Geoscience Colloquia for Fall 2007 Semester
Friday October 19, 2007 3:00 pm
Dr. Marc Laflamme
Queen's University, Kingston, ON
Title: "The Ediacara Biota and Early Ecosystems"
Lapham Hall 262
The terminal Neoproterozoic Ediacaran Period marks a fundamental change in the early evolution of life, with the sudden appearance of large, soft-bodied and structurally complex eukaryotes (collectively referred to as the Ediacara Biota) after a billion years dominance by microscopic, morphologically simple fossils. The Ediacara Bitoa is a distinct group of centimetre- to meter-scale soft-bodied organisms preserved as impressions beneath event beds (storm deposits, turbidites, volcanic ash) that flourished some 575 to 543 million years ago.
The affinities of the Ediacara Biota have always been of great interest and controversy. Earliest attempts to classify these organisms, based on morphological comparisons with modern taxa, resulted in them being considered as primitive examples of crown groups of basal animals, principally jellyfish, flatworms, or sea pens. Over time, the Ediacara Biota have been regarded as representatives of a number of groups spanning several Kingdoms including prokaryotic colonies, marine fungi, algae, and lichens. The primary difficulty in elucidating the affinities of the Ediacara Biota lies in the fact that representatives of modern animal lineages, if present, are present only as stem-group members in the Ediacaran. For example, the Rangeomorpha, characterized by at least three orders of identical, repetitive "fractal" branching, represent an extinct clade of Metazoan-grade organisms that have no representatives in the Phanerozoic, thus representing a failed experiment in the early evolution of life.
The Ediacara Biota has a worldwide distribution, but the oldest known large and architecturally complex representatives of the Ediacara Biota are from the Avalon assemblage of Mistaken Point, Newfoundland, age-dated between 575 and 560 Ma. Mistaken Point has been interpreted as deep-water locality, composed of fine-grained turbiditic strata deposited well below storm-wave-base and the photic zone. The overwhelming majority of Ediacaran organisms from Mistaken Point comprise endemic members of the Rangeomorpha in addition to more cosmopolitan forms such as Charniodiscus. These organisms were the first to effectively partition the water column on a macroscopic level, resulting in a strikingly modern tiered ecosystem.