Caelistiventus

In 2018 paleontologists Brooks Britt and colleagues named a new dimorphodontid pterosaur, Caelestiventus hanseni, from the Saints & Sinners Quarry in the Nugget Sandstone near Dinosaur National Monument in Utah, USA. Caelestiventus is known from a single partial specimen in several blocks of sandstone with the bones preserved in three dimensions. The genus name translates to “heavenly wind” in Latin, and the species name honors BLM geologist Robin L. Hansen, who facilitated work at the quarry. The thin and delicate bones are preserved in sandstone, but have only been partially exposed. Instead, the blocks of fossiliferous sandstone were CT-scanned, digitally reconstructed, and 3D printed. In the skull, much of the cheek region, skull roof, and lower jaws of Caelestiventus are present, missing the end and upper part of the rostrum and the ear region. The rest of the body is only known from the last wing phalanx from the right wing, and a few unidentifiable bone fragments. What’s known of the skull of Caelestiventus is generally similar to close relative Dimorphodon known from Lower Jurassic rocks in the UK. The nostril was extremely large and triangular, occupying most of the front of the snout. It’s separated from the antorbital fenestra by a very narrow strut of bone angled up and back. Unlike Dimorphodon, the jugal is deep and the orbit is smaller and was probably circular rather than triangular. The skull roof shows that the eyes were directed slightly forward rather than to the sides as in many other pterosaurs. Like Dimorphodon, its profile may have superficially resembled a puffin or toucan, but without the upper part of the snout it’s impossible to know for sure. The maxillae had 12 pairs of large leaf- or lance-shaped teeth. The teeth are widely spaced at the front of the maxillae, but the spaces between teeth decrease moving back so that the last six or seven pairs of teeth nearly contact their neighbors. The first nine pairs of maxillary teeth are roughly the same size, with the final three pairs being smaller. Each tooth is strongly laterally compressed and bears a narrow ridge on both the labial and lingual surfaces. Each tooth has two small apices, but no serrations. The rostrum, including the premaxillae and any premaxillary teeth, is missing, but Dimorphodon had four sets of large fang-like premaxillary teeth. The mandibles are both present and mostly complete. Overall, they are long and narrow, with a significant thickened and downturned tip. The lower edge of the mandibles have a very thin keel of bone, with the keel directed downward near the ends of the jaws, and then folding inward further back. Britt and colleagues suggest that the structure may have anchored a throat pouch for food storage or display. The tips of the mandibles had two pairs of large widely spaced teeth. Following a gap after the second tooth were 38 pairs of small closely-packed cone-shaped teeth taking up most of the remainder of the mandible. Overall, the dental formula of the upper and lower jaws are similar, but not identical to what’s seen in Dimorphodon. Dimorphodontids were predators of small terrestrial animals, using their fang-like rostral teeth to grasp prey, and the cheek teeth to process prey once captured. The only identifiable bone from the rest of the body is the final wing phalanx from the right wing. Comparing the size of the skull and wing phalanx in Caelestiventus to complete specimens of Dimorphodon shows that Caelestiventus had a relatively small skull or longer wings than its relative. The skull was roughly 18-20 cm (7-8 inches) long, and in life this specimen had a wingspan of about 1.5 m (5 feet). Dimorphodontids, like all early pterosaurs, had relatively short necks, long tails, and short hand bones. Many early pterosaurs may have spent time on the ground and in trees using both hand and foot claws to climb. The exact age of the Nugget Sandstone is unknown. It conformably overlies the Upper Triassic Chinle Formation and is thought to record the latest part of the Triassic and the earliest part of the Jurassic Periods. It marks a significant change in environment near the end of the Triassic Period. The underlying Chinle Formation was deposited in a warm wet environment with many lakes and rivers. Over a relatively short period of time, the tropical environment was replaced by a sandy desert forming thick dune sandstones. The sediments of the Saints & Sinners Quarry were formed at the bottom of a shallow oasis lake that was later overtaken by shifting dunes. In addition to Caelestiventus, the oasis was home to a drepanosaurid species known from many specimens, a procolophonid species, two sphenodontian species known from multiple specimens, two sphenosuchian species including one known from dozens of specimens, a coelophysid species known from several specimens, and a larger theropod. There are many theropod tracks and insect burrows, and the flora was dominated by cycads. The quarry is in the lower portion of the formation, and is thought to have been formed in the Late Triassic Period, roughly 200-210 million years ago. However, without volcanic ash layers within the formation, an exact date cannot be determined and the oasis deposits may have been formed in the Early Jurassic. Britt and colleagues placed Caelestiventus into a phylogenetic analysis of early pterosaurs. Their results show that it was indeed a close relative of Dimorphodon, and that dimorphodontids were one of the earliest branching groups of pterosaurs, known only from rocks of the Upper Triassic and Lower Jurassic. Unlike many recent analyses, they found that the multi-cusped pterosaurs of the Triassic like Eudimorphodon don’t form a monophyletic lineage called the eopterosaurs. Instead, multi-cusped teeth appear to be the primitive condition for all pterosaurs. Their analysis found the branching order of the long-tailed pterosaurs to be preondactylians, austriadraconids, Peteinosaurus, dimorphodontids, eudimorphodontids, Campylognathoides, anurognathids, rhamphorhynchids, with the wukongopterids being most-closely related to the short-tailed pterodactyloids. They also found that a second purported species of Dimorphodon from Lower Jurassic rocks of northern Tamaulipas, Mexico, D. weintraubi, represents the largest and earliest member of the anurognathid lineage.