Mammalogy IB 462

Instructors:

Ed Heske

eheske@illinois.edu

Adam Ahlers

aahlers2@illinois.edu

Mammalian diversity

• 28 Extant

Orders

• 153 Families

• 1230+ Genera

• 5,500+ Species

Wilson and Reeder 2006.

Mammalian Species of

the World. Johns Hopkins

University Press.

Is that a lot?

• Amphibians 7,000 species

• Reptiles 8,950 species

• Birds 10,000 species

• Fish 25,000 species

• >350,000 described plants

• >1,000,000 described insects

Not impressed?

Still, Cenozoic is often called

“The Age of Mammals”

Mammals are the most

geographically widespread and

morphologically diverse group

of vertebrates

Largest range of body sizes • Smallest: Etruscan shrew or bumblebee bat, 2 g

• Largest terrestrial: African elephant, 6 metric

tonnes = 6 million g

• Largest vertebrate: Blue whale, 103-150 tonnes

= 150,000,000 g (75 million shrews!)

Typical terrestrial

Truly volant

Truly subterranean

Semi-aquatic

Mostly aquatic

Truly aquatic

True or false?

Mammals evolved

after the dinosaurs.

Eoraptor 228 mya

oldest dinosaur fossil

Adelobasileus 220 mya

oldest mammal fossil

Both Late Triassic

Actually,

about the

same time....

1) Reptiles diverged

from amphibians

sometime in

Mississippian, >320

MYA, with

development of

amniote egg

Brief look at

relationship

between mammals

and other

terrestrial

vertebrates

2) Early Permian,

appearance of

pelycosaurs,

dominant terrestrial

predators.

Therapsids,

lineage of

mammal-like

reptiles, radiated

during mid-

Permian. Most

extinct at end of

Permian, but

Cynodonts persist,

eventually give rise

to earliest true

mammals.

3) Reptile lineage

gives rise to various

groups: crocodiles,

turtles, tuatara,

lizards and snakes,

dinosaurs and birds

4) Mammalian

lineage giving rise to

modern mammals

(therians) is only one

of several lines of

mammaliaformes in

Mesozoic, but world

dominated by

dinosaurs

5) Therians diverge

into Eutherians

(placentals) and

Metatherians

(marsupials)

sometime in

Cretaceous, about

125 MYA

6) After extinction

of dinosaurs at

Cretaceous-

Tertiary boundary,

radiation of

mammals takes off

So, what makes it a mammal?

• Lactogenic: produces milk to feed young

• Viviparous: live birth*

• Hirsute: epidermis has hair*

• Endothermic homeothermy: produces

heat metabolically instead of absorbing it

from environment, regulates body temp

at a stable level*

But lots of other things, too....

Selected skeletal features -

cranial

• Stronger jaw structure (single bony

element in lower jaw = dentary;

stronger, simpler jaw articulation

between dentary and squamosal bones)

• Improved hearing (3 ear ossicles =

malleus, incus, stapes; tympanic bone

supports tympanic membrane)

Change in

jaw structure

to both

strengthen

jaw and

improve

hearing

Skeletal - cranial

• Specialized teeth (restricted to margin

of jaw, diphyodont, thecodont, generally

heterodont and multicuspidate; process

food better = improved mastication)

• Secondary hard palate (more efficient

air flow, allows breathing while eating,

suckling)

Secondary

palate allows

breathing

while mouth

full

• 5 zones of vertebral column (cervical,

thoracic, lumbar, sacral, caudal)

• Double occipital condyles plus atlas/axis

complex (reduces stress on spinal

column while permitting flexion and

extension [atlas] and rotation [axis],

finer control of head movements)

Selected skeletal features -

axial

Axial skeleton

• Thoracic ribs only (no cervical or lumbar

ribs; lighter skeleton, more flexible

movement of spine)

• Zygapophyses on vertebrae

(strengthens vertebral column while

permitting flexion/extension and torque)

Selected skeletal features -

appendicular

• Epiphyses on long bones (allows

development of well-formed joints)

• General trend to decrease complexity and

number of bones in various functional units

of skeleton (Esp. pectoral girdle and pelvis;

less energy required for development and

maintenance of skeleton, lighter frame for

quicker movement)

• 4-chambered heart (improved circulation, better oxygen delivery)

• Enucleated red blood cells (carry more oxygen)

• Highest concentration of mitochondria (supports higher metabolic rate)

• Large complex lungs, muscular diaphragm (enhanced breathing, gas exchange rate)

Selected non-skeletal

characteristics

Selected non-skeletal

characteristics

• Masseter muscles associated with jaw

(new set of muscles in mammals for

greater control of jaw movements)

• Enlarged neopallium (cerebral

hemispheres of brain, greater

coordination and learning ability =

larger, more complex brain)

Sustained energy production ...all of these features did not evolve independently!

More or less related to a general trend for a greater

capacity for sustained energy production (including

acquisition and processing), which is essential for

endothermic homeothermy at high body temperatures,

and high levels of activity.

Mammals need about 10X more energy (food and

oxygen) than a reptile of the same mass.

Bottom line: endothermic homeothermy

at high Tb requires lots of energy

mammals need to obtain and process

food quickly and efficiently

Capable of prolonged exertion because

can supply O2 and metabolic substrates

to active muscles more effectively than

reptiles… this has been a unifying theme

in mammalian anatomy and physiology

We’ll discuss the evolution of endothermic homeothermy

in next lecture

From Lecture 1 you should know: 1. About how many species of mammal are currently

described? How does this number compare to

other groups of vertebrates?

2. What are the 4 characteristics most commonly

used to define “mammals”?

3. How do selected characteristics of mammals

(could be any from the list provided) relate to the

general trend in mammalian evolution for high

metabolic rates and sustained energy production?

(more on this in lecture 2)

A quick dash

through the extant

mammalian

orders....

Monotremata (monotremes)

2 Families, 5 species

Mostly South American marsupials

3 Orders, 3 Families, 21 species

Mostly Australian and New Guinean

marsupials

4 Orders, 18 Families, 237 species

Afrosoricida (golden moles

and tenrecs)

2 Families, 51 species

Macroscelidea (elephant shrews)

1 Family, 15 species

Tubulidentata (aardvark)

1 Family, 1 species

Hyracoidea (hyraxes)

1 Family, 4 species

Proboscidea (elephants)

1 Family, 3 species

Sirenia (dugongs and

manatees)

2 Families, 5 species

Cingulata (armadillos)

1 Family, 21 species

Pilosa (anteaters and sloths)

4 Families, 10 species

Scandentia (tree shrews)

2 Families, 20 species Dermoptera (colugos)

1 Family, 2 species

Primates (lemurs, lorises,

monkeys, apes, students, etc.)

15 Families, 376 species

Rodentia (rodents)

31 Families, 2277 species

Half of all mammal species!

Lagomorpha (rabbits and pikas)

3 Families, 92 species

Erinaceomorpha (hedgehogs)

1 Family, 24 species

Soricomorpha (shrews, moles, solenodons)

4 Families, 428 species

Chiroptera (bats)

18 Families, 1116 species

> 20% of mammal species!

Pholidota (pangolins)

1 Family, 8 species

Carnivora (dogs, cats,

bears, mustelids,

pinnipeds, raccoons, etc)

15 Families, 286 species

Perissodactyla (horses, rhinos, tapirs)

3 Families, 17 species

Artiodactyla (pigs, hippos,

camels, deer, giraffes,

antelopes, cattle, goats,

sheep, etc.)

10 Families, 240 species

Cetaceans (whales,

dolphins, porpoises)

11 Families, 84 species