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.
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