Evolutionary Biology

Miocene to Recent species of planktic foraminifera in the Globorotalia (Globoconella) lineage evolved entirely within the thermocline. All species are most abundant within subtropical-temperate watermasses throughout their history. The near stasis in distribution within the thermocline and the subtropical convergence suggests the major morphological changes in Globorotalia (Globoconella) may have occurred through habitat subdivision rather than by vicariant shifts into new watermasses. At the Rio Grande Rise, in the South Atlantic, modern G. inflata is 0.66-0.84?

The disappearance at ~10 Ma of the deep dwelling planktonic foraminifer Globoquadrina dehiscens from the western Pacific including the South China Sea was about 3 Myr earlier than its final extinction elsewhere. Accompanying this event at ~10 Ma was a series of faunal turnover characterized by increase in mixed layer, warm-water species and decrease to a minimum in deepwater species. Paleobiological and isotopic evidence indicates sea surface warming and a deepened local thermocline that we interpret as related to the development of an early western Pacific warm pool.

A mass extinction of deep-sea benthic foraminifera has been documented globally, coeval with the negative carbon isotope excursion (CIE) at the Paleocene-Eocene boundary, which was probably caused by dissociation of methane hydrate. A detailed record of benthic foraminiferal faunal change over ~30 k.y. across the carbon isotopic excursion at the Ocean Drilling Program Site 690 (Southern Ocean) shows that shortly before the CIE absolute benthic foraminiferal abundance at that site started to increase. 'Doomed species' began to decrease in abundance at the CIE by a few thousand years.

Planktic foraminifera across the Paleocene-Eocene transition at DSDP Site 401 indicate that the benthic foraminiferal mass extinction occurred within Subzone P 6a of Berggren and Miller (1988), or PS of Berggren et al. (1995) and coincident with a sudden 2.0? excursion in 6r3C values.

Micropaleontologists have traditionally recognized the mid-Miocene Fohsella lineage as a flagship for phyletic gradualism within the planktic foraminifera. However, study of a deep-sea record from the western equatorial Pacific (ODP Site 806) reveals that coiling ratios within this clade suddenly (<5 kyr) shift after a prolonged, ancestral state of near randomness (~50%) to a transient phase (13.42?13.43 Ma) of dextral dominance (~75%) immediately following the first common occurrence of keeled fohsellids.

Benthic foraminiferal assemblages from Santa Barbara Basin exhibit major faunal and ecological switches associated with late Quaternary millennial- to decadal-scale global climate oscillations. Repeated turnovers of entire faunas occurred rapidly (<40-400 yr) without extinction or speciation in conjunction with Dansgaard-Oeschger shifts in thermohaline circulation, ventilation, and climate, confirming evolutionary model predictions of Roy et al.

Joseph B. Martin Conference Center,
Harvard Medical School, Boston, Massachusetts, USA

Joseph B. Martin Conference Center, Harvard Medical School, Boston, Massachusetts, USA

Oregon Convention Center, Oregon, USA

Winclada is a full-featured menu and mouse driven windows program for displaying, manipulating and printing cladograms (phylogenetic trees)