the bodies of some organisms decay faster than others do. For
example, an animal with a hard exoskeleton (such as a crab) would
have a better chance of becoming fossilized than would a soft-
bodied organism, such as an earthworm.
Although the fossil record will never be complete, it presents
strong evidence that evolution has taken place. ,sci-
entists who study fossils, can determine the age of fossils fairly
accurately by using radiometric dating. Radiometric dating the
sediments in which a fossil is found enables paleontologists to
arrange fossils in sequence from oldest to youngest. When this is
done, orderly patterns of evolution can be seen. Based on existing
fossils, Figure 8shows an artist’s idea of the appearance of three
extinct species that might have been ancestral to modern whales.
They are arranged in the order that they evolved, based on their
fossil’s age as determined by radiometric dating.
PaleontologistsSECTION 2 Evidence of Evolution 285
Modern whales have forelimbs that are flippers
and hind limbs that have been reduced to only a
few internal functionless hind-limb bones.Rodhocetus kasrani, a more recent ancestor of
modern whales, probably spent little time on land.
Its reduced hind limbs could not have aided in
walking or swimming. It is thought to have existed
about 40 million years ago.
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Topic: Paleontology
Keyword: HX4134