PALEOECOLOGICAL CONSIDERATIONS OF GROWTH 

 AND FORM OF FOSSIL PROTISTS 



Paul Tasch 

 Department of Geology, University of Wichita, Wichita, Kansas 



Protists known as fossils range from bacteria (0.5 n in size) lo foraminifers 

 and tintinnids (from 10 to 1000 n or greater in size). Some protists, for exam- 

 ple, bacteria and lime secreting algae, are first recorded as fossils in rocks of 

 Pre-Cambrian age; others, including radiolarians, hystrichosphaerids,* and 

 foraminifers, apparently make their first appearance in Paleozoic time. Finally, 

 Mesozoic rocks bear the first record of a dominant element of the living phyto- 

 plankton, namely, the diatoms, as well as other protists, such as, the coccolitho- 

 phorids, silicoflagellates, tintinnids, and the Chrysomonadina. 



There are numerous studies by protozoologists on variations in size and form, 

 as well as structure and physiological characteristics of protozoans. They have 

 found it necessary to distinguish races, varieties, and strains within a given 

 species to italicize the observed variation.- By contrast, studies on the skeleton 

 of various protists in which the differential morphology, as well as causative 

 factors, is considered, are relatively few. 



Thompson^ approached protist skeletal morphology and factors influencing 

 it from a different point of view. With mathematical-physical considerations, 

 he reached some insightful conclusions. One need but regard the minute mass 

 of protoplasm that is involved in secreting a protist skeleton as a fluid drop 

 and subject to all the physical forces known to affect such a drop to explain its 

 form by the laws of surface tension. It is apparent that many protists tend to 

 have skeletons of spherical configuration. The sphere, of course, offers the 

 least surface area for a given volume. Because a chain of such drops is possible, 

 and any individual drop can be acted on by gravity, the observed variation in 

 protist skeletal morphology can be simply explained. 



Ecology and Paleoecology of Protists 



There is a very extensive literature on ecological factors that influence 

 growth of living phytoplankton.^"^ Nitrogen and phosphorus are primary 

 nutrient factors.^ Other elements of importance include: silicon, ^'^^ iron,i-'i* 

 and possibly manganese.^ A sudden increase in vitamin B12 may be the stimu- 

 lus for certain phytoplankton blooms.^* Among physical factors, tempera- 

 ture and salinity are effective "selective agents" on the species level. The 

 species specific salinity response has recently been attributed to "special re- 

 quirements for the concentration of sodium ions in the medium. "^^ Radiation 

 is obviousl}^ of primary importance affecting as it does, latitudinal and seasonal 

 variations in phytoplankton production. In addition, the photic zone must 

 be replenished by nutrients from deeper waters. This redistribution is attained 

 in coastal waters by vertical circulation.^''' 



* Affinities to dinoflagellates are indicated for several, but not all, hystrichosphaerids.' 

 Tasch (in press) has found undoubted dinoflagellates in the Permian of Kansas. These were 

 associated with hystrichosphaerids. 



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