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Armadillos on the Trail Camera: Fossils of Two Continents

Grade 8 fossil record practice: a wildlife refuge exhibit compares North and South American fossils to find when mammal groups appeared, spread and died out.

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11 questions
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Format: Interactive · Printable
Grade: Grade 8
Subject: Science
Question types: Fill in the blank, Multiple choice, Circle the answer, Sorting, Short answer

About this worksheet

What students practice

Students read where and in which rock ages fossil groups appear to find patterns in the fossil record.
Students use the order of fossil appearances to infer when land animals spread between continents.
Students argue from fossil evidence about how the mix of living things in a region changed over time.

How to use

Show North and South America on a map and point out Panama before students read. Remind them that older rock layers hold older fossils and that mya means million years ago.

Curriculum

NGSS standard covered

MS-LS4-1

Read the fossil record for patterns in the existence, diversity, extinction and change of life over Earth's history.

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Armadillos on the Trail Camera: Fossils of Two Continents

Use the fossil record of North and South America to find when and how mammal groups spread.

Part 1: Who turns up where?

Read the refuge notes, then use them and Table 1 to answer the questions.

The Fossil Exhibit at the Refuge Visitor Center

1On Saturdays, eighth grader Ezequiel Montoya volunteers at a wildlife refuge in southern Texas. He helps the refuge biologist, Ms. Annelie Grosvenor, check trail cameras that photograph the animals along the brushy trails at night. The cameras catch white-tailed deer, bobcats, coyotes, javelinas and many nine-banded armadillos. One morning Ezequiel asked why armadillos, which he had seen in films about South American forests, are so common in Texas. Ms. Grosvenor said the fossil record holds the answer and walked him to the exhibit in the visitor center.

2The exhibit compares fossils from North America and South America. Today the two continents are joined by a narrow strip of land in Panama. Rock layers in Central America also hold fossils of sea life. In rocks older than about 4 million years, the fossil shells and fish from the Caribbean side of Panama and from the Pacific side are much alike. In younger rocks, the shells and fish on the two sides become more and more different.

3Table 1 shows five groups of land mammals. The column "Most early fossils" tells on which continent the oldest fossils of each group are found. Glyptodons were giant armored relatives of armadillos, some as big as a small car. Litopterns were hoofed plant-eaters, some with long necks. No glyptodons or litopterns are alive today. In the table, "before 5 mya" means rocks older than 5 million years, and "after 2 mya" means rocks younger than 2 million years.

4A few ground sloth fossils turn up in North American rocks about 8 to 9 million years old, millions of years before most other South American groups appear there. Scientists think a few kinds of animals crossed earlier by swimming or floating between islands.

5Some groups also died out in one place but not another. The youngest camel-family fossils in North America are about 11,000 years old, and no wild members of the family live there today. Their wild relatives, the guanacos and vicuñas, still live in South America. Wild members of the horse family died out in both continents at about the same time.

6For Table 2, Ezequiel sorted the casts in the exhibit's teaching drawers. Each cast is a copy of a fossil jaw or tooth of a land mammal from a dated site in Texas or Florida. He sorted them by the age of the site and by where the group's oldest fossils are found, which Ms. Grosvenor calls the group's roots.

Table 1: Where Five Mammal Groups Are Found
Group	Most early fossils	N. Am. before 5 mya	N. Am. after 2 mya	S. Am. before 5 mya	S. Am. after 2 mya
Camel family	North America	Found	Found	Not found	Found
Horse family	North America	Found	Found	Not found	Found
Armadillos and glyptodons	South America	Not found	Found	Found	Found
New World porcupines	South America	Not found	Found	Found	Found
Litopterns	South America	Not found	Not found	Found	Found

Which statement best describes the pattern in Table 1?

A. Camel and horse fossils turn up in South America before they turn up in North America.
B. Litoptern fossils are found in North American rocks younger than 2 mya but not older ones.
C. Armadillo relatives and porcupines are found in North American rocks older than 5 mya.
D. Groups with roots on one continent turn up on the other one only in rocks younger than 2 mya.

Use Table 1. Sort each group by what its fossils show.

Camel familyNew World porcupinesLitopternsHorse familyArmadillos and glyptodons

Spread from North to South America	Spread from South to North America	Found only in South America

Use paragraph 2 and Table 1. When were North and South America most likely first joined by land?

A. About 9 million years ago, when the first ground sloths reached North America
B. Sometime between about 5 and 2 million years ago
C. More than 50 million years ago, before any of these groups appeared
D. About 11,000 years ago, when the camel family died out in North America

Use paragraph 2. Why did the fossil sea life on the two sides of Panama become more and more different in younger rocks?

A. New land split the sea, so sea animals on the two sides could no longer mix.
B. The Caribbean side is warmer, so shells there fossilized while Pacific shells dissolved.
C. Sea animals on both sides traveled back and forth more often in younger times.
D. Land animals crossing Panama ate most of the shellfish on the Pacific side.

Use Table 1 and paragraph 5. Which history of the camel family fits the evidence best?

A. It began in North America, spread south, and later died out in North America.
B. It began in South America about 11,000 years ago and spread north soon after.
C. It began in South America, spread north, and still lives wild on both continents.
D. It began in North America and reached South America with people about 11,000 years ago.

Part 2: The teaching drawers

Use paragraphs 4 and 6 and Table 2 to answer the questions. The 2 casts with South American roots from the 8 mya sites are ground sloths.

Table 2: Land Mammal Casts in the Teaching Drawers (Texas and Florida sites)
Age of sites	North American roots	South American roots
8 mya	46	2
2 mya	41	14
20,000 years ago	38	12

Use Table 2. Think about all the casts from the 2 mya sites.

Casts with South American roots make up % of the casts from the 2 mya sites. (Round to the nearest whole percent.)

Use Table 2. Compare the 8 mya sites with the 2 mya sites. How many more casts with South American roots came from the 2 mya sites?

The number of casts with South American roots grew by .

Use paragraph 4 and Table 2. Two ground sloth casts come from the 8 mya sites. What is the most careful conclusion?

A. The ages of the 8 mya sites are most likely wrong by about 6 million years.
B. A few animals likely crossed the water earlier, before most groups could spread.
C. The continents were already joined by land 8 million years ago, so most groups crossed then.
D. Ground sloths began in North America and spread south about 8 million years ago.

Circle the two results that, used together, are evidence that land mammals spread between the continents in both directions.

Horse-family fossils are found in South American rocks younger than 2 mya.Litopterns are found only in South American rocks.Porcupine fossils are found in North American rocks younger than 2 mya.Camel-family fossils are found in North American rocks older than 5 mya.Shells on the two sides of Panama become less alike in younger rocks.

10.

A new fossil site in Florida is about 1 million years old. Based on Tables 1 and 2, which casts would you most expect from it?

A. Camel and horse relatives, but no armadillo or porcupine relatives
B. Litoptern and glyptodon relatives, but no camel or horse relatives
C. Camel and horse relatives along with glyptodon and porcupine relatives
D. Ground sloths with no other South American groups, like the 8 mya sites

11.

A visitor looks at the trail camera photos and says, "Armadillos and their relatives have always lived in North America." Write a claim that answers the visitor. Give at least two pieces of evidence from Tables 1 and 2 or the refuge notes, and explain your reasoning.