The two-meter skull of a newly discovered species of giant ichthyosaur, the earliest known, sheds new light on the marine reptiles’ rapid evolution into behemoths of the Dinosaurian oceans and aids in our understanding of how modern cetaceans (whales and dolphins) became the largest animals to ever inhabit the Earth.
While dinosaurs dominated the land, ichthyosaurs and other aquatic reptiles (that were obviously not dinosaurs) dominated the seas, attaining comparably gigantic sizes and species diversity. Ichthyosaurs, with their evolving fins and hydrodynamic body forms similar to those of fish and whales, sailed the ancient oceans for virtually the whole duration of the Age of Dinosaurs.
“Ichthyosaurs descended from an unknown group of land-dwelling reptiles and were themselves air-breathing,” explains lead author Dr. Martin Sander, a paleontologist at the University of Bonn and Research Associate at the Natural History Museum of Los Angeles . “From their discovery in southern England and Germany over 250 years ago, these ‘fish-saurians’ were among the earliest massive fossil reptiles known to science, long before the dinosaurs, and they have captivated the popular imagination ever since.”
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The well-preserved head, along with a section of the backbone, shoulder, and forefin, was discovered in the Augusta Mountains of Nevada. It dates to the Middle Triassic (247.2-237 million years ago), and is the earliest example of an ichthyosaur reaching epic proportions. At almost 17 meters (55.78 feet) in length, the newly named Cymbospondylus youngorum is the largest animal yet discovered from that time period, on land or sea. Indeed, it was the first known enormous monster to occupy the Earth.
“The significance of the discovery was initially overlooked,” Dr. Sander recalls, “since only a few vertebrae were visible on the canyon’s edge.” However, the vertebral anatomy revealed that the animal’s front end may still be submerged beneath the rocks. Then, on a chilly September day in 2011, the crew required a warm-up and investigated this notion, discovering the head, forelimbs, and chest region.”
The new species name, C. youngorum, commemorates a fortunate coincidence.
Since 1902, paleontologists have been recovering fossils from the Fossil Hill Member’s limestone, shale, and siltstone in various mountain ranges of Nevada, providing a window into the Triassic. The mountains connect our modern world to ancient waters and have generated numerous ammonites, the shelled progenitors of modern cephalopods like as cuttlefish and octopuses, as well as marine reptiles. All of these animal fossils are together referred to as the Fossil Hill Fauna, and they represent numerous prey and competitors of C. youngorum.
C. youngorum roamed the oceans approximately 246 million years ago, or only about three million years after the earliest ichthyosaurs got their fins wet, an astonishingly short time for a creature of this size to grow to this size. C. youngorum’s extended snout and conical teeth indicate that it preyed on squid and fish, but its size suggests that it may have also hunted smaller and immature marine reptiles.
The colossal predator almost certainly faced stiff competition. The authors evaluated the likely energy flowing through the Fossil Hill Fauna’s food web using sophisticated computational modeling, recreating the ancient ecosystem through data, and discovered that marine food webs were capable of supporting a few more massive meat-eating ichthyosaurs. Ichthyosaurs of various sizes and survival tactics flourished, akin to modern cetaceans’—from very small dolphins to gigantic filter-feeding baleen whales and giant sperm whales that hunted squid.
Dr. Eva Maria Griebeler of the University of Mainz in Germany, co-author and ecological modeler, notes that “due to their large size and associated energy demands, the densities of the largest ichthyosaurs from the Fossil Hill Fauna, including C. youngourum, must have been significantly lower than suggested by our field census.” Ecological modeling revealed an intriguing ecological function for this food network, as modern highly productive primary producers were absent from Mesozoic food webs and were a significant driver of whale size evolution.”
Whales and ichthyosaurs are related in more ways than one. They share a similar body layout and both evolved during major extinctions. Due to their commonalities, they are scientifically useful for comparative studies. The authors used a combination of computer modeling and classical paleontology to investigate how these sea species independently attained record-breaking sizes.
“A really unusual feature of this endeavor is our integrative approach. We needed to first thoroughly describe the gigantic skull’s anatomy and establish its relationship to other ichthyosaurs,” explains senior author Dr. Lars Schmitz, an associate professor of biology at Scripps College and a Dinosaur Institute Research Associate. “We did not stop there; we wanted to grasp the relevance of the new discovery in relation to the large-scale evolutionary pattern of ichthyosaur and whale body proportions, as well as how the Fossil Hill Fauna’s fossil ecology would have functioned.” Both evolutionary and ecological investigations necessitated considerable calculation, resulting in a synthesis of modeling and classical paleontology.”
They discovered that while both cetaceans and ichthyosaurs developed to have extremely huge bodies, their evolutionary paths to gigantism were rather different. Ichthyosaurs experienced an initial growth spurt, becoming giants early in their evolutionary history, whereas whales took much longer to reach the extremes of giganticity. They discovered a link between great size and raptorial hunting—think of a sperm whale diving down to kill giant squid—and a link between large size and tooth loss—think of the world’s largest mammals, the giant filter-feeding whales.
Ichthyosaurs’ initial journey into gigantism was very certainly facilitated by the proliferation of ammonites and jawless eel-like conodonts that filled the ecological hole left by the end-Permian mass extinction. While their evolutionary paths diverged, both whales and ichthyosaurs thrived by exploiting food chain niches.
“As researchers, we frequently discuss the similarities between ichthyosaurs and cetaceans without delving into the intricacies. That is one way in which this work stands out, as it enabled us to investigate and acquire more insight into the development of body size in different groups of marine tetrapods,” explains Dr. Jorge Velez-Juarbe, Associate Curator of Mammalogy (Marine Mammals) at the Natural History Museum. “Another fascinating element is that Cymbospondylus youngorum and the rest of the Fossil Hill Fauna serve as a monument to the ocean’s resiliency following the largest mass extinction in Earth’s history. You may claim that this is the first significant appearance of tetrapods in the oceans.”