Mammalian Radiation Flashcards
Lec 11
Competitive exclusion principle
two species sharing the same niche will compete until one remains in that niche
Resource partitioning / character displacement
differentiation of niches enabling similar species to coexist in a community
species will evolve traits that reduce direct competition
modern mammals united by (6)
endothermy
presence of hair
lactation
heterodonty, milk teeth
live birth mostly
sociality
Amniotes
reptile-like ancestors with
scales + eggs that can survive on land
led to reptiles, dinosaurs, mammals
synapsid characteristics (4)
opening in the skull behind the eye
heterodentition (distinct molar, canines, incisors
jaw with few bones
separate the nasal cavity from the mouth (second palate)
therapsids characteristics (4)
Feet directly under the body, not a crocodile
hair, sensory perception, whiskers
highly vascularized bones
baby teeth and adult teeth
cynodonts characteristics ~250MYA
lactation
interlocking teeth for cutting up food (easier to digest)
jaw muscles moved outside the brain case
evolution of ear bones, airborne sound
highly diversified, many niches
what happened with the dinosaurs?
~200MYA drove the disappearance of large cynodonts, only small species
Triassic to the End Cretaceous
Nocturnal Bottleneck Hypothesis
dinosaurs mainly diurnal (active during the day) because they needed the heat for energy
prey species specialized into being active at night
what is required for a species active at night? (6)
large eyes
smell and hearing perception heightened
complex brain, skull that can accommodate changing brain size
carnivore to support large brain
lactation to feed young
hair for endothermy
relation between lactation and sociality
increased parental care leads to prolonged interaction between parent and offspring –> sociality (seen in all mammals), at least between parent-offspring
end cretaceous bolide impact
the end of dominant dinosaurs
what traits did some mammals have that helped them have a lower extinction risk?
small, little food, generalist food preference, lots of offspring ever generation, start reproducing quickly
mammalian raddiation ~100 or 60 MYA (during or a little after dinosaurs)
only small, rat-size mammals survived
took ~100,000 years for mammals to reach raccoon size again
took 10 million years to diversify to fill the niches of dinosaurs
Miocene Cooling
temperatures dropped 5C
changed dominant plant life, forest –> grasses (very low nutrients, hard to digest)
led to herbivores, mammals that can eat grass with slow digestion
