23. W. K. Kroeze, D. J. Sheffler, B. L. Roth, J. Cell Sci. 116,
24. J. S. Gutkind, Sci. STKE 2000, re1 (2000).
25. M. J. Marinissen, J. S. Gutkind, Trends Pharmacol. Sci.
22, 368–376 (2001).
Acknowledgments: We thank the anonymous reviewers for their
thoughtful and insightful critiques, which substantively improved
this manuscript. Supported by the Singapore University of Technology
and Design–Massachusetts Institute of Technology International
Design Center (IDG31300103) and by Natural Sciences and
Engineering Research Council (Discovery Grant 125517855).
Materials and Methods
Figs. S1 to S4
Tables S1 and S2
18 June 2013; accepted 31 January 2014
Fossilized Nuclei and Chromosomes
Reveal 180 Million Years of
Genomic Stasis in Royal Ferns
Rapidly permineralized fossils can provide exceptional insights into the evolution of life over geological
time. Here, we present an exquisitely preserved, calcified stem of a royal fern (Osmundaceae)
from Early Jurassic lahar deposits of Sweden in which authigenic mineral precipitation from
hydrothermal brines occurred so rapidly that it preserved cytoplasm, cytosol granules, nuclei, and even
chromosomes in various stages of cell division. Morphometric parameters of interphase nuclei match
those of extant Osmundaceae, indicating that the genome size of these reputed “living fossils”has
remained unchanged over at least 180 million years—a paramount example of evolutionary stasis.
Royal ferns (Osmundaceae) are a basal
group of leptosporangiate ferns that have
undergone little morphological and an-
atomical change since Mesozoic times (1–6).
Well-preserved fossil plants from 220-million-
year-old rocks already exhibit the distinctive ar-
chitecture of the extant interrupted fern (Osmunda
claytoniana)(2), and many permineralized os-
mundaceous rhizomes from the Mesozoic are
practically indistinguishable from those of mod-
ern genera (3–5)orspecies(6). Furthermore, with
the exception of one natural polyploid hybrid
(7), all extant Osmundaceae have an invariant
and unusually low chromosome count (7,8), sug-
gesting that the genome structure of these ferns
may have remained unchanged over long periods
of geologic time (8). To date, evidence for evo-
lutionary conservatism in fern genomes has been
exclusively based on studies of extant plants
(9,10). Here, we present direct paleontological
evidence for long-term genomic stasis in this
family in the form of a calcified osmundaceous
rhizome from the Lower Jurassic of Sweden with
pristinely preserved cellular contents, including
nuclei and chromosomes.
The specimen was collected from mafic vol-
caniclastic rocks [informally named the “Djupadal
formation”(11)] at Korsaröd near Höör, Scania,
Sweden [fig. S1 of (12)]. Palynological analysis in-
dicates an Early Jurassic (P li ensbachian) age for
these deposits (11) (fig. S2), which agrees with
radiometric dates obtained from nearby volcanic
necks (13) from which the basaltic debris or igina ted.
The fern rhizome was permineralized in vivo by
calcite from hydrothermal brines (11,14)thatper-
Department of Palaeobiology, Swedish Museum of Natural
History, PostOffice Box 50007, SE-104 05 Stockholm, Sweden.
Department of Geology, Lund University, Sölvegatan 12,
SE-223 62 Lund, Sweden.
*Corresponding author. E-mail: benjamin.bomfleur@
nrm.se (B.B.); firstname.lastname@example.org (S.M.)
Fi g. 1 . Cytological features preserved in the apical region
of the Korsaröd fern fossil. (A) transverse section through
the rhizome; (B) detail of radial longitudinal section showing
typical pith-parenchyma cells with preserved cell membranes
(arrow), cytoplasm and cytosol particles, and interphase nuclei
with prominent nucleoli; (C) interphase nucleus with nucleolus
and intact nuclear membrane; (D) early prophase nucleus with
condensing chromatin and disintegrating nucleolus and
nuclear membrane; (Eand F)lateprophasecellswithcoiled
chromosomes and with nucleolus and nuclear membrane
completely disintegrated; (Gand H)prometaphasecells
showing chromosomes aligning at the equator of the nucleus;
(Iand J) possible anaphase cells showing chromosomes at-
tenuated toward opposite poles. (A), (C to E), (G), and (I)
are from NRM S069656. (B), (F), (H), and (J) are from NRM
S069658. Scale bars: (A) 500 mm; (B) 20 mm; (C to J) 5 mm.
21 MARCH 2014 VOL 343 SCIENCE www.sciencemag.org1376
col ated through the coarse-grained sed iment s shor t-
ly after deposition (table S1). The fossil is 6 cm
long and 4 cm wide and consists of a small (~7 mm
diameter) central stem surrounded by a dense man-
tle of persistent frond bases with interspersed rootl ets
(Fig. 1). Its complex reticulate vascular cylinder
(ectophloic dictyoxylic siphonostele), parenchym-
atous pith and inner cortex, and thick fibrous outer
cortex are characteristic features of Osmundaceae
(1,3–5,12) (fig. S3). Moreover, the frond bases
mantling the rhizome contain a heterogeneous scle-
renchyma ring that is typical of extant Osmunda
sensu lato (1,3,4,12) (fig. S4). The presence of
a single root per leaf trace favors affinities with
(sub)genus Osmundastrum (1,3,6,12).
The specimen is preserved in exquisite sub-
cellular detail (Fig. 1 and figs. S4 and S5). Pa-
renchyma cells in the pith and cortex show
preserved cell contents, including membrane-
bound cytoplasm, cytosol granules, and possible
amyloplasts (Fig. 1 and fig. S5). Most cells con-
tain interphase nuclei with conspicuous nucleoli
(Fig. 1, figs. S4 and S5, and movies S1 and S2).
Transverse and longitudinal sections through the
apical part of the stem also reveal sporadic dividing
parenchyma cells, mainly in the pith periphery
(Fig. 1). These are typically preserved in prophase
or telophase stages, in which the nucleolus and nu-
clear envelope are more or less unresolved and the
chromatin occurs in the form of diffuse, granular
material or as distinct chromatid strands. A few
cells contain chromosomes that are aligned at the
equator of the nucleus, indicative of early meta-
phase, and two cells were found to contain chromo-
somes that appear to be attenuated toward opposite
poles, representing possible anaphase stages.
Some tissue portions in the stem cortex and the
outer leaf bases show signs of necrosis and pro-
grammed cell death (fig. S6).
Such fine subcellular detail has rarely been
documented in fossils (15–17) because the chances
for fossilization of delicate organelles are small
(16) and their features are commonly ambiguous
(17). The consistent distribution and architec-
ture of the cellular contents in the Korsaröd fern
fossil resolved via light microscopy (Fig. 1 and
fig. S4), scanning electron microscopy (fig. S5),
and synchrotron radiation x-ray tomographic
microscopy (SRXTM) (fig. S5 and movies S1
and S2) provide unequivocal evidence for three-
dimensionally preserved organelles.
Positive scaling relationships rooted in DNA
content can be used to extrapolate relative ge-
nome sizes and ploidy levels of plants (18–21).
We measured minimum and maximum diame-
ters, perimeters, and maximum cross-sectional
areas of interphase nuclei in pith and cortical
parenchyma cells of the fossil and of its extant
relative Osmundastrum cinnamomeum.Themea-
surements match very closely (Fig. 2), with mean
nuclear perimeters of 32.2 versus 32.6 mmand
mean areas of 82.2 versus 84.9 mm
in the fossil
and in extant Osmundastrum, respectively. The
equivalent nuclear sizes demonstrate that the
Korsaröd fern fossil and extant Osmundaceae
likely share the same chromosome count and DNA
content, and thus suggest that neither ploidization
events nor notable amounts of gene loss have
occurred in the genome of the royal ferns since
the Early Jurassic ~180 million years ago [(8),
see also discussion in (9,10)]. These results, in
concert with morphological and anatomical evi-
dence (1–6), indicate that the Osmundaceae rep-
resents a notable example of evolutionary stasis
References and Notes
1. W. Hewitson, Ann. Mo. Bot. Gard. 49,57–93 (1962).
2. C. Phipps et al., Am. J. Bot. 85, 888–895 (1998).
3. C. N. Miller, Contrib. Mus. Paleontol. 23, 105–169 (1971).
4. G. W. Rothwell, E. L. Taylor, T. N. Taylor, Am. J. Bot. 89,
5. N. Tian, Y.-D. Wang, Z.-K. Jiang, Palaeoworld 17,
6. R. Serbet, G. W. Rothwell, Int. J. Plant Sci. 160, 425–433
7. C. Tsutsumi, S. Matsumoto, Y. Yatabe-Kakugawa,
Y. Hirayama, M. Kato, Syst. Bot. 36, 836–844 (2011).
8. E. J. Klekowski, Am. J. Bot. 57, 1122–1138 (1970).
9. M. S. Barker, P. G. Wolf, Bioscience 60, 177–185 (2010).
10. I. J. Leitch, A. R. Leitch, in Plant Genome Diversity,
I. J. Leitch, J. Greilhuber, J. Doležel, J. F. Wendel, Eds.
(Springer-Verlag, Wien, 2013), vol. 2, pp. 307–322.
11. C. Augustsson, GFF 123,23–28 (2001).
12. See supplementary materials available on Science Online.
13. I. Bergelin, GFF 131, 165–175 (2009).
14. A. Ahlberg, U. Sivhed, M. Erlström, Geol. Surv. Denm.
Greenl. Bull. 1, 527–541 (2003).
15. S. D. Brack-Hanes, J. C. Vaughn, Science 200,
16. K. J. Niklas, Am. J. Bot. 69, 325–334 (1982).
17. J. W. Hagadorn et al., Science 314, 291–294 (2006).
18. A. E. DeMaggio, R. H. Wetmore, J. E. Hannaford,
D. E. Stetler, V. Raghavan, Bioscience 21,313–316 (1971).
19. J. Masterson, Science 264, 421–424 (1994).
20. I. Símová, T. Herben, Proc. Biol. Sci. 279, 867–875 (2012).
21. B. H. Lomax et al., New Phytol. 201, 636–644 (2014).
Acknowledgments: We thank E. M. Friis and S. Bengtson
(Stockholm) and F. Marone and M. Stampanoni (Villigen) for
assistance with SRXTM analyses at the Swiss Light Source, Paul
Scherrer Institute (Villigen); G. Grimm (Stockholm) for assistance
with statistical analyses; B. Bremer and G. Larsson (Stockholm)
for providing live material of Osmunda;M.A.GandolfoNixon
from the Cornell University Plant Anatomy Collection (CUPAC;
http://cupac.bh.cornell.edu/); the members of Tjörnarps
N. Tian (Shenyang), Y.-D. Wang (Nanjing), and T. E. Wood
(Flagstaff, Arizona) for discussion; and two anonymous referees for
constructive comments. This research was jointly supported by the
Swedish Research Council (VR), Lund University Carbon Cycle
Centre (LUCCI), and the Royal Swedish Academy of Sciences. The
material is curated at the Swedish Museum of Natural History
(Stockholm, Sweden) under accession nos. S069649 to S069658
and S089687 to S089693.
Materials and Methods
Figs. S1 to S6
Movies S1 and S2
17 December 2013; accepted 21 February 2014
Fig. 2. Morphometric
parameters of inter-
phase nuclei of extant
O. cinnamomeum com-
pared to those of the
Korsaröd fern fossil. Col-
ored box-and-whiskers plots
in upper graph indicate
interquartile ranges (box)
with mean (square), me-
dian (solid transverse bar),
and extrema (whiskers);
dashed colored lines in
lower graph indicate linear
measured nuclei for extant
O. cinnamomeum versus
www.sciencemag.org SCIENCE VOL 343 21 MARCH 2014 1377
Supplementary Materials for
Fossilized Nuclei and Chromosomes Reveal 180 Million Years of
Genomic Stasis in Royal Ferns
Benjamin Bomfleur,* Stephen McLoughlin,* Vivi Vajda
*Corresponding author. E-mail: email@example.com (B.B.); firstname.lastname@example.org (S.M.)
Published 21 March 2014, Science 343, 1376 (2014)
This PDF file includes:
Materials and Methods
Figs. S1 and S6
Captions for Movies S1 and S2
Other Supplementary Material for this manuscript includes the following:
(available at www.sciencemag.org/content/343/6177/1376/suppl/DC1)
Movies S1 and S2
Materials and Methods:
Standard 30 μm thin sections (22, 23) of the fossil and of extant Osmundastrum were
studied with an BX51 compound microscope (Olympus; Vendelsö, Sweden) and
photographed using an DP71 digital camera (Olympus). Nuclear parameters were
measured using cellSens© Dimension version 1.6 (Olympus Soft Imaging Systems;
Münster, Germany), and analysed using Origin© version 8 (OriginLab; Northampton,
MA). Transverse and radial longitudinal surfaces of the permineralized rhizome were
polished and then etched in 5% HCl for 5–10 seconds; after drying, these specimens were
sputter-coated with gold for 90 seconds, and examined and imaged using a S-4300 field
emission scanning electron microscope (Hitachi; Krefeld, Germany) at the Swedish
Museum of Natural History (Naturhistoriska Riksmuseet). In addition, a portion of a
permineralized stipe (petiole) was removed and analysed using synchrotron X-ray
tomographic microscopy at the TOMCAT beam-line of the Swiss Light Source, Paul
Scherrer Institute (Villigen, Switzerland) [see (24–26)]. The tomographic data were
processed and reconstructed using Avizo© Fire version 8 (FEI Visualization Sciences
Group; Hillsboro, OR). We applied conventional adjustments of brightness, contrast, and
saturation to the digital images using Adobe© Photoshop© CS5 Extended version 12.0
(Adobe Systems Incorporated; San Jose, CA).
Five samples of the host rock (NRM S069690, NRM S069730, NRM S06738, NRM
S069740, and NRM S069644) were processed for palynological analysis following the
standard methods at Global GeoLab Ltd. (Medicine Hat, Canada). One entire strew slide
per sample was analysed for presence/absence data, and 200 palynomorphs per sample
were counted for relative abundance data where possible.
Measurements of major and trace elements were obtained using a Niton XL3t
Goldd+ X-ray fluorescence (XRF) analyzer (Thermo Scientific; Örebro, Sweden) at the
Department of Geology, Lund University; calibration and drift detection was undertaken
using standard sample NIST 2709a with known reference values. The volcaniclastic host
rock (sample NRM S069645) and a polished surface of the fern fossil (sample NRM
S069649) were both analyzed for elemental constituents over target areas of 8 mm
diameter. Fossil material (NRM S069649–S069658) and measured slides of extant
Osmundastrum cinnamomeum (NRM S089694) are housed in the Department of
Palaeobiology at the Swedish Museum of Natural History, Stockholm, Sweden.
The samples yielded low- to moderate-diversity assemblages of non-marine
palynomorphs, including spores, pollen, and fresh-water algae. Abundance data were
assessed for samples NRM S069690 and NRM S069730, which are both dominated by
fern spores (52% and 63%, respectively) followed by gymnosperm pollen grains (33%
and 43%, respectively). Taxa occurring in high relative abundances include the spores
Osmundacidites wellmanii Couper 1953 (Osmundaceae: up to 12% in sample NRM
S069690), Cyathidites minor Couper 1953 (Cyatheaceae), Deltoidospora toralis
(Leschik) Lund 1977 (Matoniaceae, Dicksoniaceae, Cyatheaceae, or Dipteridaceae), and
Marattisporites scabratus Couper 1958 (Marattiales). Gymnosperm pollen grains are
mainly represented by Perinopollenites elatoides Couper 1958, Classopollis spp.,
Alisporites spp., Chasmatosporites spp., and Eucommiidites troedssonii Erdtman 1948.
Additional taxa include Striatella seebergensis Mädler, 1964, Retitriletes clavatoides
(Cookson 1953) Döring et al. in Krutzsch 1963, Spheripollenites psilatus Couper 1958,
and a few specimens of Cerebropollenites thiergartii Schulz 1967 and Vitreisporites
pallidus (Reissinger) Nilsson 1958.
The high relative abundance of fern spores, Chasmatosporites spp., and Alisporites
spp. together with the scarcity of Classopollis and Spheripollenites psilatus and absence
of Toarcian key-taxa (e.g., Clavatipollenites hughesii and Callialasporites spp.) indicate
a late Pliensbachian age for the assemblage. The spore-pollen suite correlates with the
Sinemurian–Pliensbachian Cerebropollenites macroverrucosus Zone (27) and with the
Pliensbachian Chasmatosporites Zone (28)established in southern Scandinavia. It also
closely matches palynofloras from the late Pliensbachian Assemblage Zone 3
(Chasmatosporites–Cerebropollenites thiergartii–Botryococcus Zone) (29) and the late
Pliensbachian Assemblage A (A2) (30) established in Greenland.
A further important observation is the unusually common occurrence of large, intact
clusters of Marattisporites scabratus Couper 1953, indicating a short transport distance
for the palynomorphs.
List of taxonomically diagnostic characters of the permineralized fern rhizome (Fig. S3):
(a) Rhizome radially symmetrical with a dense mantle of leaf bases and rootlets
(b) Siphonostele, ectophloic-dictyoxylic
(c) Pith parenchymatous
(d) Xylem cylinder thin (<15 tracheids thick), dissected by mostly complete leaf gaps
(e) Inner cortex thin, parenchymatous; outer cortex thick, homogeneous, fibrous
(f) Leaf traces endarch, initially oblong to slightly curved with one protoxylem cluster
(g) Adventitious roots arising singly from each leaf trace
(h) Stipe-base vascular strand C-shaped, enclosing a mass of thick-walled fibers in its
(i) Stipe-base sclerenchyma ring heterogeneous, containing thin- and thick-walled fibers
Following systematic treatments of Osmundaceae (1, 3–5),
(a, b) are diagnostic of family Osmundaceae,
(b, c) are diagnostic of subfamily Osmundoideae,
(d–f) are diagnostic of genus Osmunda s.l. and of the fossil form-genus Ashicaulis,
(h, i) are diagnostic of genus Osmunda s.l.,
and (g) is typical of subgenus Osmundastrum.
Fossils with overall comparable character combinations have been assigned to the form-
genus Ashicaulis [see (4, 5, 31–34)] or described as fossil representatives of Osmunda
(e.g., O. pluma, O. arnoldii, O. dowkeri, and fossil O. cinnamomea) (3). Preliminary
analyses indicate that the studied specimen shows a unique combination of specific
anatomical characters, and probably represents a new species.
X-ray fluorescence analysis:
In decreasing abundance, the most common elements detected in the volcaniclastic host
rock are Si (36.65%), Fe (26.8%), Al (16.6%), Mg (8.65%), K (6.77%), Ti (2.34%), and
Ca (1.47%) indicating a dominance of Fe-, Al- and Mg- silicate minerals in the mafic
volcaniclastic matrix (table S1). Other elements constitute < 1% of the rock composition
(table S1). Note that the XRF analyser does not detect elements with atomic numbers less
than that of Mg, so the registered percentages (table S1) are exclusive of those elements.
The composition of the host rock is thus consistent with that of the mafic alkaline
magmatic rocks of the central Skåne volcanic province (35). The results from the XRF
analysis of the fossil fern, by contrast, show an extremely high value of Ca (91.84%),
followed by Si (3.21%) and P (1.96%). The very different compositions of the fossil and
rock matrix demonstrate that calcite cement precipitated preferentially around and within
the entombed plant remains, which we infer to be a result of contrasting local porosity
and chemical environments within and around buried plant tissues.
Map of southern Sweden showing the location of the Korsaröd fossil site in the central
Skåne volcanic province.
Light micrographs of representative fossil spores and pollen grains from the 'Djupadal
formation' at the Korsaröd locality; taxon, rock sample number, palynomorph specimen
number, and microscope X/Y calibration position.
(A–C) Osmundacidites wellmanii Couper 1953; (A) NRM S069738, NRMS089691-01,
127/15; (B) NRM S069690, NRMS089687-01, 119/7; (C) NRM S069730,
NRMS089689-01, 144/17; (D) Stereisporites psilatus (Ross) Pflug in Thomson & Pflug
1953, NRM S069690, NRMS089687-02, 137/5; (E) Stereisporites seebergensis Schulz
1966, NRM S069730, NRMS089689-02, 132/10; (F) Retitriletes clavatoides Döring
1963, NRM S069690, NRMS089687-03, 134/5; (G) Retitriletes semimuris (Danze-
Corsin & Laveine 1963) McKellar 1974, NRM S069730, NRMS089689-03, 114/18;
(H) Cibotiumspora jurienensis (Balme) Filatoff 1975, NRM S069690, NRMS089687-04,
113/14; (I) Deltoidospora toralis (Leschik) Lund 1977, NRM S069730, NRMS089689-
04, 140/20; (J) Striatella seebergensis Mädler 1964, NRM S069690, NRMS089687-05,
132/10; (K) Marattisporites scabratus Couper 1958, NRM S069730, NRMS089689-05,
142/8; (L) Classopollis classoides (Pflug) Pocock & Jansonius 1961, NRM S069690,
NRMS089687-06, 125/15; (M) Vitreisporites pallidus (Reissinger) Nilsson 1958, NRM
S069738, NRMS089691-02, 124/16; (N) Chasmatosporites hians Nilsson 1958, NRM
S069730, NRMS089689-06, 139/18; (O) Chasmatosporites apertus (Rogalska) Nilsson
1958, NRM S069690, NRMS089687-07, 137/2; (P) Monosulcites punctatus Orlowska-
Zwolinska 1966, NRM S069730, NRMS089689-07, 133/8;
(Q) Eucommiidites troedssonii Erdtman 1948, NRM S069690, NRMS089687-08,
144/15; (R) Perinopollenites elatoides Couper 1958, NRM S069690, NRMS089687-09,
137/15. Scale bars 10 μm.
Transmitted-light micrographs illustrating the diagnostic morphological and anatomical
features of the Korsaröd fern fossil. (A) Transverse section through the radially
symmetrical rhizome with a dense mantle of stipe bases and rootlets (a), NRM S069656;
(B) detail of transverse section through the stem showing the ectophloic-dictyoxylic
siphonostele (b), the parenchymatous pith (c), the thin xylem cylinder dissected by
complete gaps (d), the thin parenchymatous inner cortex and fibrous outer cortex (e), and
the single root per leaf trace (g), NRM S069656; (C) transverse section through an
endarch, slightly reniform leaf trace with a single protoxylem cluster (f) in the inner
cortex of the stem, NRM S069656; (D) transverse section through a stipe base showing
the C-shaped leaf trace and enclosed sclerenchyma mass (h) and an arch of thick-walled
fibers in the sclerenchyma ring (i), NRM S069657. Scale bars (A) 5 mm; (B, D) 500 µm;
(C) 50 µm.
Morphological, anatomical, and cytological features of the Korsaröd fern fossil (A–F)
compared to those of extant Osmunda regalis (G) and Osmundastrum cinnamomeum (H–
L). (A, G) Gross morphology of rhizome showing dense mantle of persistent stipe bases
and fine roots; (B, H) stem cross sections showing the equivalent ectophloic-dictyoxylic
siphonostele; (C, I) longitudinal sections of stem portions showing xylem cylinder with
scalariform-pitted tracheids of the stele (left) and organelle-bearing parenchyma cells of
the pith (right); (D, J) details of three cortical parenchyma cells, each containing a
nucleus; (E, F, K, L) details of interphase nuclei with intact nuclear membranes and
prominent nucleoli. Images H and I used with kind permission of the Cornell University
Plant Anatomy Collection (CUPAC; http://cupac.bh.cornell.edu/). Fossil specimens: (A)
reassembly of original fossil now cut into blocks NRM S069649–S069655; (B) thin
section S069656; (C) thin section NRM S069658; (D–E) NRM S069656. (J–L) Thin
section of extant O. cinnamomeum, NRM S089694. Scale bars (A, G) 1 cm; (B, H) 500
μm; (C, I) 100 μm; (D–F, K–L) 5 μm.
Intracellular details of the Korsaröd fern fossil revealed through SEM of acid-etched
surfaces (A–E) and through synchrotron X-ray tomographic microscopy of a stipe
portion (F, G). (A) Vascular-bundle tracheids (left), parenchyma cell walls, and
preserved nuclei projecting from etched surface of longitudinal section of a stipe, NRM
S069655; (B, C) details of etched longitudinal sections through a stipe showing
projecting nuclei (arrows in B), NRM S069655; (D, E) etched surface of a transverse
section of a stipe showing tracheid cells with characteristic scalariform pitting and an
associated parenchyma cell containing putative amyloplasts (arrows), NRM S069649; (F,
G) semi-translucent box reconstructions of small portions of cortical parenchyma in a
stipe showing distribution of nuclei, some with visible nucleoli (arrow in G; see movies
S1, S2), NRM S069654. Scale bars (A, B, D) 25 μm; (C, G) 10 μm; (E) 5 μm; (F) 50
Signs of necrosis and programmed cell death in the Korsaröd fern fossil. (A) Radial
longitudinal section through the stem showing (from left to right) cortical tissues, xylem
cylinder, and pith, with a darker patch of apparently necrotic tissue in the inner cortex
(image center); (B) detail of the same, showing shrunken cytoplasm and pyknotic nuclei
(arrow) typical of apoptosis (36); (C, D) details showing pyknotic nuclei containing
homogeneous nuclear contents condensed into a distinctive dark crescent at one pole of
the former nuclear envelope. All images from NRM S069658. Scale bars (A) 500 µm;
(B) 40 µm; (C) 10 µm; (D) 5 µm.
Results of X-ray fluorescence analysis of the volcaniclastic host rock and the fern fossil
from the Korsaröd site, showing the proportions of major (bold font), minor (regular font)
and trace (gray) elemental components.
∅ 8 mm (ppm)
∅ 8 mm (ppm)
Conventional tomographic reconstruction of a cuboidal portion of stipe parenchyma from
the Korsaröd fern fossil showing cell walls and distribution of nuclei. Note nucleoli, e.g.,
within a nucleus in the upper left corner of the box after ca ¼ rotation.
Red-cyan stereoscopic tomographic reconstruction of the same.
References and Notes
1. W. Hewitson, Comparative morphology of the Osmundaceae. Ann. Mo. Bot. Gard. 49, 57–93
2. C. Phipps, T. Taylor, E. Taylor, R. Cúneo, L. Boucher, X. Yao, Osmunda (Osmundaceae)
from the Triassic of Antarctica: An example of evolutionary stasis. Am. J. Bot. 85, 888–
895 (1998). Medline doi:10.2307/2446424
3. C. N. Miller, Contrib. Mus. Paleontol. 23, 105–169 (1971).
4. G. W. Rothwell, E. L. Taylor, T. N. Taylor, Ashicaulis woolfei n. sp.: Additional evidence for
the antiquity of osmundaceous ferns from the Triassic of Antarctica. Am. J. Bot. 89, 352–
361 (2002). Medline doi:10.3732/ajb.89.2.352
5. N. Tian, Y.-D. Wang, Z.-K. Jiang, Permineralized rhizomes of the Osmundaceae (Filicales):
Diversity and tempo-spatial distribution pattern. Palaeoworld 17, 183–200 (2008).
6. R. Serbet, G. W. Rothwell, Osmunda cinnamomea (Osmundaceae) in the Upper Cretaceous of
Western North America: Additional Evidence for Exceptional Species Longevity among
Filicalean Ferns. Int. J. Plant Sci. 160, 425–433 (1999). doi:10.1086/314134
7. C. Tsutsumi, S. Matsumoto, Y. Yatabe-Kakugawa, Y. Hirayama, M. Kato, A New
Allotetraploid Species of Osmunda (Osmundaceae). Syst. Bot. 36, 836–844 (2011).
8. E. J. Klekowski, Populational and genetic studies of a homosporous fern-Osmunda regalis.
Am. J. Bot. 57, 1122–1138 (1970). doi:10.2307/2441278
9. M. S. Barker, P. G. Wolf, Unfurling Fern Biology in the Genomics Age. Bioscience 60, 177–
185 (2010). doi:10.1525/bio.2010.60.3.4
10. I. J. Leitch, A. R. Leitch, in Plant Genome Diversity, I. J. Leitch, J. Greilhuber, J. Doležel, J.
F. Wendel, Eds. (Springer Verlag, Wien, 2013), vol. 2, pp. 307–322.
11. C. Augustsson, Lapilli tuff as evidence of Early Jurassic Strombolian-type volcanism in
Scania, southern Sweden. GFF 123, 23–28 (2001). doi:10.1080/11035890101231023
12. See supplementary materials available on Science Online.
13. I. Bergelin, Jurassic volcanism in Skåne, southern Sweden, and its relation to coeval regional
and global events. GFF 131, 165–175 (2009). doi:10.1080/11035890902851278
14. A. Ahlberg, U. Sivhed, M. Erlström, Geol. Surv. Denm. Greenl. Bull. 1, 527–541 (2003).
15. S. D. Brack-Hanes, J. C. Vaughn, Evidence of paleozoic chromosomes from lycopod
microgametophytes. Science 200, 1383–1385 (1978). Medline
16. K. J. Niklas, Differential preservation of protoplasm in fossil angiosperm leaf tissues. Am. J.
Bot. 69, 325–334 (1982). doi:10.2307/2443136
17. J. W. Hagadorn, S. Xiao, P. C. Donoghue, S. Bengtson, N. J. Gostling, M. Pawlowska, E. C.
Raff, R. A. Raff, F. R. Turner, Y. Chongyu, C. Zhou, X. Yuan, M. B. McFeely, M.
Stampanoni, K. H. Nealson, Cellular and subcellular structure of neoproterozoic animal
embryos. Science 314, 291–294 (2006). Medline doi:10.1126/science.1133129
18. A. E. DeMaggio, R. H. Wetmore, J. E. Hannaford, D. E. Stetler, V. Raghavan, Ferns as a
model system for studying polyploidy and gene dosage effects. Bioscience 21, 313–316
19. J. Masterson, Stomatal size in fossil plants: Evidence for polyploidy in majority of
angiosperms. Science 264, 421–424 (1994). Medline doi:10.1126/science.264.5157.421
20. I. Símová, T. Herben, Geometrical constraints in the scaling relationships between genome
size, cell size and cell cycle length in herbaceous plants. Proc. Biol. Sci. 279, 867–875
(2012). Medline doi:10.1098/rspb.2011.1284
21. B. H. Lomax, J. Hilton, R. M. Bateman, G. R. Upchurch, J. A. Lake, I. J. Leitch, A.
Cromwell, C. A. Knight, Reconstructing relative genome size of vascular plants through
geological time. New Phytol. 201, 636–644 (2014). doi:10.1111/nph.12523
22. H. Hass, N. P. Rowe, in Fossil Plants and Spores: Modern Techniques, T. P. Jones, N. P.
Rowe, Eds. (Geological Society, London, 1999), pp. 76–81.
23. T. N. Taylor, M. Krings, N. Dotzler, J. Galtier, The advantage of thin section preparations
over acetate peels in the study of Late Paleozoic fungi and other microorganisms. Palaios
26, 239–244 (2011). doi:10.2110/palo.2010.p10-131r
24. P. C. J. Donoghue, S. Bengtson, X. P. Dong, N. J. Gostling, T. Huldtgren, J. A. Cunningham,
C. Yin, Z. Yue, F. Peng, M. Stampanoni, Synchrotron X-ray tomographic microscopy of
fossil embryos. Nature 442, 680–683 (2006). Medline doi:10.1038/nature04890
25. E. M. Friis, P. R. Crane, K. R. Pedersen, S. Bengtson, P. C. Donoghue, G. W. Grimm, M.
Stampanoni, Phase-contrast X-ray microtomography links Cretaceous seeds with
Gnetales and Bennettitales. Nature 450, 549–552 (2007). Medline
26. M. D. Sutton, Tomographic techniques for the study of exceptionally preserved fossils. Proc.
Biol. Sci. 275, 1587–1593 (2008). Medline doi:10.1098/rspb.2008.0263
27. K. Dybkjær, Palynological zonation and palynofacies investigation of the Fjerritslev
Formation (Lower Jurassic–basal Middle Jurassic) in the Danish Subbasin. Danm. Geol.
Undersøg. Ser. A 30, 1–150 (1991).
28. E. B. Koppelhus, L. H. Nielsen, Palynostratigraphy and palaeoenvironments of the lower to
middle jurassic bagå formation of bornholm, denmark. Palynology 18, 139–194 (1994).
29. E. B. Koppelhus, G. Dam, Geol. Surv. Denm. Greenl. Bull. 1, 723–775 (2003).
30. J. J. Lund, K. R. Pedersen, Bull. Geol. Soc. Den. 33, 371–400 (1985).
31. W. D. Tidwell, SIDA Contrib. Bot. 16, 253–261 (1994).
32. Y.-M. Cheng, A new species of Ashicaulis (Osmundaceae) from the Mesozoic of China: A
close relative of living Osmunda claystoniana L. Rev. Palaeobot. Palynol. 165, 96–102
33. N. Tian et al., A specialized new species of Ashicaulis (Osmundaceae, Filicales) from the
Jurassic of Liaoning, NE China. J. Plant Res. 127, 209–219 (2014).
34. N. Tian et al., Sci. China Earth Sci. 10.1007/s11430-013-4767-2 (2013).
35. S. Tappe, Mesozoic mafic alkaline magmatism of southern Scandinavia. Contrib. Mineral.
Petrol. 148, 312–334 (2004). doi:10.1007/s00410-004-0606-y
36. G. Majno, I. Joris, Apoptosis, oncosis, and necrosis. An overview of cell death. Am. J.
Pathol. 146, 3–15 (1995). Medline