Wishbones and Feathers in the Fossil Hall

Compare dinosaur, bird and reptile skeletons to infer how they are related.

Part 1: The skeleton table

Read the passage and the table, then answer the questions.

The New Dinosaur Hall

1The natural history museum downtown has opened a new hall of skeletons. At one end stand casts of two fossil animals: Velociraptor, a turkey-sized meat-eating dinosaur about 75 million years old, and Archaeopteryx, a crow-sized animal about 150 million years old with feathered wings. Beside them are skeletons of three living animals: a pigeon, an American alligator and a green iguana. Ezekiel Nakamura, an eighth grader, is writing a report on the hall, and museum educator Halina Brzezinski is helping him compare the skeletons.

2Ms. Brzezinski pointed out five features. A wishbone is a V-shaped bone in the chest, formed from two collarbones joined in the middle. Air-filled bones have hollow spaces inside that connect to the lungs, which makes them light for their size. The hand is the end of the front limb, which can have separate clawed fingers or fingers joined into one piece. Teeth grow in the jaws, while a beak has none. Feathers rarely fossilize, but in many birds the big wing feathers anchor to a row of small bumps on a forearm bone, and a Velociraptor fossil has the same row of bumps.

3She also showed Ezekiel the tails. Velociraptor, Archaeopteryx, the alligator and the iguana all have long tails with many separate bones. The fossil of Archaeopteryx even shows a row of feathers along each side of its long tail. The pigeon's tail feathers sit on a short tail that ends in a small knob of joined bones.

4Not every feature shows up in a skeleton. Ms. Brzezinski explained that alligators and birds both have a heart with four chambers and a muscular gizzard that grinds food. Most lizards, including the iguana, have a heart with three chambers and no gizzard.

5Scientists use patterns like these to work out relationships. Organisms that share many detailed features of anatomy most likely share a more recent common ancestor than organisms that share fewer features. Scientists also watch for features that two animals share only because they do the same job. Bats and birds both fly, for example, but a bat's wing is skin stretched between long finger bones, with no feathers at all, and bats have no wishbone.

Features in the hall (Ezekiel's notes)
Organism (age)	Wishbone	Air-filled bones	Hand	Teeth	Feathers
Green iguana (living)	No	No	5 clawed fingers	Yes	No
Alligator (living)	No	No	5 fingers, 3 clawed	Yes	No
Velociraptor (75 mya)	Yes	Yes	3 clawed fingers	Yes	Yes
Archaeopteryx (150 mya)	Yes	Yes	3 clawed fingers	Yes	Yes
Pigeon (living)	Yes	Yes	3 fingers, joined	No	Yes

Count only features that both organisms have, such as "Yes" in both rows. For the hand, count it only when both rows say the same thing.

Archaeopteryx and Velociraptor share of the five table features. Archaeopteryx and the pigeon share of them.

Based on the table, which living animal shares the most features with Velociraptor?

A. The pigeon, since both have a wishbone, air-filled bones and feathers
B. The alligator, since both are large meat-eating hunters
C. The alligator, since both have teeth and scaly skin
D. The iguana, since both have long tails with many bones

Use the table and paragraph 3. Circle the three features that Archaeopteryx shares with Velociraptor but not with the pigeon.

TeethA wishboneThree separate clawed fingersFeathersA long tail with many bonesAir-filled bones

Ezekiel writes, "Archaeopteryx evolved from Velociraptor." Which response fits the evidence on the page best?

A. No. Velociraptor had feathers, but Archaeopteryx did not.
B. Yes. They share all five table features, so one must have come from the other.
C. No. Archaeopteryx is older, so the two more likely share an older common ancestor.
D. Yes. Velociraptor was larger, so it is the ancestor of the smaller animal.

Part 2: Who is related to whom?

Use the whole passage and the table to answer the questions.

The alligator and the pigeon share none of the five table features. Which evidence from the passage still suggests alligators are more closely related to birds than iguanas are?

A. Alligators and pigeons both have three separate clawed fingers.
B. Alligators and birds have a four-chambered heart and a gizzard, but most lizards do not.
C. Alligators and iguanas both have long tails with many separate bones.
D. Alligators have teeth, and pigeons have a beak with no teeth.

Suppose a new fossil about 125 million years old is found. It has feathers, a wishbone, teeth and three clawed fingers, and its short tail ends in a knob of joined bones. Which conclusion fits best?

A. It is most closely related to iguanas, since it has teeth and claws.
B. It is unrelated to the hall's animals, since its mix of features matches no row.
C. It is an early alligator, since alligators also have teeth and claws.
D. It is related to birds, and its tail is more like a pigeon's than Archaeopteryx's.

A visitor says the pigeon is more closely related to the iguana than to Velociraptor, because the pigeon and the iguana are both alive today. What is the best reply?

A. Disagree. The pigeon shares three detailed features with Velociraptor and none with the iguana.
B. Agree. The pigeon and the iguana both lay eggs, so they are closest.
C. Agree. Animals living at the same time share more recent ancestors.
D. Disagree. Fossils are too old to compare with animals alive today.

Archaeopteryx lived about million years before Velociraptor, yet the two share every feature in the table.

Ezekiel's report claims, "Birds are living relatives of dinosaurs such as Velociraptor." Do you agree? Write a claim, give at least two pieces of anatomical evidence from the table or passage and explain your reasoning.