Diversity and Evolution of Hunter-Schreger Band Configuration in Tooth Enamel of Perissodactyl Mammals (original) (raw)
Palaeontologia Electronica
The late early Miocene Béon 1 locality has yielded an abundant vertebrate fauna with more than 5,000 remains assigned to four rhinocerotid species: the stem rhinocerotine Plesiaceratherium mirallesi, the teleoceratines Prosantorhinus douvillei and Brachypotherium brachypus, and the early-diverging elasmotheriine Hispanotherium beonense. Such a profusion of closely related large herbivore species co-occurring raises questions about habitat capacity and niche partitioning. To investigate potential niche partitioning of Béon 1 rhinocerotids, we studied their ecology through texture microwear (short-term diet proxy), mesowear (long-term diet proxy), and enamel hypoplasia (environmental stress proxy). The mesowear revealed no significant differences between the species, with low scores suggesting browsing preferences, while microwear suggested subtle dietary variations. We concluded that Plesiaceratherium mirallesi and Prosantorhinus douvillei were browsers probably consuming a lot of leaves, while Brachypotherium brachypus and Hispanotherium beonense were mixedfeeders. Concerning hypoplasia, the overall prevalence was high at Béon 1, with more than 25 % of the teeth affected (216 teeth out of 832). There were, however, huge discrepancies depending on the species, tooth loci, or type of hypoplasia considered. Interestingly, H. beonense had the greatest dietary flexibility and the lowest hypoplasia prevalence (13.04 %). Both teleoceratines were very affected by hypoplasia, suggesting whether a comparable high sensitivity to stress (phylogeny) or similar habitatrelated stresses (environment). The most affected loci were p4 (48.15 %), m3 (46.81 %), and D4 (46.15 %), reflecting vulnerability periods around weaning, environmentrelated, and near birth, respectively.
Four groups of equids, ''Anchitheriinae,'' Merychippine-grade Equinae, Hipparionini, and Equini, coexisted in the middle Miocene, but only the Equini remains after 16 Myr of evolution and extinction. Each group is distinct in its occlusal enamel pattern. These patterns have been compared qualitatively but rarely quantitatively. The processes influencing the evolution of these occlusal patterns have not been thoroughly investigated with respect to phylogeny, tooth position, and climate through geologic time. We investigated Occlusal Enamel Index, a quantitative method for the analysis of the complexity of occlusal patterns. We used analyses of variance and an analysis of co-variance to test whether equid teeth increase resistive cutting area for food processing during mastication, as expressed in occlusal enamel complexity, in response to increased abrasion in their diet. Results suggest that occlusal enamel complexity was influenced by climate, phylogeny, and tooth position through time. Occlusal enamel complexity in middle Miocene to Modern horses increased as the animals experienced increased tooth abrasion and a cooling climate.
PalZ, 2018
The dentition of Cambaytherium was investigated in terms of dental wear, tooth replacement and enamel microstructure. The postcanine tooth row shows a significant wear gradient, with flattened premolars and anterior molars at a time when the last molars are only little worn. This wear gradient, which is more intensive in Cambaytherium thewissi than in Cambaytherium gracilis, and the resulting flattened occlusal surfaces, may indicate a preference for a durophagous diet. The tooth replacement (known only in C. thewissi) shows an early eruption of the permanent premolars. They are in function before the third molars are fully erupted. During the dominant phase I of the chewing cycle the jaw movement is very steep, almost orthal, with a slight mesiolingual direction and changes into a horizontal movement during phase II. The enamel microstructure shows Hunter-Schreger-bands (HSB) in the inner zone of the enamel. In some teeth the transverse orientation of the HSB is modified into a zigzag pattern, possibly an additional indicator of a durophagous diet.
Ungulate cheek teeth: developmental, functional, and evolutionary interrelations
1985
Developmental and functional factors interact in complex ways reflected in evolutionary patterns. The paper addresses problems of coronal morphogenesis, amelogenesis, food comminution and digestion, mastication, tooth eruption and wear, in order to identify functional interrelations and developmental constraints in the evolution of cheek tooth morphology. A general mechanism explaining differen tial (levelling) wear of teeth in a row is proposed. The paradox of predicted positive allometry but observed isometry of tooth size to body size is resolved by inclusion of the time dimension in the equation. The reasons for the commonness of isometric scal ing in animals are discussed. Relative width of antagonists is found to discriminate be tween functional categories in terms of the dynamics of the power stroke in mastica tion, and can be used to interpret the functional meaning of major patterns of dental morphological radiation. Enamel structure at the level of arrangement of Hunter Schreger bands is interpreted in terms of different mechanical requirements (resis tance to crack propagation) in major morphological and functional categories. It is concluded that many aptive features probably or certainly did not arise for their cur rent functions, but are one-time constraints which have become incorporated into functional systems (exaptations rather than adaptations).
Journal of Mammalian Evolution, 2005
The previously unknown enamel microstructure of a variety of Mesozoic and Paleogene mammals ranging from monotremes and docodonts to therians is described and characterized here. The novel information is used to explore the structural diversity of enamel in early mammals and to explore the impact of the new information for systematics. It is presently unclear whether enamel prisms arose several times during mammalian evolution or arose only once with several reversals to prismless structure. At least two undisputed reversions or simplifications are known-in the monotreme clade from Obdurodon to Ornithorhynchus (via Monotrematum?), and (perhaps more than once) within the clade from archaeocete to a variety of odontocete whales. Similarly, both prismatic and nonprismatic enamel is present among docodonts. Seven discrete characters showing enough morphological diversity to be of potential importance in phylogenetic reconstructions may be identified as a more appropriate summary of enamel microstructural diversity among mammaliaforms than the single character "prismatic enamel-present/absent" employed in recent matrices. Inclusion of five of these characters in the matrix of Luo et al. (2002) modifies the original topology by collapsing several nodes involving triconodonts and other nontribosphenic taxa. There is considerable support for prismatic enamel as a synapomorphy of trithelodonts plus Mammaliamorpha, and multituberculates appear to have small or "normal" sized prisms as the ancestral condition, with some (as yet) enigmatic changes to nonprismatic structure in some basal members of the group and the appearance of "gigantoprismatic" structure as an autapomorphic state of less inclusive clades. Other potential qualitative characters and the need for attaining appropriate methods to incorporate quantitative features may be important for future analyses.
Four groups of equids, "Anchitheriinae," Merychippine-grade Equinae, Hipparionini, and Equini, coexisted in the middle Miocene, and only the Equini remains after 16 million years of evolution and extinction. Each group is distinct in its occlusal enamel pattern. These patterns have been compared qualitatively but rarely quantitatively. The processes controlling the evolution of these occlusal patterns have not been thoroughly investigated with respect to phylogeny, tooth position, and climate through geologic time. I investigated two methods of quantitative analysis, Occlusal Enamel Index for shape and fractal dimensionality for complexity. I used analyses of variance and an analysis of co-variance to test hypotheses of process. Results suggest that enamel shape was controlled by phylogeny, tooth position, and climate. The lower taxonomic levels are shown to have a strong effect on complexity, suggesting behavior is driving complexity rather than overarching phylogenetic constraint.
Enamel patterns on the occlusal surfaces of equid teeth are asserted to have tribal-level differences. The most notable example compares the Equini and Hipparionini, where Equini have higher crowned teeth with less enamel-band complexity and less total occlusal enamel than Hipparionini. Whereas previous work has successfully quantified differences in enamel band shape by dividing the length of enamel band by the square root of the occlusal surface area (Occlusal Enamel Index, OEI), it was clear that OEI only partially removes the effect of body size. Because enamel band length scales allometrically, body size still has an influence on OEI, with larger individuals having relatively longer enamel bands than smaller individuals. Fractal dimensionality (D) can be scaled to any level, so we have used it to quantify occlusal enamel complexity in a way that allows us to get at an accurate representation of the relationship between complexity and body size. To test the hypothesis of tribal-level complexity differences between Equini and Hipparionini, we digitally traced a sample of 98 teeth, one tooth per individual; 31 Hipparionini and 67 Equini. We restricted our sampling to the P3-M2 to reduce the effect of tooth position. After calculating the D of these teeth with the fractal box method which uses the number of boxes of various sizes to calculate the D of a line, we performed a t-test on the individual values of D for each specimen, comparing the means between the two tribes, and a phylogenetically informed generalized least squares regression (PGLS) for each tribe with occlusal surface area as the independent variable and D as the dependent variable. The slopes of both PGLS analyses were compared using a t-test to determine if the same linear relationship existed between the two tribes. The t-test between tribes was significant (p < 0.0001), suggesting different D populations for each lineage. The PGLS for Hipparionini was a positive but not significant (p = 0.4912) relationship between D and occlusal surface area, but the relationship for Equini was significantly negative (p = 0.0177). λ was 0 for both tests, indicating no important phylogenetic signal is present in the relationship between these two characters, thus the PGLS collapses down to a non-phylogenetic generalized least squares (GLS) model. The t-test comparing the slopes of the regressions was not significant, indicating that the two lineages could have the same relationship between D and occlusal surface area. Our results suggest that the two tribes have the same negative relationship between D and occlusal surface area but the Hipparionini are offset to higher values than the Equini. This offset reflects the divergence between the two lineages since their last common ancestor and may have constrained their ability to respond to environmental change over the Neogene, leading to the differential survival of the Equini. How to cite this article Famoso and Davis. (2016), On the relationship between enamel band complexity and occlusal surface area in
Are Hypsodonty and Occlusal Enamel Complexity Evolutionarily Correlated in Ungulates?
Journal of Mammalian Evolution, 2015
The spread of grasslands and cooling climate in the Miocene contributed to an increasingly abrasive diet for ungulates. This increase in abrasiveness is proposed to select for both hypsodonty and increasing complexity of occlusal enamel bands. If these traits evolved in response to strong selection to resist tooth wear while feeding in grassland habitats, we might expect them to have evolved in a correlated fashion. If, on the other hand, there was a developmental or physiological constraint, or if selection was not strong on total enamel production, we would expect species to have evolved one or the other of these traits at a time, producing an uncorrelated, or even inversely correlated, pattern of trait evolution. To test these hypotheses, we examined the Occlusal Enamel Index (OEI) and Hypsodonty Index (HI) of 773 ungulate teeth. We tested the dependence of OEI on HI for the orders Artiodactyla and Perissodactyla using phylogenetic generalized least squares regression (PGLS). The two traits are not significantly correlated in the PGLS, for Artiodactyla and Perissodactyla. Despite their physical proximity, close functional utility, and conventional correlation, our results reject the hypothesis that HI and OEI are evolutionarily linked in these lineages, suggesting that selection to resist tooth wear was not so strong as to drive the overall evolutionary trajectory of both these traits at the same time.