Mammal + ology = ? Mammalology ? Mammology ? Mammalogy !!!

Mammalian diversity 28 Extant Orders 153 Families 1230 Genera 5,420 Species Wilson and Reeder Mammalian Species of the World. Johns Hopkins University Press.

Is that a lot? Amphibians4,020 species Reptiles6,600 species Birds10,000 species Fish25,000 species 250,000 described plants 1,000,000 described insects

So, 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 ever vertebrate: Blue whale, tonnes = 150,000,000 g

Typical terrestrial

Truly volant

Truly subterranean

Mostly aquatic

Truly aquatic

True or false? Mammals evolved before the dinosaurs.

True!

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 Stronger jaw structure (single bony element in lower jaw = dentary; stronger, simpler jaw articulation dentary and squamosal bones) Improved hearing (3 ear ossicles = malleus, incus, stapes; tympanic bone supports tympanic membrane) Secondary hard palate (more efficient air flow, allows breathing while eating, suckling) Specialized teeth (restricted to margin of jaw, diphyodont, thecodont, generally heterodont and multicuspidate; process food better)

5 zones of vertebral column (cervical, thoracic, lumbar, sacral, caudal) Double occipital condyles (atlas/axis complex, reduces stress on spinal column while permitting flexion and extension [atlas] and rotation [axis], finer control of head movements) 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) 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) Masseter muscles associated with jaw (new set of muscles in mammals for greater control of jaw movements) Sweat and sebaceous glands (aid thermoregulation) Enlarged neopallium (cerebral hemispheres of brain, greater coordination and learning ability)

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.

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