However, the new fossil, described by Kear and colleagues at The University of New South Wales and the Australian Museum, both in Sydney, hints that this extinction event might not explain the demise of all ichthyosaurs. Dissolving the ancient skeleton's limestone substrate with acid revealed several unexpected menu items.
The pregnant female Platypterigius specimen (unlike most reptiles, ichthyosaurs bore live young) was found not with squid remains in its gut, but a mass of vertebrate bone fragments.
These included the bones of fish, hatchling turtlesprobably snapped up while they bobbed along at the water's surface-and an extinct bird. Some modern bird groups appear during the Cretaceous period. The bird may have been a floating carcass scavenged after it washed into the sea from woodland, said Kear.
"It is exciting to have a turtle and bird in an ichthyosaur stomach," but many don't agree that the reptiles fed exclusively on squid anyway, commented paleontologist Ryosuke Motani at the University of Oregon in Eugene. "All we know is that the disappearance of ichthyosaurs roughly corresponded with the [squid-like animal] extinction event," said Motani. We just don't have any better guess about the cause of the demise, he said.
"The problem is we have so little data," added McGowan, "Most of our theories are pure guesswork," he said.
Nevertheless, the new fossil hints that Cretaceous ichthyosaurs may have been far more opportunistic feeders than believed, says the study, which argues that the decline of ichthyosaurs may therefore be linked to competition with other types of speedy pursuit predators.
"Competitors might include bony fish," said Kear. Many of the modern types of fish had evolved by then and some of these would have been direct rivals. Another competitor may have been a different marine reptile, which returned to the sea quite independently of ichthyosaurs.
Long-necked, paddle-footed plesiosaurs may have caused ichthyosaur declines. The earliest members of one group, known as polycotylid plesiosaurs, are found in many of the same deposits as ichthyosaurs, said Kear, and like those animals, have physical characteristics ideal for the swift pursuit of small prey.
More National Geographic News Stories on Dinosaurs:
Loch Ness Sea Monster Fossil a Hoax, Say Scientists
Newly Rediscovered Dinosaur Fossil is Missing Link to Jurassic Giants
Dinosaur Cannibal: Fossil Evidence Found in Africa
Bizarre Dinosaurs Shed Light on Adaptation
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Dino Dung: Paleontology's Next Frontier?
Do They Really Look Like That? The Science of Dino Art
Dinosaur Footprints: Tracks Tell Prehistoric Secrets
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Utah Dinos May Have Been Killed By Drought
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Fossil Implies Our Early Kin Lived in Trees, Study Says
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Fossil of Dog-Size Horned Dinosaur Unearthed in China
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Researchers Rethink Dinosaur Die Off Scenario
Researchers Melt Polar Dinosaur Mysteries
Scientist's Finds Spur New Thinking on Dino Evolution
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Study Paints New Picture of Dinosaur's Nose
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Dinosaur Beak Probably Used to Strain Food, Not Kill Prey
Additional Dinosaur Resources from National Geographic:
Paul Sereno: National Geographic Explorer-in-Residence and Dinosaur Hunter
Destinations: Dinosaur National Monument
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