mammalogy ib 462 - university of illinois 1 - intro to mammals.pdf · mammalogy ib 462 instructors:...
TRANSCRIPT
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