Sinornithosaurus

Abstract: Dromaeosaurids, despite their notoriety, are poorly characterized meat-eating dinosaurs, and were previously known only from disarticulated or fragmentary specimens1. Many studies have denied their close relationship to birds2,3. Here we report the best represented and probably the earliest dromaeosaurid yet discovered, Sinornithosaurus millenii gen. et sp. nov., from Sihetun, the famous Mesozoic fish–dinosaur–bird locality in China4,5. Sinornithosaurus not only greatly increases our knowledge of Dromaeosauridae but also provides evidence for a filamentous integument in this group. It is remarkably similar to early birds postcranially. The shoulder girdle shows that terrestrial dromaeosaurids had attained the prerequisites for powered, flapping flight6, supporting the idea that bird flight originated from the ground up7,8. The discovery of Sinornithosaurus widens the distribution of integumentary filaments among non-avian theropods5,9,10. Phylogenetic analysis indicates that, among known theropods with integumentary filaments or feathers2,5, Dromaeosauridae is the most bird-like, and is more closely related to birds than is Troodontidae.

Abstract: A new theropod dinosaur, Shanag ashile, from the Early Cretaceous Oosh deposits of Mongolia is described here. The new specimen (IGM 100/1119) comprises a well-preserved right maxilla, dentary, and partial splenial. This specimen exhibits a number of derived theropod features, including a triangular anteriorly tapering maxilla, a large antorbital fossa, and maxillary participation in the caudally elongate external nares. These features resemble the Early Cretaceous dromaeosaurids Sinornithosaurus millenii and Microraptor zhaoianus, as well as the basal avialan Archaeopteryx lithographica. A comprehensive phylogenetic analysis including 58 theropod taxa unambiguously depicts the new Oosh theropod as a member of Dromaeosauridae. Relative to other dromaeosaurids, Shanag ashile is autapomorphic in its lack of a promaxillary fenestra and in the presence of interalveolar pneumatic cavities. The discovery of IGM 100/1119 expands our knowledge of Early Cretaceous dromaeosaurids and the faunal similarity ...

Abstract: Two skeletons of the large compsognathid Sinocalliopteryx gigas include intact abdominal contents. Both specimens come from the Jianshangou Beds of the lower Yixian Formation (Neocomian), Liaoning, China. The holotype of S. gigas preserves a partial dromaeosaurid leg in the abdominal cavity, here attributed to Sinornithosaurus. A second, newly-discovered specimen preserves the remains of at least two individuals of the primitive avialan, Confuciusornis sanctus, in addition to acid-etched bones from a possible ornithischian. Although it cannot be stated whether such prey items were scavenged or actively hunted, the presence of two Confuciusornis in a grossly similar state of digestion suggests they were consumed in rapid succession. Given the lack of clear arboreal adaptations in Sinocalliopteryx, we suggest it may have been an adept stealth hunter.

Abstract: Gong and colleagues recently described unusual traits in the dromaeosaurid Sinornithosaurus that were interpreted as the first evidence of a venomous dinosaur. This interpretation was based on extremely elongated maxillary teeth, morphologically similar to those present in poisonous snakes; labial grooves on maxillary and dentary tooth crowns; and an additional ornamented depression in the lateral surface of the maxillary bone (subfenestral fossa). A reappraisal of each of these morphological traits is provided here in light of comparisons with other theropod dinosaurs and previous discussions for inferring poisonous capabilities in fossil taxa. We fail to recognize unambiguous evidence supporting the presence of a venom delivery system in Sinornithosaurus. For example, the extremely elongated teeth seem to be a taphonomic artifact due to the displacement of teeth outside the alveoli; the labial grooves are present in a wide variety of theropods; and no strong evidence for the lodging of a venomous gland is recognized. In contrast, the cranial and dental anatomy of Sinornithosaurus is congruent with that of other dromaeosaurids. The weak support for a venomous Sinornithosaurus renders unlikely the ecological model proposed by Gong and colleagues for this predatory dinosaur.