Why were the Tiktaalik fossils an exciting discovery for scientists studying tetrapod evolution?a. They are the earliest frog-like animal discovered to date.b. They show that tetrapods successfully colonized land much earlier than previously thought.c. They have a roughly equal combination of fishlike and tetrapod-like characteristics.d. They demonstrate conclusively that limbs evolved as lobe-fins dragged themselves from pond to pond during droughts.

A lamprey, a shark, a lizard, and a rabbit share all the following characteristics excepta. pharyngeal slits in the embryo or adult.b. vertebrae.c. hinged jaws.d. a dorsal, hollow nerve cord.

In Figure 34.25, which of the following is the sister taxon to the archosaurs? (A) synapsids (B) crocodilians (C) turtles (D) lepidosaurs

Which clade does not include humans?a. synapsidsb. lobe-finsc. diapsidsd. osteichthyans

Two black female mice are crossed with a brown male. In several litters, female I produced 9 black offspring and 7 brown; female II produced 57 black offspring. What deductions can you make about the inheritance of black and brown coat color in mice? What are the genotypes of the parents?

Which of the following could be considered the most recent common ancestor of living tetrapods?a. a sturdy-finned, shallow-water lobe-fin whose appendages had skeletal supports similar to those of terrestrial vertebratesb. an armored, jawed placoderm with two pairs of appendagesc. an early ray-finned fish that developed bony skeletal supports in its paired finsd. a salamander that had legs supported by a bony skeleton but moved with the side-to-side bending typical of fishes

To estimate the relative abundance of the major phyla, calculate how many named species of arthropods, mollusks, and nematode worms exist per named species of chordate (the phylum containing vertebrates, including humans; see Table 30.1). Do you think these calculations are likely to be underestimates or overestimates? Why?

EVOLUTION CONNECTION Living members of a vertebrate lineage can be very different from early members of the lineage, and evolutionary reversals (character losses) are common. Give examples that illustrate these observations, and explain their evolutionary causes.

There is some evidence that pharyngeal slits occur in certain species of echinoderms that appear early in the fossil record. If confirmed, what do these data suggest?a. Echinoderms are chordates.b. Pharyngeal slits were present in the earliest echinoderms and lost later.c. Some lineages of echinoderms are more closely related to chordates than others.d. Pharyngeal slits should not be used as a trait in phylogenetic analysis.