Synapsida --> Mammals Flashcards
What is one reason why the first mammals to evolve during the dinosaur era were so tiny but after the dinosaur era, they grew to be in larger sizes?
one reason is that the dinosaurs prevented mammals form growing in size therefore, they were always hiding in small places to avoid getting preyed on by dinosaurs. After they went extinct though, mammals came out of hiding areas and found less competition for food resources and ended up dominating the areas they were in and grew to be bigger sizes
When did mammals start to diversify?
after the extinction of dinosaurs
What are some characteristics of synapsids?
they have one hold in the skull used for jail muscles
- they include mammals
- all of the non-mammalian members of synapsids are extinct, these included:
sailbacks, therapsida’s and close relatives of mammals
What were the derived traits of Therapsids (extinct mammal species)?
they had an enlarged dentary bone in the jaw (and also larger other bones in jaw) but in modern mammals, the other bones are tiny and the dentary bone is our main jaw bone.
- they also developed a secondary palate which is a parting to separate the nasal passages from their oral cavities which allowed them to chew an breathe at the same time(humans can’t do this)
What are mammary glands? What is the origin of these glands
- they are glands that secrete nutrias fluid (milk) to feed offspring
origin is not clear
What happened to the modification of the jaw in mammals today vs. reptile jaws?
the movement of the left over jaw bones (the small ones) to the middle ear (causing the 3 bones in our ears) and reptile ears only have 1 bone
- this caused our eardrums to move deeper into our heads
What does exaptation mean?
structures that existed in an ancestral species and served a function but then co-opted into a function of something else in modified species millions of years later
Are mammals endothermic or ectothermic? What properties help out this process?
they are endodermic, and the hair and fat help with homeostasis (thermal regulation)
What is the difference between mammalian dentition and reptile dentition?
mammalian dentition is more differentiated than reptiles
- it has different diversity of tooth forms and they correlate with greater diversity of diet
- mammals teeth occlude more closely than replies which allows more food to be ground finely and the greater surface area of the teeth allow more nutrients to be extracted more rapidly (bottom and top teeth fit into each other to ensure chewing)
- mammals also have two sets of teeth across lifespan (milk teeth and adult teeth) when reptiles continually replace teeth in their lifespan
What is an adaptation in mammals that helps them have greater efficiency in movement ?
the vertical placement of limbs beneath the body which allows for better support of the body
- in reptiles, they are sprawling which makes them have less support and less efficiency
- dinosaurs and mammals have this vertical placement
What type of structure is the hair in mammals homologous to?
they are homologous to scales and feathers in birds … because they are fine keratin fibers
What is the diaphragm? how does it help mammals?
its dome shaped muscle at the base of the rib cage that helps with breathing
- it makes breathing more efficient because it draws in more oxygen to the lungs and increases efficiency of gas exchange (also mammals have bigger brains so they need more oxygen)
What are some reasons why some mammals returned to the water? How many lineages did do this? and after how many years on land?
7 lineages of mammals returned to the water after spending 300 million years on land
they did this because the water was warm and shallow, there was abundant food source, few competitors (since all of them moved to land) and fewer predators
Which species of mammals that returned back into the water are sister taxa of ungulates?
artiodactyla
What are some adaptations for RETURNING to life on water for those mammals that did?
- reduced pelvis size and separation of pelvis from backbone
- increase use of whole vertebral column including their back and tail in locomotion
- movement of tails up an down instead of side to side in swimming (indicates that they are mammals)
- reduced neck function (improves hydrodynamic movement as their neck fuses with their vertebrate)
- they have other adaptations for feeding in the water
- their nostrils also moved from the front of their face to the top of their heads creating a blow hole
