BioEd Online

In the caves of a hilly Oklahoma ghost town, researchers have found what may be the first evidence of preserved insect remains in the mouths of fossilized vertebrates. The find is compelling evidence that early reptiles, the equivalent of modern-day lizards, fed on insects.

Sean Modesto, a biologist at Cape Breton University in Nova Scotia, Canada, and his colleagues found pieces of arthropod skeleton on the teeth inside two 280-million-year-old skulls of a species of reptile they have yet to fully describe. They report the discovery in the journal Biology Letters¹.

One skull contained a cuticle with five segments that seemed to be part of an antenna, and the other had a long cuticle fragment that was narrow at one end and broader at the tip. This could have been part of a rear appendage.

"It is extremely uncommon to find the remains of organisms in the mouths of fossilized predators," says Matthew Vickaryous, who studies the anatomy of fossil vertebrates at the University of Guelph in Ontario, Canada. "To the best of my knowledge, this is a one of a kind find."

Lucky find

Modesto and his collaborators made this discovery entirely by chance. "You don't expect to see the last meal lodged in the teeth of fossils," Modesto says. "The modern equivalent is finding a popcorn kernel shell in the tooth of an ancient Mayan."

The two skulls come from an enigmatic group called parareptiles, which first appeared nearly 300 million years ago and for the most part became extinct by the end of the Permian period, with just a few species lingering into the age of dinosaurs.

"To have pieces of both vertebrate and invertebrate preserved at the same time is very unusual," Vickaryous says. Vertebrate palaeontologists may overlook small pieces of invertebrate remains when excavating spectacular vertebrate fossils. Beyond the initial detection, preserving the remains requires careful recovery and preparation, he adds.

In younger specimens, researchers have found mollusc shell fragments in the gut of a fossil sea turtle², preserved fish remains in a bird's stomach³, lizard and mammal skeletons in fossil dinosaur stomachs⁴ and dinosaur remains in a fossil mammal's stomach⁵. In fossil reptiles from the Permian, scientists have found plant material in the gut⁶ and reptile bones in the mouth⁷.

But little other evidence is available for the dietary habits of the vertebrates that lived during the Permian, says Conrad Labandeira, palaeoecologist at the National Museum of Natural History in Washington DC. "This paper may be more important in the long run than the original description of the fossil bones."

Insectivorous evidence

Roy Beckemeyer, palaeoentomologist at the University of Kansas Natural History Museum in Lawrence, has studied Permian insect fossils in Oklahoma. He evaluated photographs of the finds and verified that the fragments were from an arthropod. "We know of roughly 200 species of insects in this area during that time," Beckemeyer says. "There's a very good chance that these reptiles were insectivorous."

Scientists had long suspected that early reptiles were insectivorous because of the shape of their teeth, which are sharp and curve inward, making them ideal for piercing insect skeletons and holding struggling prey in place. But that evidence is indirect because it relies on comparisons between extinct and living animals.

"It's pretty much smoking-gun type of evidence when you actually have the organism in the part of the anatomy responsible for feeding," Labandeira says. "It's very compelling evidence that closes the case."