Lesson 22 - Mannals Flashcards
what was the most abundant terrestrial
synapsids
^^ they were the top carnivores in the permian
key feature of synapsids
- the one hole in the side of the skull
- in the mammals, thise hole for the most past has been lost
- most were medium to large in size
- most mammals were quite small
—– maybe that is what allowed these groups to snek through and not be driven to extinction
sailback dinosaur
- basal ones were lizard like
- refereed to as the sailbacks of the lae paleozoic
- were anmiotes
- didn’t have the increased motor capacity like the later groups
- not thought of as being endothermic
- most were carnivores
- if the scales had blood supply – then a major reason behind it would be thermoregulation
comparing dimmetridon and dog
- go from homodont to heterodont
- temporal fenestra chanfes
- orbits are differnt
— totally lateral in the dimetridon but more medial in the dog
HINGE OF JAW
- between quadrate and articular
^^^^ lost in mammals
- condoloid process is what articulates with the squamosal (new hinge for mammalian jaw)
- articulate and the quadrate moved to the middle ear
^^^^^ the critical bones that form the amplification system
- presence of just a single occipital condyle i the dimetrodon vs the paired occipital condyle on the dog
basal therapsid
- larger tempral fonestra – probably for larger jaw muscles
— increasing level of activity – needing to eat more
we lack gastralia
- more present in basal equlipisaurs
dicynodont
- had skull specialized in herbivery
- some had cartilagenous maxilla turbinates
- so important in capturing heat and moistute
- ossification of the maxilla turbinates only occur later with the mammals
cynidonts
- early ones were sort of dog sized
- in the mid-triasic they kind of shrunk
- then they shrunk even more to mouse sized –> leading into mammals
- had cusped cheek teeth
-the top teeth work together with the bottom teeth coming together in a certain fashion
—— for efficiency processing of food material
late triassic probainognathian
- rat sized
- they had the early form of the double jaw joint
- started to get a new jaw
- also had an enlarged infraorbital foramen
—– allowed the passage of nerve fibers to face
—– you really only have facial expressions in mammals
—– serves the communication role
—– —– nursing —— need facial musculature
mammaliaformes
the first known specimen of mammals — morganucodon (gonna go with it being a mammal)
—– had larger brains compared to earlier synapsid
—– have the true dentary jount
—– precise tooth exclusion
—– why is it a mammal
—– —– hair and mammary glang
—– —– problem with fossils ^^^ soft tisue – does not fossilize
not viviparity
- platapuses lay eggs
mammals have the hardarian gland
secretions travel down the nasal lacrimal duct
– mammals with lots of pellage will get these secretions with an oil like quality that they use to treat their pellage
- ergoooo the morganucodon had hair –> had these 2 thins
- you do not find this duct in the more basal species
features of earliest mammals
diphyodonty
- 2 teeth generations (ex: baby and adult)
- mammals have precise occlusion of teeth
- mastication
– thoroughly grinding up food
- teeth that suggests insectiverous diet
– suggesting nocturnal and solitary lifestyle
transition from homodonty to heterodonty
- also get interdigitation of ()
- rows of teeth in the lower jaw are the same distance of the rows of teeth in the upper jaw
features of earliest mammals: tribosphenic molars
- additional cusps
- important with shearing food matter
features of earliest mammals – evolution of lactation and suckeling
- polyphydonty enables this
- you can get much more growth with dipholydonty
- meaning you have to delay the growth of teeth
- in order to enable diphodonty to give rise to the larger brain and jaw –> lactation needs to occur because they will not be able to chew their food
lactation must come first
first before diphiodonty
- aspect of the species but applies to the indivisual
- mammals have diphiodonty
— enables growth of the skull
— upper and lower jaws get bigger and bigger and bigger
— if you are stuck with the teeth you have when your head was little
———- there would be a lot of gaps
- if you were trying to grow your skull and minimuze the number of teeth generations – you needed to be able to eat without your teeth for a little 000 hypothesis for why lactation is what it is
