Theropod Teeth Research Articles

Evolution of high tooth replacement rates in theropod dinosaurs.

Tooth replacement rate is an important contributor to feeding ecology for polyphyodont animals. Dinosaurs exhibit a wide range of tooth replacement rates, mirroring their diverse craniofacial specializations, but little is known about broad-scale allometric or evolutionary patterns within the group. In the current broad but sparse dinosaurian sample, only three non-avian theropod tooth replacement rates have been estimated. We estimated tooth formation and replacement rates in three additional non-avian theropod dinosaurs, the derived latest Cretaceous abelisaurid Majungasaurus and the more generalized Late Jurassic Allosaurus and Ceratosaurus. We created the largest dental histological and CT dataset for any theropod dinosaur, sectioning and scanning over a dozen toothed elements of Majungasaurus and several additional elements from the other two genera. Using this large sample, we created models of tooth formation time that allow for theropod replacement rates to be estimated non-destructively. In contrast to previous results for theropods, we found high tooth replacement rates in all three genera, with Allosaurus and Ceratosaurus rates of ~100 days and 56 days for Majungasaurus. The latter rate is on par with those of derived herbivorous dinosaurs including some neosauropods, hadrosaurids, and ceratopsians. This elevated rate may be a response to high rates of tooth wear in Majungasaurus. Within Dinosauria, there is no relationship between body mass and tooth replacement rate and no trends in replacement rate over time. Rather, tooth replacement rate is clade-specific, with elevated rates in abelisaurids and diplodocoids and lower rates in coelurosaurs.

Taxonomic identification of isolated theropod teeth: The case of the shed tooth crown associated with Aerosteon (Theropoda: Megaraptora) and the dentition of Abelisauridae

Shed teeth are usually the most abundant theropod material on a dinosaur fossil site and are constantly reported in the literature. Although new quantitative techniques have emerged to identify isolated theropod teeth with better accuracy, they remain difficult to assign to a certain family-level or genus-level taxon because of the presence of rampant homoplasy in their morphology and the lack of thorough descriptions. Here we test three methods to investigate the phylogenetic position of a tooth previously considered to be part of the holotype of the megaraptoran Aerosteon riocoloradensis (MCNA-PV-3137): a cladistic analysis performed on a dentition-based data matrix scored across 105 theropod species and using a backbone topology as constraint, as well as discriminant and cluster analyses conducted on a dataset of non-avian theropod crown measurements. Even though the cladistic technique appears to be the most reliable method to investigate the phylogenetic affinities of theropod teeth, we recommend using the three techniques conjointly to corroborate the identification of isolated dental material. The results of the cladistic and discriminant analyses support the assignment of the tooth associated with MCNA-PV-3137 to an abelisaurid theropod. It should therefore be excluded from the holotype of Aerosteon. A thorough description of the dental anatomy of Abelisauridae is also provided. The current study is the first to evaluate different methodological tools to identify isolated theropod teeth. With the added detailed description of the dental anatomy of Abelisauridae, it will also assist future authors to investigate the systematic palaeontology of isolated theropod teeth with more confidence.

New records of theropods from the latest Cretaceous of New Jersey and the Maastrichtian Appalachian fauna.

The faunal changes that occurred in the few million years before the Cretaceous–Palaeogene extinction are of much interest to vertebrate palaeontologists. Western North America preserves arguably the best fossil record from this time, whereas terrestrial vertebrate fossils from the eastern portion of the continent are usually limited to isolated, eroded postcranial remains. Examination of fragmentary specimens from the American east, which was isolated for the majority of the Cretaceous as the landmass Appalachia, is nonetheless important for better understanding dinosaur diversity at the end of the Mesozoic. Here, I report on two theropod teeth from the Mount Laurel Formation, a lower-middle Maastrichtian unit from northeastern North America. One of these preserves in detail the structure of the outer enamel and resembles the dentition of the tyrannosauroid Dryptosaurus aquilunguis among latest Cretaceous forms in being heavily mediolaterally compressed and showing many moderately developed enamel crenulations. Along with previously reported tyrannosauroid material from the Mt Laurel and overlying Cretaceous units, this fossil supports the presence of non-tyrannosaurid tyrannosauroids in the Campanian–Maastrichtian of eastern North America and provides evidence for the hypothesis that the area was still home to relictual vertebrates through the end of the Mesozoic. The other tooth is assignable to a dromaeosaurid and represents both the youngest occurrence of a non-avian maniraptoran in eastern North America and the first from the Maastrichtian reported east of the Mississippi. This tooth, which belonged to a 3–4 m dromaeosaurid based on size comparisons with the teeth of taxa for which skeletons are known, increases the diversity of the Maastrichtian dinosaur fauna of Appalachia. Along with previously reported dromaeosaurid teeth, the Mt Laurel specimen supports the presence of mid-sized to large dromaeosaurids in eastern North America throughout the Cretaceous.

Theropod teeth from the Lower Cretaceous Ilek Formation of Western Siberia, Russia

A sample of 136 isolated theropod teeth from nine vertebrate localities within the Lower Cretaceous (Barremian-Aptian) Ilek Formation in West Siberia, Russia, can be separated into five dental morphotypes referred to five оr six theropod taxa based on morphological characters. The Morphotype A includes small to large lateral teeth with relatively large distal denticles and smaller mesial denticles. Some of these teeth can be attributed to the Dromaeosauridae, while other teeth may belong to a basal member of the Tyrannosauroidea. The distinctly smaller lateral teeth referred to the Morphotype B are similar with Morphotype A in most respects but differ in the lack of mesial denticles and mesial carina, or having a lingually displaced mesial carina. These teeth may belong to juvenile individuals of the same dromaeosaurid taxon. The teeth belonging to Morphotype C also lack mesial denticles and differ from Morphotype B by a flattened area on the lingual side, which is also often present on the labial side. These teeth may belong to either Troodontidae or Microraptorinae, or to both groups. The mesial and lateral teeth of Morphotype E are characterized by unserrated mesial and distal carinae. These teeth most likely belong to a distinct taxon of Troodontidae with unserrated dentition. The teeth of the Morphotype D include mesial teeth with the mesial carina displaced lingually at various extent and denticles present on both carinae. The teeth with moderately displaced lingual carina can be referred to the same dromaeosaurid taxon, which lateral teeth represented by Morphotype A. The teeth with more displaced mesial carina and deeply U-shaped basal crown section belong to an indeterminate Tyrannosauroidea.

Diet preferences and climate inferred from oxygen and carbon isotopes of tooth enamel of Tarbosaurus bataar (Nemegt Formation, Upper Cretaceous, Mongolia)

Stable isotopes of oxygen and carbon of tooth enamel are increasingly being used as tracers to study palaeoecology and the diet preferences of fossil vertebrates. We serially sampled tooth enamel carbonate along the growth axes of five Early Maastrichtian carnivorous dinosaur teeth (Tarbosaurus bataar tyrannosaurid) from the Nemegt Formation, Mongolia, in order to identify seasonal climatic variations and determine the diet of this apex predator. Additional bulk samples of dentine, bone, and surrounding sediment were analyzed in order to exclude diagenetic obfuscation of the isotopic record. Enamel samples of potential prey species for dietary studies were also analyzed. In the case of the largest specimens, the sampled teeth usually recorded annual cycles ranging between two-thirds and a full year. Fluctuations in δ18O values in tyrannosaurid teeth suggest seasonality (high annual temperatures with distinct precipitation/humidity maxima during summer months) with mean annual temperatures (MAT) ten degrees higher than those of present-day Mongolia. The seasonal pattern of δ18O shows similarities to that of the modern-day Shijiazhuang Global Network of Isotopes in Precipitation station, northern China, and suggests that the Nemegt biota flourished when exposed to a cool temperate monsoon-influenced climate. Herbivore and carnivore carbon isotopes (δ13C) values from tooth enamel imply the presence of a woodland ecosystem dominated by coniferous trees such as Araucariaceae, and are consistent with the hypothesis that large sauropods and hadrosaurids were the preferred prey of Tarbosaurus. Mean annual precipitation (MAP), based on the relationship between modern-day C3 gymnosperms and local average MAP, is estimated at 775–835 mm/yr. These results show that large theropod teeth can serve as valuable archives for palaeoenvironmental studies.

New theropod dinosaur teeth from the Middle Jurassic of the Isle of Skye, Scotland

The Middle Jurassic is a largely mysterious interval in dinosaur evolution, as few fossils of this age are known worldwide. In recent years, the Isle of Skye has yielded a substantial record of trackways, and a more limited inventory of body fossils, that indicate a diverse fauna of Middle Jurassic dinosaurs living in and around lagoons and deltas. Comparatively little is known about the predators in these faunas (particularly theropod dinosaurs), as their fossils are among the rarest discoveries. We here report two new isolated theropod teeth, from the Valtos Sandstone Formation and Lealt Shale Formation of Skye, which we visualized and measured using high-resolution x-ray computed microtomographic scanning (µCT) and identified via statistical and phylogenetic analyses of a large comparative dental dataset. We argue that these teeth most likely represent at least two theropod species – one small-bodied and the other large-bodied – which likely belonged to one or several clades of basal avetheropods (ceratosaurs, megalosauroids, or allosauroids). These groups, which were diversifying during the Middle Jurassic and would become dominant in the Late Jurassic, filled various niches in the food chain of Skye, probably both on land and in the lagoons. Supplementary material : Character lists, datasets, and measurements are available at https://doi.org/10.6084/m9.figshare.c.4452533

Spinosaurid teeth from the Lower Cretaceous of Ko Kut, eastern Thailand

Isolated theropod dinosaur teeth from Ko Kut (Kut Island) in eastern Thailand are referred to an indeterminate spinosaurid on the basis of their morphology and ornamentation. On the basis of other spinosaurid occurrences in Thailand and other parts of Asia, they support the attribution of the fossil-bearing beds on Ko Kut to the Lower Cretaceous rather than the Jurassic. The lack of ornithischian remains in the Ko Kut faunal assemblage suggests that it is coeval with the Sao Khua Formation (Barremian) of NE Thailand.

A new microvertebrate assemblage from the Mussentuchit Member, Cedar Mountain Formation: insights into the paleobiodiversity and paleobiogeography of early Late Cretaceous ecosystems in western North America.

The vertebrate fauna of the Late Cretaceous Mussentuchit Member of the Cedar Mountain Formation has been studied for nearly three decades, yet the fossil-rich unit continues to produce new information about life in western North America approximately 97 million years ago. Here we report on the composition of the Cliffs of Insanity (COI) microvertebrate locality, a newly sampled site containing perhaps one of the densest concentrations of microvertebrate fossils yet discovered in the Mussentuchit Member. The COI locality preserves osteichthyan, lissamphibian, testudinatan, mesoeucrocodylian, dinosaurian, metatherian, and trace fossil remains and is among the most taxonomically rich microvertebrate localities in the Mussentuchit Member. To better refine taxonomic identifications of isolated theropod dinosaur teeth, we used quantitative analyses of taxonomically comprehensive databases of theropod tooth measurements, adding new data on theropod tooth morphodiversity in this poorly understood interval. We further provide the first descriptions of tyrannosauroid premaxillary teeth and document the earliest North American record of adocid remains, extending the appearance of this ancestrally Asian clade by 5 million years in western North America and supporting studies of pre-Cenomaninan Laurasian faunal exchange across Beringia. The overabundance of mesoeucrocodylian remains at the COI locality produces a comparatively low measure of relative biodiversity when compared to other microvertebrate sites in the Mussentuchit Member using both raw and subsampling methods. Much more microvertebrate research is necessary to understand the roles of changing ecology and taphonomy that may be linked to transgression of the Western Interior Seaway or microhabitat variation.

Puncture-and-Pull Biomechanics in the Teeth of Predatory Coelurosaurian Dinosaurs

The teeth of putatively carnivorous dinosaurs are often blade-shaped with well-defined serrated cutting edges (Figure1). These ziphodont teeth are often easily differentiated based on the morphology and density of the denticles [1, 2]. A tearing function has been proposed for theropod denticles in general [3], but the functional significance of denticle phenotypic variation has received less attention. In particular, the unusual hooked denticles found in troodontids suggest a different feeding strategy or diet compared to other small theropods. We used a two-pronged approach to investigate the function of denticle shape variation across theropods with both congruent body shapes and sizes (e.g., dromaeosaurids versus troodontids) and highly disparate body shapes and sizes (e.g., troodontids versus tyrannosaurids), using microwear and finite element analyses (Figure1). We found that many toothed coelurosaurian theropods employed a puncture-and-pull feeding movement, in which parallel scratches form while biting down into prey and oblique scratches form as the head is pulled backward with the jaws closed. In finite element simulations, theropod teeth had the lowest stresses when bite forces were aligned with the oblique family of microwear scratches. Different denticle morphologies performed differently under a variety of simulated biting angles: Dromaeosaurus and Saurornitholestes were well-adapted for handling struggling prey, whereas troodontid teeth were more likely to fail at non-optimal bite angles. Troodontids may have favored softer, smaller, or immobile prey.

TYRANNOSAUR CANNIBALISM: A CASE OF A TOOTH-TRACED TYRANNOSAURID BONE IN THE LANCE FORMATION (MAASTRICHTIAN), WYOMING

A recently discovered tyrannosaurid metatarsal IV (SWAU HRS13997) from the uppermost Cretaceous (Maastrichtian) Lance Formation is heavily marked with several long grooves on its cortical surface, concentrated on the bone's distal end. At least 10 separate grooves of varying width are present, which we interpret to be scores made by theropod teeth. In addition, the tooth ichnospecies Knethichnus parallelum is present at the end of the distal-most groove. Knethichnus parallelum is caused by denticles of a serrated tooth dragging along the surface of the bone. Through comparing the groove widths in the Knethichnus parallelum to denticle widths on Lance Formation theropod teeth, we conclude that the bite was from a Tyrannosaurus rex. The shape, location, and orientation of the scores suggest that they are feeding traces. The osteohistology of SWAU HRS13997 suggests that it came from a young animal, based on evidence that it was still rapidly growing at time of death. The tooth traces on SWAU HRS13997 are strong evidence for tyrannosaurid cannibalism—a large Tyrannosaurus feeding on a young Tyrannosaurus.

New dinosaur remains from the Quiricó Formation, Sanfranciscana Basin (Lower Cretaceous), Southwestern Brazil

The vertebrate fossil record from the Quiricó Formation, Sanfranciscana Basin (Lower Cretaceous), is scarce, but the remains yet found are of great importance for the understanding of the paleobiogeographic and biogeographic processes that took place during the initial stages that led to the opening of the Atlantic Ocean. In this work, new occurrences of sauropod dinosaur bones and theropod teeth from the Barremian–Aptian Quiricó Formation, collected in Campo Azul and Olhos D'Água, State of Minas Gerais, Brazil, are described. The fossils comprise isolated bones of sauropod dinosaurs, such as fragments of sauropod vertebrae, and isolated theropod teeth, both preserved in lacustrine siltstones and associated sandstones. The anatomical features of the sauropod bones suggest that they can be assigned to Rebbachisauridae and the morphological analysis of the isolated theropod teeth placed them within Abelisauridae and Carcharodontosauridae. This suggests that during the Early Cretaceous, the dinosaurian fauna from the southeastern Brazil was more closely related to African faunas than to other South-American ones.

Evolutionary implications of tooth attachment versus tooth implantation: A case study using dinosaur, crocodilian, and mammal teeth

ABSTRACTTooth attachment and implantation are two classical descriptors of dental anatomy. Tooth attachment distinguishes between teeth that are either fused to the jaw by bone, or suspended within a socket by a periodontal ligament. Tooth implantation describes the geometry of this attachment and has been broadly divided into acrodonty, pleurodonty, and thecodonty. Among extant amniotes, only mammals and crocodilians are considered truly thecodont, because they possess a complex attachment system that includes a periodontal ligament and true tooth sockets. These two amniote groups diverged from a common ancestor over 300 million years ago and are thought to have evolved thecodonty independently. This view has recently come under a great deal of scrutiny with the discovery of complex tooth attachment systems, including the presence of a ligamentous tooth attachment in numerous non-mammalian, non-crocodilian amniotes. This has spurred debate and inconsistencies over the conventional usage of tooth attachment and implantation categories and their evolutionary significance. We provide a comparative histological approach for describing tooth attachment and implantation in an exemplary, traditionally thecodont taxonomic group: the non-avian dinosaurs. The comparisons between theropod, hadrosaurid, and ceratopsid teeth show that all dinosaurs have ligamentous tooth attachments composed of identical dental tissues to those in mammals and crocodilians, but they show a diverse array of tooth attachment geometries, replacement modes, and bone architectures supporting the dentition. The methodology we follow allows researchers to tease apart phylogenetically and functionally significant features of tooth attachment and implantation that could be used in future studies.Citation for this article: LeBlanc, A. R. H., K. S. Brink, T. M. Cullen, and R. R. Reisz. 2017. Evolutionary implications of tooth attachment versus tooth implantation: a case study using dinosaur, crocodilian, and mammal teeth. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1354006.

Isolated theropod teeth associated with sauropod remains from El Oterillo II (Early Cretaceous) site of Salas de los Infantes (Burgos, Spain)

The relationship between dinosaur carcasses and isolated theropod teeth is well known in the fossil record. The usual explanation is that theropod dinosaurs fed on the herbivore carcass. Other evidence is provided by theropod tooth marks on the surface of herbivore skeletal remains. In this work we study isolated theropod teeth and the tooth marks in evidence on the bones of the sauropod from El Oterillo II (Salas de los Infantes, Spain, Lower Cretaceous). Theropod and crocodylomorph teeth have been found in relationship with the sauropod carcass. The fossils lie on channel lag deposits composed of sandstones with quartzite gravel. Thirty theropod teeth have been studied using qualitative features, statistical and cladistics analysis in addition to the tooth marks present on the vertebrae. The morphology of the theropod teeth has revealed greater palaeobiodiversity in these faunas than previously known, including baryonychine spinosaurids, basal tetanurans, dromaeosaurids and a singular coelurosaurian. The presence of tooth marks and isolated theropod teeth in close relationship with the sauropod carcass could also provide new evidence of the scavenging of theropod dinosaurs on the sauropods of this age and location. Six morphotypes of theropod teeth have been distinguished; the combination of basal and derived tetanurans is congruent with the known record from the Early Cretaceous of the Iberian Peninsula. The most probable explanation for the association of isolated theropod teeth and sauropod remains is the scavenging of the carcass by theropod dinosaurs.

Analysis of diversity, stratigraphic and geographical distribution of isolated theropod teeth from the Upper Jurassic of the Lusitanian Basin, Portugal

Isolated theropod teeth are abundant in the Upper Jurassic of the Lusitanian Basin and are an important source to reconstruct the diversity of this group as well as its geographic and stratigraphic distribution. However, reliably identification of isolated teeth is complex, especially for those morphotypes related to poorly represented groups. Herein a set of isolated theropod teeth collected in different sites from the Upper Jurassic of the Lusitanian Basin ranging from the late Kimmeridgian to late Tithonian in age are described and discussed. These teeth were grouped in seventeen distinct morphotypes based first on morphology and comparative anatomy. Multivariate statistical analyses were performed in order to assign each morphotype to a certain taxon. The current analysis shows the presence of several groups of theropods such as Ceratosaurus, Torvosaurus, and Allosaurus beside morphotypes identified as belonging to indeterminate Megalosauroidea and Allosauroidea and morphotypes tentatively assigned to Tyrannosauroidea, Dromaeosauridae, and Richardoestesia. This faunal composition, namely the presence of a non-megalosaurid megalosauroid possibly related to the piatnitzkysaurid Marshosaurus, indicates a higher diversity of theropods in the Late Jurassic of the Lusitanian Basin than previously known, based on more complete specimens. Results obtained from this analysis partially agree with previous studies of other collections with isolated theropod teeth from the Upper Jurassic of Portugal such as those of the Guimarota coal mine. However, the presence of velociraptorine dromaeosaurids, compsognathids, and troodontids reported from this site could not be confirmed in the sample herein analyzed. This analysis also indicates a great similarity of the theropod faunas from the Late Jurassic of the Lusitanian Basin and other European chronocorrelative localities such as those from Spain and Germany.

First occurrence of tyrannosaurid theropods from the Corral de Enmedio Formation (Upper Cretaceous) Sonora, México

The Cabullona Basin in the state of Sonora, Mexico is becoming recognized due to its diversity of southern Laramidian continental vertebrates, especially dinosaurs. In this study we describe and analyze three theropod teeth (ERNO specimens) that were found isolated and surface collected in the Corral de Enmedio Formation (Cabullona Group, Upper Cretaceous). The three specimens possess similar morphological characteristics that match the ones present in Late Cretaceous Laramidian tyrannosaurids, so they were referred to the Tyrannosauridae, probably belonging to a new unknown taxon. The implementation of statistical and cladistic analyses corroborated their taxonomical assignment. ERNO specimens correspond to the first record of tyrannosaurid dinosaurs in the basal Corral de Enmedio Formation, extending the stratigraphic distribution of these dinosaurs in the Cabullona Basin. Although tyrannosaurids have been previously described in the Cabullona Basin, the ERNO specimens of the Corral de Enmedio Formation seem to be different, because they possess more labiolingually compressed teeth. This new evidence could indicate a higher taxonomic diversity of the tyrannosaurid theropods that were present in the Cabullona Basin, adding more information to the Tyrannosauridae diversification on one of the most southern Laramidian regions during the Late Cretaceous.

Multivariate and Cladistic Analyses of Isolated Teeth Reveal Sympatry of Theropod Dinosaurs in the Late Jurassic of Northern Germany.

Remains of theropod dinosaurs are very rare in Northern Germany because the area was repeatedly submerged by a shallow epicontinental sea during the Mesozoic. Here, 80 Late Jurassic theropod teeth are described of which the majority were collected over decades from marine carbonates in nowadays abandoned and backfilled quarries of the 19th century. Eighteen different morphotypes (A—R) could be distinguished and 3D models based on micro-CT scans of the best examples of all morphotypes are included as supplements. The teeth were identified with the assistance of discriminant function analysis and cladistic analysis based on updated datamatrices. The results show that a large variety of theropod groups were present in the Late Jurassic of northern Germany. Identified specimens comprise basal Tyrannosauroidea, as well as Allosauroidea, Megalosauroidea cf. Marshosaurus, Megalosauridae cf. Torvosaurus and probably Ceratosauria. The formerly reported presence of Dromaeosauridae in the Late Jurassic of northern Germany could not be confirmed. Some teeth of this study resemble specimens described as pertaining to Carcharodontosauria (morphotype A) and Abelisauridae (morphotype K). This interpretation is however, not supported by discriminant function analysis and cladistic analysis. Two smaller morphotypes (N and Q) differ only in some probably size-related characteristics from larger morphotypes (B and C) and could well represent juveniles of adult specimens. The similarity of the northern German theropods with groups from contemporaneous localities suggests faunal exchange via land-connections in the Late Jurassic between Germany, Portugal and North America.

PALEOECOLOGY OF THE GADDIS SITE IN THE UPPER CRETACEOUS AGUJA FORMATION, TERLINGUA, TEXAS

Diverse faunas at the Gaddis site near Terlingua, Texas are present at four stratigraphic levels along a hill in the Upper Cretaceous Aguja Formation providing a rich fossil record of the transition from an aquatic environment to dry land while recording exceptional events such as predation and wildfires. Given evidence for minimal transport the microvertebrates, macrovertebrates, coprolites, and plants may be reliably utilized for paleoecological analysis. Paleoenvironments shift upsection from nearshore marine, through tidal channel, to swamp, and, finally, to well-vegetated dry land. The faunas change from a basal layer of oysters with shark teeth to a microvertebrate assemblage just above logs with Teredolites borings and pristine leaves. Above the microvertebrates are diverse macrovertebrates including numerous dinosaurs associated with leaves, logs, and scrambling vines. The macrovertebrate layer is a rich assemblage of herbivorous and carnivorous dinosaurs, crocodiles, turtles, and rare pterosaurs. Several skeletal elements exhibit signs of predation that include punctures and gouges that precisely match crocodile and theropod teeth also recovered at the site. Abundant plant material that includes charred vines and logs is likely evidence of wildfires having ranged across the area. The preponderance of young dinosaur remains may support a wildfire scenario. An exposed surface with 24 coprolites, two hadrosaur vertebrae, logs, and in situ stumps caps the section. The larger coprolites are likely dinosaurian. Most contain plant materials while one contains a bone fragments suggesting the presence of herbivorous and carnivorous dinosaurs on the same surface, an occurrence that echoes herbivore/carnivore interactions in the underlying bonebed.

PRELIMINARY INVESTIGATION OF SEASONAL PATTERNS RECORDED IN THE OXYGEN ISOTOPE COMPOSITIONS OF THEROPOD DINOSAUR TOOTH ENAMEL

Abstract Oxygen isotope compositions of tooth enamel increments in theropod dinosaurs are investigated as potential proxies of climate seasonality. Six teeth of large carnivorous theropods collected from four Cretaceous formations deposited under contrasted climates have been sampled. These teeth have been analyzed for the oxygen isotope compositions of their apatite phosphate (δ18Op) through incremental sampling performed along the major growth axis. Significant fluctuations in oxygen isotope compositions along the growth axis of each tooth are observed and interpreted as reflecting seasonality in ingested local surface water δ18Ow values. Fluctuations in δ18Op values of theropod teeth from the Aptian of Thailand and Cenomanian of Morocco vary similarly to meteoric water δ18Omw values occurring today in sub-tropical regions subjected to large seasonal amounts of precipitations. A dinosaur tooth recovered from the more inland and mid-latitude Nemegt Formation of Mongolia shows a seasonal pattern similar t...

The dentary of Australovenator wintonensis (Theropoda, Megaraptoridae); implications for megaraptorid dentition.

Megaraptorid theropods were an enigmatic group of medium-sized predatory dinosaurs, infamous for the hypertrophied claw on the first manual digit. Megaraptorid dentition is largely restricted to isolated teeth found in association with skeletal parts; however, the in situ maxillary dentition of Megaraptor was recently described. A newly discovered right dentary pertaining to the Australovenator holotype preserves in situ dentition, permitting unambiguous characterisation of the dentary tooth morphology. The new jaw is virtually complete, with an overall elongate, shallow profile, and fifteen visible in situ teeth at varying stages of eruption. In situ teeth confirm Australovenator exhibited modest pseudoheterodonty, recurved lateral teeth with a serrate distal carina and reduced mesial carina, similar to other megaraptorids. Australovenator also combines of figure-of-eight basal cross-section with a lanceolate shape due to the presence of labial and lingual depressions and the lingual twist of the distal carina. Computed tomography and three-dimensional imagery provided superior characterisation of the dentary morphology and enabled an accurate reconstruction to a pre-fossilised state. The newly established dental morphology also afforded re-evaluation of isolated theropod teeth discovered at the Australovenator holotype locality and from several additional Winton Formation localities. The isolated Winton teeth are qualitatively and quantitatively similar to the in situ dentary teeth of Australovenator, but are also morphometrically similar to Abelisauridae, Allosauridae, Coelophysoidea, Megalosauridae and basal Tyrannosauroidea. Qualitative characters, however, clearly distinguish the teeth of Australovenator and the isolated Winton teeth from all other theropods. Evidence from teeth suggests megaraptorids were the dominant predators in the Winton Formation, which contrasts with other penecontemporaneous Gondwanan ecosystems.

A proposed terminology of theropod teeth (Dinosauria, Saurischia)

ABSTRACTTheropod teeth are typically not described in detail, yet these abundant vertebrate fossils are not only frequently reported in the literature, but also preserve extensive anatomical information. Often in descriptions, important characters of the crown and ornamentations are omitted, and in many instances, authors do not include a description of theropod dentition at all. The paucity of information makes identification of isolated teeth difficult and taxonomic assignments uncertain. Therefore, we here propose a standardization of the anatomical and morphometric terms for tooth anatomical subunits, as well as a methodology to describe isolated teeth comprehensively. As a corollary, this study exposes the importance of detailed anatomical descriptions with the utilitarian purpose of clarifying taxonomy and identifying isolated theropod teeth.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/ujvp