MEASURING, MODELING, AND COMPARING GROWTH OF FUSULINIDS (FORAMINIFERIDA)

Fusulinids are late Paleozoic single-celled organisms that grow fusiform, granular calcite skeletons up to 1.8 cm and have an excellent fossil record. These benthic, shallow marine protists can occur in rock-forming abundance, and have been widely applied in biostratigraphic studies. Although, fusulinids have historically been important for biostratigraphic correlation in petroleum exploration, relatively little is known about their life histories and paleoecology. From fossil fusulinids, I measured features that correspond to parameters in functions for generating a mathematical coil (Raup, 1966). By manipulating variables of whorl translation and position relative to axis and aperture shape and expansion rate, the coiled test of most fusulinids can be quantified and compared directly to any other coil (natural and hypothetical). These methods have been developed and widely applied to mollusks, but have rarely been applied to single-celled organisms.

In this study, methods had to be adapted from molluscan coiling parameters. Independent reproducible results were obtained for most fusulinid specimens studied. Problems in applications of the method are associated with preparation of individual specimens (precise longitudinal sections required) and potentially poor preservation. Variations exists for all parameters within individuals, however, the magnitude of individual variation is far less than among species. Within the growth of an individual, there is a tendency for sequential non-random variation. Initial results demonstrate that the coiling parameters of S (the shape of the whorl), D (the distance of the generating whorl from the rotational axis), W (increase in the width of the whorl) as a combination serve to differentiate among fusulinid taxa in a theoretical coiling morphospace. This holds promise for direct comparison of both closely and distantly related groups in a wide range of paleobiological studies.