📸 An artist's conception of a group of Ichthyosaurs
During the Mesozoic Era, as the shifting continents were stalked by dinosaurs, even more ferocious predators lurked below the sea. The massive Panthalassan Ocean was the hunting grounds of marine reptiles which ruled the ancient oceans with brutal tactics. Of the five main Mesozoic marine reptile groups, four were predators: the Thalattosuchians, Mosasaurs, Plesiosaurs, and Ichthyosaurs. The discovery of this group of reptiles was a watershed moment in paleontology, upending our understanding of ancient life.
📸 A fossilized Ichthyosaur vertebra
Among the Mesozoic marine reptiles, the Ichthyosaur occupies a special place. Its origins are debated, but its evolutionary line stretches from the terrestrial realm before the animal’s ancestors made the jump back to the seas. From there, Ichthyosaurs evolved into a wide variety of specialized species, occupying hunting niches left unfilled in the ocean following the Periman-Triassic extinction.
Ichthyosaurs were marine reptiles with streamlined bodies, no necks, and smooth heads. They were air-breathing creatures with two nostrils situated far back on the top of the head, generally similar in shape to a modern porpoise. Ichthyosaurs likely fed on fish, using their numerous sharp teeth and enormous eyes to locate prey in deep water. Most abundant and diverse during the Triassic and Jurassic Periods, their fossils have been uncovered around the world and were extant through the Early Cretaceous.
📸 Chaohusaurus brevifemoralis, a basal ichthyosauriform. Huang (2019)
In the Triassic Period, Ichthyosaurs were long-bodied, undulating swimmers. Fossils from the Late Triassic in North America indicate they could grow to 40 feet in length and were deep-bodied with long fins. Some, like the genus Shastasaurus, could even measure 65 feet long! This creature differed from other Ichthyosaurs as it was slender in profile and had a short, toothless snout.
By the Early Jurassic, some lineages had evolved a body plan similar to modern tuna, as the earlier shape became extinct. The newer, more fishlike shape likely provided greater mobility and speed. Fossils from Early Jurassic deposits in England of the Ichthyosaurus genus represent a reptile about 3 m in length where the limbs had fully modified into paddles, and the body had a fishlike tail. They continued on into the Cretaceous, but in fewer numbers and demonstrating less diversity than at their peak in the Triassic.
📸 Temnodontosaurus (originally Ichthyosaurus) skull discovered by Joseph Anning. Philosophical Transactions of the Royal Society of London. v. 104. 1814.
Early humans strode over exposed bedrock, looked down, and found exposed in the rocks underfoot, very hard bones. Bones of known animals would be readily recognized. But fossil bones of large unknown creatures would seem to be enormous monsters. The bones of reptiles such as ichthyosaurs and pliosaurs would have been found in sediments from the Mesozoic Era which are widely exposed throughout the world.
With no concept of deep time or the tectonic or eustatic movements of the earth and ocean, these fossils would appear to be old bones from enormous carnivorous land monsters. The concept of extinction would not have existed without a sense of deep time, so these giant "serpents" or "dragons" could exist somewhere on the land and would therefore instill great fear.
📸 The Icthyosaur and Plesiosaur, 19th century paleoart from Édouard Riou
These fossil remains would suggest many forms for these monsters, but in general, they would have moved like huge undulating snakes and had enormous mouths and teeth. The bones from their paddles may have inspired the idea of wings. Dragons are a common mythical beast in many ancient cultures around the world, such as China. In Greek mythology, Jason and the Argonauts must kill a dragon that guards the Golden Fleece. The dragon in these stories is described as a giant serpent.
It was finally in the 19th century that concepts of time began to deepen. Other new ideas were also taking hold; land moves and shifts, and that oceans transgress and regress from the land. Early paleontologists were able to recognize these fossils as extinct marine reptiles. New knowledge was replacing the ancient fear and the Ichthyosaur was soon to be understood.
📸 A Statue of Anning in Lyme Regis
Ichthyosaurs have a long history of study that parallels the growth of paleontology. Much of our early understanding of these creatures is owed to paleontologist Mary Anning. Born in 1799, Anning grew up in Lyme Regis, a village along England’s Southern Coast. Her parents had made their way there a few years before, in part lured by tales of the mysterious “curiosities” found embedded in the Blue Lias limestone formation. Her father Richard hoped to make some money off selling these fossils and would spend his free time walking the beach on the prowl, accompanied by his young daughter.
After her father’s death, the young Anning helped support the family by selling ammonites and other small fossils to travelers and other passersby. Her first major find came in 1811 after her brother Joseph found a massive skull embedded in the Black Ven shale cliffs near Lyme Regis. He eagerly reported his find to Anning and had some local men unearth the skull. Anning spent nearly a year searching for the rest of the beast, finally finding some vertebrae that were discharged after a storm. After many more months of digging, the first nearly complete Ichthyosaur skeleton was revealed.
📸 Ichthyosaur found by Anning (Source: Oxford)
Smaller bits and pieces of the animal's fossil had been found before, but the Anning discovery was unlike anything else. Combined with the skull her brother had uncovered, the piece eventually ended up in the London Museum of Natural History. These aquatic reptiles hunted for much of the Mesozoic Era’s 200 million years, looking like a cross between a dolphin and a crocodile. The Annings were paid only £23 (about £2,400 in modern times), and Mary received even less in scientific credit despite her diligence.
Anning’s Ichthyosaur and other finds were a serious challenge to the still-prevailing Creationism of the time. To this point, religiously-minded scientists had suggested fossils were simply the remains of animal species still living that had not been discovered yet. These marine reptiles could not be dismissed this way; they were so unlike any living animal they had to come from extinct species, counter to the idea of all life being created at once. Ichthyosaurs and their fellow marine reptiles are not just fascinating creatures, they form the bedrock of our understanding of paleontology that persists to this day.
📸 A sketch of an Ichthyosaur skull, based on Joseph Anning's find
Rulers of Mesozoic seas
This specimen from Mini Museum is an Ichthyosaur vertebra recovered from Jurassic Period formations in the United Kingdom. Recorded discoveries of partial Ichthyosaur fossils in this region date back to the 18th century, though they were often mistaken for fish. It's also thought their fossils may have influenced dragon mythology in early England. It was not until 1811 when Joseph and Mary Anning uncovered a complete fossil skeleton that a better understanding of Ichthyosaurs began to develop.
Both fossil fragments and complete vertebra are available! This magnificent specimen is both an important step in the history of paleontology and a piece of one of the most successful predators to ever swim in Earth's oceans.
Deng, Tao, et al. "Implications of vertebrate fossils for paleo-elevations of the Tibetan Plateau." Global and Planetary Change (2019).
Huang, Jian-dong, et al. "The new ichthyosauriform Chaohusaurus brevifemoralis (Reptilia, Ichthyosauromorpha) from Majiashan, Chaohu, Anhui Province, China." PeerJ 7 (2019): e7561.
Lindgren, Johan, et al. "Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur." Nature 564.7736 (2018): 359.
Nicholls, Elizabeth L., and Jack M. Callaway. Ancient Marine Reptiles. San Diego: Academic Press. 1997. EBSCOhost. Web. 19 June 2019.
Rich AK. Mary Anning. Great Neck Publishing; 2006.