Bad Breathosaurus.

A dinosaur that could blow you away with poisonous breath? Recently two Mexican paleontologists (dino experts) produced the first and sole evidence so far that some dinos may have used their teeth to lethally inject their prey with venom. The evidence: a fossilized (preserved) dinosaur tooth from Mexico's Baja Peninsula.

The curved 2 centimeter (0.8 inch)-long broken tooth features a thin, lengthwise groove--similar to the cobra's hollow fang. Paleontologist Ruben Rodriguez-de la Rosa at the Museum of the Desert in Saltillo, Mexico, thinks the groove, like those found in modern snakes, could have channeled poison produced in venomous glands (chemical-secreting organs). The tooth may have belonged to an unknown wolf-size species of theropod--two-footed carnivores (meat-eaters) that include T. Rex. The theropod may have roamed Earth 144 to 65 million years ago during the late Cretaceous period.

But some scientists aren't biting: "There's no reason to suspect dinosaurs were incapable of producing poison," says University of Maryland theropod expert Tom Holtz. "But no other theropod is known to have had a grooved, smooth-edged tooth like this." Meat-eating dino teeth usually feature serrated or jagged edges. So if this theropod didn't possess a poison gland, the groove may have served to trap decaying meat and spawn bacteria (microorganisms), Holtz speculates. Then, like today's Komodo dragons, these dinos could have killed prey by breathing out the stinky, toxic gunk.

Another possibility: bad dentistry. "It could simply be a malformed tooth," says Holtz.