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

Illustration by Stephanie Abramowitz, courtesy of the Natural History Museum of Los Angeles County 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.

  • 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.
  • 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 tetrapod’s 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.”

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.

Scientists believe they can compare whales and ichthyosaurs regarding size range due to similar “body plans” and how both initially arose after mass extinctions, the museum described. A combination of computer modeling and traditional paleontology will study how both marine species reached record-setting sizes independently.

“This discovery and the results of our study highlight how different groups of marine tetrapods evolved body sizes of epic proportions under somewhat similar circumstances, but at surprisingly different rates,” said Jorge Velez-Juarbe, study co-author and the Natural History Museum’s associate curator of mammalogy. “Moving forward, with the data set we’ve compiled and analytical methods we’ve tested, we can start thinking about including other groups of secondarily aquatic vertebrates to understand this aspect of their evolutionary history.”