Crawfordsville crinoid fossil site

Crawfordsville Indiana is known for its spectacular crinoid faunal assemblage. There are more than 60 species of crinoids among more than 40 genera found in the Crawfordsville area. All major groups of Lower Mississippian crinoids represented: Cladids, Camerates, Disparids, and Flexibles. What is most noteworthy about the Crawfordsville crinoids is the size of the calices, with some approaching and even exceeding 10 cm in length, rendering them most appealing to collectors. A most appealing characteristic of this fauna is the amazing diversity of well-preserved specimens found in exquisite 3-D relief. While the sheer diversity alone is astonishing, the fact that many complete crowns with attached stems are found is a further attraction. Nearly half of all species are known from complete specimens. This Lagerstatt fossil site makes for a golden opportunity for researchers to formulate observations about the morphology, ecology, and behavior of the crinoids of Late Mississippian age.

The first crinoid calyx collected from the Crawfordsville, Indiana area was by 9 year old Horace Hovey in 1842, who was collecting "encrinites" along the banks of Sugar Creek for sale. The magnificently-preserved specimens have been sought after ever since by scholars and collectors alike. While crinoids are found in a number of locations in the Crawfordsville area, the most abundant beds are those of Corey's Bluff and along Indian Creek, both of which are currently thought to be within the Edwardsville Formation (approximately 340 million years old). The Edwardsville Formation is dated as Late Osagean Stage in central and southern Indiana.

The crinoids are found with differing stem lengths, allowing each to find its own feeding niche in the water column, using its filter-feeding apparatus to strain the food contained within its target stratum. Additionally, some crinoids with similar length stems were further subdivided according to the size prey species targeted. In these ways, the amazing diversity could be maintained while minimizing competition between species. Such a method of tiering has subsequently been found to be an important aspect of many seafloor communities.

Seafloor conditions in the Crawfordsville area were obviously vary favorable to the proliferation of crinoids, an environment that had both shallow water conditions and an influx of silt from a neighboring delta. The crinoids, living in high densities in their tired habitat were periodically buried alive by storm-generated slumping or silt flows. Such tempestites or turbidites must be of sufficient depth to prevent later re-excavation. Collectors are fortunate that the resultant siltstone deposits of Crawfordville are sufficiently soft to allow microabrasive preparation techniques to expose the crinoids in all their past glory, affording the treasures we see today.