No Legs, Not a Snake: The Glass Lizard at the Reptile Rescue

Compare living reptiles and a fossil snake to infer who is related to whom.

Part 1: Four living reptiles

Read the passage and the table, then answer questions 1 to 4.

The Box Said "Snake"

1The Cedar Hollow Reptile Rescue takes in pet reptiles whose owners can no longer care for them and finds them new homes. Eighth grader Noor Rasmussen volunteers there on Saturdays. One morning a box arrived labeled "snake, about 1 m long." Inside was a long, brown, legless animal. The rescue's coordinator, Ms. Philippa Oyelowo, watched it for a minute and said it was not a snake at all. It was a European glass lizard. She asked Noor to compare it with three other animals at the rescue, a Burmese python, a corn snake and a four-legged southern alligator lizard, and to decide which of them the glass lizard is most closely related to.

2Ms. Oyelowo explained how scientists infer relationships from anatomy. They compare many body parts, not just one. Animals that share many detailed features most likely share a recent common ancestor. A similar body shape is weaker evidence, because unrelated animals that live in similar ways, such as moving through thick grass, can evolve similar shapes.

3Noor watched the glass lizard blink, closing its eyelids over its eyes. She found a small ear opening behind each eye and a deep fold of skin running along each side of its body. The alligator lizard has the same kind of side fold, and an X-ray of it shows small bony plates under its scales. Neither snake has eyelids; a clear scale covers each eye like a contact lens. Snakes have no ear openings, and the two halves of a snake's lower jaw are joined at the chin by stretchy tissue, so its mouth can open very wide. The rescue's X-rays also showed tiny hip bones inside the glass lizard and the python. The python has two small claw-like spurs near the base of its tail, and the glass lizard has two tiny stubs, about 2 mm long, in the same place.

4Ms. Oyelowo also showed Noor pictures of Najash, a fossil found in Argentina in rocks about 95 million years old. Najash had a long body, no front legs and two small but complete hind legs. Scientists group it with snakes because its skull and backbone bones are shaped much like those of living snakes. Noor added Najash to her table.

Noor's Comparison Table (— = not preserved)
Animal	Legs	Eyelids that close	Ear openings	Belly scales	Hip bones
Alligator lizard	Four legs	Yes	Yes	Many small rows	Joined to backbone
Glass lizard	None (2 tiny stubs)	Yes	Yes	Many small rows	Tiny, not joined
Burmese python	None (2 spurs)	No	No	One row, wide	Tiny, not joined
Corn snake	None	No	No	One row, wide	None
Najash (fossil)	Two hind legs	—	—	—	Joined to backbone

Use the passage and the table. Which animal is the glass lizard most closely related to?

A. The alligator lizard, because both have eyelids, ear openings and a side fold
B. The corn snake, because both have long bodies with no legs
C. Najash, because both have hind leg parts and no front legs
D. The python, because both have tiny hip bones and two small bumps near the tail

Use the passage and the table. Circle the three features of the glass lizard that it shares with the alligator lizard and that neither snake has.

Eyelids that closeNo legs on the outsideA fold of skin along each sideTiny hip bones inside the bodyEar openingsA long, narrow body

The glass lizard and the corn snake both have no legs and move by bending their bodies through grass. Use paragraph 2. Why is this weak evidence that they are close relatives?

A. The glass lizard grew its legs back after it arrived at the rescue.
B. Unrelated animals that move the same way can evolve similar shapes.
C. Both animals were kept as pets, and pets kept together grow to look alike.
D. The corn snake is a reptile, but the glass lizard is an amphibian.

Use the passage and the table. Sort each feature by the pair of living animals that has it.

A clear scale covering each eyeMany small rows of belly scalesLower jaw halves joined by stretchy tissueA small ear opening behind each eyeOne row of wide belly scales

Glass lizard and alligator lizard	Python and corn snake

Part 2: Hips, legs and a fossil snake

Use the table and paragraphs 3 and 4 to answer questions 5 to 10.

Use the Hip bones column of the table. Count all five animals.

of the five animals have hip bones. Of those, have hip bones joined to the backbone.

Najash had small hind legs with hip bones joined to its backbone, and its skull and backbone are shaped like a snake's. What does this fossil suggest?

A. Early snakes grew legs during their lives and lost them as they got older.
B. Snakes evolved from fish, while lizards evolved from four-legged animals.
C. Najash was a glass lizard, because it had no front legs and a long body.
D. Snakes come from legged ancestors, and some early snakes had hind legs.

The python has tiny hip bones and two spurs, but it does not walk. What do these parts most likely suggest?

A. The python's ancestors had hind legs, like Najash.
B. The python is a close relative of the alligator lizard.
C. The python is about to grow legs as it gets older.
D. The python uses its hip bones to walk on land at night.

Scientists group the glass lizard with the alligator lizard. Based on paragraph 3, which feature would you predict a closer look at the glass lizard's X-ray shows?

A. Hip bones joined to the backbone, like those of Najash
B. A stretchy joint at the chin, like the python's
C. Small bony plates under its scales, like the alligator lizard
D. A single row of wide belly scales, like the corn snake's

Suppose a new fossil about 90 million years old is found. It has a long body, no front legs and two tiny hind legs. Its skull and backbone are shaped like a snake's, and the halves of its lower jaw were not joined firmly at the chin. Which conclusion fits best?

A. It is an early glass lizard, because it had tiny legs.
B. It is an early relative of snakes, like Najash.
C. It is not a reptile, because reptiles have four legs.
D. It is a fossil alligator lizard that lost its front legs.

10.

Noor's friend says, "That animal has no legs and a long body, so the box was right. It's a snake, and its closest relative here is the corn snake." Do you agree? Write a claim, give at least two pieces of anatomical evidence from the passage or the table and explain your reasoning.