The palaeobiology and systematics of some Jurassic bryozoa

Abstract

Morphological studies of some non-fasciculate Jurassic tubuloporinids and comparative studies of other cyclostomatous Bryozoa have enabled aspects of their palaeobiology to be elucidated and their sytematics to be revised. Skeletal ultrastructure ha been surveyed in a number of species and it relevance a taxonomic character assessed. Zooid structure and variation are considered. Factors influencing ontogenetic and astogenetic zonation is postulated. The functional morphology and genesis of tubuloporinid heterozooids have been elucidated. Quantitative studies have shown that ecophenotypic within-colony zooidal variation is high and tends to dominate between-colony comparisons of zoocium size. Differences in colony growth-form are a product of differing styles of zooecial budding, forms of budding zones, and positions of budding loci. Unilamellr, bilamellar, multilamellar, non-lamellar, and composite (Terebellaia) patterns of colony growth are described. 8 Jurassic tubuloporinid growth-forms are recognised and their ecological significant assessed by functional morphological inference and comparison with living analogues. Strengh and stability, integrated zooid feeding, and differential modes of resource utilization are shown to be reflected by colony growth-form. The ecological succession of bryozoan growth-forms is inferred. Three families of non-fasciculate tubuloporinids are recognised in the Jurassic; Stomatoporidae, Multisparsidae and Plagioeciidae. Emended diagnoses are given of 9 genera together with a key to the identification of all accepted genera and systematic descriptions of 15 species including two new species, Reptomultisparsa tumida and Reptoclausa porcata. The palaeoecology of Jurassic bryozoans has been examined and their distribution is shown to be largely facies controlled whilst species exhibit extended longevities.