Newly Discovered Fossil From 246 Million Years Ago Believed to Be Earth's 'First Giant'

A newly discovered fossil dating to the age of the dinosaurs has provided insight into the evolution of aquatic species that exist today.

Research published December 24, 2021, in Science describes how the two-meter skull of Earth's "first giant" ichthyosaur species predated both extinct marine animals and modern whales, simultaneously revealing a faster evolution of large body size in ichthyosaurs than in cetaceans.

According to the Natural History Museum of Los Angeles County, the fossil of a skull was excavated from the Fossil Hill Member rock unit in Nevada's Augusta Mountains of Nevada. The preserved skull and part of its backbone, shoulder and arm date back to the Middle Triassic time period, approximately sometime between 237 and 247.2 million years ago.

It represents the earliest case of an ichthyosaur, described as fish-shaped marine reptiles of the Mesozoic Era, reaching such size proportions. While a sperm whale found today can measure over 55 feet long, the newly named Cymbospondylus youngorum is the largest animal newly discovered from that time period, on land or in water.

A newly discovered fossil reveals how ichthyosaurs evolved large body sizes earlier in history than modern aquatic life like whales. The fossil was discovered in Nevada. Illustration by Stephanie Abramowicz, courtesy of the Natural History Museum of Los Angeles County

Jorge Velez-Juarbe, study co-author and the Natural History Museum's associate curator of mammalogy, was not directly involved in the collecting of the specimen. However, he gathered and analyzed data on the fossil and living cetaceans that was crucial to understanding their rates of body size evolution to be able to compare them with ichthyosaurs.

"We often talk about cetaceans and ichthyosaurs having many similar traits, but seldom it is put into paper and properly analyzed, so this was a very satisfying experience and collaboration," Velez-Juarbe told Newsweek.

The largest animals to have lived on Earth occupied the marine environment, the study describes. While modern cetaceans—which include whales, porpoises and dolphins—evolved over tens of millions of years in response to increased productivity of cold marine waters, whales were not the first marine giants to evolve.

Study author P. Martin Sander, a German paleontologist, and co-authors describe how the newly discovered 244-million-year-old ichthyosaur—which existed at most 8 million years after the emergence of the first ichthyosaurs—would have rivaled modern cetaceans in size due to a "much more rapid size expansion that may have been fueled by processes after the Permian mass extinction."

"The iterative evolution of secondarily marine tetrapods since the Paleozoic offers the promise of better understanding how the anatomy and ecology of animals change when returning to the sea," the study said. "Recurring patterns of convergence in the geological past may suggest predictability of evolution when transitioning from full-time life on land to full-time life in the ocean.

"Ichthyosaurs and today's cetaceans are two of the most informative lineages to exemplify secondary returns to the sea. The notable resemblance in body shape and lifestyle of ichthyosaurs and cetaceans contrasts with their separation in time by nearly 200 million years, providing an often-cited example of convergent evolution. Ichthyosaurs arose 249 million years ago and populated the oceans for the next 150 million years. Cetaceans did not evolve until about 56 million years ago. As tail-propelled swimmers, ichthyosaurs and cetaceans evolved not only convergent body shapes but also large body sizes."

Natural History Museum of Los Angeles County Dinosaur Institute volunteer Viji Shook lays next to the skull of Cymbospondylus youngorum for scale. Photo by Martin Sander, courtesy of the Natural History Museum of Los Angeles County

The study, as referenced by the Natural History Museum of Los Angeles County, describes how ichthyosaurs occupied the waters while dinosaurs occupied the land hundreds of millions of years ago, with each species reaching massive size. Fish and whales today exemplify the evolution of fins and hydrodynamic body shapes.

While dinosaurs ruled the land, the study notes, ichthyosaurs and other aquatic reptiles, which were not dinosaurs, ruled the waves, reaching similarly huge sizes and species diversity. Evolving fins and hydrodynamic body shapes that are seen in both fish and whales, ichthyosaurs swam the ancient oceans for almost the whole era of dinosaurs.

"This discovery highlights how quickly life recovered in the oceans after the world's worst mass extinction, which occurred at the Permo-Triassic boundary (about 252 million years ago) where 90 percent of species became extinct," Velez-Juarbe said. "The recovery was so fast that 6 million years later we have a unique ichthyosaur fauna that includes small and gigantic species like the one we just described. It also shows that once there's plenty of food available and little to no competition, organisms will adapt and diversify very quickly."

What does this mean for future research? Velez-Juarbe borrowed an aquatic term, saying, "This is just the tip of the iceberg."

"We can now start looking at similar fossil assemblages, as well as explore other aspects that highlight the convergent evolution between cetaceans, ichthyosaurs and other secondarily aquatic tetrapods," he said.

Newsweek reached out to Martin Sander for further comment.

Update 1/4/2022 4:10 p.m. ET: This story has been updated to include comments from Velez-Juarbe.