RESEARCH ARTICLE
Alectorioid Morphologies in Paleogene
Lichens: New Evidence and Re-Evaluation of
the Fossil Alectoria succiniMägdefrau
Ulla Kaasalainen1*, Jochen Heinrichs2, Michael Krings3, Leena Myllys4,
Heinrich Grabenhorst5, Jouko Rikkinen6, Alexander R. Schmidt1
1 Department of Geobiology, University of Göttingen, Göttingen, Germany, 2 Department of Biology and
Geobio-Center, University of Munich (LMU), Munich, Germany, 3 Department of Earth and Environmental
Sciences, University of Munich (LMU), and Bavarian State Collection for Palaeontology and Geology,
Munich, Germany, 4 Finnish Museum of Natural History, University of Helsinki, Helsinki, Finland, 5 c/o
Amber Study Group, Geological-Palaeontological Institute and Museum, University of Hamburg, Hamburg,
Germany, 6 Department of Biosciences, University of Helsinki, Helsinki, Finland
* ulla.kaasalainen@geo.uni-goettingen.de
Abstract
One of the most important issues in molecular dating studies concerns the incorporation of
reliable fossil taxa into the phylogenies reconstructed from DNA sequence variation in ex-
tant taxa. Lichens are symbiotic associations between fungi and algae and/or cyanobacte-
ria. Several lichen fossils have been used as minimum age constraints in recent studies
concerning the diversification of the Ascomycota. Recent evolutionary studies of Lecanoro-
mycetes, an almost exclusively lichen-forming class in the Ascomycota, have utilized the
Eocene amber inclusion Alectoria succinic as a minimum age constraint. However, a re-in-
vestigation of the type material revealed that this inclusion in fact represents poorly pre-
served plant remains, most probably of a root. Consequently, this fossil cannot be used as
evidence of the presence of the genus Alectoria (Parmeliaceae, Lecanorales) or any other
lichens in the Paleogene. However, newly discovered inclusions from Paleogene Baltic and
Bitterfeld amber verify that alectorioid morphologies in lichens were in existence by the Pa-
leogene. The new fossils represent either a lineage within the alectorioid group or belong to
the genus Oropogon.
Introduction
Lichen symbioses represent stable mutualistic associations in which photoautotrophic algae
and/or cyanobacteria provide carbohydrates for heterotrophic fungi. This nutritional strategy
has been adopted several times independently in various fungal lineages, and today approxi-
mately 20% of all known fungal species are lichenized [1–3]. Despite the prevalence of lichens
in certain modern ecosystems, their documented fossil record remains scarce. The oldest fossil
indicating a lichen-like symbiosis has been described from approximately 600 Ma old marine
PLOSONE | DOI:10.1371/journal.pone.0129526 June 8, 2015 1 / 12
OPEN ACCESS
Citation: Kaasalainen U, Heinrichs J, Krings M,
Myllys L, Grabenhorst H, Rikkinen J, et al. (2015)
Alectorioid Morphologies in Paleogene Lichens: New
Evidence and Re-Evaluation of the Fossil Alectoria
succini Mägdefrau. PLoS ONE 10(6): e0129526.
doi:10.1371/journal.pone.0129526
Academic Editor: Peter Wilf, Penn State University,
UNITED STATES
Received: April 17, 2015
Accepted: May 11, 2015
Published: June 8, 2015
Copyright: © 2015 Kaasalainen et al. This is an
open access article distributed under the terms of the
Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any
medium, provided the original author and source are
credited.
Data Availability Statement: All relevant data are
within the paper.
Funding: This work was supported by the Alexander
von Humboldt foundation (fellowship to UK): The
funder had no role in study design, data collection
and analysis, decision to publish, or preparation of
the manuscript. It also received support from the
Open Access Grant Program of the German
Research Foundation (DFG) and the Open Access
Publication Fund of the University of Göttingen: The
publication fee in an open access publication will be
covered by the funders.
phosphorite [4], and the earliest records of internally stratified lichens with cyanobacterial and
presumably algal photobionts are from ca 410 Ma old Lower Devonian rocks [5–6].
Amber, formed by the hardened resin of trees, is famous for its ability to capture ancient life
and preserves even soft-bodied microorganisms in cellular and ultrastructural fidelity. Several
well-preserved lichens have been described from 35–50 Ma old Baltic and 16 Ma old Domini-
can amber (for age estimation, see [7–8]), and identified as representatives of extant genera [9–
12]. These rare lichen fossils have served as minimum age constraints in several recent studies
assessing the evolutionary history of the Lecanoromycetes [13–15]. There is always some level
of uncertainty when morphologies of fossils are incorporated into phylogenetic trees that are
based on DNA sequence variation of extant taxa [16–19], but this inherent problem can often
be minimized by a thorough inspection of the fossils and assessment of their characteristics
[20–22]. An inclusion in Baltic amber described as Alectoria succini by Karl Mägdefrau [23]
has recently been used as an age constraint for the genus Alectoria [13–14]. However, the fossil
that formed the basis for A. succini has not been revisited since the initial publication.
Here we show that the fossil described as Alectoria succini does not possess morphological
attributes characterizing alectorioid lichens, but rather represents a degraded plant part, proba-
bly a root, and consequently is unfit to be used in calibrating ascomycete phylogenies in geolog-
ic time. On the other hand, newly discovered fossils from Baltic and Bitterfeld amber
demonstrate that Alectoria-like morphologies resembling extant lineages within the alectorioid
group (sensuMiadlikowska et al. [24]) or the genus Oropogon were actually present in lichens
in Europe during the Paleogene.
Material and Methods
The piece of Baltic amber containing Alectoria succini is ~6.2 x 3.5 x 1.2 cm large. It is part of a
historical amber collection assembled by Alexander Scheele that is today housed in the Bavari-
an State Collection for Palaeontology and Geology at Munich, Germany (specimen accession
number SNSB-BSPG 1967 XX 1). The amber piece containing A. succini also includes a spider,
spider web, and composite plant hairs of Fagaceae as syninclusions. The Eocene sediments that
yield the majority of Baltic amber in the Kaliningrad area (Russia) are 35–47 million years old,
whereas fewer specimens are found in up to 50 million-year-old strata [7,25].
The other amber fossils of Alectoria-like lichens included in this study come from Baltic and
Bitterfeld amber. The fossil contained in Baltic amber is part of the historic Königsberg Amber
Collection housed at the University of Göttingen (collection number GZG.BST.21889 [B
14234]). The piece is ~17 x 10 x 7 mm large and contains several fagaceous trichomes as synin-
clusions. The fossil in Bitterfeld amber is part of the Geoscientific Collections of the University
of Göttingen (collection number GZG.BST.27313). The piece is ~9 x 7 x 2 mm large and con-
tains a fagaceous trichome and scattered dark hyphae and conidial chains of a dematiaceous
hyphomycete as syninclusions. The amber piece was collected from the Goitzsche mine near
the city of Bitterfeld in central Germany and was recovered from the Chattian 'Bernsteinschluff'
Horizon in the upper part of the Cottbus Formation. The Upper Oligocene amber-bearing sed-
iment has an absolute age of 23.8–25.3 million years [26–27].
Baltic amber is usually considered at least 35 million years old [25]; however, providing a
precise minimum age for Bitterfeld amber is still challenging. There is conflicting evidence re-
garding whether the uppermost Oligocene age of the amber-bearing strata of the Bitterfeld
amber mine reflects the actual age of the Bitterfeld amber. The fact that there is a significant
proportion of identical arthropod morphologies in amber from both localities resulted in the
hypothesis that Bitterfeld amber perhaps represents re-deposited Eocene Baltic amber [28]. Re-
deposition of Baltic amber is, however, unlikely considering the overall geological setting of the
Alectorioid Morphologies in Paleogene Lichens
PLOS ONE | DOI:10.1371/journal.pone.0129526 June 8, 2015 2 / 12
Competing Interests: The authors have declared
that no competing interests exist.
Bitterfeld strata and palaeogeographic conditions [25], but local reworking of pre-Chattian
amber in the Bitterfeld area has not been refuted so far (see [29], for discussion). In any case,
Bitterfeld amber is also Paleogene in age, and its minimum age should be regarded as 23.8
million years.
Amber inclusions were studied using a compound microscope (Carl Zeiss AxioScope A1)
equipped with a Canon 60D digital camera. In some instances, incident and transmitted light
were used simultaneously. Before imaging the new amber pieces were ground and polished
manually using a series of wet silicon carbide papers (grit from FEPA P 600 to 4000, particle
size 25.8–5 μm, Struers). In order to better illustrate the three-dimensional inclusions, a series
of photomicrographs of different focal planes were combined using the software package Heli-
conFocus 4.45. The images in Figs 1–3 were obtained from the merger of up to 60 optical
sections.
For scanning electron microscopy (SEM) minute pieces were removed from a branch of
Alectoria succini, fixed onto an SEM-mount, sputter-coated with a 12 nm thick Pt/Pd coating
using an Automatic Sputter Coater (Canemco Inc.), and examined and imaged with a field
emission scanning electron microscope Carl Zeiss LEO 1530 Gemini.
After initial imaging and sampling of the Alectoria succini fossil, a drop of a high-grade
epoxy (Buehler Epoxicure) resin was applied to one of the filaments reaching to the surface of
the amber piece (for protocols, see [30]). When placed under vacuum, the epoxy resin entered
the inclusion and surrounding fissures for several millimeters providing a better visualization
of the specimen surface. The image of Fig 1E was taken after epoxy treatment.
No permits were required for the described study, which complied with all relevant
regulations.
Results
Alectoria succiniMägdefrau
The inclusion is approximately 20 x 15 mm large (Fig 1A). The opaque fossil consists of elon-
gate, branched structures; three prominent thickenings that occur on the branches (Fig 1B and
1C) have been interpreted as apothecia by Mägdefrau [23]. The fossil is not well preserved be-
cause all structures are surrounded by tiny fissures that hinder a more specific visual inspection
(Fig 1D). Even after epoxy treatment, only a small portion of the fissures was covered, and no
clear image of the surface could be obtained (Fig 1E). The structures believed to represent apo-
thecia (Fig 1B and 1C) are also entirely covered with fissures that prevent in-depth evaluation
of their nature. Moreover, they are situated deep within the amber, rendering it impossible to
access them without destroying the specimen.
Scanning electron microscopy imaging of the inclusion revealed a highly degraded tissue
with numerous tiny pyrite crystals (Fig 1F). However, at the interface of the amber and inclu-
sion, cell-like structures have remained intact, most likely because the resin compounds were
able to better penetrate and preserve the tissue (Fig 1G). The cell-like structures are oval in
shape, ~24 μm long and up to 8 μmwide, and some appear to be hollow, while others are filled
with pyrite crystals. Based on the shape and size, these structures most probably represent rem-
nants of plant cells. Evidence of fungal hyphae, photobiont cells, or any other structures argu-
ing in favor of lichen affinities of the fossil were not found.
Lichen fossil from Baltic amber
This amber inclusion consists of several slender, terete branches, the longest of which is more
than 11 mm long (Fig 2A). Branches are up to 90 μm wide. Branching pattern is wide and
some of the subordinate branches extend more or less perpendicularly. The color of the
Alectorioid Morphologies in Paleogene Lichens
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Alectorioid Morphologies in Paleogene Lichens
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branches appears to be dark brown, and some show twisting (Fig 2B and 2C). All branches
are bounded by what appears to be a prosoplectenchymatous cortex composed of hyphae ex-
tending longitudinally and spiraling around the circumference of the branch (Fig 2B and 2C).
Several small air bubbles are present in the amber along the branches that might suggest the
existence of pseudocyphellae which permitted air to be released from the interior of the thal-
lus during embedding (Fig 2B and 2C). Apothecia or vegetative propagules have not been
observed.
Lichen fossil from Bitterfeld amber
The amber inclusion consists of several slender, terete branches, the largest of which is ~7 mm
long (Fig 3A). Branches are up to 140 μmwide; there is no clear differentiation into main and
subordinate branches (Fig 3A and 3C). Branching pattern is wide, and some of the branches
extend perpendicularly. The color of the branches appears to be brownish (Fig 3D). A cylindri-
cal structure seen in cross-sectional view (Fig 3E) represents the dense cortex, while the looser
internal layers (photobiont layer and medulla) of the lichen are not preserved. The cortex
bounding the branches is up to 20 μm thick and appears to be prosoplectenchymatous and
Fig 1. Light (A–E) and scanning electron (F, G) microscope images of Alectoria succini (specimen SNSB-BSPG 1967 XX 1). (A) Overview of
specimen (scale bar 1 mm). (B) Fossil imaged the same way as in Mägdefrau’s paper [23] (scale bar 1 mm). Arrowheads point to two thickenings initially
interpreted as apothecia. (C) Smaller apothecium-like structure (scale bar 200 μm). Note surface fissures in amber. (D) Portion of fossil showing numerous
fissures (scale bar 200 μm). (E) Portion of fossil imaged after adding epoxy under vacuum (scale bar 200 μm). (F) Extracted portion of fossil showing
decayed tissue and pyrite crystals (left) and surrounding amber (right) (scale bar 10 μm). (G) Several well-preserved structures resembling parenchymatous
cells, some filled with tiny pyrite crystals (scale bar 1 μm).
doi:10.1371/journal.pone.0129526.g001
Fig 2. Lichen fossil from Baltic amber (specimen GZG.BST.21889). (A) Overview of specimen (scale bar 1 mm). (B) Branch with possible
pseudocyphellae indicated by air bubbles (scale bar 100 μm). C) Detail of specimen, showing twisted branch (scale bar 100 μm).
doi:10.1371/journal.pone.0129526.g002
Alectorioid Morphologies in Paleogene Lichens
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composed of hyphae mostly extending along the long axis of the branches (Fig 3D). The thallus
was probably hollow or possessed only a very loose medulla because the center of the branches
is filled with amber (Fig 3E). However, evidence of medullary hyphae is not present. The cross
Fig 3. Lichen fossil from Bitterfeld amber (specimen GZG.BST.27313). (A–C) Overviews of specimen (scale bars 1 mm in A and B, and 500 μm in (C).
(D) Detail showing surface of one of the thinner branches (scale bar 10 μm). (E) Cross section of one of the thicker branches. Central void or canal in thallus
filled with amber (scale bar 50 μm). (F) Close up of perforate formations leading from central void to thallus surface (scale bar 10 μm). (G) Close up of putative
linear pseudocyphella on surface of smaller branch (arrowhead) (scale bar 50 μm).
doi:10.1371/journal.pone.0129526.g003
Alectorioid Morphologies in Paleogene Lichens
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section shows several openings reaching from the hollow center to the thallus surface (Fig 3E
and 3F). Two of the openings rise slightly above the generally smooth outer surface of the cor-
tex. A linear pseudocyphella of approximately 180 μm long and 10 μmwide is also visible on
the surface of one of the smaller branches (Fig 3G). No apothecia or vegetative propagules
are visible.
Discussion
Identity of Alectoria succini
Our re-investigation of the type (and only) specimen of Alectoria succini suggests that this fos-
sil most likely does not represent a lichen, but rather comes from a plant, probably from a root
based on the branching pattern and the presence of structures strongly resembling a parenchy-
matous cortical tissue. Unfortunately, the multiple fissures surrounding the inclusion, along
with the heavy degradation of the fossil, make a more conclusive assessment of the biological
nature of the inclusion impossible. Such superficial fissures frequently develop in amber inclu-
sions as a result of weathering processes, including oxidation [31].
When initially describing Alectoria succini, Mägdefrau [23] was convinced that the fossil
represented a lichen, but assignment to the extant genus Alectoria was regarded tentative.
Moreover, the only illustration included in the initial publication (plate XII, figure 5 in [23]) is
an overview at low magnification and of relatively poor quality, suggesting that the surface fis-
sures were present already when Mägdefrau studied the specimen. The most important features
used by Mägdefrau to interpret the fossil as a lichen are the three prominent thickenings be-
lieved to represent apothecia. However, with the exception of overall size which corresponds to
the size of typical Alectoria apothecia (e.g. [32]), there are no structural details recognizable in
the thickenings that could be used to determine their nature. We therefore conclude that the
fossil named Alectoria succini is in no way persuasive with regard to systematic affinities, and
thus it cannot be used as evidence of the existence of the genus Alectoria or any other lichen
group in the Paleogene.
New fossils from Baltic and Bitterfeld amber
Both new fossils from Baltic and Bitterfeld amber are quite similar in overall morphology: thin
branches with a wide branching pattern, and hyphae primarily oriented longitudinally along
the branches (Figs 2 and 3A–3D). The cross-section of the Bitterfeld specimen shows a relative-
ly wide central void or canal, which might represent a natural feature, but could also have been
caused by destruction and/or degradation of the medulla prior to or during embedding (Fig
3E). The branches of the Baltic specimen are arranged in a helix (Fig 2B and 2C). Both speci-
mens seem to possess pseudocyphellae: in the Bitterfeld specimen one elongate opening is visi-
ble on the surface of one of the branches (Fig 3G), while the Baltic specimen suggests the
presence of pseudocyphellae because small air bubbles occur in abundance on some of the
branches (Fig 2B and 2C). The pseudocyphellae of both specimens are inconspicuous and likely
narrow, because they are rarely visible on the thallus surface. Overall morphology and growth
form, together with the presence of a central void or canal in the radially symmetrical thallus
and the presence of pseudocyphellae, suggests affinities to the extant lineage of either alector-
ioid lichens (Alectoria-group sensuMiadlikowska et al. [24]) or, alternatively, the genus Oropo-
gon, both belonging to the family Parmeliaceae (Lecanorales). Based on morphological
similarities, Oropogon was previously also considered part of the alectorioid group [32], but
this relationship is not supported by recent molecular studies [24,33]. In addition to molecular
characters, the main distinguishing feature between these morphologically partially very simi-
lar genera are the ascospores, which unfortunately are not preserved in either of the fossils.
Alectorioid Morphologies in Paleogene Lichens
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Oropogon is a genus of approximately 40 species occurring in eastern and southern Asia
and Central and South America [34]. In addition to ascospores, the genus is characterized by
predominately isodichotomous branching and conspicuous, perforate pseudocyphellae, which
are, however, not present in all species [34]. The central, amber filled void or canal with perfo-
rations seen in cross-sections (Fig 3E and 3F) is reminiscent of what can be observed in some
extant Oropogon species. However, the number of perforations visible in a single cross-section
is high (at least seven) in the fossil, whereas extant species usually show only one, or at best two
pseudocyphellae per cross-section. However, it is also possible that some of the less prominent
perforations in the fossil are of taphonomic origin (e.g. ruptures due to shrinkage of the thallus
during embedding).
The monophyletic lineage of alectorioid lichens presently includes five genera of which
three produce fruticose, often pendent and beard-like thalli: Alectoria, Bryoria, and Sulcaria
[24,33,35]. Alectoria is a genus of seven species presently recognized with Northern Hemi-
sphere or bipolar distribution, while Bryoria consists of 30–40 mainly circumboreal species,
and Sulcaria contains six species restricted to either Asia or North America [35–38]. Typically,
Alectoria produce raised and elongate fusiform to ovoid pseudocyphellae [39] that remotely re-
semble the slightly raised cracks observed in the cross section of the fossil thallus from Bitter-
feld amber (Fig 3E). On the other hand, several species of Bryoria produce relatively
inconspicuous, linear pseudocyphellae [40] that are similar to the linear pseudocyphella ob-
served on the branch surface of the Bitterfeld fossil (Fig 3G). In most species of Sulcaria pseu-
docyphellae form conspicuous, long, and spiraling grooves [36,41].
Another character distinguishing the aforementioned extant genera is the thickness of cor-
tex: in members of the genus Alectoria, this layer is generally thick (50–80 μm), while it is rela-
tively thinner in other alectorioid genera and in Oropogon (30–40 μm) [32]. The cortex of the
Bitterfeld lichen only reaches up to 20 μm. In addition, the branches in the Baltic fossil are
twisted (Fig 2B and 2C), thus resembling the often twisted appearance of the branches seen in
Sulcaria. Twisting of the branches also occurs in certain species of Alectoria and Bryoria, but
we are not aware of any report in Oropogon. In conclusion, even though the two new lichen fos-
sils are morphologically similar to each other, they are not identical. There is a close resem-
blance to several extant taxa, but the morphological features of the fossils are not of sufficient
clarity to assign them to any extant lineage of lichens with confidence.
Reliable lichen fossils for the calibration of molecular clocks
Many studies of molecular evolution have demonstrated the importance of constraining mo-
lecular clocks with fossil evidence (e.g. [42–48]). However, as shown by Taylor and Berbee
[49], great care should be taken when choosing fossils because the use of age constraints has
significant effects on divergence time estimates and therefore the systematic placement of the
fossils is of prime importance. Evaluation of all lichen inclusions in amber described to date
shows four fossils that have confidently been assigned to extant genera, the oldest of which is
Eocene in age.
Representatives of the genera Anzia, Calicium, and Chaenotheca have been described from
Baltic amber. The fossils all are very well preserved, and thus allow reliable identification
[10,12,15]. The fossil Anzia electra was first described from Bitterfeld amber [10] and later the
genus was also identified from a Baltic amber inclusion [15]. Anzia, a member of the family
Parmeliaceae (Lecanorales), is characterized by the presence of a distinctive spongiostratum
composed of one cell wide hyphae [50]. Spongiostratum is a structure of spongy cushions on
the ventral side of the thallus formed by anastomosing hyphae. It is a characteristic of only two
extant genera, Anzia and Pannoparmelia, which can be discriminated based on the
Alectorioid Morphologies in Paleogene Lichens
PLOS ONE | DOI:10.1371/journal.pone.0129526 June 8, 2015 8 / 12
construction of the spongiostratum hyphae, i.e. uniseriate in Anzia vs. multiseriate in Panno-
parmelia [50].
Calicium and Chaenotheca include lichens with pin-like ascomata. Despite superficial simi-
larity, the genera are not closely related, but rather belong to two families, i.e. the Caliciaceae
(Lecanorales) and Coniocybaceae (Coniocybales). The fossil Calicium sp. consists of a single
detached ascoma and of numerous ellipsoidal 2-celled spores [12], which are characteristic of
the extant representatives of Calicium and clearly distinguish the genus from most other ‘stub-
ble lichens’. The fossil Chaenotheca can also be identified with confidence based on the pres-
ence of a well-developed thallus, relatively stout and short-stalked apothecia, well-developed
excipulum, and spherical, and relatively large 1-celled spores [12].
In addition to the Paleogene fossils, younger (~16 Ma old) lichen fossils from the Miocene
have been described from Dominican amber. One of these, the squamulose Phyllopsora domin-
icanus (Ramalinaceae, Lecanorales), closely resembles the extant Phyllopsora species [11]. Two
fossils described as representatives of the genus Parmelia (Parmeliaceae, Lecanorales), i.e. P.
ambra and P. isidiiveteris [9], most probably do not belong to Parmelia as presently circum-
scribed, but represent other foliose genera within the diverse lineage of parmelioid lichens.
Re-evaluation of Alectoria succinimight result in a shift of the previously estimated diver-
gence times within the Lecanoromycetes. This is because Mägdefrau's fossil can currently only
be replaced by lichen fossils that are not with confidence assignable at generic level. To some
extent, the probable alterations can be inferred from the previous analyses run with and with-
out the fossil [13,14]. These analyses showed that the omission of Alectoria succini does not sig-
nificantly change the estimated divergence times of the major lineages of the Ascomycota,
because there are other reliable fossils that can be used [14,15]. However, the divergence times
of the parmelioid clades may be younger than previously estimated [13]. Considering the un-
certain assignment of the Miocene Parmelia and our new Paleogene fossils, the only reliable
fossil Parmeliaceae is Anzia. However, the precise position of the genus inside the family is still
uncertain, despite the recent phylogenetic studies.
Conclusions
The Baltic amber inclusion described as Alectoria succiniiMägdefrau 1957 does not possess
any bona fide anatomical features of lichens, and it probably represents a poorly preserved
plant part. Hence, the fossil does not prove the presence of the genus Alectoria in the Paleo-
gene. However, new fossils from Baltic and Bitterfeld amber show that lichens morphologically
similar to Alectoria were in fact present in the Paleogene, some 24 to 35 million years ago.
These new fossils either represent members of the extant genus Oropogon or a lineage within
the alectorioid group.
The previous treatment of Alectoria succini points to the importance of following careful
procedures for using fossils as minimum age constraints in molecular phylogenetic studies
[19]. Whenever possible, the original fossil material should be re-investigated, an apomorphy-
based diagnosis of the specimens should be performed in order to justify the phylogenetic posi-
tion of the fossil, and the most recent geologic data should be considered.
Acknowledgments
We would like to thank Martin Nose (Munich, Germany) for making the holotype specimen of
Alectoria succini available and for granting permission to take samples from the specimen, and
Dorothea Hause-Reitner (Göttingen) for assistance with field-emission SEM.
Alectorioid Morphologies in Paleogene Lichens
PLOS ONE | DOI:10.1371/journal.pone.0129526 June 8, 2015 9 / 12
Author Contributions
Conceived and designed the experiments: UK JR ARS. Performed the experiments: UK LM JR
ARS. Analyzed the data: UK JHMK LMHG JR ARS. Contributed reagents/materials/analysis
tools: HG. Wrote the paper: UK JHMK LM JR ARS.
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