BackWhy 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.
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 vertebrates
b. An armored, jawed placoderm with two pairs of appendages
c. An early ray-finned fish that developed bony skeletal supports in its paired fins
d. 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?
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.
In garden peas, yellow seeds (Y) are dominant to green seeds (y), and inflated pods (I) are dominant to constricted pods (i). Suppose you have crossed YYII parents with yyii parents. List the genotype(s) of gametes produced by F1 individuals.
Consider the evolution of protostomes and deuterostomes (this chapter):
Compare adaptations in protostomes and deuterostomes for living on land.
Recall that changes in the expression patterns of tool-kit genes in arthropods such as insects enabled a dramatic diversification of their segmented appendages and bodies.
Design an experiment to test whether this concept applies to vertebrates.
The smooth feathers on the back of the neck in pigeons can be reversed by a mutation to produce a 'crested' appearance in which feathers form a distinctive spike at the back of the head. A pigeon breeder examined offspring produced by a single pair of non-crested birds and recorded the following: 22 non-crested and 7 crested. She then made a series of crosses using offspring from the first cross. When she crossed two of the crested birds, all 20 of the offspring were crested. When she crossed a non-crested bird with a crested bird, 7 offspring were non-crested and 6 were crested. For these three crosses, provide genotypes for parents and offspring that are consistent with these results.
As a genetic counselor, you advise couples about the possibility of genetic disease in their offspring. Today you met with an engaged couple, both of whom are phenotypically normal. The man, however, has a brother who died of Duchenne-type muscular dystrophy, an X-linked recessive condition. His fiancée, whose family has no history of the disease, is worried that the couple's sons or daughters might be afflicted. The sister of this man is planning to marry his fiancée's brother. How would you advise this second couple?
As a genetic counselor, you advise couples about the possibility of genetic disease in their offspring. Today you met with an engaged couple, both of whom are phenotypically normal. The man, however, has a brother who died of Duchenne-type muscular dystrophy, an X-linked recessive condition. His fiancée, whose family has no history of the disease, is worried that the couple's sons or daughters might be afflicted. How would you advise this couple?
The size and shape of the vertebrate skull can reveal a great deal about an animal's lifestyle and evolutionary relationships. Consider your own skull. If you put your finger in your ear and move your jaw up and down, you can feel the space near the hinge of your jaw. Nestled in this space are the tiny bones that make your hearing possible: the malleus, incus, and stapes. All mammals have these three ear bones, but reptiles such as this T. rex don't.
Where did ear bones come from?
Analyze the morphological data shown here and write a hypothesis to explain the origin of mammalian ear bones. (The cynodont shown is one of many extinct synapsid amniotes that lived early in the lineage that gave rise to mammals.)
The size and shape of the vertebrate skull can reveal a great deal about an animal's lifestyle and evolutionary relationships. Consider your own skull. If you put your finger in your ear and move your jaw up and down, you can feel the space near the hinge of your jaw. Nestled in this space are the tiny bones that make your hearing possible: the malleus, incus, and stapes. All mammals have these three ear bones, but reptiles such as this T. rex don't. Where did ear bones come from? How is the opossum related to you?
Select True or False for each statement.
T/F An opossum is an animal, but I am a human.
T/F An opossum is a mammal, but I am a human.
T/F An opossum is a marsupial, but I am a placental mammal.
T/F The opossum and I are both tetrapods.
The size and shape of the vertebrate skull can reveal a great deal about an animal's lifestyle and evolutionary relationships. Consider your own skull. If you put your finger in your ear and move your jaw up and down, you can feel the space near the hinge of your jaw. Nestled in this space are the tiny bones that make your hearing possible: the malleus, incus, and stapes. All mammals have these three ear bones, but reptiles such as this T. rex don't. Where did ear bones come from? The illustration of the opossum skull shows that the ear bones are completely separated from the jawbone (as they are in all mammals).
Pose a hypothesis to explain why this separation could be an adaptation that contributed to the radiation of mammals into diverse niches, including a nocturnal lifestyle.