58-1 Did Harpiform Trilobites Evolve to Plow Sediment?: Finally Putting a 100-Year-Old Hypothesis to the Test
Session: Future Leaders in Paleontology
Presenting Author:
James BeechAuthors:
Beech, James D.1, Hebdon, Nicholas2, Dorgan, Kelly M.3, Soni, Priyanka4, Duncan, Jennifer L.5, Bottjer, David J.6(1) Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA, (2) Department of Geosciences, Baylor University, Waco, TX, USA; Invertebrate Paleontology, Natural History Museum of Los Angeles County, Los Angeles, CA, USA, (3) Marine Science Institute, University of Texas at Austin, Port Aransas, TX, USA, (4) Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA, (5) Marine Science Institute, University of Texas at Austin, Port Aransas, TX, USA, (6) Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA; Invertebrate Paleontology, Natural History Museum of Los Angeles County, Los Angeles, CA, USA,
Abstract:
During the Ordovician, trilobites of the order Harpetida and the superfamily Trinucleioidea evolved unusual cephalic brims, quite unlike any structure known in modern arthropods. Brimmed trilobites were broadly successful, but paleontologists still do not fully understand why the harpiform brim evolved or the role it played in their success. Many authors have speculated about the brim’s function, generating many untested hypotheses. We 3D-printed model cephalons with various brim shapes and moved them through natural sediments to test the hypothesis that the brim evolved as a sediment plow. We found that increased horizontal brim width allowed a cephalon to efficiently displace more sediment, while increased brim height merely impeded the cephalon’s progress. However, there is no clear evolutionary trend among harpetids or trinculeids towards wider or flatter brims, indicating that plowing did not exert a strong selective pressure on brimmed trilobites. This work also serves as a case study in researching taxa without modern biomechanical analogs, demonstrating that many functional hypotheses can be adequately tested by straightforward experimental methods.
Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025
doi: 10.1130/abs/2025AM-7483
© Copyright 2025 The Geological Society of America (GSA), all rights reserved.
Did Harpiform Trilobites Evolve to Plow Sediment?: Finally Putting a 100-Year-Old Hypothesis to the Test
Category
Topical Sessions
Description
Session Format: Oral
Presentation Date: 10/19/2025
Presentation Start Time: 01:35 PM
Presentation Room: HBGCC, 305
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