Vol.5, No.11, 1154-1164 (2013) Natural Science
The most northerly record of the sirenian Protosiren
and the possible polyphyletic evolution of manatees
and dugongs
Cajus G. Diedrich
Paleologic, Petra Bezruce 96, Zdice, Czech Republic; cdiedri@gmx.net, www.paleologic.eu
Received 6 April 2013; revised 6 May 2013; accepted 14 May 2013
Copyright © 2013 Cajus G. Diedrich. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Newly discovered remains of the early Middle
Eocene (Lutetian) sirenian Protosiren (Protosi-
renidae) in shark tooth rich conglomerates from
a coastal delta environment northwest of the
European Rhenish Massif at Fürstenau (north-
western Germany), represent the most northerly
occurrence of this genus w hose global distribu-
tion was generally restricted to warm waters. Its
presence of the remains so far north can be ex-
plained by seasonal inflow of warm Tethys sur-
face water into the cool, upwelling-influenced,
basin. The existence of two discrete centers of
sirenian evolution can be explained by the
opening of the Atlantic and the upwelling that
separated the North American warm water fau-
nal province from those of Africa and Eurasia. A
slightly modified evolutionary model is pre-
sented in which the oldest Early Eocene mana-
tee sirenians evol ved in the Caribbea n of Centr al
America. Protosiren, however, appears to have
developed polyphyletically along the African
coastline of the Tethys, and represents the old-
est known dugong ancestor. Younger (Oligo-
cene) European sirenian skeletons of Halith-
erium and Anomotherium are included in the
phylostratigraphic model in which sirenians had
generally reduced their teeth by 28 Ma as an
adaptation for feeding on sea-plants (macroal-
gae/seagrass). Teeth from early megatooth
sharks, which preyed on sirenians, have been
recorded from shallow marine Eocene and Oli-
gocene coastlines of the southern proto-North
Sea Basin, and shark bite marks have been
found on sirenian skeletons.
Keyw ords: Sirenian Remains; Early Middle Eocene;
Palaeobiogeography; Olde st Sirenians of the
Proto-North Sea Basin of Central Europe
Extant manatees and dugongs, together with the re-
cently extinct Steller’s seacow, are three distinct types of
modern sirenian [1] that have their earliest origins in the
Late Palaeocene to Early Eocene (Figure 1) [2-4]. The
most primitive skeletons of quadrupedal sirenians (Ypre-
sian, Early Eocene) ever found in the shallow marine
palaeoenvironments of the Middle American Caribbean
are of the primitive Prorastomus and the slightly more
evolved Pezosiren (Figure 1) [5]. The global fossil re-
cord for sirenians in the Eocene is much poorer, as it is
also in the Oligocene and Miocene [1], and therefore
new discoveries, especially well dated material in a bio-
diverse and palaeoecological context, are important to
our understanding of the evolution and life of the basal
Early Middle Eocene (Lutetian) sirenian remains from
the new sirenian locality at Dalum, near Fürstenau
(north-western Germany, Figure 2) are also considered
herein. The shallow coastal and slightly carbonatic Eo-
cene sands at this locality have been bioturbated by
crustaceans and are interrupted by a transgressive con-
glomerate bed in which phosphorite nodules and verte-
brate remains are concentrated [6]. Those conglomerates
within the Fürstenau Formation are extraordinarily rich
in shark teeth, and also contain coprolites from several
different sharks, including megatooth and white shark
forms [6-8]. The rich shark biodiversity, which includes
about 15 species with tooth sizes larger than 5 mm, also
includes more rare large, serrated teeth up to eight cen-
time tres from th e megatooth Otodus and teeth up to four
centimetres from the white shark Carcharodon [8]. The
relationship between megatooth sharks and their first
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C. G. Diedrich / Natural Scienc e 5 (2013) 1154-1164 1155
Figure 1. Polyphyletic model of sirenian evolution. General tooth reduction took place as an adaptation for feeding on
sea-plants (with the greatest reduction occurring already in Dusisiren of the Hydrodamalinae). Northern German
Proto-North Sea Basin records are marked in red, after [5-37,34-48]. The relative position of Anomotherium has been
altered and the ancestral connection for the Trichechidae remains open. Sirenians may have coevolved, with conver-
gent marine adaptation, in two different parts of the world.
marine mammal prey (Figure 3) has been recently dis-
cussed in detail with respect to their coevolution [8].
Megatooth sharks as extinct top predators on sirenians
are also discussed herein for the Oligocene of Germany,
to explain their coincident appearances as fossils in many
warm water palaeoenvironments around the world [8,9].
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Figure 2. (A) Newly discovered and most northerly record of Protosiren (rib), and large teeth of Otodus megatooth sharks (all
coll. HF), from the north-western German site at Fürstenau. (B) Map after [6]. (C) Stratigraphic position of the sirenian and
shark-rich vertebrate conglomerate layer at the two Fürstenau sites.
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C. G. Diedrich / Natural Scienc e 5 (2013) 1154-1164 1157
Figure 3. Global paleobiogeography of Eocene sirenians, which was dependent on the distribution of warm
waters and on ocean upwelling (after [6-40,47,48]), with the Protosiren genus having the widest range. The
distribution of the sirenians overlapped with that of the early megatooth shark Otodus [8].
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C. G. Diedrich / Natural Scienc e 5 (2013) 1154-1164
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A small number of Tertiary sirenian fossils have been
described from central Europe, from the proto-North Sea
Basin [10-14]. Three different Paleogene (Eocene to
Oligocene) genera from northern Germany are reviewed
herein: Protosiren (Middle Eocene, single bones), Hali-
therium (lower/basal Upper Oligocene, several skele-
tons), and Anomotherium (Upper Oligocene, two skele-
tons) from the proto-North Sea Basin are placed within
the cladistic models based on former descriptions [1-5].
An extended model of sirenian evolution that includes a
phylostratigraphic and possibly polyphyletic evolution of
manatees and dugongs is presented, reviewing most of
the known important global material and including new
Eocene (Lutetian) fossil remains from northern Germany
(Figure 2). These most northern global records of the
Protosiren genus are also signifycant in the reconstruc-
tion of ancient, climate-influenced palaeocurrents (e.g.,
cold upwellings and warm surface currents), and of
global paleob iogeography.
About 250,000 shark teeth, 12,000 fish otoliths, some
terrestrial mammal teeth, marine seal remains, shark
coprolites, teleostean fish remains, and invertebrate fos-
sils have been collected by H. Felker (HF) from two Eo-
cene fossil sites at Bippen and Dalum, near Fürstenau
(Figure 2), over the past 30 years. This collection has
now been examined for marine mammal remains. About
60 higher vertebrate bone fragments are present, include-
ing some mosasaur remains reworked from Upper Cre-
taceous horizons, making small fragments difficult to
determine macroscopically using only their osteological
morphology. The sirenian material from Dalum is repre-
sented by at least one almost complete sirenian rib (Fig-
ure 1), a few other rib fragments, and a possible verte-
bral neural arch fragment. Possible whale remains are
also present but these bone fragments, especially the
vertebra fragments, can as yet not be firmly distinguish
from those of sirenians. The cross sections of the frac-
tured sirenian ribs were examined in order to verify that
they were pachyostotic ribs, with concentric growth rings.
The material was then compared with a Protosiren fraasi
skeleton from the Stuttgart State Museum for Natural
History (SMNS), with skeletons or bones (from younger
Oligocene horizons) of Halitherium schinzii from the
Senckenberg Museum in Frankfurt (SMF), and with
Anomotherium langewieschei remains from the Do-
bergmuseum Geological Museum of Ostwestfalen-Lippe
in Bünde (DMB). Megatooth shark teeth in the private
collection of U. Beye (UB) are from Barleben, near
Magdeburg. Finally, the teeth of predatorial megatooth
sharks from Fürstenau and sirenian skeletons with evi-
dence of shark-bites have also been included in these
investigations in order to understand the relationships
between, and palaeobiogeographical distributions of,
these predators and their prey.
Order Sirenia Illiger 1811
Family Protosirenidae Sickenberg 1934
Protosiren Abel 1907
Protosiren cf. fraasi Abel 1904
Material: One almost complete rib 27 cm long (Figure
2), some small rib fragments, and a possible vertebral
neural arch fragment (HF collection).
Comparison: Material from this genus is scarce and no
complete skeletons are known. All material is therefore
fragmentary, but several “species” of the Eocene Proto-
siren have been established in different parts of the world,
such as P. e othene Zalmout et al. (2003) [15], P. fraasi
Abel (1904) [16,17], P. sattaensis Gingerich et al. (1995)
[18], P. smithae Domning and Gingerich (1994) [19],
and P. minima Desmarest (1822) [15-17], which are
clearly in need of global revision. The almost complete
rib from Germany illustrated herein (Figure 2) is very
similar in shape and cross section to a middle thoracic rib
from P. cf. fraasi (SMNS 11090), which is of similar age,
coming from the early Middle Eocene of Egypt [16], but
the surface of the German rib has been corroded by
ocean waters. The inner side of the pachyostotic rib is
flattened, while the outer side is convex. The articular
facet on the rib capitulum is relatively flat to concave,
which is typical of Protosiren ribs [16-20]. Some other
fragments are also from ribs, but the exact number of ribs
is difficult to estimate for the freshly fractured material.
A neural arch fragment is also possibly preserved, but it
is too small to permit positive identification.
3.1. Sirenian Species during the Eocene
The substantial morphological diversity and global
distribution of the Eocene sirenians Prorastomus, Pe-
zosien, Protosiren, Eotheroides and Prototherium (Fig-
ures 1 and 3) [1-5,15-41,47] suggests that they must
have already evolved from terrestrial mammals by the
late Paleocene [1-5].
Early Eocene (Ypresian): The oldest known sirenians
are the Prorastomidae, of Early Eocene age. Prorastomus
sirenoides Owen, 1855 and Pezosiren portelli Domning,
2011, in the late Ypresian/early Lutetian, are still primi-
tive and quadrupedal, with fully developed legs. Both
have been recorded from Jamaica, in the Caribbean [1,5]
(Figures 1 and 3). If the newest described remain from
Senegal (Prorastomidae indet.) [47] does not belong into
this time-frame must remain unclear, because this strong-
ly damaged vertebra could also have been reworked ma-
rine from older layers. It would then, indicate the ex-
change between Carribean and West-African populations
(cf. Figure 3).
C. G. Diedrich / Natural Scienc e 5 (2013) 1154-1164 1159
Figure 4. Sirenian species from the Lower/Upper Oligocene boundary of the proto-North Sea Basin and a Halitherium skeleton with
large shark bite marks on many ribs and vertebrae (after [14]). Anomotherium skeleton (in DMB), Halitherium skeleton (in SMF).
arge serrated teeth from the megatooth shark Otodus angustidens, from the German Oligocene (teeth in DMB, HB, UB, and PMN). L
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Early Middle Eocene (Lutetian): The best-preserved
and most abundant sirenian specimens with a similar age
to the Fürstenau material are the Protosirenidae from
Egypt (Protosiren fraasi) [16,18,34], and Pakistan (Pro-
tosiren eothene) [15,37] (Figures 1 and 3). Most of the
material from Hungary, Germany, and Spain, as well as
that from Kazakhstan, should probably be attributed to P.
fraasi Abel, 1904 [16-17,19,23]. There may have been
only a single species distributed throughout the Tethys
(Figure 3), but the fossil record is sparse and fragmen-
Upper Middle Eocene to lower Late Eocene (Barto-
nian): The protosiren P. sattaensis, which is represented
mainly by ribs and a small quantity of other Protosireni-
dae material found along the east coast of North America
(Carolina, Florida), and which has also been suggested
from Pakistan (Figures 1 and 3), has been accurately
dated from the North American discoveries [27]. Other
protosiren remains from P. smithae have been reported
from Egypt [19]. The possible P. m i n ima remains from
France are problematic as far as species identification
and dating are concerned. Two other Dugongidae genera
also developed during the Bartonian, these being Eother-
oides [1,21], which has been found along the northern
coastline of Africa [37,42], and Eosiren Andrews 1902,
which is from the Late Eocene (Bartonian to Priabonian)
(Figures 1 and 3) [1].
Late Eocene (Priabonian): The dugongid Prototherium
veronense de Zigno, 1875 has been found in Italy [28]
and ranged from the upper Middle to the Late Eocene
(Figures 1 and 3). The E. libyca Andrews, 1902 has been
recorded from the Late Eocene of Egypt [42] (Figures 1
and 3).
3.2. Origin, Palaeobiogeography and Habitat
of Early European Sirenians
The distribution of early sirenians is related to that of
warm ocean waters with seagrass meadows [1,2,4,14].
These aquatic mammals may have had polyphyletic de-
velopment from two separate centers (Figure 3). Classi-
cal models [1-5] describe an origin in the warm shallow
waters of Central America [5], and a subsequent disper-
sal to Eurasia. The palaeooceanography of the Early Eo-
cene (Ypresian), however, indicates that the opening of
the North Atlantic resulted in massive upwellings of cold,
arctic bottom currents, which are likely to have inh ibited
any such migration.
These upwellings extended not only into the proto-
North Sea Basin, but also as far south as north-western
Morocco, where the absence of any sirenian remains in
shark-rich phosphatic b onebeds lends support to the idea
that the upwellin gs presented a barrier to sirenian migra-
tion (Figure 3). The modern Trichechidae and Dugongi-
dae are therefore more likely to have had different ori-
gins and ancestors (Figures 1 and 3), one in the Carib-
bean, and the other in the very different habitat provided
by the shallow, warm, marine waters off northern Africa
(Figure 3). The monophyletic model is based on classi-
cal monophyly [1-5], but th e “evolution of the sirenians”
presented herein is a little different (Figures 1 and 3),
bringing together all of the data, and leaving open any
gaps in the fossil record or unclear phylogenetic rela-
tionships betw een families and subfamili es.
The Middle Eocene Protosiren (Protosirenidae) is be-
lieved herein to be known after reviewing the descrip-
tions and figures of single finds in the Lutetian from Italy,
Spain [26], Hungary [16], Romania [32], Egypt [17,19],
Kazakhstan, and Pakistan [15-40], and now also from
Germany. These early sirenians have recently been re-
corded from along the equator and further north in the
Tethys, the northern Indian Ocean, the proto-North Sea
Basin, and the western coastlines of the already opened
North Atlantic (Figure 3) [15-40], but they always ap-
pear to have been in shallow marine habitats of warm
oceans, or in areas influenced by warm surface waters.
The remains from the proto-North Sea Basin, which are
the most northerly sirenian record for that time, are from
a slightly different environment from other discoveries in
that this was primarily a cold shallow marine basin, in-
fluenced by up wel l ing ( Figure 2(B)) [6].
Periodic influxes of warm surface waters from the
Tethys are, however, clearly documented by the presence
of the remains of sirenians, whales, and megatooth
sharks (Figure 2) [8], that must have come into the area
from the east or southeast, at least during the Lutetian
(Figure 3).
The early Lutetian Protosiren appears from the re-
cently discovered fossil record not to have originated in
Central America, but from the coastline of northern Af-
rica [1,27], as is also the case for the Early Eocene
primitive quadrupedal sirenians (ancestors of Trichechi-
dae). Their distribution appears to have been clearly re-
stricted by the cold water upwelling, which had already
started in the Paleocene. The North Atlantic therefore
would have been a barrier to dispersal, which would also
explain another polyphyletic development-the emergence
of the Dugongidae in Eurasian coastal Tethys habitats
(Figures 1 and 3). These did not arrive on the east coast
of North America before the Bartonian [1,27], which
would again appear to support an origin in Eurasia (Fig-
ures 1 and 3). Their original habitat was more likely to
have been along the more gently sloping coastlines cov-
ered with seagrass (and possibly also macroalgae) that
had already become the main food source for sirenians
during the Eocene [1-5,14,45]. Adaptation to feeding on
seagrass caused a general tooth reduction in sirenians
between the Eocene and the Pliocene (Figure 1). Com-
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C. G. Diedrich / Natural Scienc e 5 (2013) 1154-1164 1161
plete incisor, premolar, and anterior molar tooth reduce-
tion occurred within the Trichechidae and the Dugongi-
nae, but the greatest reduction (including the anterior
procumbent teeth) occurring in the Hydrodamalinae
(Figure 1). Further support for a polyphyletic develop-
ment is provided by the major sirenian radiation in Eura-
sia (Figures 1 and 3). Within the Barthonian, the Du-
gongidae Eotheroides and Prototherium developed on
the shallow marine shelves of northern Africa, and in the
Tethys area in general (Figure 3), as did the Protosireni-
dae (a little later) which are believed to have been distant
non-ancestors of modern Dugongs [1-5].
3.3. Younger Sirenian Records from the
Proto-North Sea Basin
Focusing only on the pro to-North Sea Basin of central
Europe, Miosirenidae and Halitherinae are now known
from horizons of various ages (Figure 2), which include
the Early to lower Late Oligocene Halitherium schinzii
Kaup, 1838 [10,11,44] (also distributed in the Cologne
and Leipzig bays, in northern Germany at Doberg, in the
Molasse Basin, and in the Rhine Graben: Figure 4 [14,
46]), and the large Upper Olig ocene form Anomotherium
langewieschei Siegfried, 1965 [12,14] (only recorded in
the southern proto-North Sea Basin, Figure 4, with two
skeletons found near Bünde [14] and Schaumburg-Hof
The Anomotherium discoveries coincide with the dis-
tribution of a carbonate facies in which indirect evidence
for macroalgae and seagrass is provided by the xeno-
morphic attachment surfaces of various oysters [14,45]
(Figure 4).
The new phylogenetic position suggested herein for
Anomotherium within the evolutionary model is a pre-
liminary step based on characteristics such as the ex-
tremely massive thickened ribs, which are 6 - 8 cm in
width (as typically seen in hydrodamalines, and similar
to those in Hydrodamalis). The much larger-proportioned
and more massive forelegs in Anomotherium and Hy-
drodamalis (in contrast to the reduced forelegs of
Halitherum; Figure 4) are also important. These postcra-
nial skeleton characteristics allow the parallel-living
Anomotherium/Halitherium genera to be separated from
each other, especially in the proto-North Sea Basin [14].
This distinction is thus based on the large robust general
habitus and body size, which in the case of Anomoth-
erium is close to that of the Steller’s seacow (Hydro-
damalis). Cranial characteristics can not be used due to
the high degree of damage to the skull: the presence or
absence of procumbent teeth would help to position
Anomotherium more accurately within the systematics,
which are mainly based on cranial characteristics. How-
ever, the systematic position will need to be revised in
the future using the two known Anomotherium skeletons
from Germany The holotype is currently spread over
three collections and many bone fragments have not yet
been included in the skeleton but are still in boxes: the
reassembled skeleton presented herein in Figure 4 is
therefore not fully rep resentative of the holotype skeleton.
Finally, the palaeobiogeography of Anomotherium,
which is only present globally in the northern proto-
North Sea Basin, seems to suggest a large sirenian al-
ready adapted to seagrass feeding and temperate waters-
a habitat that was already occupied by the hydrodama-
3.4. The Sirenians’ Predators
The megatooth shark ancestor Otodus sokolovi was
already present in the Middle Eocene as a large form
(with teeth up to 8 cm long, Figure 2(A)), indicating the
parallel evolution of these large sharks with their main
prey, the whales and sirenians [8]. Several large teeth
have also been found at Fürstenau, suggesting a spatial
correlation with their prey, the sirenians (and probably
whales) [8], and also reflecting their presence in warm
waters only.
The same spatial correlation can also be reported from
the Upper Oligocene horizons in the proto-North Sea
Basin, where toothed whales (Eosqualodon) and sireni-
ans (Anomotherium) again appear together with mega-
tooth shark remains, but in this case from the more
highly evolved Otodus angustidens (Figure 4) [8,14].
The bite marks that are commonly found on the ribs and
vertebrae of Halitherium (Figure 4) and other sirenians
[14,46] indicate that they were scavenged, and possibly
preyed upon, by large sharks. In contrast, the smaller
white shark ancestor Carcharodon auriculatus, from
which some thousands of teeth have been found in the
Middle Eocene gravels at Fürstenau, was adapted to cold
water, as were its main prey, the seals [8].
Early Eocene (Ypresian) sirenians (the world’s oldest
sirenians) appear to have already developed in the Car-
ibbean by the Late Paleocene (Thanetian), in tropical
shallow coastal waters and freshwater river environments.
Two different sirenian genera, Pezosiren and Prorasto-
mus, which are known from “New World” skeletons, did
possibly not spread over the Atlan tic to the “Old World”,
because the continents were separated by cold upwelling
currents in the northern Atlantic. These quadrupedal
basal sirenian forms are likely to have been the ancestors
of the modern manatees (and their predecessors), which
have a similar geographical distribution and also live in
coastal brackish and freshwater environments. The rela-
tionship between the oldest sirenians and the manatees
remains unresolved and the phylostratigraphic model is
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C. G. Diedrich / Natural Scienc e 5 (2013) 1154-1164
therefore not yet complete.
The newly discovered marine Middle Eocene (Lu-
tetian) sirenians (including Protosiren), which may have
had a polyphyletic development, appear to have been
evolved on the shallow marine coastlines of the Tethys,
such as along northern Africa, or between Eurasia and
India. The most northern discoveries (from Germany, in
the proto-North Sea Basin) resulted from seasonal varia-
tions between warm surface waters of the Tethys and
cold upwelling currents from the North Atlantic that
were responsible for a rich fish fauna and the presence of
three types of mammal: seals, sirenians, and whales. The
Protosirenidae are seen herein to appear to be possible
polyphyletic or even “ancestors” of the Dugongidae
(Figure 1), which was seen different by other authors.
Within this lineage, it is placed herein as the massive
European Oligocene form Anomotherium from the proto-
North Sea Basin, which has only been recorded from
temperate carbonate seagrass-meadow environments.
This little-reported form, which is only recorded from the
northern hemisphere, is best placed on the basis of
anatomy (from postcranial characteristics of massive,
thickened ribs and large massive forelimbs) and palaeo-
geography within the Hydrodamalinae lineage, with its
adaptation to temperate and cold waters. The tooth re-
duction and horny pad development started in the Eocene
as an adaptation to feeding on seagrass/macroalgae, con-
tinued in tooth reduction by 28 Ma in the Oligocene, and
is best evolved in the Hydrodamalinae; in contrast to the
other forms, that the Hydrodamalinae-Dusosiren already
had no procumbent teeth by the early Miocene (23 Ma).
The first indirect evidence of sirenians having been
hunted by megatooth sharks is found in the Middle Eo-
cene of north-western Germany, where they are both
(occasionally) present in the same horizons. The coinci-
dental occurrence of both sirenians and megatooth sharks
at several different locations around the globe in Paleo-
gene to Neogene sediments also provides supporting
evidence for early development of a predator-prey co-
evolutionary relationship. The best examples of bite
damage on ribs and vertebrae are found on skeletons of
Halitherium, the most common Oligocene sirenian in
Europe. Sirenians in general appear to have been hunted
and killed (in a similar way to whales) by megatooth
sharks (Otodus), but were also scavenged by other sharks
(Isurus, and others).
The sirenian remains described herein were discovered by the hobby
palaeontologist, Mr. H. Felker, who kindly allowed the specimens to be
studied. A cast of the original rib (which not a holotype) is in the public
collection of the Seehundstation Nationalpark-Haus and Waloseum
Museum, Vogelpflegestation Norden-Norddeich. The private company
PaleoLogic was responsible for the scientific research and funding. M.
Strauss from the Dobergmuseum Bünde (DMB) allowed the study of
the sirenian skeleton and shark tooth material. Dr. B. H erkner from the
Senkenbergmuseum Frankfurt (SMF) made the sirenian skeleton in the
exhibition available. I thank H. Stapf of the Paläontologisches Museum
Nierstein (PMN) for providing a photo of a shark tooth from Alzey. H.
Breitkreutz (HB) permitted the study of his private tooth collection
from the Doberg. U. Beye supported with a photo of a tooth in his
collection from Barleben. Finally E. Manning supported much with the
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