Loxsomopteris anasilla, a New Fossil Fern Rhizome from the Cretaceous of Maryland

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A fusinized fern rhizome from the Lower Cretaceous beds of the Patuxent Formation (Potomac Group) in College Park, Maryland, is here described as a new genus and species. This rhizome is the first from a locality that was uncovered after the flooding of tropical storm Agnes in 1972. Locality and stratigraphy.-In June 1972, flooding that followed a tropical storm uncovered Cretaceous clays containing plant remains in College Park, Maryland, near Washington, D.C. The predominantly grey to dark grey color, sandy lithology, and mica content of the outcrop, as well as its geographic position to the west of overlying Arundel and Patapsco strata, indicate its placement in the Patuxent Formation (L. J. Hickey, pers. comm.), the lowest of the three of the Potomac Group. A preliminary examination of a pollen preparation from the fossil-bearing bed is consistent with its placement in Zone I of the Brenner (1963) and Doyle (1969) classifications. The age of this zone is probably Aptian, but may range into the Barremian (Fig. 1). Materials and methods.-Many fossils of gymnosperms and ferns corresponding to forms described by Fontaine (1889) and Berry (1911) occur in the clay lens, mainly as small fragments. Although some fragmentation probably occurred prior to fossilization, numerous planes of slippage (slickensides) in the clay are evidence of internal motion subsequent to burial. The clay material containing the plants was maintained in a wet condition until further preparation was possible. It was bulk macerated in hydrofluoric acid. Larger plant fragments were sieved out; then the smalle: fragments were sorted under a dissecting microscope. Some of the remaining residue was centrifuged and prepared for pollen and spore analysis. Fragments for sectioning were embedded in plastic, either in Epon 812 (50% A and 50% B mixture) or in Spurr Firm Embedding Medium. Sections were cut on a rotary microtome and mounted on microscope slides in Canada balsam. Observations and photographs were made using a Wild M-5 microscope and a Nikon S-Kt microscope with a combination of transmitted and reflected light. Photographs utilized Kodak Plus-X Pan film. Description.-The well-preserved rhizome is approximately 2 cm long and 5 mm in diameter, with several roots (2.6 mm in diam.), two nodes, and a covering of hairs (some pointed and some blunt) that is more dense at the nodes. The carbonized remains of the rhizome are preserved as fusain (Schopf, pers. comm.) of a type not derived through fire (Schopf, 1975). The cell walls are opaque, brittle,