Biodiversity and Conservation Chapter 20: Mammals

5,700

Number of living species of mammals

Origin of mammals

Small, ectothermic, hairless organisms that originated over 150 million years ago evolved into today’s endothermic, furry mammals

Synapsid

Skull type of mammals; associated with the attachment of mandibular muscles

Early synapsids

Group that included diverse herbivorous and carnivorous pelycosaurs

Therapsids

Group of early carnivorous synapsids; all but the cynodonts went extinct before the Mesozoic

Cynodonts

Therapsid subgroup with a high metabolic rate, a strong bite, heterodont teeth, turbinate bones in nasal cavity, secondary palate, and the loss of the lumbar ribs

Heterodont teeth

Having some pointy teeth and some flat teeth; improved food processing for a variety of foods

Turbinate bones in nasal cavity

Cynodont feature that aided in body heat retention

Secondary palate

Cynodont feature that enabled breathing while eating

Loss of lumbar ribs

Cynodont feature that is correlated with the evolution of the diaphragm

29

Number of orders of Mammalia as a whole

1

Number of orders of monotremes

7

Number of orders of marsupials

21

Number of orders of placental mammals

Hair

Characteristic of all mammals, but can be reduced in thickness or number; grows continuously via rapid proliferation of cels

Hair follicle

Location of hair growth; an epidermal structure that is sunk into the dermis of the skin

Cortex

Part of mammal hair; strongest part of the hair and contains the pigments; internal

Cuticle

Part of mammal hair; covers the hair in scales; external

Medulla

Part of mammal hair; innermost part

Under hair

Dense and soft hair that serves as insulation by trapping a layer of air

Guard hair

Coarse, longer hair that protects against wear and provides coloration

Aquatic under hair

Hair so dense that it is almost impossible to wet

Aquatic guard hair

Hair that adheres to each other when wet, forming a protective layer over the under hairs

Hair adaptations

Disguising presence, sensory purposes, and protection

Hair that disguises presence

Often has a disruptive pattern to conceal the animal

Vibrissae

Also known as whiskers; sensory hairs

Porcupines, hedgehogs, and echidnas

Mammals with hair modified into spines

Pangolins

Mammals with hair modified into scales

Mammal skin

Thicker than in other vertebrates and comprised of an epidermis and dermis, with a dermis that is thicker than the epidermis

Integumentary glands

Derived from the epidermis and serve a variety of purposes, with four main categories: sweat, scent, sebaceous, and mammary

Sweat

Type of integumentary gland that helps with thermoregulation

Scent

Type of integumentary gland that can be used for communication

Sebaceous

Type of integumentary gland that protects the hair

Mammary

Type of integumentary gland that is a modification of the sweat gland in order to nourish the young

Heterodont and diphydont

The two types of teeth that most mammals have

Incisors

Teeth with sharp edges for snipping or biting

Canines

Teeth that are specialized for piercing

Premolar and molar

Teeth with compressed crowns and one or more cusps for shearing, slicing, crushing, and grinding; never replaced

Diphydont

Teeth type that do not continually get replaced; present in most mammals

Deciduous teeth

Baby teeth; teeth that are lost and then replaced

Insectivore

Trophic category of mammal with a short intestine and no cecum

Nonruminant herbivore

Trophic category of mammal with a simple stomach, large cecum, and colon

Ruminant herbivore

Trophic category of mammal with a four chambered stomach including a large rumen, a long small intestine, and a colon

Carnivore

Trophic category of mammal with a short small intestine and colon, and a small cecum

Bats

Only mammal that can fly; usually nocturnal or crepuscular, and often have echolocation

Crepuscular

Active at twilight

Monotremes

Egg laying mammals consisting of echidnas and the platypus; usually have a cloaca and are not entirely homeothermic, meaning they are poor at maintaining a constant body temperature during extreme conditions

Platypi

Have electroreceptors in their bill to help locate prey

Marsupials

Group of mammals in which the embryo develops within the choriovitelline placenta in the uterus before it is born early and continues development in a marsupium; brief gestation and prolonged lactation with maternal care; includes opossums, kangaroos, and koalas

Marsupium

A maternal pouch in marsupials in which the young continues development

Marsupial embryo

Encapsulated by a shell membrane and floats free in the uterine fluid for several days, before it “hatches” and erodes a shallow depression i the uterine wall, through which it absorbs nutrients from the yolk sac

4,000

Number of species of placental mammals

Eutherians

Another name for placental mammals

Placental mammals

Have a more complex placenta than marsupials; young complete development in the uterus; viviparous; long gestation period that increases with species size

Placental mammal embryo

First nourished in the uterus through the chorvitelline placenta, which is then replaced in most with the chorioallantoic placenta, both of which are highly vascularized, allowing for nutrients, water, and gas to diffuse between mother and young