Conifers of the ‘Baltic Amber Forest’ and their palaeoecological Significance

2017·11.5 MB·English

by  Sadowski, Eva-Maria

EVA-MARIA SADOWSKI,
ALEXANDER R. SCHMIDT,
LEYLA J. SEYFULLAH
& LUTZ KUNZMANN
CONIFERS OF THE
‘BALTIC AMBER FOREST’ AND
THEIR pALAEOECOLOgICAL
SIgNIFICANCE
Stapfia 106 (2017)
Stapfia 106 (2017), ISSN 0252-192X
Land Oberösterreich
Biologiezentrum des Oberösterreichischen
Landesmuseums, Linz, Austria
Eva-Maria SadowSki, Alexander R. Schmidt, Leyla J. Seyfullah & Lutz kunzmann
Conifers of the ‘Baltic amber forest’ and
their palaeoecological significance
Abstract: Eocene Baltic amber constitutes the largest amber deposit on Earth, however, knowledge about
the vegetation and habitat diversity of its source area is very fragmentary. We analysed coniferous foliage from
several historic Baltic amber collections and from new material, and consequently verify the occurrence of
Calocedrus, Quasisequoia and Taxodium (Cupressaceae), Cupressospermum (Geinitziaceae), Abies, Cathaya,
Nothotsuga, Pseudolarix and Pinus (Pinaceae) in the ‘Baltic amber forest’. Except for Pinus, these taxa have
not been unambiguously reported from Baltic amber. The historic descriptions of putative Abies inclusions
from Baltic amber are revised as these specimens are angiosperm leaves, but we provide evidence for the
presence of this genus based on a newly found fossil. The amber fossils of these nine conifer genera, along
with recently described cladodes of Sciadopitys cf. tertiaria (Sciadopityaceae), indicate the presence of coastal
swamps and mixed mesophytic conifer-angiosperm forests. Available data from extant and extinct analogues of
these conifers suggest that Baltic amber derives from humid warm-temperate forests, with the closest modern
analogues being the warm-temperate zonobiome of East Asia and North America. Comparison of the conifer
diversity from Baltic amber to other Eocene floras from Europe furthermore suggests a late Eocene age of the
Baltic amber. Our results thus challenge previous notions that Baltic amber derives from early Eocene tropical
or ‘subtropical’ forests.
Keywords: Baltic amber age, Baltic amber flora, fossil conifers, palaeoecology.
SadowSki, E.-M., SchMidt, a. R., SEyfullah, l. J. & kunzMann, L. (2017): Conifers of the ‘Baltic amber
forest’ and their palaeoecological significance. — Stapfia 106: 1–73. - ISSN 0252-192X
2 | STApFIA 106 (2017)
Stapfia 106 (2017), ISSN 0252-192X
Land Oberösterreich
Biologiezentrum des Oberösterreichischen
Landesmuseums, Linz, Austria
Eva-Maria SadowSki, Alexander R. Schmidt, Leyla J. Seyfullah & Lutz kunzmann
Die Koniferen des ‚Baltischen Bernsteinwaldes‘
und ihre paläoökologische Bedeutung
Zusammenfassung: Der eozäne Baltische Bernstein bildet die weltweit größte Bernsteinlagerstätte, je-
doch sind unsere Kenntnisse über die Vegetation und die Vielfalt der Lebensräume seines Herkunftsgebie-
tes sehr fragmentarisch. Die Untersuchung von Koniferennadeln aus historischen Bernsteinsammlungen und
von neuen Fundstücken zeigt das Vorkommen von Calocedrus, Quasisequoia und Taxodium (Cupressaceae),
Cupressospermum (Geinitziaceae), Abies, Cathaya, Nothotsuga, Pseudolarix und Pinus (Pinaceae) im
‚Baltischen Bernsteinwald‘. Mit der Ausnahme von Pinus waren diese Gattungen bisher noch nicht zweifelsfrei
aus Baltischem Bernstein nachgewiesen worden. Die bisher als Abies identifizierten Inklusen aus historischen
Sammlungen wurden revidiert, da es sich bei ihnen um Angiospermenblätter handelt, jedoch konnte eine neu
entdeckte Inkluse zweifelsfrei der Gattung Abies zugeordnet werden. Zusammen mit den kürzlich beschrie-
benen Kladodien von Sciadopitys cf. tertiaria (Sciadopityaceae) zeigen diese neun Koniferengattungen das
Vorkommen von Küstensümpfen sowie gemischten mesophytischen Koniferen-Angiospermenwäldern an. Die
verfügbaren ökologischen Daten der zu den Konifereneinschlüssen analogen rezenten und ausgestorbenen Taxa
verweisen auf feuchte warm-temperate Waldgebiete, die denen des heutigen warm-temperaten Zonobioms Ost-
asiens und Nordamerikas ähneln. Der Vergleich der Koniferendiversität des Baltischen Bernsteins mit anderen
eozänen Floren Europas deutet zudem auf ein späteozänes Alter des Bernsteins hin, was bisherigen Annahmen
eines tropischen bis ‚subtropischen‘ früheozänen ‚Baltischen Bernsteinwaldes‘ widerspricht.
Keywords: Alter des Baltischen Bernsteins, Baltische Bernstein Flora, Fossile Koniferen, Paläoökologie.
SadowSki, E.-M., SchMidt, a. R., SEyfullah, l. J. & kunzMann, L. (2017): Conifers of the ‘Baltic amber
forest’ and their palaeoecological significance. — Stapfia 106: 1–73. - ISSN 0252-192X
STApFIA 106 (2017) | 3
ADRESSES OF AUTHORS
Eva-Maria SadowSki*, Alexander R. SchMidt, Leyla J. SEyfullah
Department of Geobiology, University of Göttingen, Goldschmidtstraße 3, 37077 Göttingen, Germany
Lutz kunzMann
Senckenberg Natural History Collections Dresden, Museum of Mineralogy and Geology,
Königsbrücker Landstraße 159, 01109 Dresden, Germany
*Correspondence to: [email protected]
4 | STApFIA 106 (2017)
SYSTEMATIC PIANLTAREOODBUOCTTAIONNY
INTRODUCTION
With estimated over 600,000 tons, Baltic amber forms the altitudinal zones. ander (1942) further described the ‘Baltic am-
largest deposit of any fossil resin on Earth. It is renowned for a ber forest’ as a warm-temperate, moist, dense, and cool ‘jungle’
vast diversity of organismic inclusions, predominantly arthro- mainly composed of conifer trees.
pods (Weitschat & Wichard 2010). Although Baltic amber A similar picture of the ‘Baltic amber forest’ was suggested
yields highly diverse and significant fossils, only little is known
by bachofen-echt (1949) and larsson (1978) who emphasized
about the structure and composition of the amber-bearing
the various climatic implications of taxa from the Baltic amber
forests, mainly because of the scarcity of determinable plant in-
flora and fauna. These taxa comprised elements which today
clusions. In contrast to over 3,000 species of arthropods, only
occur in (sub)tropical to temperate zones, hinting to a diverse
approximately 200 plant taxa have so far been described from
landscape which combined lowlands and mountain ranges cov-
Baltic amber (Czeczott 1961; Weitschat & Wichard 2010). ered by mixed forests, few meadows, as well as stagnant water
Although it is generally accepted that succinite, the main bodies and arid areas (Bachofen-Echt 1949, larsson 1978).
chemical variety (>90%) of Baltic amber (Langenheim 2003), In a comprehensive paper about the Baltic amber flora,
derives from a conifer, there is conflicting evidence from
czeczott (1961) summarized the described Baltic amber plants
macrofossils and resin chemistry about its precise botanical
from the last decades and their extant analogous taxa. She high-
source (Wolfe et al. 2009; Dolezych et al. 2011). Comprehen- lighted the high proportion of tropical and subtropical plant taxa
sive knowledge about the diversity of resinous trees is needed
(23% of the total number of species) in the Baltic amber flora
to solve the question of the botanical provenance of succinite,
and confirmed ander’s (1942) suggestions of a moist dense
and to elucidate the so called Baltic amber forest as a habitat.
amber forest. She further saw evidence that open glades existed
Gymnosperm inclusions from Baltic amber had been intensi-
which were inhabited by deciduous trees (Czeczott 1961).
vely investigated from the mid-19th up to the early 20th century
(Goeppert & Berendt 1845; Conwentz 1886, 1890; Goeppert & Contrary to ander (1942) and czeczott (1961), schubert
Menge 1883; Caspary & Klebs 1907; Bachofen-Echt 1949). In (1953, 1961) and rüffle & helms (1970) proposed drier condi-
tions for the Baltic amber source area, similar to the ‘hammocks’
these comprehensive studies a high number of different conifer
of Florida or mountain steppe forests of Cuba. Following the
taxa were described, with the Cupressaceae and Pinaceae being
interpretation of the latter authors, the ‘Baltic amber forest’ was
most abundant, and few species assigned to the former Taxodi-
aceae (now included in the Cupressaceae), Podocarpaceae and dominated by pines and palms with sclerophyllous vegetation
Sciadopityaceae (Spahr 1993). The most recent review of these along rivers and pine-oak forests in higher montane areas. In
conifers (Czeczott 1961) suggested that some of the assignments her re-evaluation of previous Baltic amber studies, Kohlman-
are invalid, leading to two remaining families (Cupressaceae and adamsKa (2001) placed these pine-oak steppe-forests in lower
Pinaceae) which comprise in total 33 species. However, the esti- mountainous areas and suggested that pure conifer forests were
mations by czeczott (1961) are based on literature reviews only, located at higher altitudes. Furthermore, she suggested the pres-
and the holotypes had not been re-investigated. During World ence of humid swamp habitats along river valleys at lower eleva-
War II, numerous original specimens from Baltic amber collec- tions of the Baltic amber source area. She concluded that the
tions were lost or destroyed, so the current whereabouts of many topography of the area, as well as the location of the ‘Baltic
holotypes are unknown. amber forest’ in the transition of the temperate to subtropical
zone led to the high diversity of the flora, ranging from a warm-
The lack of knowledge about the Baltic amber flora led to
different interpretations of the ‘Baltic amber forest’ as an eco- temperate to subtropical climate (Kohlman-AdamsKa 2001).
system, its floristic composition, and palaeoecology. goeppert In more recent publications, the ‘Baltic amber forest’ was
(1853) and caspary (1872) highlighted affinities of the Baltic often regarded as tropical, combined with mountainous subtrop-
amber vegetation to extant floras of northern latitudes which, ical rain forests (Weitschat 1997; Weitschat 2008; Wichard et
according to these authors, indicated the presence of high moun- al. 2009; Weitschat & Wichard 2010). In contrast, coleopteran
tain ranges. caspary (1872) furthermore suggested that subtro- inclusions from Baltic amber studied by aleKseev & aleKseev
pical species were located in the lowlands of the forest areas. (2016) hint to a plain landscape with a thermophilic, humid-
goeppert & menge (1883) regarded the Baltic amber vegeta- mixed climax forest community.
tion as mixture of different habitats, ranging from forests and It is the aim of this study to evaluate previously described
swamps to meadows. Contrarily, conwentz (1890) emphasized and recently found inclusions of conifer needles from Baltic am-
the role of pine trees in the ‘Baltic amber forest’ as the dominant ber taxonomically and palaeoecologically, and to use these fos-
tree taxon, forming closed and almost pure stands which were sils along with data from their closest fossil and extant analogues
only scarcely intermingled with deciduous tree species. for reconstructing habitats and climate of the source area of the
In his extensive survey of the Baltic amber fauna, ander Baltic amber. We provide evidence of nine conifer genera from
(1942) found evidence that the majority of the examined ani- Baltic amber and use them, along with the previously reported
mal species indicate a warm-temperate to subtropical climate. genus Sciadopitys siebold et zucc., to estimate habitat structure
Considering the former knowledge of the Baltic amber flora, he and climate of the Baltic amber source area. Our findings indi-
interpreted the presence of different climatic indicator taxa as cate heterogeneous warm-temperate humid forests with swampy
a result of the vertical stratification of the forest into different habitats, mesophytic forest patches and open light areas.
STAPFIA 106 (2017) | 5
MSYASTTeERMIAAlT AICN PDA MLAeTEhOOBDOSTANY
MATeRIAl AND MeThODS were used simultaneously. All figures are digitally stacked pho-
tomicrographic composites of up to 120 individual focal planes,
obtained by using the software package HeliconFocus 5.0. Some
Origin and age of the fossils
of the overview images result from merging up to four photo-
Baltic amber mainly derives from the amber-bearing ma- micrographic composites using the Adobe Photoshop CS6 soft-
rine ‘Blue Earth’ layers that are predominantly exposed in the ware (Figs 2a; 3a; 4a; 5a and e; 10b; 13e and f; 14a, d, e; 17a, b;
Samland area of Kaliningrad (Russia), but Baltic amber is also 23a; 26a, b; 30a; 32a, b). Using a micrometre eyepiece, the most
frequently found washed ashore along the coast of the Baltic Sea important morphological features of the fossils were measured,
and in adjacent areas. comprising the total size of the inclusions, the leaf size, the size
of the stomata complex and the stomatal pit (for details of the
The age of the Baltic amber is still under debate. Based on
stomata morphology, see Fig. 1).
pollen and dinoflagellate data, the main Baltic amber source lay-
er, the Blue Earth, was estimated to be upper Eocene (Priabo- Where the holotypes and other previously described mate-
nian) in age (34-38 Ma) (KosmowsKa-Ceranowicz et al. 1997). rial were lost, we used the original illustration and descriptions
Few amounts of amber also occur in older sediments (Lower from goeppert & berendt (1845), goeppert & menge (1883),
Blue Earth, Lutetian) and even in younger horizons (Lower conwentz (1890) and caspary & Klebs (1907) to evaluate the
Gestreifter Sand, upper Oligocene), leading to an estimated age fossils (Figs 6; 7; 16; 18–21; 24; 25; 33; 34).
range of approximately 23 to 48 million years for all Baltic am-
ber bearing strata (KosmowsKa-Ceranowicz et al. 1997; StandKe
1998; Kasiński & KramarsKa 2008; StandKe 2008). Terminology
The frequently cited Lutetian age of the Baltic amber from
In our study, as well as in the previous literature describing
the Blue Earth was suggested by ritzKowsKi (1997) who dated
the ‘Baltic amber forest’, the terms ‘tropical’, ‘subtropical’ and
glauconites deriving from the Blue Earth layer. However, a study
‘warm-temperate’ are used. Because these terms have been dif-
by clauer et al. (2005) showed that this dating method can lead
ferently applied in the literature, their use could easily lead to
to older age estimations if the glauconites have been reworked or
misunderstandings. The definitions of these terms are therefore
if non-glauconized detrital mica ‘contaminated’ the glauconite
shortly discussed in this section.
splits.
The tropics extend to ± 23.4° latitude which is mainly
Possible redeposition of the Baltic amber into the Blue Earth
layer also has been discussed (Weitschat & Wichard 2010). How- determined by the overhead sun (Corlett 2013). This ‘solar
definition’ is widely accepted, although more specific defini-
ever, amber from the Blue Earth layer does not show typical signs
of erosion which normally occur if amber has been re-worked, tions exist which include temperature and vegetation (Corlett
such as ‘pebble-shaped’ amber pieces or a dark oxidised crust. 2013). As summarized by domroes (2003), the tropical climate
is characterized by “homogeneous intra-annual temperature
In contrast, the majority of the Blue Earth amber is of a fresh
condition” (diurnal climate), lacking seasonality. For defining
lemon yellow colour and unoxidised (Grimaldi & Ross 2017).
the northern and southern boundary of the tropics, the mean
However, the pollen and dinoflagellate derived age estimation
of Baltic amber still needs validation by an independent data set annual temperature of 18.3°C is used (Domroes 2003). The
so called tropical rainforest is an unspecific term, since many
that is able to link the Baltic amber Lagerstätte to the global time
different forest types exist within the equatorial region and
scale. In short, a late Eocene age of both the ‘Baltic amber forest’
thus, a generalized picture is difficult to achieve. Very general-
and the main amber Lagerstätte is commonly assumed but not
ly speaking, they share features such as a highly diverse tree
unambiguously proven.
stratum divided into storeys with trees of different heights, a
We searched through several historic amber collections
dense canopy and only scarce light in the undergrowth. Further
which harbour botanical type material such as the collections
commonly used characteristics of a ‘tropical rainforest’ are a
of Carl Georg Berendt and Georg Künow at the Museum für
large leaf size of most plants, the dominance of phanerophytes
Naturkunde Berlin, and the Königsberg Amber Collection at the
(about 70% of all species) and the presence of lianas and epi-
University of Göttingen, and we also considered recently found
phytes (Walter & BrecKle 2002c).
amber pieces with conifer inclusions. Table 1 shows the reposi-
tory of all taxa described in this study. Following corlett (2013), the term ‘subtropical’ is arbi-
trary, since no unambiguous definition exists. From an etymo-
logical point of view, it describes a subdivision of the tropics,
Preparation and imaging but commonly it is applied for regions bordering the tropics
(Corlett 2013). Physical geographers define the ‘subtropics’
In order to remove scratches and fissures, most amber climatically, extending to 35 to 40° latitude. The coldest month
specimens were slightly further ground and polished manually mean temperature is also frequently used to define the north-
using wet silicon carbide papers (grit from 25.8 to 5 µm particle ern limits of the ‘subtropics’ and varies between 6°C or -3°C
size, Struers company) for creating smooth and even surfaces (Corlett 2013). The most commonly used climate classifica-
parallel to the inclusions. This allows a better visualization of tion of Köppen-Geiger does not apply the term ‘subtropics’, but
cellular details such as the stomata and cell morphology. The distinguishes between tropical, arid, temperate, cold and polar
amber inclusions were examined under a Carl Zeiss AxioScope climates with several subdivisions (Köppen 1900; Geiger 1952;
A1 compound microscope and a Carl Zeiss Stereo Discovery Peel et al. 2007). Following petersen et al. (2015), the Cfa cli-
V8 dissecting microscope, each equipped with a Canon EOS 5D mate sensu Köppen-Geiger (temperate, without dry season, hot
digital camera. In most instances incident and transmitted light summer), corresponds to a ‘humid subtropical’ climate, with
6 | STAPFIA 106 (2017)
SYSTEMATIC PALAEOBOTANY
gures g. 2 g. 3 g. 4 g. 5a-d g. 5e-g g. 6a-d g. 6e-f g. 7 g. 8 g. 10 g. 9 g. 11 g. 12 g. 13 g. 14a-c g. 14d-g g. 15 g. 16a-c g. 16d-f g. 16g-i g. 17 g. 18 g. 19a-f g. 19g-j g. 22 g. 20
Fi Fi Fi Fi Fi Fi - - Fi Fi Fi Fi Fi Fi Fi Fi Fi Fi Fi Fi - - Fi Fi Fi Fi Fi Fi Fi Fi Fi
er
b
m
u
n
n
o
Former collecti G 3616 G 3536 Gröhn P 6380 G 3537 G 3613 B 648 - - 136 - G 4397 S B 13 Hoffeins 186-1 - G 35 Hoffeins 130-1 G 1916 Casp. 159 G 3627 Hoffeins 229 Hoffeins 1069/4 - - - Gröhn P 6357 42 - 5 G 23 -
er
b
m
u
n
n
ctio 32 45 33 06 50 33 20 95 33 96 35 06 52 99 00 54
e 6 6 6 6 5 3 5 8 5 8 5 4 6 8 9 6
Current coll GZG.BST.24 GZG.BST.24 GPIH 4583 GZG.BST.24 GZG.BST.24 GZG.BST.24 Gröhn P 25 - - - GZG.BST.24 GZG.BST.23 GZG.BST.21 IX 73 GZG.BST.23 GZG.BST.21 GZG.BST.23 GZG.BST.24 GZG.BST.24 GZG.BST.21 GZG.BST.21 - - - GPIH 4584 - - - GZG.BST.24 -
gen gen urg gen gen gen gen gen gen gen gen gen gen gen gen gen urg gen
n n b n n n n n n n n n n n n n b n
ötti ötti am ötti ötti ötti ötti ötti ötti ötti ötti ötti ötti ötti ötti ötti am ötti
G G H G G G G G G G G G G G G G H G
nstitution University of University of University of University of University of University of Glinde ost ost ost University of University of University of dstein University of University of University of University of University of University of University of ost ost ost University of ost ost ost University of ost
y. I l l l I l l l l l l l
d
described and examined in this stu Name of collection Königsberg Amber Collection Königsberg Amber Collection Carsten Gröhn Amber Collection Königsberg Amber Collection Königsberg Amber Collection Königsberg Amber Collection Carsten Gröhn Amber Collection Goeppert Collection Künow Amber Collection Caspary's private collection Königsberg Amber Collection Königsberg Amber Collection Hoffeins Amber Collection Jürgen Velten Amber Collection Königsberg Amber Collection Hoffeins Amber Collection Königsberg Amber Collection Königsberg Amber Collection Königsberg Amber Collection Hoffeins Amber Collection Hoffeins Amber Collection Menge Collection Menge Collection Menge Collection Carsten Gröhn Amber Collection Künow Amber Collection Künow's private collection Collection of the ‘Physikalisch-ökonomische Gesellschaft Königsberg’ Königsberg Amber Collection Caspary's private collection
a
x
a
m t
er
p
s
o
gi
n
a
d
an m
Tab. 1: Repository of conifer Fossil taxon Cupressaceae Calocedrus sp. Calocedrus sp. Quasisequoia couttsiae Quasisequoia couttsiae Quasisequoia couttsiae Quasisequoia couttsiae Quasisequoia couttsiae Widdringtonites oblongifolius Widdringtonites oblongifolius Sequoia couttsiae Taxodium sp. Glyptostrobus europaeus Geinitziaceae Cupressospermum saxonicu Pinaceae Abies sp. Cathaya sp. Nothotsuga protogaea Nothotsuga protogaea Nothotsuga protogaea Pinus baltica Pinus baltica Pinus baltica Pinus baltica Pinus banksianoides Pinus silvatica Pinus serrata Pinus serrata Pinus künowii Pinus schiefferdeckeri Pinus aff. schiefferdeckeri Pinus dolichophylla
STAPFIA 106 (2017) | 7
SYSTEMATIC PALAEOBOTANY
es 1a-d 1e-i 3 4 5a-f 5g-m 6 7 8a-e 8f-i 9 0 1 2 3 4
gur g. 2 g. 2 g. 2 g. 2 g. 2 g. 2 g. 2 g. 2 g. 2 g. 2 g. 2 g. 3 g. 3 g. 3 g. 3 g. 3
Fi Fi Fi Fi Fi Fi Fi Fi Fi Fi Fi Fi Fi Fi Fi Fi Fi - - - - - - - - - - - - -
er
b
m
u
n
n
o
Former collecti - - Hoffeins 1187-1 - - 176 G 4560 Hoffeins 997 Casp. 210 B 14564 - B 14645 Casp. 52 IB.C17 - - - G 3517 Hoffeins 1045-2 G 1956 G 4507 G 4508 G 44 G 3548 96 268 283 288 290
er
b
m
u
n
Current collection - - GZG.BST.21897 - - - GZG.BST.24338 GZG.BST.21898 GZG.BST.23536 GZG.BST.24334 MB.Pb.1979/0591 GZG.BST.23539 GZG.BST.24355 MB.Pb.1979/0490 - - Gröhn P 3655 GZG.BST.23540 GZG.BST.21901 GZG.BST.24336 GZG.BST.24346 GZG.BST.24332 GZG.BST.24610 GZG.BST.24651 MB.Pb.1979/655 MB.Pb.1979/764 MB.Pb.1979/768l MB.Pb.1979/768qu MB.Pb.1979/768s
n n n n n n n
erli erli erli erli erli erli erli
B B B B B B B
n n n n n de n n de n n n n n n n de de de de de
e e e e e n e e n e e e e e e e n n n n n
g g g g g u g g u g g g g g g g u u u u u
n n n n n k n n k n n n n n n n k k k k k
Götti Götti Götti Götti Götti Natur Götti Götti Natur Götti Götti Götti Götti Götti Götti Götti Natur Natur Natur Natur Natur
nstitution ost ost University of ost ost ost University of University of University of University of Museum für University of University of Museum für ost ost Glinde University of University of University of University of University of University of University of Museum für Museum für Museum für Museum für Museum für
I l l l l l l l
n
o
on on on on on ecti on on on on on on
Name of collection ? ? Hoffeins Amber Collection Westpreußisches Provinzialmuseum Danzig Klebs Amber Collection Künow Amber Collection Königsberg Amber Collecti Hoffeins Amber Collection Königsberg Amber Collecti Königsberg Amber Collecti Berendt Amber Collection Königsberg Amber Collecti Königsberg Amber Collecti Berendt Amber Collection ? Künow Amber Collection Carsten Gröhn Amber Coll Königsberg Amber Collecti Hoffeins Amber Collection Königsberg Amber Collecti Königsberg Amber Collecti Königsberg Amber Collecti Königsberg Amber Collecti Königsberg Amber Collecti Künow Amber Collection Künow Amber Collection Künow Amber Collection Künow Amber Collection Künow Amber Collection
s')
u
s obtusifolius') uckerii') uckerii') ophyllites poros btusifolia') nearis')
bietite bies s bies s ermat bies o bies li
A A A D A A
Tab. 1: continued Fossil taxon Pinites rigidus Pinus subrigida Pinus cembrifolia Pinus cembrifolia Pinus cembrifolia Pinus cembrifolia Pseudolarix sp. Pseudolarix sp. Pseudolarix sp. Pseudolarix sp. Angiosperms Dicotylophyllum sp. (' Dicotylophyllum sp. (' Dicotylophyllum sp. (' Dicotylophyllum sp. (' Dicotylophyllum sp. (' Dicotylophyllum sp. (' Dicotylophyllum sp. Dicotylophyllum sp. Dicotylophyllum sp. Dicotylophyllum sp. Dicotylophyllum sp. Dicotylophyllum sp. Dicotylophyllum sp. Dicotylophyllum sp. Dicotylophyllum sp. Dicotylophyllum sp. Dicotylophyllum sp. Dicotylophyllum sp. Dicotylophyllum sp.
8 | STAPFIA 106 (2017)
SYSTEMATIC PALAEOBOTANY

Fig. 1: Terminology of the stomata morphology used in this study (from Florin 1931 and Ewin 2004). (a) Cross section through a conifer stoma,
adapted from Ewin (2004). (b) Surface view on a conifer stoma. (c) Stomata features which were measured in this study; the stomata complex is
shaded in grey.
high temperatures, convectional precipitation during the sum- al. (2006) the warm-temperate climate type (C) is subdivided
mer season and colder temperatures with occasional frosts dur- into seven sub-climates (Cfa, Cfb, Cfc, Csa, Csb, Csc, Cwa),
ing winter. encompassing fully humid climates to summer or winter dry
Beside these examples, even more definitions exist (see climates with different temperature regimes (e.g. hot summer,
corlett 2013 for details); hence, corlett reviewed the current warm summer, cool summer). In the most current update of
usage of the term ‘subtropical’ in the scientific literature and this classification by peel et al. (2007), the main climate class
summarized that in most instances the term is used to describe C was termed ‘temperate’, although the subdivision stayed the
the transitional zone between tropical and temperate regions. same. In the climatic descriptions of the ‘Baltic amber forest’,
Thus, corlett (2013) suggested to define “the subtropics as a no specific definition of the term ‘warm-temperate’ was given
fixed latitudinal belt, as we do for the tropics”, located between so far; thus, we assume that it was used following the main cli-
23.4° and 30.0°. mate C sensu Köppen-Geiger, since this classification system
Despite the unspecific meaning of the ‘subtropics’, this term is the most common climate map used among scientists (Peel
is frequently used in the scientific literature about the ‘Baltic am- et al. 2007).
ber forest’. However, the particular authors did not clarify how Since climate C (warm-temperate or temperate) sensu
they defined the ‘subtropics’. Köppen-Geiger encompasses several different sub-climates
When referring to the climate of the ‘Baltic amber forest’, and regions, we decided to refer to the more specific zono-
the term ‘warm-temperate’ also occurs. In the updated world biome concept by walter & brecKle (2002a) which not only
map of the Köppen-Geiger climate classification by KotteK et combines climatic data, but also vegetation and soil types to
STAPFIA 106 (2017) | 9