RESEARCH PAPER
The bipolar bivalve Oxytoma (Palmoxytoma) cygnipes
(Young & Bird, 1822) in the Upper Pliensbachian of Germany
Gernot Arp • Stephan Seppelt
Received: 8 March 2011 / Accepted: 3 June 2011 / Published online: 23 June 2011
 The Author(s) 2011. This article is published with open access at Springerlink.com
Abstract The morphologically conspicuous bivalve
Oxytoma (Palmoxytoma) cygnipes (Young & Bird, 1822),
known for its palaeogeographically bipolar distribution,
from a limestone bed in the boundary ‘‘Belemniten–
Schichten’’/Amaltheenton formation, Lower Jurassic, in N
Germany is described. The occurrence of this palaeocea-
nographically significant bivalve points to an influx of cool
seawater from the Arctic to the North-German Basin at the
base of the Upper Pliensbachian, just before the deposition
of the Amaltheenton formation. A review of previously
reported occurrences on the NW European Shelf indicates
two distinct stratigraphic intervals of occurrence of this
taxon: the Rhaetian–Hettangian boundary and the Upper
Pliensbachian. Whereas the former interval of occurrence
may be related to short-term cooling in the course of the
end-Triassic extinction event, the latter is interpreted as
reflecting the influx of a cool water current to the eastern
part of the NW European Shelf, which continued south-
wards parallel to the coast of the Bohemian–Vindelician
High.
Keywords Bivalvia  Germany  Triassic–Jurassic
boundary  Pliensbachian  Boreal
Kurzfassung Die morphologisch markante, bipolar
verbreitete Muschel Oxytoma (Palmoxytoma) cygnipes
(Young & Bird, 1822) wird von einer Kalksteinbank an der
Grenze ‘‘Belemnitenschichten’’/Amaltheenton-formation,
Unterer Jura, Norddeutschland beschrieben. Das Auftreten
dieser pala¨oozeanographisch bedeutsamen Muschel deutet
auf einen Einbruch ku¨hlen Meerwassers aus der Arktis in
das Norddeutsche Becken an der Basis des Oberen
Pliensbachiums hin, knapp vor der Ablagerung der
Amaltheenton-formation. Eine U¨bersicht bisher publi-
zierter Vorkommen auf dem NW-Europa¨ischen Schelf
belegt, daß dieses Taxon auf zwei stratigraphische Inter-
valle beschra¨nkt ist, und zwar den Rhaetium-Hettangium-
Grenzbereich und das Obere Pliensbachium. Wa¨hrend das
Vorkommen des ersteren Intervals mit einer kurzfristigen
Abku¨hlungsphase im Zuge des Aussterbeereignisses am
Ende der Triaszeit stehen ko¨nnte, wird das letztere Vor-
kommen als Resultat einer Kaltwasserstro¨mung auf den
o¨stlichen Teil des NW-Europa¨ischen Schelfs gedeutet,
welche dann weiter su¨dwa¨rts parallel der Ku¨ste des Bo¨h-
misch-Vindelzischen Landes verlief.
Schlu¨sselwo¨rter Bivalvia  Deutschland 
Trias–Jura-Grenze  Pliensbachium  Boreal
Introduction
Oxytoma (Palmoxytoma) is one of the morphologically
most conspicuous Jurassic bivalves. The bivalve resembles
‘‘a stretched wing of a bat’’ (Wetzel in Ho¨lder 1953) and is
‘‘one of the most beautiful morphotypes of England,
showing the inequality of valves so conspicuous’’ (Quen-
stedt 1867: 616). Oxytoma (Palmoxytoma) is regarded as
dwelling in cool-water habitats and has a striking bipolar
palaeogeographic distribution pattern in the Hettangian,
with restriction to the Boreal Realm later in the Sinemurian
G. Arp (&)
Geowissenschaftliches Zentrum der Universita¨t Go¨ttingen,
Goldschmidtstrasse 3, 37077 Go¨ttingen, Germany
e-mail: garp@gwdg.de
S. Seppelt
Platz 3, 31079 Wrisbergholzen, Germany
123
Pala¨ontol Z (2012) 86:43–57
DOI 10.1007/s12542-011-0113-1
and Pliensbachian (Damborenea 1993, 2002). At that time,
i.e., the Sinemurian–Pliensbachian, the NW European
Shelf underwent significant palaeoceanographic changes
with the opening of a marine strait connecting the Arctic
Ocean in the North with the Tethys in the South (Ziegler
1988, 1990; Bjerrum et al. 2001). Although the exact
timing of the opening of the Transcontinental Laurasian
Seaway is under discussion (Ziegler 1988; Richards 1990;
Steel and Ryseth 1990; Dore 1991; Bjerrum et al. 2001),
there is clear evidence from palynomorphs of cool water
ingression into the Spinatum Zone of the Late Pliensba-
chian (van de Schootbrugge et al. 2005).
In this paper, we report the discovery of the bivalve
Oxytoma (Palmoxytoma) cygnipes (Young and Bird, 1822)
in the lowermost Margaritatus Zone of the Upper Pli-
ensbachian in Beierstedt, Northern Germany. Although
previously found in the Lower Jurassic of Northern
Germany by von Seebach (1864) and Brauns (1871), this
species is documented for the first time from a distinct
stratigraphic horizon of a detailed section, and its palae-
oceanographic significance is discussed.
Materials and methods
Five valves of Oxytoma (Palmoxytoma) cygnipes (Young
and Bird, 1822) have been recovered during a sampling
campaign in August 2006. Bivalve specimens were pre-
pared using a variety of pneumatic preparation chisels and
pens. Seventeen thin-sections (7.5 9 10 cm), together
covering the complete limestone beds and concretions,
were prepared.
Repository: The material is stored in the Museum and
Collection of the Geoscience Centre, University of Go¨t-
tingen (GZG).
Location and geological overview
The investigated section at Beierstedt (sheet 3931 Jerxheim
R: 36 27 000; H: 57 71 650) is located 20 km southeast of
Braunschweig, south of the abandoned railway Bo¨rßum-
Hedeper-Jerxheim (Fig. 1). The area is located at the
eastern margin of the Lower Saxony Basin, a 300 km long
and 65 km wide depression with a sedimentary succession
from the Lower Permian Rotliegend Group to Tertiary
formations (Ziegler 1990) up to 5 km thick. Salt cushions
and diapirs rising from the Upper Permian Zechstein Group
resulted in numerous salt anticlines and synclines, with a
number of unconformities, mainly in the Buntsandstein
Group and between Cretaceous formations. The Beierstedt
section is located on the southern slope of the Asse-
Heeseberg salt anticline (Fig. 1). There, Hettangian to
Pliensbachian strata, which are unconformably overlain by
Hauterivian strata, dip with an angle of approximately 5 to
the SW. To date, no formal formation names have been
established for the North-German Lias Group (Mo¨nnig
2005), so traditional, informal lithostratigraphic units are
used in this paper.
The Pliensbachian section at Beierstedt
More than 60 cm of unfossiliferous, bluish–dark grey
claystones of the Upper Sinemurian ‘‘Raricostaten–
Schichten’’ (equivalent to the South German Obtususton
Formation) are exposed at the base of the section at Be-
ierstedt (Fig. 2; Table 1). The total thickness of the ‘‘Ra-
ricostaten–Schichten’’ at this locality is approximately
21 m, as demonstrated by the Wetzleben drill core (Tho-
mas 1924).
Above, the Pliensbachian starts with the 45–50 cm thick
‘‘Belemniten–Schichten’’ (equivalent to the South German
Fig. 1 Geological map of the
study area showing the location
of the section Beierstedt and
further locations mentioned in
the text
44 G. Arp, S. Seppelt
123
Numismalismergel Formation). The lower part of this highly
condensed formation is formed by a 15–20 cm thick, highly
fossiliferous limestone bed, a bioturbated bioclastic iron-ooid
wackestone to packstone (Fig. 3a, b). It contains abundant
echinoderm clasts, brachiopod and bivalve shell fragments
(among them inoceramid shell fragments with prismatic
structure), rotaliid foraminifera, and belemnite rostra bioe-
roded by endoliths. The 300–400 lm sized ooids have sider-
ite-replaced nuclei with limonitic cortices; locally calcitic
cortices with radial crystallites also occur. Most conspicuous
are cm to dm-sized grey micritic concretions with round
borings 8–10 mm in diameter. These concretions are
reworked from the underlying ‘‘Raricostaten–Schichten’’ and
indicate a discontinuity at the base of the formation. Besides
abundant belemnites, bivalves, gastropods, and brachiopods,
well preserved ammonoids occur, which indicate the Bre-
vispina to Maculatum Subzones, with a possible lack of the
Taylori to Polymorphus Subzones (Fig. 2; Table 1). The
upper part of the ‘‘Belemniten–Schichten’’ is formed by a
26–30 cm thick limestone bed, composed of a bioturbated
echinoderm packstone with scattered other bioclasts and
rotaliid foraminifera (Fig. 3c, d). Generally, the bioclasts are
smaller than in the bed below, and more corroded. Locally,
cm-sized, matrix-supported patches occur, indicating biotur-
bation. Macrofossils (ammonites, belemnites, bivalves) are
generally well preserved, with only minor signs of corrosion,
and embedded subhorizontally.
The lower bedding plane shows Amaltheus stokesi
(Sowerby, 1818), Androgynoceras maculatum (Young &
Bird, 1822), and Prodactylioceras davoei (Sowerby, 1822)
representing the condensed Maculatum and Stokesi Subz-
ones, whereas major parts of the bed contain Amaltheus
stokesi (Sowerby, 1818) and Lytoceras salebrosum Pom-
peckj, 1896 indicating the Stokesi Subzone. The upper
surface of the bed shows limonite impregnation and sharp,
discontinuous contact with the overlying marl.
The Amaltheenton formation starts with a marly pack-
stone consisting of shell debris, belemnites, and echino-
derm bioclasts, followed by claystones with thin shell
debris layers, and a second shell debris packstone with
siderite nodules (Fig. 2). The latter contain Amaltheus
gibbosus (von Schlotheim, 1820), the index fossil of the
Gibbosus Subzone; together, these shell-debris-rich marls
are 40–50 cm thick; there is no indication of the
Subnodosus Subzone, and a corresponding discontinuity is
assumed for the base of the Amaltheenton formation. Of
the remaining approximately 65 m of Amaltheenton (drill
core Hornburg; Thomas 1924), only the lowermost 110 cm
of bluish–grey, marly claystones with siderite concretions
have been exposed in this section (Fig. 2).
The three formations were deposited in an open-marine
mid-shelf environment, with higher siliciclastic supply in
the ‘‘Raricostaten–Schichten’’ and Amaltheenton forma-
tion, and strongly reduced siliciclastic influx in the
Fig. 2 Columnar section of the
‘‘Belemniten–Schichten’’ at
Beierstedt, with the position of
Oxytoma (Palmoyxtoma)
cygnipes (Young & Bird, 1822)
The bipolar bivalve Oxytoma (Palmoxytoma) cygnipes (Young & Bird, 1822) 45
123
‘‘Belemniten–Schichten’’. Contrary to previous assump-
tions (Thomas 1924), there is no indication of a high-
energy shallow water or coastal environment. A detailed
description of the section is given in Table 1.
Systematic palaeontology
Order Pterioida Newell, 1965
Family Oxytomidae Ichikawa, 1958
Genus Oxytoma Meek, 1864
Subgenus Palmoxytoma Cox, 1961
Type species: Pecten cygnipes Young & Bird, 1822,
from the ironstone bands of the aluminous strata, York-
shire, by original designation.
Oxytoma (Palmoxytoma) cygnipes (Young & Bird,
1822) (Fig. 4a–g)
*1822 Pecten cygnipes; Young & Bird: 235, pl. 9/fig. 6
1828 Pecten cygnipes; Young & Bird: 236, pl. 9/fig. 3
1829 Avicula cygnipes; Philipps: 162, pl. 14/fig. 3
1839 Avicula longicostata, Stutch.; Stutchbury: 163, fig.
1856 Avicula cygnipes; Oppel: 179
1857 Avicula cycnipes (Phillips); Dumortier: 7–10, pl.
4/figs. 1–4
1864 Avicula cygnipes Young and Bird; von Seebach: 103
1867 Avicula cygnipes Phill.; Quenstedt: 616, pl.
59/fig. 5
1869 Avicula cycnipes (Phillips); Dumortier: 294–297,
pl. 35/figs. 6–9
1871 Avicula cygnipes; Brauns: 359
1876 Monotis cygnipes Young and Bird; Tate and Blake:
370–371
1881 Avicula (Oxytoma) magnifica n.sp.; Lundgren: 19,
pl. 5/figs. 2–5
Table 1 Lithologic description of the section Beierstedt
Formation Bed
No.
Thickness Lithology
Amaltheenton 7 [110 cm Bluish–grey shaly claystone with disseminated pyrite; topmost 30 cm with reddish–brown siderite
nodules
6 10 cm Grey shaly marlstone rich in mollusc and echinoderm debris, numerous belemnites, lignified
driftwood; locally reddish-brown siderite nodules up to 10 9 30 cm in size; layer of cm-sized black
phosphorite nodules at the top of the bed; Amaltheus gibbosus (von Schlotheim), Ptychomphalus
expansus (Sowerby), Harpax spinosa (Sowerby), Myoconcha (Modiolina) sp.
5 20–30 cm Grey shaly clayey marlstone with numerous layers of mollusc and echinoderm debris and slightly
corroded small belemnites of the Subhastites group; bioturbated fabric because of small branching
burrows
4 5–10 cm Grey shaly marlstone rich in mollusc and echinoderm debris, numerous belemnites; Amaltheus sp.;
Harpax spinosa (Sowerby)
‘‘Belemniten–
Schichten’’
3 26–30 cm Grey, weathering yellow–brown, bioturbated bioclastic limestone, divided by a joint into an upper and
lower part; upper part with Amaltheus stokesi (Sowerby) and Lytoceras salebrosum Pompeckj;
middle joint plane with Amaltheus stokesi (Sowerby), Pleurotomaria sp., Oxytoma (Palmoxytoma)
cygnipes (Young & Bird), Eopecten velatus (Goldfuss), Camptonectes subulatus (Mu¨nster in
Goldfuss), Pseudopecten equivalvis (Sowerby), Myoconcha (Modiolina) decorata (Mu¨nster in
Goldfuss), lignified driftwood; lower bedding plane with numerous ammonoids; Amaltheus stokesi
(Sowerby), Androgynoceras maculatum (Young & Bird), Prodactylioceras davoei (Sowerby),
Liospiriferina rostrata (von Schlotheim), Pseudopecten equivalvis (Sowerby)
2 15–20 cm Grey, weathering yellow–brown, bioturbated oolitic limestone; ferruginous ooids dominate at the base,
calcareous ooids in top parts; highly fossiliferous; lowermost part clayey; erosive undulating lower
boundary; Androgynoceras maculatum (Young & Bird) abundant within one lense at the top,
Beaniceras luridum (Simpson), Liparoceras (Liparoceras) cheltiense (Murchison); Uptonia sp.,
Platypleuroceras brevispina (Sowerby. (5 cm above base); Lytoceras fimbriatum (Sowerby),
Tragophylloceras loscombi (Sowerby), Liospiriferina rostrata (von Schlotheim), Pseudokatosira cf.
undulata (Benz), Pinna hartmanni Zieten, Parainoceramus ventricosus (Sowerby), Entolium lunare
(Roemer), Pseudopecten equivalvis (Sowerby), Camptonectes subulatus (Mu¨nster in Goldfuss),
Eopecten velatus (Goldfuss), Chlamys textoria (von Schlotheim), ‘‘Avicula’’ calva (Schloenbach),
Terquemia difformis (von Schlotheim), Antiquilima succincta (von Schlotheim), Plagiostoma
gigantea (Sowerby), Pseudolimea pectinoides (Sowerby), Gryphaea gigantea (Sowerby),
Myoconcha (Modiolina) decorata (Mu¨nster in Goldfuss), Astarte sp., Cardinia rugulosa Tate,
Pholadomya ambigua (Sowerby), Pleuromya costata (Young & Bird), Pleuromya ovata (Roemer),
Pleuromya meridionalis Dumortier
‘‘Raricostaten–
Schichten’’
1 [60 cm Bluish–grey shaly claystone with one layer of reddish-brown siderite nodules ca. 25 cm below top, no
macrofossils observed
46 G. Arp, S. Seppelt
123
1888 Avicula scanica L.; Lundgren: 18
1888 Avicula anserina n. sp.; Moberg: 38, pl. 3/fig. 18
1891 Avicula cygnipes; von Gu¨mbel: 379
1891 Avicula cygnipes Phill.; von Ammon in von
Gu¨mbel: 690
1906 Avicula cygnipes Phil.; Fugger: 231
v 1907 Avicula cygnipes Phill.; von Koenen: 44
non 1911 Oxytoma inaequivalve Sow. aff. cycnipes
Phill. (Y. & B.); Hahn: 541, pl. 20/fig. 2
1913 Avicula (Oxytoma) cf. cycnipes, Phill.; Jeannet:
367, fig. 25
? 1923 Oxytoma sp.; Trechmann: 272, pl. 12/figs. 6–7
1933 Oxytoma longicostata (Strickland); Arkell: 602, pl.
29/fig. 1
? 1934 Oxytoma cf. cygnipes Y. et B.; Rosenkrantz: 51,
117
1934 Oxytoma cygnipes Y. et B.; Rosenkrantz: 112
v 1935 Oxytoma cf. longicostata Strickl.; Kuhn: 2, pl.
2/fig. 6
1951 Oxytoma scanica (Lundgren); Troedsson: 201, pl.
10/fig. 15
v 1953 Oxytoma scanica (Lundgren 1888); Ho¨lder: 359,
fig. 1
1957 Oxytoma cygnipes Phillips; Frebold: 67, pl.
16/figs. 1–5
1961 Oxytoma (Palmoxytoma) cygnipes (Young & Bird
1822); Cox: 593
1964 Oxytoma cf. cygnipes (Phillips); Ho¨lder: 432,
fig. 126
1967 Oxytoma (Palmoxytoma) cygnipes (J. Sow.);
Hallam: 400
1968 Oxytoma cygnipes (Young et Bird), 1822; Efimova
et al.: 46, pl. 22/figs.11–12
1976 Oxytoma (Palmoxytoma) cygnipes (Young &
Bird); Milova: 53, pl. 4/fig. 6, pl. 5/figs. 2–5
1991 Oxytoma (Palmoxytoma) cygnipes (Young and
Bird); Poulton: 26, pl. 11/figs. 14–16
? 1991 Palmoxytoma sp.; Riccardi et al.: 166, fig. 4/14
Fig. 3 Microfacies of the ‘‘Belemniten–Schichten’’, condensed
Lower Pliensbachian and Stokesi Subzone of Beierstedt. a Overview
of bioclastic iron-ooid wackestone to packstone of bed 2, Lower
Pliensbachian, with belemnite rostra and bivalve shells. Note intense
bioturbation. b Detail of a showing ooids with ferrugineous inner and
calcareous outer cortices, bioclasts, and rotaliid foraminifera
(arrows). c Overview of bioturbated echinoderm packstone of bed
3. Note cross-section of several belemnite rostra and an Amaltheus
stokesi (Sowerby, 1818). d Detail of c showing densely packed
echinoderm clasts, a corroded belemnite fragment, and scattered
rotaliid foraminifera (arrows)
The bipolar bivalve Oxytoma (Palmoxytoma) cygnipes (Young & Bird, 1822) 47
123
48 G. Arp, S. Seppelt
123
? 1992 Palmoxytoma sp.; Damborenea and Mancenido:
132, pl. 1/fig. 1
1992 Oxytoma (Palmoxytoma) cygnipes; Sey et al.: 228
1994 Oxytoma (Palmoxytoma) cf. cygnipes; Aberhan:
35, Text-fig. 16
1997 Palmoxytoma sp.; McRoberts et al.: 82, 87
1998 Oxytoma (Palmoxytoma) cygnipes (Young & Bird
1822); Aberhan: 95, pl. 9/fig. 15–16, 18–19
2002 Palmoxytoma cf. cygnipes (Young & Bird 1822);
Damborenea: 23, pl. 1/figs. 6–8
? 2002 Palmoxytoma n. sp.; Damborenea: 23, Text-fig. 9
2004 Oxytoma (Palmoxytoma) ussurica Voronetz; Kon-
ovalova and Markevich, pl. 21/figs. 1–7
2007 Oxytoma (Palmoxytoma) cygnipes (Young &
Bird); Rulleau: 82, pl. 52/5
Material: One right complete, three left complete, and
one left incomplete valves from bed 3 (Upper Pliensbachian,
Stokesi Subzone) of the ‘‘Belemniten–Schichten’’ at Beier-
stedt. One incomplete internal mould and corresponding
external imprint of a left valve from the ‘‘Gamma-Delta-
Grenzbank’’ (Upper Pliensbachian, Stokesi Subzone), top of
‘‘Belemniten–Schichten’’ of Go¨ttingen-Geismar.
Description: Shell medium-sized, very inequivalve with
left valve convex and right valve almost flat. Shape
suborbicular, equilateral to slightly opistocline. Hinge long
and straight, with a wing-like posterior auricle and a small
anterior auricle. Right valve anterior auricle triangular and
separated from valve by deep byssal notch. Ligament
groove long and narrow. Right valve with umbo not pro-
truding and slightly prosogyrous, faint ornamentation
consisting of fine radial striae. Left valve with umbo
slightly protruding and ornamentation consisting of 4–6
prominent radial ribs separated by areas with fine radial
riblets. Main ribs with ovoid to circular cross-section
resting upon a thin ridge. At major growth lines, ribs grade
into spines up to 15 mm long and projecting at the disc
margin.
Measurements These are provided in Table 2.
Remarks: The species Oxytoma (Palmoxytoma) cygni-
pes (Young & Bird, 1822) is derived from the Carnian-
Norian ancestor Oxytoma mojsisovicsi Teller, 1886
(Damborenea 1987: 160, 2002: 22). Early Hettangian
representatives have been referred to as Oxytoma (Palm-
oxytoma) longicostata (Stutchbury, 1839) (e.g., Arkell
1933; Kuhn 1935). However, the morphological differ-
ences between O. (P.) longicostata and O. (P.) cygnipes are
gradual, and reflect largely preservational effects (Fig. 4a–g).
Specifically, within limestones (e.g., Psilonotenkalk;
Ho¨lder 1953) internal moulds and inside views of shells are
obtained, and the spiny outer surface remains hidden within
the attached matrix. This is true for our specimens also; the
long projections and spines are observed only after labo-
rious preparation (Fig. 4a, b).
Apart from that, Oxytoma (Palmoxytoma) cygnipes
(Young & Bird) has, indeed, some variability with regard
to the density of ribs and the shape of the disc. Oxytoma
cygnipes (Young et Bird) from Eastern Siberia described
Fig. 4 Oxytoma (Palmoxytoma) cygnipes (Young & Bird, 1822)
from the top of the ‘‘Belemniten–Schichten’’, Stokesi Subzone, Lower
Saxony. a, b External view of left valve showing spines. Bed 3,
Beierstedt. GZG.INV. 31004. c Internal view of right valve. Bed 3,
Beierstedt. GZG.INV. 31005. d Internal mould of left valve with
spine-like rib projections. Bed 3, Beierstedt. GZG.INV. 31002.
e Internal mould of left valve with spine-like rib projections. Bed 3,
Beierstedt. GZG.INV. 31001. f, g Fragmentary internal mould and
negative imprint of left valve. Top of ‘‘Belemniten–Schichten’’,
Go¨ttingen-Geismar. GZG.INV. 30576 a & b
Table 2 Measurements of Oxytoma (Palmoxytoma) cygnipes (Young & Bird, 1822)
Specimen Location Material L (mm) H (mm) I (mm) R
GZG.INV. 31001 Beierstedt, Northern Germany LV, internal mould 65 65 9 6
GZG.INV. 31002 Beierstedt, Northern Germany LV, internal mould 50 50 9 4
GZG.INV. 31003 Beierstedt, Northern Germany LV, incomplete negative (40) (42) (5) (4)
GZG.INV. 31004 Beierstedt, Northern Germany LV, shell 50 47 9 6
GZG.INV. 31005 Beierstedt, Northern Germany RV, shell 35 37 2 –
GZG.INV. 30576 a & b Go¨ttingen, Northern Germany LV, internal mould & negative imprint (18) (21) (3) 4
GZG.INV. 30577 a Whitby, Yorkshire LV, internal mould 75 73 8 5
GZG.INV. 30577 b Whitby, Yorkshire LV, internal mould 56 58 7 5
GZG.INV. 30577 c Whitby, Yorkshire LV, internal mould (50) 50 6 5
GZG.INV. 30577 d Whitby, Yorkshire RV, external mould 48 (42) 2 –
SMNS 17361 (Kuhn 1935) Nellingen, Southern Germany LV, internal mould 52 (48) 8 7
GPIT 1028/53 (Ho¨lder 1953) Bebenhausen, Southern Germany LV, internal mould 55 54 7 6
Numbers in brackets are approximations
L length, H height, I inflation, R number of ribs
b
The bipolar bivalve Oxytoma (Palmoxytoma) cygnipes (Young & Bird, 1822) 49
123
by Efimova et al. (1968) has only four prominent ribs. The
umbo is slightly prosogyrous, and the valves are otherwise
identical with the specimens described in this paper. Three
left valves of Oxytoma (Palmoxytoma) cygnipes (Young &
Bird) published by Poulton (1991) are comparatively small,
and hence have only four ribs. Apart from that, they are
identical with our specimens in shape and ornamentation,
including spine-like rib projections. A variety with seven
ribs with rather close spacing has been described as Oxy-
toma (Palmoxytoma) ussurica Voronetz by Konovalova
and Markevich (2004). The specimens have slightly pro-
sogyrous umbones but the general shape and ornamenta-
tion, including spine-like rib projections, is almost identical
with those of Oxytoma (Palmoxytoma) cygnipes (Young &
Bird).
More pronounced differences from the specimens from
the NW European Shelf can be seen in specimens from
South America and New Zealand. The internal mould of a
right valve of Palmoxytoma cf. cygnipes (Damborenea
2002: pl. 1/8a and Riccardi 1991: fig. 4/14) from Argentina
has a very deeply incised byssal notch, not observed in our
specimen with shell preservation. An extreme variety from
New Zealand, a specimen with only three prominent ribs
and curved spines, has been illustrated by Damborenea
(1993: fig. 3b, 2002: text-fig. 9) as Palmoxytoma n. sp. In
addition, the disc margins between the prominent ribs are
curving outward, and are not concave as in the NW
European specimens with their umbrella-like appearance
(cf. Troedsson 1951: 201). Further specimens of this
Oxytoma (Palmoxytoma) variety are required to decide
whether the low rib number is a constant feature enabling
definition of a new species.
Taking these variations into account, the currently
available data are consistent with the interpretation of the
mentioned specimens as a single species, with morpho-
logical variations between specimens from the northern
and southern hemispheres.
Biogeography of Oxytoma (Palmoxytoma) cygnipes
(Young and Bird) on the Lower Jurassic NW European
Shelf
On the NW European Jurassic Shelf Oxytoma (Palmoxy-
toma) cygnipes (Young & Bird, 1822) occurs at two
distinct stratigraphic intervals. These are the Rhaetian–
Hettangian boundary strata (Pre-Planorbis beds to Planor-
bis bed) and the Upper Pliensbachian (base of Marlstone
Rock Formation, Staithes Sandstone, and Cleveland Iron-
stone Formation, Amaltheenton formation) (Table 3).
Rhaetian/Hettangian. From the British Lower Jurassic,
one of the stratigraphically oldest records of Oxytoma
(Palmoxytoma) cygnipes is that of Stutchbury (1839) from
the Saltford Shale (Blue Lias Formation), a long-spined
variety initially described as Avicula longicostata Stutch-
bury, 1839. A precise bed has not been identified, but the
Saltwick Shale is confined to the Planorbis to lower
Angulata Zones (Ambrose 2001).
Hodges in Cope (1991) mentioned Palmoxytoma from
the Pre-Planorbis Beds, i.e. the basal part of the Blue Lias
Formation. The precise position below or above the
Rhaetian–Hettangian boundary is not clear. In addition, the
Bath Royal Literary and Scientific Institution hosts several
specimens of O. (P.) longicostata from ‘‘Lower Lias clay
with White & Blue Lias Lst.’’, Montpelier, Bristol (col-
lection C. Moore). From the same location, Oxytoma
longicostata has been illustrated by Arkell (1933) as a
characteristic fossil of the Pre-Planorbis beds.
A further occurrence from the Rhaetian–Hettangian
transition is represented by Palmoxytoma sp. from the
Upper Schattwald Shales of Loru¨ns/Vorarlberg (McRo-
berts et al. 1997), above the negative d13C excursion pre-
ceding the Triassic–Jurassic boundary (von Hillebrandt
et al. 2007). Again, it is not clear whether the specimen is
still latest Rhaetian or earliest Hettangian.
Of lowermost Hettangian age seems to be Avicula
(Oxytoma) cf. cycnipes Phill. described and illustrated by
Jeannet (1913). He obtained four valves of this taxon from
approximately 6 m below the ‘‘Niveau a` Planorbis’’ but
still 20 m above typical Rhaetian limestones. Again, the
precise position of the Rhaetian–Hettangian boundary is
not evident from currently available information.
Clearly of Hettangian age are the reports of O. (Palm-
oxytoma) from the Swabian Jurassic (South Germany), i.e.
findings from the Psilonoten Limestone. These are one
fragmentary internal mould assigned to Oxytoma cf.
longicostata Strickl. from Nellingen (Kuhn 1935) and one
internal mould described as Oxytoma scanica (Lundgren,
1888) from Bebenhausen (Ho¨lder 1953). The latter speci-
men is associated with Psiloceras plicatulum (Quenstedt,
1883). Recently, Schweigert and Klaschka (2011) discov-
ered a further specimen comparable with Oxytoma
(Palmoxytoma) from the Psilonoten Limestone of Beben-
hausen. The Psilonoten Limestone is a 30–40 cm thick,
condensed transgressive bed including ammonites of the
lower Planorbis Zone, Psilonotum and Plicatulum horizons,
locally underlain by a Neophyllites horizon (Bloos 1999).
These ammonite horizons rest unconformably upon Rhae-
tian marine-deltaic sandstones.
Possibly younger but still within the Planorbis Zone are
the youngest published occurrences from the Hettangian of
the Northern Calcareous Alps. From top parts of the
Hettangian Kendlbach Formation (still below Psiloceras
calliphyllum (Neumayr, 1879) and Psiloceras costosum
Lange, 1952) at the Ochsentaljoch section, Karwendel, von
50 G. Arp, S. Seppelt
123
T
a
b
le
3
O
cc
u
rr
en
ce
s
o
f
O
xy
to
m
a
(P
a
lm
o
xy
to
m
a
)
cy
g
n
ip
es
(Y
o
u
n
g
&
B
ir
d
,
1
8
2
2
)
o
n
th
e
N
W
E
u
ro
p
ea
n
S
h
el
f
an
d
ad
ja
ce
n
t
ar
ea
s
C
h
ro
n
o
st
ra
ti
g
ra
p
h
ic
u
n
it
L
it
h
o
st
ra
ti
g
ra
p
h
ic
u
n
it
L
o
ca
ti
o
n
R
ef
.
R
h
ae
ti
an
–
H
et
ta
n
g
ia
n
b
o
u
n
d
ar
y
P
re
-P
la
n
o
rb
is
B
ed
s
E
n
g
la
n
d
,
B
ri
st
o
l
A
rk
el
l
(1
9
3
3
):
P
re
-P
la
n
o
rb
is
b
ed
s,
M
o
n
tp
el
ie
r,
B
ri
st
o
l
R
h
ae
ti
an
–
H
et
ta
n
g
ia
n
b
o
u
n
d
ar
y
P
re
-P
la
n
o
rb
is
B
ed
s
E
n
g
la
n
d
H
o
d
g
es
in
C
o
p
e
(1
9
9
1
)
R
h
ae
ti
an
–
H
et
ta
n
g
ia
n
b
o
u
n
d
ar
y
o
r
H
et
ta
n
g
ia
n
B
lu
e
L
ia
s
F
m
.,
S
al
tf
o
rd
S
h
al
e
M
b
r.
E
n
g
la
n
d
,
S
o
m
er
se
t
S
tu
tc
h
b
u
ry
(1
8
3
9
):
li
as
sh
al
es
at
S
al
tf
o
rd
,
b
et
w
ee
n
B
ri
st
o
l
an
d
B
at
h
,
S
o
m
er
se
ts
h
ir
e
R
h
ae
ti
an
–
H
et
ta
n
g
ia
n
b
o
u
n
d
ar
y
F
m
.
d
e
P
la
n
F
al
co
n
S
w
it
ze
rl
an
d
,
P
re´
al
p
es
Je
an
n
et
(1
9
1
3
):
H
et
ta
n
g
ie
n
in
fe
ri
eu
r,
P
la
n
-F
al
co
n
su
r
C
o
rb
ey
ri
er
,
P
re´
al
p
es
R
h
ae
ti
an
–
H
et
ta
n
g
ia
n
b
o
u
n
d
ar
y
K
en
d
lb
ac
h
F
m
.
A
u
st
ri
a,
A
u
st
ro
al
p
in
e
M
cR
o
b
er
ts
et
al
.
(1
9
9
7
):
U
p
p
er
S
ch
at
tw
al
d
S
h
al
e,
L
o
ru¨
n
s/
V
o
ra
rl
b
er
g
L
o
w
er
H
et
ta
n
g
ia
n
,
P
la
n
o
rb
is
Z
o
n
e
K
en
d
lb
ac
h
F
m
.
A
u
st
ri
a,
A
u
st
ro
al
p
in
e
F
u
g
g
er
(1
9
0
6
)
‘‘
g
ra
u
e
H
o
rn
st
ei
n
k
al
k
e
d
er
P
si
lo
n
o
te
n
-S
ch
ic
h
te
n
,
G
la
se
n
b
ac
h
k
la
m
m
b
ei
S
al
zb
u
rg
L
o
w
er
H
et
ta
n
g
ia
n
,
P
la
n
o
rb
is
Z
o
n
e
P
si
lo
n
o
te
n
to
n
F
m
.
G
er
m
an
y
,
B
ad
en
-W
u¨
rt
te
m
b
er
g
K
u
h
n
(1
9
3
5
):
P
si
lo
n
o
te
n
k
al
k
,
N
el
li
n
g
en
L
o
w
er
H
et
ta
n
g
ia
n
,
P
la
n
o
rb
is
Z
o
n
e
P
si
lo
n
o
te
n
to
n
F
m
.
G
er
m
an
y
,
B
ad
en
-W
u¨
rt
te
m
b
er
g
H
o¨
ld
er
(1
9
5
3
):
P
la
n
o
rb
is
-B
an
k
,
H
et
ta
n
g
iu
m
,
B
eb
en
h
au
se
n
?U
p
p
er
P
li
en
sb
ac
h
ia
n
N
ei
ll
K
li
n
te
r
G
ro
u
p
,
G
u
le
h
o
rn
F
m
.
G
re
en
la
n
d
,
Ja
m
es
o
n
L
an
d
R
o
se
n
k
ra
n
tz
(1
9
3
4
):
C
h
ar
m
o
u
th
ia
n
,
E
as
t
G
re
en
la
n
d
C
o
n
d
en
se
d
L
o
w
.
P
li
en
sb
ac
h
ia
n
p
lu
s
S
to
k
es
i
S
u
b
zo
n
e
‘‘
B
el
em
n
it
en
–
S
ch
ic
h
te
n
’’
G
er
m
an
y
,
N
ie
d
er
sa
ch
se
n
B
ra
u
n
s
(1
8
7
1
):
N
iv
ea
u
d
es
A
m
m
.
ce
n
ta
u
ru
s
b
ei
S
ch
ep
p
en
st
ed
t,
in
d
er
G
eg
en
d
v
o
n
O
k
er
,
b
ei
Je
rx
h
ei
m
-
u
n
d
d
es
A
m
m
.
D
av
o
ei
b
ei
L
u¨
er
d
is
se
n
am
It
h
C
o
n
d
en
se
d
L
o
w
.
P
li
en
sb
ac
h
ia
n
p
lu
s
S
to
k
es
i
S
u
b
zo
n
e
‘‘
B
el
em
n
it
en
–
S
ch
ic
h
te
n
’’
G
er
m
an
y
,
G
o¨
tt
in
g
en
,
N
ie
d
er
sa
ch
se
n
v
o
n
K
o
en
en
(1
9
0
7
):
M
it
tl
er
er
L
ia
s,
sa¨
m
tl
ic
h
o
d
er
d
o
ch
g
ro¨
ß
te
n
te
il
s
au
s
d
er
Z
o
n
e
d
es
A
m
m
.
D
av
o
ei
L
o
w
er
/U
p
p
er
P
li
en
sb
ac
h
ia
n
b
o
u
n
d
ar
y
‘‘
B
el
em
n
it
en
–
S
ch
ic
h
te
n
’’
L
o
w
er
S
ax
o
n
y
,
H
il
s
sy
n
cl
in
e
v
o
n
S
ee
b
ac
h
(1
8
6
4
):
S
ch
ic
h
te
n
d
es
A
m
.
ca
p
ri
co
rn
u
s
b
ei
L
u¨
rd
is
se
n
am
It
h
U
p
p
er
P
li
en
sb
ac
h
ia
n
,
M
ar
g
ar
it
at
u
s
Z
o
n
e
C
le
v
el
an
d
Ir
o
n
st
o
n
e
F
m
.
E
n
g
la
n
d
,
Y
o
rk
sh
ir
e
P
h
il
ip
p
s
(1
8
2
9
):
M
ar
ls
to
n
e
S
er
ie
s,
B
il
sd
al
e,
W
il
to
n
C
as
tl
e/
Y
o
rk
sh
ir
e
U
p
p
er
P
li
en
sb
ac
h
ia
n
,
M
ar
g
ar
it
at
u
s
Z
o
n
e
C
le
v
el
an
d
Ir
o
n
st
o
n
e
F
m
.
E
n
g
la
n
d
,
Y
o
rk
sh
ir
e
O
p
p
el
(1
8
5
6
):
B
as
is
d
es
M
ar
ls
to
n
e,
u
n
te
r
A
m
m
.
m
ar
g
ar
it
at
u
s,
R
o
b
in
H
o
o
d
s
B
ay
U
p
p
er
P
li
en
sb
ac
h
ia
n
,
M
ar
g
ar
it
at
u
s
-
S
p
in
at
u
m
Z
o
n
e
S
ta
it
h
es
S
an
d
st
o
n
e
F
m
.,
C
le
v
el
an
d
Ir
o
n
st
o
n
e
F
m
.
E
n
g
la
n
d
,
Y
o
rk
sh
ir
e
T
at
e
an
d
B
la
k
e
(1
8
7
6
)
Z
o
n
es
o
f
A
m
.
m
ar
g
ar
it
at
u
s,
S
ta
it
h
es
,
R
o
ck
cl
if
f,
H
u
m
m
er
se
a,
H
u
n
tc
li
ff
,
B
il
sd
al
e,
b
o
tt
o
m
se
am
o
f
ir
o
n
st
o
n
e,
S
la
p
ew
at
h
,
G
ro
sm
o
n
t,
G
la
iz
ed
al
e;
A
m
.
sp
in
at
u
s,
S
ta
it
h
es
,
E
st
o
n
,
U
p
le
at
h
am
,
G
u
is
b
ro
’.
U
p
p
er
P
li
en
sb
ac
h
ia
n
,
M
ar
g
ar
it
at
u
s
-
S
p
in
at
u
m
Z
o
n
e
A
m
al
th
ee
n
to
n
fm
.
G
er
m
an
y
,
B
av
ar
ia
,
B
o
d
en
w
o¨
h
r
v
o
n
G
u¨
m
b
el
(1
8
9
1
):
S
o
h
le
rz
d
es
m
it
tl
er
en
L
ia
s
m
it
A
m
.
m
ar
g
ar
it
at
u
s
u
n
d
sp
in
at
u
s,
B
o
d
en
w
o¨
h
re
r
B
ec
k
en
U
p
p
er
P
li
en
sb
ac
h
ia
n
,
S
p
in
at
u
m
Z
o
n
e
C
le
v
el
an
d
Ir
o
n
st
o
n
e
F
m
.
E
n
g
la
n
d
,
Y
o
rk
sh
ir
e
Y
o
u
n
g
an
d
B
ir
d
(1
8
2
2
,
1
8
2
8
):
fr
o
m
th
e
ir
o
n
st
o
n
e
b
an
d
s
o
f
th
e
al
u
m
in
o
u
s
st
ra
ta
U
p
p
er
P
li
en
sb
ac
h
ia
n
,
S
p
in
at
u
m
Z
o
n
e
L
ia
s
G
ro
u
p
Y
o
rk
sh
ir
e,
M
id
la
n
d
s,
E
n
g
la
n
d
,
H
eb
ri
d
es
H
al
la
m
(1
9
6
7
):
S
p
in
at
u
m
Z
o
n
e,
Y
o
rk
sh
ir
e
(c
o
m
m
o
n
),
M
id
la
n
d
s
(o
cc
u
rs
),
S
W
-E
n
g
la
n
d
(o
cc
u
rs
),
H
eb
ri
d
es
(o
cc
u
rs
)
U
p
p
er
P
li
en
sb
ac
h
ia
n
,
S
p
in
at
u
m
Z
o
n
e
L
u
m
ac
h
el
le
a`
H
ar
p
ax
F
ra
n
ce
,
R
h
oˆ
n
e,
Is
e`r
e
D
u
m
o
rt
ie
r
(1
8
5
7
):
S
t.
F
o
rt
u
n
at
au
M
o
n
t
d
’O
r/
R
h
oˆ
n
e,
C
h
am
ag
n
ie
u
/
Is
e`r
e,
la
p
ar
ti
e
su
p
er
ie
u
r
d
u
li
as
m
o
y
en
U
p
p
er
P
li
en
sb
ac
h
ia
n
,
S
p
in
at
u
m
Z
o
n
e
L
u
m
ac
h
el
le
a`
H
ar
p
ax
F
ra
n
ce
,
R
h
oˆ
n
e
D
u
m
o
rt
ie
r
(1
8
6
9
):
G
iv
er
d
y
,
zo
n
e
d
u
P
ec
te
n
ae
q
u
iv
al
v
is
U
p
p
er
P
li
en
sb
ac
h
ia
n
,
S
p
in
at
u
m
Z
o
n
e
L
u
m
ac
h
el
le
a`
H
ar
p
ax
F
ra
n
ce
,
R
h
oˆ
n
e
R
u
ll
ea
u
(2
0
0
7
):
D
o
m
e´r
ie
n
su
p
e´r
ie
u
r,
C
ro
ix
R
am
p
au
d
,
P
o
le
y
m
ie
u
x
-a
u
-M
o
n
t-
d
’O
r
The bipolar bivalve Oxytoma (Palmoxytoma) cygnipes (Young & Bird, 1822) 51
123
Hillebrandt et al. (2007: fig. 9) illustrated an ‘‘Oxytoma’’,
which can be identified as the left valve of O. (Palmoxy-
toma) cygnipes. In addition, Fugger (1906) mentioned
Avicula cygnipes Phil. from Lower Hettangian siliceous
limestones with cherts at the Glasenbachklamm near
Salzburg.
Taking all these published occurrences into account,
Oxytoma (Palmoxytoma) cygnipes (Young & Bird, 1822)
seems to have been widespread in the Rhaetian–Hettangian
boundary strata of the NW European Shelf and its margin
to the Tethys. By contrast, the following Upper Hettangian
to Lower Pliensbachian deposits of this area appear to be
devoid of this species.
Pliensbachian. The type species of Young and Bird
(1822) comes from the Upper Pliensbachian Cleveland
Ironstone Formation (‘‘hard bands in the alum shale’’),
where it is most abundant in the ‘‘Avicula seam’’ (i.e., top
of the Subnodosus Subzone; Howarth 1955; Rawson and
Wright 1996: 206). This coincides with the descriptions of
Harries and Little (1999), who mention Palmoxytoma
cygnipes from the upper Staithes Sandstone and Cleveland
Ironstone Formations (Stokesi to Apyrenum Subzone) of
the Yorkshire coast (Staithes Harbor and Saltwick Nab).
Similarly, Hallam (1967) reports Oxytoma (Palmoxytoma)
cygnipes (Young & Bird, 1822) from the Spinatum Zone of
Yorkshire (common), in addition to the Midlands (occurs),
SW-England (occurs) and the Hebrides (occurs).
From East Greenland, Oxytoma cygnipes Y. et B. is
reported by Rosenkrantz (1934: 112) from the Pliensba-
chian (Charmouthian), though without illustration. From
the sections described and the few ammonites found, it
seems possible that the fossil-bearing strata range into the
Upper Pliensbachian.
Also, the early reports of Oxytoma (Palmoxytoma) from
southern Sweden (Lundgren 1881, 1888) apparently show
specimens from the Pliensbachian. The fine-grained sand-
stone that contained the Oxytoma (Palmoxytoma) specimen
of Moberg (1888) is also most likely Pliensbachian in age
(cf. Reyment 1959; Ahlberg et al. 2003). However, a more
precise biostratigraphic designation is not available,
because the material is derived from glacial till deposits
(Brandsberga sandstone, Middle Liassic; Sivhed 1984).
In Northern Germany the Lower–Upper Pliensbachian
boundary strata yield Palmoxytoma specimens, as noted by
von Seebach (1864) and Brauns (1871). These authors
mention Avicula cygnipes Young and Bird from the
‘‘Belemniten–Schichten’’ of the Hils syncline and Subh-
ercynian syncline and from the margin of the Asse-
Heeseberg anticline (von Seebach 1864; Brauns 1871).
Unfortunately, these reports are without illustration and
without described sections, so the precise stratigraphic
position (Davoei Zone or Stokesi Subzone), crucial forT
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palaeoceanographic interpretations, in these condensed
beds remains unclear. Similarly, the precise biostrati-
graphic level of Avicula cygnipes Phill. of von Koenen
(1907: 44) from the Middle Lias of Go¨ttingen is not clear
from this publication. However, the corresponding speci-
men is in the GZG collection (‘‘Avicula cycnipes Phill., M.
Lias, d d [donum dedit] Wolf, Go¨ttingen-Geismar’’;
Fig. 4f, g), preserved within an echinoderm packstone,
which is likely to be derived from the top of the ‘‘Bel-
emniten–Schichten’’, i.e. the Stokesi Subzone.
From Southern Germany, von Ammon (in von Gu¨mbel
1891: 690) lists Avicula cygnipes from the Upper Pli-
ensbachian iron ores of Bodenwo¨hr, Eastern Bavaria.
These highly condensed, 0.2–1.5 m thick fissile goethite-
haematite deposits comprise the Margaritatus and Spina-
tum Zones (von Gu¨mbel 1891; Meyer and Bauberger
1998). This is currently the southeasternmost occurrence of
Oxytoma (Palmoxytoma) cygnipes. Unfortunately, no cor-
responding specimen exists in the Gu¨mbel collection of the
Bavarian Geological Survey.
Further specimens have been discovered in southeastern
France, as already described and illustrated by Dumortier
(1857) from the upper part of the Pliensbachian east of
Lyon (St Fortuna), and from the Upper Pliensbachian
(‘‘Zone du Pecten aequivalvis’’) of Giverdy in the Mont
d’Or area (Dumortier 1869). In the region of Lyon, Oxy-
toma (Palmoxytoma) cygnipes occurs within a highly
condensed limestone bed (Calcaire a` Harpax) together with
Gryphaea (Bilobissa) sportella (Dumortier, 1869), Cardi-
nia crassissima (Sowerby, 1817) and rare Pleuroceras
spinatum (Bruguiere 1789) and Pleuroceras solare (Phil-
lips, 1829), pointing to the top parts of the Apyrenum
Subzone of the Spinatum Zone (Louis Rulleau, personal
communication).
In summary, Late Pliensbachian occurrences of the
bivalve Oxytoma (Palmoxytoma) cygnipes (Young & Bird,
1822) are evident for England, southern Sweden to south-
eastern Bavaria, and southeastern France (Fig. 5) whereas
specimens are rare or absent on the western shelf parts of
NW Europe and the Mediterranean region.
Toarcian. The only published occurrence in the Toarcian
known to the authors is Oxytoma cf. cygnipes Y. et B. of
Rosenkrantz (1934) from Jameson Land, East Greenland,
but the taxon has not been illustrated.
Discussion
The Lower Jurassic sedimentary pattern on the NW
European Shelf has predominantly been interpreted on the
basis of sea-level changes being the major controlling
factor (Brandt 1985; de Graciansky et al. 1998; Hesselbo
and Jenkyns 1998). However, changes in the current sys-
tems may have played an equally important role. Specifi-
cally, the palaeogeographic situation of the NW European
Shelf, with a narrow seaway to the North (Viking Corridor:
Westermann 1993; Transcontinental Laurasian seaway:
Bjerrum et al. 2001) implies that the sedimentary system of
the shelf was susceptible to changes in current direction,
dependent on the density differences between Arctic and
Tethyian seawater (Bjerrum et al. 2001).
The Late Pliensbachian has been interpreted as a rela-
tively cool period in NW Europe, mainly as a result of
general climatic cooling in the Northern Hemisphere (Price
1999; Guex et al. 2001). Alternatively, cool water condi-
tions, as reflected in palynomorph assemblages and d18O
values from belemnites, were considered to reflect influx of
cool water masses from boreal regions (Riding and Hub-
bard 1999; van de Schootbrugge et al. 2005). In addition,
there is increasing geochemical evidence that changes in
current directions occurred on the NW European Shelf
during the Early Jurassic (Dera et al. 2009).
In Germany, major parts of the Upper Pliensbachian are
represented by the comparatively thick, monotonous suc-
cession of dark marly claystones, the Amaltheenton forma-
tion, which is dominated by macrobenthos assemblages of
comparatively low diversity (see, e.g., Paleobiology Data-
base collection numbers 23624–23628 and 23812–23818),
although species listings by Brauns (1871), Monke (1889)
and Kuhn (1936) give a contrary impression. By contrast, the
Lower Pliensbachian of Germany contains calcareous sedi-
ments (marlstone–limestone alternations), with iron–oolitic
Fig. 5 Possible seawater current pattern on the NW European Shelf
based on the occurrences/non-occurrences of Oxytoma (Palmoyxtom-
a) cygnipes (Young & Bird, 1822) and model calculations of Bjerrum
et al. (2001). Palaeogeography based on Ziegler (1988)
The bipolar bivalve Oxytoma (Palmoxytoma) cygnipes (Young & Bird, 1822) 53
123
intercalations in the north and phosphoritic intercalations in
the south. The macrobenthos shows more diverse bivalve
assemblages (Wollemann 1892). Although these differences
in macrobenthos assemblages may be partly explained by
substrate changes, the—albeit scattered—occurrence of
coralline sponges in the Numismalismergel Formation sug-
gest an influx of warmer seawater from Tethyan regions in
the Early Pliensbachian.
In this context, the new finds of the bivalve Oxytoma
(Palmoxytoma) are of palaeozeanographic significance.
This taxon has been extensively reviewed by Damborenea
(1993, 2002) as a bivalve with a pronounced bipolar dis-
tribution, including occurrences from southern South
America and New Zealand, and from northern boreal areas
(NE Siberia, far-east Russia, Japan, Canada) and England,
Sweden, and France.
Accordingly, the occurrence of Oxytoma (Palmoxytoma)
at the top of the ‘‘Belemniten–Schichten’’ in Northern
Germany may indicate an influx of cool seawater to the
eastern part of the NW European Shelf at the base of the
Upper Pliensbachian (Fig. 5), i.e. just before the onset of
the Amaltheenton formation. This carbonate top bed of the
‘‘Belemniten–Schichten’’ consists of echinoderm wacke/
packstones with reduced macrobenthos species richness.
Indeed, at Beierstedt this condensed bed contained only
five bivalve species, compared with 20 bivalve species in
the condensed Lower Pliensbachian carbonate bed below
(Table 1). Certainly, these species counts provide only a
first hint, and quantitative benthos analysis of sections less
affected by time-averaging (Fu¨rsich and Aberhan 1990) are
required to verify this trend. This supposed cool water
current may have extended (during the upper Margaritatus
to Spinatum Zones) farther south to eastern Bavaria and
southeastern France, as suggested by the specimens
reported by von Ammon in von Gu¨mbel (1891), by
Dumortier (1857, 1869) and by Rulleau (2007) (Fig. 5).
Continuing cool water conditions during deposition of
the Amaltheenton formation in Northern Germany are
evident from glendonites, which have been reported from
the upper part of the Amaltheenton formation (motorway A
39 at Wolfsburg; Luppold and Teichert 2007), although
their significance as an indicator of low temperatures has
subsequently been questioned by the same authors (Teic-
hert and Luppold 2009). However, the temperature–pres-
sure stability field of ikaite, the precursor of glendonites, is
well constrained, and the significance of the associated
species-rich and supposed thermophile microfauna men-
tioned by these authors must be verified.
For the Rhaetian–Hettangian boundary, the palaeoenvi-
ronmental implications of the Oxytoma (Palmoxytoma)
occurrences are more difficult to determine. Assuming a
cool water preference of Oxytoma (Palmoxytoma) for this
time interval also, the occurrences within the Alpine region
may point to a cool deeper-water setting, or alternatively to
a global cooling interval. Although the causes of the Tri-
assic–Jurassic boundary extinction event are still under
discussion (Tanner et al. 2004), climatic fluctuations with a
short-term cooling period (induced by aerosols) immedi-
ately after the negative d13C excursion, followed by a
warming period (induced by increased atmospheric CO2)
seem well constrained (reviewed by, e.g., Wignall 2001;
Guex et al. 2004; Pien´kowski et al. 2008). Also, the higher
extinction rate of tropical than non-tropical genera in the
Rhaetian point to a palaeoclimatic factor in the end-Tri-
assic mass extinction (Kiessling and Aberhan 2007). A
short-term cooling interval may hence be assumed for the
English Pre-Planorbis beds and the Southwest German
Psilonotenkalk, both deposited in shallow-water settings on
the NW European Shelf. However, the occurrence of the
coral Isastrea in the Psilonotenkalk (Schweigert et al.
2010), a zooxanthellate warm-water coral rather than an
azooxanthellate cool-water coral, challenges this hypothe-
sis. Here, further investigations are required to assess
faunal mixing by reworking of stratigraphically older
material into the transgressive Psilonoten Limestone.
Conclusions
Oxytoma (Palmoxytoma) cygnipes (Young & Bird, 1822)
from the Lower Jurassic of Northern Germany (to be pre-
cise, from the basal Upper Pliensbachium), is described
and illustrated for the first time. Comparison of published
specimens of Oxytoma (Palmoxytoma) suggests there is
only one species in the Lower Jurassic, i.e. cygnipes
(Young & Bird, 1822). This species ranges from the
Rhaetian–Hettangian boundary to the Upper Pliensbachian,
probably extending into the Toarcian. A review of pub-
lished occurrences on the Early Jurassic NW European
Shelf indicates two distinct stratigraphic intervals: the
Rhaetian–Hettangian boundary and the Upper Pliensba-
chian. The occurrence of Oxytoma (Palmoxytoma) cygni-
pes at the base of the Upper Pliensbachian, just before the
onset of the Amaltheenton sedimentation, is interpreted as
reflecting an influx of cool water from the Boreal Ocean on
to the eastern NW European Shelf. This cool water current
may have extended southwards as far as Southern Ger-
many, with a possible counter current on the western shelf
parts. For the occurrences of the species at the Triassic–
Jurassic boundary of the NW European Shelf, a short-term
cooling interval at the same time as the extinction event
might provide an explanation.
Acknowledgments We are indebted to Fritz-Hermann Mu¨ller, Be-
ierstedt and Joachim Reitner, University of Go¨ttingen, for their gen-
erous support of the field campaign at Beierstedt. Alexander Satmari,
54 G. Arp, S. Seppelt
123
Go¨ttingen, prepared the thin-sections. Winfried Werner and Erwin
Geiss, Mu¨nchen, carried out a search for Oxytoma (Palmoxytoma) in
the Gu¨mbel collection of the Bavarian Geological Survey. Christine
Heim, Go¨ttingen, helped with translating Swedish publications. We
are indebted to Louis Rulleau, Chasselay, for providing detailed
information on the occurrence of Oxytoma (Palmoxytoma) in the
region of Lyon. Gu¨nter Schweigert and Philipe Havlik kindly pro-
vided access to original specimens in the collections of Stuttgart and
Tu¨bingen, respectively. Franz T. Fu¨rsich, Erlangen, and an anony-
mous reviewer provided helpful comments, corrections, and
suggestions.
Open Access This article is distributed under the terms of the
Creative Commons Attribution Noncommercial License which per-
mits any noncommercial use, distribution, and reproduction in any
medium, provided the original author(s) and source are credited.
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