| Planktonic foraminifera possess a long history and excellent fossil record. They are abundant, well preserved, and stratigraphically well defined. Their diverse morphologies are easily quantified and their extant representatives have undergone extensive genetic and isotopic testing. Planktonic foraminifera are unsurpassed as a subject for research into life's patterns. This two-part study examined both macroevolutionary and microevolutionary patterns.; From the standpoint of macroevolution, survivorship within Middle Cretaceous to Recent planktonic foraminifera reveals intriguing patterns. As suggested by previous authors, extinction in planktonic foraminifera is age-dependent. Short-ranged species (longevities of <4 m.y.) account for much of this effect. The first application of the Cox proportional hazards model to paleontological data allowed the separation of time-dependent and age-dependent extinction in the context of geologic time. The results show significant increases in age-dependence for species following two extinction boundaries: Cenomanian-Turonian (C-T) and Cretaceous-Tertiary (K-T); survivors were short-lived with rapid turnover. The boundary events are followed by long recovery intervals. These results have implications for the Red Queen hypothesis and the effects of mass extinctions on surviving biota. Red Queen behavior appears to be the time-averaged result of boundary-generated oscillations between short-term positive age dependence and longer-term, nearly age-independent, Red Queen behavior.; The Globigerinoides trilobus-Orbulina universa series, one of the best known transitions in the fossil record, provides detailed documentation of cladogenesis. Phylogenetic analysis of small subunit ribosomal DNA (SSU rDNA) affirms monophyly of the extant G. sacculifer-O. universa clade; tree topology suggests possible synonomy. A global survey of Ocean Drilling Program (ODP) data shows speciation occurred near or on the equator. Morphometric analysis of material from ODP Site 871A reveals that the final chamber area/area of total test is strongly unimodal in the ancestral population throughout the transition; the Orbulina genus appears as a second mode in the population after a rapid transition. Preliminary isotopic analyses of single chambers at Deep Sea Drilling Project (DSDP) Site 516 suggest little evidence for habitat differences during the transition; further study is warranted. Widespread geographic speciation, coupled with lack of vertical migration, argues against depth-parapatry and for a sympatric mode of speciation during the transition. |
