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Publication Date
2023-5
First Advisor
Sara B. Pruss
Document Type
Honors Project
Degree Name
Bachelor of Arts
Department
Physics
Keywords
Geosciences, geoscience, paleontology, geobiology, ecology, paleoecology, early Cambrian, reefs, buildups, extinction, microbialite, archaeocythid, stromatolite
Abstract
Archaeocyath sponges are the first animal reef-builders of the Phanerozoic. Archaeocyaths, divided into two different subgroups—regular and irregular—based on the complexity of morphology, diversified greatly until the Stage 3 to Stage 4 boundary. By the end of the early Cambrian (Series 2 Stage 4), archaeocyaths faced total extinction. The exact timing of this extinction varies regionally. This research presents archaeocyaths that are stratigraphically younger than the extinction from several small patch reef mounds in the lowermost part of the upper unit of the Mule Spring Limestone near Split Mountain, Nevada (upper Stage 4). Thin section analysis revealed the presence of archaeocyaths and microbial fabrics, such as stromatolites, thrombolites, and encrusting microbes, along with other reef-dwelling organisms, including trilobites and echinoderms. Archaeocyathus, an irregular genus, was the only genus present and identified in the Mule Spring Limestone thin sections. Individuals of Archaeocyathus were found in all of the reef mounds. Fossil debris—trilobites and echinoderms—was sparse within the reef mounds but was abundant in beds below and regions between the mounds. Here, Archaeocyathus could represent the last gasp of archaeocyathan reef building in the early Cambrian before their extinction. The Mule Spring Limestone differs from the underlying Harkless Formation, as this was characterized by higher biodiversity and abundance of archaeocyaths and reef-dwellers. Thus, this occurrence of Archaeocyathus is interpreted to be an example of a dead clade walking—the last true archaeocyaths that persisted in this region beyond the archaeocyath extinction during mid-Stage 4. As some of the youngest-known archaeocyaths in Laurentia, the archaeocyaths of the Mule Spring Limestone provide an opportunity to better understand ii the environmental and ecological conditions surrounding animal reefs in the early Cambrian. It is possible that the irregularity and modularity of Archaeocyathus allowed this genus to briefly persist beyond the extinction of archaeocyaths in Laurentia.
Rights
©2023 Grace Karbowski. Access limited to the Smith College community and other researchers while on campus. Smith College community members also may access from off-campus using a Smith College log-in. Other off-campus researchers may request a copy through Interlibrary Loan for personal use.
Language
English
Recommended Citation
Karbowski, Grace, "Dead Clade Walking: Archaeocyaths in the Lower Cambrian Mule Spring Limestone, Nevada" (2023). Honors Project, Smith College, Northampton, MA.
https://scholarworks.smith.edu/theses/2560
Comments
v, 50 pages : color illustrations, charts. Includes bibliographical references (pages 46-50).