The northernmost sauropod record in the Northern Hemisphere

Isolated sauropod teeth from the Early Cretaceous Teete locality in Yakutia (Eastern Siberia, Russia) are the only evidence that sauropods lived in high latitudes (palaeolatitude estimate of N 62°) in the Northern Hemisphere. The spatulate broad tooth crowns of adult individuals lack marginal denticles while these are present in a juvenile tooth. The teeth have overlapping facets and likely belong to a basal macronarian. The juvenile tooth indicates that sauropods reproduced in high latitudes and possibly stayed there around the year. The Teete vertebrate assemblage comprises both endothermic, or presumably endothermic tetrapods (theropod dinosaurs, tritylodontids and mammals), and ectothermic tetrapods (salamanders, turtles, choristoderes and lizards), but no crocodyliforms. This suggests a temperate climate, with an annual mean temperature well above freezing level but below 14°C.     

Small Theropod Teeth from the Late Cretaceous of the San Juan Basin,Northwestern New Mexico and Their Implications for Understanding Latest Cretaceous Dinosaur Evolution

Studying the evolution and biogeographic distribution of dinosaurs during the latest Cretaceous is critical for better understanding the end-Cretaceous extinction event that killed off all non-avian dinosaurs. Western North America contains among the best records of Late Cretaceous terrestrial vertebrates in the world, but is biased against small-bodied dinosaurs. Isolated teeth are the primary evidence for understanding the diversity and evolution of small-bodied theropod dinosaurs during the Late Cretaceous, but few such specimens have been well documented from outside of the northern Rockies, making it difficult to assess Late Cretaceous dinosaur diversity and biogeographic patterns. We describe small theropod teeth from the San Juan Basin of northwestern New Mexico. These specimens were collected from strata spanning Santonian – Maastrichtian. We grouped isolated theropod teeth into several morphotypes, which we assigned to higher-level theropod clades based on possession of phylogenetic synapomorphies. We then used principal components analysis and discriminant function analyses to gauge whether the San Juan Basin teeth overlap with, or are quantitatively distinct from, similar tooth morphotypes from other geographic areas. The San Juan Basin contains a diverse record of small theropods. Late Campanian assemblages differ from approximately co-eval assemblages of the northern Rockies in being less diverse with only rare representatives of troodontids and a Dromaeosaurus-like taxon. We also provide evidence that erect and recurved morphs of a Richardoestesia-like taxon represent a single heterodont species. A late Maastrichtian assemblage is dominated by a distinct troodontid. The differences between northern and southern faunas based on isolated theropod teeth provide evidence for provinciality in the late Campanian and the late Maastrichtian of North America. However, there is no indication that major components of small-bodied theropod diversity were lost during the Maastrichtian in New Mexico. The same pattern seen in northern faunas, which may provide evidence for an abrupt dinosaur extinction.     

Additional dinosaur teeth from the Cenomanian (Late Cretaceous) of Charentes,southwestern France

Some isolated teeth of theropod and sauropod dinosaurs from the Cenomanian (Late Cretaceous) of Charentes are described. Two new teeth of Troodontidae confirm the presence of this theropod family, previously based on a single specimen. New dental morphotypes are recognized within Dromaeosauridae and Brachiosauridae in comparison with those already known from Charentes. Lastly, a very small tooth is tentatively assigned to an embryonic or neonatal sauropod. The palaeobiogeographical history of European hadrosauroids is briefly discussed. This history was probably more complex than it appears, involving exchanges with both North America and Asia as early as the mid-Cretaceous (Albian–Cenomanian).     

A late-surviving basal theropod dinosaur from the latest Triassic of North America

The oldest theropod dinosaurs are known from the Carnian of Argentina and Brazil. However, the evolutionary diversification of this group after its initial radiation but prior to the Triassic-Jurassic boundary is still poorly understood because of a sparse fossil record near that boundary. Here, we report on a new basal theropod, Daemonosaurus chauliodus gen. et sp. nov., from the latest Triassic 'siltstone member' of the Chinle Formation of the Coelophysis Quarry at Ghost Ranch, New Mexico. Based on a comprehensive phylogenetic analysis, Daemonosaurus is more closely related to coeval neotheropods (e.g. Coelophysis bauri) than to Herrerasauridae and Eoraptor. The skeletal structure of Daemonosaurus and the recently discovered Tawa bridge a morphological gap between Eoraptor and Herrerasauridae on one hand and neotheropods on the other, providing additional support for the theropod affinities of both Eoraptor and Herrerasauridae and demonstrating that lineages from the initial radiation of Dinosauria persisted until the end of the Triassic. Various features of the skull of Daemonosaurus, including the procumbent dentary and premaxillary teeth and greatly enlarged premaxillary and anterior maxillary teeth, clearly set this taxon apart from coeval neotheropods and demonstrate unexpected disparity in cranial shape among theropod dinosaurs just prior to the end of the Triassic.     

Morphological and functional diversity in therizinosaur claws and the implications for theropod claw evolution

Therizinosaurs are a group of herbivorous theropod dinosaurs from the Cretaceous of North America and Asia, best known for their iconically large and elongate manual claws. However, among Therizinosauria, ungual morphology is highly variable, reflecting a general trend found in derived theropod dinosaurs (Maniraptoriformes). A combined approach of shape analysis to characterize changes in manual ungual morphology across theropods and finite-element analysis to assess the biomechanical properties of different ungual shapes in therizinosaurs reveals a functional diversity related to ungual morphology. While some therizinosaur taxa used their claws in a generalist fashion, other taxa were functionally adapted to use the claws as grasping hooks during foraging. Results further indicate that maniraptoriform dinosaurs deviated from the plesiomorphic theropod ungual morphology resulting in increased functional diversity. This trend parallels modifications of the cranial skeleton in derived theropods in response to dietary adaptation, suggesting that dietary diversification was a major driver for morphological and functional disparity in theropod evolution.     

Diet of prosauropod dinosaurs from the late Triassic and early Jurassic

Prosauropods were not scavenger-predators, rather they were the dominant large terrestrial herbivores during the late Triassic and early Jurassic. The herbivorous adaptations of anchisaurids include spatulate teeth with anteroposteriorly expanded crowns (maximum width apical to base of crown) which are obliquely inclined with respect to the jaws so each slightly overlaps the tooth behind it, and which have coarse marginal serrations at 45° to the cutting edges. Most of the teeth of yunnanosaurids lack serrations and resemble those of sauropod dinosaurs in form and in having self-sharpening surfaces, formed by tooth-to-tooth wear, which increased the efficiency of dealing with more resistant plant material. Anchisaurids and yunnanosaurids had a ventrally set jaw articulation; the teeth and skull of melanorosaurids are unknown. All prosauropods were high browsers that extended the feeding range with a long neck and tripodal feeding (long hindlimbs and stout tail for support). They used herding and the enormous claw on the pollex for defense, and probably had a muscular gastric mill with stones that was used for grinding the food. They account for at least 95% of the biomass in their respective faunas.     

On a theropod scapula (Upper Cretaceous) from the Marília Formation, Bauru Group, Brazil

The record of theropod dinosaurs in Brazil is very scarce. One of the most promising lithostratigraphic units for those reptiles is the Bauru Group. The dinosaur remains found in this unit are mainly those of sauropods, while theropods are represented mostly by teeth. Here we describe a right scapula (housed at the Earth Science Museum of the Departamento Nacional de Produção Mineral/Rio de Janeiro) that is the first theropod scapula reported from the Cretaceous of Brazil and only the second osteological evidence of the Tetanurae from the Bauru Group. The specimen was recovered from the outskirts of Peirópolis, in Minas Gerais State. Comparisons with other theropod dinosaurs are limited, but the overall morphology of the new specimen indicates that it is neither a member of the Abelisauridae nor a member of the Avialae. It also differs from more basal members of the Theropoda, but its overall shape is consistent with several derived members of the Tetanurae, likely a non-avialan maniraptoran. Despite the lack of precision in its taxonomic position, the new specimen confirms the presence of non-avialan Maniraptora in the Bauru Group.     

New information on cranial and dental features of the Triassic archosauriform reptile Euparkeria capensis

The course of the nasolacrimal duct, interdental plate morphology, and most details of tooth and denticle morphology have not previously been described in non–archosauriform reptilkes. Here I describe these details in the Triassic archosauriform Euparkeria capensis. The nasolacrimal canal opens orbitally via a pair of foramina between the lacrimal and prefrontal. The canal arches over the antorbital fenestra, as in archosaurs. The term ‘interdental unit’ is introduced for the unit composed of an interdental septum and its accompanying interdental plate. There is no demarcation between interdental plate and septum in E. capensis. The interdental units are heavily pitted on exposed surfaces. Like teeth, they are implanted in the dental groove and are separate from the surrounding bone and from each other. They are well positioned to serve as spacers between teeth, and to resist sagittal forces on teeth during prey capture. The teeth of E. capensis are labiolingually compressed, except for the nearly conical premaxillary teeth and mesialmost dentary tooth. Lateral teeth are serrated on mesial and distal keels. The denticles are low, rounded, and separated by grooves, and are slightly larger on the distal keel. Tooth morphology suggests carnivorous habits for Euparkeria.     

A molecular model for the evolution of endothermy in the theropod-bird lineage.

Ectothermy is a primitive state; therefore, a shared common ancestor of crocodiles, dinosaurs, and birds was at some point ectothermic. Birds, the extant descendants of the dinosaurs, are endothermic. Neither the metabolic transition within this lineage nor the place the dinosaurs held along the ectothermic-endothermic continuum is defined. This paper presents a conceptual model for the evolution of endothermy in the theropod-bird lineage. It is recognized that other animals (some fish, insects, etc.) are functionally endothermic. However, endothermy in other clades is beyond the scope of this paper, and we address the onset of endothermy in only the theropod/bird clade. The model begins with simple changes in a single gene of a common ancestor, and it includes a series of concomitant physiological and morphological changes, beginning perhaps as early as the first archosaurian common ancestor of dinosaurs and crocodiles. These changes continued to accumulate within the theropod-avian lineage, were maintained and refined through selective forces, and culminated in extant birds. Metabolic convergence or homoplasy is evident in the inherent differences between the endothermy of mammals and the endothermy of extant birds. The strength and usefulness of this model lie in the phylogenetic, genetic, evolutionary, and adaptive plausibility of each of the suggested developmental steps toward endothermy. The model, although conceptual in nature, relies on an extensive knowledge base developed by numerous workers in each of these areas. In addition, the model integrates known genetic, metabolic, and developmental aspects of extant taxa that phylogenetically bracket theropod dinosaurs for comparison with information derived from the fossil record of related extinct taxa.     

A new species of Azendohsaurus (Diapsida: Archosauromorpha) from the Triassic Isalo Group of southwestern Madagascar: cranium and mandible

Abstract: Here, we describe a new species of Azendohsaurus from the Middle–Late Triassic of Madagascar, extending the geographical range of a taxon known otherwise only by a single species from Morocco. Although Azendohsaurus has consistently been regarded as an early dinosaur (based on various advanced dental and gnathic features resembling those characterizing certain dinosaur subgroups), the relatively complete skeletal material, now available from Madagascar, argues strongly against its dinosaurian affinities. Rather, the retention of numerous primitive cranial and postcranial features indicates a surprisingly early divergence of Azendohsaurus within Archosauromorpha and an unusual mosaic of characters in this taxon. Features considered diagnostic of Sauropodomorpha thus are inferred to occur homoplastically in at least one clade of nondinosaurian archosauromorphs, indicating a complex evolution and distribution of features traditionally thought to be derived within archosaurs. Azendohsaurus has teeth resembling those of both early sauropodomorph and ornithischian dinosaurs, yet also possesses numerous inarguable basal archosauromorph cranial and postcranial attributes. This highlights the risk of uncritically referring isolated, Middle–Late Triassic (or even later), ‘leaf‐shaped’ teeth with denticles to the Dinosauria. Similarly, the occurrence of such teeth in an early diverging archosauromorph indicates that specializations for herbivory originated more frequently within this clade than conventionally assumed. For example, Azendohsaurus and numerous basal sauropodomorph dinosaur taxa share an array of convergently acquired features associated with herbivory, including tooth denticles, expanded tooth crowns, a downturned dentary and the articular located at the ventral margin of the mandible. Some of these features (denticles, expanded crowns and the ventrally deflected articular) are even more widespread among archosauromorphs, including aetosaurs, silesaurs and ornithischian dinosaurs. A downturned dentary also occurs in Trilophosaurus, a taxon further marked by unique specializations for herbivory, including transversely lophate, tricuspid teeth. An array of features associated with herbivory also occurs in rhynchosaurs and certain crocodilians (e.g. Simosuchus). This distribution suggests that craniodental features associated with herbivory were much more pervasive across the archosauromorph clade than previously recognized, possibly evolving at least six to eight times independently.     

Small theropod teeth from the Upper Jurassic coal mine of Guimarota (Portugal)

Isolated teeth of small theropod dinosaurs from the Upper Jurassic lignite coal mine of Guimarota (near Leiria, Portugal) are described and illustrated. The well known Upper Jurassic theropods from Europe,Archaeopteryx andCompsognathus, are the most common taxa in the Guimarota assemblage. One morphotype is closely related to an allosaurid theropod. Six further morphotypes of theropod teeth are also described, which are closely related to Cretaceous theropods such as dromaeosaurids, troodontids, tyrannosaurids,Richardoestesia andParonychodon. A Late Jurassic origin of these groups of theropods, which is very often postulated, is discussed.     

The mechanics of cutting and the form of shark teeth (Chondrichthyes,Elasmobranchii)

Summary A rich engineering literature exists that is applicable to many aspects of vertebrate jaw mechanics and has been referred to in many studies in this sector. But mechanical engineering technology has provided few theoretical bases that are directly helpful in the study of predator teeth. Hence, analyses of puncturing and slicing functions of these teeth have lacked a firm physical technology as a background. Predator teeth have evolved to pierce and cut animal tissues that are usually compliant in that they readily undergo relatively large deformations under applied stress before they actually yield. The bulk of engineering theory is directed toward such noncompliant materials as wood and metal, the design of tools that cut them, and the mechanics involved in this. The purpose of the present paper is to scan the mechanical implications of different tooth designs, pose hypotheses that relate to primary considerations of the physics of cutting compliant substrates, and offer a preliminary approach that is intended as a useful guide to further studies on sharks and on other vertebrate groups. Thus, in this paper I have attempted to formulate some tentative and preliminary generalizations concerning the mechanics of cutting compliant materials. Then comes a survey of the teeth of a particular group of predators, three families of sharks, in terms of these preliminary formulations. The approach views the shark teeth in isolation from the complex cranial mechanism (presently under study) that functionally integrates with the teeth. Therefore, adaptive conclusions are minimal, because the evolutionary significance of tooth form cannot properly be assessed outside of an integrated study. However, certain correlations do exist between structural tooth characteristics and mechanics. Slender, smooth-edged (or nearly so) teeth can readily pierce prey, but are of less use in slicing it. Such teeth are typical of the lower jaw dentition in many sharks and, in a few species, they are present in both upper and lower jaws. Usually these slender teeth display a reversed curvature at their tips, so that although most of the tooth's crown is curved inward toward the mouth cavity, the tip is turned outward. This outward turning of the tip can enhance the probability of initial prey penetration, without much compromising the prey-retaining properties of the inward curvature of the greater, more proximal portion of the tooth. Many sharks possess upper teeth with serrations along the edges. The serrations vary from one species to another in coarseness and in distribution along tooth edges. Serrated teeth can make greater use of the available biting forces, and they have a greater cutting effect than do smooth-edged teeth. These latter depend upon friction which, because the coefficient friction is always less than 1.0 (often very much less), can make use of only a fraction of the total bite force. However, smooth tooth blades can pierce prey with less resistance and are less prone to binding (becoming immobilized) in the prey tissue. In many shark species serrations are concentrated along the proximal portions of the tooth crown, where the bases of adjacent teeth are in near contact along the jaw margin. In these regions food can be pressed during feeding, resulting in a binding of the teeth in the prey. Release of the binding must be accomplished by cutting the jammed food, to permit clearance of the prey material so it can slip past the tooth rows. The more prominent serrations in such regions may act to puncture and slice the jammed tissue. It is noted that commercial saws are typically designed in various ways to promote clearance between adjacent saw teeth. The pitch or rake of the teeth of sharks is discussed, as is the overall form of the tooth rows along the jaw margins. The relationship between the distribution of teeth along the jaw margins and surface irregularities of the prey surfaces is also considered.     

Conodont element function

There are close similarities between conodont elements and teeth both in general shape and in that they possess pointed tips and have expanded bases with more porous tissue. A number of examples of conodont elements which parallel specific kinds of tooth shapes and organizations are added to earlier known similarities. Both in teeth and in conodont elements the surface structures include cutting edges, striations, and barbs. The change in strength of the conodont denticles caused by the evolution of white matter is also shown to agree with a tooth function. On the other hand, the elements grew throughout the life of the animal by lamellae added to the surface. The solution of this paradox is found in the elements alternating between a growth phase and a functional phase. During growth the oral surface of the elements was enveloped in folds of secreting soft tissue. Structures henceforth termed burrs were formed at the contacts between the folds. Parts of the burrs evolved into cutting edges. Three different bite types occurred among the conodont elements. Many (all?) conodonts were predators which used their elements to seize and to process the food mechanically. The shape of the conodont elements cannot be used for conclusions regarding the affinities of the conodonts. Similarly, an identification of a fossil as belonging to the conodonts must be supported by other evidence than just shape.     

Vertical sections through dinosaur tracks (Late Triassic lake deposits, East Greenland) – undertracks and other subsurface deformation structures revealed

Tracks and trackways of theropod dinosaurs (Grallator footprints) are abundant in the Late Triassic lake sediments of East Greenland. For this study we selected a rather diffuse theropod track preserved on the upper surface of a red heterolithic mudrock, and a better preserved track seen on the upper surface of a greyish mudrock. In order to examine undertracks and other subsurface deformation structures, both slabs were sectioned vertically at closely-spaced intervals, perpendicular to the length of the axis of the impression of digit III. Each section was subsequently polished and internal structures revealed. The digit impressions of both tracks were associated with well-defined undertracks which were cut by deep and narrow claw imprints at the distal end of the digit impressions. Marginal ridges at the tracking surfaces were typically associated with subsurface marginal folds. The marginal ridges were asymmetrically developed suggesting an outward movement of the proximal part of the foot, probably during the kick-off; this is in contrast to what is observed in tracks from Lower Jurassic theropods. The study shows that cross-sections through dinosaur tracks display large structural variation and it is suggested that some disturbed layers in continental deposits could be the result of trampling by vertebrates.     

Late Triassic dinosaur teeth from southern Belgium

Isolated Dinosaur teeth have been discovered in the Upper Triassic locality of Habay-la-Vieille, in southern Belgium. Ornithischia are represented by three dental morphotypes; two of them closely resemble isolated teeth from the Middle or Upper Jurassic of Portugal and England. The presence of sauropods in the Upper Triassic of Europe is confirmed. Sauropods already had a wide geographical distribution during the Latest Triassic, as fossils have been discovered in South Africa, Thailand and western Europe. At Habay-la-Vieille, sauropods and prosauropods co-existed at the end of the Triassic. Two dental morphotypes may tentatively be referred to as theropod dinosaurs. The study of isolated teeth indicates that dinosaurs were already well diversified in the Latest Triassic of western Europe. To cite this article: P. Godefroit, F. Knoll, C. R. Palevol 2 (2003) 3–11.     

A review of theropod dinosaurs from the Late Jurassic to mid-Cretaceous of Southeast Asia

Several non-avian theropod dinosaurs, as well as some Mesozoic birds, have been reported from Southeast Asia. The fossils are dominantly found in northeastern Thailand, however, one bizarre theropod has been described from Laos, one theropod has been reported from Malaysia, and some avian and non-avian theropods have been recently reported from Myanmar. The temporal distribution of Southeast Asian theropods ranges from the Late Jurassic to the mid-Cretaceous. All non-avian theropod faunas from Southeast Asia consist of non-maniraptoran tetanurans. They show similarity to Chinese plus Japanese theropods during the Early Cretaceous in broad systematic terms. During this time, megaraptorans can be found only in Japan, Australia, Brazil, and possibly Thailand, whereas tyrannosauroids can be found in China, Europe, possibly Brazil and Australia. Spinosaurids, carcharodontosaurians, and some coelurosaurs such as ornithomimosaurs were almost cosmopolitan. Metriacanthosaurids, on the other hand, were endemic to Europe and Asia including China and Thailand during the Middle to Late Jurassic.     

Dental histology of Coelophysis bauri and the evolution of tooth attachment tissues in early dinosaurs

Studies of dinosaur teeth have focused primarily on external crown morphology and thus, use shed or in situ tooth crowns, and are limited to the enamel and dentine dental tissues. As a result, the full suites of periodontal tissues that attach teeth to the jaws remain poorly documented, particularly in early dinosaurs. These tissues are an integral part of the tooth and thus essential to a more complete understanding of dental anatomy, development, and evolution in dinosaurs. To identify the tooth attachment tissues in early dinosaurs, histological thin sections were prepared from the maxilla and dentary of a partial skull of the early theropod Coelophysis bauri from the Upper Triassic (Rhaetian‐ 209–201 Ma) Whitaker Quarry, New Mexico, USA. As one of the phylogenetically and geologically oldest dinosaurs, it is an ideal candidate for examining dental tissues near the base of the dinosaurian clade. The teeth of C. bauri exhibited a fibrous tooth attachment in which the teeth possessed five tissues: enamel, dentine, cementum, periodontal ligament (PDL), and alveolar bone. Our findings, coupled with those of more recent studies of ornithischian teeth, indicate that a tripartite periodontium, similar to that of crocodilians and mammals, is the plesiomorphic condition for dinosaurs. The occurrence of a tripartite periodontium in dinosaurs adds to the growing consensus that the presence of these tissues is the plesiomorphic condition for the major amniote clades. Furthermore, this study establishes the relative timing of tissue development and growth directions of periodontal tissues and provides the first comparative framework for future studies of dinosaur periodontal development, tooth replacement, and histology. J. Morphol. 277:916–924, 2016. © 2016 Wiley Periodicals, Inc.     

The predatory ecology of Deinonychus and the origin of flapping in birds

Most non-avian theropod dinosaurs are characterized by fearsome serrated teeth and sharp recurved claws. Interpretation of theropod predatory ecology is typically based on functional morphological analysis of these and other physical features. The notorious hypertrophied 'killing claw' on pedal digit (D) II of the maniraptoran theropod Deinonychus (Paraves: Dromaeosauridae) is hypothesized to have been a predatory adaptation for slashing or climbing, leading to the suggestion that Deinonychus and other dromaeosaurids were cursorial predators specialized for actively attacking and killing prey several times larger than themselves. However, this hypothesis is problematic as extant animals that possess similarly hypertrophied claws do not use them to slash or climb up prey. Here we offer an alternative interpretation: that the hypertrophied D-II claw of dromaeosaurids was functionally analogous to the enlarged talon also found on D-II of extant Accipitridae (hawks and eagles; one family of the birds commonly known as "raptors"). Here, the talon is used to maintain grip on prey of subequal body size to the predator, while the victim is pinned down by the body weight of the raptor and dismembered by the beak. The foot of Deinonychus exhibits morphology consistent with a grasping function, supportive of the prey immobilisation behavior model. Opposite morphological trends within Deinonychosauria (Dromaeosauridae + Troodontidae) are indicative of ecological separation. Placed in context of avian evolution, the grasping foot of Deinonychus and other terrestrial predatory paravians is hypothesized to have been an exaptation for the grasping foot of arboreal perching birds. Here we also describe "stability flapping", a novel behaviour executed for positioning and stability during the initial stages of prey immobilisation, which may have been pivotal to the evolution of the flapping stroke. These findings overhaul our perception of predatory dinosaurs and highlight the role of exaptation in the evolution of novel structures and behaviours.     

The colour of fossil feathers

Feathers are complex integumentary appendages of birds and some other theropod dinosaurs. They are frequently coloured and function in camouflage and display. Previous investigations have concluded that fossil feathers are preserved as carbonized traces composed of feather-degrading bacteria. Here, an investigation of a colour-banded feather from the Lower Cretaceous Crato Formation of Brazil revealed that the dark bands are preserved as elongate, oblate carbonaceous bodies 1-2mum long, whereas the light bands retain only relief traces on the rock matrix. Energy dispersive X-ray analysis showed that the dark bands preserve a substantial amount of carbon, whereas the light bands show no carbon residue. Comparison of these oblate fossil bodies with the structure of black feathers from a living bird indicates that they are the eumelanin-containing melanosomes. We conclude that most fossil feathers are preserved as melanosomes, and that the distribution of these structures in fossil feathers can preserve the colour pattern in the original feather. The discovery of preserved melanosomes opens up the possibility of interpreting the colour of extinct birds and other dinosaurs.     

The dentition of Manidens condorensis (Ornithischia; Heterodontosauridae) from the Jurassic Cañadón Asfalto Formation of Patagonia: morphology,heterodonty and the use of statistical methods for identifying isolated teeth

The recently described Manidens condorensis is one of the most completely known taxa of the family Heterodontosauridae from the southern landmasses. However, some dental aspects are not well known due to preservational problems in the type material. This contribution reports new isolated teeth found in the Cañadón Asfalto Formation (Early-Middle Jurassic). These teeth are referred to Manidens condorensis based on the presence of autapomorphic characters of the unusual dentition of this taxon, such as the highly asymmetric tooth crowns and small crenulations on each denticles. The isolated crowns are well preserved and reveal the presence of undescribed and new autapomorphical features, including apical and basal wear facets on the occlusal surface of isolated crowns and a wear surface also in the caniniform tooth. We carried out statistical analyses (including morphogeometrical and discriminant analyses), using the holotype crowns as a morphological starting point, for characterising shape variation of the crowns along the toothrow and for identifying the position of isolated crowns. These analyses allow defining morphological regions within the postcaniniform toothrow and produce a metrically based discriminant function to predict the hypothetical position of future discoveries, providing a methodological framework that could be applied to other extinct heterodont dinosaurs.