Xu Xing

A New Rhamphorhynchid Pterosaur from the Upper Jurassic of Xinjiang, China, and the Phylogenetic Relationships of Basal Pterosaurs

ABSTRACT n A new rhamphorhynchid pterosaur species, Sericipterus wucaiwanensis, gen. et sp. nov., is described from the Upper Jurassic part of the Shishugou Formation in the Xinjiang Autonomous Region of northwest China. Pterosaurs from this unit are the earliest and only records of pterosaurs in the Jurassic of northwest China. The individual specimen is one of the largest known among ‘rhamphorhynchoids,’ or non-pterodactyloid pterosaurs. The holotype comprises an associated skeleton of mostly disarticulated, largely three-dimensional material. Although partly crushed, the preservation in this specimen reveals morphology rarely seen in non-pterodactyloid pterosaurs. This includes a distinct cervical intervertebral articulation morphology that is proposed to be widespread among the non-pterodactyloids. The skull of this new specimen is most similar to that of other rhamphorhynchids, Angustinaripterus longicephalus and Harpactognathus gentryii, found in terrestrial deposits. A phylogenetic analysis of 18 non-pterodactyloid pterosaurs and the Pterodactyloidea places Sericipterus wucaiwanensis with these species within the Rhamphorhynchinae and a monophyletic Rhamphorhynchidae. Unlike previous phylogenetic analyses, the Dimorphodontidae is paraphyletic, the Campylognathoididae is polyphyletic, and the Anurognathidae is the sister group of the Pterodactyloidea. Sericipterus wucaiwanensis, Angustinaripterus longicephalus, Harpactognathus gentryii represent a clade of large pterosaurs that likely lived in the terrestrial settings in which they preserved.

Dinosaur death pits from the Jurassic of China

Abstract Three newly discovered bonebeds from the Shishugou Formation of Xinjiang, China, are unusual in preserving vertically stacked and articulated to associated skeletons of at least 18 small, non-avian theropod dinosaurs in pits that are 1–2 m deep. The pits host a soft sediment-deformed mixture of alluvial and volcanic mudstone and sandstone. There is no evidence that the pits were discrete depressions in the topography that filled through time. Rather, they appear to have been highly localized areas of liquefaction caused by large-dinosaur (possibly sauropod) trampling of saturated sediments. Evidence indicates that the small theropods, and some other small vertebrates, became mired and died in these mud-filled pits. High quality skeletal preservation suggests that most individuals were buried within days to months after their deaths. Carcasses were buried successively, coming to rest above previously buried individuals. In some cases, skeletal body parts became separated or were removed, probably during scavenging. Given the large sizes of the pits relative to the small body sizes of the vertebrates contained within them, we conclude that small vertebrates (<3 m long and <1 m tall) were particularly susceptible to miring at these sites. Although the small, presumably herbivorous ceratosaur, Limusaurus inextricabilis, dominates the combined small theropod assemblage from these bonebeds (minimum number of individuals [MNI] u200a=u200a 15), there is no evidence that any biological features other than its small size and a large, and possibly, gregarious local population were responsible for its becoming mired in large numbers. A bias for small theropods in these bonebeds, compared to their relatively low abundance in the overall Shishugou Formation fauna, underscores that small theropods are underrepresented in Mesozoic fossil assemblages collected from other ancient alluvial and paludal settings.

Convergent Evolution of a Eusuchian-Type Secondary Palate within Shartegosuchidae

ABSTRACT Shartegosuchids are a poorly known, early-branching group of Asian and North American crocodylomorphs. Shartegosuchids have been hypothesized to have eusuchian-type secondary palates, but a paucity of described material makes assessing this difficult. Our fieldwork in western Mongolia recovered cranial material of a new Shartegosuchus specimen from the Ulan Malgait Formation, which we CT-scanned and digitally reconstructed to investigate its palatal morphology. We then incorporated this new anatomical information into a revised phylogenetic dataset to assess its affinities. Our study confirms that Shartegosuchus has a posteriorly placed choana that is fully enclosed by the pterygoids, but differs from Eusuchia in possessing a secondary palatal fenestra and reduced palatine bones. Shartegosuchus, together with Adzhosuchus, Fruitachampsa, and Nominosuchus, forms the monophyletic group Shartegosuchidae. Shartegosuchidae is nested within a larger clade Shartegosuchoidea, and this clade is an earlier-diverging lineage than Eusuchia, showing that a eusuchian-type secondary palate evolved multiple times in crocodylomorphs, including very early in the groups evolutionary history. The co-occurrence of Nominosuchus in the Ulan Malgait Formation and the Shishigou Formation allows us to assign an early Oxfordian age to Shartegosuchus. The independent evolution of a eusuchian-type secondary palate in an oreinorostral group suggests that the link between platyrostry and a closed secondary palate has been overstated.