Answers to Guiding Questions

Use the Guiding Questions in the Teaching in the Exhibition section as a springboard for discussion, which may go in many directions. The answers to the guiding questions, provided below, summarize key concepts of the exhibition. (For in-depth information about the exhibition content, visit the exhibition website at amnh.org/extrememammals.) For a PDF version of this, click here.

1. Introduction

What do the largest and the smallest mammals have in common with each other?
By looking at these reconstructions, the similarities that can be seen between Batodonoides and Indricotherium are that they both have heads, fur or hair (mostly around the eyes and on the tail in Indricotherium), four limbs, and tails.

With humans?
Humans share all these traits except tails, which have been lost later in our evolution, although we do retain a remnant of the tail as a "tailbone" (coccyx).

2. What is a Mammal?

Most living mammals have certain traits in common. Why? What are they?
All mammals, living and extinct, share certain traits in common because they're all descended from a common ancestor. These traits include having fur and producing milk to nourish their young.

How do scientists determine what a mammal is?
By ancestry. But all mammals—and only mammals—have three bones inside the middle ear. This is one of the ways scientists recognize a mammal, along with tracing their evolutionary history back to a common ancestor and looking at the traits they share because of this.

3. What is Extreme?

What are some examples of extreme and normal characteristics in these three mammals?
Uintatherium—Extreme characteristics include its tiny brain, huge body, 3 pairs of horns on its head, and massive, dagger-like canine teeth. Normal characteristics include four limbs, chewing teeth with cusps and ridges, and three ear bones.

Opossum—Extreme characteristics include its flexible, prehensile tail, hands with grasping thumbs, and the fact that it carries its babies in a pouch (extreme compared to most mammals, but normal for marsupials). Normal characteristics: average size, walks on four legs, typical "differentiated" mammal teeth (four types: incisors, canines, premolars, molars).

Humans—Our teeth, constant warm body temperature and overall skeleton structures are pretty normal for mammals, but our exceptionally large brains, legs adapted for walking upright, small tailbone, and highly specialized thumbs are extreme.

Are humans extreme or normal? Why?
Like all mammals, humans have a mixture of normal and extreme features.

4. Head to Tail: Heads

What are some of the functions of headgear?
Nearly all mammals with headgear on their skulls are prey animals, and sometimes use their headgear for defense. Headgear can also be a quick way to recognize members of their own species, a way to attract mates, or to advertise social dominance.

What are different kinds of teeth used for?
Different kinds of teeth can be specialized for diet. Mammals use incisors to grab, slice or cut their food, and canines, premolars and molars for a variety of functions, such as to slice, grind food, shear meat or crush bone.

5. Head to Tail: Reproduction

How do different types of mammalian mothers care for their young?
Monotreme moms do things like make nests in which they lay their eggs, holding them until they hatch, and nursing the young with milk that seeps from glands in patches on their chests.

Newborn marsupials are born extremely immaturely, after only a short time inside their mother's wombs. After birth, they find shelter in their mother's pouch, in a fold of skin on her belly, or simply attached to a nipple. There they continue to drink milk and to grow.

All placentals develop for longer periods of times than marsupials inside their mother's womb. Human babies, like some other placentals, are born quite helpless. Humans are completely dependent on their parents longer than many other species.

How do the gestation periods for each of the three major groups compare?
For a particular body size, placentals generally are pregnant the longest, and marsupials and monotremes for a shorter period. Large mammals generally have longer gestation periods than smaller mammal species.

What are some of the benefits of a longer pregnancy?
Because human mothers and other placental mammals can nourish their growing babies inside their bodies for long periods (as long as two years), their babies are born more fully developed than marsupial babies or ones that hatch from an egg (monotremes). Some newborn placental mammals, like whales and giraffes, are born with eyes open, ready to go.

The drawbacks?
Drawbacks include birth of fewer babies over time.

6. Head to Tail: Bodies

What are the various functions of hair and fur?
Mammals use hair for insulation, which is associated with warm-bloodedness (endothermy); wooing mates; fending off predators for camouflage; and, in the case of whiskers, navigating through darkness or narrow spaces.

How do different body coverings benefit those mammals?
In addition to having hair and fur to keep warm, mammal hair and skin have sometimes been transformed into quills, scales, and bony armor for protection.

How does hair relate to the environments?
Early mammals evolved hair to help heat their small bodies.

Which would you rather have, venom or armor? Why?
Answers will vary.

7. Mammals in Motion

How do most mammal bipeds (those that move on two legs) get around?
Although bipedal is defined as walking on two legs, the specific answer to this question in this section is a special kind of bipedalism—hopping.

Many groups of mammals evolved to live in water. How did their bodies change?
Adaptations to life in water, particularly in the oceans, include: limbs evolving into flippers; blubber; webbed feet; flat, wide tails or hind flippers/flukes; losing teeth and instead evolving baleen; collapsible lungs; and specialized underwater echolocation.

8. Extreme Climate

How are the mammals in each scene adapted to their environment?
50 million years ago: Coryphodon had massive, sharp-edged tusks that helped it uproot swamp plants. Like modern tapirs, Thuliadanta presumably used its flexible, sensitive, trunklike snout to gather food, bathe, and find its way through dense forests. Vulpavus had a long, thin body like a weasel and was an agile hunter both in trees and on the ground.

Today: The musk ox's long, shaggy winter fur is exceptionally warm and long. The arctic fox has fur covering its entire paws, its ears and legs are short to reduce heat loss, and its fur turns brown in the summer and white in the winter for camouflage.

What are some of the ways in which major climate change has affected mammal diversity?
Major climate change causes habitats to change, which affects where different animals can live. It can lead to extinctions if species cannot adapt, while other groups flourish if they can evolve new adaptations that are beneficial in the new environments. For example, 50 million years ago the Arctic was warm and swampy, so it was home to mammals well adapted to wading, marshy land, or climbing trees. Today no tree-dwelling mammals live in the Arctic because of the long, frigid winters, and because the tallest plants are only a few inches high. Arctic lands are now home only to species of plants and animals that have adapted to survive the bitter winter cold and extremely short growing season.

9. Extreme Isolation

What kinds of extreme forms have evolved in places that once were isolated?
Examples include giant rodents; lemurs found only on the island of Madagascar; huge plant-eaters; or gliding opossums. Dwarf elephants, water buffaloes, and pygmy hippos all evolved on isolated islands or continents.

Why is isolation so important in the origin of different, distinctive, and "extreme" forms?
Isolated mammals evolve on their own unique paths. Adaptations that help ensure survival in a certain kind of environment tend to evolve again and again. For instance, suppose a habitat contains tough, abrasive grasses that can be chewed only by animals with hard, continuously growing, grinding teeth. That type of tooth may evolve separately in several distantly related groups. This pattern is called "convergent evolution."

10. Extreme Extinction

What kinds of human behaviors contribute to extinction?
Human behaviors that may contribute to extinction include overhunting, polluting, and taking over or destroying unique habitats.

What conservation activities can slow the rate of extinction worldwide?
Humans can slow extinction rates by tracking the conservation status of endangered species, raising rare or endangered species in captive breeding programs, banning or restricting hunting of rare species, or protecting habitats that are home to threatened or endangered species.

How can preserving existing habitats lead to discovery of new species?
Species rely on healthy habitats to survive. By exploring remote or poorly explored habitats like deserts, mountaintops and tropical rainforests, we can still find new species of mammals. And by protecting these habitats, we can help these species to survive.