Worksheet

Counting Teeth at the Orthodontist: Monkeys, Apes and Fossil Jaws

Grade 8 practice comparing the teeth, molars and tails of humans, apes, monkeys and three fossil primates to infer which are most closely related.

Grade 8ScienceInteractive · Printable

Aligned toMS-LS4-2

Play online Play as a game

PrintLetter-size worksheet Answer keyPrintable answers

Assign to classAssign to your classes, or get a join code

What’s included

Single worksheet
Auto-graded online
1 NGSS standard
Printable answer key
10 questions
Classroom-ready

Details

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 compare tooth counts, molar shapes and tails of living and fossil primates.
Students use shared anatomical features to infer which primates are most closely related.
Students explain why a shared way of moving can be weaker evidence of relationship than shared detailed structures.

How to use

Have students count their own teeth on one side of one jaw with a mirror before reading. Point out the counting rule for the dashes in Table 1.

Curriculum

NGSS standard covered

MS-LS4-2

Compare anatomical similarities and differences among living and fossil organisms to infer how they are related.

Preview

OwlSheets.com

Name Date

Counting Teeth at the Orthodontist: Monkeys, Apes and Fossil Jaws

Compare teeth and tails of living and fossil primates to infer how they are related.

Part 1: Teeth of living primates

Read the notes from the visit, then use them and Table 1 to answer the questions. In Table 1, — means the casts do not show that feature, and a — never counts as a shared feature.

What the X-Ray Showed

1Keanu Abiodun, an eighth grader, went to his orthodontist for a check before getting braces. Dr. Mireille Kostova took an X-ray that showed every tooth in his mouth at once, including the wisdom teeth still hidden in his jaw. She pointed out four kinds of teeth: flat incisors at the front, pointed canines, premolars and wide molars at the back. Dentists often count teeth on one side of one jaw. Keanu's count is 2-1-2-3: 2 incisors, 1 canine, 2 premolars and 3 molars, counting the wisdom tooth as the third molar.

2On a shelf in her office, Dr. Kostova keeps casts of primate skulls and jaws from a university course she took. She told Keanu that scientists compare body structures, including small details of teeth and bones, to infer how organisms are related. Organisms that share many detailed features most likely inherited them from a common ancestor, so the more such features two organisms share, the more closely related they probably are.

3The crown of the first lower molar is one of those details. In humans and apes, this tooth usually has five rounded bumps, called cusps, with grooves between them that form a Y. In Old World monkeys, such as the macaques of Asia, it has four cusps lined up in two ridges across the tooth. In New World monkeys, such as the capuchins of Central and South America, it has four low, rounded cusps with no Y pattern.

4Three of the casts are fossils from Africa. Aegyptopithecus lived about 30 million years ago, Proconsul about 20 million years ago and Victoriapithecus about 15 million years ago. Fossil bones from the lower back of Proconsul show that it had no tail. For the other two fossils, the office has only casts of skulls and jaws.

5Before Keanu left, Dr. Kostova showed him one more pair of casts. Spider monkeys of Central and South America travel through the treetops by swinging under branches with their long arms. Gibbons, small apes of Southeast Asia, travel the same way. Dr. Kostova asked Keanu whether that shared way of moving makes the two of them close relatives, and told him to check the teeth before he answered.

Table 1: Primate Casts in Dr. Kostova's Office
Primate	Living or fossil	Teeth per side (I-C-P-M)	First lower molar	Tail
Human	Living	2-1-2-3	5 cusps, Y grooves	None
Chimpanzee (ape)	Living	2-1-2-3	5 cusps, Y grooves	None
Rhesus macaque (Old World monkey)	Living	2-1-2-3	4 cusps in 2 ridges	Yes
Capuchin (New World monkey)	Living	2-1-3-3	4 low rounded cusps	Yes
Aegyptopithecus	Fossil, about 30 mya	2-1-2-3	—	—
Proconsul	Fossil, about 20 mya	2-1-2-3	5 cusps, Y grooves	None
Victoriapithecus	Fossil, about 15 mya	2-1-2-3	4 cusps in 2 ridges	—

Use paragraph 1 and Table 1. An adult mouth has four sides: upper left, upper right, lower left and lower right, each with the same count.

An adult capuchin has teeth in its whole mouth.

Use the three feature columns of Table 1: teeth per side, first lower molar and tail. Count a feature as shared only when both primates have the same entry.

Proconsul shares of these features with the chimpanzee and of them with the rhesus macaque.

Use the four living primates in Table 1. Sort each feature by which of them have it.

1 canine on each side of each jawA first lower molar with 5 cusps and Y grooves2 premolars on each side of each jaw3 molars on each side of each jawNo tail2 incisors on each side of each jaw

All four living primates	Humans, chimpanzees and macaques, not capuchins	Humans and chimpanzees only

Use your sort in question 3 and paragraph 2. Which model of how the four living primates are related fits the evidence best?

A. Capuchins and chimpanzees are closest, because both have 2 incisors and 1 canine on each side.
B. Humans and macaques are closest, chimpanzees come next, and capuchins are the most distant.
C. Macaques and capuchins are closest, because both have tails, and humans are the most distant.
D. Humans and chimpanzees are closest, macaques come next, and capuchins are the most distant.

Part 2: The fossil jaws

Use paragraphs 2 to 5, Table 1 and Table 2.

Which inference about Proconsul fits Table 1 best?

A. It was more closely related to apes and humans than to monkeys.
B. It was most closely related to the capuchin, a New World monkey.
C. It was a kind of Old World monkey that later lost its tail.
D. It was more closely related to capuchins than to chimpanzees.

Which living primate in Table 1 is Victoriapithecus most likely most closely related to?

A. The rhesus macaque, because both have molars with 4 cusps in 2 ridges
B. The capuchin, because both lived in forests long ago
C. The chimpanzee, because both have 2 premolars on each side
D. The human, because Victoriapithecus has no tail shown in the casts

Aegyptopithecus, the oldest fossil in Table 1, has 2 premolars on each side, like humans, apes and Old World monkeys, but unlike capuchins. Which inference is best supported?

A. Aegyptopithecus was a human ancestor that lived after Proconsul.
B. Aegyptopithecus was a New World monkey that crossed the ocean to Africa.
C. The 2-premolar pattern was likely present before the ape and Old World monkey lines split.
D. Aegyptopithecus had a Y-shaped five-cusp molar like Proconsul's.

Circle the two features of Proconsul that are evidence it is more closely related to chimpanzees than to rhesus macaques.

2 premolars on each sideA first lower molar with 5 cusps and Y grooves1 canine on each sideNo tail3 molars on each side

Table 2: Two Primates That Swing by Their Arms
Primate	Teeth per side (I-C-P-M)	First lower molar	Tail
Spider monkey (New World monkey)	2-1-3-3	4 low rounded cusps	Yes, long and grasping
Gibbon (ape)	2-1-2-3	5 cusps, Y grooves	None

Use paragraph 5 and Tables 1 and 2. Spider monkeys and gibbons both swing under branches with long arms. Which conclusion is best supported?

A. Spider monkeys are closer relatives of gibbons, because the way an animal moves shows its closest relatives.
B. Spider monkeys are closer relatives of capuchins, and arm swinging most likely arose separately in the two groups.
C. Spider monkeys are closer relatives of macaques, because both have tails and live in Central America.
D. Spider monkeys are closer relatives of humans, because humans also have long arms that can hang from bars.

10.

Keanu's friend says, "Monkeys and apes are basically the same thing. A macaque is just as closely related to us as a chimpanzee is." Do you agree? Write a claim, give at least two pieces of anatomical evidence from Table 1, and explain your reasoning.