Subsurface Laboratory Methods 105 



Radiolaria 



Radiolaria are single-celled, pelagic, open-sea, marine Protozoa hav- 

 ing diameters of about 0.1 to 0.5 millimeters. The skeleton or shell 

 (fig. 45), consisting of silica which is secreted by the protoplasm, makes 

 up an important part of the animal. Little attention has been given to 

 fossil radiolarian faunas because of the complex classification, general 

 scarcity, and difficulties encountered in procuring well-preserved speci- 

 mens. The classification of this group of organisms is based upon the 

 structure and composition of the hard parts. 



The majority of the many forms developed within the Radiolaria are 

 adaptive to flotation and to lowering the rate of sinking in the water. The 

 presence of long spines, many of which are multiplied, of surface spines and 

 thorns, and the high development of the hat or cuplike shape of the lattice- 

 shell in some are all responses to a reduction in the rate of sinking. These 

 structures also allow less effort on the part of the animal to keep it well within 

 the photosynthetic zone. . . . Radiolaria occur in all the seas of the world, 

 in all climatic zones, and at all depths. However, the Pacific Ocean appears 

 to be the richest both quantitatively and qualitatively in these creatures, ex- 

 celling both the Indian and Atlantic oceans.^^ 



Radiolaria should be more seriously considered in the future by 

 micropaleontologists as a basis for establishing long-range correlations 

 because of their pelagic character and the siliceous nature of their skeleton. 



CONODONTS 



Conodonts are small, tooth-shaped, single- or multiple-pointed, or 

 platelike fossils occurring locally and in considerable number in Paleo- 

 zoic shales (fig. 46). These structures have been interpreted by various 

 workers as fish remains, annelid jaws, and gastropod teeth. In greatest 

 dimension they range from one to two millimeters. For practical purposes, 

 according to Ellison,^*' conodonts can be divided into four groups as 

 follows: (1) fibrous, (2) simple cones, (3) blades and bars, and (4) 

 platforms. Ellison states further: 



The fibrous and simple cone groups have many genera that serve as ex- 

 cellent guides to the Ordovician. The blade and bar group is mainly long 

 ranging. However, a few genera serve as guides in the Ordovician, Devonian, 

 and Mississippian. The genera in the platform group are best guides to beds 

 younger than Silurian. Many of these are remarkably restricted. 



Ellison ^^ concludes that (1) the composition of conodonts is the 

 same as the mineral matter in fossil and modern vertebrate hard parts; 

 (2) conodonts may be classified as fish or lower vertebrates on the basis 

 of their composition, size, shape, assemblage associations, internal struc- 



*' Clark, B. L., and Campbell, A. S., Eocene Radiolarian Faunas from the Mt. Diablo Area, Cali- 

 fornia: Geol. Soc. America Special Paper 39, pp. 1-112, 9 pis., 1942. 



^'Ellison, S. P., Jr., Conodonts as Paleozoic Guide Fossils: Jour. Paleontology, vol. 30, no. 1, pp. 

 93-110, 1946. 



"Ellison, S. P., Jr., The Composition of Conodonts: Jour. Paleontology, vol. 18, no. 2, pp. 133- 

 140, 1944. 



