2010 GSA Denver Annual Meeting (31 October 3 November 2010)
Paper No. 125-1
Presentation Time: 1:30 PM-1:45 PM


HAGADORN, James W., Department of Earth Sciences, Denver Museum of Nature & Science, 2001 Colorado Blvd, Denver, CO 80205, jwhagadorn@dmns.org, SCHOTTENFELD, Mariel T., Department of Geology, University of Massachusetts, Amherst, MA 01003, and MCGOWAN, Daniel, Department of Mechanical Engineering, University of Massachusetts, Amherst, MA 01003

Anomalocaridids have a circular mouth consisting of 32 inwardly-facing pointed plates that cap a plate-studded esophageal area. How these structures functioned or what they were used to eat is not understood. To address these knowledge gaps, we constructed CAD models of an anomalocaridid mouth and twelve possible trilobite ‘prey’, and characterized their response to different biting kinematics and stresses.

In life, anomalocaridid mouth plates were connected along their long edges by flexible tissue, and mouth plates, esophageal plates and preoral appendages were composed of unmineralized cuticle. The mouth could close like a sphincter, and its plates could have moved synchronously or moved asynchronously with opening initiated by four large cardinal plates. Whether moving in an inverted, everted, or in-plane position, a rapidly closing anomalocaridid mouth could generate sufficient external pressure change to allow suctorial feeding - yet no anomalocaridid mouth could close more than half-way.

To test the hypothesis that anomalocaridids ate trilobites, we conducted finite element analyses of how different biting stresses would deform and cause failure of twelve commonly malformed Cambrian trilobites. A spectrum of trilobite sizes, shapes, thicknesses, and ornamentation were subjected to both horizontal and vertical bite-impact angles, using the known range of anomalocaridid plate tip sizes. Young’s modulus, Poisson’s ratio, and ultimate tensile strength were derived from strain measurements on modern marine arthropod cuticle ranging from freshly molted Callinectes sapidus to well sclerotized claws of Homarus americanus. These cuticle material properties were applied to each possible combination of anomalocaridid biting geometry and trilobite type. In the absence of significant bending stresses, cuticle failure always occured at the locus of bite impact in all trilobites modeled; where bending stresses predominated, failure occurred near the axial furrow. FEA suggests that although tiny or protaspid trilobites could be eaten whole by most anomalocaridids, and some freshly molted trilobites could possibly be deformed by interacting with anomalocaridid mouth plates or preoral appendages, anomalocaridid mouth plates would break before most trilobite thoracic cuticle would fail.

2010 GSA Denver Annual Meeting (31 October 3 November 2010)
General Information for this Meeting
Session No. 125
Paleontology V - Predation and Biological Interactions
Colorado Convention Center: Room 503
1:30 PM-5:30 PM, Monday, 1 November 2010

Geological Society of America Abstracts with Programs, Vol. 42, No. 5, p. 320

© Copyright 2010 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.