Latest Ordovician to earliest Silurian colonial corals of the East-Central United States - BAP #347
A distinctive assemblage of colonial corals occurs in uppermost Ordovician (Gamachian) to lowermost Silurian (Lower Rhuddanian) strata within the east-central United States. This Edgewood Assemblage is strikingly different from Late Ordovician assemblage that preceded it in other parts of the North American cratonic interior, and differs from the Silurian assemblage that succeeded it. The Edgewood Assemblage existed during an important time of global environmental change and mass extinction. Some of the taxa have an Ordovician character; these include the youngest North American tetradiid, which is among the last representatives of an important Ordovician order. Other taxa represent first appearance of typically Silurian forms: the oldest definite plasmophorid, the earliest North American Halysites, and the first pyconostylid. Our study analyzes this significant assemblage in terms of biostratigraphy, biogeography, taphonomy, paleoecology, and intraspecific variability; the Silurian assemblage is also documented. With this information, we contribute to the knowledge of corals and the history of biological and physical events during this critical time interval, and to the solution of geologic problems such as the age, correlation, and depositional environment of stratigraphic units.
Comparisons of patterns of variation in different species indicate that inherent variabilities of different coral orders are not the same, and that certain types of variation tend to recur among species and among orders. Some of the general similarities and differences among taxa are linked principally to structural factors that controlled the ways in which colonial corals grew. Genotypic and ecophenotypic factors acted in concert with the structural control of growth to determine variations within individual species.
G.A. Young, R.J. Elias
Pages: 153, 21 pls., 34 text-figs., 22 tables
Year published: 1995