99 Evolution of Life in the Cambrian Seas: Biotic, Biogeochemical, and Sedimentological Contexts, Part I

This session is dedicated to studies that illuminate the biotic, geobiological, sedimentological, and geochemical contexts of the evolution of early animal life in the oceans, with a particular focus on the Cambrian Period.

Monday, 20 October 2025
8:00 AM - 12:00 PM
HBGCC, 304B

Investigating the Cambrian seaweed conundrum with new macroalgal morphologies from the Burgess Shale

Paper number: 99-2
Program: Technical Sessions
Time: 8:20 AM – 8:35 AM

Authors

Abstract

The Burgess Shale Formation is a well-known lagerstätte that provides key details about the radiation of animal life during the Cambrian. However, the non-calcifying macroalgae (“seaweed”) component of this biota has remained a largely untold story, with recent work highlighting the importance of modern restudy. In particular, several species that were first described as macroalgae by Walcott (1919) have been reinterpreted as organic hemichordate tubes (Dalyia, Margaretia, Yuknessia). Understanding the macroalgae in the Burgess Shale is important as these organisms create benthic seafloor habitats, influence biogeochemical cycles, and possibly represent a nutrient source for early animals. Macroalgae show several diversification events during Earth’s history, but Cambrian macroalgae inherit basic morphogroups (e.g., ribbons, tubes) from the Ediacaran Period while animals rapidly diversify. This presents a conundrum that has been hypothesised to be related to a persistence of relatively low grazing pressures. The Royal Ontario Museum (ROM; Toronto, Canada) Burgess Shale collection presents an opportunity to survey Cambrian macroalgae at various localities in the Burgess Shale Formation, which have been collected over the last 50 years with high stratigraphic control, as a means to further evaluate this hypothesis. Here, we will review the Burgess Shale macroalgae and their distribution across three sites in Yoho National Park, British Columbia, Canada (Walcott Quarry, Tulip Beds and the Trilobite Beds). In addition, we will present two new species of macroalgae and discuss morphological adaptions related to sediment binding (via haptera) and benthic tiering.  These results will aid in addressing the "Cambrian seaweed conundrum" and understanding the ecological influence of macroalgae on early animal communities.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413406

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