ENVIRONMENTAL AFFECTS ON THE SKELETAL PHENOTYPE OF A FOSSIL BRYOZOA (RHOMBOPORA)

Bryozoans are colonial, mostly marine, filter feeding organisms that generate calcareous skeletons that are generally well preserved. The phenotype (skeletal hard parts) of an individual within the colony is determined by the genetic code and by the environmental conditions during the time of the colony's growth. Studies of evolution in paleontology generally assume that the genotypic influence on the physical characteristics is dominant. However, environmental factors can also play a role in the formation of the external characteristics of an organism. By measuring zooecial characteristics (center of aperture along the branch, center of apertures diagonally, and the perpendicular width of the branch) along individual branches of a large proposed single colony of Rhombopora, from the lower Carboniferous of Ireland, variation can be documented among the branches and within each branch. Through single factor analysis of variance, the significance of each character within and among branches can be determined. Because a colony of Bryozoa are composed of genetic clones the genetic code for individual zooids within the colony is the same; therefore, fluctuating measurements of a single characteristic suggest morphological changes consistent with a changing environment. Patterns found in the data of two characteristics also suggest short term (calendar scale) episodic environmental controls which in turn influence zooecial growth habits.