During the Age of Dinosaurs, some 200 million years ago, fish-shaped ichthyosaurs and long-necked plesiosaurs ruled the seas. Both types of sea dragons were air-breathing reptiles. They started out as lizard-esqe land animals that later inhabited shallow coastal seas. Over millions of years, they evolved body designs suitable for efficient swimming and took command of the open ocean.
Both reptile lineages owe their discovery to Mary Anning, an early Victorian fossil collector who lived and worked on England’s Jurassic Coast. This year marks the 200th anniversary of Anning’s famous discovery of the first complete skeleton of an ichthyosaur; she found the first plesiosaur in 1823.
BLOG: Happy Discovery Day, Ichthyosaur: 200 Years Later
To commemorate the anniversary of Mary Anning’s discovery, I spoke to Ryosuke Motani, an ichthyosaur expert from the University of California, Davis:
DNews: Why do you study ichthyosaurs?
Motani: Because they are beautiful, and somehow they touched my mind. And of course they are interesting from a scientific perspective—they are air-breathing reptiles that turned into a fish shape!
DNews: Have you been to England’s Jurassic Coast, to the limestone cliffs where Mary Anning discovered the first complete skeleton in 1811?
Motani: The first time I went there, I went with my professor, Chris McGowan. He was English, so he knew where that skeleton came from, and he took me to the spot. I thought, gosh, that’s history from the long past right in front of me.
DNews: When you first saw Mary Anning’s first ichthyosaur skeleton, did you notice anything special about it?
One thing I found somewhat strange is that it is not the typical species from there. The common ichthyosaur from the Jurassic Coast is Ichthyosaurus communis, but hers was a much larger one, a Temnodontosaurus. Bigger species have fewer individuals, so you have fewer fossils. It’s just the chance factor.
DNews: Could you tell me about your most memorable search for ichthyosaur fossils?
We right now are looking in China, near the Yangtze River in Anhui province, for the earliest marine reptiles. Many different ichthyosaurs and several marine reptiles appeared almost simultaneously, but we don’t know exactly what time they appeared. And we don’t have the exact ancestor of ichthyosaur, the one with a limb rather than a fin. Last September we were doing systematic excavation with machinery, but we weren’t really finding anything. I was starting to get worried. We had three days left, and then that day, I walked around frantically and bumped up on this small ichthyosaur. You know how they have that large eye? It almost looked like it was smiling at me. Then in May 2011, we went back to the same spot and started systematic digging and found about 80 reptile specimens. We found something surprising there, but it’s still under preparation.
DNews: What made ichthyosaurs such successful predators of the Jurassic seas?
I think they were lucky, but they were able to take advantage of that luck. They evolved certain traits, such as a higher metabolism and the ability to cruise, that got them ready to cope with changing environment.
DNews: What are the top five discoveries about ichthyosaurs over the past 10 years?
HUGE NUMBERS: There have been a huge number of ichthyosaurs coming out of China in the past 10 years, and they fill a time horizon not represented elsewhere and strengthen the knowledge of other time periods with better specimens.
GREAT CRUISERS: Sea level change in the Triassic Period really affected the evolution of ichthy in their early days. So when sea level was rising, shallow ichthy appeared and were successful. At the time, they were mostly lizard-shaped, coastal animals because there were lots of shallow waters. As sea level dropped over a long period, those shallow waters disappeared and only the great cruisers survived. That’s when fish-shaped ichthyosaurs appeared.
WARM-BLOODED: Whether they were truly warm-blooded or not is still being debated. But at least there seems to be agreement that their metabolism was higher than other reptiles’. If your metabolism is stable at different temperatures, it makes you more flexible. That’s the advantage mammals have.
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FAST AS TUNAS: There was one publication showing ichthyosaurs were as fast as tunas. It was basically a hydrodynamic calculation from the body outline.
BIG AND SCARY: There was this news last year or the year before about the giant ichthyosaur with the sharp teeth. It’s not from the second oldest time horizon, which means that large, 10-meter-long ichthyosaurs evolved in the first 500 million years.
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IMAGES:
Temnodontosaurus burgundiae attack Stenopterygius hauffianus. Courtesy Dmitry Bogdanov via Wikimedia Commons
Paleontologist Ryosuke Motani. Courtesy Ryosuke Motani
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