Foss. Rec., 20, 147–157, 2017
www.foss-rec.net/20/147/2017/
doi:10.5194/fr-20-147-2017
© Author(s) 2017. CC Attribution 3.0 License.
Problems related to the taxonomic placement of incompletely
preserved amber fossils: transfer of the Paleogene liverwort
Cylindrocolea dimorpha (Cephaloziellaceae) to the extant
Odontoschisma sect. Iwatsukia (Cephaloziaceae)
Kathrin Feldberg1, Jirˇí Vánˇa2, Alfons Schäfer-Verwimp3, Michael Krings4, Carsten Gröhn5, Alexander R. Schmidt6,
and Jochen Heinrichs1
1Ludwig-Maximilians-Universität München, Department für Biologie I, Systematische Botanik und Mykologie,
Geobio-Center, Menzinger Straße 67, 80638 Munich, Germany
2Department of Botany, Charles University, Benátská 2, 128 01 Prague 2, Czech Republic
3Mittlere Letten 11, 88634 Herdwangen-Schönach, Germany
4Department für Geo- und Umweltwissenschaften, Paläontologie und Geobiologie, Ludwig-Maximilians-Universität, and
SNSB-Bayerische Staatssammlung für Paläontologie und Geologie, Richard-Wagner-Straße 10, 80333 Munich, Germany
5Amber Study Group, c/o Geological-Palaeontological Museum of the University of Hamburg, Bundesstraße 55,
20146 Hamburg, Germany
6Georg-August-Universität Göttingen, Abteilung Geobiologie, Goldschmidtstraße 3, 37077 Göttingen, Germany
Correspondence to: Jochen Heinrichs (jheinrichs@lmu.de)
Received: 2 March 2017 – Accepted: 20 March 2017 – Published: 12 April 2017
Abstract. A revision of the Baltic and Bitterfeld amber fos-
sils assigned to Cylindrocolea dimorpha (Cephaloziellaceae)
has yielded evidence of the presence of multicellular, bifid
underleaves, which have not previously been reported for
this species and conflict with the current circumscription of
the family. We transfer the fossil species to Odontoschisma
(sect. Iwatsukia) and propose the new combination O. di-
morpha of the Cephaloziaceae. Characteristics of the fossil
include an overall small size of the plant, entire-margined,
bifid leaves and underleaves, more or less equally thickened
leaf cell walls, ventral branching that includes stoloniform
branches with reduced leaves, and the lack of a stem hyalo-
dermis and gemmae. Placement of the fossil in Cephalozi-
aceae profoundly affects divergence time estimates for liver-
worts based on DNA sequence variation with integrated in-
formation from the fossil record. Our reclassification concurs
with hypotheses on the divergence times of Cephaloziaceae
derived from DNA sequence data that provide evidence of
a late Early Cretaceous to early Eocene age of the Odon-
toschisma crown group and an origin ofO. sect. Iwatsukia in
the Late Cretaceous to Oligocene.
1 Introduction
Liverworts belong to the oldest lineages of plants on land
and date back to the early Paleozoic (Taylor et al., 2009).
They are characterized by a life cycle with a prominent leafy
or thalloid gametophyte, an unbranched sporophyte, and the
frequent presence of oil bodies and elaters (Renzaglia et al.,
2007). Liverwort diversity today includes some 7000 species
in ∼ 400 genera; however, both species level and supraspe-
cific classifications remain unstable despite considerable re-
cent efforts to record the global diversity (Söderström et al.,
2016). Accordingly, taxonomic studies still identify incon-
gruences between morphology-based taxonomic hypotheses
and DNA-based phylogenies and, consequently, genus and
family concepts are frequently revised (e.g., Bechteler et al.,
2016; Long et al., 2016; Patzak et al., 2016). Taking the con-
siderable difficulties into account that hamper the classifi-
cation of the present-day liverwort diversity (Renner et al.,
2017), it comes as no surprise that fossils of liverworts of-
ten have an even complexer and more confusing taxonomic
history (Grolle and Meister, 2004), especially if only frag-
ments, rather than entire plants, are preserved (Heinrichs et
Published by Copernicus Publications on behalf of the Museum für Naturkunde Berlin.
148 K. Feldberg et al.: Taxonomic placement of incompletely preserved amber fossils
al., 2016). These fragments often do not display the whole
complement of relevant taxonomic characters, and thus the
classification of these forms often needs to be revised when
additional, more completely preserved specimens become
available.
Jungermannia dimorpha Casp. was initially described by
Caspary (1887) based on a single inclusion of an unbranched,
male shoot enshrined in a piece of Baltic amber that is today
kept in the Museum für Naturkunde Berlin. Baltic amber is
considered Eocene in age (35 to 47 Myr old; Standke, 1998).
The shoot lacks a hyalodermis and underleaves, and has two
rows of bifid, entire-margined leaves consisting of relatively
thin-walled cells lacking trigones, and an apical androecium
with 5 pairs of shallowly bifid bracts (Grolle, 1980). Caspary
and Klebs (1907) noted similarities of the fossil to the ex-
tant Jungermannia divaricata Sm. (= Cephaloziella divar-
icata (Sm.) Schiffn.; Söderström et al., 2016), and Grolle
(1980) subsequently transferred the species to Cephaloziella
(Spruce) Schiffn. (as Cephaloziella dimorpha (Casp.) Grolle)
of the Cephaloziellaceae. Grolle and Meister (2004) de-
scribed additional inclusions supposed to belong to this
species from Baltic and Bitterfeld amber. However, no gem-
mae, which are a characteristic feature of most Cephaloziella
species, were detected by these authors. As a result, they
suggested that the fossils belong to the genus Cylindrocolea
R.M.Schust., rather than Cephaloziella and, consequently,
proposed the name Cylindrocolea dimorpha (Casp.) Grolle
for the taxon.
Using the geological age of Cylindrocolea dimorpha as a
minimum age constraint for Cylindrocolea in DNA-based di-
vergence time estimates of liverworts results in estimates that
indicate roughly 3 times older ages than analyses conducted
without this fossil constraint (Feldberg et al., 2013, 2014;
Laenen et al., 2014). This observation led us to reinvestigate
the type material and additional fossils of Cylindrocolea di-
morpha. We found that bifid underleaves occur in ascending
shoots, while they are usually missing in prostrate shoots.
The results from thorough re-analysis of the specimens, to-
gether with additional evidence from DNA-based divergence
time estimates, are used in this study to transfer Cylindro-
colea dimorpha to Odontoschisma sect. Iwatsukia (N.Kitag.)
Gradst., S.C.Aranda & Vanderp. (Cephaloziaceae).
2 Materials and methods
2.1 Investigation of amber inclusions
The amber inclusions (12 from Baltic and 6 from Bit-
terfeld amber) used in this study are housed at the Mu-
seum für Naturkunde at Berlin, the Georg August Univer-
sity of Göttingen (numbers preceded by GZG.BST), the
SNSB-Bavarian State Collection for Palaeontology and Ge-
ology (numbers preceded by SNSB-BSPG), and the Carsten
Gröhn amber collection. Specimens from the Museum für
Naturkunde at Berlin were previously published under
BHU-Palaeo collection numbers (e.g., Grolle and Meister,
2004). However, this acronym has recently been replaced by
“MB.Pb”.
The surface of some of the amber pieces was polished
manually with a series of wet silicon carbide abrasive pa-
pers (grit size from FEPA P 600–4000 (particle size: 25.8
to 5 µm), Struers) to minimize light scattering during anal-
ysis and photographic documentation. Specimens were then
placed on a glass microscope slide with a drop of water added
to the upper surface and covered with a coverslip. The am-
ber inclusions were studied under a Leica M50 incident-light
microscope and a Carl Zeiss AxioScope A1 compound mi-
croscope, the latter equipped with a Canon 60D digital cam-
era. Incident and transmitted light were used simultaneously.
The images compiled in Figs. 1 and 2 are digitally stacked
photomicrographic composites of up to 145 individual focal
planes obtained by using the software package HeliconFocus
5.0.
2.2 Divergence time estimates
Divergence time estimates based on the DNA sequence vari-
ation obtained from extant representatives of cephalozioid
liverworts were conducted to assess the level of con-
gruence with our taxonomic placement of Cylindro-
colea/Odontoschisma dimorpha. The DNA dataset that was
used included 67 accessions of the family Cephaloziaceae
and 2 outgroup species from Adelanthaceae (see Supple-
ment). Sequences of the chloroplast rbcL gene and trnL-
trnF-region, as well as the nuclear ITS1-5.8S-ITS2 region,
were extracted from GenBank (https://www.ncbi.nlm.nih.
gov/genbank/), and were published previously in Feldberg
et al. (2010, 2016) and Vilnet et al. (2010, 2012). Se-
quences were aligned manually in Bioedit version 7.0.5.2
(Hall, 1999); missing data were coded as missing.
jModelTest 2.1.7 (Guindon and Gascuel, 2003; Darriba
et al., 2012) was employed to choose a nucleotide substi-
tution model for both nuclear and plastid DNA datasets.
With regard to the nuclear marker, the Bayesian informa-
tion criterion (BIC) supported the TIM3+0+ I model; re-
garding the combined chloroplast markers, BIC supported
the TPM1uf+0+ I model.
Bayesian divergence time estimates were generated in
BEAST 1.8.4 (Drummond et al., 2012). The DNA dataset
was split into a nuclear and a chloroplast partition, with
unlinked substitution and clock models, and linked trees.
An uncorrelated relaxed (lognormal) clock was employed
for both partitions and the substitution models were imple-
mented according to the results of the jModelTest analyses.
A birth–death model for incomplete sampling was employed.
The root of the tree was calibrated at 202.01 Ma based on es-
timates in Laenen et al. (2014) for the split between the Ade-
lanthaceae and Cephaloziaceae in an analysis not factoring
Cylindrocolea dimorpha as an age constraint. The prior had
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K. Feldberg et al.: Taxonomic placement of incompletely preserved amber fossils 149
Figure 1. The Paleogene amber fossil Odontoschisma (sect. Iwatsukia) dimorpha. (a) Male shoot in ventral view; (b) androecium in dorsal
view; (c) male shoot in dorsal view; (d) portion of shoot in dorsal view; (e) portion of shoot in dorsal view; leaf-free cell strip discernible;
(f) shoot pp. in lateral and pp. in dorsal view, with asterisk indicating ventral branch; and (g) close-up from (f) (a–d from holotype; e–g from
Gröhn 2082).
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150 K. Feldberg et al.: Taxonomic placement of incompletely preserved amber fossils
Figure 2. Odontoschisma dimorpha. (a) Two ascending shoots in top view – note physical connection to small bark fragments; (b) ascending
shoots in ventral view – arrow points to underleaf; (c) deeply bifid underleaf; (d) leaf; (e) dense mat of creeping and ascending shoots on
bark fragment; (f) portion of ascending shoot, arrow points to underleaf; and (g) portion of shoot – arrows point to underleaves on ventral
side of shoot (a–d from Hoffeins 930-3; e, f from Gröhn 2038; g from Grolle M 12-8).
Foss. Rec., 20, 147–157, 2017 www.foss-rec.net/20/147/2017/
K. Feldberg et al.: Taxonomic placement of incompletely preserved amber fossils 151
a normal distribution with a mean of 202.01 and standard
deviation of 20 to account for the unknown confidence in-
terval. The analysis was run for 500 000 000 generations and
by sampling every 50 000th tree. Consequently, the final tree
file contained 10 000 trees. After a burn-in of 25 % a maxi-
mum credibility tree was compiled in TreeAnnotator 1.8.4,
which is part of the BEAST package. Effective sample size
was analyzed in TRACER v1.6 (Rambaut et al., 2014).
3 Results
3.1 Systematic paleontology
Odontoschisma (sect. Iwatsukia (N.Kitag.) Gradst.,
S.C.Aranda & Vanderp.) dimorpha (Casp.) Heinrichs,
K.Feldberg, Vánˇa & Schäf.-Verw., comb. nov.
Basionym: Jungermannia dimorpha Casp., Schr. Phys.-
Ökon. Ges. Königsberg 27:2. 1887.
≡ Cephaloziella dimorpha (Casp.) Grolle, Feddes Repert.
91:184. 1980.
≡ Cylindrocolea dimorpha (Casp.) Grolle, Liverw. Baltic
Bitterfeld Amber 14. 2004.
Holotype: MB.Pb.1979/687 (Künow amber collection
144a) (Fig. 1a–d).
Description
Plants small, prostrate or ascending, brown or reddish brown
(sometimes appearing whitish-green or yellowish as a result
of shrinking subsequent to embedding), creeping or form-
ing dense mats; leafy shoots 1–14 mm long, 0.10–0.56 mm
wide, sparingly ventral-intercalary branched (gyrothecal),
leafy, flagelliform or stoloniform; leafy shoots often tapering
into a long flagella or sectors with reduced, scaly leaves al-
ternating with sectors producing well-developed leaves. Rhi-
zoids diffusely distributed along ventral side of stem. Stems
rigid, 0.05–0.11(–0.14) mm in diameter, 3–6(–ca. 8) cells
high, epidermal cells surrounding slightly smaller or similar-
sized inner cells (discernible in two broken edges of stems),
epidermal cells short rectangular to rectangular, 15–25× 18–
30(–40) µm, walls moderately and evenly thickened, without
trigones. Leaves bilobed to about 30–50(–60) % of length,
more or less concave, distant to densely imbricate, suc-
cubously inserted, standing upwards to spreading or leaning
on the stem, insertion line oblique to subtransverse, usually
not extending to dorsal midline, dorsal leaf-free strip narrow,
(0–)1–2 cells wide; leaves variable in size and shape, some-
times reduced, scaly, if well-developed ovate to ovate-oblong
to rectangular, ca. 0.12–0.28 mm long (including lobes),
0.10–0.2 mm wide, as long as wide to somewhat longer than
wide, widest in or slightly below the middle and narrow-
ing towards base and apex, subsymmetrical, margins entire,
lobes broadly triangular to triangular, (2–)3–6(–8) cells wide
at base, apex acute, usually ending in a (bluntly) triangular
cell, sinus acute, narrowly to widely V-shaped. Leaf cells
more or less isodiametrical, some slightly elongate, 14–20(–
25) µm in midleaf, slightly smaller along margins, not be-
coming larger toward base, walls evenly thickened or becom-
ing slightly thicker towards corners, sometimes thin-walled,
cuticle verruculose, asperulate or smooth. Underleaves ab-
sent or well developed, especially on ascending but also on
some of the creeping shoots, up to ca. 0.12 mm long, elon-
gate triangular or elongate-ovate to almost rectangular, undi-
vided to deeply bifid, lobes 1–2 cells wide. Gemmae absent.
Dioicous (?, only sterile or male plants known). Androecia
with 3–8 pairs of bracts; bracts less deeply bifid and some-
what larger than leaves, terminal on elongate branches or
becoming intercalary by continued vegetative growth of the
branch; antheridia not observed. Gynoecia and sporophyte
unknown.
3.2 Additional specimens examined
3.2.1 Baltic amber
Bavarian State Collection for Palaeontology and Geology,
Munich, Germany:
SNSB-BSPG 1958 VIII 44 (Bachoven-Echt amber col-
lection P44); SNSB-BSPG 1958 VIII 95 (Bachoven-Echt
amber collection P95)
Geoscientific collections, Georg August University Göttin-
gen, Germany:
GZG.BST.21957 (Hoffeins amber collection 5-43);
GZG.BST.21959 (K7.319)
Gröhn amber collection, Glinde, Germany:
2015, 2038, 2082
Museum für Naturkunde Berlin, Germany:
MB.Pb.1979/654 (Künow amber collection 95);
MB.Pb.1979/688 (Künow amber collection 145);
MB.Pb.1979/689 (Künow amber collection 146);
MB.Pb.1979/708 (Künow amber collection 165a)
3.2.2 Bitterfeld amber
Geoscientific collections, Georg August University Göttin-
gen, Germany:
GZG.BST.21958 (Hoffeins amber collection 930-3)
Museum für Naturkunde Berlin, Germany:
MB.Pb.1997/2 (Kutscher amber collection H006);
MB.Pb.1997/16 (Kutscher amber collection M 8/6);
MB.Pb.1997/24 (Grolle amber collection M 10/5);
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152 K. Feldberg et al.: Taxonomic placement of incompletely preserved amber fossils
MB.Pb.1997/36 (Grolle amber collection M 12/8);
MB.Pb.1997/36 (Grolle amber collection M 12/9)
3.3 Divergence time estimates
The DNA-based divergence time estimates (Fig. 3) support
a late Early Cretaceous to early Eocene age of the Odon-
toschisma crown group (53.5–102.2 Myr). Odontoschisma
sect. Iwatsukia originated sometime between the Late Cre-
taceous and Oligocene (28.5–66.1 Myr).
4 Discussion
4.1 Morphological evidence and ecology
Grolle and Meister (2004) transferred the Eocene amber fos-
sil Cephaloziella dimorpha to Cylindrocolea (Cephaloziel-
laceae) because they regarded the complement of morpho-
logical features displayed by the fossil (i.e., small size of the
plant, the presence of entire-margined, bifid leaves with uni-
formly thickened leaf cell walls, ventral branching, and the
absence of a stem hyalodermis, underleaves and gemmae) as
more congruent with features seen in the latter genus than the
former. Our evaluation of the taxon based on series of amber
inclusions (Figs. 1, 2) corroborates the species circumscrip-
tions in Grolle (1980) and Grolle and Meister (2004). How-
ever, multicellular, deeply bifid underleaves may sometimes
occur, e.g., on the arcuately ascending shoots of specimens
Gröhn 2038 and Hoffeins 930-3, as well as on a prostrate
shoot in specimen Grolle M 12/8. These specimens are listed
as Cylindrocolea dimorpha in Grolle and Meister (2004:15).
Moreover, specimen Gröhn 2038 is regarded as particularly
“interesting” because it contains a small mat comprised of
several creeping and ascending shoots (Fig. 2e), substantiat-
ing the hypothesis that morphologically different shoots in
fact belong to the same species. Underleaves are not entirely
unknown in Cephaloziellaceae but typically are unlobed and
comprise only a few cells (Grolle, 1980; Schuster, 2002).
Based on the presence of bilobed underleaves (Fig. 2c,
g), we dismiss assignment of Cylindrocolea dimorpha to
Cephaloziellaceae. Rather, we propose affinities of the taxon
to Cephaloziaceae where deeply bifid underleaves occur
in Odontoschisma (Dumort.) Dumort. (Gradstein and Ilkiu-
Borges, 2015). The name Odontoschisma has long been used
exclusively for species with undivided leaves; however, the
genus concept was significantly expanded based on molec-
ular phylogenies (Vilnet et al., 2012; Aranda et al., 2014;
Feldberg et al., 2016). As currently circumscribed the genus
Odontoschisma also includes several species with divided
leaves that were earlier placed in the genera Cladopodiella
and Iwatsukia, two new synonyms of Odontoschisma (see
Gradstein and Ilkiu-Borges, 2015, for a review). Iwatsukia
had earlier been placed in a separate family, the Clado-
mastigaceae (Fulford, 1968), or was accommodated in the
Cephaloziaceae, and is currently treated as Odontoschisma
sect. Iwatsukia. This section is characterized by a greenish
color, exclusively ventral-intercalary branching, bifid leaves
with acute to long-acuminate apices and unbordered margins,
mid-leaf cells 10–30 µm long, with walls uniformly thick-
ened, a cuticle usually covered by wax crystals, and the an-
droecia occurring on specialized short branches or elongate
branches. The section includes the pantropical O. jishibae
(Steph.) L.Söderstr. & Vánˇa, as well as the neotropical O.
bifidum (Fulford) Gradst., S.C.Aranda & Vanderp. and O.
spinosum (Fulford) Gradst., S.C.Aranda & Vanderp. (Grad-
stein et al., 2014). Odontoschisma jishibae is one of the
smallest species in the genus and has also been described as
Cephaloziella flagellaris S.Hatt. (Hattori, 1950). The species
is regarded as morphologically variable, with leafy shoots
only a few millimeters long and at best 0.5 mm wide; it is
easily recognized by its deeply bifid leaves, cells with evenly
thickened walls, and the presence of numerous plasmodes-
mata in the transverse cell walls (Gradstein and Ilkiu-Borges,
2015). Leaves are densely imbricate and oriented towards the
stem apex or distant and spreading, with transverse to oblique
leaf insertions; underleaves are rudimentary or well devel-
oped and variable in size (Schuster, 1968; Vánˇa, 1993; Kon-
stantinova, 2004; Gradstein and Ilkiu-Borges, 2015). Cylin-
drocolea dimorpha resembles O. jishibae with regard to size
and habit, branching pattern, stem anatomy, leaf and under-
leaf shape, and the presence of more or less uniformly thick-
ened cell walls. Based on these similarities, we are confident
in interpreting C. dimorpha as a species of Odontoschisma,
and therefore propose the new combination Odontoschisma
dimorpha for the taxon. It is impossible to determine whether
wax crystals were present in the fossil; however, a few leaves
display a striately papillose cuticle that might constitute of
surface wax. Moreover, no plasmodesmata were detected in
the fossil leaf cells, but this might as well be a preservation
artifact. Finally, it is interesting to note that most O. dimor-
pha fossils are brownish to reddish-brown in color because
this coloration is unknown in extant representatives of sect.
Iwatsukia, but is characteristic of several other extant Odon-
toschisma species.
Based on the preceding considerations and comparison,
we believe that O. dimorpha should be retained as a sepa-
rate species, rather than regarded as fossil O. jishibae. Cas-
pary (1887), in his initial report on the holotype specimen,
selected the epithet “dimorpha” for the name because he
failed to correctly identify the androecia. Rather, this author
assumed that the plant produced two different types of leaves
(see Grolle, 1980). Although originally based on a simple
misinterpretation, the epithet is actually quite fitting for the
species. Leaves of ascending O. dimorpha shoots may be
more robust than those of prostrate shoots, which often are
somewhat scaly and more loosely arranged.
The extant Odontoschisma jishibae occurs in tropical and
warm-temperate regions of South Siberia, Japan, South Ko-
rea, Nepal, Malaysia and Papua New Guinea, East Africa,
Guinea and Costa Rica, from the lowlands to ca. 2700 m alti-
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K. Feldberg et al.: Taxonomic placement of incompletely preserved amber fossils 153
Figure 3. Phylogenetic chronogram of Cephaloziaceae based on DNA sequence variation of extant species, with secondary calibration from
Laenen et al. (2014). Confidence age estimate intervals shown as horizontal bars. Vertical bar indicates age interval of Baltic amber. Transfer
of the fossil Jungermannia dimorpha to Odontoschisma sect. Iwatsukia concurs with presented age estimates.
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154 K. Feldberg et al.: Taxonomic placement of incompletely preserved amber fossils
tude, and typically grows on decaying wood, trunk bases and
soil (Gradstein and Ilkiu-Borges, 2015). Several specimens
of O. dimorpha are enshrined together with small bark frag-
ments, suggesting that they grew on trunk bases of the resin-
exuding trees, i.e., conifers in the families Pinaceae or Sci-
adopityaceae (Wolfe et al., 2016). Other fossils of O. dimor-
pha occur in the amber without providing insights into the
substrate on which they grew; however, the presence of these
liverworts in amber indicates that they must have grown in
close proximity to a resin-exuding tree. Odontoschisma sect.
Iwatsukia today does not occur in the Baltic region; how-
ever, the Baltic amber forest grew in a distinctly warmer cli-
mate (Zachos et al., 2001). Most Baltic amber-bearing strata
have been dated as Priabonian, but a few likely extend into
the Lutetian. Baltic amber therefore ranges in absolute age
from 47 to 35 Myr (Standke, 2008). Although there is some
evidence to suggest that most Baltic amber fossils originate
from the youngest strata, the exact provenance and geologic
age of the O. dimorpha fossils remain unknown. Liverwort
fossils similar to O. dimorpha have also been reported in Bit-
terfeld amber, which is usually interpreted as late Oligocene
in age (24–25 Myr; Knuth et al., 2002; Blumenstengel, 2004;
Führmann, 2004; Standke, 2008). If the age estimates for
both ambers are correct, then morphological stasis occurred
in O. dimorpha over a period of at least 10 million years.
However, the incomplete preservation of the fossils has to
be taken into account; female structures, sporophytes and oil
bodies remain unknown.
Odontoschisma dimorpha appears to be a relatively com-
mon element in both the Baltic and Bitterfeld amber liver-
wort floras. Originally based on a single individual (Caspary,
1887), additional specimens have been reported over the
years (Caspary and Klebs, 1907). Grolle and Meister (2004)
list some 12 specimens from Baltic and 9 from Bitterfeld
amber. Additional specimens were reported by Frahm and
Gröhn (2013a, b). Odontoschisma dimorpha is not the first
fossil representative of the family Cephaloziaceae. Katagiri
(2015) recently described the Baltic amber fossil Cephalozia
veltenii T.Katag. and separated this form from O. dimorpha
based on the alleged presence of a hyalodermis. However, the
images of C. veltenii in Katagiri’s study suggest that the fos-
sil shrank subsequent to the curing of the resin and, as a re-
sult, is preserved in a cavity which depicts the original size of
the plant. We therefore submit that what appear as brownish
stem portions in this specimen represent the plant material,
while the whitish stem layers surrounding the brownish stem
represent the amber cavity with imprints of the outer plant
surface on the cavity wall. Cephalozia veltenii thus may be
synonymous with O. dimorpha.
4.2 DNA-based divergence time estimates
Deviations from DNA standard substitution rates are com-
monplace and have been documented for seed plants
(Bromham et al., 2013), ferns (Rothfels and Schuettpelz,
2014; Zhong et al., 2014; Crusz et al., 2016), and liver-
worts (Villarreal et al., 2016). As a result, age estimates for
Cylindrocolea that turn out roughly 3 times older by using
the Baltic amber fossil as a minimum age constraint than
estimates based solely on DNA sequence variation (Feld-
berg et al., 2013) come as no surprise. However, with regard
to the amber fossils detailed in this study these differences
are based on a misinterpretation of morphological evidence
(Grolle and Meister, 2004). Interpretation of Jungermannia
dimorpha as a member of Odontoschisma, rather than Cylin-
drocolea, favors estimates indicating a Miocene age (Laenen
et al., 2014) over others that suggest an Eocene age (Feldberg
et al., 2014) of Cylindrocolea.
Lineages of plants usually are somewhat older than their
oldest indisputable fossil representatives. Heinrichs et al.
(2015a) and Schneider et al. (2016) therefore proposed to in-
volve age hypotheses from independently generated molec-
ular chronograms in the taxonomic treatment of fossils.
These integrative approaches, which focus on the integra-
tion of evidence from different origins (Dayrat, 2005; Will
et al., 2005), may be misleading if the molecular clocks
greatly vary; however, extreme rate variations (Rothfels and
Schuettpelz, 2014) have rarely been reconstructed for seed-
free land plants, and approaches involving secondary calibra-
tions and standard substitution rates have therefore been ad-
vocated (Villarreal and Renner, 2014). We present divergence
time estimates of Cephaloziaceae based on a secondary cal-
ibration obtained from the most comprehensive chronogram
of liverworts generated without using the fossil Jungerman-
nia dimorpha as an age constraint (Laenen et al., 2014). Our
divergence time estimates support a late Early Cretaceous to
early Eocene age of the Odontoschisma crown group, and
suggest thatO. sect. Iwatsukia originated sometime between
the Late Cretaceous and Oligocene. Assignment of Junger-
mannia dimorpha to Odontoschisma sect. Iwatsukia does not
conflict with current hypotheses relative to the evolution of
Cephaloziaceae and lends further support to assumptions of
a minimum age of 35 Ma of O. sect. Iwatsukia based on the
age reconstruction of Baltic amber (Standke, 1998).
The chronogram for Cephaloziaceae shown in Fig. 3 is the
most comprehensive assessment to date with regard to taxon
sampling. The results are congruent with the divergence time
estimates provided in Feldberg et al. (2013, 2014) and Lae-
nen (2014), and support a Cretaceous to Paleogene age of
most generic crown groups, a recurrent pattern in the evo-
lution of leafy liverworts (Cooper et al., 2012). Similar hy-
potheses have been derived from amber fossils of liverworts
that usually match the morphology of extant genera (Hein-
richs et al., 2015b). Taxonomic conclusions drawn on the ba-
sis of the gross morphology of incompletely preserved am-
ber fossils are problematic, and hence additional evidence
is always intensively sought after and highly welcome. In-
tegrative approaches using a combination of morphological
evidence and evidence generated from the DNA variation
of extant species (Heinrichs et al., 2007, 2015a) have dis-
Foss. Rec., 20, 147–157, 2017 www.foss-rec.net/20/147/2017/
K. Feldberg et al.: Taxonomic placement of incompletely preserved amber fossils 155
missed hypotheses on affinities of certain Eocene amber fos-
sils to the extant species Nipponolejeunea subalpina (Horik.)
S.Hatt. and Ptilidium pulcherrimum (Weber) Vaino (Grolle
and Meister, 2004). Cylindrocolea dimorpha is only the third
example of a fossil liverwort in which molecular data were
used to substantiate or revise a taxonomic decision that was
based on morphological evidence.
5 Conclusions
An integrative taxonomic approach using morphological and
independent, DNA-based evidence suggests that the fossil
liverwort Cylindrocolea dimorpha needs to be transferred
from Cephaloziellaceae to Cephaloziaceae, and supports
affinities of the fossil to the extant genus Odontoschisma.
This study underlines the importance of correctly identified
fossils for our understanding of evolutionary patterns in liv-
erworts, an early diverging lineage of land plants with a poor
fossil record (Taylor et al., 2009), and advocates the assess-
ment and integration of different lines of evidence in taxo-
nomic studies of incompletely preserved fossils. We antici-
pate that such integrative studies will lead to a better under-
standing of the liverwort fossil record and will provide more
precise insights into the evolution of this early land plant lin-
eage than studies considering only a single line of evidence.
Data availability. All necessary data are available in the Supple-
ment.
Information about the Supplement
Taxa used in the divergence time estimates, including infor-
mation about the origin of the studied material, voucher in-
formation, and GenBank accession numbers.
The Supplement related to this article is available online
at doi:10.5194/fr-20-147-2017-supplement.
Competing interests. The authors declare that they have no conflict
of interest.
Acknowledgements. We thank Christel and Hans Werner Hoffeins
(Hamburg) for providing their liverwort fossils to the Geoscientific
Museum Göttingen, and Alexander Gehler (Göttingen), Christian
Neumann (Berlin) and Martin Nose (Munich) for making the amber
collections of the Geoscientific Museum Göttingen, the Museum
für Naturkunde at Berlin and the Bavarian State Collection for
Palaeontology and Geology available for study.
Edited by: C. Bickelmann
Reviewed by: A. Hagborg and one anonymous referee
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