Evolutionary radiation 1422728 220938840 2008-06-22T08:59:41Z Firsfron 158443 correct link to [[Dinosaur]], Replaced: [[dinosaurs]] → [[dinosaur]]s using [[Project:AutoWikiBrowser|AWB]] An '''evolutionary radiation''' is an increase in taxonomic diversity or morphological disparity, due to adaptive change or the opening of ecospace.<ref name=Wesley-Hunt2005>{{cite doi|10.1666/0094-8373(2005)031<0035:TMDOCI>2.0.CO;2}}</ref> Radiations may affect one clade or many, and be rapid or gradual; where they are rapid, and driven by a single linage's adaptation to their environment, they are termed [[adaptive radiations]].<ref name=Schluter2000>{{cite book | author = Schluter, D. | year = 2000 | title = The Ecology of Adaptive Radiation | publisher = Oxford University Press | isbn = }}</ref> ==Examples of evolutionary radiation== Perhaps the most familiar example of an evolutionary radiation is that of [[Eutheria|placental mammals]] immediately after the [[extinction]] of the [[dinosaur]]s at the end of the [[Cretaceous]], about 65 million years ago. At that time, the placental mammals were mostly small, insect-eating animals similar in size and shape to modern [[shrew]]s. By the [[Eocene]] (58-37 million years ago), they had evolved into such diverse forms as bats, whales, and horses. <ref>This topic is covered in a very accessible manner in Chapter 11 of Richard Fortey's ''Life: An Unauthorised Biography'' (1997)</ref> Other familiar radiations include the [[Cambrian explosion]], the radiation of land plants after their [[Evolutionary history of plants#land|colonisation of land]], the Cretaceous [[Evolutionary history of plants#flowers|radiation of angiosperms]], and the diversification of insects, a radiation that has continued almost unabated since the [[Devonian]], {{Ma|400}}.<ref>The radiation only suffered one hiccup, when the [[Permo-Triassic extinction event]] wiped out many species.</ref> ==Types of radiation== Radiations may be discordant, with either diversity or disparity increasing almost independently of the other, or concordant, where both increase at a similar rate.<ref name=Wesley-Hunt2005/> ==Evolutionary radiation in the fossil record== Much of the work carried out by palaeontologists studying evolutionary radiations has been using marine [[invertebrate]] [[fossil]]s simply because these tend to be much more numerous and easy to collect in quantity than large land [[vertebrate]]s such as mammals or dinosaurs. Brachiopods, for example, underwent major bursts of evolutionary radiation in the Early [[Cambrian]], Early [[Ordovician]], to a lesser degree throughout the [[Silurian]] and [[Devonian]], and then again during the [[Carboniferous]]. During these periods, different species of brachiopods independently assumed a similar morphology, and presumably mode of life, to species that had lived millions of years before. This phenomenon, known as [[homeomorphy]] is explained by [[convergent evolution]]: when subjected to similar selective pressures, organisms will often evolve similar adaptations. <ref>''Living and Fossil Brachiopods'' by M. J. S. Rudwick (1970)</ref>. Further examples of rapid evolutionary radiation can be observed among ammonites, which suffer a series of extinctions from which they repeatedly re-diversify; and [[trilobite]]s which, during the Cambrian, rapidly evolved into a variety of forms occupying many of the niches exploited by [[crustacean]]s today <ref>''Aquagenesis, The Origins and Evolution of Life in the Sea'' by Richard Ellis (2001)</ref>, <ref>''Ammonites'' by Neale Monks & Philip Palmer (2002)</ref>, <ref>''Trilobite, Eyewitness to Evolution'' by Richard Fortey (2000)</ref> ==Recent evolutionary radiations== A number of groups have undergone evolutionary radiation in relatively recent times. The [[Cichlidae|cichlids]] in particular have been much studied by biologists. In places such as [[Lake Malawi]] they have evolved into a very wide variety of forms, including species that are filter feeders, snail eaters, brood parasites, algal grazers, and fish-eaters. <ref>The Cichlid Fishes: Nature's Grand Experiment in Evolution by George Barlow (2002)</ref> [[Grass]]es have been another success, evolving in parallel with [[grazing]] herbivores such as [[horses]] and [[antelope]] [http://www.palaeos.com/Cenozoic/Cenozoic.htm]. ==References== <references/> [[Category:Evolution]]