by chert fragments, suggesting analysis of enamel microfracture patterns may provide clues as to early hominid dietary adaptations.     

Nonalimentary tooth use in prehistory: an example from early Holocene in Central Sahara (Uan Muhuggiag,Tadrart Acacus,Libya)

Signs of nonalimentary tooth use were observed on the dentition of an adult male from a single burial excavated in an area close to the Uan Muhuggiag rock shelter (Tadrart Acacus, Libya), dated to more than 7800 uncalibrated years BP, that represents the most ancient human remain found in the Libyan Sahara, and provides a first glimpse of human adaptation in the early Holocene of this region. The wear pattern shows large grooves running across the occlusal surfaces of maxillary and mandibular anterior teeth and premolars. The results of macroscopic and microscopic observation, together with scanning electron microscope (SEM) examination and experimental tests, suggest that the microdamage might be due to repeated friction of vegetal fibers, probably as a consequence of basket making, net production, or mat processing. Further data are needed to allow us to distinguish among plant-oriented activities related to food acquisition (e.g., rope and net processing), food storage (e.g., basket making), or domestic handicraft (e.g., mat processing), whose implications may generate different interpretations of sexual division of labor.     

Tooth wear and dental pathology at the advent of agriculture: new evidence from the Levant

Differences in patterns of diet and subsistence through the analysis of dental pathology and tooth wear were studied in skeletal populations of Natufian hunter-gatherers (10,500-8300 BC) and Neolithic populations (8300-5500 BC, noncalibrated) from the southern Levant. 1,160 Natufians and 804 Neolithic teeth were examined for rate of attrition, caries, antemortem tooth loss, calculus, periapical lesions, and periodontal processes. While the Natufian people manifest a higher rate of dental attrition and periodontal disease (36.4% vs. 19%), Neolithic people show a higher rate of calculus. Both populations manifested low and similar rates of caries (6.4% in the Natufian vs. 6.7% in the Neolithic), periapical lesions (not over 1.5%), and antemortem tooth loss (3.7% vs. 4.5%, respectively). Molar wear pattern in the Neolithic is different than in the Natufian. The current study shows that the dental picture obtained from the two populations is multifactorial in nature, and not exclusively of dietary origin, i.e., the higher rate and unique pattern of attrition seen in the Natufian could result from a greater consumption of fibrous plants, the use of pestles and mortars (which introduce large quantities of stone-dust to the food), and/or the use of teeth as a "third hand." The two major conclusions of this study are: 1) The transition from hunting and gathering to a food-producing economy in the Levant did not promote changes in dental health, as previously believed. This generally indicates that the Natufians and Neolithic people of the Levant may have differed in their ecosystem management (i.e., gathering vs. growing grains), but not in the type of food consumed. 2) Changes in food-preparation techniques and nondietary usage of the teeth explain much of the variation in tooth condition in populations before and after the agricultural revolution.