In This Chapter
^ Sizing up fossils from the smallest to the biggest ^ Finding strange things on islands
^ Seeing how fossils can tell us about the past and help us in the present
■X ou can't talk about evolutionary biology without talking about fossils. They're the only physical evidence of plant, animal, and microbial forms that existed long before the first primordial human.
In this chapter, I offer ten fossil finds. I chose these fossils because they reveal information not only about specific organisms (such as miniature mammoths), but also about evolution and the world. I didn't organize this chapter in any particular order, but really, how can you begin a discussion of fossils and not begin with dinosaurs? You can't. So I start there.
Since the early 1800s, when the first dinosaur fossil was discovered (and recognized for what it was), people's imaginations have been fired by dinosaurs — not only because of their size (they included some of the largest animals the world has known), but also because they seem so unlike animals today.
What does the fossil record say about these beasts? Quite a bit, actually, but not nearly as much as you'd think, despite the attributes given to them by movie directors and novelists:
1 They lived from approximately 230 million to 65 million years ago — a period long enough for them to see some species go extinct and other species arise.
1 They were not lizards, even though the word dinosaur comes from the Greek, meaning "terrible lizard" and they have a common ancestor with lizards. The skeletal differences between lizards and dinosaurs are pronounced enough that dinosaurs get their own branch of the tree of life.
Dinosaurs' legs, for example, were directly under the body rather than off to the side, as is the case with lizards and crocodilians.
1 They didn't live at the same time as humans. Modern humans have been here for only a few hundred thousand years, and the dinosaurs went extinct (mostly) 65 million years ago.
1 No one can claim to know what color dinosaurs were (the fossil record doesn't give information about color), though it's reasonable to assume that, like every other group of animals, they came in a variety of colors.
1 The largest dinosaurs may have weighed 100 tons or more. Why the uncertainty? Many dinosaur fossils are incomplete. It's reasonably straightforward to come up with a good estimate of an animal's weight based just on its skeleton — if you have a complete skeleton. The largest dinosaur species for which scientists have found all the various bits is Brachiosaurus, which weighed in at about 30 to 40 tons, but bones from much larger species have been found. Unfortunately, without all the bones, paleontologists can't be sure exactly what those dinosaurs looked like.
1 Some species had social behavior. Fossilized tracks indicate that large groups of dinosaurs traveled together. Nesting areas where several dinosaurs made nests together have also been found. Evidence even exists that baby dinosaurs remained in the nest and were cared for by the parents (because fossils of young but not newly hatched dinosaurs have been found in nests).
1 No one knows for sure what caused the dinosaurs to go extinct. One theory is that a large meteor smashed into the Earth, raising a cloud of dust big enough to alter sunlight and weather around the globe. As it turns out, scientists have found evidence that a large meteor struck the Earth around the time when the dinosaurs went extinct. The geological boundary corresponding to the time when the dinosaurs disappeared contains a layer of iridium — an element that is rare on Earth's surface but plentiful in some meteors; it would have settled on the Earth as dust from the sky after a meteor impact.
1 One group of dinosaurs is still around today. You know this group as birds. The bird lineage has its origin within the dinosaur branch of the tree of life — an initially controversial idea that's now widely accepted.
The first "scientific" discovery of dinosaur fossils occurred in the early 1800s, ^/tJjSfN but it's surmised that ancient peoples (such as the Romans and Chinese) dis-¡¡¡y w® ) covered dinosaur fossils earlier. Those fossils could be the source of myths about dragons and other fantastical beasts that crop up in lore and literature from ancient times.
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