Lecture 15 Flashcards
Mammals in modern world
- 3 lineages
- monotremes: egg laying (first kind)
- marsupials: develop in pouch
- placental: reproduction via placenta
Defining characteristic of mammals
- not fur/reproduction
- ear
- incus and malleus form from old jaw articulation
- defining feature that distinguished mammals from reptiles
What makes a mammal a mammal?
- hair
- three middle ear bones
- mammary gland in female
- neocortex
- did not all arise at same time
Synapsid skull
-positioning of holes behind eye are what defined it as a synapsid
Therapsid
- evidence of vibrissae-means it has the ability to have hair
- less upright, not sprawling
- these early creatures were acquiring warm-bloodedness and other such mammalian characteristics that we have today
Dentition-later therapsids
- changes so that reptilian teeth out front but has molar like teeth in back
- for chewing and grinding, not ripping
- something on its way to being a mammal
Teeth
- reptiles eat prey item whole and are capable of absorbing that much of animal into gut
- mammals can’t do this so they need teeth for grinding
- can’t hold breath very long
- can breathe while chewing because of palate that separates mouth from air duct
- warm blooded
Jaw Evolution
-as you get toward mammals the dentary bone that has the teeth get’s increasingly larger and the contact between the jaw and skull that’s present in the reptilian ancestor is co-opted to do something else
Evolution of Female Reproductive systems in mammals
- monotreme: see what’s present in reptiles: uterus and anal canal same tube and feed down to cloaca
- marsupial anal canal not separate from cloaca but eggs and urine come out of cloaca
- placental all three functions now separate tubes
Modern orders of mammal radiation?
- present already in mesozoic or do they arise only after non-avian dinosaurs are extinct
- two views
- in the cretaceous
- post cretaceous
- molecular extrapolations suggested one thing, and fossil data demonstrated something else
First model
- can use rate of gene evolution to determine when animals diverged from each other
- says primates arose in Mesozoic but you don’t find fossils of them in that period
Second model
-classes and orders arise a couple million years after the extinction
Gliders
-have gliders living today that are a couple million years after the extinction
Evolution in size
- over evolutionary time mammals get bigger
- common trend for many species
Horses
- occasionally horses are still born with three toes because they used to have three toes and they still have the genes for this so it shows how recent it really is
- mammals don’t generate new teeth but have tactics used to prolong lifetime of teeth
- low crown vs. high crown in new horses
High crown vs. low crown
- dinos didn’t have tall crowns so they couldn’t chew their food
- if they had short crowns and chewed their food they wouldn’t have any teeth left
- horses chew so much grass which is hard on their teeth so their teeth are long so as the grass wears them down they just push though a little more.
Brian Evolution
- cerebral cortex much larger than most other animals because we have higher functioning
- brains from lemurs are similar to those seen in Eocene
- midbrain and hindbrain features also vary in size between animals through time
Primates, Major features
- binocular vision
- grasping hands and feet and opposable thumbs
- closed eye sockets
- fingernails
- some adapted brachiation (body made for reaching upward like they do when they’re swinging)
- enhanced brains and intelligence
- strong social organization in many: dominance, territorial, long parental care
Human characteristics
-lots are really exaggerations of functions and such that evolved from our primate ancestors
Old Phylogeny
- showed humans as separate from apes but that’s not the case, we are apes so says new phylogeny tree
- Homo sapiens are right in middle of chimps, gorillas, and orangutans so we are a branch of giant apes
Mammal evolution
- evolve from synapsids (major clades of reptiles) appear in late Carboniferous
- by permian evolve into therapsids (likely warm blooded and covered by hair) and begin developing mammal like detention
- mammals evolve from therapsids in the Triassic
Skeletal and dental features
- allow us to determine relationships of fossil animals
- tell marsupial skeleton from placental?
- marsupials have pouch, which gets some skeletal support–epipubic bone
Primate adaptive history
Terrestrial ancestor–>arboreal–>humans terrestrial (secondary)
Terrestrail ancestor
- small forest floor animals
- no stereovision smell primary
- plantigrade
- claws
Arboreal
- small/moderate size
- intelligence
- stereovision
- reduced
- sense of smell
- vertical body
- balance
- nails
- grasping hand
Humans Terrestrial (secondarily)
- bipedal
- vertical spine
- foramen magnum
- under skull
- reduced hair
- carnivory
- enlarged brain
- precision grip
- tool making
Higher Primates-classic tree
- anthropoids-first appear in oligocene
- platyrrhines=new world monkeys
- south america: prehensile tails, relative primitive monkeys
- catarrhines=old world monkeys Africa, Asia
Pongids
-classical term for all apes
Newer Tree of primate relationships
- based on cladistic analysis
- no more pongids instead have homminoids (humans and apes)
