Research Training Program

Smithsonian Institution
National Museum of Natural History

PROJECT SUMMARY
1995

Gene Hunt
Duke University
Durham, NC
Ralph Chapman
Supervising Scientist
Department of Paleobiology
"The Research Training Program is the opportunity of a lifetime for an aspiring young scientist. There is no other program that can combine an excellent research internship with the unmatched resources of the National Museum of Natural History."

Growth and Variation in Agnostic Trilobites

ABSTRACT
Agnostids were a morphologically distinct group of trilobites that were small, eyeless, with large pygidia and only two thoracic segments as adults. Although the ontogenetic sequences of some agnostics have been described, there has been almost no quantitative research done on their growth and shape. Using both an ocular micrometer and a video digitizing system, measurements were taken of the cephala and pygidia of 2 species of agnostic trilobite: Peronopsis interstricta and Agnostus pisiformis. Bivariate, multivariate (Principal Components Analysis) and landmark shape analyses (RFTRA) were performed to characterize and quantify the shape change that occurs throughout the ontogeny of these two agnostic species. The results of the analyses may be summed by the following: 1) All three analytic methods indicated that the amount of shape change occurring is relatively small 2) Instar clusterings were not very discrete for either species 3) PCA and landmark shape analyses both revealed that certain dimensions of the cephala and pygidia tend change consistently with respect to one another 4) The landmark shape analyses refined the PCA results by revealing the timing and direction of localized shape changes 5) Landmark shape analyses of published drawings of juvenile stages (meraspid) of Agnostus pisiformis suggest that the large amounts of shape change may be concentrated in juvenile stages of agnostics.

This research was supported by a grant from the National Science Foundation Research Experiences for Undergraduates program, Award Number BIR-9300225.

Letter of Gratitude