Ib 104: Vertebrate Natural History - Mammals

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late pleistocene extinctions

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60-10 mya, correlates with arrival of humans (agriculture), disproportionally affected large vertebrates, first suggested by Richard Owen

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Madagascar

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much endemicity, used to be huge lemurs that are mostly extinct now, correlate with arrival of humans

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La Brea

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fossil deposits in LA, many well-preserved mammals, both herbivores and carnivores

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smilodon

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state fossil, ambush carnivore, not sure how fragile canines were used

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basal synapsids

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broad lineage of reptile-like mammals, dominated late triassic

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Milestones in synapsid evolution

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1. finer regulation of body temp
2. control of internal environment
3. reorganization of mastication, 2ndary palate to separate breathing/swallowing
4. reorientation of pectoral/pelvic girdles for upright limbs
5. evolution of inner ear

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Dimetrodon

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basal synapsid, skin-covered fin thought to help regulate temperature

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Evolution of jaw joint and inner ear

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only 1 jaw bone now: most vertebrates have several bones in lower jaw that take part in hearing by sensing vibration --> incus/malleus/stapes only in mammals because old jaw bones migrated up to inner ear and still serve the same purpose, just different location
- movement can be followed in fossil record

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Mesozoic mammaliforms

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Dino period, mostly shrew-like mammals scuttling in bushing after insects, nocturnal, relied on smell/hearing, weak vision, good metabolic control, lactation, more precise dental occlusion and jaw control, parental care

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Hadrocodium

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Lower Jurrassic period in China, found intact skull
- possible challenges with endothermy because of high surface area and high metabolic rate

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Castorocauda

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Middle Jurassic period, fur indentations, skeleton suggests burrowing/swimming adaptations; dentition = sharp triangular molars, piscivorous; diurnal, semiaquatic carnivore

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Fruitafossor

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Upper Jurassic period, reconstructed as scratch-digging myrmecophage, armadillo dentition

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Repenomamus

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lower cretaceous period, carnivorous teeth, ate dinosaurs, found remains in stomach

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Monotremata

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- only egg-laying mammals
- one orifice for intestinal, genital, and urinary tracts
- 3 extant species
- make milk through fur, no nipples

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Marsupialia

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- short gestation period, longer lactation period )too long in the mother, more likely immune system senses embryo and attacks)
- good hands to climb into mother's pouch
- baby stuck to swollen nipple until big enough
- thecodont and heterodont teeth

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Juramaia sinensis

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earliest eutherian

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Eomaia scansoria

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early eutherian

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Placental radiation

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- rapid explosion and radiation, made mammal supertree to determine time of radiation/waves
- long-fuse model (2 pulses) vs. traditional explosion (more supported in recent paper)
- by Eocene, most familiar lineages had appeared

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Origin of Cetaceans

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4-limbed ancestors
- first thought to be derived from mesonychids (wolf-like carnivores), but later shown to be descended from artiodactyls and connected via DNA evidence and double-trochleated ankle (skeletal match found)
- renamed cetartiodactyla

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Mammalia characteristics

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- 3 ear ossicles
- fised atlas vertebrate
- hair
- mammary glands
- epiphyses
- muscular diaphragm

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Theria characteristics

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- viviparity
- molar tribosphenic teeth
- modified hips and ankle bones

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Afrotheria

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Afrosoricida
Macroscelidea
Tubulidentata
Hyracoidea
Sirenia
Proboscidea

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Afrosoricia

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Tenrecs, golden moles

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Macroscelidea

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Elephant shrews

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Tubulidentata

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Aardvark

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Hyracoidea

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Hyraxes

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Sirenia

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Dugongs, manatees

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Proboscidea

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Elephants

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Xenarthra

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Cingulata
Pilosa

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Cingulata

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Armadillos

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Pilosa

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Sloths, anteaters

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Euarchonoglires

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Lagomorpha
Rodentia
Scanentia
Dermoptera
Primates

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Scandentia

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Tree shrews

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Dermoptera

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Flying lemurs

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Laurasiatheria

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Lipotyphla
Pholidora
Carnivora
Chiroptera
Perissodactyla
Artiodactyla

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Pholidota

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Pangolins

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Perissodactyla

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Odd-toed ungulates

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Mammal Skull

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Cranium and mandible (1 bone)
- hyoid apparatus connected via cartilage/tissue

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Masticatory apparatus

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- tongue
- muscles for chewing (tempralis, masseter, pterygoids)

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Teeth

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- cemented into bone
- inorganic enamel
- nerves and blood vessels via pulp cavity
- mammals are heterodonts (functional diversity)
- diphyodont = baby teeth replaced by permanent teeth

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Rodent teeth

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2 gnawing incisors, self-sharpening chisels
- diastema - gap without canine
- red-brown patina = iron, layer of enamel
- murid rodents = 3 cheek teeth, no premolars

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Bones

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long bones: diaphyses and epiphyses elongate bone until epiphyseal plate is fused
- determinate growth = rapid growth, then levels off
- fibula and ulna often fused or lost
- limbs evolved from tetrapodomorphs with paired aquatic (webbed) feet
- mammal dexterity associated with brain development

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Baculum

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penis bone
- primates, rodents, insectivores, chiroptera, carnivora, colugos

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tapetum lucidum

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reflects light back into retina for another look
- more rods in nocturnal mammals

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Brain characteristics

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well-developed finger sensitivity
- echolocation mapping with hearing
vibbrissae implanted in blood sinus that amplifies movement, directly connected to brain (mystacial = around nose)

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Hairs

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- made of keratin, arrector pili muscles
- non-living tissue, but bulb is living/growing
- pigment granules in medulla
- melanin for UV protection
- seasonal or age molts
- facial masks: medium mammals warning larger mammals away, almost exclusively terrestrial

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Scansoriality

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climbing, mostly small branches
- sharp claws, in trees

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Arboreality

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Locomotion via trees
- highly mobile limbs, long sharp claws
- prehensile tail often
- some climb headfirst and turn ankle sideways for better grip (pes reversal), aka raccoon

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Gliding

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flying squirrels
- skin flaps and outstretched limbs
- tall canopy tree areas, often scansorial

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Volancy

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true flight (bats)
- radius makes up most of forearm
-thin, flexible patagium
-short/broad wings for maneuvering, not long-distance

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Cursoriality

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running
- reduce distal weight, loss/fusion of bones
- spinter = bursts of speed
- stayer = slow start, but can run for longer periods
- springing ligament = inserts at sesamoid bone, cocked and loaded when animal is standing
- gazelle pronk = bounding - altruism? boasting?

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Ungulate manus structure

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Paraxony = axis b/w digit 3 and 4
mesaxony = axis through digit 3
- plantigrade (human), digitigrade (dog), unguligrade (hoof)
- graviportal - pillar limbs, stacked vertically
- digital vs. metapodial pads

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Retractile claws

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pulled back for walking (cats)
- flexor muscle relaxes, retractor ligament holds claw in retracted position
- cheetahs have semi-retractable claws for extra grip

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Ricochetal saltators

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jumpers (kangaroos)
- bipedal vs. quadripedal
- elongate plantigrade pes, reduced forelimbs, long tail

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Saxicoly

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rock dwelling
- rubber pads on feet deliver secretions that give them traction on rocks

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Fossorial

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toothdiggers and scratchdiggers
- lips behind incisors in some
mole = builds mole hills
vole = open holes, tunnel without grass cover
gopher = plug holes

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Eskers

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Tubular deposits of earth produced by rodents in winter
- thomomys leaves thick tubes
- microtus leaves narrow tubes

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ambulatory

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flat-footed, all 5 toes on ground
- hedgehogs, porcupines to hide short legs

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Bipedality

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functional or obligatory
- often begins with wading through water
- only a few true bipedal primates

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Ecomorphology of gut

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- directly relates to diet
- teeth are very key, diagnostic to species (dental enamel provides chemical info related to ecology/geology)
- herbivore has enlarged cecum and massive colon for hindgut fermentation
- ruminant = multiple-chambered stomach, foregut fermentation

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Insectivory

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invertebrates
- priginal diet of mammals
- tribosphenic teeth ideal (possum) to pierce chitinous exoskeleton and crunch it up

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Myrmecophagy

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social insects (ants, termites)
- hyenid = premolars specialized for crushing

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Vermivory

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earthworms
- easy to digest, use long/narrow skulls
- scat will have citae or gizzard (undigestable)

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Piscivory

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fish
- long sharp teeth
- many homodonts

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Hunting Association

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- coyote and badger team up to hunt ground squirrels, curious companionship
- mesovertebrate predators often have defense mechanisms (quills, gas)
- large vertebrate predators often hunt in large packs

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Osteophagy

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bone marrow
- requires powerful jaw muscles and dense skull bones, strong blunt teeth
- hyenas

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Sanguivory

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lap up blood, vampire bats (3 sp)
- sharp incisors, anticoagulant in saliva
- can eat their body mass in blood in one night
- share blood

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Zooplanktivory

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baleen whales filter krill from water
- gulpers and skimmers
- crab-eater seals have seive-like teeth

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Frugivory

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fruit
- seasonal, trees separated and require long traveling times between patches
- arboreal or terrestrial

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Granivory

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seeds
- ever-growing incisors for chiseling
-high water content of seeds
- cheek pouches (Dipodomys)

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Graminivory

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Grazing
- hypsodont = high-crowned
- hypselodont = ever-growing teeth leads to high-crowned
- bambusivory = bamboo eating

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Folivory

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browsing leaves, not as course as grass, teeth are lower-crowned and not evergrowing

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Gummivores

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nectar-feeding, pollinators

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Lignivore

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bark and pith, lichen, fungi
- beavers and elephants

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coprophagous

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eat wet clusters of cecal pellets (bunnies)

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Durophagy

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hard-shelled invertebrates
- puffy teeth = hyperbunodonty
- wetland = dextrous hands, big brain, powerful jaws, extractive foraging

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Migration

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- for food, temp, breeding
- cetaceans and bats are long-distance
- don't migrate if large or have low metabolism, or too small to handle distance
- mule deer is local migrator

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Hibernation

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denning in cold weather
- some torpor
- bears are slightly active, no torpor
- some prepare food caches (pika)
- small mammals dump heat against burrow walls, won't be very active = estivation

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Olfaction funcitons

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- trigger reproduction
- indicate when female is ready
- pregnancy blocker (Bruce effect)
- copulation inducer
- sexual maturation
- recognition

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Monotreme/marsupial reproduction

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monotreme: uteri enter urogenital tract
marsupial: 2 vagina, uteri enter vaginal sinus

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Estrous cycle

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when females are sexually active; follicular and luteal phases
estrogen = stimulates development of endometrium, peaks at ovulation
progesterone = maintains endometrium, withdraws during luteal phase
monestrous vs. polyestrous
- fertilization can be delayed after successful breeding
- postpartum = next litter born while still lactating, heavy impact on female

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Fertility factors

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- number of estrous event per year
- litter size
- population-level pregnancy rate
- time to sexual maturity
- lifespan

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Reproductive strategies

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- female takes more of the cost, more incentive to be choosey
- pays for males to mate with as many as possible
monogamy = rare, evolves with low population density
- may work to defend territory together (beavers)
polygyny = female defense or resource defence

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Canid social systems

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Canis lupus = dominant male and female, previous offspring are helpers, division of labor, sub-dominants don't reproduce as much

Canis latrans = fems/males share home range, may form pairs across seasons

Vulpes vulpes = fems/males have separate territories, form short bond for mating and raise young independently

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infrasound

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travels long distances, low Hz (elephants, tigers)

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ultrasound

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very fast, must be slowed down for us to hear, high Hz, (peromyscus californicus)

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Group foraging

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requires highly social animals
- humpback whales bubblenet feed, blow bubbles under fish to draw them up
- canids work together in relay fashion to take over long-distance prey
- dolphins/fish.birds

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Tool use

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- otters use stones to hammer abalone open
- bottlenose dolphins use sponges on nose to probe for prey, only females, from mother to daughter, taught or observed?

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cognitive flexibility

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subadults learn more easily, more risk-taking
- older individuals take longer to learn
- japanese macaques and sweet potatoes

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Great apes and tools

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- chimps fish for termites with grass stems
- orangutans and gorillas too

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Culture

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- sum total of all shared, learned experiences in a given time/place
- tool use
- cultural behavior = passed down through social interaction
- Gorillas use sticks to test water depth
- unknown if other organisms use tools to make tools

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Social rank

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80% prediction based on gene expression
- lower ranking individuals have increased immunity due to stress
- baboons