title: Geograpehic variation and episodic evolution in an ordovician trilobite.
abstract: A single lineage of the trilobite Flexicalymene shows two evolutionary "punctuated equilibria" within a 2-million-year, 1000-square-kilometer stratigraphic interval. The 2 x 10(5)-year-long "punctuation" may represent parapatric speciation. Commonness of depth-related clines before, during and after this event suggests that short-term adjustment to local conditions was important in long-term evolution.
authors.forename: J L
authors.initials: JL
authors.lastname: Cisne
authors.forename: G O
authors.initials: GO
authors.lastname: Chandlee
authors.forename: B D
authors.initials: BD
authors.lastname: Rabe
authors.forename: J A
authors.initials: JA
authors.lastname: Cohen