A LATE PLEISTOCENE COLEOPTERAN FAUNA FROM PRESUMPSCOT FORMATION SEDIMENTS IN PORTLAND, MAINE

The Presumpscot Formation of coastal Maine and southern New Hampshire consists of early postglacial glaciomarine silts deposited on an isostatically depressed coastline. Excavations in summer, 2007, revealed terrestrial organics, including logs, embedded at the base of these deposits, ¹⁴C dated at 11,750 ± 55 and 11,900 ± 55 yrs b.p. Stratigraphy of the site, plant remains and dating are discussed by Thompson et al. and Griggs and Miller (this session).

The organics yielded a diverse terrestrial arthropod assemblage, dominated by Coleoptera (beetles). The fauna indicates climatic conditions comparable to modern Maine, and a forested coastal environment with local open sand and marsh; all species thus far identified occur in the modern Maine fauna.

Elaphrus clairvillei, Bradycellus badipennis, Agonum (Melanagonum) sp. and Bembidion versicolor are ground beetles (family Carabidae) that live on organic-rich, wet substrates, shaded by standing vegetation. This habitat would have suited the rove beetle Stenus (Staphylinidae), the water scavenger beetle Cercyon (Hydrophilidae) and the moss-feeding pill beetle Cytilus alternatus. Plateumaris, represented by numerous small fragments, is a leaf beetle (Chrysomelidae) that feeds on emergent aquatics, particularly sedges. Predaceous diving beetles (Dytiscidae) are represented by at least two fragments of Hydroporus sp., suggesting at least minimal standing fresh water in the source area.

A carpenter ant (Camponotus sp.) is consistent with logs found in the deposit, as are numerous bark beetles (Scolytidae) representing at least three species. A forest duff component is suggested by the presence of at least six individuals of the detritovore Aegialia rufescens (Scarabaeidae: Aphodiinae), and the round fungus beetle Agathidium (Leiodidae). Orsodacne atra is leaf beetle that feeds on wildflower pollen as an adult and suggests at least some open space.

At least localized open, sandy substrates are also indicated by Bembidion nitidum (Carabidae) and Aegialia (s.s.) sp., the latter represented by multiple specimens; members of this subgenus are generally restricted to coastal sand dunes and comparable environments.

Work on the fauna is continuing.