Scientists unearthed a skull from a fossil-rich area of northern Nevada that reveals striking answers about ocean life — both past and present.
What’s new — In a study published Thursday in the journal Science, researchers identified a new species of ichthyosaur — an enormous fish-shaped marine reptile that emerged 250 million years ago not long after the Permian mass extinction wiped out most of life on Earth.
The new species is dubbed Cymbospondylus youngorum — a massive creature comparable in size to the largest animal on Earth today: the blue whale.
The researchers’ findings tease a fascinating insight into the rapid evolution of ichthyosaurs’ enormous bodies compared to similarly large cetaceans — a class of marine animals that includes whales.
“We have discovered that ichthyosaurs and whales, two iconic groups of giant ocean predators that both evolved from land-living ancestors, evolved gigantism in very different ways,” Lars Schmitz, a co-author on the study and an associate professor of biology at Claremont McKenna, tells Inverse.
How they made the discovery — The researchers identified the new ichthyosaur species from bones found in an area of northern Nevada known as the Fossil Hill Fauna.
The fossil is a very large skull, found along with a few other specimens of C. youngorum.
After analyzing the old bones, researchers both estimated the animal’s body size and constructed a phylogenetic tree to tease out how fast their bodies evolved compared to whales.
Finally, they used mathematical models to try and retrace how food webs could have supported large animals like C. youngorum so early on in the Mesozoic period.
What they found — The scientists say this C. youngorum clocked in at a massive weight of more than 80,000 pounds and had a body length of more than 59 feet. Its skull alone is 6.2 feet in length — the size of an adult man.
“No other vertebrate group appears to have evolved gigantism this quickly,” Nicholas Pyenson tells Inverse. Pyenson is a curator of fossil marine mammals at the Smithsonian and co-author of a related article regarding the study.
The massive creature lived roughly 246 million years ago. Other large land animals would not appear until 40 million years later, with the arrival of sauropod dinosaurs during the Jurassic period.
The body shape of the newfound ichthyosaur was remarkably similar to modern whales, even though whales evolved nearly 200 million years after the ancient marine reptile.
But what was even more impressive was the rapid nature of the ichthyosaur’s evolution. Within just three million years of their origin — or the first one percent of its evolutionary history — some species of ichthyosaur had evolved to more than 55 feet in length.
Contrast that with the whale, which also evolved to gigantism much later in its evolutionary life.
“When we look at the evolutionary history of whales, it took most of their 50 million-year history to achieve the gigantic body sizes of today's fin whales, blue whales, sperm whales, and right whales,” Schmitz explains.
“The big surprise here is that ichthyosaurs are the ones who attained gigantism fast.”
This evolution is also remarkable because it took place not long after the Permian mass extinction or the “Great Dying” which killed off most animals on Earth.
“We believe that the land-living ancestors of the ichthyosaurs became marine [animals] after this extinction, and reaching the large size this fast is impressive,” Lene Delsett, a paleontologist working at the Smithsonian and a co-author on a related article on the study, tells Inverse.
Since the ichthyosaur would go on to dominate the Earth’s oceans for another 150 million years before becoming extinct, its gigantism was clearly an evolutionary advantage.
Why it matters — Researchers have long held that the size of ocean creatures during the Mesozoic period (66-252 million years ago) was limited by the lack of primary producers like plankton, who provide energy, and, thus, food for creatures higher up in the food chain.
This study blows that theory out of the water, suggesting that Mesozoic ocean ecosystems were more than able to support large animals like the ichthyosaur. The findings provide unprecedented insight into these early ocean ecosystems.
“We infer that the pelagic ecosystems of the early Middle Triassic (244 million years ago) could, surprisingly, support several large tetrapod ocean consumers,” the researchers write.
But the findings are important to a broader, non-scientific audience as well. Since the study finds analogies between the now-extinct ichthyosaurs and modern marine life, we’d do well to pay attention to the implications of those similarities— lest we want current ocean giants to disappear, too.
“Ichthyosaur evolution tells us that ocean giants are not guaranteed features of ocean ecosystems, and that we ought to understand the threats and solutions to keeping the giants today alongside us.”
Failure to learn from the lessons of the ancient marine past could doom ocean ecosystems in the present.
“We should be concerned about the fate of ocean giants because many of the largest whales today are ecosystem engineers and contribute to the health and productivity of the oceans that we need for ourselves,” Pyenson adds.
What’s next — The findings, in turn, could spur on further research about not just ichthyosaurs and whales, but “also other vertebrate animals that have returned to life at sea such as mosasaurs and others,” Schmitz explains.
Further studies could help explain the ecological conditions driving the evolution of ocean gigantism that paleontologists are seeing in the fossil record.
“The one thing that the fossil record tells us over and over again is that if environmental conditions are not quite right, we sometimes see a dramatic loss of species,” Schmitz says. But there’s one big caveat.
“On the other hand, if the environment allows [it], life diversifies, not only in the number of species but also in terms of diversity of anatomy and ecology,” Schmitz adds.
So, the environmental clues illuminating the evolution of diverse modern marine ecosystems — and the giants that dwell within — may still be hidden within the Earth’s crust.
Abstract: Body sizes of marine amniotes span six orders of magnitude, yet the factors that governed the evolution of this diversity are largely unknown. High primary production of modern oceans is considered a prerequisite for the emergence of cetacean giants, but that condition cannot explain gigantism in Triassic ichthyosaurs. We describe the new giant ichthyosaur Cymbospondyus youngorum sp. nov. with a 2-meter-long skull from the Middle Triassic Fossil Hill Fauna of Nevada, USA, underscoring rapid size evolution despite the absence of many modern primary producers. Surprisingly, the Fossil Hill Fauna rivaled the composition of modern marine mammal faunas in terms of size range, and energy-flux models suggest that Middle Triassic marine food webs were able to support several large-bodied ichthyosaurs at high trophic levels, shortly after ichthyosaur origins.