THE BEAR GULCH FAUNA AND THE RESEARCH VALUE OF THE UNIVERSITY OF MONTANA PALEONTOLOGY CENTER COLLECTIONS

The Bear Gulch Limestone, Heath Formation, well exposed in central Montana, stands as one of the outstanding Mississippian marine konservat lagerstätten in the United States. The fine preservation of diverse hard and soft-bodied fossil marine biotas of the Bear Gulch provides a rare glimpse into this kind of Mississippian life. Systematic studies have helped clarify a portion of the Bear Gulch invertebrate fossils, yet no detailed community study of the remarkable assemblages has been undertaken of the benthic invertebrates. The Bear Gulch is best known for soft-tissue preservation of fish, but there are abundant and diverse invertebrates remaining to be studied. The University of Montana paleontology collections contain an excellent survey of Bear Gulch biota, acquired since the discovery of the biota in the early 1960s. The Bear Gulch Limestone contains three limestone lenses, The Becket Beds, The Bear Gulch Beds, and the Surenough Beds. All three beds contain fossils, but only the Bear Gulch beds have been extensively quarried as it contains the finest fossils. The Bear Gulch fauna is considered to be ecologically restricted with respect to typical Mississippian communities. Missing are classic Mississippian organisms such as crinozoan echinoderms and trilobites. Instead, the invertebrate fauna is dominated by high-growing sponges, with lesser abundant ammonoids and nautiloid cephalopods, and inarticulate brachiopods, among others. A project currently underway, aims to describe the paleoecology of the Bear Gulch Limestone and compare it to other environmentally similar basins to discern if restricted communities are the rule or the exception for epicontinental seas. The extensive vouchered University of Montana collections provide preliminary results that are reported here.