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Facies of two important Early Triassic gastropod lagerstätten: Implications for diversity patterns in the aftermath of the end-Permian mass extinction

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Two important lagersttten of Early Triassic gastropods, the Sinbad Limestone (Utah, USA) and the Gastropod Oolite (North Italy) yield about 40% of all described Early Triassic species. This great contribution to the global diversity and the exceptional good preservation render high information content, which characterizes fossil lagersttten. The Smithian Sinbad Limestone contains the most diverse Early Triassic gastropod fauna. At the type locality, it occurs in single, probably storm-induced shell bed within a series of high energy deposits underlain by intertidal microbial mats and subtidal oolite/peloid shoals. The main shell bed contains about 40 invertebrate taxa. Gastropods, scaphopods, and bivalves are most abundant and form an assemblage, which is dominated by small neritaemorphs, the opisthobranch Cylindrobullina convexa and the scaphopod Plagioglypta (annulated tubes). This assemblage lived on shallow, subtidal soft-bottoms based on sedimentological and ecological characteristics. The Dienerian (to Smithian?) Gastropod Oolite Member (North Italy) has extremely abundant, probably salinity-controlled gastropod faunas with low species richness. Almost monospecific assemblages of Pseudomurchisonia kokeni as well as assemblages with about four species are present in the Gastropod Oolite. Modern hydrobiid mudsnail faunas which are adapted to strongly fluctuating salinity in intertidal to shallow subtidal coastal areas form probably a suitable model for the Gastropod Oolite biota. Gastropods from the Werfen- and Moenkopi-Formation lagersttten are well preserved compared to other Early Triassic deposits. The high contribution to the global diversity of just two sites suggests very incomplete sampling and preservational bias. However, the low richness of the major faunas reflects depauperate Early Triassic faunas and slow recovery from the Permian/Triassic crisis.
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Facies (2005) 51: 480–500
DOI 10.1007/s10347-005-0074-5
ORIGINAL ARTICLE
Alexander N
¨
utzel · Christian Schulbert
Facies of two important Early Triassic gastropod lagerst
¨
atten:
implications for diversity patterns in the aftermath
of the end-Permian mass extinction
Received: 11 January 2005 / Accepted: 23 March 2005 / Published online: 26 May 2005
C
Springer-Verlag 2005
Abstract Two important lagerst
¨
atten of Early Triassic
gastropods, the Sinbad Limestone (Utah, USA) and the
Gastropod Oolite (North Italy) yield about 40% of all
described Early Triassic species. This great contribution to
the global diversity and the exceptional good preservation
render high information content, which characterizes fossil
lagerst
¨
atten. The Smithian Sinbad Limestone contains the
most diverse Early Triassic gastropod fauna. At the type
locality, it occurs in single, probably storm-induced shell
bed within a series of high energy deposits underlain by
intertidal microbial mats and subtidal oolite/peloid shoals.
The main shell bed contains about 40 invertebrate taxa.
Gastropods, scaphopods, and bivalves are most abundant
and form an assemblage, which is dominated by small
neritaemorphs, the opisthobranch Cylindrobullina convexa
and the scaphopod Plagioglypta (annulated tubes). This
assemblage lived on shallow, subtidal soft-bottoms based
on sedimentological and ecological characteristics. The
Dienerian (to Smithian?) Gastropod Oolite Member (North
Italy) has extremely abundant, probably salinity-controlled
gastropod faunas with low species richness. Almost
monospecific assemblages of Pseudomurchisonia kokeni
as well as assemblages with about four species are present
in the Gastropod Oolite. Modern hydrobiid mudsnail
faunas which are adapted to strongly fluctuating salinity in
intertidal to shallow subtidal coastal areas form probably a
suitable model for the Gastropod Oolite biota. Gastropods
from the Werfen- and Moenkopi-Formation lagerst
¨
atten
are well preserved compared to other Early Triassic
deposits. The high contribution to the global diversity
of just two sites suggests very incomplete sampling and
preservational bias. However, the low richness of the major
faunas reflects depauperate Early Triassic faunas and slow
recovery from the Permian/Triassic crisis.
A. N
¨
utzel (
) · C. Schulbert
Institute of Palaeontology, University Erlangen-N
¨
urnberg,
Loewenichstrasse 28,
D-91054 Erlangen, Germany
e-mail: nuetzel@pal.uni-erlangen.de
Tel.: +49-(0)9131-8524849
Fax: +49-(0)9131-8522690
Keywords Gastropoda
.
USA
.
Italy
.
Early Triassic
.
Recovery
.
Permian/Triassic mass extinction
Introduction
Fossil lagerst
¨
atten are rock bodies with exceptional high pa-
leontological information content (Seilacher et al. 1985).
For four reasons, the Sinbad Limestone Member (Utah,
USA) and the Gastropod Oolite Member (North Italy) rep-
resent outstanding Early Triassic fossil lagerst
¨
atten:
1. They contain beds with extremely abundant gastropods
and other molluscs (concentration lagerst
¨
atten).
2. They were deposited in a particularly critical time-
interval: the aftermath of the end-Permian biotic crisis.
3. They contribute a great portion to the global Early Trias-
sic species richness, as is indicated by our own species-
level database (as much as 40% of nominate species).
4. They are exceptionally well preserved (especially gas-
tropods from the Sinbad Limestone).
This paper describes and interprets microfacies, sedimen-
tology, fossil preservation, and faunal content of shell beds
from both members. Generally, shell beds form an impor-
tant source of paleontological, paleoecological, and tapho-
nomic information (e.g., Kidwell 1991a, b;F
¨
ursich and
Oschmann 1993; Boyer et al. 2004). The concentration of
shells in distinct beds was produced by storms (tempestites)
or they represent lag deposits (e.g., Kidwell 1991a, b).
The shell beds studied here represent benthic mollusc co-
quinas. We use this term in order to separate such shell beds
from cephalopod coquinas (e.g., the Jurassic Ammonitico
Rosso Facies, or the Paleozoic Orthoceras Limestones),
which represent another distinct type of mollusc concen-
trations and depositional environment. Benthic mollusc
coquinas are more common in the post-Paleozoic reflecting
the rise of modern bivalve- and gastropod-dominated
faunas (Sepkoski et al. 1991; Kidwell and Brenchley
1994). The increase of this facies was accentuated by the
end-Permian mass extinction event, which removed or di-
minished typical Paleozoic faunal elements, e.g., articulate
481
brachiopods. The analysis of Early Triassic shell beds helps
to understand the evolutionary history of the gastropods at
the Paleozoic/Mesozoic transition and the recovery from
the end-Permian mass extinction. It is particularly interest-
ing which factors potentially limited the diversity during the
aftermath of the end-Permian catastrophe. This aftermath is
considered to be extremely long lasting and was obviously
connected with major high-frequent perturbations of the
carbon cycle (Payne et al. 2004). Among other possible
reasons, anoxia was discussed as limiting factor, especially
for biota during the earliest Triassic (Griesbachian; Wignall
and Twitchett 2002). However, the proximate limiting con-
ditions during the whole length of the recovery interval are
still poorly understood. An important step to unravel these
factors is the analysis of the faciesand depositional environ-
ments of the main fossil lagerst
¨
atten of the Early Triassic.
Gastropods play an important role in any recovery analysis
because they form one of the most diverse invertebrate
groups in the Early Triassic. This study is about the facies
and depositional environments of two important Early Tri-
assic gastropod occurrences: the Sinbad Limestone locality
where the collection of Batten and Stokes (1986) comes
from (American Museum of Natural History (AMNH)
Locality #3026; Fig. 1) and one of Wittenburg’s (1908a,
b) collecting sites (Gastropod Oolite Member, Valsugana,
near Trento; Fig. 2). The Sinbad Limestone Member is of
Smithian (Olenekian) age and the Gastropod Oolite is of
Dienerian age (maybe ranging into the Smithian; Fig. 3).
Previous microfacies, sedimentological and paleoecolog-
ical studies exist for both members (Sinbad: Blakey 1974;
Dean 1981; Schubert and Bottjer 1995; Fraiser and Bottjer
2004; Gastropod Oolite: e.g., Broglio Loriga et al. 1983;
Boeckelmann 1988; Wignall and Twitchett 1999). How-
ever, no detailed analysis was made specifically for the
Fig. 1 Location of the studied sites of the Early Triassic Sinbad
Limestone (Utah, San Rafael Swell and Capitol Reef, near Torrey)
Fig. 2 Location of the studied sites of the Early Triassic Gastropod
Oolite Member (Valsugana, N Italy)
Fig. 3 Approximate stratigraphic position of the Sinbad Limestone
Member (Smithian) and the Gastropod Oolite Member (Dienerian
and probably Smithian) in the Early Triassic
main fossil bearing units and previous studies were not
primarily concentrated on the gastropod occurrence but
generally stood in a wider frame or dealt with particular
phenomena, such as small size of the shells (e.g., Fraiser
and Bottjer 2004).
To date, only 74 described gastropod species are known
from Early Triassic rocks around the world as is indicated
by our own species-level database (see also N
¨
utzel 2005, in
press). This number accounts for the reported actual occur-
rences of nominate species and does not consider Lazarus
taxa and species in open nomenclature. Diversity seems
to be extremely low in the immediate aftermath of the
end-Permian mass extinction event. Lowermost Triassic
(Induan, Griesbachian) gastropod faunas usually comprise
only a few species and reports of single species occurrences
are common. The state of preservation of Early Triassic gas-
tropods (especially those from the Griesbachian) is gener-
ally poor. The only relatively diverse Griesbachian fauna is
from the Wadi Wasit Block in Oman (Twitchett et al. 2004;
Wheeley and Twitchett in press). This fauna comprises
about 10 species and genera and is considered to represent
the only Griesbachian fauna from a well-oxygenated envi-
ronment (Twitchettet al. 2004). These Oman gastropods are
coarsely silicified so that taxonomic assignments are ten-
tative. The number of reported species rises considerably
in the Olenekian. Most Olenekian gastropod occurrences
482
were reported from the Werfen Formation (Alps) and the
Sinbad Limestone (Moenkopi Formation, Utah). Together,
the Sinbad Limestone Member of the Moenkopi Formation
and the entire Werfen Formation contribute about 50% to
the global number of described nominate gastropod species
from the Early Triassic. The Olenekian (Smithian) fauna
from the Sinbad Limestone (Moenkopi Formation) com-
prises 26 described gastropod species. Faunas with more
than 100 gastropod species have not been reported prior to
the Late Anisian (Stiller 2001a). Early Triassic gastropod
faunas, including those from the Werfen and Moenkopi
Formations, have been interpreted as disaster faunas, which
were dominated by small, commonly abundant, r-selected
species and are characterized by a relatively low species
richness (Batten 1973; Schubert and Bottjer 1995; Fraiser
and Bottjer 2004). The impact of the Permian/Triassic
mass extinction event on the evolution of the Gastropoda
was substantial (Erwin 1990;N
¨
utzel 2005, in press).
For instance, the Sinbad Limestone Member contains
abundant heterostrophic opisthobranchs, small neritae-
morphs, and several Mesozoic caenogastropod genera (see
below) which represents an assemblage not found in the
Paleozoic (N
¨
utzel 2005, in press). Typical Late Paleozoic
elements are absent or uncommon, e.g., bellerophontids,
pleurotomarioids, euomphalids, and pseudozygopleurids.
There are some Paleozoic holdovers present in the Sinbad
Limestone Member, but they do not form the dominant
elements. Similarly, there are no typical Paleozoic gastro-
pod genera present in the Gastropod Oolite Member and in
the Upper Werfen Formation of the European Alps. With
all caution and considering the insufficient preservation
of most Early Triassic gastropods, this suggests that the
end-Permian mass extinction and the subsequent recovery
period caused major shifts within the Gastropoda (N
¨
utzel
2005, in press).
Methods
Shell beds were disaggregated with the hammer and
cracked out fossils were collected in the field (Sinbad
Limestone April 2003; Werfen Formation June 2004). The
remaining rock debris and powder (about 50 kg disaggre-
gated of rock samples) were wet sieved at 0.5 mm mesh
size. The residues were picked under a stereomicroscope
and obtained invertebrate fossils were studied with a
Scanning Electron Microscope. About 50 thin-sections
and polished slabs were studied from representative facies
types which were recognized in the field. Most of the thin-
sections were made from oriented samples of measured
sections. The intensity of this study is uneven for both the
sites. At the Sinbad Limestone locality, a well-exposed sec-
tion was studied in detail and the vertical facies succession
is documented here. However, the Gastropod Oolite from
Valsugana is not as well exposed and only the fossil bearing
shell beds could be studied regarding microfacies and fossil
preservation.
Geological setting
Geological setting of the Sinbad Limestone Member
(Moenkopi Formation)
The studied section belongs to the Sinbad Limestone
Member and is exposed in the San Rafael Swell, south
Utah. The Sinbad Limestone Member is a 15–30 m thick
carbonate unit within the predominantly siliciclastic,
terrestrial Moenkopi Formation (e.g., Blakey 1974; Dean
1981). It is Smithian (Olenekian) in age. The Moenkopi
Formation uncomformably overlies Late Paleozoic
deposits of the Colorado Plateau. The Sinbad Limestone
Member represents a marine episode (transgression) in
the Moenkopi siliciclastic beds and contains fossiliferous
limestones, dolostones, and calcareous siltstones. The
Sinbad Limestone was deposited in an epicontinental sea
with free access to the Paleo-Pacific Ocean Panthalassa
to the west. Blakey (1974) provided a comprehensive
overview of the Moenkopi Formation in southeastern Utah.
Dean (1981) studied the Sinbad Limestone Member in the
Teasdale Uplift area (near Torrey; Fig. 1). Blakey (1974)
and Dean (1981) reported all major facies types of the Sin-
bad Limestone which are also present in the section studied
here, e.g., skeletal calcarenites and oolitic grainstones, all
formed in a shallow, epicontinental sea. Storm deposition
seems to be common in the Sinbad Limestone (e.g., Blakey
1974). However, Blakey’s (1974) and Dean’s (1981) study
were not primarily focused on the fossil occurrences.
Subsequently, a rich Early Triassic gastropod fauna was
described from the Sinbad Limestone, comprising 26
species representing 16 genera (Batten and Stokes 1986).
Stromatolites were repeatedly reported from the Sinbad
Limestone (Blakey 1974; Dean 1981; Schubert and Bottjer
1992). Generally, the presence of stromatolites in normal
subtidal, marine environments was interpreted as a disaster
phenomenon (Schubert and Bottjer 1992). Stromatolites
and oolites in the marine limestones of the Moenkopi
Formation indicate warm, shallow-marine conditions.
Stromatolites are absent at the gastropod type locality of
Batten and Stokes (1986) which is reported here in detail
(see below). However, stromatolites were studied by us at
the Miners Mountain section near Torrey (Capitol Reef,
Teasdale Uplift; Figs. 1 and 4). These stromatolites show a
variety of growth forms: laminar (Fig. 4A), wavy (Fig. 4B),
columnar (Fig. 4C, right), and microstromatolitic (Fig. 4C,
left). They commonly occur together with gastropods and
even grew on gastropods (Fig. 4C).
Geological setting of the Gastropod Oolite Member
(Werfen Formation)
The Early Triassic Werfen Formation crops out in a vast
area of the South Alps (Italian Dolomites) and North
Alps (Germany, Austria) and overlies the Late Permian
(Wuchiapingian to Changhsingian) Bellerophon Forma-
tion, which yields a rich, typical Late Paleozoic marine
483
Fig. 4 Polished slabs showing stromatolites (bindstones) from
Sinbad Limestone near Torrey (Miners Mountain, Wide Hollow,
2315 m, 38
13
40.0

N, 111
18
38.6

W); in contrast to the section
at the gastropod collection site of Batten and Stokes (1986), stro-
matolites are abundant in the Torrey area. A Stromatolitic bindstone
with plane lamination. B Wavy stromatolites at base covered by a
bioclastic layer and laminated bindstone on top. C On right side two
columnar stromatolites growing on gastropod shells; left: microstro-
matolites with sparitic cavities (no birdseyes)
484
fauna with brachiopods and bellerophontids in its upper
part. The Werfen Formation is up to several hundred metres
thick and comprises the entire Early Triassic. Its abundant
fauna is dominated by bivalves and gastropods. Microgas-
tropods are very abundant and rock-forming in a facies
which is called ‘Gastropod Oolite’. This term is also used
in a lithostratigraphic sense for a member between the Seis
and Campil Members. However, this facies-type seems to
recur throughout the Werfen Formation (e.g., Boeckelmann
1988) and is also present in the Servino Formation (e.g.,
Assereto and Rizzini 1975). The Gastropod Oolite Member
has probably a Dienerian age as is indicated by conodonts
(Twitchett 1999; Wignall and Twitchett 1999) and is there-
fore somewhat older than the Smithian Sinbad Limestone.
However, the Gastropod Oolite-facies is also contempo-
raneous and inter-fingering with the Seis (Siusi) Member
and could be Smithian in its upper part. It is also hetero-
geneous and comprises a variety of different facies types
(e.g., Broglio Loriga et al. 1983; Boeckelmann 1988). The
Gastropod Oolite Member consists of oolites in which gas-
tropods and other bioclasts form the cores of the ooids or
they occur as iron oxide encrusted bioclasts of wackestones
and grainstones. This facies is also widely distributed in
Early Triassic platform carbonates and is known from the
Alpine-Mediterranean region to Iran and China (e.g., As-
sereto and Rizzini 1975;Fl
¨
ugel 2004). Transported ferroan
dolomites were reported from the Gastropod Oolite equiva-
lent in the Servino Formation (Assereto and Rizzini 1975).
Wignall and Twitchett (1999) reported gastropod grain-
stones with erosive base, intraclasts (flat pebbles), multidi-
rectional tool marks, and graded bedding for the Gastropod
Oolite and discussed a tempestitic deposition of such beds.
Here, the Gastropod Oolite was studied at two localities
from the Valsugana and Trento area in Northern Italy at the
southern border of the Dolomites. One locality lies 4.6 km
SW Borgo Valsugana (GPS (WGS 84): 46
01
32.5

N,
11
24
39.6

E; Fig. 2). Relatively well-preserved gas-
tropods were reported from this site by Wittenburg (1908a,
b). A second location was studied and sampled 750 m south
of Cimirlo (near the road from Cimirlo to Busa del Vent,
where road crosses creek in a narrow curve; GPS (WGS
84): 46
03
50.5

N, 11
10
58.0

E; Fig. 2). At this location,
well-preserved gastropods occur in rocks of the same facies
as were found near Borgo Valsugana.
Results and discussion
Facies of the Sinbad Limestone at the gastropod
type locality
Description and interpretation of the section
The section at the gastropod collection locality of Batten
and Stokes (1986) (Sinbad Limestone, AMNH Locality
#3026 GPS (WGS 84): 38
59
51.0

N, 110
40
53.2

W;
Fig. 1) was studied and measured (Table 1). The section
comprises about 12 m of essentially calcareous beds with
considerable siliciclastic input in its uppermost beds.
Thirteen units (Bed I–XIII; Figs. 513D; Table 1) with
distinct facies are recognized. Bed VIII is the main fossil-
bearing unit where the described Sinbad Limestone gas-
tropod fauna originates from. The lateral extension of the
present beds was only followed for some 10–100 m because
sampling was primarily focused on the fossil occurrence at
Batten and Stokes’s (1986) collecting locality. The studied
section represents probably a part of a single transgressive–
regressive cycle and comprises a wide range of different
microfacies-types and different faunal compositions. This
heterogeneity is probably a result of the shallow-water con-
ditions and sea-level changes combined with several storm-
or other high-energy events. The lower part of the section
from Bed I to Bed IV/V is characterized by intertidal
microbial mats (laminated bindstones) and oolitic/peloidal
shoals. Peloids in Beds I and II represent micritized ooids
as is indicated by micritic grains which show relicts of
concentric striation (see also Blakey 1974). Current ripples
and abrupt grain-size changes in the oolitic/peloidal shoals
suggest that the material was transported. Gastropods are
common but not abundant in these beds. Bed III represents
intertidal algal mats, which were moderately reworked
in a semi-consolidated state and finally cemented with
sparry calcite. The lower units (Beds I–IV/V) are not very
fossiliferous and lack benthic mollusc coquinas. The few
fossils are generally not well preserved.
Bed V represents an intraclast/peloid/ooid shoal with
incised channels. The breccia-like channel fill represents a
high-energy event and could be a proximal tempestite (or
tsunami deposit) as is indicated by poor sorting and the
large size of the clasts which are commonly suspended in
a fine-grained matrix. Similar deposits were reported from
the Sinbad Limestone of the Torrey area (Dean 1981).
Deposition in tidal channels during transgression is also
possible (see Fl
¨
ugel 2004 for comparable deposits). The
relatively large clasts of the channel fills represent probably
a mixture of marine intertidal to shallow subtidal and
eventually supratidal mudstones. The channel fill seems to
belong to the so-called flat pebble conglomerates, which
have been interpreted as anachronistic, non-actualistic
facies. Accordingly, such conglomerates were common
during the Cambro–Ordovician and in the aftermath of the
end-Permian extinction mainly due to low bioturbation
which allowed preservation of thin beds and rapid lithi-
fication (e.g., Sepkoski et al. 1991; Wignall and Twitchett
1999).
Bed V marks a change in sedimentation: above it, several
shell beds and other fossiliferous units occur (Bed VI–XII).
Of these, Bed VI, VIII, and XII are probably tempestites
based on sharp erosive base, graded bedding and a
faunal content which differs strongly from that of the
under- or overlying beds. Thus, from Bed V onward, storm
sedimentation repeatedly re-deposited marine, subtidal
biota. Storm sedimentation was previously reported for the
Sinbad Limestone (Blakey 1974; Schubert and Bottjer
1995; Boyer et al. 2004). It is remarkable that the main
shell beds (Beds VI, VIII, XII) differ strongly from each
other in faunal content and microfacies. Bed VI contains
two distinct units: a rather coarse biosparite in the lower
485
Table 1 Descriptions and interpretations of microfacies and sedimentary fabrics of the studied Sinbad Limestone section
Bed Figure Thickness (cm) Facies type Dominant clasts Sedimentary fabric and other features Interpretation
XIII
13D
300 Sandstone with micritic
matrix
Angular quartz, fine sand to silt
size; few bivalve steinkerns
Plane bed lamination and asymmetric
cross-bedding
Strong siliciclastic input; end of
predominately calcareous
sedimentation
XII 13B and C 60 Rudstone Thin-shelled pteriomorph bivalves;
strongly deformed and
compacted; few gastropods; small
round objects with micritic rims
Erosional base; with several (about 7)
horizontal partitioning planes
Probably tempestite (faunal
content very different from
that of upper and lower beds)
XI 35 Mudstone, silty No larger clasts, unfossiliferous Homogeneous, nodular weathering Probably low energy; resembles
Bed IX
X 12H and 13A 35 Floatstone with packstone
matrix
Thin-shelled bivalves,
disarticulated, convex up; rare
gastropods; matrix with small
unidentifiable bioclasts and
quartz in fine sand to silt size
Sheltered porosity filled with sparitic
cement under bivalves; plane bed
lamination; several horizontal
partitioning planes
Deposition under moderate
current conditions with some
siliciclastic input
IX 50 Mudstone No larger clasts Homogeneous Probably low energy
VIII 8D, 9F and G, 10,
11 and 12A–G
40 Rud-, grain- and packstones Abundant molluscs (gastropods,
scaphopods, bivalves), commonly
with micritic envelopes;
echinoderm ossicles (ophiuroids,
echinoids); intraclasts; small
peloids
Base sharp; graded bedding common;
molluscs commonly filled with
micrite even if sparite between
bioclasts; clast-supported fabric;
bivalves commonly with articulated
valves
Tempestite (sharp, erosional
base, graded bedding;
intraclasts); faunal content
differs from that of upper and
lower beds; Main fossil
bearing unit (= lagerst
¨
atten)
VII 8D and 9E 30 Wacke- packstone Rare echinoderms; quartz in silt
and fine sand size
Chip-like weathering Probably distal tempestite with
terrigenous quartz
VI 8C, D and 9A–D 30–40 Grain- and rudstones Lower part: mostly bivalves,
completely micritized; upper part:
peloids and ooids
Sharp, erosional base and eroded top;
large sparitic spots with sparite,
commonly as syntaxial cement of
echinoderm ossicles
Lowermost shell bed in the
section; lower part probably
eroded tempestite
Vb 7F–H and 8B and C Rudstone; conglomerates,
mostly matrix supported
Large intraclasts (several cm to
dm), commonly flat and rounded
Laterally-linked channels; upper and
lower erosional contact
Flat pebble conglomerate;
proximal tempestites or fill of
tidal channels; high energy
(maybe tsunami deposit)
Va 7 DE 75 Grain- and packstones Ooids, peloids, oncoids, bioclasts
with micritic rims
Cross-bedding (field observation) Shallow, subtidal oolite shoal
IV 40 Mudstone No larger clasts, unfossilifreous Homogeneous Probably low energy
III 7A–C and 8A 120m Reworked bindstones Bindstone-slabs; peloids; rare,
poorly preserved gastropods
Sparitic cement between large
bindstone slabs
Moderately reworked,
parautochthonous, intertidal
algal mats
II 6C–H 100 Grain- and packstones Ooids and peloids; well-rounded
intraclasts; rare gastropods
(poorly preserved)
Massive, hard, edge-forming; current
ripples observed in the field; abrupt
grain-size changes
Shallow, subtidal; transported
I6AandB 260 Pack- and grainstones,
laminated bindstones
Ooids and micritized ooids
(peloids); bioclasts rare to absent
Thin-bedded, thickening upward;
mud-cracks in bindstones
Subtidal peloid/oolite shoal and
intertidal microbial mats
This section is exposed at the type locality of the gastropod fauna studied by Batten and Stokes (1986) (AMNH locality 3026; Fig. 1)
486
Fig. 5 Section of Sinbad Limestone at gastropod collection locality
of Batten and Stokes (1986), American Museum of Natural History
(AMNH) locality 3026, with 13 distinct beds (I–XIII). The lower
beds (I–V) are dominated by laminated intertidal bindstones and
oolitic/peloidal shoals. The upper part of Bed V is a coarse channel
fill. From this bed onward, several tempestitic shell beds occur; one
of these beds (Bed VIII) is the main fossil bearing unit (lagerst
¨
atte)
which yields an abundant, well-preserved gastropod fauna as well as
abundant bivalves and scaphopods. Bed XIII is essentially siliciclas-
tic and indicates an increasing terrestrial input
487
Fig. 6 Microfacies of Bed I
and II of the Sinbad Limestone
at AMNH locality 3026. A–B
Bed I, laminated bindstone
(intertidal algal mats). A
Overview of laminated
bindstone with an alternation of
dark and light layers;
interruption of layers in lower
portion could suggest
bioturbation or presence of mud
cracks. B Close-up of laminated
bindstone with dark, micritic
layers and light, somewhat
coarser grained layers. C–H
Bed II, oolitic/peloidal/intraclast
grainstones. C Abrupt change in
grain size within Bed II
indicating transport; fine
grained peloids and ooids in
lower part; coarser peloids/ooids
and intraclasts in upper part. D
Weathered surface of
oolitic/peloidal bed with several
poorly preserved gastropods. E
Peloids, intraclasts, shells with
geopetal fabric and sparry
cementation. F Peloidal
grainstone. G Intraclast/peloidal
grainstone. H Peloidal/oolitic
grainstone; ooids/peloids with
relics of concentric striation,
indicating that peloids are
mainly micritized ooids
portion with micritized mollusc shells (mainly bivalves)
and an upper portion with more fine-grained material and
large sparitic areas which contain echinoderm ossicles
with syntaxial cements. The micritized shell coquina
probably represents a partly eroded tempestite which
overlies the channel fill. Bed VI represents the lowermost
shell bed in this section. It is also the first appearance of
common echinoderm ossicles. This suggests that the biota
came from a fairly normal marine, subtidal environment.
Due to micritization, the bed does not yield well-preserved
fossils. Gastropods are rare to absent. Bed VIII is the main
fossil-bearing unit and essentially the fossil lagerst
¨
atte
which yields the well-preserved gastropod, bivalve and
scaphopod material (Figs. 10 and 11). The marked
488
Fig. 7 Microfacies of Beds III
and V of the Sinbad Limestone
at AMNH locality 3026. A–C
Bed III, slightly reworked,
parautochthonous bindstones
formed by intertidal algal mats,
cemented with sparite; contains
rare gastropods (see also
Fig. 8A). A Overview showing
fabric of deformed mudstones.
B Laminated, deformed
mudstone (bindstone) slab and
peloidal grainstone. C Peloidal
grainstone layer with
gastropods between mudstone
(bindstone) slabs. D–E Lower
portion of Bed V (i.e., Bed Va),
oolite/peloidal/intraclast
grainstones; in this unit,
laterally linked channels are
incised(BedVb).D Grainstone
with peloids, intraclasts and
biolasts with micritc rims. E
Grainstone with ooids, peloids
(commonly micritized ooids)
and oncoids. F–H Bed Vb,
channel fill within Bed V with
large clasts, “flat pebble
conglomerate” (see also
Figs. 8B and C). F
Predominantly
matrix-supported intraclast
floatstone to rudstone. G Detail
with several rounded clasts. H
Detail of large clast
(thin-section from lowermost
large clast in Fig. 8B) showing
probably microbial tubes
(bacteria)
lithological and faunal differences to the underlying and
overlying beds, graded bedding, and presence of intraclasts
indicate that this bed is a tempestite. Such beds correspond
to the “skeletal calcarenite facies”, which was previously
reported for the Sinbad Limestone Member (Blakey 1974).
The paleoecology and preservation of Bed VIII is dis-
cussed below. Bed XII is very rich in thin-shelled, densely
packed bivalves. The bivalves cannot be isolated form
the rock because cementation and packing is too intense.
Apart from the main fossil bearing unit (Bed VIII), this
bed (XII) has the highest fossil concentration. The strong
dominance of thin-shelled, probably pteriomorph bivalves
and the rarity of gastropods shows that the assemblage of
Bed XII differs strongly from that of Bed VIII.
489
Fig. 8 A Polished slab of Bed
III, slightly reworked,
parautochthonous bindstones
formed by intertidal algal mats,
cemented with sparite (see also
Figs. 7A–C). B Polished slab of
channel fill within Bed V (Bed
Vb); with large, flat clasts; see
also Figs. 7F–H, 8C, 9A;
thin-section of large, lowermost
clast in Fig. 7H. C Bed V,
oolite/peloidal/intraclast
grainstones (Bed Va) with
incised channel fill with large
clasts (Bed Vb; triangle marks
base of channel fill) and sharp
contact to overlying shell bed
(Bed VI). D Outcrop
photograph of Beds V–VIII
Biota, preservation and paleoecology of the Sinbad
Limestone gastropod lagerst
¨
atte
The diverse and well-preserved gastropod fauna of the Sin-
bad Limestone occurs largely in a single, probably tem-
pestitic bed of the studied section (Bed VIII). This shell
bed represents a benthic mollusc coquina of 20–40 cm
thickness. It consists of rudstones, packstones and grain-
stones with common graded bedding. The fabric is gener-
ally clast-supported with sparry cement or is poorly washed
with portions with micritic matrix.
Biota
Bed VIII contains 26 gastropod species (Batten and Stokes
1986), about 10 bivalve species (unstudied according to
their taxonomy), and one scaphopod species. Moreover one
serpulid species, an echinoid species and ophiurid ossicles
are present although not as common. A few ammonoids
were found, amongst them Anawasatchites sp. confirming
a Smithian age of this fauna. Thus, Bed VIII contains about
40 invertebrate species. Small gastropods (<10 mm) con-
tribute most to species richness and some of these species
are extremely abundant (see also Batten and Stokes 1986;
Fraiser and Bottjer 2004). Small neritaemorphs and the
opisthobranch Cylindrobullina convexa are most abundant.
Some examples for well-preserved gastropods from Bed
VIII are illustrated in Fig. 11.
Annulated tubes (supposed scaphopods of the genus Pla-
gioglypta) are abundant in the main fossil bearing unit (Bed
VIII) and are here illustrated for the first time (Figs. 10O–
S). Their great abundance even becomes obvious in thin-
sections (Figs. 12B–D and G), where they appear cicular in
transverse section, elliptical in oblique section, and tube-
like in longitudinal section. The presence of scaphopods in
the Sinbad Limestone was previously noted (Stewart et al.
1972; Blakey 1974; Fraiser and Bottjer 2004) but they were
not considered in paleoecological studies. Plagioglypta has
its type species in the Late Triassic Cassian Formation
and was reported from the Anisian of South West China
(Stiller 2001b). Plagioglypta has also a rich Late Paleozoic
record but the mollusc affinity of these species is question-
able (Yochelson and N
¨
utzel, own observation). The great
abundance of Plagioglypta in the Sinbad limestone as seen
in some of the thin-sections represents a remarkable phe-
nomenon unknown from other Early Triassic sites.
Serpulids are relatively common in Bed VIII and are
documented here for the first time from the Sinbad Lime-
stone (Figs. 10A–F). They are mostly detached from their
substratum but are sometimes found attached to bivalve
shells (Fig. 10C). The serpulids from the Sinbad Limestone
are similar to Spirorbis valvata Berger 1859, a widespread
species in the Anisian/Ladinian Muschelkalk of Central
Europe. Similar serpulids are also present in the Werfen
Formation (e.g., Boeckelmann 1988), where they are
assigned to Spirorbis valvata and Spirorbis phlyctaena
490
Fig. 9 Microfacies of Beds
V–VIII of the Sinbad Limestone
at AMNH locality 3026. A
Transition of Bed V (lower dark
portion with intraclasts) to Bed
VI (upper light portion); lower
triangle marks sharp contact
between channel fill at base and
biosparite (rudstone) with
completely micritized mollusc
shells (between both triangles);
upper triangle marks erosional
surface; above it,
oolitic/peloidal grainstone with
large sparitic areas with
syntaxial echinoderm cements
(see C, D for details). B Bed VI,
detail from A (between
triangles), biosparite (rudstone)
with completely micritized
mollusc shells. C, D Bed VI,
detail from A, echinoderm
ossicles with syntaxial cement
forming idiomorphic crystals. E
Bed VII, packstone/wackestone
with echinoid spine. F–G Bed
VIII main fossil-bearing unit,
grain-, rud- and wackestones
with abundant mollusc shells;
graded bedding. F Poorly
washed grain- to rudstone with
graded bedding. G Pack- to
floatstone with large dark
intraclast in lower portion, with
graded bedding
(Br
¨
onnimann and Zaninetti 1972) (e.g., Broglio Loriga et
al. 1986; Boeckelmann 1988). The genus Spirorbis itself
seems to represent a dustbin taxon for coiled sessile worm
tubes.
Echinoderms occur always as isolated ossicles. They
occur from Bed VI to XII and are also present in the main
fossil bearing unit (Bed VIII). Ossicles are common but not
very abundant. They represent ophiuriods (Figs. 10G–I)
and cidaroid sea urchins (Figs. 10J–L). These ossicles
probably indicate normal marine salinity. Echinoid ossicles
were studied from the main fossil bearing unit (Bed VIII).
They represent interambulacral plates of Lenticidaris uta-
hensis Kier, 1968 (Hans Hagdorn, written communication
2004). This species was originally described from the
491
Fig. 10 Fossils other than
gastropods from the Sinbad
Limestone, Bed VIII, main
fossil bearing unit. A–F
Polychaete “Spirorbis”cf.
valvata. A Upper view. B
Oblique side view. C Attached
to bivalve shell with prismatic
structure. D Rare specimen with
intact erect tube, side view. E
Detail of microgranular shell
structure. F Detail of
microgranular shell structure.
G–I Ophiuroid ossicles. J–L
Echinoid (cidaroid) plates. M–N
Examples for small bivalves
representing two species; such
bivalves commonly have
attached valves. O–S Annulated
tubes of the Plagioglypta type
(supposed scaphopods) are
extremely abundant in Bed VIII
Virgin Limestone, which is slightly younger (Spathian)
than the Sinbad Limestone. Lenticidaris was considered to
represent a synonym of Miocidaris (Schubert and Bottjer
1995). However, this synonymization is probably not
justified (Hans Hagdorn, written communication 2004).
No crinoid ossicles have been recovered from the section
studied here although they are abundant in the slightly
younger (Spathian) Virgin and Thaynes Limestones
(Schubert and Bottjer 1995).
Fossil preservation in the Sinbad Limestone lagerst
¨
atte
The gastropods (and other molluscs) from Bed VIII are
uniquely well preserved (Figs. 10M–S and 11) when com-
pared with gastropods from other Early Triassic locali-
ties. Most of the molluscs were originally aragonitic and
are replaced by a sparry calcite. Shells commonly have
dark micritic rims which suggests bioersion by microbor-
ers prior to deposition (e.g., Fl
¨
ugel 2004). In thin-section,
these rims are mostly uninterrupted around the bioclasts.
This indicates that breakage during storm transport was not
important and fragmentation happened prior to deposition.
Bivalves with articulated valves are common. An isopa-
chous rim cement covers the bioclasts where no micritic
matrix is present (e.g., Figs. 12E and F). Micritic rims and
the presence of micritic matrix in poorly washed parts of the
shell beds cause discontinuities with the pore-filling cement
and facilitate the good fossil preservation. Together with
492
Fig. 11 Examples for
exceptionally well-preserved
Early Triassic gastropods from
the Sinbad Limestone, Bed
VIII, main fossil bearing unit;
this good preservation is unique
for the Early Triassic. A
Cylindrobullina convexa in
peloidal limestone. B Neritaria
sp. C Kittliconcha
sciaphostera. D, I
Ampezzopleura rugosa with
well-preserved planktotrophic
larval shell with axial ribs. E, F
Battenizyga eotriassica. F
Juvenile specimen of
Battenizyga eotriassica with
well-preserved protoconch. G
Cylindrobullina convexa, with
well-preserved heterostrophic,
transaxial larval shell. H
Worthenia windowblindensis
with shell repair
certain state of weathering, these factors allow mechanical
isolation of the fossils from the rock (crack-out). Bivalves,
scaphopods, and gastropods are commonly filled with mud
(micrite; see also Blakey 1974). The Sinbad Limestone is
the only Triassic formation with well-preserved gastropod
protoconchs (Figs. 11A, D, F, G and I) except for the Late
Triassic (Early Carnian) Cassian Formation in the Italian
Alps. Protoconch morphology is crucial for a correct tax-
onomy, phylogeny, systematics, and recognition of larval
strategies of gastropods. The excellent fossil preservation
is a main reason for the high information content of the
Sinbad lagerst
¨
atte.
Discussion of the Sinbad Limestone lagerst
¨
atte
It is striking that about one-third of the reported global
gastropod diversity can be found in a single shell bed (tem-
pestite) of 20–40 cm thickness (Bed VIII). Several of the
gastropod genera originally reported by Batten and Stokes
(1986) were also found in other Early Triassic strata of the
western United States (e.g., in the slightly younger Virgin
and Thaynes Limestones), but these occurrences are not as
rich and diverse (Schubert and Bottjer 1995; Fraiser and
Bottjer 2004). However, the other locations were not stud-
ied with a primarily taxonomic purpose and these stud-
ies commonly lack species-level identifications. Instead,
generic identifications and open nomenclature were used.
Moreover, there are no reports of the Sinbad gastropod
species outside the western United States. Given the pa-
leogeographic position as an epicontinental sea with free
access to Panthalassa, it is very unlikely that the Sinbad
gastropod fauna was really endemic in this area. This
pseudo-endemism is probably produced by preservational
or sampling bias.
The micritic infillings of gastropods, scaphopods and ar-
ticulated bivalves suggest that the original habitat of the
molluscs was a fine-grained, muddy subtidal soft bottom.
The scaphopods, some of the bivalves, and the gastro-
pod Cylindrobullina convexa were probably infaunal while
the other species were epifaunal. Most of the small gas-
tropods (except Cylindrobullina convexa) were either liv-
ing directly on the muddy sea bottom, or on non-calcifying
algae. Recent small-sized neritaemorphs commonly live in
tropical seagrass environments (seagrass, an angiosperm,
is only known from the Late Cretaceous onward). The
great abundance of small neritaemorphs in the Sinbad lime-
stone could indicate that an analogous habitat existed (e.g.,
thickets of non calcifying algae). A rigorous census and
statistical analysis has not been undertaken here, but it is
obvious that small neritaemorph gastropods and the
opisthobranch Cylindrobullina as well as scaphopods
(Plagioglypta) form the most abundant fossils in this
assemblage. This Plagioglypta-Cylindrobullina-small ner-
itaemorph assemblage is newly recognized in this study.
However, it is likely that size-sorting by storm transport bi-
ased the original composition of the fauna in the source area
to an unknown degree. Such bias was shown for Miocene
tempestites from Austria (Zuschin etal. 2005). In these tem-
pestitic beds, size-sorting (measured as standard deviation
from mean shell size) is a significant predictor of diversity,
i.e., diversity increases with decreasing sorting (Zuschin
et al. 2005: 147). But transport-related size-sorting is not
the only factor which controls diversity in shell beds. The
other important factor is the availability of shells and di-
versity of the primary communities in the source area prior
to transport. The good preservation of the molluscs in Bed
VIII of the Sinbad Limestone (even with preserved larval
shells) and the fact that bivalves are commonly articulated
suggests that the storm took up a living assemblage or that
493
Fig. 12 Microfacies of Beds
VIII and X of the Sinbad
Limestone at AMNH locality
3026. A–G Bed VIII; main
fossil-bearing unit; grain-, rud-
and wackestones with abundant
mollusc shells. A
Rud-packstone with distinct
graded bedding. B Gastropods
and scaphopods (circular in
section) filled with micrite and
having dark micritic rims
(bioerosion); matrix sparry to
micritic. C Mollusc packstone
with several scaphopods
(Plagioglypta) in longitudinal
section. D Mollusc packstone
with dark, well-rounded clast in
lower part. E Bivalve with
articulated valves and micritic
infilling; note that no rim
cement is present on the upper
side of shell because micritic
matrix is present. In contrast,
the lower shell (where micritic
matrix is absent) is partly
covered with a rim cement and
subsequent sparry cement. F
Detail of E, upper part with dark
micritic infilling, below sparitic
shell replacement; original shell
surface as micritic rim; this rim
is covered on inner and outer
side by a fibrous rim cement
(narrow on inner side wide on
outer side). G Poorly washed
mollusc grain- to packstone
with abundant scaphopods
(Plagioglypta) and gastropods,
commonly with micritic
infillings and micritic rims. H
Bed X, bivalve floatstone;
thin-shelled disarticulated
pteriomorphs with convex side
up, indicating currents during
deposition; note geopetal fabric
with sheltered porosity, filled
with sparry cement
the bioclasts were not strongly reworked and time averaged
before storm deposition. Therefore, this assemblage prob-
ably reflects the gone living assemblage to a relatively high
degree. The species richness and diversity of the Sinbad
gastropod fauna is not extraordinarily low for a non-reefal
Early Mesozoic environment. However, rarefaction anal-
yses of the most diverse Late Triassic gastropod faunas
have shown that the Sinbad fauna (i.e., the most diverse
Early Triassic gastropod fauna) is clearly less diverse than
the most diverse Late Triassic faunas (N
¨
utzel and Erwin
2004).
Most of the Moenkopi snails have an adult size
smaller than 10 mm (Batten and Stokes 1986; Fraiser
and Bottjer 2004; own observation). The dominance of
494
Fig. 13 A–D Microfacies of
Beds X, XII, and XIII of the
Sinbad Limestone at AMNH
locality 3026. A Bed X, bivalve
floatstone (as in Fig. 12H);
thin-shelled disarticulated
pteriomorphs with convex side
up, geopetal fabric with
sheltered porosity, filled with
sparry cement; packstone
matrix with small, dark peloids;
gastropod fragment. B Bed XII;
coquina of densely packed,
thin-shelled bivalves, deformed
and fractured by compaction. C
Detail of Bed XII showing
small, round objects with
micritic rims. D Bed XIII
(uppermost bed of section)
parallel-laminated siltstone and
fine sandstone, unfossiliferous.
E–H Gastropod Oolite Member
of North Italy. E From Cimirlo
near Trento; gastropod/bivalve
wacke- and floatstone;
alternating layers with small and
large bioclasts have stylolitic
contact, therefore layering does
not represent a primary
sedimentary fabric. F–H From
Valsugana near Borgo (“Monte
Zaccon” locality); all represent
gastropod/bivalve wacke- and
floatstones with oolitic, iron
oxide coated bivalve and
gastropods shells; at least four
gastropod species can be
recognized in thin-sections (see
Fig. 14 for details). F Overview,
no apparent graded bedding. G
Largest gastropod represents the
problematic taxon “Polygyrina
gracilior”; other gastropods
enlarged in Figs. 14B and D. H
Largest gastropod represents the
problematic taxon “Polygyrina
gracilior
microgastropods and the lack of large gastropods in the
Early Triassic seem to be global phenomena (Fraiser and
Bottjer 2004) and small body size was interpreted as result
of a productivity decline (Twitchett 2001). However, even
most Recent gastropods are small (e.g., Bouchet et al.
2002) and there are also larger gastropods in the Early
Triassic: the abundant gastropod Werfenella rectecostata
and Natiria costata from the Upper Werfen Formation are
as large as 20–35 mm and therefore no microgastropods
(<10 mm) (N
¨
utzel and Erwin 2002;N
¨
utzel 2005). The
relatively small size of the Sinbad gastropods could also re-
flect size-sorting during storm transport to some degree. As
outlined above, the effect of size sorting was demonstrated
for other tempestitic shell beds (Zuschin et al. 2005).
495
Fig. 14 Gastropod/bivalve
wacke- and floatstones with
microsparitic matrix from the
Gastropod Oolite Member from
near Borgo, Valsugana (“Monte
Zaccon” locality); bivalve and
gastropod shells very thin,
present as calcite replacements
of original aragonite;
gastropods are covered with thin
brown to reddish sheets of iron
oxide; bivalve fragments
commonly with thick, layered
coatings. A Several thin bivalve
fragments as ellipsoidal ooids;
due to flat ooid cores (bivalve
shells), they did not grow to a
spherical shape. B High-spired
gastropod representing the
problematic dustbin taxon
Polygyrina gracilior”; as in the
other gastropods and in contrast
to the bivalve fragments, the
iron oxide coating has a
relatively constant thickness. C
Pseudomurchisonia kokeni,
preservation as in B. D Minutely
phaneromphalous gastropod
(Coelostylina werfensis?),
preservation as in B. E Several
thin bivalve fragments as
ellipsoidal, spindle-shaped
ooids (as in Fig. 14A); ooids
show distinct layering; in
contrast, gastropod on upper left
has relatively thin coating of
constant thickness. F Bivalve
fragment as ellipsoidal ooid (as
in Figs. 14A and E); ooid shows
distinct layering and faint radial
structures. G Detail of E
showing thin gastropod shell,
calcite replacement of aragonite
and outer iron oxide coating. H
Pseudomurchisonia kokeni
fractured by compaction due to
point contacts between shells
(compare Zuschin et al. 2003)
The Gastropod Oolite Member of the Werfen
Formation
Microfacies of the Gastropod Oolite near Borgo,
Valsugana (Monte Zaccon) (Figs. 13EH and 14)
Vividly reddish-brown blocks of mollusc coquinas occur
near a forest road near Borgo Valsugana (Wittenburg’s
(1908a, b) “Monte Zaccon” locality). They represent
wackestones, packstones, and floatstones with bivalves and
gastropods in a fine-grained, microsparitic, calcitic matrix
(staining with Alizarin Red). Blocky calcitic cement as
well as idiomorphic dolomite crystals may also be devel-
oped. The size of the bioclasts is usually less than 2–4 mm
and does not exceed 10 mm. Graded bedding was not ob-
served. Gastropods are commonly fractured by compaction
496
Fig. 15 Crack surface of Gastropod Oolite, near Borgo, Valsugana
(“Monte Zaccon” locality of Wittenburg 1908b); gastropods (Pseu-
domurchisonia kokeni and Polygyrina gracilior”) as well as other
clasts covered with iron oxide; Wittenburg’s (1908a, b) material,
collection of University of T
¨
ubingen
due to point contacts between shells (compare Zuschin
et al. 2003). Geopetal fabrics are common, e.g., sparry cal-
cite within gastropod shells restricted to the upper part and
microsparite in the lower part. All shells are coated with
brown-reddish crusts (probably iron oxide, hematite). The
crusts are relatively thin with a constant thickness around
the gastropod shells. On bivalve fragments, the coatings
are relatively thick in the centre of the fragment and thin
to absent at its edge (forming flattened ellipsoidal chips;
Figs. 14A, E and F). Some of the crusts show a distinct
layering and faint radial striation. Spherical ooids are ab-
sent. The rock breaks along the red crusts on the bioclasts
so that the breakage surfaces are vividly red (Fig. 15).
However, the matrix is light grey to white or only slightly
reddish. The shells of the bivalves and gastropods are very
thin and present as calcite replacements of aragonite below
the crusts. The thickness of these shell remains is usually
40–60 µm. There are probably not more than three or four
gastropod species. A high-spired gastropod (“Polygyrina
gracilior”) and more low-spired forms which represent the
genus Pseudomurchisonia are abundant. The bivalves were
not determined but seem to be of lowspecies diversity. They
were never found with articulated valves.
Microfacies of the Gastropod Oolite near Cimirlo
(Fig. 13E)
A limestone bed of about 40 cm thickness crops out above
the road from Cimirlo to Busa del Vent. Its facies is ba-
sically identical to that of the previously described facies
from Borgo Valsugana. However, the gastropod assemblage
seems to be almost monospecific with Pseudomurchisonia
kokeni Wittenburg 1908a, b (isolated specimens are illus-
trated in Fig. 16). The bivalves represent a low-diversity
assemblage of Entoliidae and Neoschizodus(?) (Michael
Hautmannn, written communication 2004). The bed expe-
rienced considerable pressure solution and stylolites are
abundant throughout. Layers displaying different micro-
facies are separated by stylolites. Layers with few, rel-
atively large shells and dominant microsparite alternate
with layers of smaller bioclasts and grain-supported fab-
ric. The stylolites suggest that the abrupt changes be-
tween these layers do not represent an original depositional
fabric.
Interpretation of the facies and paleoecology
of the Gastropod Oolite samples
The investigated thin-sections of the Gastropod Oolite show
a characteristic facies that reflects a depositional environ-
ment which differs strongly from that of the Sinbad Lime-
stone Member. Thin-sections of the Gastropod Oolite stud-
ied here, resemble gastropod wackestones from the Wer-
fen Formation from Austria (Gartnerkofel; Fl
¨
ugel 2004:
pl. 89.1) and oolitic gastropod-bivalve grainstones from
the Precaucasian fordeep (Russia; Fl
¨
ugel 2004: fig. 10.43).
The oolitic, reddish coatings (iron oxides) were probably
formed in shallow water and the iron was probably trans-
ported from nearby land areas with intensive weathering.
The chemical regime leading to this kind of oolitic iron
oxide precipitation is not clear but it seems to be likely
that microbial activity played a role in this process as is
suggested by the layered oolitic coatings. There is no clear
evidence for oxygen depletion during deposition. Iron ox-
ide coatings on the gastropods are of continuous thickness
and relatively thin when compared to the crusts on the bi-
valves or bivalve fragments. This reflects the round, conical
shape of the gastropods which allowed a more or less con-
stant rolling even under low water energy conditions. The
constant movement of the gastropod shells could also ex-
plain why the coatings are thinner than on the bivalves. Due
to the flat shape of the bivalves and bivalve fragments, the
iron ooids are not spherical but flat and spindle-shaped in
transverse section. The uneven thickness of the crusts sug-
gests that the bivalve shells were turned more rarely than
the round gastropod shells. Otherwise, these clasts seem
to represent typical ooids with distinct layering and radial
structures.
Shell beds of the Gastropod Oolite were interpreted as
tempestites (e.g., Broglio Loriga et al. 1983; Boeckelmann
1988; Wignall and Twitchett 1999). Broglio Loriga et al.
(1986) mentioned that the Gastropod Oolite in the Adige
Valley (Trento) and the Valsugana area consists of tidal-
controlled oolitic bars alternating with muddy siltstones.
The currently studied samples of the Gastropod Oolite
show no clear indication for storm deposition (e.g., no
graded bedding and intraclasts). Abundant geopetal and
clast-supported fabric could point to storm deposition. In
other areas, storm deposition seems to be more obvious.
Wignall and Twitchett (1999) reported intraclasts (flat peb-
bles) in the Gastropod Oolite at the l’Uomo section of the
central Dolomites.
Gastropods are highly abundant at both studied sites
of the southern Dolomites. The samples form the Monte
Zaccon locality near Borgo Valsugana contain only a few
(probably three to five) species all of which are abundant.
497
Fig. 16 A–I, L Examples for well-preserved Early Triassic gas-
tropods the Gastropod Oolite (Werfen Formation) Pseudomurchiso-
nia kokeni forms an almost monospecific gastropod assemblage in
beds of the Gastropod Oolite near Cimirlo (Werfen Formation); the
species has a characteristic shape and a slit-like structure at the shoul-
der (well visible in L); it displays a considerable intraspecific vari-
ability. J Microsparitic matrix with ooid. K Microsparitic matrix
In contrast, Pseudomurchisonia kokeni (Figs. 14C, H
and 16) forms an almost monospecific assemblage near
Cimirlo. Wittenburg (1908a, b) described P. kokeni based
on a single specimen (holotype) from the Col di Rodella
(North Italy, South Tyrol, near the Sella Group, about
46
30

N, 11
45

E). The holotype (collection of the
University of T
¨
ubingen) was studied by the senior author.
As the specimens from Cimirlo, it is coated with iron oxides
and therefore probably comes from the same lithofacies.
Apart form the mentioned taxa, no other gastropods
could be found in the present samples, neither as body
fossils nor in thin-sections. For instance, neritaemorphs
are absent although this group is abundant in other Early
Triassic rocks (e.g., the Sinbad Limestone Member) and
have a characteristic low-spired shape. Only microgas-
tropods (<10 mm) are known from the Gastropod Oolite
and relatively few species have been reported, amongst
them Polygyrina gracilior, Coelostylina werfensis,“Nat-
ica gregaria, and Pseudomurchisonia kokeni. Generic
assignments and species identity of these taxa are generally
questionable due to poor preservation. However, it is
obvious that more or less high-spired, smooth, Hydrobia-
resembling snails were extremely abundant during the
deposition Gastropod Oolite and that these gastropods
formed assemblages of low species richness and high
abundance. A possible analogy of the Gastropod Oolite
snails with modern hydrobiids was casually mentioned by
Zapfe (1958: 163) and Wignall and Twitchett (1999: 314).
Some Recent hydrobiid mudsnail species occur in great
densities (>300,000 individuals per m
2
) in the marine
and estuarine intertidal zones (Barnes 1999). As in the
Gastropod Oolite, they form monospecific or paucispecific
assemblages of small, high-spired gastropods. Due to their
ability to swim at the air/water-interface, they are able to
populate areas quickly. They are euryhaline, e.g., Hydrobia
ulvae tolerates a salinity range of 10–33‰. Hydrobiid
498
mudsnails can also live in the subtidal zone and are able to
burrow. Thus, Recent mudsnails are well adapted to tidally
influenced ephemeric habitats with a brackish or strongly
fluctuating salinity and they may serve as a model for small
high-spired gastropods from the Gastropod Oolite. The
high abundance and low species richness of the gastropods
and bivalves from the Gastropod Oolite indicate a stressed,
not normal marine environment. Invertebrates other than
bivalves and gastropods are absent in the present samples.
There are no unequivocal indicators for normal marine
conditions, such as echinoderms.
In summary, facies and faunal content suggest the fol-
lowing conclusions about biota from the Gastropod Oolite:
The biota probably came from a shallow subtidal to in-
tertidal source area with fine-grained bottoms. Salinity was
not euhaline but probably decreased or strongly fluctuating.
A community of a few gastropod and bivalve species was
adapted to this environment. This community was charac-
terized by low diversity and extreme abundance. Modern
hydrobiid mudsnail communities may serve as a model for
the Gastropod Oolite snails. Iron coating and ooids were
formed in shallow water above fair-weather wave base.
Shells were then probably concentrated and deposited un-
der storm conditions.
Conclusion and discussion
Two major lagerst
¨
atten of Early Triassic gastropods, the
Sinbad Limestone (Utah, USA) and the Gastropod Oolite
from Valsugana (North Italy) were studied regarding
facies, paleoecology, fossil preservation, and depositional
environment. About 30 nominate gastropod species were
reported from these localities which represents about 40%
of the global Early Triassic gastropod species richness
(and more than 50% the gastropod species, if the entire
Werfen Formation is considered). The studied samples
from the Sinbad Limestone and the Gastropod Oolite
represent benthic mollusc coquinas. These shell beds are
composed of bivalves, gastropods, and of scaphopods
(Sinbad Limestone). Shells were probably concentrated
and transported by storms (tempestites) as is indicated
by clast-supported fabric, presence of graded bedding,
common geopetal fabrics and the presence of intraclasts.
Gastropods are very abundant in the Smithian
(Olenekian) Sinbad Limestone Member at the collecting
locality of Batten and Stokes (1986). They occur in a sin-
gle bed of grain- and packstones while they are rare in the
over-and underlying beds. This bedwasprobably deposited
under storm influence. It yields a relatively diverse inver-
tebrate fauna of about 40 taxa. Gastropods, scaphopods
(Plagioglypta), and bivalves are most abundant. Serpulids
(“Spirorbis”cf.valvata) and echinoderm ossicles (echi-
noids and ophiurids) are present but not as abundant as
molluscs. The biota lived in a shallow subtidal, soft bottom
environment prior to transport as is indicated by micrite fill-
ings in gastropods, scaphopods, and articulated bivalves as
well as by the fact that some of these organisms were prob-
ably infaunal and burrowing. The gastropods of the Sinbad
Limestone of the San Rafael Swell are exceptionally well
preserved as calcite replacement of the originally arago-
nitic shells. Teleoconch details and even larval shells are
commonly preserved. Protoconch preservation is almost
unique for the Early Triassic and the only other Triassic
fauna with well-preserved protoconchs is the Late Triassic
(Early Carnian) Cassian Formation. The good preservation
and the relatively high diversity of the gastropods from the
studied shell bed of the Sinbad Limestone make it the most
important Early Triassic gastropod largerst
¨
atte.
About 15 nominate gastropod species were reported from
the Werfen Formation (e.g., Wittenburg 1908a, b; Leonardi
1935) and a maximum of about five species occur in each
of its members. The gastropod faunas are characterized by
high abundance but low species richness. The abundance
of gastropods in several beds of the Werfen Formation
shows that this group formed a considerable part of the
benthic fauna in the Early Triassic of the Western Tethys.
The studied samples of the Gastropod Oolite Member near
Borgo Valsugana and Trento (North Italy) are characterized
by extremely abundant gastropods and bivalves. They
represent mostly oolitic gastropod/bivalve packstones,
wackestones, and floatstones. At Cimirlo (near Trento), an
almost monospecific gastropod fauna of Pseudomurchiso-
nia kokeni occurs. The fauna near Borgo Valsugana is more
diverse comprising at least four species. Thin-sections
show that these molluscs were thin-shelled and coated with
iron oxides. Clearly, the studied Gastropod Oolite faunas
lack the diversity and complexity of the Sinbad Limestone
fauna. Similar to modern gastropod faunas with high
abundance and low species richness (e.g., modern hydro-
biid mudsnail assemblages), gastropod assemblages of the
Gastropod Oolite were possibly controlled by a strongly
fluctuating salinity in a tidal-influenced environment. The
shells were subsequently concentrated and transported.
Other parts of the Gastropod Oolite facies were probably
deposited under normal marine conditions as is indicated
by the presence of conodonts and echinoderms.
Although similar at a first glance, beds with small,
extremely abundant gastropods from the Sinbad Limestone
and the Gastropod Oolite differ strongly from each other,
regarding species richness and taxonomic inventory.
Species richness is much higher in the Sinbad fauna
(26 species) than in the Gastropod Oolite (probably
not more than five species). No species and probably
also no genus is shared between both occurrences. This
suggests that gastropods were not cosmopolitan during the
Dienerian/Smithian. The fauna of the Sinbad Limestone
is marine with a normal salinity as is indicated by the
presence of planktonic larval shells (access to the ocean),
echinoderm ossicles, the abundance of scaphopods, and
the relatively high diversity. In contrast, biota of the
Gastropod Oolite were probably salinity-controlled and
not formed under normal marine conditions.
The fact that a couple of shell beds from two areas of the
world contain as many as 40% of the global Early Trias-
sic gastropod richness corroborates earlier suggestions that
the Early Triassic fossil record is exceptionally poor. For
instance, any two samples of even the richest Recent shell
499
accumulations, could not possibly produce 1% of the extant
global species richness. However, the fact that the richest
known Early Triassic gastropod fauna contains less than 30
species, preserves probably an original signal of a strongly
reduced global species richness during the Early Triassic.
Acknowledgements We dedicate this work to the late Erik Fl
¨
ugel,
an excellent scientist and inspiring teacher. We would like to thank
Roger L. Batten (Phoenix) for help in the field and stimulating discus-
sions, Hans Hagdorn (Ingelfingen) for the identification of the echi-
noid ossicles, Mrs Barbara Seuß and Mrs Birgit Leipner-Mata (both
Erlangen) for making the thin-sections and polished slabs. We thank
Martin Zuschin (Vienna) and Oliver Weidlich (London) for the re-
views which improved this paper. The Deutsche Forschungsgemein-
schaft is acknowledged for financial support (Grant NU 96/6-1, 6-2).
References
Assereto RL, Rizzini A (1975) Reworked ferroan dolomite grains in
the Triassic “Oolite a Gasteropodi” of Camoniche Alps (Italy)
as indicators of early diagenesis. N Jb Geol Pal
¨
aontol Abh
2:215–232
Barnes RSK (1999) What determines the distribution of coastal
hydrobiid mudsnails within north-western Europe. Mar Ecol
20:97–110
Batten RL (1973) The vicissitudes of the gastropods during the
interval of the Guadalupian-Ladinian time. In: Logan A, Hills
A (eds) The Permian and Triassic systems and their mutual
boundaries. Can Soc Petrol Geol Mem 2:596–607
Batten RL, Stokes WL (1986) Early Triassic gastropods from the
Sinbad Member of the Moenkopi Formation, San Rafael Swell,
Utah. Amer Mus Novitates 2864:1–33
Berger HAC (1859) Die Versteinerungen des R
¨
ot von Hild-
burghausen. N Jb Min Geol Pal
¨
aontol Abh 1859:68–171
Blakey RC (1974) Stratigraphic depositional analysis of the
Moenkopi Formation, Southeastern Utah. Utah Geol Min Surv
Bull 104:1–81
Boeckelmann K (1988) Die Werfener Schichten in den Karnischen
Alpen und westlichen Karawanken (
¨
Osterreich und Italien).
Unpublished PhD thesis, Rheinisch-Westf
¨
alische Tech Hochsch
Aachen, 213 pp
Bouchet P, Lozouet P, Maestrati P, Heros V (2002) Assessing the
magnitude of species richness in tropical marine environments:
exceptionally high numbers of molluscs at a New Caledonia
site. Biol J Linn Soc 75:421–436
Boyer DL, Bottjer DJ, Droser M (2004) Ecological signature of
Lower Triassic shell beds of the western United States. Palaios
19:372–380
Br
¨
onnimann P, Zaninetti L (1972) On the occurrence of the Serpulid
Spirorbis Daudin, 1800 (Annelida, Polychaetia, Sedentarida)
in thin sections of Triassic Rocks of Europe and Iran. Riv Ital
Paleontol 78:67–90
Broglio Loriga C, Masetti D, Neri C (1983) La formazione di
Werfen (Scitico) delle Dolomiti occidentali: sedimentologia e
biostratigrafia. Riv Ital Palaeontol Stratigr 88:501–598
Broglio Loriga C, Neri C, Posenato R (1986) Excursion B: the
Werfen Formation (Lower Triassic) in the Costabela Mt., Uomo
section. In: Italian IGCP 203 Group Members (eds) Excursion
Guidepook, Field Conference on Permian and Permian-Triassic
boundary in the south-alpine segment of the Western Tethys
(July 4–12, 1986), pp 116–133
Dean JS (1981) Carbonate petrology and depositional environment
of the Sinbad Limestone Member of the Moenkopi Formation
in the Teasdale Dome area, Wayne and Garfield Counties, Utah.
Brigham Young Univ Geol Ser 28:19–51
Erwin DH (1990) Carboniferous-Triassic gastropod diversity
patterns and the Permo-Triassic mass extinction. Paleobiology
16:187–203
Fl
¨
ugel E (2004) Microfacies of carbonate rocks. Springer, Berlin
Heidelberg New York
Fraiser ML, Bottjer DJ (2004) The non-actualistic Early Triassic
gastropod fauna: a case study of the Lower Triassic Sinbad
Limestone Member. Palaios 19:259–275
F
¨
ursich FT, Oschmann W (1993) Shell beds as tool in facies
analysis: the Jurassic of Kachchh, western India. J Geol Soc
Lond 150:169–185
Kidwell SM (1991a) Taphonomic feedback (live/dead interactions)
in the genesis of bioclastic beds: keys to reconstructing
sedimentary dynamics. In: Einsele G, Ricken W, Seilacher
A (eds) Cycles and events in stratigraphy. Springer, Berlin
Heidelberg New York, pp 268–282
Kidwell SM (1991b) The stratigraphy of shell concentrations. In:
Allison D, Briggs DE (eds) Taphonomy: releasing the data
locked in the fossil record. Plenum, New York, pp 211–290
Kidwell SM, Brenchley PJ (1994) Patterns in bioclastic accumulation
through the Phanerozoic: changes in input or in destruction?
Geology 22:1139–1143
Kier PM (1968) The Triassic echinoids of North America. J
Paleontol 42:1000–1006
Leonardi P (1935) Il Trias inferiore delle Venezie. Mem Inst Geol
Min Univ Padova 11:1–136
N
¨
utzel A (2005) A new gastropod genus from the Early Triassic
Werfen Formation and its meaning for the recovery of gas-
tropods from the Permian/Triassic mass extinction event. Acta
Palaeontol Pol 50:19–24
N
¨
utzel A (in press) Recovery of gastropods in the Early Triassic.
CR Palevol 4
N
¨
utzel A, Erwin DH (2002) Battenizyga, a new early Triassic
gastropod genus with a discussion on the gastropod evolution
at the Permian/Triassic boundary. Pal
¨
aontol Z 76:21–27
N
¨
utzel A, Erwin DH (2004) Late Triassic (Late Norian) gastropods
from the Wallowa terrane (Idaho, USA). Pal
¨
aontol Z 78:361–
416
Payne JL, Lehrmann DJ, Wie J, Orchard MJ, Schrag DP, Knoll AH
(2004) Large perturbations of the carbon cycle during recovery
from the end-Permian mass extinction. Science 305:506–509
Schubert JK, Bottjer DJ (1992) Early Triassic stromatolites as
post-mass extinction disaster forms. Geology 20:883–886
Schubert JK, Bottjer DJ (1995) Aftermath of the Permian-Triassic
mass extinction event: paleoecology of Lower Triassic car-
bonates in the western USA. Palaeogeogr Palaeoclimatol
Palaeoecol 116:1–39
Seilacher A, Reif W-E, Westphal F (1985) Sedimentological,
ecological and temporal patterns of fossil Lagerst
¨
atten. Phil
Trans R Soc Lond B 311:5–23
Sepkoski JJJr, Bambach RK, Droser ML (1991) Secular changes
in Phanerozoic event bedding and biological overprint. In:
Einsele G, Ricken W, Seilacher A (eds) Cycles and events in
stratigraphy. Springer, Berlin Heidelberg New York, pp 298–
312
Stewart JH, Poole FB, Wilson RF (1972) Stratigraphy and origin
of the Triassic Moenkopi Formation and related strata in the
Colorado Plateau region. US Geol Surv Prof Pap 961:1–195
Stiller F (2001a) Fossilvergesellschaftungen, Pal
¨
ao
¨
okologie und
pal
¨
aosyn
¨
okologische Entwicklung im oberen Anisium (Mittlere
Trias) von Qingyan, insbesondere Bangtoupo, Provinz Guizhou,
S
¨
udwestchina. M
¨
unstersche Forsch Geol Pal
¨
aontol 92:1–523
Stiller F (2001b) Scaphopods from the Upper Anisian (Middle
Triassic) of Qingyan, south-western China. N Jb Geol Pal
¨
aontol
Mh 10:617–632
Twitchett RJ (1999) A high resolution biostratigraphy for the Lower
Triassic of northern Italy. Palaeontol Newsl 43:19–22
Twitchett RJ (2001) Incompleteness of the Permian-Triassic
fossil record: a consequence of productivity decline? Geol J
36:341–353
Twitchett RJ, Krystyn L, Baud A, Wheeley JR, Richoz S (2004)
Rapid marine recovery after the end-Permian mass extinction
event in the absence of marine anoxia. Geology 32:805–808
Wheeley J, Twitchett RJ (in press) Palaeoecological significance of
a new Early Triassic gastropod assemblage from Oman. Lethaia
500
Wignall PB, Twitchett RJ (1999) Unusual intraclastic limestones in
Lower Triassic carbonates and their bearing on the aftermath of
the end-Permian mass extinction. Sedimentology 46:303–316
Wignall PB, Twitchett RJ (2002) Extent, duration, and nature of the
Permian-Triassic superanoxic event. Geol Soc Amer Spec Pap
356:395–413
Wittenburg P (1908a) Einige neue Fossilien aus den Werfener
Schichten S
¨
udtirols. N Jb Geol Palaeontol Abh 1:16–21
Wittenburg P (1908b) Beitr
¨
age zur Kenntnis der Werfener Schichten
S
¨
udtirols. Geol Palaeontol Abh 8:251–289
Zapfe H (1958) Die Fauna der Werfener Schichten vom Ulrichsberg
bei Klagenfurt in K
¨
arnten. Verh Geol Bundesanst 2:155–
164
Zuschin M, Stachowitsch M, Stanton RJ Jr (2003) Patterns and
processes of shell fragmention in modern and ancient marine
environments. Earth Sci Rev 63:33–82
Zuschin M, Harzhauser M, Mandic O (2005) Influence of
size-sorting on diversity estimates from tempestitic shell
beds in the Middle Miocene of Austria. Palaios 20:142–
158
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The Early Permian (Kungurian) Khao Khad Formation of Central Thailand consists mostly of carbonates deposited on the western margin of the Indochina Terrane. This formation has yielded unusual microbial-fusulinid limestones with large gastropods which contribute most to the rock volume. With a height of more than 6 cm, the gastropods are amongst the largest Early Permian gastropods ever reported. Gastropods as major rock formers are rare in the Palaeozoic. This, and other recently reported invertebrate faunas from Thailand show that gastropods may dominate Permian fossil assemblages not only in diversity, but also regarding abundance and in some cases also regarding biomass. Besides gastropods, fusulinids, various calcareous algae, intraclasts and thick microbial-cyanobacterial (Girvanella and Archaeolithoporella) coatings and reticular microbial patches as well as thick inter-and intragranular radial fibrous cement crusts are present. The gastropods represent at least four species and belong probably to undescribed taxa. The fusulinid genus Pseudofusulina and Misellina (M.) termieri are reported from the Khao Khad Formation for the first time and indicate a Bolorian age. Calcareous algae are dominated by dasycladaceans followed by gymnocodiaceans and solenoporaceans. The studied limestone almost completely lacks metazoan reef builders such as corals and sponges. Likewise, brachiopods and bivalves are absent in the studied samples and echinoderms are very scarce. The carbonate is interpreted as product of shallow water, back-reef lagoonal platform community with a high productivity providing the large gastropods with sufficient food. However, conditions were too eutrophic for sessile filter feeders including metazoan reef builders.
... Remarks. This is a typical representative of a group of "shelled opisthobranchs" which occurs in the Early Triassic (Batten & Stokes 1986;Nützel 2005;Nützel & Schulbert 2005) and ranges into the Cretaceous (Kaim 2004). ...
Thesis
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Changes in alpha and gamma diversity throughout the Phanerozoic have long been of interest in paleontology, but beta diversity remains understudied, particularly in the post-Paleozoic. Beta diversity – the compositional variation among communities or assemblages – is a key aspect of biodiversity and is crucial to revealing the principles of diversity assembly. Studying the biodiversity patterns of well-preserved fossil and modern assemblages can provide insight into how these patterns arise, how they change through time, and whether there are unifying principles in community composition and assembly. Taphonomic effects and sampling biases complicate the assessment of changes in biodiversity over time. Intensively sampled and well-preserved fossil assemblages are ideal to study biodiversity patterns and compare them with modern assemblages. The Middle to Late Triassic (Ladinian–Carnian) Cassian Formation, exposed in the Dolomites, Southern Alps, northern Italy, is characterized by high diversity and excellent preservation of fossils. The Cassian Formation comprises shallow and deeper water sediments deposited between carbonate platforms in a warm, tropical setting in the Western Tethys, comparable with modern tropical environments. A wide breadth of depositional environments are recorded in the Cassian Formation: a nearshore back-reef area with patch reefs and the sediments intercalated between these, the carbonate platform, and the shallow and deeper reef basin. With 1421 invertebrate species, the Cassian Formation yields the highest species richness reported from any known spatially constrained pre-Quaternary formation. This is due to (1) excellent presservation of fossils and the ease with which they are extracted from the poorly lithified sediments as well as (2) the high primary diversity, which is probably due to the tropical reef-associated setting, high alpha diversity, and a wide breadth of habitat types, driving beta diversity. Beta diversity is partitioned into a large species turnover and a small nestedness component. Particularly notable for a fossil assemblage is the high proportion of molluscs, particularly gastropods. Molluscs comprise 67% of all invertebrate species in the Cassian Formation, and the proportion of gastropods (39%) is almost level with modern tropical settings. Studying more 'liberation lagerstätten' like the Cassian Formation can greatly contribute to our understanding of biodiversity of reef basin assemblages and other habitats, and may lead us to rethink the concept of a substantial rise of gastropods in the Cenozoic. Testing which factors drive biodiversity, specifically beta diversity, in the Cassian Formation and other comparable assemblages is the main focus of this thesis. Mean pairwise proportional dissimilarity is a very suitable measure to express beta diversity, as it is relatively robust to differences in sample size and grain and can be used to quantify overall beta diversity in a region or between samples as well as along gradients. Beta diversity as pairwise proportional dissimilarity is driven by dominant species. The role of rare species can be neglected in large-scale assessments of beta diversity. This finding not only makes it easier to accumulate larger amounts of data to be used in beta diversity studies but also makes incorrect taxon identification less significant. To disentangle the drivers of biodiversity patterns in the Cassian Formation and another reefassociated soft-bottom environment from the modern Bay of Safaga in the Red Sea, Egypt, beta diversity is evaluated with regard to age, water depth, and geographic distance. Results are compares with a null model to evaluate the stochasticity of community assembly. Only the ten most abundant species per sample are included to determine mean pairwise proportional dissimilarity. As in the previous studies, overall beta diversity is found to be very high in the Cassian Formation. The Bay of Safaga yields a similarly high value. The variation in community composition is found to be independent of geographic or temporal distance. Beta diversity between shallow- and deep-water communities is relatively high. Samples from deeper-water settings yield a slightly higher beta diversity than those from shallower areas. A similar pattern is seen in both assemblages. Although water depth has been a driving factor in other studies on beta diversity, it is not considered to be a major driver in the studied assemblages. Priority effects are postulated to be the main driver of beta diversity in these reef basin assemblages. In summary, results from this thesis show that dominant species drive beta diversity. Species turnover, not species loss, are the ecological cause of beta diversity in the Cassian Formation, probably resulting from the evolution of new species within this heterogeneous environment. The high diversity in the Cassian Formation results from high local diversity and large differences in community composition between assemblages driving beta diversity. Reasons for the high preserved diversity are ascribed to taphonomic conditions. Biodiversity in the Cassian Formation is similar to comparable modern environments. The high number of species and the large proportion of gastropods in the Cassian Formation are close to those found in modern soft-bottom assemblages. Values of alpha, beta and gamma diversity are similarly high. And while the heterogeneity and breadth of environments is thought to increase beta diversity, priority effects may also play an important role.
Article
Twelve species of small gastropods are extracted using the sodium tetraphenylborate method from the strongly lithified shallow marine deposits of the Barremian (Lower Cretaceous) Kimigahama Formation of the Choshi Group, central Japan. They belong to the following families and subfamilies; Eudaroniidae, Pseudomelaniidae, Ampezzopleurinae, Metacerithiidae, Procerithiidae, Nystiellidae, Metaxiinae, Stuoraxidae and Ebalinae, including six new species and one new genus. Pseudomelania yamadai sp. nov., Ampezzopleura barremica sp. nov., Choshipleura striata gen. et sp. nov., Metacerithium boshuae sp. nov., Antiphora aurora sp. nov. and Stuoraxis kasei sp. nov. are described as new species. Pseudomelania yamadai, Metacerithium boshuae and Cirsocerithium subspinosum are closely related to or identical with the species from the Lower Cretaceous in western Europe. Ampezzopleura barremica and Choshipleura striata are the first Cretaceous records of the subfamily Ampezzopleurinae that has hitherto been limited to the Triassic deposits. Antiphora aurora is the first record of the family Triphoridae from Mesozoic deposits, suggesting that the sinistral triphorids originated from the dextral ancestor. Stuoraxis kasei is the youngest occurrence of the heterostrophan family Stuoraxidae that has hitherto been reported from the Permian to Middle Jurassic deposits. The sodium tetraphenylborate method for finding the small molluscs from the strongly lithified deposits is an effective tool with which to reveal the true diversity of the fossil molluscan fauna.
Chapter
Parasitism and similar life styles such as carnivorous grazing or mucus feeding without killing the prey are important in marine gastropods. Some of the most diverse living gastropod families have this feeding behavior. Taxonomic uniformitarianism is the most important tool to infer parasitism or similar life styles in fossil gastropods. The extant family groups in question (Eulimidae, Epitoniidae, Pyramidellidae, Architectonicidae, Coralliophilinae, Ovulidae, Cerithiopsidae and Triphoridae) originate mostly in the Late Cretaceous (Cerithiopsidae in the Middle Jurassic) and Paleocene. They are performing an ongoing adaptive radiation and some of the mentioned families belong to the most diverse gastropod groups forming a considerable part of marine ecosystems regarding species richness and relative abundance. At the same time, origination and radiation of the carnivorous, commonly predatory Neogastropoda took place. This points to a trophic revolution in Gastropoda that forms an important aspect of the Mesozoic Marine Revolution. Most modern parasitic gastropods are small, high-spired, show high diversity and low disparity within families and belong to Apogastropoda. By analogy, some extinct gastropod families which show the same properties might have lived parasitic too (e.g., Pseudozygopleuridae, Zygopleuridae, Meekospiridae, Donaldinidae). However, this will remain speculative to a large degree until direct host associations are found. Direct evidence for parasitism is exceptional with the Palaeozoic platyceratid/crinoid interaction being one of the best studied examples. In Gastropoda, functional shell morphology may help to identify parasitism in the fossil record but this field is scarcely studied.
Article
We describe aggregative microconchid (Lophophorata) tubes from the uppermost Permian (upper Changhsingian) and Lower Triassic (Olenekian) lacustrine and fluvial strata of the Tunguska and Kuznetsk basins and the southern Cis-Urals, Russia. These attach to clam shrimp carapaces, bivalve shells, terrestrial plant fragments and a horseshoe crab head shield, and also form their own monospecific agglomerations. Planispiral tubes of a wide size range (0.1-2.5 mm) create dense settlements on these firm substrates, which likely comprise multiple generations of the same species. These finds confirm that this extinct lophophorate group was inhabiting non-marine continental basins during latest Permian and earliest Triassic time, when they were major suspension feeders in such limnic ecosystems. Microconchids dispersed extensively and rapidly in the aftermath of the Permian-Triassic mass extinction into both marine and continental basins at low and moderately high latitudes, which were notably different in salinity, temperature, depth and redox conditions. This confirms that small lightly calcified microconchids were a genuine disaster eurytopic group, whose expansion may have been promoted by low predator pressure and low competition for substrate.
Article
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To further our understanding of the evolution, selectivity and ecological composition of marine communities following the latest Permian mass extinction, new collections from underrepresented regions in the immediate extinction aftermath are required. Here, we provide new systematic data and the first palaeobiological account of the benthic invertebrate community from the Great Bank of Guizhou, South China. We systematically describe three brachiopod species, 26 bivalve species, 11 gastropod species, 1 microconchid and 1 crinoid species. The descriptions include 5 new species; 2 bivalve species (Hoernesia? danisae, Atomodesma? hautmanni) and 3 gastropod species (Donald-ina erwini, Cossmannina alfischeri and Vernelia samae). This is the most species-rich benthic community known so far from the extinction aftermath, which is typically characterized by a high proportion of Permian holdover genera and cosmopolitan taxa. Taxonomically, this community is different from coeval faunas with dissimilarity values >60%. Ecologically, however, this fauna is similar to faunas from the Dolomites (Italy) and East Greenland. This new data, therefore, suggests that the lower Griesbachian invertebrate faunas were taxonomically heterogeneous, whereas ecologically they were relatively homogenous. The marine community on the Great Bank of Guizhou records genera that survived the mass extinction event with some, but not all, recording a size reduction, that is, the Lilliput effect. The absence of large body fossils and the preferential survival of small species suggest that the mass extinction event was size-selective.
Conference Paper
Analysis of published data shows that, for most animal groups, the fossil record in the immediate aftermath of the end-Permian biotic crisis is less complete than during the Late Permian or Middle Triassic. Completeness is measured by the Simple Completeness Metric. The interval of poor quality fossil record spans the entire Lower Triassic and may have serious consequences for our perception of the magnitude of the end-Permian event. A model is presented which seeks to explain this phenomenon. There is abundant evidence that levels of primary productivity were severely reduced in the very latest Permian. In response to this, animal biomass must also have been reduced. The biomass of a particular taxon is the product of the size of individual organisms multiplied by the number of individuals. Those taxa that reduced population size, but maintained original body size, would tend not to be preserved (apparent extinction) and would also be more prone to 'real' extinction. Those taxa that retained large population sizes, but reduced body size, would resist extinction and would also maintain their presence in the fossil record. One testable prediction is that taxa present in the fossil record in the immediate aftermath of the end-Permian crisis will have smaller body size than their pre-event relatives, regardless of their initial size. Anecdotal evidence supports this prediction. Such a biomass reduction model may also be applicable to other mass extinction events. Copyright (C) 2001 John Wiley & Sons, Ltd.
Article
As part of a study of the diversity history of upper Paleozoic and Triassic gastropods, to test the extent to which taxonomic and morphologic trends established in the late Paleozoic are continued after the extinction, and to determine the patterns of selectivity operating during the extinction, I assembled generic and morphologic diversity data for 396 genera in 75 families from the Famennian through the Norian stages. Within this interval, gastropod genera underwent an adaptive radiation during the Visean and Namurian, a subsequent period of dynamic stability through the Leonardian, a broad-based decline during the end-Permian mass extinction, and a two-phase post-extinction rebound during the Triassic. Taxonomic affinity, previous clade history, generic age, and gross morphology did not determine survival probability of genera during the end-Permian extinction, with the exception of the bellerophontids, nor did increasing diversity within clades or expansion of particular morphologies prior to the extinction facilitate survival during the extinction or success after it. Survival was a consequence of broad geographic and environmental distribution, as was the case during background periods. -from Author