Angela Marshall, age 11, of St. Louis, Missouri, for her question:
What is the dinosaur's closest living relative?
Modern animals come in a vast variety of shapes and sizes, though only about 5,000 of them are reptiles. If we could see the earth as it teas 100 million years ago, we might be surprised to find almost as many different shaped animals though most of them would be reptiles. This was, of course, the Age of Reptiles, when the fantastic dinosaurs dominated the realm of animals. They were the remote ancestors of the more than 5,000 reptiles that now inhabit the earth.
Almost 2,500 modern lizards are classified in the Suborder Sauria, the same group in which the ancient dinosaurs belonged. These fantastic reptiles of the Mesozoic Era thrived for more than 100 million years. Then quite suddenly, four families of their largest, most monstrous species disappeared from the land and the seas. This was about 60 million years ago. However, all of the reptiles did not perish and the Order Reptilia is a great one for branching out in assorted shapes and sizes. For example, long after the dinosaurs departed, the snakes developed from reptile ancestors that had legs.
Though young reptiles resemble their parents, some species tend to change very slightly from generation to generation. The differences are too small to notice during, 60 thousand years but after 60 million years the descendants may be different species. Without a doubt, all our lizards of the sauria group descended from ancestors that belonged to a fabulous dinosaur clan of 100 million years ago. All of them share basic reptilian features with their remote ancestors. However, time has shrunk their sizes and even the largest modern lizard is a midget beside one of the giant dinosaurs of the past. Our biggest lizard is the ten foot long eomodo dragon, who strongly resembles many of the long gone dinosaurs, though on a smaller scale. He has a similar elongated body and tail, plus squat legs, mighty muscles and fierce meat eating teeth. Like his ancient reptilian ancestors, he also is a scaly skinned, cold blooded animal who hatches from a soft shelled egg.
Most of these basic features are shared by all our saurian lizards and many of them look like small versions of the ancient dinosaur relatives. We have lizards with spikes and horns, neck frills and various flaps of skins. There were dinosaurs with all of these features. However, there also were many dinosaurs that ran around on their hind legs and others that wore fantastic plates of bony armor. These monsters perished, though the turtle and tortoise group of the reptilian clan still wear armored shells.
We tend to think of the dinosaurs as failures, though for longer than 100 million years they were the ruling animals of the earth. Their reptilian order did not perish with them. The turtles survived with little or no changes and so did the crocodiles. Our lizards still resemble saurian ancestors, though on a mini scale.