LOWER MIDDLE DEVONIAN EURYPTERID REMAINS FROM THE TROUT VALLEY FORMATION OF NORTH-CENTRAL MAINE

The fossiliferous terrestrial to transitional Trout Valley Formation of early Middle Devonian age lies entirely within Baxter State Park in north-central Maine. This study's objective was to explore evidence of early terrestrial arthropods. Samples were collected from twelve sites; materials from two sites have been studied intensively. Broken rock samples were inspected over all surfaces with a dissecting microscope, then dissolved in 48% HF, and residues dry-sieved into 0.25-0.5 mm, 0.5-1.0 mm, 1.0-2.0 mm and >2.0 mm size ranges. All sample residues were picked under a microscope at 3.5X; recovered arthropod remains were mounted on modified microfossil slides. Paleoenvironments for the two study sites represent estuarine and braidplain settings. The estuarine facies consists of siltstone and fine to coarse sandstone cycles of various scales. Braidplain facies consists of a basal conglomerate of an undetermined thickness, overlain by cycles of granule conglomerate, very coarse sandstone, coarse to medium sandstone, and sandy mudstone. The estuarine sample yielded the only arthropod fragments thus far identified, while the braidplain sample had the greatest density of fossils and best preservation, although these were solely of plant material. All fossil remains recovered have been graphitized; arthropod remains are three-dimensional and only slightly flattened. All recovered arthropod remains were material within the 0.25-0.5 mm sieve range. The parts are so small, however, that accurate identification is difficult. At least one body fragment apparently is derived from the Eurypterid family Stylonuridae, based on well-developed sculptural tubercles and knobs. A terminal tarsal (leg) segment bearing a single ancillary spine, and a stout intermediate leg segment, are more consistent with the leg structure of Grossopterus of the family Hughmilleridae. Both are consistent with the known age of the Trout Valley Formation. To date, the braidplain facies has only yielded large quantities of plant remains. Based on other Paleozoic studies of terrestrial arthropods this setting may yet yield early terrestrial arthropods. Further macerations are planned.