Section 2: Groups of Mammals Preview Bellringer Key Ideas Monotremes Marsupials Placental Mammals Summary

Bellringer Copy the following categories on a sheet of paper: Terrestrial, Marine, Carnivorous, and Herbivorous. Make a list of mammals that fit into each category.

Key Ideas What key characteristic sets monotremes apart from all other mammals? What are the key characteristics of marsupials? How common are placental mammals, and how does their development differ from the development of monotremes and marsupials?

Monotremes Monotremes are a small group of mammals found only in Australia and New Guinea. Monotremes share more traits with reptiles than with other mammals. Monotremes are also the only living mammals that lay eggs.

Monotremes, continued Like reptiles, monotremes have legs that sprawl to the side instead of being under the body. Also like reptiles, monotremes are the only mammals that have a cloaca, a common passageway for the digestive, reproductive, and urinary systems. Finally, adult monotremes do not have teeth.

Monotremes, continued Monotremes are mammals because they have hair. They produce milk to feed young. However, female monotremes do not have nipples. Instead of nursing, the young lap up milk that oozes from glands located on their mother’s belly. The only living monotremes are the duckbill platypus and echidnas.

Marsupials Marsupials include kangaroos, wombats, koalas, and opossums. The females of most marsupials have a pouch, and their young spend most of their time developing inside this pouch while they nurse and grow. Marsupials are the most diverse group of mammals in Australia.

Marsupials, continued Marsupials are also found in South America. Only one marsupial, the Virginia opossum, is native to North America. Scientists believe that marsupials probably moved into Australia from South America before the breakup of Pangaea.

Marsupials, continued At that time, South America and Australia were connected via Antarctica. After the continents separated, marsupials evolved and diversified in isolation from placental mammals. The habitats and lifestyles of marsupials in Australia, New Zealand, and nearby islands are similar to those of placental mammals.

Marsupials, continued Kangaroos and wallabies often live in large groups and, like deer, are herbivores. Much like monkeys, tree kangaroos are able to climb trees and jump from limb to limb. Gliders and possums are similar in habits to squirrels.

Marsupials, continued Some marsupial predators are similar to small cats. Tasmanian devils are similar to badgers in some ways. The Tasmanian tiger, a marsupial wolf, was hunted to extinction by European settlers.

Placental Mammals Placental mammals are the most familiar mammals. Cats, dogs, cows, horses, and humans are placental mammals. Placental mammals make up nearly 95% of all mammal species.

Visual Concept: Types of Terrestrial Placental Mammals Click the button below to watch the Visual Concept.

Placental Mammals, continued The young of placental mammals develop inside the female’s uterus, where they are nourished by nutrients from her blood. Placental mammals have a longer period of internal development than marsupials do. The young of most placentals are more developed at birth than the young of marsupials are.

Placental Mammals, continued There are many types of placental mammals, which vary greatly in size, shape, diet, and habits. The orders of placental animals and their relationships to each other and the other mammal groups are shown on the following slide. The characteristics of each major group of placental mammals are also listed on the following slides.

Phylogenetic Diagram of Mammals

Placental Mammals, continued Artiodactyla Includes pigs, camel, deer, antelopes, and cattle Have an even number of toes within their hooves Also called ungulates

Placental Mammals, continued Perissodactyla Includes horses, zebras, tapirs, and rhinos Have an odd number of toes within their hooves Like artiodactyls, also called ungulates

Placental Mammals, continued Cetacea Includes whales and dolphins Have a streamlined body and move through water with a powerful fluke Have a layer of blubber to keep them warm

Visual Concept: Types of Placental Marine Mammals Click the button below to watch the Visual Concept.

Placental Mammals, continued Rodentia Includes rats, mice, and beavers Have teeth that are specialized for gnawing More than 40% of all placental mammals are rodents

Placental Mammals, continued Primates Includes humans, apes, lemurs, and monkeys Most are tree dwellers Have grasping hands and feet and long arms and legs that aid in climbing Have excellent eyesight and depth perception

Placental Mammals, continued Chiroptera Includes all bats Only mammal capable of flight Most bats are carnivorous and use echolocation to find insects Other bats eat fruit or nectar from night-blooming flowers

Placental Mammals, continued Xenarthra Includes anteaters, sloths, and armadillos Anteaters use long, sticky tongues to capture insects Sloths eat mostly leaves Armadillos have simple teeth and are omnivorous

Placental Mammals, continued Lagomorpha Includes rabbits, hares, and pikas Rabbits and hares have long hind legs and are specialized for hopping Pikas have short limbs and live in mountainous regions of North America and central Asia

Placental Mammals, continued Sirenia Includes manatees and dugongs Relatives of elephants Have front flippers and a flattened tail for swimming Sometimes called sea cows, sirenians graze on aquatic plants

Placental Mammals, continued Insectivora Includes shrews, hedgehogs, and moles Mainly eat insects Moles have adaptations for burrowing, including short, powerful forelimbs with long claws

Placental Mammals, continued Proboscidea The order of elephants, the largest land animals alive today Trunk is an elongated nose Upper lip can be used for picking up food, water, and objects An elephant’s tusks are modified upper incisors

Placental Mammals, continued Carnivora Cats, dogs, foxes, bears, raccoons, pandas, and hyenas are carnivores Long canine teeth are specialized for capturing prey and tearing flesh Some carnivores eat more than meat. Raccoons and bears are omnivores, pandas are herbivores

Placental Mammals, continued Domestic Mammals Domestic animals are animals that have been kept and bred by people for special purposes. Domestic animals may provide work, food, clothing, or companionship. Most domestic animals are placental mammals whose association with humans dates back at least 2,000 years.

Placental Mammals, continued Domestic animals include dogs, cats, cattle, horses, donkeys, mules, rabbits, sheep, goats, pigs, camels, llamas, and alpacas. Various breeds of domestic mammals have been developed through selective breeding. For example, some breeds of goats produce more milk than others.

Placental Mammals, continued Other goats, such as angora goats, are bred for their fine hair, which is spun into yarn. Some domestic mammals are hybrids of two species. Mules, for example, are the offspring of a female horse and a male donkey.

Summary Monotremes share more traits with reptiles than with other mammals. Monotremes are the only living mammals that lay eggs. The females of most marsupials have a pouch, and their young spend most of their time developing inside the pouch while they nurse and grow

Summary, continued Placental mammals make up nearly 95% of all mammalian species. The young of placental mammals develop inside the female’s uterus, where they are nourished by nutrients from her blood.