The two-meter skull of a newly discovered species of giant ichthyosaur, the oldest known, sheds new light on the rapid growth of marine reptiles into behemoths of the dinosaur oceans, and helps us better understand the journey of modern cetaceans ( whales and dolphins) to become the largest animal to ever live on Earth.
While dinosaurs ruled the earth, ichthyosaurs and other aquatic reptiles (which were definitely not dinosaurs) ruled the waves, reaching equally gargantuan sizes and species diversity. The evolving fins and hydrodynamic shapes of the body seen in both fish and whales, ichthyosaurs swam the ancient oceans for most of the dinosaur era.
“Ichthyosaurs derive from a still unknown group of terrestrial reptiles and themselves breathe air,” says lead author Dr Martin Sander, paleontologist at the University of Bonn and research associate at the Institute dinosaurs at the Los Angeles County Natural History Museum (NHM). “Since the first discoveries of skeletons in southern England and Germany over 250 years ago, these” saurian fish “have been among the first large fossil reptiles known to science, long before dinosaurs , and they have captured the popular imagination ever since. “
Unearthed from a rock unit called the Fossil Hill Member in the Augusta Mountains of Nevada, the well-preserved skull, as well as part of the spine, shoulder, and forefin, date back to the Middle Triassic (there are 247, 2-237 million years ago), representing the first case of an ichthyosaur reaching epic proportions. As big as a large sperm whale over 17 meters (55.78 feet) long, the new name Cymbospondylus youngorum is the largest animal ever discovered at that time, on land or in the sea. In fact, it was the first giant creature to have ever inhabited Earth to our knowledge.
“The significance of the find was not immediately apparent, “notes Dr Sander,” as only a few vertebrae were exposed on the side of the canyon. However, the anatomy of the vertebrae suggested that the animal’s front end may still be hidden in the rocks. Then, on a cold day in September 2011, the crew needed a warm-up and tested this suggestion by excavation, finding the skull, forelimbs and chest area. “
The new name of the species, VS. youngorum, honors a happy coincidence, the sponsorship of fieldwork by the Great Basin Brewery of Reno, owned and operated by Tom and Bonda Young, the inventors of the famous Icky beer which features an ichthyosaur on its label.
In other Nevada mountain ranges, paleontologists have been collecting fossils from limestone, shale, and siltstone from the Fossil Hill member since 1902, opening a window to the Triassic. The mountains connect our present to the ancient oceans and have produced many species of ammonites, the shell ancestors of modern cephalopods like cuttlefish and octopus, as well as marine reptiles. All of these animal specimens are collectively known as the Fossil Hill Fauna, representing many C. youngorumits prey and its competitors.
C. youngorum roamed the oceans about 246 million years ago, or only about three million years after the first ichthyosaurs wet their fins, a surprisingly short time to grow this big. The elongated muzzle and conical teeth suggest that C. youngorum preyed on squid and fish, but its size meant it could have hunted smaller, juvenile marine reptiles as well.
The giant predator probably had fierce competition. Using sophisticated computer modeling, the authors examined the likely energy flowing through the food web of fossil hill fauna, recreating the ancient environment using data, finding that marine food webs were able to support a few. Colossal meat-eating ichthyosaurs. Ichthyosaurs of different sizes and survival strategies have proliferated, comparable to modern cetaceans – from relatively small dolphins to huge baleen filtering whales and giant squid-hunting sperm whales.
Co-author and ecological modeler Dr Eva Maria Griebeler of the University of Mainz in Germany notes, “Due to their large size and the resulting energy demands, the densities of the largest ichthyosaurs in the fossil hill fauna , including C. youngourum must have been significantly lower than what our field census suggested. The ecological functioning of this food web from ecological modeling was very exciting as modern highly productive primary producers were absent from Mesozoic food webs and were a major driver in whale size evolution. “
Whales and ichthyosaurs share more than a size range. They have similar body plans, and both first appeared after mass extinctions. These similarities make them scientifically valuable for a comparative study. The authors combined computer modeling and traditional paleontology to study how these marine animals reached record sizes independently.
“A fairly unique aspect of this project is the integrative nature of our approach. We first had to describe in detail the anatomy of the giant skull and determine how this animal relates to other ichthyosaurs,” says the lead author. , Dr Lars Schmitz, Associate Professor of Biology at Scripps College and Research Associate at the Dinosaur Institute. “We didn’t stop there, as we wanted to understand the importance of the new discovery in the context of the large-scale evolutionary model of ichthyosaur and whale body size, and how the fossil fauna ecosystem of the Fossil hills may have worked. Both evolutionary and ecological analyzes required a substantial amount of computation, ultimately leading to a confluence of modeling with traditional paleontology. “
They found that while cetaceans and ichthyosaurs evolved to very large body sizes, their respective evolutionary trajectories to gigantism were different. Ichthyosaurs experienced an initial boom in size, becoming giants early in their evolutionary history, while whales took much longer to reach the outer limits of the immense. They found a link between large size and raptor hunting – think of a sperm whale diving to hunt giant squid – and a link between large size and loss of teeth – think giant filter-feeding whales which are the largest animals forever live on Earth.
The ichthyosaurs’ initial foray into gigantism was likely due to the boom in jawless, eel-like ammonites and conodonts filling the ecological void after the late Permian mass extinction. Although their evolutionary pathways are different, whales and ichthyosaurs have relied on exploiting niches in the food chain to make it really big.
“As researchers, we often talk about the similarities between ichthyosaurs and cetaceans, but we rarely delve into the details. This is one of the reasons this study stands out, because it allowed us to explore and to obtain additional information on the evolution of body size 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 bear witness to the resilience of life in the oceans after the worst mass extinction in Earth history. You could say this is the first large splash of tetrapods in the oceans. “
C. youngorum will be permanently installed at the Natural History Museum of Los Angeles County, where it is currently on display.