Mammalogy IB 462 Instructors: Ed Heske eheske@illinois.edu Adam Ahlers aahlers2@illinois.edu
28 Extant Orders Mammalian diversity 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 Reptiles Birds Fish 7,000 species 8,950 species 10,000 species 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