Earth’s Oldest Ocean Giant Was a Reptile With an Eight-Foot Skull

The newly discovered specimen sheds light on how the sea creatures, known as ichthyosaurs, evolved their gargantuan size so quickly

An illustration of C. youngorum swimming. It has a snake-like body, a whale-like torso and a pointed snout. Ammonites swim away from it.
Though ichthyosaurs and whales never existed at the same time, they both evolved from species that walked on Earth and transitioned to the sea.  Stephanie Abramowicz, courtesy of the Natural History Museum of Los Angeles County

During the time dinosaurs dominated the land, giant marine reptiles called ichthyosaurs ruled the sea. They're known as the planet's first giants, and they could grow to more than 50 feet long, around the size of modern-day sperm whales, Vishwam Sankaran reports for the Independent.

"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," study author Martin Sander, a paleontologist at the University of Bonn and researcher at the Natural History Museum of Los Angeles County (NHM), says in a press release.

In 2011, scientists excavated an eight-foot-long ichthyosaurus skull from the mountains of Nevada. The creature had a long, dolphin-like snout and conical teeth. It was excavated along with part of the animal's spine, fin and shoulder, Alexandra Larkin reports for CBS.

The fossil belongs to a new species named Cymbospondylus youngorum that is estimated to have lived some 246 million years ago, making it the largest fossil from that era ever found. 

A researcher lays down next to the skull. The scientist's head is near the tip of the snout, and their legs reach part of the jaw, around two feet shorter than the end of the skull.
The skull belonged to a creature from 246 million years ago and is the largest fossil from that era ever found. Martin Sander, courtesy of the Natural History Museum of Los Angeles County

The specimen offers new insights into what ocean was like millions of years ago and how ichthyosaurs grew to be so large. Scientists reported their findings last month in the journal Science.  

Though ichthyosaurs and whales never existed at the same time, they have more in common than just their similar body size and shape. They both evolved from ancestors that walked on land, and their ginormous bodies made them the largest animals in the oceans during their time.

On the vast evolutionary timeline, ichthyosaurs evolved their enormity at lightning speed, Sabrina Imbler reports for the New York Times. After their ancestors moved from land to sea, it only took ichthyosaurs three million years to evolve their ginormous body size. By comparison, it took whales 45 million years to reach such enormity, the Times reports.

To understand how ichthyosaurs grew so quickly, the team of scientists reconstructed their food web at the time. Around 252 million years ago, the Permian extinction wiped out about 96 percent of the ocean's species, but it left the door open for critters like ammonites—a type of mollusks—and eel-like critters called conodonts to flourish, according to the press release.

Many of the largest modern whales—like humpbacks and blue whales—filter feed on tiny organisms like plankton, which helped them reach such large sizes. But a similar food web wasn't possible for ichthyosaurs. Plankton wasn't around during their time, and instead ammonites formed the base of food webs. The reptiles didn't feed directly on the shellfish, but they ate the critters that ate them, like fish and squid, the Times reports.

Though scientists aren't fully sure how ichthyosaurs grew so large so quickly, one reason could be that the boom of ammonites and conodonts filled an empty void in the food chain that the reptiles could exploit, according to the press release.

"As researchers, we often talk about similarities between ichthyosaurs and [whales and dolphins], but rarely dive into the details," Jorge Velez-Juarbe, a curator at the NHM, says in the press release. "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."