Geological Magazine

Short Communication


Evolutionary response by bivalves to changing Phanerozoic sea-water chemistry

E. M. HARPER a1, T. J. PALMER a2 and J. R. ALPHEY a3
a1 Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
a2 Institute of Earth Studies, University of Wales, Aberystwyth SY23 3DB, UK
a3 Gonville & Caius College, Cambridge CB2 1TA, UK


Sedimentological evidence suggests that sea-water chemistry has oscillated between ‘Aragonite’ and ‘Calcite’ seas during the course of Phanerozoic time. During ‘Calcite’ sea periods aragonite was soluble and dissolved on the sea-floor. Here we propose, using a survey of familial diversity, that during times of such corrosive seas bivalved molluscs which secreted their shells entirely of aragonite were at a selective disadvantage compared to those with calcitic outer shell layers. This is the first case in which it has been suggested that there was a dynamic link between sea-water chemistry and the evolution of a particular taxon throughout Phanerozoic time.

(Received November 25 1996)
(Accepted February 26 1997)