MIDDLE DEVONIAN ESTUARINE MACROFAUNA FROM THE TROUT VALLEY FORMATION OF NORTH-CENTRAL MAINE

The Middle Devonian (Eifelian) Trout Valley Formation outcropped in the northeastern corner of Baxter State Park, Maine, is noted for its abundant plant fossils and palynomorphs. However, to date, there have been no detailed reports of any invertebrate macrofaunal assemblages in this fluvial-to-marine sequence. Isolated eurypterid parts have been reported previously, the first in the 1960s, but no associated or additional benthic taxa have been recovered. During the summer of 2002, an outcrop of coarse-to-medium grained siltstone was discovered in which a restricted, transported invertebrate assemblage was preserved. The depositional environment is characterized by mega-ripples containing macrofossils in varied orientation. Fossils were most abundant at the crests of the mega-ripples, and surveillance of the troughs showed minimal fossil preservation. Similar sedimentological features in other parts of the stratigraphic section are indicative of an estuarine and tidally influenced depositional regime.

The macrofauna consists, in rank order abundance, of bivalves, spiral and planispiral gastropods, possible nuculid gastropods, (?) ostracodes, brachiopods, and one nearly complete eurypterid, cf. Erieopterus. The most common bivalve is cf. Phthonia sectifrons, distinguished by its elliptical shape with a short anterior end, which ranges in length from 1 cm to 3 cm. Spiral gastropods are small, and are all roughly 2 mm in size. The eurypterid is approximately 3 cm by 1.25 cm with virtually all parts preserved in a single bedding plane. This is the first report of a nearly complete eurypterid of any age from Maine.