The Original Sea Monster
If an extra terrestrial civilization were to study the history of Earth, they would most likely conclude that this is the planet of the dinosaurs, giant reptiles who ruled the world for hundreds of millions of years. Humans, currently the dominant species, have not even existed for one percent of that time. The iconic species that people associate with dinosaurs are usually the land-based ones: Tyrannosaurus Rex, Brontosaurus, Velociraptor. Equally important were the dinosaurs of the sea. A new study from the University of Bristol examines one of them, a deadly marine predator known as Icthyosaurs. This original sea monster met its demise in a mass extinction event 200 million years ago.
Its fossils were first discovered 200 years ago by Mary Anning on the Jurassic coast of Dorset at Lyme Regis in Southern Great Britain. They were an abundant predator in the Jurassic Era (145-200 million years ago). However, the Jurassic Icthyosaurs were shrunken remnants of their ancestors. The first Icthyosaurs originated in the early Triassic Era (250 million years ago).
The Triassic Icthyosaurs grew up to 20 meters long (60 feet), a dolphin-like predator, the size of a whale. They thrived in their environment as the top predator, and gradually branched off into a large variety of species with many shapes and forms. Their long fish-like bodies were ideally built for speed. Their enormous mouths could gulp down entire schools of prey such as squid.
The mass extinction event at the end of the Triassic put an end to the great Icthyosaur. The event devastated all life on the planet, on land and sea. It was triggered by massive volcanic eruptions from the splitting of North America and Europe to create the Atlantic Ocean. The gases released from under the earth's crust caused flash heating and a loss of oxygen in the oceans. The ichthyosaur survived the event but at a huge price. Its range of shapes and sizes was only one tenth of its former glory.
Research was done by Philippa Thorne, Master in Paleobiology, of the University of Bristol, along with Dr. Marcello Ruta and Professor Michael Benton. "We applied a set of demanding numerical approaches to a data set that contained character codings for all major Triassic and Jurassic ichthyosaurs," said Philippa. "These methods allow us to explore rates of character change through time, and to compare the amount of variation in all aspects of the body shape and adaptations of different groups and different times. We were amazed at the result."
Prior research had already shown that the Early Jurassic period was the heyday for the Icthyosaur. They bounced back from the mass extinction event to become the dominant marine reptile. However, their evolutionary breadth of form had been drastically cut. This shows how a catastrophic environmental event can unexpectedly alter the course of evolution.
This research has been published in the journal, Proceedings of the National Academy of Science.
Link to published article: http://www.pnas.org/content/early/2011/04/27/1018959108.full.pdf+html