Evolution of postcanine complexity in Gomphodontia (Therapsida: Cynodontia).

Gomphodonts form a Triassic radiation of small to medium-bodied (<0.5-2.5 m in length) quadrupedal cynodonts characterized by labiolingually expanded gomphodont postcanines. They were the dominant cynodont group in Middle and Late Triassic ecosystems from the Southern Hemisphere and the first predominantly herbivorous cynodonts to evolve. Gomphodonts were also the first therapsids to develop hypsodonty and a dentition with complex occlusal patterns, and their highly diagnostic upper and lower postcanines show many different morphologies. Here, we explored dental complexity in gomphodont cynodonts through time using geographic information system analysis and orientation patch count applied on 3D crown surfaces of upper and lower gomphodont postcanines belonging to 32 gomphodont taxa. This study reveals that the peak in postcanine complexity was reached early in the evolution of gomphodonts with the emergence in the Early Triassic of omnivorous or insectivorous forms with postcanines made of well-separated cusps and cingular cuspules. Traversodontids evolved simpler postcanines via coalescence of cusps into crests and the development of large occlusal basins, and the Middle Triassic radiation of traversodontids led to a sharp decrease in mean postcanine complexity. Simplification of the postcanines in traversodontids is interpreted as being related to a gradual increase in the consumption of plant material. Interestingly, the trend of insectivory/omnivory high postcanine complexity and herbivory low dental complexity in gomphodonts is opposite to the trend of dental complexity reported in some extant mammals, with omnivorous having low dental complexity and herbivorous higher. Postcanine complexity remained relatively stable throughout the evolution of traversodontids and only slightly diminished in the Late Triassic due to the presence of minute forms with particularly simple postcanines in the Rhaetian. The major phylogenetic diversity and taxonomic richness of Gomphodontia are represented in two periods of time: at the end of the Anisian, an age in which the postcanine complexity is simplifying, and at the early Carnian when the postcanine complexity in traversodontids, the only Gomphodontia represented, is stable.

Bite and tooth marks on sauropod dinosaurs from the Morrison Formation.

Tooth-marked bones provide important evidence for feeding choices made by extinct carnivorous animals. In the case of the dinosaurs, most bite traces are attributed to the large and robust osteophagous tyrannosaurs, but those of other large carnivores remain underreported. Here we report on an extensive survey of the literature and some fossil collections cataloging a large number of sauropod bones (68) from the Upper Jurassic Morrison Formation of the USA that bear bite traces that can be attributed to theropods. We find that such bites on large sauropods, although less common than in tyrannosaur-dominated faunas, are known in large numbers from the Morrison Formation, and that none of the observed traces showed evidence of healing. The presence of tooth wear in non-tyrannosaur theropods further shows that they were biting into bone, but it remains difficult to assign individual bite traces to theropod taxa in the presence of multiple credible candidate biters. The widespread occurrence of bite traces without evidence of perimortem bites or healed bite traces, and of theropod tooth wear in Morrison Formation taxa suggests preferential feeding by theropods on juvenile sauropods, and likely scavenging of large-sized sauropod carcasses.

The exquisitely preserved integument of Psittacosaurus and the scaly skin of ceratopsian dinosaurs.

The Frankfurt specimen of the early-branching ceratopsian dinosaur Psittacosaurus is remarkable for the exquisite preservation of squamous (scaly) skin and other soft tissues that cover almost its entire body. New observations under Laser-Stimulated Fluorescence (LSF) reveal the complexity of the squamous skin of Psittacosaurus, including several unique features and details of newly detected and previously-described integumentary structures. Variations in the scaly skin are found to be strongly regionalized in Psittacosaurus. For example, feature scales consist of truncated cone-shaped scales on the shoulder, but form a longitudinal row of quadrangular scales on the tail. Re-examined through LSF, the cloaca of Psittacosaurus has a longitudinal opening, or vent; a condition that it shares only with crocodylians. This implies that the cloaca may have had crocodylian-like internal anatomy, including a single, ventrally-positioned copulatory organ. Combined with these new integumentary data, a comprehensive review of integument in ceratopsian dinosaurs reveals that scalation was generally conservative in ceratopsians and typically consisted of large subcircular-to-polygonal feature scales surrounded by a network of smaller non-overlapping polygonal basement scales. This study highlights the importance of combining exceptional specimens with modern imaging techniques, which are helping to redefine the perceived complexity of squamation in ceratopsians and other dinosaurs.

Oldest preserved umbilical scar reveals dinosaurs had 'belly buttons'.

BACKGROUND: In egg-laying amniotes, the developing embryo is tethered to a number of the extraembryonic membranes including the yolk sac and allantois that deliver oxygen and nutrients and remove metabolic waste products throughout embryonic development. Prior to, or soon after hatching, these membranes detach from the animal leaving a temporary or permanent umbilical scar (umbilicus) equivalent to the navel or 'belly button' in some placental mammals, including humans. Although ubiquitous in modern mammals and reptiles (including birds), at least early in their ontogeny, the umbilicus has not been identified in any pre-Cenozoic amniote. RESULTS: We report the oldest preserved umbilicus in a fossil amniote from a ~130-million-year-old early-branching ceratopsian dinosaur, Psittacosaurus. Under laser-stimulated fluorescence (LSF), the umbilicus is revealed as an elongate midline structure delimited by a row of paired scales on the abdomen. The relatively late ontogenetic stage (close to sexual maturity) estimated for the individual indicates that the umbilicus was probably retained throughout life. CONCLUSIONS: Unlike most extant reptiles and birds that lose this scar within days to weeks after hatching, the umbilicus of Psittacosaurus persisted at least until sexual maturity, similar to some lizards and crocodylians with which it shares the closest morphological resemblance. This discovery is the oldest record of an amniote umbilicus and the first in a non-avian dinosaur. However, given the variability of this structure in extant reptilian analogues, a persistent umbilical scar may not have been present in all non-avian dinosaurs.

Morphology and distribution of scales, dermal ossifications, and other non-feather integumentary structures in non-avialan theropod dinosaurs.

Modern birds are typified by the presence of feathers, complex evolutionary innovations that were already widespread in the group of theropod dinosaurs (Maniraptoriformes) that include crown Aves. Squamous or scaly reptilian-like skin is, however, considered the plesiomorphic condition for theropods and dinosaurs more broadly. Here, we review the morphology and distribution of non-feathered integumentary structures in non-avialan theropods, covering squamous skin and naked skin as well as dermal ossifications. The integumentary record of non-averostran theropods is limited to tracks, which ubiquitously show a covering of tiny reticulate scales on the plantar surface of the pes. This is consistent also with younger averostran body fossils, which confirm an arthral arrangement of the digital pads. Among averostrans, squamous skin is confirmed in Ceratosauria (Carnotaurus), Allosauroidea (Allosaurus, Concavenator, Lourinhanosaurus), Compsognathidae (Juravenator), and Tyrannosauroidea (Santanaraptor, Albertosaurus, Daspletosaurus, Gorgosaurus, Tarbosaurus, Tyrannosaurus), whereas dermal ossifications consisting of sagittate and mosaic osteoderms are restricted to Ceratosaurus. Naked, non-scale bearing skin is found in the contentious tetanuran Sciurumimus, ornithomimosaurians (Ornithomimus) and possibly tyrannosauroids (Santanaraptor), and also on the patagia of scansoriopterygids (Ambopteryx, Yi). Scales are surprisingly conservative among non-avialan theropods compared to some dinosaurian groups (e.g. hadrosaurids); however, the limited preservation of tegument on most specimens hinders further interrogation. Scale patterns vary among and/or within body regions in Carnotaurus, Concavenator and Juravenator, and include polarised, snake-like ventral scales on the tail of the latter two genera. Unusual but more uniformly distributed patterning also occurs in Tyrannosaurus, whereas feature scales are present only in Albertosaurus and Carnotaurus. Few theropods currently show compelling evidence for the co-occurrence of scales and feathers (e.g. Juravenator, Sinornithosaurus), although reticulate scales were probably retained on the mani and pedes of many theropods with a heavy plumage. Feathers and filamentous structures appear to have replaced widespread scaly integuments in maniraptorans. Theropod skin, and that of dinosaurs more broadly, remains a virtually untapped area of study and the appropriation of commonly used techniques in other palaeontological fields to the study of skin holds great promise for future insights into the biology, taphonomy and relationships of these extinct animals.

Crocodile-like sensory scales in a Late Jurassic theropod dinosaur.

Early in amniote evolution, epidermal scales evolved in stem reptiles as an efficient barrier against water loss and ultraviolet radiation, making them a key development in the transition to a fully terrestrial existence [1]. Accordingly, epidermal scales are not simple inert structures but highly-evolved organs suited to perform a broad suite of functions. Here, we provide new data on the epidermal complexity of a non-avian theropod, Juravenator starki, from the Torleite Formation (upper Kimmeridgian), Bavaria, Germany [2]. Although epidermal scales have been noted previously on the tail of Juravenator, we report a unique scale type with distinctive circular nodes that we identify as integumentary sense organs, analogous to those in modern crocodylians. The surprising presence of such structures suggests the tail had a sensory function, which is nevertheless congruent with the inferred ecology of Juravenator and the evolution of integumentary sense organs among archosaurs.

A proposed terminology for the dentition of gomphodont cynodonts and dental morphology in Diademodontidae and Trirachodontidae.

Gomphodont cynodonts were close relatives of mammals and one of the Mesozoic lineages of cynodont therapsids that became extinct at the end of the Triassic. Gomphodonts were omnivorous to herbivorous animals characterized by labiolingually expanded postcanines, which allowed tooth-to-tooth occlusion. The morphology of the upper and lower postcanines presents important means of distinguishing among major lineages within Gomphodontia, that is, Diademodontidae, Trirachodontidae, and Traversodontidae, but the dentition of most Diademodontidae and Trirachodontidae remain poorly documented. Here, we present a comprehensive description of the dentition of each diademodontid and trirachodontid species, as well as detailed illustrations of each dental unit, after firsthand examination of material and 3D reconstructions of postcanine teeth. Based on dental morphology, Trirachodon berryi and "Trirachodon kannemeyeri," considered as separate taxa by some authors are here interpreted as representing different ontogenetic stages of the same species. Likewise, Sinognathus and Beishanodon, thought to belong to non-cynognathian cynodonts and traversodontids by some authors, are referred to Trirachodontidae and Gomphodontia based on dental characters, respectively. Finally, we propose a standardized list of terms and abbreviations for incisors, canines, and postcanines anatomical entities, with the goal of facilitating future descriptions and communication between researchers studying the gomphodont dentition.

Morphofunctional Analysis of the Quadrate of Spinosauridae (Dinosauria: Theropoda) and the Presence of Spinosaurus and a Second Spinosaurine Taxon in the Cenomanian of North Africa.

Six quadrate bones, of which two almost certainly come from the Kem Kem beds (Cenomanian, Upper Cretaceous) of south-eastern Morocco, are determined to be from juvenile and adult individuals of Spinosaurinae based on phylogenetic, geometric morphometric, and phylogenetic morphometric analyses. Their morphology indicates two morphotypes evidencing the presence of two spinosaurine taxa ascribed to Spinosaurus aegyptiacus and? Sigilmassasaurus brevicollis in the Cenomanian of North Africa, casting doubt on the accuracy of some recent skeletal reconstructions which may be based on elements from several distinct species. Morphofunctional analysis of the mandibular articulation of the quadrate has shown that the jaw mechanics was peculiar in Spinosauridae. In mature spinosaurids, the posterior parts of the two mandibular rami displaced laterally when the jaw was depressed due to a lateromedially oriented intercondylar sulcus of the quadrate. Such lateral movement of the mandibular ramus was possible due to a movable mandibular symphysis in spinosaurids, allowing the pharynx to be widened. Similar jaw mechanics also occur in some pterosaurs and living pelecanids which are both adapted to capture and swallow large prey items. Spinosauridae, which were engaged, at least partially, in a piscivorous lifestyle, were able to consume large fish and may have occasionally fed on other prey such as pterosaurs and juvenile dinosaurs.

The non-avian theropod quadrate I: standardized terminology with an overview of the anatomy and function.

The quadrate of reptiles and most other tetrapods plays an important morphofunctional role by allowing the articulation of the mandible with the cranium. In Theropoda, the morphology of the quadrate is particularly complex and varies importantly among different clades of non-avian theropods, therefore conferring a strong taxonomic potential. Inconsistencies in the notation and terminology used in discussions of the theropod quadrate anatomy have been noticed, including at least one instance when no less than eight different terms were given to the same structure. A standardized list of terms and notations for each quadrate anatomical entity is proposed here, with the goal of facilitating future descriptions of this important cranial bone. In addition, an overview of the literature on quadrate function and pneumaticity in non-avian theropods is presented, along with a discussion of the inferences that could be made from this research. Specifically, the quadrate of the large majority of non-avian theropods is akinetic but the diagonally oriented intercondylar sulcus of the mandibular articulation allowed both rami of the mandible to move laterally when opening the mouth in many of theropods. Pneumaticity of the quadrate is also present in most averostran clades and the pneumatic chamber-invaded by the quadrate diverticulum of the mandibular arch pneumatic system-was connected to one or several pneumatic foramina on the medial, lateral, posterior, anterior or ventral sides of the quadrate.

Abelisauridae (Dinosauria: Theropoda) from the Late Jurassic of Portugal and dentition-based phylogeny as a contribution for the identification of isolated theropod teeth.

Theropod dinosaurs form a highly diversified clade, and their teeth are some of the most common components of the Mesozoic dinosaur fossil record. This is the case in the Lourinhã Formation (Late Jurassic, Kimmeridgian-Tithonian) of Portugal, where theropod teeth are particularly abundant and diverse. Four isolated theropod teeth are here described and identified based on morphometric and anatomical data. They are included in a cladistic analysis performed on a data matrix of 141 dentition-based characters coded in 60 taxa, as well as a supermatrix combining our dataset with six recent datamatrices based on the whole theropod skeleton. The consensus tree resulting from the dentition-based data matrix reveals that theropod teeth provide reliable data for identification at approximately family level. Therefore, phylogenetic methods will help identifying theropod teeth with more confidence in the future. Although dental characters do not reliably indicate relationships among higher clades of theropods, they demonstrate interesting patterns of homoplasy suggesting dietary convergence in (1) alvarezsauroids, therizinosaurs and troodontids; (2) coelophysoids and spinosaurids; (3) compsognathids and dromaeosaurids; and (4) ceratosaurids, allosauroids and megalosaurids.        Based on morphometric and cladistic analyses, the biggest tooth from Lourinhã is referred to a mesial crown of the megalosaurid Torvosaurus tanneri, due to the elliptical cross section of the crown base, the large size and elongation of the crown, medially positioned mesial and distal carinae, and the coarse denticles. The smallest tooth is identified as Richardoestesia, and as a close relative of R. gilmorei based on the weak constriction between crown and root, the "eight-shaped" outline of the base crown and, on the distal carina, the average of ten symmetrically rounded denticles per mm, as well as a subequal number of denticles basally and at mid-crown. Finally, the two medium-sized teeth belong to the same taxon and exhibit pronounced interdenticular sulci between distal denticles, hooked distal denticles for one of them, an irregular enamel texture, and a straight distal margin, a combination of features only observed in abelisaurids. They provide the first record of Abelisauridae in the Jurassic of Laurasia and one of the oldest records of this clade in the world, suggesting a possible radiation of Abelisauridae in Europe well before the Upper Cretaceous.

Torvosaurus gurneyi n. sp., the largest terrestrial predator from Europe, and a proposed terminology of the maxilla anatomy in nonavian theropods.

The Lourinhã Formation (Kimmeridgian-Tithonian) of Central West Portugal is well known for its diversified dinosaur fauna similar to that of the Morrison Formation of North America; both areas share dinosaur taxa including the top predator Torvosaurus, reported in Portugal. The material assigned to the Portuguese T. tanneri, consisting of a right maxilla and an incomplete caudal centrum, was briefly described in the literature and a thorough description of these bones is here given for the first time. A comparison with material referred to Torvosaurus tanneri allows us to highlight some important differences justifying the creation of a distinct Eastern species. Torvosaurus gurneyi n. sp. displays two autapomorphies among Megalosauroidea, a maxilla possessing fewer than eleven teeth and an interdental wall nearly coincidental with the lateral wall of the maxillary body. In addition, it differs from T. tanneri by a reduced number of maxillary teeth, the absence of interdental plates terminating ventrally by broad V-shaped points and falling short relative to the lateral maxillary wall, and the absence of a protuberant ridge on the anterior part of the medial shelf, posterior to the anteromedial process. T. gurneyi is the largest theropod from the Lourinhã Formation of Portugal and the largest land predator discovered in Europe hitherto. This taxon supports the mechanism of vicariance that occurred in the Iberian Meseta during the Late Jurassic when the proto-Atlantic was already well formed. A fragment of maxilla from the Lourinhã Formation referred to Torvosaurus sp. is ascribed to this new species, and several other bones, including a femur, a tibia and embryonic material all from the Kimmeridgian-Tithonian of Portugal, are tentatively assigned to T. gurneyi. A standard terminology and notation of the theropod maxilla is also proposed and a record of the Torvosaurus material from Portugal is given.

Filling the gaps of dinosaur eggshell phylogeny: Late Jurassic Theropod clutch with embryos from Portugal.

The non-avian saurischians that have associated eggshells and embryos are represented only by the sauropodomorph Massospondylus and Coelurosauria (derived theropods), thus missing the basal theropod representatives. We report a dinosaur clutch containing several crushed eggs and embryonic material ascribed to the megalosaurid theropod Torvosaurus. It represents the first associated eggshells and embryos of megalosauroids, thus filling an important phylogenetic gap between two distantly related groups of saurischians. These fossils represent the only unequivocal basal theropod embryos found to date. The assemblage was found in early Tithonian fluvial overbank deposits of the Lourinhã Formation in West Portugal. The morphological, microstructural and chemical characterization results of the eggshell fragments indicate very mild diagenesis. Furthermore, these fossils allow unambiguous association of basal theropod osteology with a specific and unique new eggshell morphology.