Fangs bared The poison-spitting dinosaurs in the film Jurassic Park were pure Hollywood invention, but some dinosaurs may really have had a venomous bite. The revelation comes from a two-centimetre tooth found in Mexico that has a longitudinal groove like those in the venom-channelling fangs of some snakes. It's the first evidence that any dinosaurs were venomous. The curved, blade-like tooth came from a small theropod, a family of two-legged predators that included Velociraptor, Tyrannosaurus and Dilophosaurus, a real dinosaur given fictional poison-spitting powers in Jurassic Park. "The general features of this tooth could be found in most theropod taxa," says Francisco Aranda-Manteca of the University of Baja California in Ensenada, Mexico, who studied the tooth along with his colleague Ruben Rodriguez de la Rosa. However, the groove-like structure is unique among dinosaurs. It resembles the venom-delivering front teeth of snakes in the cobra family and poisonous lizards such as the Gila monster and the Mexican beaded lizard, Aranda-Manteca told a meeting of the Society of Vertebrate Paleontology in Mexico City last month. Other palaeontologists are intrigued, but cautious. "It is not unquestionable evidence of venomous theropods," says Tom Holtz of the University of Maryland in College Park. "However, it does have an inverted serration pattern and groove down the back edge of the tooth, and indeed other animals which have a groove in that position are known to be poisonous." So far, only one tooth has been found, in rocks between 70 and 80 million years old. Measuring 5.6 by 9.5 millimetres at its base, the tooth could have come from several types of theropods. Though other theropods have been found in the same formation, what the rest of the animal was like isn't clear.