The influence of heterochrony on the stratigraphic occurrence of Morozovella angulata

Praemurica uncinata displays pronounced allometry during its evolutionary t ransformation into Morozovella angulata, an important species in Paleocene planktic foraminiferal biostratigraphy. The allometry is such that smaller specimens of P. uncinata resemble large specimens of the descendant, M. ang ulata. Biometric analysis of populations spanning this paedomorphic evoluti onary transition reveals that the event is recorded over an interval of 10. 69 meters in sediments from the DeSoto Canyon, Gulf of Mexico, and involves specimens ranging in size from less than 100 to more than 300 mu m, Over t his size range, failure to recognize the interdependence of size and shape can lead to discordant zonations when biostratigraphers identify the first appearance datum of Morozovella angulata after using different sieve sizes during standard laboratory treatment of their samples.