TELLTALE grooves in the fangs of a 60-million-year-old fossilised mammal suggest that it injected venom to paralyse its prey. It is the only extinct mammal known to have delivered poison.
Bisonalveus browni was a 10 to 15-centimetre-long predator with pointed teeth. But its bite had something extra 鈥� two long upper canines with grooves that seemingly allowed it to deliver poisonous saliva into the flesh of its prey (Nature, vol 435, p 1091). According to Richard Fox and Craig Scott of the University of Alberta in Edmonton, Canada, the grooves are unlike any venom-delivery system sported by living mammals. But they are similar to those of a poisonous snake called the boomslang (Dispholidus typus).
Fox and Scott are sure that the groove is not due to fossilisation because it is lined with enamel. And it cannot result from injury because it鈥檚 been found in six separate fossils.
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鈥淭he fossil suggests that mammals developed the ability to poison prey several times in their history鈥�
One of the few living mammals with poisonous saliva is the Haitian solenodon. This small shrew-like insectivore has grooves in its lower incisors through which it transmits poison to paralyse prey. A handful of shrews also have poisonous saliva but no grooves on their teeth.
B. browni is not closely related to any of these species, suggesting that mammals developed the ability to poison prey several times in their history.
Venomous mammals
Duck-billed platypus
Males have a poisonous spur on their heels which they use in self-defence and in fights over females.
Haitian solenodon
This small, nocturnal insectivore uses poisonous saliva to paralyse and kill prey. Found only on Hispaniola island.
North American short-tailed shrew
European water shrew
Mediterranean shrew
Shrews use poisonous saliva to paralyse prey such as frogs.
