Helen Tappan

Evolution of the oceanic plankton

Abstract In its evolution through geologic time, the oceanic plankton has reflected many changes in the physical environment while both causing and being affected by evolutionary change in the associated biota. Temporal variations in the vertical and latitudinal habitat partitioning also affected geochemical balances in the oceans and accumulation rates of biogenic sediments, and perhaps the atmospheric oxygen pressure. Advantages of the oceanic plankton habitat that led to its occupation by a varied sequence of organisms include its extensive geographic area, the possibility for rapid dispersal by currents, the availability of resources (ranging from light, carbon dioxide, and dissolved nutrients for the autotrophic organisms to the various lower trophic levels required by the heterotrophs), and the better oxygenation of the upper water layers. Convergent morphology of the plankton represents adaptations for suspension in the water column, for movement within this water mass to increase nutrient uptake, and for protection against grazing or predation. Necessary attributes for cosmopolitan species include eurythermy and euryhalinity. The patchiness of plankton diversity results from small-scale variations in water masses, the low level of interorganism contact or competition, and the possibility of rapid exploitation of favorable conditions by species present in the local area. Parallel evolution, radiation, and extinction of the various components of the oceanic plankton are similar in pattern to an ecologic succession — early evolution and conditions following major periods of extinction being homologous with the physically controlled or immature modern ecosystem associated with high stress levels and characterized by high net but low gross productivity, low diversity but great intraspecific variability, and small biomass. Evolutionary radiation is associated with more stable physical conditions and, like the seral progression, of an ecosystem, results in high diversity but less intraspecific variability. Increased biological interaction leads to higher gross but lower net productivity, hence more efficient energy and resource utilization. The drop in gross oceanic productivity at times of major extinction is associated with low diversity and decreased rate of accumulation of biogenic ooze, hence the apparent worldwide disconformities, as at the Cretaceous-Tertiary boundary, even in the deep sea.

Surface sculpture of the wall in Lower Paleozoic acritarchs

Taxonomy, 11 new genera, 12 new species, morphology, terminology for surface sculpture, Ordovician, Silurian, Oklahoma, Indiana

PHYTOPLANKTON: BELOW THE SALT AT THE GLOBAL TABLE

The abundance and diversity of marine phytoplankton and the geologic timing of its major innovations and extinctions show a broad but inverse relationship to stages of terrestrial plant evolution. Successively, the first appearance of land plants, and the later major increases in global live terrestrial biomass and dead biomass in the form of plant litter, peat, coal, and soil humus, increased the retention on land of carbon, nitrogen, and phosphorus, and decreased the amount of these nutrients that was transported by rivers to the seas. Each major increase in terrestrial nutrient retention resulted in extensive changes in the marine ecosystem, as it adapted to the new conditions. From its time of origin in the early Paleozoic, the terrestrial biota figuratively occupied the position at the head of the table, and only the unutilized nutrient excess trickled down to the oceanic phytoplankton and its dependent food web.

Possible eucaryotic algae (Bangiophycidae) among early Proterozoic microfossils

Recent data concerning extant planktonic red algae, chrysophytes, and haptophytes suggest possible reallocation of certain previously described middle and late Precambrian microfossils to one or more of these eucaryotic groups. Both binary fission and budding reproductive methods characterize Huroniospora of the Gunflint Iron Formation and Palaeocryptidium of the Bohemian Proterozoic. Their reproduction, morphology, habitat, and wide geographic distribution, as well as phylogenetic interpretations based on morphology, life cycles, and biochemistry of extant algae, suggest possible assignment of the Precambrian fossils to the unicellular red algal Order Porphyridiales (Subclass Bangiophycidae) rather than to the procaryotic blue-green algae or to the terrestrial fungi as recently suggested. Living Porphyridium may show peripheral multiple budding, with the resultant small cells held in the mucilaginous sheath that surrounds the parent cell, suggesting a similar relationship of Eosphaera tyleri Barghoorn and the Type 4 organism of Hofmann and Jackson. Eucapsis ? from the Paradise Creek Formation also might be referable to the Rhodophyta (spore packets of Bangiales) or Chromophyta (colony stage of Haptophyceae or Chrysophyceae) rather than to the blue-green algae. Reassignment of the Gunflint taxa to the red algal Subclass Bangiophycidae would make this the earliest fossil record of this group; preservation of these unicellular organisms is due to the exceptional nature of the enclosing chert. The suggested reassignment also would date the evolution of the eucaryotic cell and of vegetative mitotic cell division by binary fission and budding by at least 1.9 × 10 9 yr B.P., about the time previously hypothesized as representing the final transition from an anoxic to an oxygenic atmosphere. Genetic recombination resulting from sexual reproduction, with nuclear fusion and meiosis, first appeared in red or green algae at some time within the succeeding 1 b.y.

A revision of mid-Cretaceous textularian foraminifers from Texas

As Cretaceous species previously placed in Bigenerina, Siphotextularia, and Textularia differ from typical Cenozoic representatives of these genera in having solid non-canaliculate walls, 16 species from the Fredericksburg and Washita Groups (Albian-Cenomanian) of Texas and Oklahoma have been restudied. The new genera Heterantyx with type species H. antonovae sp. nov. and Quasispiroplectammina with type species Spiroplectammina longa are assigned to the family Spiroplectamminidae. A new family Textulariopsidae is proposed for basically biserial taxa with solid walls and includes Plectinella, Textulariopsis, of which two species T. lechriosa and T. texhomensis are new, the reinstated genus Bimonilina, with a new species B. reciprocata, and three new genera, Aaptoioichus, Haimasiella and Minyaichme.

Peridinialean cyst affinity rather than gymnodinialean motile stage of the late cretaceous dinoflagellate dinogymnium

TAPPAN, H. & LOEBLICH, A. R. JR. 1977. Peridinialean cyst affinity, rather than Gymnodinialean motile stage, of the Late Cretaceous dinoflagellate Dinogymnium. Trans. Amer. Micros. Soc., 96: 497-505. Morphological comparison of fossil Dinogymnium to both motile cells and cysts of living representatives of the orders Gymnodiniales and Peridiniales suggests an affinity with the modern family Lophodiniaceae (Peridiniales). The thick, acid-resistant, highly punctate to perforated wall resembles the exospore layer of the resting zygote cyst of Woloszynskia and probably of Lophodinium. The meridional ridges of some Dinogymnium, interrupted only by the median cingulum, are similar to features of Lophodinium. The archeopyle of Dinogymnium develops at the time of excystment. The rarely present flagellar pores result from the late retention of the flagella by the planozygote, prior to completion of the thick cellulosic endospore layer of the wall of the later hypnozygote stage. Within the perforated exospore, this thicker endospore layer protects the pre-meiotic zygote, although the cellulosic composition precludes its preservation. Other than the endoskeletal Actiniscaceae, all fossil dinoflagellates thus appear to represent cysts, and from analogy with modern species, probably all are hypnozygotes.

PROTISTAN PHYLOGENY: MULTIPLE WORKING HYPOTHESES*

Summary The method of the multiple working hypothesis is best applied to those subjects in which, while much is known, more remains to be known, a description which certainly is applicable to the Phylogeny of the Protista. Although various proposed phylogenies have been stoutly defended by their authors as unassailable, each has been based on one or another line of evidence, generalization or previous assumption which is contested strongly by others. Previous workers have regarded the Protista as animals or as plants, as one distinct kingdom, or as including representatives of two, three or as many as 13 kingdoms. Classifications and phylogenetic interpretations have been based on various aspects of morphology, cytology, ultrastructure, biochemistry, physiology, life cycles, or the fossil record. Each resulting classification has much supporting evidence but leaves unanswered other vexing problems. The present symposium includes only a sampling of the types of approach currently being used, but may aid in stimulating additional interest and study of the highly diverse and intriguing organisms known as the Protista.