Abstract

Studies of the Stichocorys and Lamprocyrtis lineages suggest that allopatric speciation as peripheral isolates is important. Sympatric speciation is also a possible mode of evolution in these lineages. Hybridization may play a role in the evolution of one subspecies and one species. Allopatrically evolved subspecies and species require some time to inhabit their maximum geographical range after evolving in an isolated and peripheral part of that "environment", whereas the supposedly sympatrically evolved forms do not. Cooling trends and water mass reorganization may be related to the speciation events. Similar, but much less controlled, studies on a macroevolutionary scale (evolution above the species level, essentially the "family" level) suggest that there have been about half a dozen periods of major adaptive breakthroughs resulting in quantum, or macro, evolution. Global coolings and the initiations of "new" cold-water spheres and related water masses, appear to have allowed these macroevolutionary steps during the Ordovician, Devonian-Carboniferous, Permian, and early Neogene. Ecological pressure from diatoms and planktonic foraminiferans appears to have been related to macroevolutionary events bounding the Cretaceous-Tertiary transition.

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