Introduction to Mammals

And Diversity of Mammals

Introduction to Mammals

• Endothermic animals (generate their body heat internally = an example of homeostasis), most viviparous (live-bearing, the exception being monotremes), all have mammary glands and hair, breathe air, and have four-chambered hearts

Mammal Evolution and Diversity

• First true mammals appeared about 200 million years ago

• Most mammals are terrestrial, although dolphins, porpoises, and whales are totally aquatic.

• 3 major groups of mammals:– Monotremes– Marsupials– Placentals (aka eutherians)

Monotremes

– Egg-laying mammals– Six species found in Australia and New Guinea –

duck-billed platypus, spiny anteaters– Both the reproductive system and the urinary system

open into a cloaca that is similar to the cloaca of reptiles

Marsupials – Mammals bearing live young that complete their development in

an external pouch. Once inside the marsupium (pouch), the embryo locates a nipple, attaches, and spends several months there

– Mostly found in Australia– Opposum only North American marsupial– Kangaroo, koala, wallabies

Placentals (aka Eutherians)

• Mammals in which egg implants in the uterus• In placental mammals, nutrients, oxygen, carbon

dioxide, and wastes are exchanged between the embryo and mother through the placenta

• Eutherian placentas provide more intimate and long-lasting association between the mother and her developing young than do marsupial placentas

• Most widespread – dogs, cats, humans

Feeding in Mammals• Teeth tell the tale – lots of incisors and canines = predator, lots of

molars = herbivore, both = omnivore (humans, bears)

CARNIVORE HERBIVORE

Molars crush and grind food. The ridged shape of the wolf’s molars and premolarsallows them to interlock during chewing, like the blades of scissors. The broad,flattened molars and premolars of horses are adapted for grinding tough plants.

Chisel-like incisors are used forcutting, gnawing, and grooming.

Canines are pointed teeth. Carnivoresuse them for piercing, gripping, and tearing.In herbivores, they are reduced or absent.

Jaw jointJawjoint

WolfHorse

Feeding in Mammals (continued)

• Most consume a lot to maintain metabolism• Rumen – specialized stomach allows some herbivores to

digest cellulose (cows)• Cecum – large, dead-end sack off intestine; acts like

rumen and in humans is the appendix• Blood feeders – vampire bats• Filter feeders – baleen whales

Respiration

• Lungs powered by two sets of muscles – chest and diaphragm (diaphragm increases volume in chest cavity)

Circulation in Mammals

• Four chambered heart with double loop system – lungs and body loops

Excretion in Mammals

• Kidneys filter urea from blood and recycle other compounds (sugars and salts)

• Best kidney of all animals

Response in Mammals

• Most highly developed brain of all animals– Cerebrum – controls thinking and

learning – large in mammals– Cerebellum – coordinates

movement– Medulla – regulates body

functions

• Well-developed sense of sight, hearing, and smell

Movement in Mammals

• Have a variety of adaptations – shoulders and pelvic girdles

• 4 limbs – hooves, hands, wings, flippers

Reproduction in Mammals

• Internal fertilization• Most are viviparous• Pouch – marsupial• Placenta – nutrients, oxygen and wastes

exchanged through this sac-like organ• Gestation period – length of time spent

developing in uterus – can range from a few weeks (mice) to almost two years (elephants) – larger the young, longer the gestation period

Reproduction in Mammals (continued)

• Young spend a long time developing with mother after birth – important reason for evolutionary success– Advantages?

• More likely to survive and reproduce with great success

– Disadvantages? • Takes a lot of energy and prevents parents from

reproducing until young are on their own

Orders of Mammals • Insectivora – shrews and moles – eat insects• Chiroptera – bats – eat insects, frogs, fish, fruit• Edentata – sloths, anteaters, and armadillos• Rodentia – mice, rats, squirrels, beavers – incisors constantly grow

during entire lifetime• Lagomorpha – rabbits and hares – herbivores• Carnivora – cats, dogs, wolves, bears, weasles, seals, hyenas• Cetacea – whales, dolphins, porpoises• Sirenia – manatees and sea cows• Artiodactyla – cattle, sheep, goats, hippo, giraffe, pigs – even

number of toes• Perissodactyla – horses, zebras, tapirs, rhinos – odd number of toes• Proboscidea – elephant (African and Asian)• Primates – humans, monkeys, apes