This winter researchers from California and Germany report fossilized remains of a new, really big species of ichthyosaur, tagged Cymbospondylus youngorum [3]. This animal lived about 250 million years ago, which is relatively close to the time when lizards evolved to live in the sea. This makes it the earliest known “ocean giant”, and implies that these species “got big” really fast. Surprisingly fast. (This ichthyosaur was the largest dinosaur until large sauropods evolved, 40 million years later.)
The large size and early date of this fossil raise interesting question about how these species evolved to be so big, so fast, much faster than whales evolved to be huge. Big animals need a lot of food, so there must have been a lot to eat. And generally, there must be some advantage to getting really big, e.g., protection from predators or ability to catch food, or something.
The C. youngorum was found in a deposit cleverly called “Fossil Hill” in Nevada [2], which contains remains a a number of marine reptiles of various sizes. Fish and other smaller organisms aren’t well preserved, so it isn’t clear what everybody ate, though none of the large animals was a filter feeder like modern whales. This deep water ecosystem is quite different from the shallow warm water areas where the earliest, smaller, ichthyosaurs have been found.
This complex ecology, including the very large C. youngorum existed at a time when the oceans were just recovering from the Permian-Triassic mass extinction. So these animals not only got big fast, they did so in a “recovering” ocean, which presumably was not at peak productivity [1].
The researchers report theoretical analysis of the hypothesized food web. This work indicates that the ecosystem was stable, but considerably different from contemporary plankton-heavy ocean systems.
“Although both cetaceans and ichthyosaurs evolved very large body sizes, their respective evolutionary trajectories toward gigantism were different.”
([3], p. 9)
- Liebe Delsett Lene and D. Pyenson Nicholas, Early and fast rise of Mesozoic ocean giants. Science, 374 (6575):1554-1555, 2021/12/24 2021. https://doi.org/10.1126/science.abm3751
- Sabrina Imbler, This Sea Lizard Had a Grand Piano-Size Head and a Big Appetite, in New York Times. 2021: New York. https://www.nytimes.com/2021/12/23/science/ichthyosaurs-whale-dinosaur-evolution.html
- P. Martin Sander, Eva Maria Griebeler, Nicole Klein, Jorge Velez Juarbe, Tanja Wintrich, Liam J. Revell, and Lars Schmitz, Early giant reveals faster evolution of large body size in ichthyosaurs than in cetaceans. Science, 374 (6575):eabf5787, https://doi.org/10.1126/science.abf5787
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