Zoology: Mammals lecture 1

Pelycosaurs

~ 308 - 260 million years ago

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Shared characteristics with both mammals & reptiles

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Emerged (& many went extinct) before the dinosaurs arose

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Lacked reptilian scales, had horny scutes made of keratin

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Synapsid skulls

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Reptile-like sprawling legs

Therapsids

appeared ~275 million years ago

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Includes ancestors of mammals (Cynodonts, next slide)

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Lacked reptilian scales, some had hair

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legs positioned more vertically beneath the body

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Like modern mammals

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Synapsid skulls

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Like modern mammals

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Likely endothermic

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Like modern mammals

Cynodontia

arose ~ 250 - 225 million years ago

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Synapsid skull

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Like modern mammals

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Probably laid eggs

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Unlike most modern mammals

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Specialized teeth for chewing food

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Like modern mammals

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One set of deciduous teeth & one set of permanent teeth

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Like modern mammals

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Fewer jaw bones

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Secondary palate

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Probably rapid metabolism

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Like modern mammals

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Probably endothermic

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Like modern mammals

Defining characteristics of mammals

-Synapsid skull

-Complex skin with numerous types of glands

-Hair

-Fewer jaw bones

-Secondary palate

-2 sets of teeth

-External ear

-4 chambered heart

-Endothermic

-Young are nourished by milk from mother

Be able to describe mammalian skin, skulls, and structures.

Natatorial body plan

swimming

Volant body plan

flying

Cursorial body plan

walk or run for long distances

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Plantigrade locomotion

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Digitigrade locomotion

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Unguligrade locomotion

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Graviportal locomotion

Scansorial body plan

climbing

Saltatorial body plan

hopping

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Example: rabbits

Ricochetal body plan

use hind limbs for jumping, often in a bipedal (on two legs) position

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Example: kangaroos

Fossorial body plan

diggers

Bipedal (non-hopping) locomotion body plan

walking upright on hind legs as primary form of locomotion

Class Mammalia: Skin

Mammalian skin is complex with numerous glands

-Sweat

-Scent

-Sebaceous

-Mammary

•Two main functions:

-Sensory

-Protection

•Mammalian skin is thicker than other vertebrates'

•composed of epidermis and dermis

•Outer layer of epidermis is thick and filled with keratin, a fibrous protein that is also the main substance composing nails, claws, hooves, and hair

Class Mammalia: Hair

•Hair is used for insulation, protection & for tactile sensing

-Primarily composed of keratin

•Vibrissae: sensory hairs or whiskers, surrounding snout

-usually long & stiffer than other types of hair

-Advantageous to animals that can't always rely on sight to navigate or find food

•Two kinds of protective hair:

-Under hair: dense & soft for insulation

-Guard hair: coarse & longer for protection from outer elements

Hair color is often under natural selection pressure

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crypsis

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sexual selection

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aposematism

Class Mammalia: Skull morphology

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Skull is comprised of a large cranium & jaws

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A Secondary palate allows continuous breathing while feeding

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Lower jaw is a

single bone

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In some species, horns or antlers grow out from the skull

Antlers

-made of bone & fibrous tissue

-initially covered with skin & velvet (soft hair), which is later shed

-grow seasonally

-typically absent in females (except caribou)

-used by males during the breeding season to compete for females

-fall off at the end of breeding season

•Mammals with true antlers:

-Moose

-Deer

-Elk

-Caribou (reindeer)

Horns

-Usually made of bone covered in keratin

-Grow throughout the life of the animal

•No seasonal shedding and re-growing

-For many species, both males & females have them

-Males use horns to fight during breeding season

-Females use horns in defense

•Mammals with true horns:

-Bison

-Cows

-Sheep

-goats

Mammalia teeth

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Early synapsids had teeth that were all the same

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Many modern mammals are heterodonts, especially omnivorous mammals

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The more diverse the diet, the more diverse the teeth

Horns or antlers

•"Horns" of rhinoceroses are not true horns or true antlers because they are composed of hair-like keratinized filaments forming a cemented group of dermal papillae.

•"Horns" of pronghorn antelope are also not true horns or true antlers, because they have a permanent bony core, but shed their keratin sheath annually

heterodonts

an animal with different tooth forms that serve a range of functions:

-Incisors have sharp edges for snipping & biting

-Canines are pointy for piercing

-Premolars are for shearing & slicing

-Molars are for crushing & grinding

Class Mammalia: Feeding & Digestion

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Tooth shape and diversity of tooth shape differs dramatically among mammals depending on what they eat.

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The same is true for gut morphology.

Herbivores - plants

Carnivores - (vertebrate) meat

Insectivores - insects

Omnivores - a mixture of different foods

Herbivores

Teeth

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Reduced or absent canines

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Large, flat molars

Guts

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Long intestines

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Sometimes have pouched stomachs

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Often have specialized cellulose-digesting microbiota in an enlarged coecum

Ruminants

(special type of herbivore that includes cattle, goats, sheep, camels, deer, etc.) bring cud back up from stomach for more chewing (mechanical digestion)

Carnivores

Teeth

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Large, sharp canines & incisors

(for ripping)

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Reduced molars

Guts

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Short intestines

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Small stomach

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No stomach pouches

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Coecum is reduced or absent

Insectivores

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Short, pointy teeth (except anteaters & pangolins)

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No large canines (no need to rip meat)

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Short digestive systems

Omnivores

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Lots of different types of teeth in the same mouth

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Teeth lack extreme specializations of carnivores or herbivores

Class Mammalia: Excretion

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Pair of kidneys excrete urea in a liquid form

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Loop of the nephron (loop of Henle) is a tubule system that allows the kidneys to produce urine with higher salt concentration than blood

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Convergently evolved similar structures as birds

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Birds & mammals are the only vertebrates that can produce urine more concentrated than blood.

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Mammals adapted to drier environments have longer loops of Henle

Adaptations to hot, dry climates:

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Some radiate heat from especially large ears

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Some have long legs to keep them farther from superheated ground.

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Small mammals seek shade during the day; active at night

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Burrow

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Water-saving strategies

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Long loop of Henle

Adaptations to cold climates:

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Extra fur

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Extra fat

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Shorter ears & limbs

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Allow temperature of skin to drop to maintain internal temperature

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Countercurrent heat exchange in limbs

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Migration

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Hibernation

Hibernation

extended period of inactivity in the winter when body temperature drops, and metabolism slows

Winter sleep

body temperature and metabolic rate decrease, but the animal isn't inactive all winter

Daily torpor

animal's body temperature & metabolism drop at night causing a period of cold-induced inactivity; returns to normal activity during the day.

Cerebrum

thinking, learning, interpretation of senses

Cerebellum

coordinates muscular movements

Medulla

regulates autonomic body functions

pinna

external ear

Class Mammalia: Reproduction

Things you can say about reproduction in all mammals:

•Dioecious, internal fertilization

•All mammals nurse young with milk produced by specialized glands

•Often have well defined mating seasons

•Females go into estrus when ready to mate.

Estrus

a period of sexual receptivity & fertility in female mammals

Monoestrus

when females go into estrus once, during a specific breeding season

Polyestrous

when females of some species (e.g. humans) go into estrus at regular intervals throughout the year

Sexual "dimorphism" is common, but not a rule

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Mane of male lion

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Antlers in male deer

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Inflatable nose pouch is male elephant seal

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Larger males in many species

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Upon closer inspection though, a lot of these species are less dimorphic than we used to think