Superb Isotelus gigas Trilobite

Description: Isotelus gigas is an Asaphid trilobite (Order: Asaphida; Family: Asaphidae) coming from the famous Walcott-Rust Quarry. The Walcott-Rust Quarry was discovered in 1870 by Charles Doolittle Walcott of Burgess Shale fame and William Palmer Rust. Many well-preserved trilobites were found there and both Walcott and Rust sold them to collectors and institutions. It is Walcott’s association with Louis Agassiz of Harvard University that encouraged him to pursue a career in academic rather than commercial paleontology. The site was subsequently forgotten, only to be reworked by Tom Whiteley starting in 1990. Many excellently preserved specimens have been recovered from this site which is known as an obrution Lagerstätte, signifying a site in which the specimens were rapidly buried. This is a fine prone example of a trilobite whose maximum length exceeded 40 centimeters. It is part of a triumvirate of huge trilobites (Isotelus gigas, Isotelus maximus & Isotelus rex) whose largest known complete example is 70 centimeters in length! Isotelus gigas is a trilobite that undergoes ontogenic changes. As the trilobite grows, the genal spines degenerate until mature adults have none remaining. While the length of the genal spines varies with age, the size at which they are lost can vary from location to location within the trilobite’s range. The streamlined shape is indicative a trilobite that made its living plowing through the sediment in search of a meal. Notice the fine pitting of the surface of the exoskeleton. These pits are thought by some researchers to have harbored fine sensory “hairs” which allowed the trilobite to detect nearby predators and potential prey.