A new study, published in the journal Science, reveals more information about the oldest ocean giant to ever roam the earth. After discovering a two-meter skull of a newly discovered species of giant ichthyosaur named Cymbospondylus youngorum that is believed to have lived around 246 million years ago, a research team at the Natural History Museum of Los Angeles County sheds new light on the marine reptiles’ rapid growth. The findings of the largest fossil from that era ever found are significant because they help us better understand the journey of modern cetaceans to becoming the largest animals to live in our times.
“Ichthyosaurs derive from an as yet unknown group of land-living reptiles and were air-breathing themselves,” says lead author Dr. Martin Sander, paleontologist at the University of Bonn and Research Associate with the Dinosaur Institute at the Natural History Museum of Los Angeles County (NHM). He continues: “From the first skeleton discoveries in southern England and Germany over 250 years ago, these ‘fish-saurians’ were among the first large fossil reptiles known to science, long before the dinosaurs, and they have captured the popular imagination ever since.”
The well-preserved skull was found in the Augusta Mountains of Nevada, along with part of the backbone, shoulder, and forefin. The bones date back to the Middle Triassic (247.2-237 million years ago), thus representing the earliest case of an ichthyosaur reaching epic proportions. The species is believed to reach lengths of 17 metres, making it the largest animal discovered from that time period, on land or in sea.
“The importance of the find was not immediately apparent,” notes Dr. Sander, ”because only a few vertebrae were exposed on the side of the canyon. However, the anatomy of the vertebrae suggested that the front end of the animal might still be hidden in the rocks. Then, one cold September day in 2011, the crew needed a warm-up and tested this suggestion by excavation, finding the skull, forelimbs, and chest region.”
C. youngorum inhabited the oceans around 246 million years ago. Its elongated snout and conical teeth suggest that C. youngorum preyed on squid and fish, but its size meant that it could have hunted smaller and juvenile marine reptiles as well.
Co-author and ecological modeler Dr. Eva Maria Griebeler from the University of Mainz in Germany notes: “Due to their large size and resulting energy demands, the densities of the largest ichthyosaurs from the Fossil Hill Fauna including C. youngourum must have been substantially lower than suggested by our field census. The ecological functioning of this food web from ecological modeling was very exciting as modern highly productive primary producers were absent in Mesozoic food webs and were an important driver in the size evolution of whales.”
The researchers found that whales and ichthyosaurs don’t only have similar sizes, they also have similar body plans and both came to exist after mass extinctions. According to them, cetaceans and ichthyosaurs had different evolutionary growing mechanisms involved, despite evolving very large body sizes. Ichthyosaurs had an initial boom in size, becoming giants early on in their evolutionary history, while whales took much longer to reach the outer limits of huge. They found a connection between large size and raptorial hunting and a connection between large size and a loss of teeth as can be seen in filter-feeding whales, for example.
Ichthyosaurs’ initial foray into gigantism was likely thanks to the boom in ammonites and jawless eel-like conodonts filling the ecological void following the end-Permian mass extinction. While their evolutionary routes were different, both whales and ichthyosaurs relied on exploiting niches in the food chain to make it really big.
“As researchers, we often talk about similarities between ichthyosaurs and cetaceans, but rarely dive into the details. That’s one way this study stands out, as it allowed us to explore and gain some additional insight into body size evolution within these groups of marine tetrapods,” says NHM’s Associate Curator of Mammalogy (Marine Mammals), Dr. Jorge Velez-Juarbe. “Another interesting aspect is that Cymbospondylus youngorum and the rest of the Fossil Hill Fauna are a testament to the resilience of life in the oceans after the worst mass extinction in Earth’s history. You can say this is the first big splash for tetrapods in the oceans.”
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Photography courtesy of Unsplash (cover image), Natalja Kent, courtesy of the Natural History Museum of Los Angeles County (first image) and Martin Sander, courtesy of the Natural History Museum of Los Angeles County (second image). Illustration by Stephanie Abramowicz, courtesy of the Natural History Museum of Los Angeles County.