Slides 29 Flashcards
derived characters of mammals
mammary glands which produce milk to feed young, hair and fat layer under skin for insulation, kidneys which conserve water from wastes, endothermy (warm-blooded) and high metabolic rate, efficient respiratory system and circulatory systems, large brain-to-body ratio, extensive parental care, teeth modified for shearing, crushing, or grinding
early evolution of mammals- synapsids
amniotes that include mammals; early lacked hair, had sprawling gait, laid egg; distinguished by single temporal fenestra (hole behind eye socket)
early evolution of mammals- jaw
new jaw joint formed between the dentary and squamosal bones, became incorporated into middle ear, transmit sound from ear drum to middle ear
mammal evolution
synapids by end of Triassic period, true mammals during Jurassic, radiated with loss of dinos!! open niches
major lineages of mammals
monotremes, marsupials, eutherians
monotremes
egg-laying mammals, only in Australia and New Guinea, four species of echidnas and platypus, lack nipples and secrete mile from glands on bellies
marsupials
share derived traits with eutherians, higher metabolic rates, nipples to provide milk, birth of live young, embryonic development in uterus, placenta for nutrient transfer
evolution of placenta
extraembryonic membranes in fish, birds, and mammals, yolk sac dates back to aquatic ancestors; amnion, chorion, and allantois are innovations of amniotic egg which have been adapted to support embryonic development inside uterus
marsupial evolution
only live in Australia and Americas, split and diverged following split of Pangea, could look similar to eutherians due to convergent evolution
marsupial birth and nutritional dependence
baby is born, crawls back into pouch and sucks milk from mom, only comes out months later
eutherians
complex placenta, longer pregnancies, young eutherians complete embryonic development within a uterus, joined to the mother by the placenta
eutherian diversity
larger morphospace, more diverse, possible as increase in placentals could cause more advantageous life history traits or increased ecological opportunity
primates
arose as adaptations to living trees, big toes and relatively moveable thumbs to grasp branches, fully opposable thumbs that can touch the ventral surface of all four fingers improved dexterity, enhanced depth perception and eye-hand coordination
living primate 3 main groups
lemurs, tarsiers, anthropoids
monkey evolution and divergence
arose in old world, new world monkeys 25 million years ago, experienced separate adaptive radiations over millions of years of separation
ape evolution and diversity
apes evolved from old world monkeys 25-30 million years ago, include four genera: pongo, gorrilla, pan, and homo
derived characters of humans
upright posture and bipedal locomotion, larger brans capable off language, symbolic thought, and artistic expression, production and use of tools, reduced jawbones and jaw muscles, shorter digestive tract
homo sapien evolution
arose 200,000 years ago, homonins are extinct but more closely related to humans, fossils of 25 species
earliest homonins similarities
oldest is sahelanthropus, share derived traits with humans: reduced canine teeth, relatively flat faces, increasingly bipedal, placement of foramen magnum underneath skull
earliest homonins differences
small brains, larger teeth, projected jaws, smaller in stature
human evolution misconceptions
hominins are separate lineages from chimps and diverges from a common ancestor, evolution of apes and humans is incomplete; human evolution is like a ladder directly from an ape but there are many branches, homo sapiens as survivors
australopiths
paraphyletic assemblage of hominins 4-2 million years ago; anamensis, africanus, afarensis
A. anamensis
earliest known australopith
A. africanus
walked fully erect, humanlike hands and teeth
