Chapter 45 Mammals Study Guide

This flashcard set covers the essential characteristics, biological systems, evolutionary history, and the various orders of mammals based on the Chapter 45 study guide.

What are the six characteristics of mammals?

Endothermy, hair, completely divided heart, milk, single jawbone, and specialized teeth.

What are two primary functions of hair in mammals?

Insulation and camouflage.

Which group of organisms is considered the earliest ancestors of mammals and is characterized by a single opening in the skull behind the eye socket?

Synapsids.

Which group is the direct ancestor of mammals?

Therapsids.

What specific traits link therapsids with mammals?

Legs positioned directly under the body and teeth that differ in shape, size, and function.

How are early mammals described in terms of their size, activity time, and diet?

They were small, nocturnal, and ate insects.

What are the definitions of monotremes, marsupials, and placental mammals?

Monotremes are egg layers; marsupials give birth to live young at a very early stage to complete development in a pouch; placental mammals give birth to more developed young nourished inside the mother by a placenta.

Why did mammals diversify at the end of the Cretaceous period?

Because dinosaurs became extinct.

What is endothermy and what are its two main advantages?

Endothermy is the ability to maintain a constant internal temperature; its advantages include being able to live in cold climates and being capable of sustained activity.

What are two ways mammals conserve heat?

Using hair and a layer of fat under the skin.

How does the four-chambered structure of the mammalian heart assist metabolism?

The $4$ chambers keep oxygenated blood from mixing with deoxygenated blood, helping maintain a high metabolism.

What two adaptations of the mammalian respiratory system improve efficiency?

A large surface area of the lungs for gas exchange and the diaphragm.

What is the function of the diaphragm?

The contraction of this muscle helps fill the lungs with air.

Why are mammals unable to digest plant material on their own?

They do not produce enzymes capable of breaking down cellulose.

Describe the function of a rumen in mammalian digestion.

It is part of a $4$-chambered stomach where food is swallowed, partially broken down by microorganisms, regurgitated, chewed again, and swallowed again.

What is a cecum and what is its role in digestion?

A large sac branching from the small intestine that acts as a fermentation chamber for microorganisms to partially break down plant material.

What are the functions of the cerebrum in mammals?

It evaluates input from senses, controls movement, regulates behavior, and is involved in memory and learning.

What are the five senses of terrestrial mammals?

Hearing, vision, smell, taste, and touch.

Explain the reproductive strategy of monotremes.

They lay $1$ or $2$ eggs and incubate them with the mother's body heat; the young hatch partially developed and are protected by the mother while being nourished by milk.

Explain the reproductive strategy of marsupials.

Young are born at a very early stage of development and crawl into the mother's pouch, where they attach to a nipple to complete development.

How does the placenta function in placental mammals?

It contains tissue from both the mother and fetus, provides food and oxygen to the fetus, and removes wastes and carbon dioxide.

What is the primary source of nourishment for young mammals after birth?

Milk from mammary glands.

What are the characteristics and examples of Order Monotremata?

Egg-laying mammals, most primitive, found in Australia and New Guinea; examples include the duck-billed platypus and echidna (spiny anteaters).

Describe Order Marsupialia and provide examples.

Pouched mammals found in Australia and America; examples include the opossum, kangaroo, and koala.

Describe Order Rodentia, the largest mammalian order.

It makes up over $40\%$ of all placental mammals, lives on all continents except Antarctica, and has $2$ pair of incisors that grow throughout life; examples include rats, mice, and squirrels.

What characterizes Order Edentata?

Found only in the Americas, these "toothless" mammals have long claws for digging and feed on insects; examples include sloths, anteaters, and armadillos.

What are the distinct dental traits and examples of Order Lagomorpha?

They have a double row of upper incisors (large in front, smaller in back) that grow throughout life; examples include rabbits, hares, and pikas.

Describe Order Insectivora.

Small animals with high metabolic rates, long pointed noses, and sharp piercing teeth for eating insects; examples include shrews, moles, and hedgehogs.

What are the physical traits and group categories of Order Primates?

Omnivores with large brains, $2$ forward-looking eyes, grasping hands and feet, and opposable thumbs; groups include prosimians and anthropoids.

Describe the wings and navigation of Order Chiroptera.

Flying mammals with wings made of skin stretched over long fingers; most use echolocation to find insects; examples include bats.

Describe Order Carnivora and its two subgroups.

Meat eaters with long canine teeth and strong jaws; terrestrial members have long limbs for speed, and aquatic members (pinnipeds) have streamlined bodies; examples include tigers and seals.

What are Artiodactyla and what is their digestive adaptation?

Even-toed ungulates (hoofed mammals) that are mostly herbivores; they have large flat teeth for grinding and a rumen; examples include deer, bison, and cattle.

What are Perissodactyla and how do they differ from Artiodactyla in digestion?

Odd-toed ungulates native to Asia and Africa that are mostly herbivores and possess a cecum; examples include horses, zebras, and rhinoceroses.

Describe the physical adaptations and groups of Order Cetacea.

Fish-like bodies with flippers, no hind limbs, blowholes, and blubber; they navigate by echolocation and include toothed whales (dolphins, orcas) and baleen whales (blue whales).

Describe Order Sirenia and its relation to other orders.

Large herbivores inhabiting tropical waters with front limbs modified into flippers and no hind limbs; they are related to elephants; examples include manatees and dugongs.

What are the characteristics of Order Proboscidea?

Large land animals with a boneless trunked nose, tusks (modified incisors), and the longest gestation period; examples include elephants and mammoths.