Mammalogy Notes: Classification of Mammals - PDF

Classification -​ Can be tricky -​ Taxon -​ May or may not make sense where they fit in -​ Ex. Platypus -​ Not always easy to figure out where animals fit -​ Caught up biologists originally -​ As taxonomists, attempt to assign animals to taxon via...

Classification -​ Can be tricky -​ Taxon -​ May or may not make sense where they fit in -​ Ex. Platypus -​ Not always easy to figure out where animals fit -​ Caught up biologists originally -​ As taxonomists, attempt to assign animals to taxon via phenotypic varieties -​ Phenotype = physical characteristics -​ More recently began including genotypes (genetic characteristics) -​ Work to create phylogenies -​ Phylogenetics = study of evolutionary history of life on earth -​ DNA, morphology -​ Goal is to create phylogenetic trees -​ Branching patterns that represent how we believe things are connected -​ Cladograms very similar to phylogenetic trees -​ Organize based on ancestors -​ When looking at characteristics of organisms, MAY or MAY NOT be a sign of relatedness -​ Not all physical traits are because of relatedness -​ Homoplasies -​ Homoplastic features are superficially homologous and independently acquired ​ -​ NOT because of relatedness, but another reason -​ Dolphins are fish-shaped because its hydrodynamic. “Torpedo Shaped” -​ Convergent evolution -​ Dolphins & sharks -​ Homologous -​ Homologies -​ Structures derived from recent common ancestors -​ Relatedness -​ Evolution doesn’t invent things, things that turned out to be useful were kept. -​ Things inherent through processes -​ 2 breakdown categories -​ Plesiomorphic characteristics -​ Subcategory of homology -​ Characteristics present in ancestors and still present today -​ Shared ancestral characteristics -​ Ex. Vertebrae -​ Synaptomorphic characteristic -​ Characteristics that are unique to a group of interest -​ Ex. Hair -​ Mammals have hair. Only mammals have hair.  -​ Ex. Retractable claws -​ Traits in cats -​ Same traits can be both, it depends on context -​ What is the group being talked about? -​ Hair in dogs -​ Plesiomorphic -​ Inherited via being a mammal -​ Hair in mammals -​ Synaptomorphic -​ Bird airway -​ Synaptomorphic -​ We don’t know ‘real’ evolutionary tree -​ Phenetics -​ Consider all cats listed (domesticated, wild) -​ All cats listed vertically, and traits listed horizontally -​ Became popular in 1980s -​ Computers became accessible. -​ Massive amounts of data could be inputted and sorted automatically -​ Downside of phenetics -​ Characteristics are phenotypes, a computer cannot discern homoplasies and homologous features. -​ Older system, was the only option at first. Outdated. -​ Late 1800s -​ Cladistics -​ Phylogenetic systematics -​ 1960s - took ab 20 yrs to take hold -​ Method of arranging that aims to get rid of homoplasies -​ Emphasises geneology -​ Looks backwards at history of organisms -​ Homoplasies taken out to get rid of flaws in phenetics -​ Worried about the past -​ “Birds are part of class reptiles, are a subclass at best” -​ Harder lines on taxonomy tree -​ Evolutionary systematics -​ Likes to focus on homologies -​ Studies diversity of organisms and evolutionary processes that underlie it -​ Focuses on extent of divergence instead of genealogy -​ Birds deserve their own group (avies), because their divergence goes far beyond -​ Softer lines on taxonomy tree -​ Whales evolved from artiodactyls (deer) -​ Liberals and their damn classifications -​ Parsimony -​ “Simplest answer must be the right one” Mammals -​ less diverse than many groups -​ New species are discovered every year -​ Currently 6,753 species living and extinct -​ 6640 LIVING Species of mammals -​ 27 LIVING orders - fluctuates constantly -​ Learning 110 species this class -​ Species is the only fixed classification -​ Everything above it (family, order, class, kingdom) subject to opinion -​ Moved around -​ Relatedness is difficult to sort -​ The current naming system is binomial nomenclature -​ Linnaeus 1758 -​ 3 parts -​ Genus -​ Epithet -​ Authority -​ First to describe species -​ Scientific Name, Authority -​ Homosapian Linnaeus -​ The whole thing together is a species -​ Says Homosapians was the name given by Linnaeus in 1758 -​ Homosapian (Linnaeus 1758) -​ Says homosapians was a changed name but originally discovered by Linnaeus in 1758. -​ Why latin? -​ Universal -​ Dead language -​ No one gets an advantage -​ Most are classical greek or Latinized words in current day -​ Genus needs latin noun with distinctive gender -​ Ephihet must match gender -​ Gendering words usually a issue with other languages - English doesn’t do that really -​ Zoological nomenclature regulated by ICZN -​ International commission of zoological nomenclature -​ Founded in 1895 -​ Purpose: create, publish, and revise the code -​ They make up the naming rules -​ To describe a new species: -​ 1. Name must be Latinized -​ 2. Description needed -​ 3. Needs type -​ Holotype  -​ A single specimen, designated by the author, upon which a description of a new species is based -​ Ex. Used to be 2 types of elephants - Asian and African. Recently African elephants have been split to 2 species. -​ When Linnaeus named species, the original specimen is the representative of the species name. In case of elephant, the original specimen found is used to determine which elephant was named African Elephant and keeps the name -​ Syntypes -​ Series -​ Neotype -​ If old holotype is lost -​ Lectotypes -​ Paratypes -​ Topotypes -​ ^ types on blue paper -​ 4. Geographic Range -​ 5. Differential diagnosis -​ How to tell species apart -​ 6. Measurements -​ 7. Has to be a remarks section -​ 8. List of specimens examined -​ 9. Distinguishing characteristics -​ How to identify looking at it -​ 10. Cannot be anonymous -​ In the days of Darwin, being a biologist was blasphemy -​ In the biologist's closet -​ 11. Can’t be a synonym or homonym -​ 2 species cannot share a name -​ 1 species cannot have 2 names 1/14 -​ Scientific names are fixed, but can be changed -​ 4 reasons why scientific names can change -​ 1. Homonym -​ A single species is actually 2 species -​ Go back to the holotype to decide which species keeps the original name -​ 2. Reorganization  -​ Old world and new world names -​ 3. Correct grammar -​ 4. If reorganization leads to homonym -​ Mountain lion/puma/cougar -​ Puma concolor, was moved to felis concolor because it shares more traits with felis genus (don’t roar like big cats, can purr like small cats) -​ felis concolor already existed at this point -​ Law of priority. Whoever was named first keeps the name. -​ Even though felis concolor had the name originally, Puma was discovered first. Puma gets the name Marsupials -​ Monotremes - 2 extant families -​ Extant = still alive -​ Ornithorichidae -​ platypus -​ George Shaw described platypus as the most ‘extraordinary’ -​ Thought it was a joke -​ Tachyglossidae -​ Echidna -​ Both species found in Australia -​ Both species Oviparous (egg layer) -​ Monotremes not ancestral to therians -​ Has a lot of reptilian like features -​ Incomplete right atrium article valve -​ Lack corpus collosum -​ Bridge of neural tissue that connects left and right side of brain. Needed for complex though. -​ (also lacked in marsupials) -​ Reptilian like pectoral girdle -​ Possess cloaca -​ Sperm in monotremes reptilian like -​ No ‘head’ looks threadlike -​ Homeothermic -​ Challenging time maintaining body temp -​ Chromosomes -​ Mammals have macrochromosomes -​ Birds, reptiles, fish have microchromosomes -​ Monotremes have both. -​ Epipubic bones -​ (also found in marsupials) -​ No teeth -​ Edentate  -​ Immature platypus have teeth in gums that dissolve -​ Babies have egg tooth -​ Males have a horn-like spurr on rear ankles -​ On the duckbill platypus, there is a venom gland associated with that spur. -​ Like birds, only left side of the female reproduction system is functional -​ Like this so if something happens, there is a backup -​ Also eggs. -​ Lay cledoic egg -​ Egg with protective shell -​ Eggs are meroblastic -​ Opposite of holoblastic -​ Yolk broken up and distributed among cells evenly -​ Placement of yolk. (nutrients) -​ Meroblastic is a single large reserve of nutrients. -​ Monotremes are meroblastic -​ Young platypus are altricial -​ Blind underdeveloped -​ Like a baby mouse or robin or cardinal -​ Opposite of precocial -​ A baby chicken or duck -​ Nitifugous -​ “Nest fugitive” -​ Don’t return to the nest, leave nest quickly -​ Nidicolous -​ Stay in the nest for a long time -​ Monotremes are Nidicolous and Altricial -​ Mammary glands do not have nipples, excreted from skin and suckled from hair tuffs -​ Milk has high iron because young are unable to store it like other mammals can -​ Platypus is semi-aquatic omnivore -​ Metatherians -​ Suborder Marsupilia (marsupials) -​ North america, south america, australia primarily -​ Marsupials evolved in south america -​ Moved over to australia during Pangea or whatever its called -​ When continents were a single mass -​ Marsupials colonized australia in isolation. No eutherians. Had no real competition -​ Pathetic animals -​ Make up over 50% mammals in australia but 6% of mammals worldwide  -​ Characteristics -​ Marsupium (pouch) not developed in ALL groups -​ Those with pouch can have it open in front (kangaroo) or back (wombat) -​ Testes anterior to penis in males -​ Have a lot of teeth -​ More than eutherians generally -​ 5/4, 1/1, 3/3, 4/4 = 50 for marsupials -​ 3/3 (incisors) ,1/1 (canines),4/4 (premolars),3/3 (molars) = 44 eutherians -​ Small braincase -​ Lack corpus callosum (neural band connecting hemispheres) -​ No complex thought -​ Epipubic bones -​ Structurally, most notable difference between marsupials and eutherians is reproduction -​ Dynamic Alternative -​ Marsupial reproductive system -​ TLDR -​ Pregnancy -​ Longest in marsupials is 2 weeks -​ Short period of time -​ Baby has eyes, ears, and developed arms to crawl itself from birth canal to the pouch -​ Lactation phase is extremely long -​ Takes longer to make a baby because its less efficient than in eutero -​ The upside is short pregnancy, easier to terminate birth -​ Kangaroos can have 3 joeys in different cycles at the same time -​ 1 in eutero, one developing in pouch, one outside of pouch -​ No marsupial weighs more than 1% mom’s body weight at birth -​ Starting life with claws and arms limits what you can become -​ Conservative body plan because of birth requirements -​ Decent size difference -​ 4 orders of magnitude -​ No carnivorous marsupials -​ 7 orders BONES -​ Dentary bone -​ In mammals, there is 1 lower jaw bone -​ Joints make weakness -​ Single lower jaw bone substantially stronger than bones fused together -​ Articulates with cranium and squamosal bone -​ In metatheriums, jugal is involved too -​ All mammals have 3 middle ear bones behind the eardrum. -​ Malleus -​ Incus -​ Stapes -​ Sterup, U shaped. Attached to Coplia -​ Some people consider mammals have 2 auxipital condiles -​ 2 pivot points where spine meets head. Side to side movement & up to down movement seperate joints -​ Not totally unique -​ Soft anatomy -​ All mammals have hair at some point in life -​ Mammary glands -​ 4 chamber heart w/left aeortic arch -​ Crocodillians & birds have 4 chamber heart with right aortic arch -​ Enuculate Erythrocytes -​ Red blood cells without nucleus -​ Benefit is allows for more oxygen room -​ Muscular diaphragm -​ Between abominable cavity and thoracic cavity -​ Helps w/ breathing 1/21 notes -​ 7 unique mammalian characteristics -​ Skeletal -​ All mammals have 1 lower jaw bone - the dentary bone. -​ 3 osicle (inner ear) bones -​ Malleus -​ Incus -​ Stapes -​ 2 articulating occipital condyles (not “unique”) -​ Soft anatomy -​ Hair -​ Mammary glands -​ 4 chambered heart w/left aortic arch -​ Enuculated erythrocytes -​ Muscular diaphragm  -​ (muscular tissue between gut and hearts, compresses and expands lung cavity) -​ Dental -​ Dentition: -​ Tribosphenic molar -​ 3 point molars -​ Quadritubercular Molar -​ 4 point molar - common in mammals today -​ V-shape = zalambdont tooth -​ W-shape= dilambdont tooth -​ Heterodont (teeth of different types) -​ Herbivore lineage -​ Carnivore lineage -​ Omnivore lineage -​ Diphyodont dentition = 2 sets of teeth in your life -​ Polyphyodont = multiple sets of teeth -​ Crown = above gums -​ Root = below gums -​ Opened -​ Grows throughout life -​ Beavers & mice -​ Closed -​ Determinate. Stops growing. -​ Hypsodont - high crowned -​ Herbivores -​ Teeth get worn out. -​ Brachyodont - low crowned -​ Relatively small teeth -​ Bunodont - rounded crushing tooth -​ Otters, racoons, humans -​ Lophodont - cusps form ridges for grinding -​ Herbivores -​ Selonodont - cusps form crescent shape -​ Also herbivores -​ Sectorial dentition - (aka carnassial) = 4 upper premolar & first lower molar form pair of scissors -​ 4 types of teeth -​ Incisor -​ Canines -​ Premolars -​ Molars -​ 3/3, 1/1, 4/4, 3/3 = 44 -​ Hair -​ Dead material - made of keratin -​ Medulla = center of hair -​ Hollow -​ Solid -​ Air pockets -​ Cortex = hair shaft -​ Highly packed cells -​ Cuticle -​ Scale-pattern on the outer edge -​ Melanins - blacks and browns -​ Xanthophylls - reds and yellows -​ Pelage = coat of hair -​ Insulation original function -​ Blubber in whales -​ Fat and size -​ Protective coloration - camouflage -​ Defense -​ Barbs (hedgehog and porcupines) -​ Plates (anteaters) -​ Countershading (belly lighter than back) - creates consistent color for animals in the forest -​ Alert coloration -​ “Warning” -​ Skunk -​ Abnormalities -​ Albinism -​ Genetic condition -​ Complete loss of pigment -​ Melanism -​ Genetic -​ Overabundance of melanin -​ Leucism -​ Not quite albino -​ Lack of pigment -​ Piebald -​ Vibrissae -​ Hairs with follicles that have erectile tissues -​ Whiskers -​ Tactile function -​ Active & passive -​ Body hair -​ Protection and insulation -​ Hair on neck standing up. -​ Can have erectile tissue  -​ Guard hairs -​ Spines (porcupine) -​ Bristles (mane of lion or horse) -​ Awns - overfur -​ Underhairs -​ Wool -​ Fur - short & fine (underfur) -​ Velli - embryonic hair -​ Molts = shedding of hair -​ Seasonal molt -​ 1/23 notes -​ 1000 species of bats -​ Rodents and bats the 2 most successful groups -​ Distributed worldwide -​ Absent in polar regions, isolated islands, and mountaintop regions -​ Taxonomy is a mess -​ Genus and species mostly sorted out -​ Upper taxonomy in debate -​ Bat biologist's name based on physical characteristics -​ Higher taxonomy similar -​ Original taxonomy -​ Order: Chiroptera -​ Literally means hand wing -​ 2 suborders -​ Megachiroptera -​ Old world fruitbats -​ Ie. flying foxes -​ Microchiroptera -​ Suborder names changed to -​ Yangchiroptera -​ Yingchiroptera -​ Suborder names changed again -​ Old world fruit bats are pteropiformes -​ 21 different bat families -​ Significant convergent evolution -​ Bats in different families that do the same things -​ Talk about bats not in taxonomy, talk in guilds -​ Group of things that do similar things in similar ways - not based on relatedness. Guilds are ecological roles. -​ What foods do bats use?  -​ Carnivorous Bats -​ Frogs, birds, lizards, other bats -​ Insectivores -​ Control insect populations -​ Bats in Texas save farmers 3 billion in pesticides -​ Mosquitos, corn ear wom, spotted cucumber beetles -​ Nectar & Pollen -​ Dip tongue into feeder while flying by. Hit and run method -​ Long bristles tongues -​ Tequila farms reliant on bats -​ Fruit bats -​ Plants evolved fruit for target species -​ Bats are better than birds at seed disposal -​ Bird digestive system is too efficient. Destroy everything - seeds included -​ The mammalian digestive system is not as aggressive Seeds will pass and get deposited -​ Tropical areas with fruit year round -​ Fish bats -​ Catching fits significantly different from catching frog or lizard -​ Echolocation does not penetrate water. They cannot detect it. -​ Because of water tension, where fish are causes a rise in the water. Bats can detect these rises with echolocation. Telling the size and orientation even when the fish is still -​ Only 3 species of fish eating bats. -​ Massive feet and claws. -​ Vampire bats -​ Tiny tiny -​ Only 3 species -​ 2 species feed on mammal blood -​ 1 species feeds on bird blood -​ Angled incisors are what bats use to draw blood -​ Ugly little creature. -​ Nips at animals to draw blood. Licks the wound. -​ Saliva has anticoagulant properties. Keeps wound bleeding. -​ Not a big deal -​ Physiologically -​ When vampire bats drink blood, their kidneys kick in and make them pass water while licking the wound.  -​ Lots of nitrogenous wastes due to a heavy protein diet. Extremely intense urine when digesting. Turn kidneys into conservation mode due to little water in the body. VERY concentrated urine. -​ Few carbohydrates and fats -​ Lean body structure. Ozempic bats. -​ If bats don’t feed every 2-3 days they will starve to death -​ To keep other bats alive, they share blood. Cooperative sharing, have a society for blood. Identified “cheaters” ostracize and kick cheaters out of the colony. -​ Always cold -​ Cannot tolerate temps below 68 degrees. The only place they can be found is the equatorial region. -​ Bats are the only true flying mammals -​ Eyes of bats are mostly rods - lack cones -​ Most bats have a vision as good as humans, see the world in black and white -​ Bat ecology -​ In colder zones - insectivorous bats struggle for food in wintertime -​ Hibernate -​ Not unique to bats -​ But bats have specialized hibernation -​ Caves do not have stable temps - bats must find specific hibernation sites -​ Migrate -​ Reverse migration -​ Bats in warmer regions will migrate north to hibernate in colder caves -​ Pregnancy between 30-40 days -​ Babies must be born when resources are plentiful -​ Bats feed until “very last second” before hibernation -​ Typically middle of october - first frost in location where all bats are congregated -​ All bats enter at the same time -​ In spring, bats go back to summer grounds -​ Leave at a different time. Bats from the south will depart faster  -​ Females will store sperm in the reproductive tract all winter -​ In the spring they use stored sperm when there is an abundance of food -​ Maternity colonies -​ Communal roosting -​ Females that group together -​ Can be a few or hundreds -​ Birth can be synchronous -​ Mothers only raise their young -​ R selected - many young, little commitment; small mammals -​ Rabbits, Mice -​ K selected - few young, big commitment; large mammals -​ Elephants, humans -​ Bigger mammals, longer life. Smaller mammal, shorter life -​ Bats are outliers -​ produce few offspring compared to similarly sized mammals (mice) -​ 1 pup once a year -​ Live longer than similarly sized mammals (10+ years) -​ 40 years is record in US -​ When they hibernate, they are in a state of suspended animation. -​ ¾ of their lives is spent resting -​ Echolocation -​ Very simple -​ Sense distance based on how long it takes for the call to come back as an echo. Sense size based on how loud the echo is. Sense movement based on if echo comes back at a different orientation. -​ Can’t tell color -​ Hear the world in black and white -​ Discovered in 1793 by Spallanzani -​ Saw bats roosting, and wondered how they could see. -​ Blinded a bat by poking their eyes out -​ They were fine -​ Not so fine after being dissected -​ Poured hot wax in ears to deafen them -​ Immediately bumping into walls  -​ Dissected and figured they had not eaten -​ Deduced that bats see out of their ears -​ Sure okay -​ Spallanzini bat problem not solved until 1930s -​ Donald Griffen -​ Figured out echolocation -​ Was an undergraduate -​ Echolocation is not only for bats. Dolphins, tenrics, whales, rodents -​ “Acoustical orientation” -​ Up to 20% animals can do it -​ Skepticism of how good they are -​ Only seen in microbats -​ Fruitbats & other megabats do not echolocate as far as we know -​ Except for egyptian tomb bats -​ Rousettus -​ Are a fruit bat -​ Convergent evolution - use tongue clicks to echolocate -​ Frequencies -​ Bat 10-200 Khz -​ Bats can come down to low 20s -​ Most are in 60-80s -​ High frequency sounds don’t travel well -​ Make VERY loud sounds to make up for it -​ Whispering bats -​ Calls are 200 dynes/cm^2 -​ That is about the same intensity as standing 6 ft from a jet engine -​ Humans 0.02 - 20 Khz -​ 5-15 Khz with age -​ To prevent going deaf, bats have evolved 3 traits -​ Tympanic membrane tendon tightens to reduce how much the tympanic  membrane vibrates - Dampens tympanic vibrations -​ Sound goes straight through the skull. The inner ear is insulated and separated from the skull. That way vibrations don’t go through. -​ Altenuate neural signals to brain -​ 2 reasons -​ Little interference -​ Direct relationship between frequency and prey size -​ Objects approx the same size of a wave length will project wave length particularly well -​ Size of frequency made suite size of prey -​ Bigger bats eat bigger prey, therefore have lower frequencies -​ Like “neon signs” - bugs come back super loud -​ Sonograms -​ Constant frequency = cf call -​ Bounce off bigger objects better -​ High and low spot = fm call -​ Frequency modulated -​ Bounce off small objects better -​ Doppler effect -​ Sound is in soundwaves -​ If you are travelling the same distance as the waves, the speed compacts them, compressing them to be at a higher frequency -​ Wavelength behind you drag, making them sound lower -​ Bats listen to doppler shift to know where insects are and which direction they are going -​ Bat calls have an fm and cf portion, making both types work -​ The closer they get, the faster they speed up calls to get more information  -​ Calls become so fast ears cannot process it? You hear a constant buzz -​ Called a feeding buzz -​ At terminal part of feeding buzz, bat is calling as many as 200 times in a second -​ Turn off ears, make call, turn on ears, -​ Rinse and repeat -​ Upper limit of neurons -​ Harmonic calls - 2 calls at once -​ Hibernation -​ Temperate is a big obstacle for animals -​ -60 Celcius to 60 Celcius -​ At best, mammals can survive between 0 to 45 degrees celcius -​ 32F to 106F -​ Mammals can only be active between 30-40C -​ Most animals ectothermic -​ “Cold blooded” -​ Cannot produce heat -​ Mammals are endothermic -​ As are birds -​ Why 98.6 degrees? -​ Human temperature 😭 -​ Proteins can denature at 106. That is unable to be undone. At 106-108 you’re going to die lmfao -​ 98.6 F is a safety margin (40 C give or take) -​ Can get hot without dying -​ Animals like house cats don’t need safety margin due to size (102) -​ Elephants & Hippos have lower core body temp. (97) -​ Over 90% of what is eaten goes to keeping body at 98.6 -​ +10 degrees C => 2x speed for nerve firing -​ -10 degrees C => ½ speed for nerve firing -​ High as we can go for nerve speed while keeping a safety margin -​ Focus on families and orders -​ Known higher taxonomy -​ 2 bones -​ 1 faunal region -​ Homeothermic -​ Does not fluctuate a ton  -​ -​ Heterothermic -​ Bats, chipmunks -​ Hibranators -​ Different body temps - capable of living through greater fluctuations in body temp -​ Bats core body temp low 100s -​ Can drop temp down, in state of suspended animation -​ Very energetically expensive for small mammals to be homeothermic -​ Hibernation -​ One form of temperature fluctuation -​ Turn down metabolism -​ Hibernation is not turning off metabolism -​ Reducing energy burning, which reduces heat -​ Can cool down to temp of environment around them -​ Essentially become ectothermic -​ Slow breathing -​ Don’t need to circulate bloodflow, heartrate reduced, oxygen reduced -​ Rodents, bats, monotremes, hedgehogs, marsupials, all hibernate -​ Not a lightswitch. Slow process -​ Woodchucks burrow down to depth just below frostline so hibernation chamber is not freezing -​ Hibernation is convergent -​ Hedgehogs stop breathing for 56 minutes, breath for four -​ Others keep a constant slow breathing -​ Hibernation is often not consistent -​ Hibernation is NOT sleeping -​ Bats arouse from hibernation to nap potentially -​ Can arouse to release wastes and consume water -​ Arouse to stretch and give body bloodflow -​ Muscle atrophy reduction -​ Expense of arousing is great for hibernating animals -​ Suggested energy needed to arose could have kept them going for 30 more days -​ 30% of bodyweight in fat at the beginning of hibernation -​ 10% of bodyweight in fat at the end -​ At 20%, bats can hibernate for 194 days -​ The frost free period (from first frost to last frost) is 195 days -​ Hibernation comes down to the day. -​ Torpor  -​ Mini hibernation -​ Hours to maybe a couple days -​ In summer, bats go into torpor during the day -​ Body temp goes ambient (so at 70ish) -​ Bats go into torpor for 50% of summer -​ Only active in the summer (50%) and during night (50%)​ ​ Active ¼ their life -​ Life is 4x longer -​ Estimation -​ In Serengeti -​ 2 sources of heat -​ Sun and internal metabolism -​ Reducing metabolism to minimize internal body temp in a state of torpor -​ Too hot for anything, not dangerous while zoning out. -​ Evolution -​ Time cannot be conceptualized -​ 4.5 billion year old planet (maybe) -​ Mammals evolved in parallel with reptiles initially -​ Mammals arose from synaptids -​ Synapsida (mammal like reptiles) -​ Earliest reptiles, pasted peak before dinosaurs showed up -​ Other subclasses -​ Anapcids -​ Led to turtles -​ Without hole in skull -​ Euriapsids -​ Extinct aquatic -​ Diapsids -​ Ruling reptiles (lizards and snakes) -​ 2 openings in skulls -​ Indents in the skull for muscle attachment -​ Synapsids split into 2 orders -​ Pelycosauria -​ Smaller temporal bone -​ Therapsida -​ Advanced mammal-like reptiles -​ Large temporal bone -​ Canine-like teeth. Differentiating -​ Large dentary  -​ Lasted longer -​ Cynodontia => mammals -​ Transition happened over 140 million years -​ 1. Enlargement of temporal opening -​ So what? -​ More muscles for chewing. Stronger jaws. -​ 2. Go from 1 to 2 occipital condyles -​ So what? -​ Different motion of head. More precise. -​ 3. Maxillary and palatine bones are extended posteriorly and medially (going back and toward the middle -​ So what? -​ Palatine separates nasal from oral cavity -​ Allows you to chew food while breathing -​ 4. Detention becomes heterodont -​ So what? -​ Wider range of food to eat -​ Teeth with different functions (for plant, for meat) -​ 5. Dentary bone enlarges -​ So what? -​ Stronger lower jaw. No junctions between bones -​ 6. Reduced ribs -​ So what? -​ More room for bending. More flexibility -​ 7. Moving limbs underbody -​ So what? -​ 8. Reduction of carpel & torsel bones -​ 2,3,4,5,3 => 2,3,3,3,3 -​ Easier to grab at things -​ During the mesoozic, mammals were a snack for reptiles -​ Mammals were small thing on the landscape -​ To not get eaten, they hide. Mammals begin to adapt to being nocturnal as reptiles are ectothermic. To adapt to cold, mammals adapt endothermy. A lot of eating and a lot of calories. -​ Mammals became mammals because reptiles ate them into becoming nocturnal -​ Class of mammalia (evolutionary possibilities) -​ Where do monotremes and theria split? -​ At some point, mammals came from the same lineage. Doesn’t really matter when it happened. Monotremes cut it close. Interesting to consider -​ Mesozoic mammals -​ Mammals insignificant part of faunal landscape -​ In order to survive, adapted to become nocturnal -​ Smallest dinosaur was 10x the size of the largest mammal -​ 3 feeding guilds in early mammals -​ Multitituberculates -​ Herbivores -​ Monotremes -​ Occlusal surface not in a line with articulation point -​ Triconodonts -​ Carnivores (carnivorous) -​ Died out -​ Occlusal is perfectly in a line with articulation point -​ Pantotheres -​ Omnivores -​ Theria -​ Articulation point and occlusal surface between herbivore and carnivore -​ After Mesozoic, mammals were still insignificant -​ Then the asteroid hit -​ Goodbye dinosaurs -​ How did mammals survive? -​ Dinosaurs laid eggs on surface, gender of eggs dependant on heat -​ Temperature of earth alerted so much, only 1 sex of dinosaur was around. Died out due to no mates. Dinosaurs could not adapt, but everything else could.