View - Kowalewski, M. - Virginia Tech

LIPPS AND CULVER—TROPHIC ROLE OF MARINE MICROORGANISMSforaminiferal systems. The association wasimmensely successful, and lasted some 100 millionyears. The strategy of symbioses between algalprotists and other protists and animals became morewidespread, as various animals throughoutcarbonate shelves adopted it as well.During the Paleozoic, continental configurationchanged from fairly well-dispersed Cambrian landmasses to all the Earth’s plates assembled into asingle supercontinent. These positional changeswould have caused much change in the distributionand ecology of microorganisms. The trophicstructures over the era must have been different indetail, but no interpretations for microfossils areavailable. As plates moved across latitudes andoceanography changed, different regions of theoceans were subjected to different nutrient supplies,temperature regimes, and hydroclimates that alteredtrophic structures and biogeographies (Ross, 1970).The Paleozoic ended with the largest extinction ever.This event terminated multiple animal (Erwin, 1993)and protist lineages, such as benthic foraminifera(especially fusulinids) and at least four lineages ofpelagic radiolarians (Casey, 1993; Culver, 1993).Mesozoic: 250 to 66 Ma.—The rediversificationof benthic organisms, including foraminifera, andthe radiation of the oceanic groups of skeletalmicroplankton and nekton like the ammonites, fish,and reptiles were the major events of the Mesozoic(Gale, 2000). Marine diversity remained low untilthe mid-Triassic. Microbial mats seem to haveflourished in the earliest Triassic (Fig. 6A), whenmetazoan diversity was very low. Diversity soonincreased to that of the Paleozoic, and marinecommunities developed a normal appearance(Erwin, 1996). Scleractinian corals built reefs andmade use of photoendosymbionts, most surelydinoflagellates. Benthic foraminifera diversified aswell, but their trophic functions can only beinferred. They ate small primary producers,secondary consumers of all kinds, and probablyeven larger motile invertebrates caught using theirpseudopodia (Culver and Lipps, in press). Manyspecies of symbiont-bearing foraminifera existedthroughout the Mesozoic, the fusiformalveolinellids (Fig. 7) in particular. In some placesABFIGURE 6—Phanerozoic microbial mats. A, LowerTriassic domed mats, Kockatea Shale, Blue Hills,Western Australia. B, Jurassic mats in theGeological Natural Reserve of Haute-Provence atEntrages, France. Both mats cover a wide areawith smaller domes interspersed on them. Thedomes may be true stromatolites built by microbesor they may have formed by gas accumulationsunder the mats. (Photos by J. H. Lipps.)83