13.2 - 13.3

Question 1

Fossil

Answer 1

A preserved remnant or impression of an organism.

Question 2

Note 1 —-»

Answer 2

The organic substances of a dead organism usually decay rapidly, but the hard parts of an animal that are rich in minerals, such as the bones and teeth of vertebrates and the shells of clams and snails, may remain as fossils.

Question 3

Strata

Answer 3

Rock layer formed when a new layer of sediment covers an older one and compresses it.

Question 4

Note 2 —-»

Answer 4

The fossils in a particular stratum provide a glimpse of some of the organisms that lived in the area at the time the layer formed. Because younger strata are on top of older ones, the relative ages of fossils can be determined by the layer in which they are found. Thus, the sequence in which fossils appear within layers of sedimentary rocks is a historical record of life on Earth.

Question 5

Paleontologist

Answer 5

A scientist who studies fossils.

Question 6

Fossil Record

Answer 6

The chronicle evolution over millions of years of geologic time engraved in the order in which fossils appear in rock strata.

Question 7

Note 3 —-»

Answer 7

Many of Earth’s organisms did not live in areas that favor fossilization. Many fossils that did form were in rocks later distorted or destroyed by geologic processes. Furthermore, not all fossils that have been preserved are accessible to paleontologists. Even with its limitations, however, the fossil record is remarkably detailed.

Question 8

What types of animals do you think would be most represented in the fossil record? Explain your answer.

Answer 8

Animals with hard parts, such as shells or bones that readily fossilize, and those that lived in areas where sedimentary rock may form

Question 9

Note 4 —-»

Answer 9

Whales are cetaceans, a group that also includes dolphins and porpoises. They have forelimbs in the form of flippers but lack hind limbs. If cetaceans evolved from four-legged land animals, then transitional forms should have reduced hind limb and pelvic bones. Based on the few fossils available in the 1960s, paleontologists hypothesized the ancestors of whales were hoofed, wolflike carnivores.

Question 10

Note 5 —-»

Answer 10

Paleontologists were taken aback by the contradictory results, but openness to new evidence is a hallmark of science. They turned their attention to seeking a fossil that would resolve the issue. Cloven-hoofed mammals have a unique ankle bone. If the ancestor of whales was a wolflike carnivore, then the shape of its ankle bone would be similar to most present-day mammals. Two fossils discovered in 2001 provided the answer. Both Pakicetus and Rodhocetus had the distinctive ankle bone of a cloven-hoofed mammal. Thus, as is often the case in science, scientists are becoming more certain about the evolutionary origin of whales as mounting evidence from different lines of inquiry converges.

Question 11

What anatomical feature did scientists predict in fossils of species transitional between terrestrial and aquatic mammals?

Answer 11

Reduced hind limb and pelvic bones