hist & evo of chordates

defining features of chordates

notochord, dorsal hollo nerve cord, pharyngeal slits, post-anal tail, and endostyle (at some life stage)

why is the Cambrian fossil record important for vertebrate evolution?

documents early diversification of chordates & gradual emergence of vertebrate characteristics

what Cambrian fossil record reveals ab early vertebrates?

it shows emergence of basic chordate body plan, early filter-feeding, gradual evolution of cranium & vertebral elements

when & from what did amniotes evolve?

Late Carboniferous ~370 Ma from amphibious tetrapod ancestors

what are the defining features of amniotes?

amniotic shelled egg (reproduction inde of water), keritinized skin to prevent desiccation, 3 or 4 chambered heart for improved circulation

what are the 2 main amniote lineages?

synapsids → mammals, sauropsids → reptiles & birds

why was the amniotic egg evolutionarily sig?

allowed fully terrestrial reproduction, expansion into dry enviros, reduced dependence of aquatic habitats

from which group did mammals evolve?

probainognathian cynodonts which were synapsid reptiles

when did mammals first appear

Late Triassic ~225 Ma

how did mammals survive PTME

likely burrowing, small size, low ecological req

what are 6 key mammalian synapomorphies

mammary glands, hair, three middle ear bones, heterodont dentition, large brain w/ neocortex, endothermy

why are mammalian teeth important evolutionarily?

show dietary specialization, adaptive radiation ecological diversification

what are monotremes?

egg laying mammals of only 5 species, e.g. platypus

why are placental mammals so sucessful

eutherian’s internal development allows better protection, longer growth, higher survival rates

endothermy

internal regulation of body temp via metabolism

why was endothermy important

enabled sustained activity, colonization of varied climates, increased ecological competitiveness

aerobic scope hypothesis

suggests endothermy evolved to support higher activity levels

nocturnal bottleneck hypothesis

mammals became nocturnal to avoid dinosaurs & reduce competition

evidence to support nocturnality in early mammals

eye structure, visual pigments, fossorial adaptations

limitations of nocturnal bottleneck

assumes dinos strictly diurnal oversimplifying ecological complexity

what happened during Jurassic mammal radiation

rapid diversification in diet, locomotion, ecological roles

early mammal diet

mostly insectivorous, later diversifying

what locomotor types existed in Mesozoic mammals?

arboreal, fossorial, gliding, terrestrial, semi-aquatic

what are multituberculates?

rodent-like early mammals w/ complex teeth & evidence of social behavior

transition from mid to late Jurassic

shift from stem mammals to crown mammals

Mid-Cretaceous Terrestrial Revolution

major ecological turnover causing extinctions, decline in some mammal groups, and later diversification of mammals

which mammal groups radiated after the mid-cretaceous event

metatherians, eutherians, multituberculates, dryolestoids

when did megafaunal extinctions occur

mainly late Quaternary

main hypotheses for megafaunal extinction

combined effects of climate change & human overhunting

key stages of human evolution

early hominins, Australopithecines, Homo species

key traits of Australopithecus

bipedalism, small brain, mixed arboreal/terrestrial lifestyle

what trends define human evolution

increased brain size, tool use, social complexity, reduced/jaw size

key Homo species

Homo habilis, Homo erectus, Homo neanderthalensis, Homo sapiens