CLAS: Colby Liberal Arts Symposium

Pennsylvanian Climate Fluctuation: Biotic Response to Cyclic Glacial and Interglacial Phases

Parker-Reed, SSWAC

The literature indicates that the Pennsylvanian period (323 ma to 299 ma) was characterized by fluctuating ice sheets, giving rise to shifts from humid to dry seasonal climate conditions and resulting in major alterations in terrestrial and marine ecosystem on the paleo-supercontinent known as Gondwana. Research indicates that sediments deposited by high and low sea level, caused by glacial fluctuation, greatly influenced the biogeographical ranges of the marine and terrestrial flora and fauna, drove macro- and micro-evolution, and controlled ecological compositions. Biotic records illustrate an overarching transition from humid/sub-humid conditions to dry/sub-arid and arid conditions in the early and mid-Pennsylvanian that regress to a sub-humid climate in the late Pennsylvanian. These temperature-and-moisture conditions oscillate in response to glacial-interglacial phases. On land, conifers replace wetland Coal Forests dominated by tree ferns and lycopsids, and tetrapods utilize a broader range of terrestrial habitat. An unusual decrease in both origination and extinction rates suggests previous ecological influence promoting stoic morphologies that were not sensitive to normal evolutionary pressures. In the oceans, trilobite evolutionary and brachiopod migratory responses to climate pressures further corroborate the terrestrial plant and tetrapod record. This paper examines the evidence supporting a climate-controlled biosphere and describes both short and long-term biotic responses to glacial fluctuation. This balanced account is necessary to determine the validity of biologic climate proxies as a means of verifying direct glacial records and even replacing them where cyclothems are not available.

https://digitalcommons.colby.edu/clas/2015/program/164