The two-meter-high skull of a newly discovered species of giant ichthyosaur, the earliest known, sheds new light on the rapid growth of marine reptiles into giants of dinosaurs and helps us better understand the journey of modern whales (whales and dolphins) the largest animals that ever inhabited the earth.
While dinosaurs ruled the land, ichthyosaurs and other aquatic reptiles (which were specifically not dinosaurs) ruled the waves, reaching similarly gigantic sizes and biodiversity. The evolving fins and hydrodynamic body shapes seen in both fish and whales swam through the ancient oceans for almost the entire age of the dinosaurs.
“Ichthyosaurs come from a still unknown group of land-living reptiles and breathed themselves,” says first author Dr. Martin Sander, paleontologist at the University of Bonn and research assistant at the Dinosaur Institute of the Natural History Museum Los Angeles County (NHM). “Since the first skeletons were found in southern England and Germany over 250 years ago, these ‘ichthyosaurs’ were among the first large fossil reptiles known to science, long before the dinosaurs, and have captured the imagination of the people ever since.”
Excavated from a rock called Fossil Hill Member in the Augusta Mountains of Nevada, the well-preserved skull, along with part of the spine, shoulder, and front fin, date from the Middle Triassic (247.2 to 237 million years ago). This is the earliest case of an ichthyosaur to reach epic proportions. The newly named is as tall as a great sperm whale, over 17 meters (55.78 feet) in length Cymbospondylus youngorum is the largest animal discovered on land or in the sea from this period. In fact, it was the first giant creature known to us to ever inhabit the earth.
“The significance of the find was not immediately apparent, ”notes Dr. Sander, “because only a few eddies were exposed on the side of the canyon. However, the anatomy of the vertebrae suggested that the front end of the animal might still be hidden in the rock. Then, on a cold September day in 2011, the crew needed a warm-up and tested this suggestion through excavations, which found the skull, forelegs and chest region. “
The new name for the species C.. Youngorum, honors a fortunate coincidence that the field research sponsorship by the Great Basin Brewery of Reno, owned and operated by Tom and Bonda Young, inventors of the locally famous Icky beer, which features an ichthyosaur on the label.
In other mountain ranges in Nevada, paleontologists have been recovering fossils from the limestone, slate and siltstone of the Fossil Hill Member since 1902 and opened a window into the Triassic. Linking our present to ancient oceans, the mountains have produced many species of ammonites, shelled ancestors of modern cephalopods such as cuttlefish and cuttlefish, and marine reptiles. All of these animal specimens are collectively known as the Fossil Hill Fauna and represent many of C. youngorum‘s prey and competitors.
C. youngorum Stalked the oceans about 246 million years ago, or just about three million years after the first ichthyosaurs wet their fins, an astonishingly short time to get that big. The elongated snout and conical teeth suggest that C. youngorum he hunted octopus and fish, but his size meant he could have hunted smaller and juvenile marine reptiles.
The giant predator likely faced fierce competition. Using sophisticated computer modeling, the authors examined the likely energy flowing through the food web of the Fossil Hill fauna, used data to recreate the ancient environment, and found that marine food webs were able to feed a few more colossal carnivorous ichthyosaurs. Ichthyosaurs of different sizes and survival strategies reproduced, similar to those of modern whales – from relatively small dolphins to giant baleen whales that feed by filtering and sperm whales that hunt giant squid.
Co-author and ecological modeler Dr. Eva Maria Griebeler from the University of Mainz in Germany comments: “Due to their large size and the resulting energy requirements, the densities of the largest ichthyosaurs from the Fossil Hill fauna are inclusive C. youngourum must have been much lower than our field count suggests. The ecological functioning of this food web through ecological modeling was very exciting, as modern, highly productive primary producers were absent in the Mesozoic Era food webs and were an important engine for the development of whale size. “
Whales and ichthyosaurs share more than one size range. They have similar blueprints, and both were originally created after the mass extinction. These similarities make them scientifically valuable for comparative studies. The authors combined computer modeling and traditional paleontology to study how these marine animals independently reached record-breaking sizes.
“A fairly unique aspect of this project is the integrative nature of our approach. We had to first describe the anatomy of the giant skull in detail and determine how this animal is related to other ichthyosaurs, ”says senior author Dr. Lars Schmitz, Associate Professor of Biology at Scripps College and Dinosaur Institute Research Associate. “We didn’t stop there because we wanted to understand the importance of the new discovery in relation to the large-scale evolutionary pattern of ichthyosaur and whale body sizes and how the fossil ecosystem of the Fossil Hill fauna works. Both the evolutionary and the ecological analyzes required a considerable amount of computation, which ultimately led to the modeling being merged with traditional paleontology. “
They found that both whales and ichthyosaurs developed very large sizes, but that their respective evolutionary paths to gigantism were different. Ichthyosaurs had an initial size boom and became giants early in their evolutionary history, while whales took much longer to reach the outer limits of the giants. They found a link between large size and predator hunting – think of a sperm whale diving down to hunt giant squids – and a link between large size and loss of teeth – think of the giant filter-feeding whales, which are the largest animals who ever lived on earth.
The ichthyosaurs first foray into gigantism was likely due to the boom in ammonites and jawless eel-like conodonts, which filled the ecological void after the mass extinction at the end of the Permian. Although their evolutionary routes were different, both whales and ichthyosaurs relied on exploiting niches in the food chain to get really big.
“As researchers, we often talk about similarities between ichthyosaurs and whales, but rarely go into detail. This is a special feature of this study as it enabled us to examine the development of body size within these groups of marine tetrapods and to gain additional insights, ”says Dr. Jorge Velez-Juarbe, Associate Curator of Mammalogy (Marine Mammals) at the NHM. “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’s history. It can be said that this is the first big splash for tetrapods in the oceans. “
C. youngorum will be permanently housed in the Natural History Museum of Los Angeles County, where it is currently on display.