To Swim or Not to Swim?
The amphibians needed to enter the water to lay their eggs, but when they began to evolve they started to lay their tough eggs in nests away from the beach like reptiles do. Most of the reptiles had a rough skin that kept them from drying out as they made their home on the land.
If someone asked you to name a reptile that lives in the world today, you might say a lizard, a turtle, or a snake. If so, you would be right.
Millions of years ago, reptiles came in all shapes and sizes. The Ichthyosaurus looked like a fish, but it wasn't a fish because it had to come to the top of the water to breathe. Numerous fossils have been found that prove that this creature's young were born live underwater!
For many years, scientists believed that Ichthyosaurus developed legs, came out of the water, then returned to the water, and developed fins again. They no longer believe that this is true. Modern scientists believe that Ichthyosaurus did not have any legs and spent its life in the water.
Warm-Blooded Versus Cold-Blooded
At one time, all reptiles, including the dinosaurs, were thought to be cold-blooded, which meant that their bodies were the same temperature as their surroundings. That is why you see modern-day reptiles like crocodiles, alligators, snakes, turtles, and geckos (which are all cold-blooded) sunning themselves on warm rocks and logs in the water.
Today scientists are more puzzled than ever because they are finding fossils that appear to show that the warm-blooded birds’ ancestors were the dinosaurs. A warm-blooded animal's body stays warm even if it is cold outside. A cold-blooded animal's body grows colder as the temperature drops.
There are still both cold-blooded reptiles and warmblooded birds today. Were some of the dinosaurs warm-blooded and some of them cold-blooded? Even the experts don't know for sure! Some mammal-like reptiles that came to be known as cynodonts even had hair on their skin and were believed to be warm-blooded, just as you are!
Fun Fact
Fuzzy Dinosaurs?
When you think of dinosaurs, you probably think of reptiles with scaly skin like a snake or lizard. Did you know some dinosaurs’ skin may have been covered in fur, feathers, hair, spikes, or plates?
Words to Know
ancestors:
Ancestors are the people or animals in a family that were born before this generation. You descended from your grandparents and great-grandparents, so they would be your ancestors. The dinosaurs were ancestors of the modern-day reptiles.
Reptile Roundup
After it gets dark some night, gather a few friends together (with everyone's parents’ permission) and tell them all to bring little flashlights. Tell them that you are playing a new game of hide-and-seek the way that snakes do. Snakes find their victims by sensing the heat from their bodies. In your case, you will be sensing the light from your friends’ flashlights.
Have the “snake” cover his eyes and count to 100. All the other players—the snake's “lunch”—must hide, and when the snake calls out “ready,” they need to flash their lights one time, quickly, and then wait to see if they are found as the “snake” searches for the places where he saw the light flash.
Each time the snake calls out, “Where's my lunch?” the other players must flash their lights again. The first one found is the loser, and he or she becomes the new “snake.”
Fun Fact
Talented Tails
Dinosaurs used their tails like a leg to balance, as a weapon to protect themselves, and more. Although humans have a tailbone, we don't have a tail. Can you use other parts of your body in different ways? Have you ever tried using your toes to pick something up? How about painting or drawing with your feet? Another thing you could try is game of catch with a friend using only your feet.
How Old Am I?
Dinosaurs aren't the only things that scientists study. Did you know that turtles have the longest lifespan of all of the animals and that their species has been on the earth longer than any other reptile that is alive today? One way to figure out the age of a turtle is to count the rings on its shell.
But how do we know how old some of the dinosaurs were? Many people believe that the dinosaurs lived to be more than 100 years old. Scientists have found some clues in fossils that lead them to believe this. For one thing, they think that some dinosaurs may have been unable to move their tails as they reached such old ages, because their fossils show that their joints were filled with hard tissue. Other animals today have this same condition when they become quite old.
Scientists have also noticed worn places in the fossils of the dinosaurs caused by the dinosaurs’ muscles moving back and forth across their bones for so many years. Learning the age of a dinosaur can be very important to a scientist. Many times the scientists have thought that they had discovered a new species of dinosaur, until someone else realized it was actually a baby or a smaller form of an already-discovered species.
Charlie: Why did the Triceratops cross the road?
Jesse: He didn't, the chicken crossed the road.
Charlie: Well, why did the chicken cross the road?
Jesse: To get away from the Triceratops!
Veterinarians can easily determine the age of a horse by looking at its teeth—all they have to do is see how worn down they are. Unfortunately, this easy method can't be used on dinosaur fossils. Many of the dinosaurs had several sets of teeth that were waiting in their jaws to replace the ones they lost. With these constantly changing teeth, you certainly wouldn't be able to look at their teeth to judge how old they were!
