Chapter 23

The absolute age of a geological stratum is determined by: a. the thickness of its rocks. b. the particle size in its rocks. c. the types of fossils found within it. d. its position relative to other layers. e. radiometric dating techniques.

The punctuated equilibrium hypothesis: a. recognizes that morphological evolution may occur slowly or quickly. b. suggests that major morphological novelties arise gradually. c. may help explain why there are so many "missing links" in the fossil record. d. suggests that the fossil record is usually complete. e. links mass extinctions to the impact of asteroids striking Earth.

Biologists believe that the overall similarities between marsupial mammals in Australia and placental mammals in North America were caused by: a. plate tectonics. b. dispersal. c. convergent evolution. d. homeotic genes. e. punctuated equilibria.

The differential growth of body parts is called: a. allometry. b. paedomorphosis. c. heterochrony. d. phyletic gradualism. e. evo-devo.

Exaptations are traits that: a. prepare some organisms for future environmental changes. b. appear in lineages as a result of an adaptive radiation. c. evolve in anticipation of a species' future needs. d. are useful in new situations before natural selection alters them for a new function. e. occur in animals, but not in plants.

Adaptive radiations often follow mass extinctions because: a. mass extinctions limit the impact of paedomorphosis. b. mass extinctions foster allometry and heterochrony. c. mass extinctions decimate all forms of life on Earth. d. species that form transitional fossils often survive mass extinctions. e. extinctions open adaptive zones that had been previously occupied.

Homeobox genes are defined as genes that: a. bind directly to a regulatory site on DNA. b. code for transcription factors activating or repressing genes that influence an organism's form. c. determine whether or not a morphological innovation leads to an adaptive radiation. d. have been inherited from an ancient ancestor by nearly all forms of life. e. help biologists differentiate between plants and animals.

The observation that fossils of Premedosaurus are found only in Argentina and Northern Europe provides an example of: a. a continuous distribution. b. a disjunct distribution. c. punctuated equilibrium. d. heterochrony. e. gradualism.