Theropods were the dominating apex predators in most Jurassic and Cretaceous terrestrial ecosystems. Their feeding ecology has always been of great interest, and new computational methods have yielded more detailed reconstructions of differences in theropod feeding behaviour. Many approaches, however, rely on well-preserved skulls. Dental microwear texture (DMT) analysis is potentially applicable to isolated teeth, and here employed for the first time to investigate dietary ecology of theropods. In particular, we test whether tyrannosaurids show DMT associated with more hard-object feeding than compared to Allosaurus; this would be a sign for higher levels of osteophagy, as has often been suggested. We find no significant difference in complexity and roughness of enamel surfaces between Allosaurus and tyrannosaurids, which conflicts with inferences of more frequent osteophagic behaviour in Tyrannosaurus as compared to other theropods. Orientation of wear features reveals a more pronounced bi-directional puncture-and-pull feeding mode in Allosaurus than in tyrannosaurids. Our results further indicate ontogenetic niche shift in theropods and crocodylians, based on significantly larger height parameters in juvenile theropods which might indicate frequent scavenging, resulting in more bone-tooth contact during feeding. Overall, DMT is found to be very similar between theropods and extant large, broad-snouted crocodylians and shows great similarity in feeding ecology of theropod apex predators throughout the Jurassic and Cretaceous.

Dental wear analyses are classically applied to mammals because they have evolved heterodont dentitions for sophisticated mastication. Recently, several studies have shown a correlation between pre-assigned and analytically inferred diet preferences in extant reptiles through dental microwear texture analysis (DMTA), a method using quantitative assessment of microscopic wear marks to reconstruct the diet material properties. The first tentative applications of DMTA to extinct reptiles have followed. However, for large and small mammals, microwear analyses have undergone a long time of ground-truthing through direct feeding observations, stomach content analyses, and feeding experiments. Such data are currently lacking for reptiles, but are necessary to further extend DMTA, especially to Archosauria, as the application to dinosaurs could be of great interest to the scientific community. We herein present data from a pilot feeding experiment with five juvenile American alligators (Alligator mississippiensis). Each individual received a diet of assumed different hardness for ~4 months: crocodylian pellets (control), sardines, quails, rats, or crawfish. All individuals initially received the same pellet diet, and we found them to show similar dental microwear texture patterns before they were switched to their designated experimental diet. From the first feeding bout on, dental microwear textures differed across the diets. The crawfish-feeder showed consistently higher surface complexity, followed by the rat-feeder. Quail- and fish-feeding resulted in similar wear signatures, with low complexity. Fast tooth replacement and selective tooth use likely affected microwear formation, but we were able to detect a general hard (crawfish and rat) versus soft (quail and fish) DMTA signature. Such patterns can support the identification of hard-object feeding in the fossil record.

In mammals, complex dental microwear textures (DMT) representing differently sized and shaped enamel lesions overlaying each other have traditionally been associated with the seeds and kernels in frugivorous diets, as well as with sclerotized insect cuticles. Recently, this notion has been challenged by field observations as well as in vitro experimental data. It remains unclear to what extent each food item contributes to the complexity level and is reflected by the surface texture of the respective tooth position along the molar tooth row. To clarify the potential of seeds and other abrasive dietary items to cause complex microwear textures, we conducted a controlled feeding experiment with rats. Six individual rats each received either a vegetable mix, a fruit mix, a seed mix, whole crickets, whole black soldier fly larvae, or whole day-old-chicks. These diets were subjected to material testing to obtain mechanical properties, such as Young's modulus, yield strength, and food hardness (as indicated by texture profile analysis [TPA] tests). Seeds and crickets caused the highest surface complexity. The fruit mix, seed mix, and crickets caused the deepest wear features. Moreover, several diets resulted in an increasing wear gradient from the first to the second molar, suggesting that increasing bite force along the tooth row affects dental wear in rats on these diets. Mechanical properties of the diets showed different correlations with DMT obtained for the first and second molars. The first molar wear was mostly correlated with maximum TPA hardness, while the second molar wear was strongly correlated with maximum yield stress, mean TPA hardness, and maximum TPA hardness. This indicates a complex relationship between chewing mechanics, food mechanical properties, and observed DMT. Our results show that, in rats, seeds are the main cause of complex microwear textures but that hard insect body parts can also cause high complexity. However, the similarity in parameter values of surface textures resulting from seed and cricket consumption did not allow differentiation between these two diets in our experimental approach.

<italic>Jinyunpelta sinensis</italic> is a basal ankylosaurine dinosaur excavated from the mid Cretaceous Liangtoutang Formation of Jinyun County, Zhejiang Province, China. In the present study, its dental microwear was observed using a confocal laser microscope. <italic>Jinyunpelta</italic> had steep wear facets that covered most of buccal surfaces of posterior dentary teeth. Observation of dental microwear on the wear facet revealed that scratch orientation varied according to its location within the wear facet: vertically (i.e. apicobasally) oriented scratches were dominant in the upper half of the wear facet, and horizontally (i.e. mesiolaterally) oriented ones were in the bottom of the facet. These findings indicated that <italic>Jinyunpelta</italic> adopted precise tooth occlusion and biphasal jaw movement (orthal closure and palinal lower jaw movement). The biphasal jaw movement was widely observed among nodosaurids, among ankylosaurids, it was previously only known from the Late Cretaceous North American taxa, and not known among Asian ankylosaurids. The finding of biphasal jaw movement in <italic>Jinyunpelta</italic> showed sophisticate feeding adaptations emerged among ankylosaurids much earlier (during Albian or Cenomanian) than previously thought (during Campanian). The Evolution of the biphasal jaw mechanism that contemporaneously occurred among two lineages of ankylosaurs, ankylosaurids and nodosaurids, showed high evolutionary plasticity of ankylosaur jaw mechanics.

<jats:title>Abstract</jats:title>
<jats:p>Body size is fundamental to the physiology and ecology of organisms. Crocodyliforms are no exception, and several methods have been developed to estimate their absolute body sizes from bone measurements. However, species-specific sizes, such as sexually mature sizes and the maximum sizes were not taken into account due to the challenging maturity assessment of osteological specimens. Here, we provide a vertebrae-based method to estimate absolute and species-specific body lengths in crocodylians. Lengths of cervical to anterior caudal centra were measured and relations between the body lengths (snout-vent and total lengths) and lengths of either a single centrum or a series of centra were modeled for extant species. Additionally, states of neurocentral suture closure were recorded for the maturity assessment. Comparisons of total lengths and timings of neurocentral suture closure showed that most extant crocodylians reach sexual maturity before closure of precaudal neurocentral sutures. Centrum lengths of the smallest individuals with closed precaudal neurocentral sutures within species were correlated with the species maximum total lengths in extant taxa; therefore, the upper or lower limit of the species maximum sizes can be determined from centrum lengths and states of neurocentral suture closure. The application of the current method to non-crocodylian crocodyliforms requires similar numbers of precaudal vertebrae, body proportions, and timings of neurocentral suture closure as compared to extant crocodylians.</jats:p>

Although two major clades of crocodylians (Alligatoroidea and Crocodyloidea) were split during the Cretaceous period, relatively few morphological and functional differences between them have been known. In addition, interaction of multiple morphofunctional systems that differentiated their ecology has barely been assessed. In this study, we examined the limb proportions of crocodylians to infer the differences of locomotor functions between alligatoroids and crocodyloids, and tested the correlation of locomotor and feeding morphofunctions. Our analyses revealed crocodyloids including Gavialis have longer stylopodia (humerus and femur) than alligatoroids, indicating that two groups may differ in locomotor functions. Fossil evidence suggested that alligatoroids have retained short stylopodia since the early stage of their evolution. Furthermore, rostral shape, an indicator of trophic function, is correlated with limb proportions, where slender-snouted piscivorous taxa have relatively long stylopodia and short overall limbs. In combination, trophic and locomotor functionsmight differently delimit the ecological opportunity of alligatoroids and crocodyloids in the evolution of crocodylians.

We describe remains of a new crocodyliform found from the Lower Cretaceous (Aptian) Khok Kruat Formation, northeastern Thailand. Remains consist of two caudal ends of mandibles, two rostra( symphyseal parts of right rami of mandibles, a dorsal part of postorbital, a cranial end of squamosal and one osteoderm. Phylogenetic analyses supported inclusion of this crocodyliform into the Eusuchia as it share's several morphological characters with other eusuchians, such as a dorsocaudally oriented retroarticular process, smooth lateral surface of the caudoventral region of mandible, and a craniocaudally oriented ridge on the dorsal surface of retroarticular process. The shape of symphyseal region showed this crocodyliform had a longirostrine snout shape, which is uncommon in early eusuchians. Finding of this crocodyliform draws back the oldest record of Asian eusuchians, which was Tadzhikosuchus, approximately 30 million years and it is the only Mesozoic eusuchian found in East and Southeast Asia. (C) 2017 Elsevier Ltd. All rights reserved.

Dental microwear of four postcanine teeth of Exaeretodon argentinus was analyzed using both two dimensional (2D) and three dimensional (3D) methods to infer their masticatory jaw movements. Results of both methods were congruent, showing that linear microwear features (scratches) were well aligned and mostly directed to the antero-posterior direction in all four teeth examined. These findings support the palinal masticatory jaw movement, which was inferred in previous studies based on the observation of gross morphology of wear facets. In contrast, the lack of detection of lateral scratches confirmed the absence of the lateral jaw movement that was also proposed by a previous study. Considering previous microwear studies on cynodonts, palinal jaw movements observed in Exaeretodon evolved within cynognathian cynodonts from the fully orthal jaw movement of its basal member. Although there are currently only three studies of dental microwear of non-mammalian cynodonts including the present study, microwear analysis is a useful tool for the reconstruction of masticatory jaw movement and its future application to various cynodonts will shed light on the evolutionary process of jaw movement towards the mammalian condition in more detail.

Silesaurus opolensis belongs to Silesauridae, the closest sister group to dinosaurs. The present study analyzed the dental microwear patterns of Silesaurus opolensis. Low pit-to-scratch ratios imply they did not feed on hard objects. Unimodal distributions of both wear-facet and non-facet scratch orientations indicate simple orthal jaw movement. Scratch orientation and density differ between microscopic regions in Silesaurus, and unlike hadrosaurid dinosaurs, the microwear patterns of small areas are not identical to those of whole teeth.

Fossilized trackways have rarely been analyzed quantitatively to examine major trends and patterns in evolution despite their potential utility, especially in understanding locomotory evolution. In the present study, trackways of Triassic archosauriforms were analyzed. The analyses showed foot and stride lengths of archosauriforms increased from the Early to Middle Triassic, especially those of dinosauromorphs, which tripled. Dinosauromorphs were much smaller in foot length and stride length compared to other archosauriforms during the Early Triassic. They reached similar stride length compared with other archosauriforms during the Middle Triassic and similar foot length in the Late Triassic. Stride/foot ratio is significantly higher in dinosauromorphs compared to other archosauriforms throughout the Triassic. This relatively long stride length of dinosauromorphs is attributed to either faster speed or higher relative hip height that was probably caused by their digitigrade foot posture. Analyses of trackway data sets, especially in combination with precise trackmaker assignment and age determination, would bring us more thorough knowledge about locomotory evolution of tetrapods that complements body fossil evidence. © 2013 SEPM (Society for Sedimentary Geology).

Bipedalism evolved more than twice among archosaurs, and it is a characteristic of basal dinosaurs and a prerequisite for avian flight. Nevertheless, the reasons for the evolution of bipedalism among archosaurs have barely been investigated. Comparative analysis using phylogenetically independent contrasts showed a significant correlation between bipedality (relative length of forelimb) and cursoriality (relative length of metatarsal III) among Triassic archosaurs. This result indicates that, among Triassic archosaurs, bipeds could run faster than quadrupeds. Bipedalism is probably an adaptation for cursoriality among archosaurs, which may explain why bipedalism evolved convergently in the crocodilian and bird lineages. This result also indicates that the means of acquiring cursoriality may differ between archosaurs and mammals. © 2012 The Paleontological Society. All rights reserved.

The body mass of extinct animals have never been estimated from footprints, despite its potential utility. To redeem this situation, the relationship between body mass and the areas of footprints was derived from 17 species of modern tetrapods. Body mass of seven ichnospecies of pterosaur tracks were estimated, because pterosaur body weight is an intriguing topic with reference to their flying ability. Estimated body weights of pterosaurs range from 110 g to 145 kg. The result provides evidence that large pterosaurs are about 10 times heavier than the heaviest modern bird. (C) 2010 Elsevier B.V. All rights reserved.

In this study, I collected tracks and trackways from nine species of extant lizards representing all five major lizard clades. Previously, tracks from species of only two of these clades were described. Lizard tracks conventionally are regarded as having curved digit imprints that progressively increase in length from digit I to IV, with a smaller digit V directing antero-laterally. However, the zygodactylous feet of chameleons (Calumma parsonii and Furcifer pardalis), the posteriorly directed digit V in the pes of ground-dwelling geckos (Eublepharis macularius) and the rounded feet of blue-tongued skinks (Tiliqua scincoides) did not make otypicalo lizard tracks, and demonstrate that even within a limited taxonomic sample there can be considerable variation in the morphologies of lizard tracks. Among the lizards examined, mode of locomotion and how the feet function have more influence on the morphology of tracks than does the phylogenetic affinities of the trackmaker. This preliminary neoichnological study increases the known variation in lizard tracks and aids in interpreting the fossil trackway record by providing comparative information that can be used to identify fossil tracks made by lizards.

Femoral abduction angle, pelvic rotation angle and motion speed of eight species of modem crocodiles and lizards were measured to determine the factors affecting pace angulation and to assess whether limb posture can be estimated from trackways. Film sequences of dorsal views of free walking reptiles were filmed with a digital video camera recorder, then positions of the ankle, knee and hip joints were digitized and x-y coordinates were obtained for each of the half frames. Pace angulation and abduction angle of the supporting femur were calculated from the coordinates, together with motion speed and pelvic rotation. Multiple stepwise regression analysis showed that the femoral abduction angle was the most influential factor. explaining 47% of the variation in pace angulation value. The parameter estimate for the femoral abduction angle (-0.71) indicates that an animal with a more erect limb posture (i.e., lower femur abduction angle) makes a trackway with a higher pace angulation. Pelvic rotation also contributed significantly to the model, whereas motion speed did not. By inverse prediction, a trackway with an average pace angulation value of 108 degrees or less is unlikely to have been produced by an animal with a fully erect gait. A major implication of our study is that limb posture of extinct tetrapods can be reconstructed from fossilized trackways. Fossil trackways are an important source of information about posture. Analyses of fossilized trackways can complement information obtained from body fossils or, in case where body fossils are rare or lacking, fossilized trackways may be the primary source of information about posture, locomotion and behavior. (c) 2009 Elsevier B.V. All rights reserved.

The Pteraichnus trackmaker is usually hypothesized to be either a pterosaur or a crocodilian. Though the latter interpretation is recently not widely accepted, more experimental work on trackways of extant crocodilians is necessary to settle the debate. Here, the trackways of three species of modern crocodiles (Paleosuchus trigonatus, Crocodylus porosus, and Tomistoma schlegelii) in all major gaits and postures, namely sprawling, walking and running, were compared with Pteraichnus trackways. In all experimentally generated crocodilian trackways pentadactyl manus tracks are recognized, the external width between pes tracks is wider than the corresponding internal width between manus tracks, and tail marks are usually present. All crocodilian trackways collected in the present study revealed significant differences from Pteraichnus, which strongly suggests a non-crocodilian origin of Pteraichnus.

During the Triassic, some 250-200 million years ago, the basal archosaurs showed a transition from sprawling to erect posture. Past studies focused on changes in bone morphology, especially on the joints, as they reorientated from a sprawling to an erect posture. Here we introduce a biomechanical model to estimate the magnitude of femur stress in different postures, in order to determine the most reasonable postures for five basal archosaurs along the line to crocodiliforms (the rhynchosaur Stenaulorhynchus, the basal archosaur Erythrosuchus, the &apos;rauisuchian&apos; Batrachotomus, the aetosaurs Desmatosuchus and Typothorax). The results confirm a sprawling posture in basal taxa and an erect posture in derived taxa. Erect posture may have evolved as a strategy to reduce large bending stresses on the limb bone caused by heavy body weights in larger forms.