CLADOGENETIC, EXTINCTION AND SURVIVORSHIP PATTERNS FROM A LINEAGE PHYLOGENY - THE PALEOGENE PLANKTONIC-FORAMINIFERA

Paleontological analyses of patterns of evolution at the 'species leve l' too often make uncritical use of taxonomic range data gathered prim arily for biostratigraphic purposes. In this contributon, taxonomic ev olution is studied from a stratophenetic lineage phylogeny of Paleogne planktonic foraminifera. This phylogeny, previously published in Micr opaleontology, was constructed to eliminate 'pseudospeciation' and 'ps eudoextinction' from the record, leaving only genuine cladogenesis (li neage branching) and terminal extinction. The phylogeny thus obtained obeys a valid cladistic geometry. Following the Cretaceous/Paleogene b oundary extinctions, the planktonic foraminifera made a rapid initial recovery in less than one million years to a more stable level of dive rsity. Lineage diversity and morphologic disparity ultimately reached a maximum in the middle Eocene. Diversity fluctuations in the group du ring most of the Paleogene result primarily from the expansion and dec line of one sub-clade, the muricates. Rates of cladogenesis and extinc tion in the planktonic foraminifera as a whole did not covary Cladogen esis peaked in the earliest Paleocene and the late early Eocene. Enhan ced extinction occurred in the mid-Paleocene and through the middle Eo cene. Neither the Paleocene/Eocene nor Eocene/Oligocene boundaries wer e exceptional events in the evolutionary history of planktonic foramin ifera. Survivorship curves, both uncorrected and normalised to variati ons in the general extinction probability (the 'corrected survivorship score' techique) are approximately straight, in contrast with the cas e of morphospecies longevities, which show a strongly age-dependent pa ttern (Pearson 1992). This suggests that the latter pattern is largely an artifact of taxonomic data gathering. A further interesting featur e is evident from the lineage phylogeny: those lineages which terminat e in branching have a mean duration which is less than half that of th ose which terminate in extinction, pointing to a strongly radiative pa ttern of evolution in the group.