ABSTRACT. Recovery of a femur of an adult Pleistocene giant beaver (Castoroides ohioensis) from a cornfield in Whitley County, Indiana, prompted an analysis of the palaeoecology of the site. Inspection of historic maps and more recent United States Geological Survey (USGS) topographic maps facilitated reconstruction of the pre-disturbance physiography of the site. What is currently a ditched agricultural area was once an extensive shallow lake associated with Spring Creek, which drains into the Eel River. The lake occurred on the interlobate Packerton Moraine created during Wisconsin glaciation. Analysis of subfossils taken from the deepest limnogenic sediments (170 cm) to the upper limit of the peat layer (60 cm) indicates that the lake was eutrophic, mineral-rich, and surrounded by boreal forest for much of its existence. A radiocarbon date of 11,240 ± 80 yr BP taken within 10 cm of the upper limit of limnogenic sediments, suggests that the lake was extinguished at an early time, perhaps before the d emise of the boreal forest. The lake was succeeded by an emergent marsh and finally a peat-forming wetland dominated by bulrushes (Scirpus spp.). Anthropogenic re-routing of Spring Creek and other ditching has desiccated the wetland, and only farmland remains. Thirteen plant species and 16 animal species (mostly mollusks) were recovered from the site. The gastropod assemblage was similar to other late-glacial and Holocene marls with only a few exceptions. One species recorded in the deposit, Lyrnnaea haldemanni, is no longer extant in Indiana. Helicodiscus parellelus and Uniomerus tetralasmus are reported as new subfossil records for the region. The giant beaver remains are presumed to have been deposited circa 10,000 yr BP, the same time that the species is thought to have gone extinct.

Keywords: Castoroides, Gastropoda, Indiana, lakes, macrofossil, palcoecology, peatland, Pleistocene

The giant beaver, the largest rodent of the North American Pleistocene, is surrounded by controversy. Much of this controversy involves whether or not the Pleistocene giant beaver (Castoroides ohicensis) shared feeding and behavioral characteristics with the modern beaver (Castor). Castoroides ohicensis attained lengths of 1.9-2.2 m (6.2-7.2 feet) and weights of 90-125 kg (200-275 lbs) (McDonald 1994). Early studies concluded that the giant beaver felled trees and built dams as does the modern beaver (e.g., Moore 1890; Hay 1912; Cahn 1932). Moreover, the medial "pinching" of the internal pterygoid plate of the skull, which constricts the posterior end of the nasal passage into upper and lower vents (Moore 1890; Hay 1912; Stirton 1965), was thought by Stirton (1965) to offer a greater air reserve for the extended underwater activity that is so common in Castor. Later studies suggest that the incisors were not efficient in cutting trees, and that the giant beaver did not, therefore, construct dams (Powell 1948; Stirton 1965; Holman 1975, 1995; Kurten & Anderson 1980; McDonald 1994). Furthermore, Hay (1912) had long before noted that the "pinching" of the internal plerygoid plate and other alterations of the skull had been an accommodation for the insertion of large internal pterygoid muscles into the pterygoid fossae, rather than...