Plants, a yardstick for measuring the environmental consequences of the Cretaceous-Tertiary boundary event

Reactions registered by plant communities to the Cretaceous-Tertiary (K-T) boundary cometary impact event include extinctions, killing events, shifts in the relative number and abundances of taxa, and, for some taxa, an appar ent insensitivity to imposed stresses. All these provide yardsticks to meas ure the extent of impact-generated environmental perturbations: extinctions by their magnitude and selectiveness, killing events by their geographic e xtent, and the survivors by their varying sensitivities to the boundary eve nt as reflected in trends in their relative abundances and distribution. In formation has been assembled from localities in western Canada and Montana that suggests: most plant extinctions involved what were likely zoophilous (animal-pollinated) angiosperms; understory vegetation may have survived th e event; there was extensive destruction of the forest canopy on a continen tal scale; and there was a variable response to the K-T boundary event by w hat were likely wind-pollinated angiosperms.