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The significance of enamel thickness in the teeth of Alligator mississippiensis and its diversity among crocodyliforms: Enamel thickness in crocodyliforms

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... Extant crocodylian teeth are thecodont, cone-shaped and unicuspid (Dauphin & Williams, 2008). They vary in shape and sharpness from the anterior to pos terior in both the upper and lower jaws (Sellers et al., 2019). Tooth size and shape may also differ with sex and age. ...
... A functional tooth would include a hollow root extending from the crown. We are unable to provide an ontogenetic age estimate for this individual, though the size of the crown (see measurements below) implies it was an adult (Sellers et al., 2019). ...
... The crocodile tooth from the Pliocene Chinchilla Sand shows microstructures that resemble features reported for other extant and extinct crocodylians -enamel is relatively thin, incremental and likely aprismatic, with incremental dentine consisting of numerous tubules (Enax et al., 2013;Sander, 2000;Sellers et al., 2019). The average width of enamel band in our specimen is in the range of measurements (100-200 μm) reported for C. porosus (Enax et al., 2013) and Alligator mississippiensis (Sato et al., 1990). ...
... This is not, however, an easy task, due to the high heterodoncy shown by archosaurs. As seen in extant Alligator mississipiensis, archosaur teeth vary in morphology along the tooth row and during ontogeny even for the same tooth position (Sellers et al. 2019). Overall, having evolved from a ziphodont ancestor, most spinosaur teeth still present some degree of lateral compression and mesial curvature, most notably in lateral teeth. ...
... Internally, the construction and ontogeny of the tooth are different for dinosaurs and crocodylomorphs. In a recent work, Sellers et al. (2019) found that the enamel of crocodyliforms is, in most cases, thicker than that of dinosaurs in relation to the tooth size. In the case of Theropoda, it is especially noteworthy that the large, bone-crushing teeth of tyrannosaurids have an enamel layer as thick as the much smaller teeth of the durophagous alligatorid Allognathosuchus. ...
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Four isolated archosaur teeth from Las Hoyas (Cuenca province, Central Spain), one ziphodont and three conical, are described. Current evidence suggests their identification as a carcharodontosaurid akin to Concavenator and a putative spinosaurid theropods, and to a goniopholidid neosuchian based on data from morphology and morphometry, and internal structure. The results of Bivariant Discriminant, and Cluster analysis places the conical teeth between the morphology of Spinosauridae, Pholidosauridae and Goniopholididae, but closer to the last one. However, the internal structure suggests distinct dinosaurian and crocodilian construction, and is proposed as a valid, diagnostic feature possibly able to discriminate between the highly convergent teeth of these lineages. Thus, these findings might represent the second carcharodontosaurid and the first spinosaurid specimens from La Huérguina Fm. (late Barremian, 127 MYA, Lower Cretaceous), and suggest the presence of larger sized crocodilian species than those currently identified by complete skeletal remains.
... These plants are abundant in the global Jurassic record and likely were important components of the diet of high browser sauropods like Bagualia due to their high energy content (Hummel et al., 2008). Teeth with a spoon shape and thick enamel, as described in Bagualia (Pol et al., 2020), allowed the intake of this type of hard vegetation (Upchurch and Barret, 2000;Sellers et al., 2019). Bagualia represents the first record of the axial characters that enabled the Eusauropoda to be a successful group in the face of the new environmental conditions that arose after the Pliensbachian-Toarcian crisis in Patagonia, which possibly helped them to become the dominant group of herbivores in Middle Jurassic ecosystems worldwide. ...
... The resampling magnitude was 7/5x for the Varanus model. The percentage of enamel in extant animals is often computed based on a volumetric approach, where the relative enamel thickness is the 3D average enamel thickness divided by the cube root of the volume of dentine (Olejniczak et al., 2008;Sellers et al., 2019). Here we used planar measurements of enamel as a proxy for enamel thickness, since the planar measurement approach enabled us to resample to the required resolution right away. ...
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Palaeontologists often use finite element analyses, in which forces propagate through objects with specific material properties, to investigate feeding biomechanics. Teeth are usually modeled with uniform properties (all bone or all enamel). In reality, most teeth are composed of pulp, dentine, andenamel. We tested how simplified teeth compare to more realistic models using mandible models of three reptiles. For each, we created models representing enamel thicknesses found in extant taxa, as well as simplified models (bone, dentine or enamel). Our results suggest that general comparisons of stress distribution among distantly related taxa do not require representation of dental tissues, as there was no noticeable effect on heatmap representations of stress. However, we find that representation of dental tissues does impact estimates of bite force and this impact is taxon specific. Thus, as other have shown, the detail necessary in a biomechanical model relates to the questions being examined.
... Our raw measurement of CAH and tooth height include both enamel and dentin thickness. The enamel layer in extant crocodylians is thin (Enax et al., 2013) and scales nearly isometrically (Schmiegelow, Sellers & Holliday, 2016;Sellers, Schmiegelow & Holliday, 2019), with minor changes related to tooth shape (intrafamilial heterodonty) (Osborn, 1975;Kieser et al., 1993;Gignac, 2010;D'Amore et al., 2019) as opposed to size. To calculate CAH as a measure of dentin only, we subtracted the average enamel thickness value, and used this corrected CAH value in our calculations. ...
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Dietary habits in extinct species cannot be directly observed; thus, in the absence of extraordinary evidence, they must be reconstructed with a combination of morphological proxies. Such proxies often include information on dental organization and function such as tooth formation time and tooth replacement rate. In extinct organisms, tooth formation times and tooth replacement rate are calculated, in part via extrapolation of the space between incremental lines in dental tissues representing daily growth (von Ebner Line Increment Width; VEIW). However, to date, little work has been conducted testing assumptions about the primary data underpinning these calculations, specifically, the potential impact of differential sampling and data extrapolation protocols. To address this, we tested a variety of intradental, intramandibular, and ontogentic sampling effects on calculations of mean VEIW, tooth formation times, and replacement rates using histological sections and CT reconstructions of a growth series of three specimens of the extant archosaurian Alligator mississippiensis. We find transect position within the tooth and transect orientation with respect to von Ebner lines to have the greatest impact on calculations of mean VEIW—a maximum number of VEIW measurements should be made as near to the central axis (CA) as possible. Measuring in regions away from the central axis can reduce mean VEIW by up to 36%, causing inflated calculations of tooth formation time. We find little demonstrable impact to calculations of mean VEIW from the practice of subsampling along a transect, or from using mean VEIW derived from one portion of the dentition to extrapolate for other regions of the dentition. Subsampling along transects contributes only minor variations in mean VEIW (
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New imaging and biomechanical approaches have heralded a renaissance in our understanding of crocodylian anatomy. Here, we review a series of approaches in the preparation, imaging, and functional analysis of the jaw muscles of crocodylians. Iodine‐contrast microCT approaches are enabling new insights into the anatomy of muscles, nerves, and other soft tissues of embryonic as well as adult specimens of alligators. These imaging data and other muscle modeling methods offer increased accuracy of muscle sizes and attachments without destructive methods like dissection. 3D modeling approaches and imaging data together now enable us to see and reconstruct 3D muscle architecture which then allows us to estimate 3D muscle resultants, but also measurements of pennation in ways not seen before. These methods have already revealed new information on the ontogeny, diversity, and function of jaw muscles and the heads of alligators and other crocodylians. Such approaches will lead to enhanced and accurate analyses of form, function, and evolution of crocodylians, their fossil ancestors and vertebrates in general.
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A single tetrapod tooth has been recovered from the Upper Jurassic Talbragar Fossil Fish Bed of New South Wales, Australia. It is the first evidence of a tetrapod to have been found at this locality in over 130 years of excavation. The tooth is likely from a temnospondyl amphibian. Herein, we document the discovery, discuss the potential explanations as to why tetrapod remains are so scarce from this locality and provide hypotheses as to how this tooth came to be preserved. Lachlan J. Hart [L.Hart@unsw.edu.au], Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences (BEES), University of New South Wales, Kensington, New South Wales 2052, Australia; Australian Museum Research Institute, 1 William Street, Sydney, New South Wales 2010, Australia; Matthew R. McCurry [Matthew.McCurry@Australian.Museum], Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences (BEES), University of New South Wales, Kensington, New South Wales 2052, Australia; Australian Museum Research Institute, 1 William Street, Sydney, New South Wales 2010, Australia; Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA; Michael Frese [Michael.Frese@canberra.edu.au], Faculty of Science and Technology, University of Canberra, Canberra, Australian Capital Territory 2601, Australia; Australian Museum Research Institute, 1 William Street, Sydney, New South Wales 2010, Australia; Thomas J. Peachey [Thomas.Peachey@Australian.Museum], Australian Museum Research Institute, 1 William Street, Sydney, New South Wales 2010, Australia; Jochen Brocks [Jochen.Brocks@anu.edu.au], Research School of Earth Sciences, The Australian National University, Australian Capital Territory 2601, Australia.
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Heterodont dentition sometimes including multicuspid crowns appeared in numerous fossil forms through all main lineages of the Crocodyliformes. Teeth in these complex dentitions frequently bear wear facets that are exclusive indicators of tooth–tooth occlusion. Besides, dental features, specialisations of the jaw apparatus, jaw adductors and mandibular movement can be recognised, all reflecting a high variability of jaw mechanism and of intraoral food processing. Comparative study of these features revealed four main types of jaw mechanism, some of which evolved independently in several lineages of Crocodyliformes. Isognathous orthal jaw closure (precise jaw joint, rough wear facets) is characteristic for heterodont protosuchians and all forms possessing crushing posterior teeth. Proal movement (protractive powerstroke) occurred independently in Malawisuchus and Chimaerasuchus is supported by the antagonistic, vertically oriented carinae. Developed external adductors are the main indicators of palinal movement (retractive powerstroke) that evolved at least two times in various South American taxa. The fourth type (in Iharkutosuchus) is characterised by lateromedial mandibular rotation supported by extensive horizontal wear facets. This evolutionary scenario resembles that of the masticatory system of mammals and suggests that the ecological roles of some mammalian groups in North America and Asia were occupied in Western Gondwana by highly specialised crocodyliforms.http://www.zoobank.org/urn:lsid:zoobank.org:pub:D6CE962F-2B38-47F8-BD4B-B9E035917F20
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Molar enamel is thicker among frugivorous extant Old World monkeys and apes than among their folivorous close relatives. Furthermore, species that have the thickest molar enamel reportedly eat fruits, seeds, and nuts that are so hard that they cannot be broken by their sympatric thinner-enameled relatives. Species with relatively thick enamel show no tendency toward a terrestrial feeding pattern. Members of the Ramapithecinae, the stock which probably gave rise to Pliocene-Recent hominids, had very thick molar enamel. This suggests that they ate hard seeds, nuts, and fruits previously available only to arboreal rodents and forest-floor pigs. There is no reason to believe that these anatomical features had to evolve in non-rain-forest environments, as others have argued.
Article
Mammalian teeth show a considerable complexity in microstructure. The arrangement of decussated enamel prisms gives enamel the functional advantages of a composite material. This prism arrangement is genetically determined and altered throughout evolution. As the evolution of hypsodont molars implies a drastic alteration of the loading conditions and of the stress pattern in teeth, it can be expected that enamel microstructure is also affected. Equids and several other ungulates evolved the modified radial enamel in adaptation to these altered conditions. As the fossil record for the phylogeny of horses is available in considerable completeness, this group is suitable to investigate the correlation of morphologic evolution and the evolution of enamel microstructure. Indeed, the same patterns of evolutionary change previously known from the morphologic level can also be demonstrated on the microstructural level. Modified radial enamel is characterized by the orientation of the inter-prismatic crystallites, the thickness of the interprismatic matrix, and the radial prism arrangement. The three characters appear step by step in a phylogenetic context. First the orientation of the interprismatic crystallites perpendicular to the prisms occurs in Mesohippus. In Parahippus, all three characters appear together for the first time, but the location and the very small amount of modified radial enamel suggests that a function in strengthening the enamel is very unlikely. In all hypsodont equids, modified radial enamel appears in a considerable amount and obviously is an adaptation to the altered stress distribution in hypsodont molars. Hypohippus shows a further combination of two of the characters; the crystallite orientation and the thickness of the interprismatic matrix is similar to the modified radial enamel, but the prisms are not arranged in radial rows but in decussating layers. Because the characters of modified radial enamel appear stepwise and preadaptively, and because some other lineages that lack the development of these characters did not evolve hypsodont molars, it seems probable that enamel microstructure influences the potential for macromorphologic phylogenetic change.
The bizarre crocodyliform Simosuchus clarki shares several derived cranial characteristics with basal notosuchian taxa. In the original phylogenetic analysis assessing placement of Simosuchus among other crocodyliforms, it was recovered as a basal notosuchian. Additional preparation of the holotype skull and postcranium, and discovery of additional specimens, provides new information on the suite of morphologies in this notosuchian. Morphological analysis of all available material of S. clarki yields 60 autapomorphies distributed across the skeleton. To provide an updated test of the phylogeny of Notosuchia and placement of Simosuchus within the clade, we added seven new characters and expanded taxon sampling to include recently described notosuchians. A phylogenetic analysis of 301 characters and 84 crocodyliforms supports the position of Simosuchus as sister to Libycosuchus, more derived than Araripesuchus and Uruguaysuchus, and basal to other ziphosuchian notosuchians. We did not recover an Anatosuchus + Simosuchus clade, nor a monophyletic Araripesuchus, but did recover a peirosaurid clade including Peirosaurus, Lomasuchus, Uberabasuchus, and Hamadasuchus (but not Stolokrosaurus). We also found weak support for inclusion of Anatosuchus, Araripesuchus, Peirosauridae, and Mahajangasuchidae within Notosuchia and therefore for the conclusion that all basal mesoeucrocodylians from Gondwana, with the exception of Stolokrosuchus, are notosuchians. The results of this analysis demonstrate that basal mesoeucrocodylian relationships are currently in a state of flux and the need for caution in naming higher-level taxa until a more stable consensus topology is achieved. Similarly, large gaps in the notosuchian record render inconclusive the biogeographic origins of Simosuchus and the clade it represents on Madagascar.
The detailed cranial osteology of Iharkutosuchus makadii is described herein. Comparisons with advanced neosuchians and basal eusuchians confirm that Iharkutosuchus is a basal eusuchian, which shares several features with the Barremian Hylaeochampsa vectiana. On the basis of in situ and isolated teeth, the complete, heterodont dentition of Iharkutosuchus is reconstructed. The dentition is composed of incisiviform, premolariform and molariform teeth with an increase in the number of cusps on the crowns posteriorly. Iharkutosuchus has robust and wide ectopterygoids and extremely large and wide posterior teeth also supposed in Hylaeochampsa. Additional special characters include the closed supratemporal fenestrae and the long, posteriorly extended process of the maxilla. These features are related to the food processing of this small-bodied animal. Iharkutosuchus confirms the hypothesis that the advanced caudal migration of the secondary palate is a consequence of the structural reinforcement of the skull.
Article
The teeth of every primate, living and extinct, are covered by a hard, durable layer of enamel. This is not unique: Almost all mammals have enamel-covered teeth. In addition, all of the variations in enamel structure that occur in primates are also found in other groups of mammals. Nevertheless, the very complexity of enamel and the variation we see in it on the teeth of living and fossil primates raise questions about its evolutionary significance. Is the complex structure of primate enamel adaptive? What, if anything, does enamel structure tell us about primate phylogeny? To answer these questions, we need to look more closely at the characteristics of prismatic enamel in primates and at the distribution of those characteristics, both in relation to our knowledge of primate dental function and feeding ecology and from a phylogenetic perspective.
Article
Temporal changes in the carbon and oxygen isotopic composition of an animal are an environmental and behavioral input signal that is recorded into the enamel of developing teeth. In this paper, we evaluate changes in phosphorus content and density along the axial lengths of three developing ungulate teeth to illustrate the protracted nature of mineral accumulation in a volume of developing enamel. The least mature enamel in these teeth contains by volume about 25% of the mineral mass of mature enamel, and the remaining 75% of the mineral accumulates during maturation. Using data from one of these teeth (a Hippopotamus amphibius canine), we develop a model for teeth growing at constant rate that describes how an input signal is recorded into tooth enamel. The model accounts for both the temporal and spatial patterns of amelogenesis (enamel formation) and the sampling geometry. The model shows that input signal attenuation occurs as a result of time-averaging during amelogenesis when the maturation interval is long compared to the duration of features in the input signal. Sampling does not induce significant attenuation, provided that the sampling interval is several times shorter than the maturation interval. We present a detailed δ13C and δ18O record for the H. amphibius canine and suggest possible input isotope signals that may have given rise to the measured isotope signal.
Article
Iharkutosuchus makadii is a basal eusuchian crocodylian with multicusped teeth discovered from the Upper Cretaceous of Hungary. Skull and dentition morphology indicates an active food processing for this crocodylian. First among crocodylians, a combination of different analyses, including cranial adductor muscle reconstruction, tooth wear pattern, and enamel microstructure studies, is applied here to support this hypothesis. Data provide unambiguous evidence for significant dental occlusion that was a result of a unique, transverse mandibular movement. Reconstruction of the jaw adductors demonstrates strong muscles responsible for slow but active jaw closure as the motor of transverse jaw movement; nevertheless muscles producing rapid jaw closure were reduced. Macrowear orientations show a dominantly transverse movement of the mandibles completed by a slight anteroposterior component. Along with quadrate morphology, macrowear further indicates that this motion was accomplished by alternate rotation of the mandibles about the quadrate condyles. Dental morphology and wear patterns suggest two types of power stroke: a slicing-crushing stroke associated dominantly with anterior tooth-food-tooth contact (with a low degree of transverse mandibular movement) during in the early stage of mastication, and a grinding stroke with significant posterior tooth-tooth contact and a dynamic transverse movement occurring later. The patterns of microwear show a diverse diet for Iharkutosuchus including both soft and hard items. This is also supported by the microstructure of the thick, wrinkled enamel built up mostly by poorly developed columnar units. Based on wear patterns, ontogenetic variation in feeding habits of Iharkutosuchus is also recognized.
Article
Recent evolutionary interpretations of Hominoidea have postulated functional relationships between tooth form, diet and masticatory biomechanics. A major consideration is the durability of the tooth under certain dietary conditions. Teeth with low cusps and thicker enamel are able to withstand heavy mastication of abrasive food bolus for a longer period. When comparisons are made between species of higher primates the variables of tooth size, cusp morphology, and enamel thickness appear to be related but until now no systematic analysis has been made to determine the functional relevance of several dental dimensions. This study provides data gained from comparisons of dentition of nine species of primates. Histological sections were made of the post canine teeth and 21 dimensions were compared. The relevant dimensions identified serve to withstand dental wear. The distribution of thicker enamel corresponded to the observed wear planes. Humans had thicker enamel than pongids while the macaque had the thinnest. These preliminary results tend to support theories which explain low, thick, enameled cusps in hominids.
Article
Maxillary and mandibular incisors of mice aged 5 wk were sectioned and ground along various planes, acidetched and observed by scanning electron microscopy (SEM). The general design of the enamel structure resembled rat incisor enamel with an uniserial lamellar pattern of prisms in the inner enamel and incisally directed parallel prisms in the outer enamel. The centrolabial thickness of the enamel was about 60 microns in the maxillary and about 95 microns in the mandibular incisor. The angle between prism rows and enamel-dentine junction was about 70 degrees in the maxillary and about 45 degrees in the mandibular incisor, while the angle of decussation, which increased from the enamel-dentine junction towards the outer enamel, was 50-95 degrees and 30-80 degrees respectively. The angle between outer enamel prisms and enamel surface was about 12 degrees in the maxillary and 5-15 degrees in the mandibular incisor. The outer 1/2-1/3 of the outer enamel contained iron and was more acid-resistant than the rest of the enamel. The superficial 3-5 microns was prismless with a Fe/Ca ratio of about 25/75 in the maxillary and about 10/90 in the mandibular incisor. The latter concentration of iron was insufficient to give visible pigmentation to the enamel. The extreme mesial and lateral enamel was neither typical of inner nor of outer enamel. Assuming that the length of the zone of enamel secretion is half the corresponding length in the rat, it could be calculated that ameloblasts in mouse mandibular incisors produce enamel at a rate of about 6 microns per day, about half the corresponding rate in the rat. In spite of this, the mouse mandibular incisor has a relatively thick layer of enamel, since the ameloblasts spend a relatively long time in the zone of enamel secretion due to a fairly slow eruption rate.
Article
Gross and microscopic examinations were undertaken on 46 cheek (molar and premolar) and 4 incisor equine teeth that were fractured, or sectioned either with a lathe or diamond saw. Specimens were examined without treatment, after decalcification or acid etching, utilising light, and scanning and transmission electron microscopy. In some horses, the occlusal surface of the teeth were covered with an organic pellicle. The occlusal surface of the underlying equine enamel contained different wear patterns, including polished areas, local fractures, wedge-shaped pits, striations and depressions. Occlusal dentine showed depressions whose depth was related to its occlusal surface area, with larger surface areas having deeper depressions. The thickness of equine enamel varied greatly throughout its folds in the transverse plane, and was thickest in areas where folds were parallel to the long axis of the maxilla and mandible. Enamel thickness remained constant in the longitudinal plane (throughout the length of the tooth). Peripheral enamel was more deeply infolded in lower than in upper cheek teeth and this appeared to compensate for the absence of infundibula (deep, cup-like enamel indentations that are partially filled with cement) in the lower cheek teeth.
Article
Many living primates that feed on hard food have been observed to have thick-enameled molars. Among platyrrhine primates, members of the tribe Pitheciini (Cacajao, Chiropotes, and Pithecia) are the most specialized seed and nut predators, and Cebus apella also includes exceptionally hard foods in its diet. To examine the hypothesized relationship between thick enamel and hard-object feeding, we sectioned small samples of molars from the platyrrhine primates Aotus trivergatus, Ateles paniscus, Callicebus moloch, Cebus apella, Cacajao calvus, Chiropotes satanas, Pithecia monachus, and Pithecia pithecia. We measured relative enamel thickness and examined enamel microstructure, paying special attention to the development of prism decussation and its optical manifestation, Hunter-Schreger Bands (HSB). Cebus apella has thick enamel with well-defined but sinuous HSB overlain by a substantial layer of radial prisms. Aotus and Callicebus have thin enamel consisting primarily of radial enamel with no HSB, Ateles has thin enamel with moderately developed HSB and an outer layer of radial prisms, and the thin enamel of the pitheciins (Cacajao, Chiropotes, and Pithecia) has extremely well-defined HSB. Among platyrrhines, two groups that feed on hard objects process these hard foods in different ways. Cebus apella masticates hard and brittle seeds with its thick-enameled cheek teeth. Pitheciin sclerocarpic foragers open hard husks with their canines but chew relatively soft and pliable seeds with their molars. These results reveal that thick enamel per se is not a prerequisite for hard object feeding. The Miocene hominoid Kenyapithecus may have included hard objects in its diet, but its thick-enameled molars indicate that its feeding adaptations differed from those of the pitheciins. The morphology of both the anterior and posterior dentition, including enamel thickness and microstructure, should be taken into consideration when inferring the dietary regime of fossil species.
Article
The tooth enamel microstructure of all the dinosaur taxa that are adequately represented in the American Museum of Natural History collections were analyzed using scanning electron microscopy. This study aims to determine whether or not better sampling within a major nonmammalian amniote (hereafter referred to descriptively as "reptile") clade will unearth phylogenetic patterns in enamel microstructure in addition to those dictated by tooth function. While interest in reptile enamel microstructure has increased in the past few years, intensive sampling focused on just one monophyletic reptile clade was not previously implemented. This study reveals that phylogenetic constraints play a larger role in shaping enamel microstructure in reptiles than previously thought. Within many monophyletic dinosaur clades the combination of enamel types and enamel features within a tooth-the schmelzmuster-is the same in all the taxa due to their common ancestry, and their schmelzmusters are diagnostic of their respective clades. While distantly related taxa with similar teeth and diets have similar schmelzmusters due to functional constraints, phylogenetic constraints keep those schmelzmusters distinct from one another. An interesting finding of this analysis is that the enamel complexity of a taxon does not necessarily coincide with the position of the taxon on a phylogenetic tree; more derived taxa do not necessarily have more derived enamel and more primitive taxa do not necessarily have more primitive enamel.
Article
Molar enamel thickness has played an important role in the taxonomic, phylogenetic, and dietary assessments of fossil primate teeth for nearly 90 years. Despite the frequency with which enamel thickness is discussed in paleoanthropological discourse, methods used to attain information about enamel thickness are destructive and record information from only a single plane of section. Such semidestructive planar methods limit sample sizes and ignore dimensional data that may be culled from the entire length of a tooth. In light of recently developed techniques to investigate enamel thickness in 3D and the frequent use of enamel thickness in dietary and phylogenetic interpretations of living and fossil primates, the study presented here aims to produce and make available to other researchers a database of 3D enamel thickness measurements of primate molars (n=182 molars). The 3D enamel thickness measurements reported here generally agree with 2D studies. Hominoids show a broad range of relative enamel thicknesses, and cercopithecoids have relatively thicker enamel than ceboids, which in turn have relatively thicker enamel than strepsirrhine primates, on average. Past studies performed using 2D sections appear to have accurately diagnosed the 3D relative enamel thickness condition in great apes and humans: Gorilla has the relatively thinnest enamel, Pan has relatively thinner enamel than Pongo, and Homo has the relatively thickest enamel. Although the data set presented here has some taxonomic gaps, it may serve as a useful reference for researchers investigating enamel thickness in fossil taxa and studies of primate gnathic biology.
Article
The considerable variation in shape, size, structure and properties of the enamel cap covering mammalian teeth is a topic of great evolutionary interest. No existing theories explain how such variations might be fit for the purpose of breaking food particles down. Borrowing from engineering materials science, we use principles of fracture and deformation of solids to provide a quantitative account of how mammalian enamel may be adapted to diet. Particular attention is paid to mammals that feed on 'hard objects' such as seeds and dry fruits, the outer casings of which appear to have evolved structures with properties similar to those of enamel. These foods are important in the diets of some primates, and have been heavily implicated as a key factor in the evolutionary history of the hominin clade. As a tissue with intrinsic weakness yet exceptional durability, enamel could be especially useful as a dietary indicator for extinct taxa.
Thick molar enamel and increased crown height as an adaptive signature of neogene aridification amongst kangaroos
  • A Couzens
Couzens, A. (2016). Thick molar enamel and increased crown height as an adaptive signature of neogene aridification amongst kangaroos. Society of Vertebrate Paleontology abstract.
Note on a new species of the Eocene crocodilian Allognathosuchus, A. wartheni
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Allognathosuchus mooki, A New Crocodile from the Puerco Formation
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Simpson, G.G.( 1930). Allognathosuchus mooki, A New Crocodile from the Puerco Formation. Am. Museum Novit. 445,1-16.