Denise McDermott, age 10, of Visalia, Calif., for her question:
What is a plesiosaur?
His name is coined from two words meaning near and lizard. We may assume, then, that the plesiosaur is a lizard type animal. This was true, for he no longer exists. He lived in the days of the dinosaurs when the lizard clan reached its prime. From his fossil bones you might take him for some kind of sea monsters which is true. The plesiosaur was one of the sizeable lizards who gave up life on the land and returned to the sea.
Our sea monster looked like a strange combination of snake and turtle. He had a round, flat turtle body with four flippers for legs. His long, slender tail was sometimes decorated with a fin. Most outstanding was his long, snake‑like neck supported by 13 to 76 vertebrae, depending upon the variety of plesiosaur. The head was small, wedge‑shaped and snaky looking. Unlike most lizards, this sea monster's tough hide was without scales. Some varieties measured 18 feet from head to tail, others measured up to 40 feet.
The reptile clan dominated the earth during the Mesozoic Era. This chapter of Earths history began about 185 million years in the past and ended some 60 million years ago when our own era began. It is divided into three smaller time periods, the Triassic, Jurassic and Cretaceous. During those 120 million years, the dinosaurs developed, thrived and perished. Some became monsters in the Triassic Period and perished long before the end of the era* Others developed later, in the Jurassic and Cretaceous Periods and survived until the final doom of the dinosaurs,
The ancestors of the plesiosaurs greeted the Mesozoic Era as land animals. They probably lived in and out of the waters around shallow seas. For this was a time of encroaching seas and shore waters teemed with soft bodied morsels, sea urchins, crabs and other crustaceans,
The land was forested with horse tail trees, giant ferns, cycads, conifers anal ginkgos. The first flowering plants had arrived and with them the first butterflies. The busy ants and countless beetles lived much as they do today. This is the land scenery which gave way to the encroaching seas.
Early in the era, the huge ichthyosaur had gone to sea and succeeded as the fish‑lizard. Somewhat later, the ancestors of the plesiosaur followed his example. Our turtle‑snake lizard reached his prime in the Jurassic Period. He thrived in the seas around Europe 150 million years ago. By the Cretaceous Period, he was well adjusted to sea life. This left him better off than many of his land dwelling relatives. For during this last period of Mesozoic Era, the seas swamped much of Europe and half of North America,
Too bad‑ but all the plesiosaurs success in coping with a changing world was doomed. For he perished from the earth some sixty million years ago, when the giant reptiles came to an end.