A bird-like dinosaur that prowled an ancient forest 125 million years ago used venom to subdue its prey, according to a new theory.
Sinornithosaurus's upper teeth resemble those of "rear-fanged" snakes which bite their prey and channel venom into the wound.
The dinosaur probably fed on the abundant birds which inhabited what is now north-east China.
The work appears in Proceedings of the National Academy of Sciences journal.
Rear-fanged snakes are considered less dangerous than other venomous snakes.
The fangs in these snakes do not inject venom, but instead channel the poison along a groove on the outer surface of teeth that pierce their prey's flesh.
Sinornithosaurus had upper teeth that were similarly long, grooved and fang-like.
David Burnham, from the University of Kansas, US, and colleagues, say the dinosaur's upper jaw also contained a pocket that could have housed a venom gland.
This is connected to the base of the teeth by a long groove.
Like rear-fanged snakes, the venom Sinornithosaurus used was probably not lethal. The researchers suggest it instead caused rapid shock, allowing the dinosaur to subdue its prey.
The researchers propose that the length of the dinosaur's fangs allowed it to penetrate the thick plumage of birds that populated the forests of north-east China during the early Cretaceous period.