Giant Sea Reptiles of the Dinosaur Age by Caroline Arnold

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.

The Age of Dinosaurs by Steve Brusatte

The Age of Dinosaurs tells the fascinating story of how scientists believe dinosaurs came to be the dominant species on Earth for over 150 million years. Their story covers the Mesozoic Era which includes the Triassic, Jurassic and Cretaceous Periods from 250 million to 66 million years ago.

The story begins in the early Triassic when there was one land mass, a supercontinent called Pangea. To understand this story this first chapter gives a short explanation of fossils and the importance of the rocks they are found in and how they can tell scientists about life long ago. A brief overview of the Earth's history is given up to the end of the Permian when great changes led to a mass extinction. Brusatte's visit to Poland to investigate the tracks of an animal called Prorotodactylus and his research there set the stage for the opening chapter title The Ancestors of Dinosaurs. Based on the tracks, paleontologists believe that this animal was an archosaur, a type of reptile that survived the Permian extinction and was a forerunner of the dinosaurs. The archosaurs were divided into two branches: one group which includes crocodiles and their extinct cousins and a second group which includes the dinosaurs.

In the early Triassic dinosaurs were not yet dominant but we know they existed from fossil evidence from the area of Pangea that is now Argentina.  They were rare throughout the rest of Pangea, likely restricted to the Argentina area of Pangea which was located south of the equator, an area cooler, wetter and more humid. Dinosaurs at this time included both meat-eaters and plant-eaters.  Instead, huge amphibians, called super salamanders dominated the waters, while thousands of species of crocodiles ruled the land.

Dinosaurs began to dominate in the Jurassic. At the end of the Triassic, the supercontinent of Pangea began to break apart. Increased volcanic activity resulted in climate change and another extinction however it was not a large as the previous Permian extinction but it was significant enough. "Many of the animals that ruled the Triassic world went extinct." This included most of the crocodile species and super salamanders. The dinosaurs survived, something that is not fully understood.

The first 30 millions years of the Jurassic Period saw dinosaurs evolve into many new species. This diversification continued throughout the Jurassic with different species inhabiting a wide range of ecosystems from the poles to the equator. Some examples of this diversity could be seen in the ornithischian dinosaurs which are plant eating dinosaurs. These dinosaurs had beaks and included stegosaurs with back plates and ankylosaurs with spiked armour. By mid-Jurassic (170 million years ago) dinosaurs were dominant, "...the most important animals in ecosystems all over the planet." 

Another group of dinosaurs, the Sauropods, were the largest animals to live on land. Sauropods, which were plant eaters, were found all over the world. The dominant predator was Allosaurus which lived in North America, Europe and possibly Africa.

The transition to the Cretaceous was much calmer with the continents continuing to move further apart, continuing climate changes, changes to sea level and the formation of islands and land bridges that allowed dinosaurs to migrate. These factors all influenced the evolution of dinosaurs. The sauropods declined but those that remained became enormous. They were the titanosaurs and were truly colossal, at more than one hundred feet long and weighing over seventy tons. Velociraptors were a new type of predator in the Cretaceous as were the carcharodontosaurs, a huge carnivore. But these were soon to be replaced by the tyranosaurs and the most famous of them all was Tyrannosaurus Rex.

From this point on, Brusatte goes on to detail the evolution of the tyrannosaurs, as well as the types of dinosaurs that dominated the various regions of the Earth (North America, Asia, the South and Europe) during the peak of their reign in the Cretaceous. There are also chapters which explain how paleontologists believe dinosaurs evolved into birds, as well as what scientists believe ended the reign of the dinosaurs.

Discussion

The Age of Dinosaurs is a book for the young dinosaur enthusiast. Brusatte, a paleontologist at the University of Edinburgh takes his readers through time beginning with the ancestors of the dinosaurs, to their rise as the dominant life form on our planet and to their sudden demise. The Age of Dinosaurs was inspired by Brusatte's book, The Rise and Fall of the Dinosaurs which was published in 2018 for adult readers. As Brusatte notes in this current edition for younger readers, "It is the story of dinosaur evolution: how dinosaurs changed over time as their world changed around them." Brusatte pieces together the story as we currently understand it, in an exciting, engaging way for young readers.

There is plenty of information about many geologic concepts in The Age of Dinosaurs including explanations about fossils, how dinosaur species are identified, the use radioisotope dating, and plate tectonics. Brusatte spends some time explaining where specific types of dinosaurs were found, for example tyrannosaurs were located mainly in the western United States and Canada and explains how the Earth's changing landmass over millions of years, influenced where certain species of dinosaurs lived. However, one drawback to this book is the lack of maps to help young readers visualize the changing Earth through the Jurassic and Cretaceous. For example maps showing Pangea separating into Gondwana, its gradual break up into the continents we see today would have been helpful. 

There are "boxes" that highlight information about the research paleontologists are undertaking to learn more about dinosaurs. The book opens with a lovely pencil illustration on the title page of a dinosaur scene. Brusatte includes a detailed timeline and a dinosaur lineage chart that readers can refer to as they read the book. In the back, there is a Further Reading section, a Glossary and an Index.  Overall, this is a fantastic book, very informative, easy to read and chock full of interesting facts about dinosaurs that is sure to please older readers who might be interested in learning more about the subject. It may even inspire a future paleontologist or two!

Book Details:

The Age of Dinosaurs: The Rise and Fall of the World's Most Remarkable Animals by Steve Brusatte
New York: Quill Tree Books       2021
249 pp.