The Origin and Evolution of Vertebrates

Divers collect a tiny, transparent marine larva. Under a microscope it has a stiff rod running the length of its body, a tubular nerve cord above that rod, several openings in the wall of its throat, and a muscular tail that extends well behind the anus. Which conclusion is best supported?

Which comparison correctly contrasts the main nerve cord of a chordate with that of a typical insect?

About four weeks after conception, a human embryo has a series of grooves and pouches along the sides of its neck region, like those that form gill slits in fish embryos. In humans, these become parts of the middle ear, the tonsils and some glands. How do these grooves count as evidence for evolution?

DNA comparisons place tunicates closer to vertebrates than lancelets are. Adult lancelets keep all four chordate hallmarks, but adult tunicates keep only their throat slits. Which inference about the common ancestor of all chordates is most reasonable?

Researchers mark neural crest cells in a chick embryo with a dye that is passed on to all their descendant cells. Several days later, in which tissues would they most expect to find the dye?

After a gene is accidentally duplicated, one copy keeps doing the gene's original job. Why can the second copy evolve a new function without harming the organism?

Among chordates, craniates were the first to have red blood cells packed with hemoglobin. In a typical mammal, 100 mL of plasma alone dissolves about 0.3 mL of O₂. The same volume of whole blood holds about 15 g of hemoglobin, and each gram binds about 1.34 mL of O₂ (approximate real values). About how many times more O₂ can 100 mL of whole blood carry than 100 mL of plasma alone?

Hagfishes were long described as having no vertebrae. Researchers later found that hagfish embryos form small cartilage pieces along the notochord, much like the earliest vertebral elements of lamprey embryos. DNA data also group hagfishes with lampreys. What do these findings most strongly suggest?

Fishery biologists tracked sea lampreys and lake trout in a large lake they had invaded. Starting in 1960, a chemical that kills lamprey larvae was applied to the streams where lampreys spawn (invented data): Year | Sea lamprey abundance (index) | Lamprey wounds per 100 lake trout 1950 | 90 | 35 1955 | 100 | 40 1960 | 98 | 39 1965 | 30 | 12 1970 | 18 | 7 1975 | 15 | 6 Which conclusion is best supported by the data?

Sea lamprey larvae spend several years buried in the mud of small streams, filter-feeding, before they change into parasitic adults that roam a large lake. To protect the lake's fish, managers treat certain stream stretches with a chemical that kills the larvae instead of treating the lake. Which reason best supports this plan?

In an adult lamprey, the main body support is a notochord with small cartilage pieces along it. In an adult trout, a column of bony vertebrae surrounds the spinal cord, and only small remnants of the notochord remain. What does this comparison suggest about how the backbone evolved?

One hypothesis says hardened (mineralized) tissue first evolved in the mouthparts of early vertebrates and only later spread to body armor and the inner skeleton. Which new discovery would most weaken this hypothesis?

Which observation best supports the hypothesis that vertebrate jaws evolved from the skeletal supports of the front gill slits?

An old museum label defines 'Pisces' (fishes) as all jawed vertebrates except tetrapods. A biologist objects that this group is not a clade. Which is the best reason for the objection?

In the bony-fish family tree, the earliest-branching living ray-finned fishes (such as bichirs) have lunglike organs they use to breathe air, and lungfishes, which are lobe-fins, have lungs too. Only later-branching ray-finned fishes have a swim bladder used for buoyancy. Which conclusion is most parsimonious?

Some open-ocean sharks die if they are held motionless, while bottom-resting nurse sharks can lie still on the seafloor for hours. Which explanation best accounts for the difference?

The hypothesis that tetrapods evolved from lobe-finned fishes makes predictions about the fossil record. Which discovery would most strongly contradict it?

The fin of a Devonian lobe-fin contains one bone nearest the body, then two side-by-side bones, then a cluster of small bones. A bird's wing has the same one-two-many layout. What best explains the match?

In a fish, the pelvic fins aren't connected to the backbone. In a tetrapod, the hip bones are fused to it. Why would this difference matter for an animal walking on land?

Lungless salamanders take in all their oxygen through their skin, and nearly all of them are small. Suppose one salamander were twice as long, twice as wide and twice as tall as another of the same shape. Its skin area would be about 4 times larger and its volume about 8 times larger. How would its skin area per unit of body volume compare with the smaller salamander's?

Eggs of a frog and a lizard, each starting at 2.00 g, were kept in dry air at 30 °C for 48 hours. The frog eggs, with only a jelly coat, fell to 0.60 g. The lizard eggs, which have a leathery shell, fell to 1.84 g. Which statement is best supported?

In a developing turtle egg, researchers block blood flow through the chorion and allantois but leave the other membranes working. Which process would most directly fail?

The table shows the body temperatures of two animals held at different air temperatures (invented data). Air temperature (°C) | Animal X body temp (°C) | Animal Y body temp (°C) 5 | 37 | 7 15 | 37 | 16 25 | 37 | 26 35 | 38 | 34 Which statement is best supported?

A 50 g lizard resting at 25 °C uses about 1.8 kJ of energy per day. A 50 g mouse at the same temperature uses about 60 kJ per day (invented but realistic values). The lizard's daily energy use is about what percent of the mouse's?

Biologists claim that the malleus and incus, two tiny bones in the mammalian middle ear, are homologous to bones that form the jaw joint in reptiles. Which observation would best support this claim?

Echidnas lay eggs, as reptiles and birds do. Marsupials and placental mammals give birth to live young. Phylogenies place monotremes on the earliest branch of the mammal tree. Which interpretation fits best?

Early marsupials reached Australia while it was still joined to Antarctica, and Australia then drifted off on its own. Today Australian marsupials include grazers, burrowers, tree-dwellers, gliders and predators. Which process best describes this pattern?

Echidnas, egg-laying mammals of Australia and New Guinea, and hedgehogs, placental mammals of Europe, Asia and Africa, both have backs covered in sharp spines made of modified hair, eat insects and other small invertebrates, and can curl into a defensive ball. DNA and many other traits show that echidnas are far more closely related to the platypus than to hedgehogs. How should a biologist building a mammal phylogeny treat the spiny coat?

A classmate says, 'If humans evolved from apes, why are there still chimpanzees?' Which response is most accurate?

In fossil hominins, a foramen magnum (the opening where the spinal cord enters the skull) placed underneath the skull is used as a sign of upright walking. A later study found that mammals that hop on two legs, such as jerboas and kangaroo rats, also have this opening set farther forward and under the skull than their four-legged relatives. Why does this finding matter for reading hominin fossils?

Genome studies estimate how much DNA in present-day people comes from Neanderthals. Rounded averages (published estimates vary from study to study): Population | Neanderthal-derived DNA (%) East Asian | 2.2 European | 1.9 South Asian | 1.9 West African | 0.5 Neanderthals lived only in Europe and western Asia. Which explanation fits the pattern best?

DNA evidence shows that Neanderthals and modern humans produced offspring whose descendants are alive today. Under the biological species concept, what does this evidence suggest?