Friday, February 23, 2007

Productivity Across The K/T Boundary

Faunal evidence for reduced productivity and uncoordinated recovery in Southern Hemisphere Cretaceous-Paleogene boundary sections. 2007. M. Aberhan,et al. Geology 35: 227-230.

Abstract [edit]: A catastrophic bolide impact is widely recognized as the trigger of the mass extinction that occurred 65 million years ago at the Cretaceous-Tertiary boundary, when animals such as dinosaurs (on land) and ammonites (in the sea) became extinct.

Devil Dinosaur created by Jack Kirby but © Marvel Comics
One possible killing mechanisms involves a global collapse of food chains due to the shutdown of photosynthesis by sun-blocking dust clouds and soot from fires. It is still unclear whether the intensity of these perturbations is related to the distance from the impact site in today’s Mexico and whether it is related to paleolatitude.

The ecological composition of organisms from high southern latitudes that lived on the sea floor at that time, such as clams, snails, corals, and sea urchins, changed significantly across the boundary and in a way that was consistent with the scenario of reduced availability of food after the impact event: Animals were less abundant for some time; starvation-resistant groups and animals not relying directly on photosynthetic organisms as a food source became more dominant; individuals with larval stages that do not need to feed on phytoplankton became proportionally more common; the average body size of individuals within communities became smaller; and individuals with low metabolic rates or inactive lifestyles became better represented.

A return to pre-extinction conditions of the various ecological attributes occurred over unequal time spans, indicating that recovery from the mass extinction was uncoordinated with respect to ecological traits.