Dinner in the Paleozoic – new-found dinosaur skeletons contain fossilized food
Paleontologists make a science of educated guesswork. Given the most meager of clues – a fossil jawbone or the imprint of an ancient fern – they try to reconstruct a vanished world. But every once in a while they get lucky and find a fossil that eliminates some of the guessing.
Hans-Dieter Sues, a paleontologist at the Royal Ontario Museum, and Wolfgang Munk, at the Karlsruhe Museum of Natural History in Germany, recently got very lucky: they found the fossilized intestinal contents of two 280-million-year-old reptiles.
“These are the earliest gut contents we have for any terrestrial vertebrate,” says Sues. What’s more, the new find is also the first direct evidence of the appearance of herbivores on land: in both fossils the gut contents turned out to be plant matter.
Sues and Munk, working in Karlsruhe, were preparing the fossil of a five-foot-long protorosaur – a relative of the family that later gave rise to dinosaurs, crocodiles, and alligators – that had been found by private collectors in a shale bed in northern Germany. While chipping away around the reptile’s rib cage, right about where the stomach would have been, the two researchers found thick clusters of conifer seeds and smooth, round stones. Sues and Munk suspect the protorosaur probably swallowed the stones and used them as gizzard stones to grind food, much as birds do today. After uncovering the rest of the fossil, and after X-raying it, they found a second bunch of seeds near the end of what would have been the intestinal tract. Those seeds looked as if they’d been ground by the stones.
In the second fossil, a three-foot-long turtle relative called a pareiasaur, the researchers found the chewed remains of plants. Both fossils came from the same shale bed, which 280 million years ago had been a thick layer of oxygen-poor muck at the bottom of a shallow sea. Sues thinks flash floods may have washed the two land-dwelling reptiles into the sea.
Until now, paleontologists had only indirect evidence – primarily the shapes of fossil teeth – for the existence of the first vertebrate herbivores. In fact, the protorosaur Sues and Munk examined had been thought to be a meat eater because it had pointy teeth rather than the flat grinding teeth characteristic of herbivores. Apparently the stones in its stomach allowed it to get along without teeth made for grinding. Says Sues: “It just once again shows how cautious you have to be in making paleontological reconstructions.”
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