Mammalogy IB 462

Instructors:

Adam Ahlers [email protected] 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. Actually, about the same time....

Eoraptor 228 mya oldest dinosaur fossil Adelobasileus 220 mya oldest mammal fossil

Both Late Triassic Brief look at relationship between mammals and other terrestrial vertebrates

1) Reptiles diverged from amphibians sometime in Mississippian, >320 MYA, with development of amniote egg 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 Selected skeletal features - axial

• 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) 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)

Selected non-skeletal characteristics

• 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 • 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