A Field and Laboratory Study of the Edicaran Fossils of Hewitt's Cove: Evidence of Tectonic Deformation and Consideration of Paleobiology

Authors

Walter Persons, Macalester College

Document Type

Honors Project On-Campus Access Only

Abstract

Ediacaran fossils have baffled scientists since their original discovery in 1868. As the oldest unambiguously organisms with tissues, Ediacaran organisms (or simply Ediacarans) represent a key stage in the evolution of life, and understanding their fossil record is essential to understanding the status of life prior to the great radiation of forms seen in the Cambrian. However, the bizarre shapes and structures of many Ediacarans have made placing them in phylogenetic context with modem taxa and determining their ecological roles difficult. Although a few remarkable sites -- such as the famous Mistaken Point and the Ediacaran Hills localities -- have yielded an. abundance of extremely well preserved specimens, the overall Edicaran record is poor, and the vast majority of specimens give few clues to the nature of the whole organisms. This has made Ediacarans difficult to interpret and identify. Here, the Ediacaran fossils of a 575 Ma argillite bed of the Cambridge Formation, exposed at Hewitt's Cove, Massachusetts, are described, and the fossils are considered in relation to current theories on Ediacaran paleobiology. All documented fossils belong to a single genus, Aspidella. The fossils were found to be elliptical in shape and to all have a similar orientation with respect to each other and to bedding. Their consistent shape and shared orientation are interpreted as likely results of tectonic stretching. This interpretation is consistent with all previously described Aspidella specimens. Size distribution among the Aspidella fossils gives no indication that more than one species is present. Examination of the size distribution also showed large members of the population to be up to 15 times the size of small members, casting doubt on the theory that Aspidella reproduced through equal (one-splits-into-two) divisions. The argillite rocks are composed of thinly laminated sediments, and thin section examination of the Aspidella fossils shows no evidence of disturbance around the fossils and, thus, no evidence that Aspidella moved through the sediment while alive (i.e. bioturbation).

Recommended Citation

Persons, Walter, "A Field and Laboratory Study of the Edicaran Fossils of Hewitt's Cove: Evidence of Tectonic Deformation and Consideration of Paleobiology" (2008). Geology Honors Projects. 2.
https://digitalcommons.macalester.edu/geology_honors/2