In 1991, a hiker in norther British Columbia discovered "fossil bones eroding out of the banks of the Sikanni Chief River." When Dr. Elizabeth Nicholls from the Royal Tyrell Museum of Paleontology visited the site, she was astonished at both the size of the fossil bones and the completeness of the find. The bones were larger than any other known marine reptile and belonged to Shonisaurus sikanniensis, a species of icthyosaur that inhabited the world's seas during the Mesozoic era, the age of reptiles. During this time, pleisosaurs and mosasaurs also inhabited the world's oceans. These three groups were the largest marine reptiles ever known.
Ichthyosaurs lived throughout the Triassic, Jurassic and Cretaceous periods, from about 240 million years to 93 million years ago. Plesiosaurs first appeared in the Jurassic period around 200 million years ago and disappeared at the end of the Cretaceous at 65 million years ago. Mosasaurs existed during the late Cretaceous period from 90 million years ago, going extinct at the end of the Cretaceous.
One of the earliest ichthyosaur fossils to be discovered was found by amateur fossil hunter, Mary Anning, in 1812 when she was only twelve-years-old. Mary and her brother discovered the fossilized skull and verterbrae of what looked like a huge crocodile, eroding out of the chalk cliffs of Lyme Regis in Southern England.
At this time, little was known about these giant marine reptiles. As more fossils were found, in Nevada by miners in the 1800's, in the black shale quarries of Holzmaden in Southern Germany and in Australia, scientists have been able to piece together where and how ichthyosaurs lived.
Pelsiosaur fossils have been found on every continent of the world. When these fossils were first discovered, they were thought to be of lizards. As with the ichthyosaurs, Mary Anning led the way, in this case finding the first well preserved pleiosaur skeleton at Lyme Regis in 1824.
Named Plesiosaurus dolichodeirus, it was a plesiosaurid, the earliest of the plesiosaurs. There are many different species of plesiosaurs, some with long necks and small heads, others with large heads and short necks. Those plesiosaurs with short necks were formidable predators who preyed on smaller reptiles as well as ichthyosaurs.
90 million years ago saw the first of the mosasaurs appear, replacing the plesiosaurs who went extinct. The first mosasaur fossil was discovered in 1780 in a limestone mine in the Netherlands. They were given the name mosasaur which means Meuse lizard because the bones were so large they were thought to belong to a whale. Although mosasaur fossils are found all over the world, they are especially plentiful in Kansas and South Dakota. This is because during the Mesozoic era, a vast inland sea covered much of central North America. The mosasaur's size, and scientists believ its ability to swim and to swiftly attack made it the top predator in this inland sea.
Like the dinosaurs, the giant marine reptiles also went extinct at the end of the Cretaceous. They were part of the great diversity of life in this era of large animals.
Discussion
Giant Sea Reptiles of the Dinosaur Age is a fascinating book about the giant sea reptiles who dominated the world's seas during the Age of Reptiles. Author Caroline Arnold takes her young readers on a journey through the Age of Reptiles, starting with the ichthyosaurs and then progressing through the Mesozoic as the plesiosaurs and mosasaurs appear.
Many interesting details about each reptile group are included. For example, readers learn that "Ichthyosaurs cruised the oceans looking for food, sometimes diving to great depths. A favourite food of many ichthyosaurs were belemnites, ancient relatives of squid. Thousands of tiny fossilized hooks from belemnite tentacles have been found in the preserved stomach contents of ichthyosaurs, and also the remains of fish, crustaceans, and other sea animals."
Historical finds, such as that of Mary Anning are discussed as well as more recent discoveries. "A Recent discovery of a short-necked plesiosaur in northwestern Mexico may be of an animal that was up to 45 feet (13.7 meters) long. It has been dubbed the "Monster of Aramberri" after the village near the fossil site."
Accompanying each entry are the realistic illustrations of Laurie Caple, rendered in watercolour, portraying these giant marine reptiles as scientists they may have looked. These beautiful illustrations add significantly to the book, helping readers to visualize life in the Age of Reptiles.
Giant Sea Reptiles of the Dinosaur Age is a must-read for those interested in geology, earth history and paleontology, and those interested in reptiles. Arnold includes a list of where to view the fossil remains of prehistoric sea reptiles as well as an index.
Book Details:
Giant Sea Reptiles of the Dinosaur Age by Caroline Arnold
New York: Clarion Books 2007
40 pp.
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