EARLY MIDDLE DEVONIAN ARTHROPOD REMAINS FROM THE TROUT VALLEY FORMATION OF NORTH-CENTRAL MAINE, USA

Early evolution of terrestrial arthropod faunas took place between the late Silurian (Pridolian: Ludford Lane fauna of England) and the middle Devonian (Givetian: Gilboa fauna of New York). Ludford Lane animals included two myriapods and a trigonotarbid, as well as fragments of eurypterids and aquatic scorpions. The Rhynie Chert of Siegenian (middle Early Devonian) age yielded collembola (the first hexapods known in the fossil record), mites, spiders and scorpions. The Gilboa fauna yielded the first undisputed true insects in the fossil record. The Trout Valley Formation of north-central Maine is believed to be early Middle Devonian (Eifelian) in age and thus uniquely positioned to offer new insight into early origins of insects and the diversification of terrestrial arthropod faunas.

Previous study of the Trout Valley Formation has focused primarily on identification of the rich flora of vascular plants, including Pertica quadrifaria, the Maine state fossil and the "giant" in the flora at perhaps as much as 4-5 m in height. The only previous animal fossil reported from the Trout Valley Formation was of a single Eurypterid scale.

Preliminary study of the detailed stratigraphy, sedimentology, and non-plant paleontology of the formation has just recently been undertaken. Samples collected in hopes of recovering arthropod remains ranges from 3-30 kg in total weight. In the summer of 2001, the first small arthropod remains were recovered from HF-insoluble residues >0.5 mm that were derived from a sample of Pertica-bearing rock. The specimens are carbonized and only slightly flattened, but are very rare: only one arthropod fragment was found per several thousand carbonized plant fragments. At least one other sample yielded abundant carbonized plant fragments but no arthropod remains.

Although not yet identified, these fossils nonetheless suggest that further study of the Trout Valley Formation strata may yet yield important new insights into the early evolution of land animals. It is hoped that processing of additional samples from different stratigraphic levels will yield additional specimens and perhaps even reveal faunal changes; this work is currently underway.

Our thanks to NSF for funding this study, and particularly to the Baxter State Park Authority and Irvin Caverly, Jr., Director, for permission to work within the park limits.