About 60 million years ago, a small shrew-like mammal captured its prey by stabbing it with dagger-like teeth that delivered a nasty dose of venom, paleontologists reported today.
"Nothing like that has ever been described before," said Richard Fox, a vertebrate paleontologist at the University of Alberta in Edmonton, Canada.
Fox and his colleague Craig Scott found fossilized teeth at two sites in central Alberta. The remains are the first evidence to suggest that extinct mammals used venom to either capture prey or fend off predators.
Venoms are common in snakes and spiders, but only four living mammal species use venom today. According to Fox, evolutionary biologists have long wondered why venom is so rare in modern mammals.
The newly discovered tooth fossils—some belonging to the extinct shrew-like Bisonalveus browni and others to an unidentified creature—indicate the toxic strategy was perhaps more widespread among early mammals, Fox said.
Fox and Scott detail their findings in tomorrow's issue of the science journal Nature.
Mark Dufton, a chemist and venom expert at the University of Strathclyde in Glasgow, Scotland, said the discovery is a fascinating contribution to the understanding of early mammals.
"If a venomous capability was a frequent feature of these creatures, it means their power-to-weight ratio was generally higher than thought previously," Dufton wrote in an e-mail to National Geographic News. "They could have posed a much more serious threat towards competing vertebrates within their niches."
Dagger Teeth
B. browni fossils were first discovered in 1956. They consisted of lower jawbone fragments containing molar teeth, and were dated to about 60 million years ago.
Analysis of these fossils showed the ancient creature to be a small mammal, possibly distantly related to the modern scaly anteater known as the pangolin.
The newly discovered B. browni fossils are the best preserved remains of the extinct mammal. They include never-before-seen front teeth and a skull fragment containing the dagger-like grooved tooth that the paleontologists say is the tell-tale signature of a venomous bite.
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