Comparisons of Paleoenvironments, Taxa, and Taphonomy of the Late Carboniferous Garnett and Hamilton Quarry Localities, Eastern Kansas

Abstract

The Garnett and Hamilton Quarry fossil localities of Kansas represent one of the most comprehensive windows into nearshore terrestrial paleoecosystems of the Late Carboniferous, approximately 299-306 million years ago. Both localities contain exceptionally preserved flora, invertebrate, and vertebrate fossils. When rare comparisons are made between the two localities, it is typically done by investigating only one aspect. The goal of this project was to make direct comparisons between Garnet and the younger Hamilton locality, based on the paleoenviroments, fossil taxa, and taphonomy to gain a better understanding of how the two localities are similar and different. The paleoenvironment of Garnett is interpreted as an estuary/lagoon shore constrained to a channel during a transgression, whereas Hamilton is interpreted as a stream channel that grades into an estuary that terminates in a sediment lobe. Garnett and Hamilton each have a total of 126 taxa each, of which only two species and 17 genera are found at both localities. In general, both Garnett and Hamilton Quarry are similar taphonomically; however, Hamilton has the uniqueness of soft tissue preservation. Garnett and Hamilton have similar faunal and floral communities but with differences in the specific taxa present and in the dominant taxa. Garnet has a coelacanth and three taxa of sharks, whereas Hamilton's fish fauna is richer, including not only a coelacanth and five shark taxa but also an acathodian, two palaeonisciforms, a rhipidistian, and two lungfish. Both Garnet and Hamilton have diapsid and synapsid tetrapods. Garnet has the oldest known diapsid, Petrolacosaurus lwnsensis, whereas Hamilton has a derived form, Spinoaequalis schultzei, as expected given their relative stratigraphic positions. In surprising contrast, Hamilton has the more primitive synapsids and Garnet the more advanced fonns. The dominate plant life at Garnett is seed ferns, whereas at Hamilton it is conifers.