Chapter 25

Term Definition
Stromalites the first single-celled organisms and the oldest known fossils; rocks formed by the accumulations of sedimentary layers on bacterial mats.
oxygen revolution from 2.7 to 2.3 billion years ago caused the extinction of many prokaryotic groups.
endosymbiotic theory proposes that mitochondria and plastids (chloroplats and related organelles) were formerly small prokaryotes living within larger host cells.
endosymbiont a cell that lives within a host cell.
serial endosymbiosis supposes that mitochondria evolved before plastids through a sequence of endosymbiotic events.
the "snowball Earth hypothesis" suggests that periods of extreme glaciation confined life to the equational region or deep sea vents from 750 to 580 million years ago.
Ediacaran biota an assemblage of larger and more diverse soft-bodied organisms that lived from 575 to 535 million years ago.
Cambrian explosion the sudden appearance of fossils resembling modern animal phyla in the Cambrian period (535 to 525 million years ago).
Permian extinction the boundary between the Paleozoic and Mesozoic eras 251 million years ago.
Cretaceous mass extinction 65.5 million years ago separates the Mesozoic from the Cenozoic; caused the extinction of the dinosaurs
adaptive radiation the evolution of diversely adapted species from a common ancestor.
heterochrony an evolutionary change in the rate or timing of developmental events
paedmorphosis the rate of reproductive development accelerates compared with somatic development.
homeotic genes determine such basic features as where wings and legs will develop on a bird or how a flower's parts are arranged.
hox genes a class of homeotic genes that provide posotional information during development.
binomial the two part scientific name of a species.
epithet unique for each species within the genus.
taxon the taxonomic unit at any level of hierarchy.

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