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
1
Faculty of Science and Engineering, Chuo University, Bunkyo, Tokyo 112-8551, Japan
E-mail: [email protected]
2
National Science Museum, Tokyo 169-0073, Japan
3
Fukui Prefectural Dinosaur Museum, Fukui 911-8601, Japan
4
Colegio Compania de Maria, Santiago, Chile
5
Facultad 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-
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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. RC09) 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
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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. E, F. Successive cross sections of rhizome. G. Part
of E enlarged, showing two protoxylem areas (arrowheads). RC-09C#4. H, I. Protostele enlarged. H. RC-09C#1. I.
RC-09Bbot#1. Arrow in I shows one of protoxylem areas enlarged in J. J. Showing an exarch protoxylem tracheid
(arrow). RC-09Bbot#1.
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Nishida et al.: Paleocene Permineralized plants of Chile
slightly larger, thicker-walled cells.
The lamina is a linear series of round cells in cross section, except at its middle part where cells
form a mound three cells thick, probably representing a midrib. The extremely small size, simple
unicellular lamina, weak tissue differentiation, and absence of vascular tissue in the axis strongly
suggest that the fossil is a bryophyte gametophyte.
Another type of round axial structure about 1.5 mm in diameter was found in the same concretion
(Figs. 3 C, D). It has more marked tissue differentiation than the former leafy axis, consisting of an
outer thick-walled layer and central transparent tissue, although no associated leaves were found.
The small size and absence of a vascular bundle in the axis indicate that the fossil is also a bryophyte.
3. Fern rhizome (Specimen RC-09, Figs. 3E-J)
The rhizome cross section is about 1.4 mm in diameter (Figs. 3E, F). Since cross sections were
obtained from both sides of a sectioned piece of a rock about 1-cm thick, it is possible that the
rhizome is long and filamentous. No leaf trace or attached leaf base was found in the observed
sections. The epidermis and some peripheral portion of the cortex are eroded and lost. The central
part of the rhizome is occupied by a protostele, which is about 0.8 mm in diameter and surrounded
by a well-marked endodermis. The cortex is weakly differentiated into outer thick-walled parenchyma
and inner rather sclerenchymatous zone.
The protostele consists of central xylem and a peripheral area where tissues are degenerated and
lost, leaving a circular empty space. The space was probably occupied by phloem and pericycle as
is common in the fern vascular bundle. The xylem consists of tracheids and parenchyma scattered
among the tracheids. There are four masses of smaller tracheids at the periphery of the xylem,
demonstrating a typical exarch protostele (Figs. 3G, I). Although there are no leaf traces in the
obtained sections, the protostele with rather sparsely distributed parenchyma indicates that the
rhizome belongs to a leptosporangiate fern rather than to the microphyllous lycopods that have a
protostele with rich xylem parenchyma often separating the metaxylem into prominent pieces.
Larger metaxylem tracheids tend to be distributed to one side of the rhizome, demonstrating
dorsiventrality (Figs. 3E, F, H, I). Within the four masses of small tracheids in the protostele, two
are larger than the other two and are located at the periphery of the larger tracheid groups. One of
the two larger masses of small tracheids shows mesarch protoxylem rather than exarch, probably
representing an earlier stage of a departing leaf trace. Therefore, the two larger masses of small
tracheids represent two rows of leaf traces. The other two masses of small tracheids are located at
the other side of the possible leaf traces and are probably root traces.
The fossil is characterized by a very slender rhizome with dorsiventral protostele and probably
departing leaves in two rows with long internodes. Judging from the rhizome size and low number
of protoxylem masses, it is possible that departing leaf traces were small with one or a few protoxylem
masses. Among leptosporangiate ferns, the protostele occurs in rather primitive families such as
the Schizaeaceae, Gleicheniaceae and the Hymenphyllaceae (Ogura 1973). The rhizome of the
Gleicheniaceae is large with a large number of mesarch protoxylem masses and larger leaf traces
departing in radial directions. The Schizaeaceae have a small, elongated rhizome with an exarch
protostele in some cases, but the leaf traces usually form an abaxially opened xylem mass,
characterizing the family. Although the proof of a departing leaf trace in successive sections is
needed, it is likely that the fossil rhizome is comparable to the Hymenophyllaceae. The rhizomes of
Hymenophyllaceae are usually string-like with departing small leaves with a V-shaped vascular
Fig. 4. A, B. Fern rachis. Specimen RC-09C#4. Scale bars for A, 0.2 mm; for B, 100 µm. B. Vascular bundle with vshaped xylem, and the endodermis as a line of cells. C-E. Serial sections of a type-1 sporangium containing spore
tetrads. RC-09#1, #2, #4, respectively. Scale bars 100 µm. F-H. Type-2 (Lohosoria) sporangium containing spore
tetrads. F, G. RC-09A#3. H. RC-09A#1. Scale bars 100 µm. F. Showing well-developed annulus. G, H. Tetrads with
prominent proximal equatorial flange, trilete arms of aperture, and coarsely tuberculate surface. I-L. Sporangia and
spores of living Lophosoria quadripinnata. Scale bars 100 µm. I, J. Specimen from south Chile (Puyehue), having
smaller spores. K, L. Specimen from Bolivia (Corani), having larger spores with strongly tuberculate surface.
Nishida et al.: Paleocene Permineralized plants of Chile
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bundle in two ventral rows at long intervals.
4. Fern rachis (Specimen RC-09, Figs. 4A, B)
The specimen is slightly elliptical in cross section and about 0.6 x 0.6 mm in diameters. A thin
dark epidermis encloses a thick parenchymatous cortex and a vascular bundle enclosed by a welldefined endodermis. The vascular tissue consists of a central V-shaped delineation of tracheids and
a peripheral transparent area, probably containing phloem and pericycle before the tissue was
disorganized. The prominent dorsiventrality and vascular bundle with V-shaped xylem enclosed by
endodermis demonstrate that the fossil is a fern rachis. Further affinity is difficult to assign, but the
extremely thin rachis, consisting of mostly parenchymatous tissue, and well-defined V-shaped xylem
are comparable to the anatomical features of the petiole of the Hymenophyllaceae (Ogura, 1973).
Finding of a hymenophyllaceous rhizome in the same concretion is highly suggestive of filmy ferns
in the original biota.
5. Fern leptosporangium 1 (Specimen RC-09, Figs. 4C-E)
The sporangium is about 200-µm wide and 220-µm long, and lacks a stalk. The annulus is probably
vertical and incomplete, consisting of more than 14 thick-walled cells. At least 45 spores were
counted from four serial sections. The spore is tetrahedral, about 29-37 µm in equatorial diameter,
and has smooth and thick walls. A proximal trilete aperture has prominent ridges. The affinity is
uncertain.
6. Fern leptosporangium 2 (Lophosoria) (Specimen RC-09, Figs. 4F-H)
The sporangium is large, about 380-µm wide and 475-µm long, and lacks a stalk. More than half
the annulus is broken and lost, but 14 thick-walled cells were counted. Only 14 spores remained in
the sporangium. The spore is large, hemispherical with spheroidal distal face and about 74-78 µm
in equatorial diameter. A prominent thick rim or flange encircles the equatorial margin of the spore.
The distal face is rough, while the proximal face is more coarsely tuberculate. A proximal trilete
aperture has thick ridges.
These features characterize the sporangium and spores of Lophosoria in the Cyatheaceae (Gastony
and Tryon, 1976; Tryon and Lugardon, 1990). Although the sporangium is not attached to the
frond, the present fossil proves that a Lophosoria-type spore is certainly produced in a sporangium
comparable to that of living Lophosoria. Lophosoria is a monotypic genus represented by L.
quadripinnata (J. F. Gmel.) C. Chr., inhabiting humid forest margins from Mexico to southern
Chile along the Andes. The southern end of its distribution is 46°25’S (Rodríguez, 1995). Fossils of
dispersed spores affiliated with Lophosoria, such as Cyathacidites are known widely in time and
space ranging from Early Cretaceous to Pliocene of Gondwanaland, including Australia, South
Africa, Kerguelen, Antarctica, Falkland Plateau, and South America (Dettmann, 1986; Kurmann
and Taylor, 1987). Cantrill (1998) reported Lohosoria-like foliage from the Lower Cretaceous of
Snow Island of the South Shetland Islands (62°47’S, 61°23’W). Biogeographic study of Lophosoria
and similar fossil morphotypes have revealed a northward emigration of Lophosoria from Antarctica
to South America, but the time is still uncertain. Our new fossil adds new evidence to help clarify
this scenario. A biostratigraphic study of dispersed Lophosoria-like spores (Cyatheacidites) during
the Late Cretaceous to Paleocene in the Antarctic Peninsula and associated islands, and in southern
Patagonia will help better understand the northward emigration history of Lophosoria.
Fig. 5. A, B. Serial sections of fern sporangium type 3. A. Spore tetrads with thin, smooth wall. Slide RC-09C#2.
Scale bar 100 µm. B. Lateral wall and part of annulus of the sporangium. RC-09C#4. C, D. Serial sections of fern
sporangium type 4, containing tetrads with prominent echinate surface. C. RC-09A#1. Scale bar 100 µm. D. Top of
sporangium stalk at upper right. RC-09A#3. E, F. Conifer leaf 1, cross sections. E. Showing entire falcate contour.
RC-09C#3. Scale bar 1 mm. F. Internal structure of midrib, showing disorganized vascular tissue at center. RC09C#4. Scale bar 200 µm. G, H. Conifer leaf 2. Cross sections. RC-08Btop#1. G. Compare size with E. Scale bar 1
mm. H. G enlarged. Note large mucilage cell. Scale bar 200 µm.
Nishida et al.: Paleocene Permineralized plants of Chile
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Nishida et al.: Paleocene Permineralized plants of Chile
The present fossil sporangium and spores are much larger than those of extant Lophosoria
quadripinnata collected at Puyehue in south Chile (40°40’S), which are about 47 µm in equatorial
diameter (Fig. 3J). However, it is well known that L. quadripinnata in the American tropics has a
diverse range of spore size (52-100 µm in Tryon and Lugardon, 1990) (Gastony and Tryon, 1976).
Spores collected in sub-Andean rain forest of Corani, Bolivia, are 62-67 µm (Fig. 3L). No reasonable
explanation has been proposed yet for these spore size variations in Lophosoria.
7. Fern leptosporangium 3 (Specimen RC-09, Figs. 5A, B)
The sporangium is oblique-transversely sectioned, with dimensions of 156 x 190 µm. The annulus
is incomplete. An intact lateral wall reveals that the sporangium was preserved before spore release,
suggesting that the fossil source vegetation was fairy close to the depositional site. About 14 spores
or their residue contours were counted in two serial sections. The spore is tetrahedral with round
corners, about 37 µm in equatorial diameter. Although the size is similar to that of spores in
sporangium 1, the present spore has a smooth and thin wall. There is a proximal trilete aperture but
it is not prominent. The affinity of the sporangium remains uncertain.
8. Fern leptosporangium 4 (Specimen RC-09, Figs. 5C, D)
The sporangium is slightly elongated and about 105-µm wide and 270-µm long. Only distal
fragments of stalk cells are preserved at the sporangium base. The annulus is incomplete. At least
39 spores or spore residues were counted. The spore is roundish tetrahedral, sometimes with a
slightly concave proximal face, and 29-39 µm in equatorial diameter. Prominent echinate
ornamentation characterizes the spore.
Further SEM and TEM studies will help clarify affinities of the spores recovered in this study.
9. Conifer leaf 1 (Specimen RC-09, Figs. 5E, F)
The fossil is a cross section of a flat, slightly falcate structure ca. 1.8-mm wide and 0.1-0.2 mm in
thickness at the laminar portion, with the thickest middle portion of about 0.3 mm. Therefore, the
fossil is regarded as a small leaf with a single midrib. The epidermis is well-preserved, but internal
tissues are only partly preserved. Groups of narrow tracheids at the center of the midrib represent
the xylem of the leaf midvein (Fig. 5F). Other more degraded tissues surrounding the xylem are
remains of other vascular tissue components. Broken space below the tissue mass including the
tracheary elements was probably occupied by phloem. The vascular bundle is enclosed by poorly
preserved endodermis. There is no indication suggesting resin ducts. The preservation of the
mesophyll is poor, but tissues near the convex side of the lamina have more air spaces, indicating
that the convex side is abaxial. No stomatal structure was confirmed on either side of the lamina.
The single-veined small lamina with tracheary elements attribute the fossil to the coniferophytes,
and probably to the Podocarpaceae or Taxaceae because of the absence of a resin duct. In southern
Chile, there are several extant Podocarpaceae species with similar leaf morphology, such as
Podocarpus nubigena Lindl., Prumnopitys andina (Poepp. Ex Lindl.) de Laub., and Saxegothaea
conspicua Lindl.. Broader comparison is needed with the Podocarpaceae species and other
familieswith similar leaf morphology.
10. Conifer leaf 2 (Specimen RC-08, Figs. 5G, H)
The fossil is a cross section of a semicircular structure ca. 1.1-mm wide and 0.7-mm thick. The
hemispherical face and part of the flat face near the lateral margins are covered by epidermal cells.
Most tissues outside the flat face are broken, so there must have been some additional tissues here.
In one section, there is an isolated tissue mass including tracheary elements in the broken area (not
shown in figure). A large resin duct ca. 200 µm in diameter occurs at the middle of the structure.
The resin duct is surrounded by developed parenchymatous tissue with large air-spaces similar to
leaf mesophyll.
The general morphology of the fossil matches a conifer needle or scale-like leaf. The hemispherical
Nishida et al.: Paleocene Permineralized plants of Chile
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Fig. 6. A-C. Araucarioxylon sp. A, B. Cross sections. Slide RC-07Btop#1. Scale bar for A 1mm, for B 200 µm. C.
Pblique radial section showing araucarioid pitting. Slide RC-07A1#1. Scale bar 100 µm. D-H. Podocarpoxylon /
Phyllocladoxylon sp. D-F. Cross sections. D, F. Slide RC05Btop#1. E. RC-08Btop#1. Scale bars for D, E 1mm, for
F 200 µm. G, H. Radial sections. G. Showing separate bordered pits. H. Showing cupressoid cross-field pits. Slide
RC-05A#3. Scale bars 100 µm.
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Nishida et al.: Paleocene Permineralized plants of Chile
face probably is the leaf abaxial side. No stomatal structure was observed. Single-veined needles or
scale-like leaves with a single large mucilage duct at the abaxial side of the vascular bundle are
usually found in the Taxodiaceae and Cupressaceae. Several species of Cupressaceae (Austrocedrus
chilensis (D. Don) Pic.-Ser. et Bizz., Fitzroya cupressoides (Mol.) Johnst., and Pilgerodendron
uviferum (D. Don) Florin) in south Chile have similar leaf morphology, but we do not have sufficient
comparative anatomical information yet. The minute, scaly leaf also occurs in Lepidothamnus fonckii
Phil.of the Podocarpaceae, which ocassionally forms a low shrub in wet habitats like sphagnum
bog. Broad comparative anatomical study is needed to clarify the affinity of this fossil.
11. Araucarioxylon sp. (Specimen RC-07, Figs. 6A-C)
The poorly preserved fossil is a conifer wood lacking vertical and radial resin canals. The fossil is
probably root wood due to the narrow growth rings less than 5-cells wide, and occasional false
rings. The latewood is very narrow with a thickness of 1-3 cells. Alternately arranged biseriate
pitting is occasionally present on radial walls of tracheids. The rays are entirely uniseriate and less
than 10 cells tall. Based on the above features the fossil is assignable to Araucarioxylon of the
Fig. 7. Podocarpoxylon / Phyllocladoxylon sp. A. Radial section showing window-like cross-field pits. Slide RC08A2#1. Scale bar 100 µm. B-D. Tangential sections. B. Showing ray distribution. Slide RC-06A3#1. Scale bar
200 µm. C. Low rays and small bordered pits on tracheid tangential wall. Slide RC-05A3#1. Scale bar 100 µm. D.
Small pits on tracheid tangential wall. Slide RC-06A3#1. Scale bar 100 µm.
Fig. 8. A-H. Nothofagoxylon cf. scalariforme Gothan. A, B. Cross sections showing diffuse-porous wood. Slide
RC-04B#1. Scale bar for A 1 mm, for B 200 µm. C, D, F-H. Radial sections. E. Tangential section. C. General
radial structure. D. Vessel-ray pitting and tylosis in vessels. E. Uniseriate rays, some with upright cells at ray
margins. C-E. Slide RC-04#1.Scale bars 100 µm. F. Wide vessel with simple perforation plates and scalariform
intervessel pitting. Slide RC-04#3. Scale bar 100 µm. G. Small vessel with scalariform perforation. Slide RC-04#4.
Scale bar 100 µm. H. Elliptical to scalariform vessel-ray pitting. Slide RC-04#4. Scale bar 100 µm. I. Nothofagoxylon
sp. Cross section showing diffuse-porous wood. Slide RC-09A#4. Scale bar 200 µm.
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Nishida et al.: Paleocene Permineralized plants of Chile
Araucariaceae.
12. Podocarpoxylon / Phyllocladoxylon sp. (Specimens: RC-05, RC-06, RC-08, Figs. 6D-H, 7AD)
The poorly-preserved fossils are conifer wood lacking vertical and radial resin canals. Growth
ring boundaries are present but indistinct. The latewoods are very narrow with 1-2 layers. False
rings are absent. The tracheid pitting is sparsely scattered uniseriate on radial walls. The pits are
bordered and round. The rays are entirely uniseriate, low and less than 10 cells tall. The cross-field
pitting is single, large and window-like on wide tracheids and cupressoid on narrow tracheids.
Based on the above features, the fossils are comparable to either Podocarpoxylon, e.g. P.
palaeoandinum Nishida (1984) or Phyllocladoxylon, e.g. P. antarcticum Gothan (1908) of the
Podocarpaceae.
13. Nothofagoxylon cf. scalariforme Gothan (1908) emend. Poole et al. (2001) (Specimen RC-04,
Figs. 8A-H)
The specimen is a small stem or branch with pith. The fossil is semi-ring porous to diffuse porous
wood with numerous and evenly distributed small vessels. The growth ring boundaries are distinct
and marked by banded layers of radially flattened fibers together with distribution of vessels. The
vessels are mostly solitary and in radial multiples of 2-3. The solitary vessels are round in outline
with slightly thick walls. The perforation plates are simple on wide vessels, and scalariform with
10-20 bars on small vessels. Inter-vessel pitting is distinct and scalariform to opposite with
horizontally elongated oval pits. Numerous thin-walled tyloses are present in vessels. The vesselray pitting is scalariform and restricted to marginal rows of rays. The fibers are non-septate,
rectangular, and square or polygonal in outline in cross section. The axial parenchyma is indistinct.
The rays are mostly uniseriate and heterocellular, consisting of procumbent body cells and squareto-upright marginal cells.
Based on the above features the fossil is attributable to either Nothofagoxylon antracticum Torres
(1984) or N. scalariforme Gothan (1908). Poole (2002) treated N. antracticum Torres as a synonym
of N. scalariforme Gothan emend. Poole et al. (2001) with which our fossil is compared.
14. Nothofagoxylon sp. (Specimen RC-09A, Fig. 8I)
The fossil is a small fragment of wood found as a cross section included in successive peels of RC-09A
concretion. The section shows diffuse porosity with numerous small vessels. The vessels are mostly
solitary and in radial multiples of 2-3. The solitary vessels are round-to-slightly radially elongated oval.
Rays are very narrow and1-2 cells in width. The fossil resembles Nothofagoxylon , e.g. N. kraeuseli
Boureau et Salard (1960) or N. scalariforme Gothan (1908), although appropriate longitudinal sections
are needed to further clarify additional features and its affinity.
15. Angiosperm wood 1 (Specimen RC-01, Figs. 9A-H)
The fossil is diffuse porous wood with numerous and evenly distributed small vessels. The growth
ring boundaries are indistinct and weakly marked by the distribution pattern of vessels together
with the differences in diameters between the latewood and earlywood of successive rings. The
vessels are mostly solitary and in radial multiples or clusters of 2-4. The solitary vessels are polygonalto-round in outline with thin-walls. The perforation plates are exclusively scalariform with 10-20
bars. Inter-vessel pitting is scalariform with horizontally elongated oval pits. Numerous thin-walled
tyloses are present in vessels. The vessel-ray pitting is indistinct because of poor preservation, but
is probably scalariform and restricted to marginal rows of rays. The fibers are non-septate, rectangular,
square or polygonal in cross section. The axial parenchyma are indistinct. The rays are 1-3 seriate,
rather low with a height of 7-15 cells, and heterocellular, consisting of procumbent body cells with
1-2 rows of square and/or upright marginal cells. Distinct small pits are observed on walls of
procumbent cells.
Nishida et al.: Paleocene Permineralized plants of Chile
25
Fig. 9. Angiosperm wood 1. A-C. Cross sections. D-F. Radial sections. G, H. Tangential sections. A-C. Diffuse
porosity and abundant2-3 seriate rays. Slide RC-01B#1. Scale bars for A 1mm, for B 200 µm, for C 100 µm. C.
Conspicuous nodular thickenings on ray walls, and sieve-like plate in some vessels. D, E. Abundant tyloses in
vessels. Slide RC-01A1#1. Scale bar for D 200 µm, for E 100 µm. F. Scalariform perforation plates. Slide RC01A2#1. Scale bar 100 µm. G, H. Ray structures. G. Slide RC-01A5#1. H. Margins with 1-2 raws of upright cells.
Slide RC-01A6#1. Scale bars 200 µm.
26
Nishida et al.: Paleocene Permineralized plants of Chile
The above features occur in extant genera of different families, such as Gomortega of the
Gomortegaceae, Laurelia of the Cunoniaceae, Caldcluvia and Weinmannia of the Monimiaceae,
Myrceugenella of the Myrtaceae, and Aextoxicon of the Aextoxicaceae. The fossil is most similar
to some fossil species such as Gomortegoxylon patagonicum Nishida, H. Nishida et Ohsawa (1989),
Laurelites doroteaensis Nishida, H. Nishida et Nasa (1988) from Cerro Dorotea of Ultina Esperanza in
Chile, and Weinmannioxylon nordenskjoeldii Poole, Cantrill, Hayes et Francis (2000) from the Cretaceous
of Livingstone Island in Antarctica. Further comparative study is needed to more precisely clarify its
affinity.
Discussion
This is the first finding of calcareous concretions containing well-preserved plant debris in Patagonia.
Although very preliminary, the new fossil assemblage exhibits a diverse array of plants and associated
biota, including fungi. The presence of small, usually fragile materials, such as Pyrenomycetous
perithecium, moss gametophytes, and spore-containing sporangia, refutes long-distance transport
of the organic materials from their original habitat to the sedimentary basin. By contrast, teredo
invasion of rather large wood fossils suggests biological activities in a marine environment before
fossilization. Investigation of the source beds for the concretions is needed to reconstruct the local
geography and vegetation at the southern tip of South America during the Early Tertiary.
The fossil assemblage is characterized by elements similar to those constituting the so-called
Valdivian rainforest presently distributed in cool temperate areas of Chile. The inferred
paleovegetation consists of a mixed conifer-broadleaf forest associated with hygrophilic elements
like mosses, filmy ferns and the tree-fern Lophosoria. The present Valdivian rainforest is represented
by Nothofagus species, such as N. dombeyi (Mirb.) Oerst. and N. obliqua (Mirb.) Oerst., other
dicotyledonous families, such as Myrtaceae, Monimiaceae and Eucryphiaceae, conifer families
Podocarpaceae, such as Podocarpus and Saxegothaea, and Cupressaceae, such as Fitzroya and
Pilgerodendron. This particular vegetation is distributed in cool temperate areas of Chile with high
annual precipitation of 4000 mm or more. Rich fern understories and epiphytes are also characteristic
of Valdivian rainforest. The Valdivian forest demonstrates high species diversity in contrast to the
sub-Antarctic forest mainly dominated by Nothofagus in southern cooler part of Patagonia.
Recent paleobotanical studies in the Antarctic Peninsula and associated islands are illustrating
the past vegetation and ecosystems of the area during the Late Cretaceous to Tertiary, particularly
until the Eocene before the cooling of Antarctica. The presence of the Valdivian-type vegetation in
Antarctica during this time has been emphasized based on either mega- and palynofloras (e.g.
Dutra and Batten, 2000; Poole et al., 2003). Similar analogues of Valdivian vegetation have been
recorded from the Paleocene-Eocene of Patagonia, including from Ligorio Márquez (Troncoso et
al., 2002; Okuda et al., 2006, in this volume). Reconstructing these Early Tertiary vegetations and
ecosystems is necessary for a better understanding of successive ecological changes during the Late
Tertiary to the present. Paleobotanical data on Early Tertiary local floras throughout Patagonia are
still insufficient compared to those from Antarctica. The new Riesco fossil assemblage adds unique
material to reconstruct the ecosystem at southern tip of South America in the Early Tertiary, as a
transient element that had emigrated from Antarctica.
We thank Concejo de Monumentos Nacionales de Chile for authorizing our research and providing
permission for fieldwork and export of samples to Japan. Special thanks are due to Mr. Peter
Kucevicz, Punta Arenas, for his field guidance, and to Mrs. Margarita Yutronic, Isla Riesco, for the
generous hospitality at her ranch during our fieldwork. Sae Otodani and Taichiro Hirano of Chuo
University made micropreparations of the specimens used in this study, to whom we acknowledge
especially.
This study was supported by Grant-in-Aid for Scientific Research No. 14255007 from the Ministry
of Education, Culture, Sports, Science and Technology, Japan to H.N.
Nishida et al.: Paleocene Permineralized plants of Chile
27
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