3.Nishida Riesco.Pmd

11 PRELIMINARY REPORT ON PERMINERALIZED PLANT REMAINS POSSIBLY FROM THE PALEOCENE CHORRILLO CHICO FORMATION, MAGALLANES REGION, CHILE Harufumi Nishida1, Kazuhiko Uemura2, Kazuo Terada3, Toshihiro Yamada2, Miguel Rancusi Herrera4, and Luis Felipe Hinojosa5 1Faculty of Science and Engineering, Chuo University, Bunkyo, Tokyo 112-8551, Japan E-mail: [email protected] 2National Science Museum, Tokyo 169-0073, Japan 3Fukui Prefectural Dinosaur Museum, Fukui 911-8601, Japan 4Colegio Compania de Maria, Santiago, Chile 5Facultad de Ciencias, Universidad de Chile, Santiago, Chile Introduction New assemblages of well-preserved permineralized plant fossils were found in southern Patagonia on the southern shore of Riesco Island (Isla Riesco), northwest of Punta Arenas, in the Magallanes (XII) Region of Chile (Figs. 1, 2A, B). The fragments of plant organs and tissues in various sizes and degrees of preservation are present in calcium-carbonate concretions collected at the mouth of the Rio Boer river near Punta Sunshine (53°01.8’S, 71°55.6’W). The concretions are marine in origin, containing molluskcs that may help age determination and biostratigraphic correlation of their source beds. Thick Upper Cretaceous to Tertiary sediments with a NW-SE trend dipping NE are well exposed at Riesco Island. The concretions are probably derived from sediments in the Palaeocene Chorrillo Chico Formation exposed along the Rio Boer running south into the Otway Sound (Seno Otway), because no other formation is distributed in the river drainage area (Mapa geologico de Chile, Escala 1: 1,000,000, 2002). This assignation is further supported by evidence that the Chorrillo Chico Formation is characterized by lithofacies containing calcareous concretions reported by Charrier and Lahsen (1969). This formation has already been dated as Late Cretaceous (Maastrichitian) to Paleocene (Charrier and Lahsen 1969), but was dated as Paleocene in the most recent publication (Mapa geologico de Chile, Escala 1: 1,000,000, 2002). Although the Cretaceous sediments are exposed in the west of the island, there is low possibility of a Cretaceous origin for the concretions. Further stratigraphically-controlled sampling in and around the island is needed to obtain more specimens with more reliable dating. Eight concretions were collected during fieldwork on Riesco Island in 2003 to obtain bog boring samples for palynological studies (Okuda et al. 2004). The concretions are well-sorted, spherical, and are either a single piece of wood or a rock containing a lot of plant debris in a fine sandy matrix. Plant fragments are sometimes packed in round muddy spheres of less than 1-cm diameter scattered in a sandy matrix. Woods are generally damaged by teredo boring, but tissue preservation is not bad. The plant fragments are also well-preserved. Tentative anatomical studies of the new fossil assemblage discovered a diverse array of plants and associated biota such as fungi that inhabited southernmost Patagonia during the early Paleogene. This paper tentatively describes selected elements of the assemblage to promote further investigation in Patagonia and clarify the biological history of the region. Full description and taxonomic treatment of each specimen will appear elsewhere. Materials and methods Eight concretions contained well-preserved materials that were used for anatomical study. Six concretions (nos. RC-01, RC-04, RC-05, RC-06, RC-07, RC-08) are wood pieces. Two (nos. RC- 12 Nishida et al.: Paleocene Permineralized plants of Chile Fig. 1. Map showing fossil collection site (arrow). 03, RC-09) are sandy calcium-carbonate concretions less than 10-cm in diameter containing abundant plant debris. Rocks were slabbed using a diamond-blade saw. Serial sections were prepared by the cellulose-acetate peel technique (Joy et al. 1956). Specimens were etched using ca. 3.6 % HCl solution for 30-40 s and then washed in water. Peels were mounted on microscope slides with Canada balsam, and were observed and photographed using an Olympus BX-50 light microscope with an attached PIXERA D-20 digital camera system. Digital images were processed using Adobe Photoshop 7.0J. Studied samples and most micropreparations will be stored at Museo Nacional de Historia Natural in Santiago, Chile. Supplementary reference micropreparations will also be deposited in the National Science Museum, Tokyo. Results Small fragments in the concretions represent a wide range of taxa. One 7 cm concretion (no. RC- 09) contained a fungal ascocarp, fern rhizome and rachis, four different types of fern leptosporangia each containing well-preserved tetrahedral spores, one conifer leaf, and various fragments of conifer and angiosperm woods. Two conifers and three different angiosperms have been identified among Fig. 2. A. Preparing a zodiac at fossil-collection site for navigation in Seno Otway to the west of Isla Riesco. B. Shoreline viewing west at fossil-collection site. C-H. Possible ascomycete perithecium. Specimen RC-09. C. Longitudinal section of entire body. White bubble is caused by partly porous rock matrix. Slide RC-09A#2. Scale bar 1 mm. D. Basal part of perithecium showing broken base and general tissue differntiation. fn: filamentous nest. RC-09A#4. All scale bars for D to H 100 µm. E. Basal portion enlarged. RC-09A#1. F. Distal end of perithecium showing a slit-like opening (possible ostiole; arrow). RC-09A#5. G. Structure of peripheral wall. External surface upside. RC-09A#1. H. Ascospore with three septa (arrow) in central hollow space. RC-09A#2. Nishida et al.: Paleocene Permineralized plants of Chile 13 14 Nishida et al.: Paleocene Permineralized plants of Chile permineralized woods. 1. Fungal ascocarp (Specimen RC-09, Figs. 2C-H) The fossil is an elongated pyriform of about 1.5-mm long in sectioned view, and 0.2-mm wide at the widest part of the pyriform base (Fig. 2C). About 3/4 of the entire length of the pyriform structure constitutes a neck-like elongation with somewhat laterally appressed middle portion. The tip of the pyriform structure is round and smooth. Tissues at the base of the pyriform are broken, indicating that the structure was detached from some other tissue or structure before fossilization (Fig. 2D). The structure appears to have a thick, continuous peripheral wall that surrounds a central hollow space (Fig. 2E). A loop-like string of brown tissue is isolated in the hollow space. In one section the peripheral wall is broken vertically at the distal end of the elongated neck, leaving a longitudinal slit that is continuous to the central hollow space (Fig. 2F). The peripheral wall is thickest at the structure base, and is typically differentiated into three layers (Figs. 2D-F). The outermost layer is one-to-four cells thick, consisting of elongated, thin-walled cells containing dark contents. In some parts, dark tissues are mostly decayed leaving a thin membranous outermost layer (Fig. 2G). The second layer is composed of loosely-packed round cells. The innermost tissue of the peripheral wall consists of parallel bunches of filamentous cells of irregular thickness. The brown loop-like tissue in the hollow space constitutes a layer of linear elongated, thin-walled cells that contain dark substance similar to that found in the outermost layer of the peripheral wall (Fig. 2E). The space between the peripheral wall and the loop-like tissue is mostly empty, except near the pyriform structure base where a loose nest of thin filamentous tissues is preserved (fn in Figs. 2D, E, H). This suggests the possibility that the entire space between the central loop-like tissue and the innermost layer of the peripheral wall was filled with similar filamentous nests, which are absent in the distal neck of the pyriform structure where the loop-like tissue adheres directly to the innermost layer of the thick peripheral wall (Fig.2 E). A spindle-shaped hyaline structure of about 40-µm long is found inside the loop-like tissue of one section (Fig. 2H). The structure is divided into four locules by three septa, and is similar to the septated ascospore of the ascomycetous fungi. Judging from the less-differentiated tissues consisting of thin-walled cells, the fossil structure can be compared to a fungal ascocarp. The presence of a hyaline septated spore (hyalophragmospore) further demonstrates a possible attribution to the ophiostoma-type perithecium of Pyrenomycetes (Samuels and Blackwell, 2001). The longitudinal slit at the distal end of the perithecium (Fig. 2F arrow) probably functioned as an ostiole for ascospore release. Most extant Pyrenomycetes are parasitic pathogens, but there are various other nutrition types. 2. Bryophyte gametophytes (Specimen RC-03, Figs. 3A-D) The fossil is a set of a round structure 0.13 mm in diameter (Fig. 3A) and an associated 0.2-mm wide lamina. A pointed projection from tangential surface of the round structure is similar in size and structure to the lamina (Fig. 3A). In one of successive sections other lamina is associated with the round structure at about 90° counterclockwise from the first mentioned lamina, which still remains as a thin fragment in the same section (Fig. 3B). Judging from elongated images of cells in slightly oblique section, we conclude that the round structure is a sectioned view of a columnar leafy axis with small leaves probably departing in decussate order. The axis shows weak tissue differentiation, with a central part consisting of smaller, thin-walled cells, and a peripheral part of Fig. 3. A, B. Bryophyte shoot. Successive sections showing a stem departing first (L1) and second leaves (L2). Slide RC-03B#1. Scale bar 100 µm. C, D. Possible bryophyte stem. RC-03A#4. Scale bars 100 µm. D. Showing parenchymatous center lacking conductive tissue. E-J. Protostelic fern rhizome. E. RC-09Bbot#1. F. RC-09C#2. Scale bars for E, F, 0.5 mm; for G, J, 100 µm; for H, I, 200 µm.

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