Mammal Flashcards

Origin and Evolution of Mammals

• Key Characteristics:
  • Endothermy: Mammals produce body heat internally through metabolism.
    • Allows activity at any time and in many environments.
  • Hair: Primarily for insulation against heat loss; also serves for camouflage.
  • Completely Divided Heart: Four-chambered heart with separate ventricles.
  • Milk: Produced by mammary glands to nourish young.
• Possible Link: Troodon, a dinosaur, is considered a possible link between dinosaurs and birds.

Distinguishing Features

• Single Lower Jawbone: Important for identifying fossils.
• Specialized Teeth: Location determines function.
  • Front of jaw: biting, cutting, and seizing prey.
  • Sides: crushing, grinding, and slicing.
  • Eothyris: A reptile-like mammal called synapsid.
• Stem Animals: Proto-animals from the Permian timeframe (Lystrosaurus and Dimetrodon).

Evolution: From Synapsids to Therapsids to Mammals

• Therapsids: Synapsids that gave rise to mammals, featuring complex teeth and legs positioned beneath their body.
• Cynodont: Thrinaxodon, considered a reptile with hair.
• Gorgonopsid: A therapsid that may have been venomous.
• Mammalian Ancestry: Mammals descended from synapsids/therapsids with a skull featuring one opening behind the eye socket.
• Evolutionary Changes: Mammalian evolution involved changes in anatomy, physiology, ecology, and behavior.
• Appearance: Mammals appeared approximately 225 million years ago.
• Earliest Mammals: Small, shrew-like, nocturnal insectivores.
• Examples: Giant anteater and howling mouse.

Survival and Diversification

• Competition with Dinosaurs: Small mammals survived by being active at night (inferred from large eye sockets) and hiding during the day to avoid dinosaur predation; teeth indicate insectivorous diets.
• Post-Dinosaur Era: After the extinction of dinosaurs (end of the Cretaceous period, 65 million years ago), mammals evolved rapidly.
• New Niches: Opened up new habitats and resources.
• Examples: Jurassic beaver, Gastornis (terror bird), Andrewsarchus (possible ancestor of hippos and whales).

Three Types of Mammals

• Monotremes
• Marsupials
• Placental

Characteristics of Mammals

• Endothermy: Generates heat internally by breaking down food.
  • Allows mammals to be active at any time and found in many environments.
• Rapid Metabolism: Provides energy for strenuous activities over long periods.
  • Requires more oxygen and food.
  • Necessitates limiting body heat loss through hair and fat layers.
• Small animals have a higher metabolic rate.

Circulatory and Respiratory Systems

• Circulatory System: Two atria and two ventricles; oxygenated and deoxygenated blood never mix.
  * High demand for $O_2$. Mammals cannot survive with a 3 heart chamber
• Respiratory System: Adapted for efficient gas exchange with large lungs and internal surface area.
  • Diaphragm: Sheet of muscle below the rib cage aids in efficiency by helping draw air into the lungs.

Feeding and Digestion

• Chewing: Most mammals chew food to begin breakdown and speed up digestion.
• Specialized Teeth: Variations in size and shape allow for differences in diet.
  • Incisors: Cut.
  • Canines: Grip, puncture, tear.
  • Premolars: Shear, shred, cut, or grind.
  • Molars: Grind, crush, or cut.
• Herbivorous and carnivorous animals can be distinguished by their teeth.

Adaptations for Digesting Plants

• Rumen: Some hoofed mammals digest cellulose with the aid of microorganisms in the rumen, the first chamber of the stomach; they chew cud.
• Cecum: Elephants, rodents, and horses digest cellulose with the aid of microorganisms in the cecum, a large sac branching from the small intestine that serves as a fermentation chamber.

Nervous System and Sense Organs

• Brain Size: Mammals have much larger brains than most other vertebrates.
• Cerebrum: The largest part of the brain, it evaluates input from sense organs, controls movement, and initiates and regulates behavior; involved in memory and learning.
• Humans have the highest brain-to-body-size ratio.
• Dependence on five major senses: vision, hearing, smell, touch, and taste.
• Importance of each sense depends on the environment.
  • Bats: Rely on sound rather than vision; use echolocation (emit high-frequency sound waves that bounce off objects).

Reproduction

• Each group (monotremes, marsupials, and placental) has a unique pattern.
  • Monotremes: Lay 1 to 2 eggs; the embryo is nourished by yolk; hatchlings are very small and partially developed.
  • Marsupials: Give birth to partially developed young that continue development in the mother’s pouch.
  • Placental: Give birth to fully developed young; the mother provides nourishment and oxygen through the placenta.
• Young of mammals are dependent on their mother for food and care.

Mammalian Classifications

• 20 orders
  • Monotremata: Oviparous (egg-laying); 3 species (duck-billed platypus and 2 species of spiny anteaters/echidna).
    • Most primitive mammals.
    • Only live in Australia and New Guinea.
  • Marsupialia: Pouched mammals.
    • Live in Australia, New Guinea, and the Americas.
    • Examples: kangaroos, wallabies, koalas, wombats, phalangers.
    • Only one in North America: opossum.
  • Placental: 95% of mammals, 18 orders, found on every continent except Antarctica.

Placental Orders

• Rodentia: Largest order (40% of all mammals); 2 pairs of incisors that continue to grow as long as they live; adapted for eating seeds, twigs, roots, and bark.
  • Examples: rats, mice, woodchucks, prairie dogs, chipmunks, gophers, muskrat, porcupines, guinea pigs.
  • Largest North American rodent: beaver.
• Edentata: Means “toothless”; have either small teeth or no teeth; feed on insects, have long sticky tongues, and large claws.
  • Examples: armadillos, sloths, anteaters.
• Insectivora: Shrews, hedgehogs, and moles.
  • Long, pointed noses for grubbing for insects, worms, and invertebrates.
  • Teeth for picking up and piercing prey.

Additional Orders

• Lagomorpha: Rabbits, hares, pikas.
  • Differ from rodents by having a double row of upper incisors, with 2 large front teeth backed by 2 smaller ones.
  • Teeth continue to grow; adaptation for herbivorous diet.
• Primates: Most are omnivores with teeth specialized for a varied diet.
  • Classified as either:
    • Prosimians: Lemurs, tarsiers, and lorises.
    • Anthropoids: Monkeys, apes, humans.
  • Large ratio of brain size to body size.
  • Complex brains; develop complex behaviors and live in organized social groups.
• Chiroptera: Bats, the only mammals capable of true flight; found everywhere except polar regions.
  • Wings consist of lengthened bones of the last 4 fingers and a membrane between them.
  • Thumb not part of wing; used for grasping, walking, and climbing.
  • Most use echolocation, have small eyes and large ears, and feed on insects.
• Carnivora: Dogs, cats, raccoons, weasels, bears, otters, seals, and sea lions.
  • Most eat meat; enlarged canine teeth, strong jaws, and clawed toes for seizing and holding prey.
  • Keen senses of sight and smell for hunting.
  • Bodies designed for fast, 4-legged locomotion; intelligent and capable of learning how to hunt.
• Pinnipedia: Water-dwelling carnivores, streamlined bodies for swimming; sea lions, seals, and walruses.
  • Spend most of their time in water feeding, returning to land to sleep and give birth.
• Artiodactyla: Even number of toes; cows, sheep, antelope, deer, elk, pigs, and bison.
  • Ungulates (mammals with hooves).
  • Fast runners; use speed as a major defense.
  • Most are herbivores; molars are large and flat.
  • Rumen for storage.
• Perissodactyla: Odd number of toes; horses, zebras, tapirs, and rhinoceroses.
  • Cecum instead of rumen for breaking down cellulose.
• Cetacea: Whales, dolphins, and porpoises.
  • Fish-like bodies, flat tails, and flippers; lack hindlimbs; breathe through a blowhole.
  • Locate food and navigate using echolocation.
  • All aquatic and give birth underwater; evolved from land-dwelling mammals.
• Divided into 2 groups:
  • Toothed whales: Sperm, beluga, narwhales, killer, dolphins, and porpoises.
    • Can have 1 to over 100 teeth; feed on fish, squid, seals, and other whales.
  • Baleen whales: Blue, gray, and humpbacked.
    • Lack teeth; have baleen – thin plates of fingernail-like material hanging from the roof of the mouth.
• Sirenia: Dugongs and manatees.
  • Large herbivores; front limbs are flippers; no hind legs present; flattened tail.
• Proboscidea: Boneless trunked nose or proboscis; only 2 living species (elephants).
  • Largest land mammals alive today.
  • Longest gestation periods of any animal (20 to 22 months).