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Soft-tissue preservation in the Middle Jurassic ammonite Cadoceras from Central Russia



The findings of fossilized ammonite soft tissues are extremely rare, so each specimen may be important for understanding the anatomy of these cephalopods. This paper deals with soft tissue fragments and imprints preserved in the rear part of the body chamber of the Middle Jurassic ammonite Cadoceras stupachenkoi from Central Russia. At the base of the body chamber of this ammonite in front of the last septum, a mantle fragment with clearly visible longitudinal fibers and imprints of the palliovisceral ligament are preserved. In front and slightly to the side of the mantle fragment, a small area with branched structures is located; probably, these structures are fragments of gills. In general, the structure of the soft tissues in the rear part of the ammonite body looks very similar to that of modern nautilids, with one exception: mantle fibers are not directed forward as observed in Nautilus, but to the mid-ventral line, probably to the ventral muscle.
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Swiss Journal of Palaeontology
ISSN 1664-2376
Volume 134
Number 2
Swiss J Palaeontol (2015) 134:281-287
DOI 10.1007/s13358-015-0082-1
Soft-tissue preservation in the Middle
Jurassic ammonite Cadoceras from Central
Aleksandr A.Mironenko
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Soft-tissue preservation in the Middle Jurassic ammonite
Cadoceras from Central Russia
Aleksandr A. Mironenko
Received: 19 February 2015 / Accepted: 19 May 2015 / Published online: 21 July 2015
ÓAkademie der Naturwissenschaften Schweiz (SCNAT) 2015
Abstract The findings of fossilized ammonite soft tissues
are extremely rare, so each specimen may be important for
understanding the anatomy of these cephalopods. This
paper deals with soft tissue fragments and imprints pre-
served in the rear part of the body chamber of the Middle
Jurassic ammonite Cadoceras stupachenkoi from Central
Russia. At the base of the body chamber of this ammonite
in front of the last septum, a mantle fragment with clearly
visible longitudinal fibers and imprints of the palliovisceral
ligament are preserved. In front and slightly to the side of
the mantle fragment, a small area with branched structures
is located; probably, these structures are fragments of gills.
In general, the structure of the soft tissues in the rear part of
the ammonite body looks very similar to that of modern
nautilids, with one exception: mantle fibers are not directed
forward as observed in Nautilus, but to the mid-ventral
line, probably to the ventral muscle.
Keywords Ammonoids Middle Jurassic Soft tissues
Cadoceras Russia
The study of fossilized soft tissue allows better under-
standing of the anatomy and biology of ancient animals.
Findings of soft tissues are particularly important for the
study of completely extinct groups, such as ammonoids,
which have left no descendants. Unfortunately, fossilized
ammonoid tissues are extremely scarce and many parts of
the ammonoid body (e.g., arms, hyponome) have never
been found. Nevertheless, several non-mineralized organs
of ammonoids such as gills, oesophagus, digestive tract,
cephalic cartilage with questionable eye capsules, mantle
tissues, and siphuncular blood vessels were found and
described (Lehmann 1967,1979,1985; Lehmann and
Weitschat 1973; Riegraf et al. 1984; Tanabe et al. 2000;
Doguzhaeva et al. 2004,2007; Wippich and Lehmann
2004; Klug and Jerjen 2012; Klug et al. 2012). Mantle
tissues can be considered as one of the rarest known types
of ammonite soft tissues: fragments of the mantle with
preserved muscle structure have been described only twice,
both times in the Late Triassic ammonoid Austrotrachyc-
eras (Doguzhaeva et al. 2004,2007). The structures which
are located at the rear part of the ammonoid body chamber,
such as ventral and dorsolateral muscle scars are well
studied (Doguzhaeva and Mutvei 1996; Klug et al. 2007),
but usually, only hard parts of the shell or occasionally
unstructured phosphatized remnants (Klug et al. 2007)
rather than the soft tissues itself are preserved.
This article describes the preserved fragment of mantle
tissue, imprints of the palliovisceral ligament and putative
remnants of gills, found in the rear part of the body
chamber of the Middle Jurassic (Lower Callovian)
ammonite Cadoceras stupachenkoi from Central Russia.
The findings of soft tissues and their imprints allow better
understanding of the structure of the rear part of the
ammonoid soft body.
Materials and methods
The specimen studied herein is a Middle Jurassic ammonite
Cadoceras stupachenkoi (Fig. 1). It is a cadiconic macro-
conch, which was found in Middle Jurassic deposits
&Aleksandr A. Mironenko
Kirovogradskaya st. 28, 117519 Moscow, Russia
Swiss J Palaeontol (2015) 134:281–287
DOI 10.1007/s13358-015-0082-1
Author's personal copy
(Lower Callovian, Elatmae Zone, Stupachenkoi Subzone)
in the Unzha-river region, not far from the town of
Makaryev in Russia (Keupp and Mitta 2013: Fig. 2). The
specimen comes from a layer of calcareous sandstone
nodules, often phosphatized, with inclusions of pyrite (see
Keupp and Mitta 2013 for taphonomy and geological set-
ting). The diameter of the specimen is about 10 cm. Only
the posterior part of the body chamber with a small frag-
ment of the phragmocone is preserved. The aragonitic shell
layers were partially preserved, but removed for exami-
nation of the internal mould of the body chamber. The
specimen is housed at Moscow State University Museum,
Russia, with the collection number MSU 119.
The ammonite was studied using a binocular microscope
and a scanning electron microscope SEM TESCAN//
VEGA with a BSE detector at the Paleontological Institute
of the Russian Academy of Science in Moscow. It was
examined in an uncoated state in low vacuum conditions at
30 kV.
A poorly preserved ventral attachment scar and the anterior
border of the annular elevation are located at a distance of
14 and 30 mm from the last siphuncle tube, respectively
(Fig. 1). Along the front edge of the annular elevation near
the ventral muscle attachment scar, a small, presumably
carbonized, piece of mantle tissue is located. It is 3–7 mm
wide, dark grey, and visible to the naked eye. The binocular
observation allows to recognize long branched longitudinal
fibers (Fig. 2). This mantle tissue is very thin with only one
layer of muscle fibers. All these fibers are directed to the
mid-ventral line of the body chamber. On the SEM images,
the remnants of dark carbonized tissues and small fibers
branching off from the large muscles are visible (Fig. 3).
Behind the anterior border of the annular elevation
(mantle myoadhesive band) and the mantle fragment,
imprints of the palliovisceral ligament are located (Fig. 4).
This area shows a double-layered structure: there are small
transverse stripes on the top layer and beneath them rough
and sharp transverse folds (Fig. 4b). There are no fossilized
soft tissues in these rough folds, but imprints of these tis-
sues composed of middle-grained sandstone, which fills the
body chamber.
The third type of preserved soft tissues is small branched
feather-like structures located in front of the annular ele-
vation. They are very tiny and mostly grouped in small
cluster, the size of the entire cluster is not more than 1 cm
(Fig. 5a, b). Nearby, separate branched structures are
located outside of this cluster at the rear part of the body
chamber. However, in the cluster, the structures are better
preserved and concentrated. The branched structures are
arranged in several layers. In SEM images, small trans-
verse ridges are visible in these objects (Fig. 5c, d). These
structures resemble small parts of gills.
Fig. 1 Cadoceras stupachenkoi with fossilized fragments of the soft tissues. aOverview over the studied specimen MSU 119/1. bScheme of the
specimen MSU 119/1
282 A. A. Mironenko
Author's personal copy
Mantle tissue and imprints of the palliovisceral
Inside the ammonite body chambers, not only ammonite
body remnants can be found, but also the fragments or
intact shells of other animals, which lived inside empty
ammonite shell on the sea bottom, or were transported into
the empty shell by sea currents (Fraaye and Ja
¨ger 1995a,b;
Klompmaker and Fraaije 2012; Vullo et al. 2009). In
several cases, the clusters of small invertebrate fragments
were interpreted as ammonite crop content (Keupp 2000;
Ritterbush et al. 2014). In addition, different epicoles can
be attached to the inner walls of the empty ammonite body
chamber (Klug and Korn 2001). The scavengers which ate
ammonite bodies or animals which lived inside empty
shells left their traces, e.g., burrows, fecal pellets, etc.,
(Fraaye and Ja
¨ger 1995a). All of these findings can be
confused with the remains of the ammonite soft body.
However, there is no doubt that the fossilized fragment in
the Cadoceras body chamber is in fact part of the
Fig. 2 Fragment of the mantle tissue of the Cadoceras stupachenkoi. aOverview of the mantle fragment. Scale bar 2.5 mm. b,c, Longitudinal
muscle fibers in the mantle fragment. Scale bars 1 mm. dTwo muscle fibers. Scale bar 0.5 mm
Soft-tissue preservation in the Middle Jurassic ammonite Cadoceras from Central Russia 283
Author's personal copy
ammonite mantle (see Allison 1988 for possible mecha-
nisms of soft-tissue fossilization). Its structure (Figs. 2,3)
is very similar to the structure of the longitudinal muscles
of fossil coleoids (Allison 1988: Fig. 5B) and mantle
muscles of living nautilids (Mutvei et al. 1993: Fig. 9B),
but it does not resemble any traces of epicoles or scav-
engers. Its position on the anterior part of the annular
elevation fully corresponds to the attachment area of
mantle muscles (Mutvei 1957; Mutvei et al. 1993).
In the mantle tissue fragment of the Cadoceras, muscle
fibers are directed to the mid-ventral line of the body
chamber. In the rear part of the mantle of recent Nautilus
pompilius, mantle fibers are pointing towards the aperture
(Mutvei et al. 1993: Fig. 9B). It appears unlikely that the
direction of the fibers in the ammonite is a result of
postmortem shifting. Although the shell orientation of the
ammonite carcass on the sea floor during the decomposi-
tion of its soft tissues is unknown, all preserved soft tissue
remnants are located on the right side of the body chamber.
Therefore, this side was most likely lower during the burial
of the shell. In this case, if the muscles shifted downward
under the influence of gravity, they must have shifted to the
right side, not to the mid-ventral line of the body chamber
as it actually is preserved. Therefore, the preserved orien-
tation of the muscle fibers might represent the syn vivo
position. Nevertheless, more material with this kind of
preservation is needed to support this hypothesis. Possibly,
these muscles were connected to the ventral muscle which
was directed forward from the ventral attachment scar, as
was earlier suggested by other authors (Jordan 1968; Dagys
Fig. 3 SEM images of the mantle tissue fragment of the Cadoceras stupachenkoi.aLarge longitudinal fibers and carbonized tissue among them.
Scale bar 500 lm. bSets of small fibers. Scale bar 50 lm
Fig. 4 Area of the palliovisceral ligament. aOverview over the area of the palliovisceral ligament. bDetail of the sharp transverse folds and
small stripes in this area. Scale bar 2.5 mm
284 A. A. Mironenko
Author's personal copy
and Keupp 1998). If this orientation of the mantle muscles
represents the syn vivo-orientation, it would resemble the
connection of the inner mantle layers of coleoids with the
ventral mantle adductor muscle (Bizikov 2004). While the
coleoid mantle is thick, the ammonite mantle appears to be
very thin, containing possibly, only one layer of muscle
tissue similar to nautilids. Unfortunately, the direction of
the fibers, located far from the central part of the myoad-
hesive band, remains unknown.
The structure of the palliovisceral ligament of Cado-
ceras resembles that described from nautilids (Mutvei et al.
1993). In general, the entire rear part of the Cadoceras soft
body is very similar to the corresponding part of the living
and ancient Nautilida (see Mutvei 1957,1964; Mutvei et al.
1993; Klug and Lehmkuhl 2004) with the exception of the
ventral muscle attachment structure. As in Nautilus, the
ammonite mantle, which was attached to the myoadhesive
band, is thin, with clearly separate and distinguishable long
fibers. However, this similarity does not mean that the front
end of the ammonite mantle was identical to the mantle of
nautilids. Several ammonite shells have parabolic nodes
(Bucher et al. 1996; Doguzhaeva 2012) and adult apertural
modifications (e.g., lappets; see Makowski 1962), which
have never been observed in modern or ancient nautilids.
The presence of such structures in ammonite shells may
indicate that the ammonite mantle edge was different from
the mantle edge of nautilids and probably was more mus-
cular and complex. However, findings of preserved anterior
Fig. 5 Gill fragments of Cadoceras stupachenkoi. aOverview of the specimen with marked location of gill imprints. bDetail of the gill
imprints. Scale bar 2 mm. c, d SEM images of the gill imprints. Scale bars 250 and 500 lm, respectively
Soft-tissue preservation in the Middle Jurassic ammonite Cadoceras from Central Russia 285
Author's personal copy
parts of the mantle are needed to clarify these assumptions;
in the specimen studied herein, there are no traces of this
part of the mantle.
Presumable ammonite gills
The author considered several versions of the origin of
small branched structures located in front of the annular
elevation (Fig. 5): imprints of scavenger jaw apparatus,
which was used to eat the ammonite mantle; fragments of
the mantle tissue; fragments of the gills. The first version,
which interprets these structures as bite or radula marks of
scavengers, seems to be unlikely due to the shape and
layered structure of these objects. The idea that these
structures are remnants of decomposed mantle tissue can-
not be completely ruled out, but it seems unlikely, since all
these objects are about the same size and shape. It is more
likely that these fragments are remnants of the ammonite
gills. Probably, these gill fragments came to rest on the
shell wall after the local decomposition of the mantle.
Structures interpreted as ammonite gills were described
several times (Lehmann and Weitschat 1973; Lehmann
1979,1985). The findings of fossilized gills of coleoid
cephalopods are also known (e.g., Reitner 2009). However,
the microstructure of fossilized gills has never been
depicted and described. In the case of Cadoceras, if the
objects described herein are actually the remains of gills,
they are only small fragments, because the length of each
object is about 1–1.2 mm.
Recent Nautilida (Nautilus and Allonautilus) have two
pairs of gills, whereas all coleoids have only one pair. The
number of ammonoid gills is still unknown. Shigeno et al.
(2008) showed that the two pairs of Nautilus gills do not
form simultaneously, but successively. This adds additional
weight to the hypothesis that earliest cephalopods had one
pair of gills (Engeser 1996; Sasaki et al. 2010), whereas, a
second pair appeared later during evolution, likely as an
adaptation to low concentrations of oxygen in nautilid
habitats (Wells et al. 1992). Due to this assumption and
closer phylogenetic relationship of ammonoids and
coleoids (Engeser 1996; Jacobs and Landman 1993; Kro
et al. 2011; Ritterbush et al. 2014), it is now widely
accepted that ammonoids likely have only one pair of gills.
Currently, it is impossible to clarify this question by the
examination of the herein described Cadoceras specimen,
as just a few parts of its gills are preserved. However, these
fragments can help to clarify the position of the ammonoid
gills: they were located (at least their posterior parts) very
deep inside the body chamber, not far from the last septum
(unless they were translocated post mortem). It may reflect
the great length of the mantle cavity of Cadoceras.This
fact should be taken into account for reconstructions of
ammonoid anatomy and calculations of the lifetime
orientation of ammonite shells (for recent calculations of
Cadoceras hatchling see Lemanis et al. 2015).
The fragments of the mantle, gills, and soft tissue imprints
preserved in the rear part of the Cadoceras stupachenkoi
body chamber indicate a similarity of the apical parts of the
soft body of ammonoids and nautilids. However, some
differences are observed: muscle fibers of the ammonite
mantle are not directed forward to the aperture as in
Nautilus, but to the center of the ventral side, likely to the
ventral muscle. The number of ammonite gills remains
unknown, but findings not far from the rear part of the
mantle of their fragments, indicate a large ammonoid
mantle cavity size.
Acknowledgments I am very grateful to Dmitry Buev (Moscow,
Russia) for donating the valuable Cadoceras specimen. SEM photos
were made with the generous help by Roman Rakitov (PIN RAS,
Moscow, Russia). I am also very grateful for the important and very
helpful comments from Christian Klug (Pala
¨ontologisches Institut
und Museum, Universita
¨rich, Switzerland), Rene
(Ruhr Universita
¨t Bochum, Germany), and an anonymous reviewer,
their comments helped to greatly improve the article.
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Soft-tissue preservation in the Middle Jurassic ammonite Cadoceras from Central Russia 287
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... The area and outline of the black mass correlates with similar lateral attachment scars of muscle for the hyponome retractor in Jurassic ammonoids from Russia 39 , see 40 . Similar structures were described as ventrolateral muscle scars in Cretaceous Aconeceras from Russia 41 . ...
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The taphonomic mechanisms of a mono- to pauci-specific ammonoid fauna comprising 3565 specimens from the lower Carnian Polzberg Konservat-Lagerstätte near Lunz am See (Northern Calcareous Alps, Lower Austria) is described. The fossiliferous layers were deposited during the Julian 2 Ib (Austrotrachyceras austriacum Zone, Austrotrachyceras minor biohorizon). The deposits comprise abundant nektic ammonoids of the trachyceratid genus Austrotrachyceras. The bivalve Halobia, dominant among the invertebrates, is followed in abundance by the ammonoids Austrotrachyceras and Paratrachyceras, the coleoid Phragmoteuthis and frequent vertebrate actinopterygian fish. The monotonous ammonoid assemblage comprises abundant Austrotrachyceras, frequent Paratrachyceras, rare Carnites and Simonyceras. Recently collected ammonoids were sampled bed-by-bed and compared to extensive historical collections from the same localities. Bromalites (coprolites and regurgitalites) produced by large durophagous fish comprise ammonoid and fish masses and accompany the ammonoid-dominated Polzberg palaeobiota. The ammonoid fauna here presents a window into the nektic cephalopod world of the Upper Triassic assemblage and palaeoenvironment during the deposition of the fossiliferous layers. The frequent occurrence of the vertically oriented (external side horizontal to bedding plane) ammonoid shell fragments hint at a deposition after lethal fish or coleoid attacks. The Polzberg ammonoids were deposited under calm and dysoxic conditions in fine-laminated marlstones and shales of the lower Carnian Polzberg Sub-Basin within the Polzberg Konservat-Lagerstätte.
... By contrast, in contemporaneous ammonoids, soft-part anatomy is primarily inferred from muscle-attachment scars inside the shell (Mironenko, 2014) and hard parts housed in the buccal mass and associated with feeding (Keupp and Mitta, 2013;Klug and Lehmann, 2015;Smith et al., 2021); indigestible (skeletal) remnants suggest a crop and stomach (Jäger and Fraaye, 1997). The only known soft tissues from Jurassic ammonites are fragments of mantle and possibly gills in a cadoceratid (Mironenko, 2015), and detached, flattened body masses of jaws and organs outside perisphinctid shells . The digestive tract and buccal mass are best known from flattened Late Cretaceous heteromorph baculitids (Klug et al., 2012). ...
The extreme rarity of soft-tissue preservation in ammonoids has meant there are open questions regarding fundamental aspects of their biology. We report an exceptionally preserved Middle Jurassic ammonite with unrivaled information on soft-body organization interpreted through correlative neutron and X-ray tomography. Three-dimensional imaging of muscles and organs of the body mass for the first time in this iconic fossil group provides key insights into functional morphology. We show that paired dorsal muscles withdrew the body into the shell, rather than acting with the funnel controlling propulsion as in Nautilus. This suggests a mobile, retractable body as a defense strategy and necessitates a distinct swimming mechanism of hyponome propulsion, a trait that we infer evolved early in the ammonoid-coleoid lineage.
... Phosphatization is the main type of preservation of soft-bodied marine animals including coleoids, in all currently known Konservat-Lagerstätten localities, such as Jurassic Posidonia Shales, Oxford Clay Formation, Solnhofen Plattenkalks, etc., their bodies are phosphatized (Donovan & Fuchs 2016). Soft tissues of ammonites, such as their mantle and muscle fragments (Mironenko 2015;Klug et al. 2021b) and siphuncle blood vessels (Tanabe et al. 2000;Mironenko 2017), are also replaced with phosphatic minerals, although the preservation of ammonite bodies is usually incomplete, with very rare exceptions (Klug et al. 2021b). ...
The first well-preserved soft-body imprint of a fossil squid was discovered from the Lower Oligocene of the Krasnodar region, Russia. The squid is perfectly preserved, with many details of its body available for study, such as imprints of eyes and head, a pair of statoliths, jaws, and stomach contents. Statoliths of this squid are the first finds of in situ statoliths in fossil non-belemnoid coleoids, and their shape is characteristic of the genus Loligo (family Loliginidae). Although some Mesozoic coleoids were previously classified as teuthids, these finds remain controversial and the squid described herein is the first unquestionable representative of fossil Teuthida known to date. It should be noted that the squid is preserved not due to phosphatization, which is typical for fossil coleoids, but by pyritization and carbonization. Numerous fish remains in the stomach contents of the squid indicate its piscivorous diet. A small cutlassfish Anenchelum angustum, which was buried together with the squid and whose bones are located near the squid's jaws, sheds light on the circumstances of the death of this animal. Most likely, the squid suffocated in the anoxic bottom waters, where it drowned along with its last prey (distraction sinking).
... Accordingly, these are the most widely reported organic hard components of soft tissues (Closs, 1967a(Closs, , 1967bHollingworth & Hilton, 1999;Klug & Jerjen, 2012;Klug & Lehmann, 2015;Klug et al., , 2016Klug et al., , 2021Kruta et al. 2011Kruta et al. , 2020Landman et al., 2010;Lehmann, 1981;Lehmann & Weitschat, 1973;Mapes et al., 2019;Tanabe, Kruta, et al., 2015;Wippich & Lehmann, 2004). Besides, a few records exist for the presence of ammonoid gills (Klug et al., 2021;Lehmann, 1985;Lehmann & Weitschat, 1973;Mironenko, 2015), and siphuncle (Mironenko, 2017 and references therein; Tanabe et al., 1982Tanabe et al., , 2000Tanabe, Sasaki, et al., 2015). The siphuncle is a long, segmented soft tissue that begins at the rear soft body. ...
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Findings of ammonoid soft tissues are extremely rare compared to the rich fossil record of ammonoid conchs ranging from the Late Devonian to the Cretaceous/Paleogene boundary. Here, we apply the computed-tomography approach to detect ammonoid soft tissue remains in well-preserved fossils from the Early Cretaceous (early Albian) of NE-Germany of Proleymeriella . The ammonites were found in glauconitic–phosphatic sandstone boulders. Analyses of the high-resolution Ct-data revealed the presence of cameral sheets, the siphuncular tube wall, and the siphuncle itself. The siphuncle is a long, segmented soft tissue that begins at the rear end of the body chamber and comprises blood vessels. Chemical analyses using energy-dispersive spectroscopy (EDS) showed that all preserved soft tissues were phosphatized and are now composed of fluorapatite. The same holds true for preserved shell remains that locally show the nacreous microstructure. We provide a short description of these soft tissue remains and briefly discuss the taphonomic pathway.
... It is possible that conellae are associated with areas of muscles attachment due to the thickening of the shell in these areas, such as in keels and ribs. Our observation of the numerous conellae on annular elevation of Quenstedtoceras confirms this hypothesis, since this feature is an area of soft tissue attachment (e.g., Mironenko 2015). The report of Riegraf et al. (1984) on conellae found associated with the crop content of Lower Jurassic ammonites from the Posidonia Shale supports the notion these features are associated with higher amounts of organic matter typical for injured area, muscle attachment sites and presumed soft tissue preservation (see Schweigert and Dietl 1999 for an Upper Jurassic Physodoceras). ...
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Conellae, enigmatic cone-shaped structures which can be found on the surface of internal moulds of cephalopod shells (predominantly of ammonoids), are regarded herein as the product of remote (biologically induced) biomineralization formed in closed-off cavities during lifetime and might be primarily composed of vaterite, aragonite, or calcite. To date conellae have been interpreted in many different ways: (i) as organisms (gastropods, cirriped crustaceans, or disciniscid brachiopods), (ii) pre-diagenetic syn vivo features, i.e., biologically controlled or induced, the product of remote biomineralization, (iii) and diagenetic, i.e., abiogenic origin and post-mortem. The proposed processes of conellae formation seem insufficient to explain conellae related phenomena. Further, their assumed primary aragonitic or calcitic mineralogy are reviewed and based on new material critically assessed. The stratigraphic range of conellae extends from the Middle Ordovician and probably to modern Nautilus. Predominantly, conellae can be found on internal moulds along the keel, ribs or nodes, umbilical shoulder, at the transition between phragmocone and body chamber, and can be associated with repaired scars. However, conellae are also common on the smooth body chambers of large macroconchs of Jurassic ammonites. Conellae, which are located on ammonite body chambers, are filled with the same material found in the body chamber and can contain small burrows, sand grains, or coprolites. Some of these conellae are partially covered with nacreous shell material. Limonitic conellae were also found on the limonitic internal moulds of orthocone nautiloids. Moreover, disciniscid brachiopods found on inoceramid bivalves were re-identified herein as conellae. A short guide for conellae identification has been provided herein.
... Ammonoids, middle-late Paleozoic and Mesozoic chambered cephalopods, also had siphuncles, but the structure of their siphuncle soft tissues is poorly known. Soft tissues are rarely preserved in ammonoids (but see Doguzhaeva et al. 2007;Klug et al. 2012;Mironenko 2015a) and siphuncles are not an exception to this general rule. Although fossilized soft tissue remains have been found in siphuncle tubes of several ammonoids (Drushchits and Doguzhaeva 1981;Weitschat 1986;Barskov 1990Barskov , 1996Weitschat and Bandel 1991;Zakharov 1996;Tanabe et al. 2000Tanabe et al. , 2015, original structure is only distinguishable in remnants of a few specimens. ...
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Ammonoid soft tissues are rarely preserved and such findings are of considerable interest. Extremely little is known about the structure of ammonoid siphuncle soft-parts. Until now indisputable fossilized siphuncle soft tissues were known only in a few ammonoid genera. This article describes phosphatized soft tissues inside the siphuncle tubes of the Upper Jurassic (upper Volgian) ammonite Kachpurites fulgens from Central Russia. Crosssectional views of several Kachpurites siphuncles show a large blood vessel in the center surrounded by four smaller ones. In several specimens, the siphuncle epithelium is preserved. The size and arrangement of the blood vessels in Kachpurites is nearly identical to previously described blood vessels in the siphuncles of Recent Nautilus and the Permian prolecanitid ammonoid Akmilleria electraensis. This similarity indicates a remarkable conservatism of ammonoid siphuncles and provides grounds for the assumption that the last common ancestors of Ammonoidea and Nautilida also had the same structure of the siphuncle soft tissues.
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Here we report new data on the Upper Triassic Polzberg Konservat-Lagerstätte in the Northern Calcarous Alps of Lower Austria. We examined new fossil material obtained from bed-by-bed collections of the well-laminated Reingraben Shales. Over 5290 new fossils of various marine taxa were collected within the fossiliferous layers from the Early Carnian (Julian 2 Ib, Austrotrachyceras austriacum Zone). The newly collected assemblage comprises ammonoids ( Austrotrachyceras , Paratrachyceras , Carnites , Simonyceras ), belemnoids ( Phragmoteuthis , Lunzoteuthis ), bivalves ( Halobia , div. indet taxa), gastropods (caenogastropods/heterobranchs), thylacocephalan arthropods ( Austriocaris, Atropicaris ), crustaceans (the decapod Platychela and isopods Obtusotelson , Discosalaputium ), branchiopods ( Euestheria ), polychaetes ( Palaeoaphrodite sp. and an unidentified eunicid polychaete), acytinopterygians ( Saurichthys , Polzbergia, Peltopleurus, Habroichthys ), cartilaginous fishes ( Acrodus ), coelacanth fish ( “Coelacanthus” ), a lungfish ( Tellerodus ), and numerous conodont clusters ( Mosherella ). Bromalites (coprolites and regurgitalites) produced by piscivorous actinopterygians and durophagous fish accompany the Polzberg palaeobiota along with rare plant remains ( Voltzia, div. indet plants). Based on new findings the palaeobiota characterises an intermittent colonisation by abundant benthic halobiid bivalves and a predator-dominated (fish, belemnoids) nektic community. The prerequisites for high-quality preservation—calm and oxygen-depleted conditions—prevailed at the sea floor of the Polzberg Konservat-Lagerstätte . Normal marine conditions prevail in the Reifling Basin, occasionally interrupted by freshwater influx. New in situ findings of benthic and nektic taxa highlight the great value of the unique Polzberg palaeobiota and the autochthonous deposition of the inhabitants within the palaeohabitat. The fauna and flora from the Polzberg Konservat-Lagerstätte , deposited during the Carnian Pluvial Episode or Carnian Wet Intermezzo, points to a carbonate platform decline followed by the deposition of laminated deposits in warmer and wetter conditions.
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Ammonoid soft parts have been rarely described. Here, we document the soft parts of a perisphinctid ammonite from the early Tithonian of Wintershof near Eichstätt (Germany). This exceptional preservation was enabled by the special depositional conditions in the marine basins of the Solnhofen Archipelago. Here, we document this find and attempt to homologize its parts with various organs such as the digestive tract, reproductive organs, the mantle cavity with gills, and the hyponome, with differing degrees of reservation. Alternative interpretations are also taken into account. We suggest that the soft parts were separated from the conch either taphonomically (following necrolytical processes affecting the attachment structures) or during a failed predation, where a predator (fish or coleoid) removed the soft parts from the conch but then dropped them. This find is interesting because it adds to the knowledge of ammonite anatomy, which is normally hidden in the conch. The reproductive organs show traces of what might have been spermatophores, thus supporting the hypothesis that the microconchs represented the males.
Ammonoids had a great variety in shape of the suture septal lines in their shells that sparked a plethora of hypotheses about the reasons for their complexity; from strengthening the shell wall against implosion to improvement of muscle attachment onto the septal wall and increased retention of the cameral liquid in the phragmocone chambers. In the present study, simultaneous presence of air and water in the last chambers of the phragmocone and change in acceleration during jet propulsive movement were briefly reviewed. As both water and air were present in the same chamber, periodic alternation of acceleration and deceleration should induce subsequent water displacement ('sloshing') due to inertia. This would periodically displace the centre of gravity of the shell making the movement less stable and energy efficient. Analysis of complexity of the suture shape in the dorsal, flank and ventral sides of the shell chambers suggests yet another hypothesis of the suture line variety. More complex suture line in the flank should decrease the water movement at maximum torque when a chamber is half full of liquid. It was hypothesized that the ammonoids evolved a unique way to obstruct the water displacement in the chambers with their fluted septa acting as 'wave breakers' that dissipate the 'wave' on the boundary between water and air. Animals that moved slowly without sudden changes in acceleration had a simple suture line and were either planktonic or grazing predators cruising with more or less constant speed. Complex sutures in advanced ammonoids indicated their ability to sharply change the velocity of their movement when chasing their prey or escaping from predators.
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Ammonoidea is a subclass of cephalopod mollusks that existed in the seas from the end of the Devonian to the very end of the Cretaceous. Due to the beauty and variety of the forms of ammonoid shells, they have become the subject of collecting, whereas their rapid evolution and widespread distribution made them an important tool for biostratigraphy. However, in spite of the abundance of ammonoid shells in Paleozoic and Mesozoic deposits, their popularity among professional and amateur paleontologists as well as their significance for stratigraphy, ammonoids themselves had remained highly enigmatic creatures until recently. However, in the last two decades the situation has improved significantly. New findings of well-preserved ammonoid shells shed light on the structure of the muscular system of ammonoids and areas of attachment of soft tissues to the shell, the structure of the siphuncle soft tissues, the digestive system and the jaw apparatus. A detailed study of the embryonic development of modern cephalopods and the latest discoveries in the evolution of the entire Cephalopoda allowed us to draw conclusions about the structure of those parts of the ammonoid soft body that have not yet been found in the fossil state. At present, it can be considered as proven that the ammonoids had well-developed eyes, a complex system of retractor muscles, a powerful hyponome and a wrinkle layer, similar to the black layer of Nautilida, which played an important role in the swimming and manoeuvrability of ammonoids. Ammonoids, like other cephalopods, initially had ten arms. The soft tissues of the siphuncle were similar to those of modern Nautilus, although they differed in some details. This publication summarizes current data on the anatomical structure of ammonoids, including those based on the findings made by the author in the Jurassic localities of Central Russia. It also discusses the paleobiology of ammonoids, such as in vivo orientation of their shells in the water, the mechanism of the swimming and ammonoid reproduction.
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New examinations of numerous steinkerns of the Middle Triassic nautiloid Germanonautilus from southern Germany revealed new anatomic, ecologic, and taphonomic details, which are compared with Recent Nautilus. The attachment structures of the cephalic retractor muscle (large scar) and of the dorsal (black layer) and the posterior mantle (posterior narrow scar, anterior band scar of the mantle and septal myoadhesive bands), some with tracking bands (recording the anteriorward movement of the soft body during ontogeny), were seen in several specimens. The shape and proportions of these soft-tissue attachment structures resemble those of Recent Nautilus macromphalus and indicate a similar soft part anatomy. Based on their conch geometry, the mode of locomotion of Germanonautilus is reconstructed. Owing to the wide whorl cross section and the high whorl expansion rate, drag of the conchs was high, the aperture was oriented at an oblique angle which made Germanonautilus a rather slow horizontal swimmer. Because of their large sizes and widths, conchs of Germanonautilus were often deposited on their broad venters, forming elevated "benthic islands" (secondary hardgrounds). A broad range of animals (fish, decapods, ophiurans, crinoids, brachiopods, bryozoans, bivalves, Spirorbis, foraminiferans) lived in and on these comparatively large secondary hardgrounds.
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The parabola-bearing shells of the Callovian ammonite Indosphinctes (Elatmites) submutatus Nikitin from Ryazan Region, Central Russia, are examined using morphological, ultrastructural and chemical approaches to clarify the functional significance of the parabola. The parabolae are missing in the embryonic shell that is comparatively large (about 1.5 mm in diameter) and has a prismatic shell wall, with the exception of the nacreous primary varix. There are no parabolae at the early post-hatching stage at which the shell wall consists of the outer prismatic, middle nacreous and inner prismatic layers. The parabolae are observed in small and medium-sized shells (about 15-30 mm in diameter) in which the bulk of the lateral and ventral portions of the shell wall are formed by the nacreous layer, and the outer prismatic layer seems to be missing. The thin dorsal wall lacks the nacreous layer, and the adjacent whorls are connected via a structureless layer showing a nano-granular ultrastructure. Beyond the contact of the whorls, the broken rolled ends of this layer are only preserved at the corners between the neighboring whorls. This perishable layer contains N (an indicator of organic ingredient preserved), C, O, Mg, Ca, Fe, Zn, and Sr. The same elements are detected in the structureless shell material from repaired injuries of the shell wall. There are about seven parabolae in a whorl. The parabolae are commonly exhibited on the exposed dorsal wall when the next whorl is broken. The parabolae are also observed on the outer shell surface not yet covered with the dorsal wall of the next whorl. The body chamber is about 330° in spiral length. The paired adorally 'opened' parabolic 'notches' are expressed either as small knobs on internal moulds, as nodes on the dorsal wall, or as a contour reinforced with minor relief on outer surface of the body chamber. A parabolic node represents a lens-like inclusion into the nacreous layer of the shell wall and is composed of flattened, loosely packed spherulites and nacreous micro-chips. Based on these observations it is suggested that (1) the shell of I. (E.) submutatus, excepting early ontogenetic stages, was coated with an organic-rich layer, possibly secreted from the outside like the outer plate in the shell wall of extant Spirula; (2) the parabolae served as attachment structures related to the mantle attachment inside and outside the body chamber.
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Black bituminous substance from the body chamber in six shells of the Late Triassic ceratitid Austrotrachyceras was investigated with the scanning electron microscopy and energy dispersive spectrometry to elucidate whether it originated from the soft body tissues. The shells come from the Carnian beds in the Northern calcareous Alps of Lunz (Lower Austria). The interpretation that the analyzed black substance in the body chamber represents fossilized mantle, in places intercalated by dispersed, fossilized ink substance, is supported by ultrastructural comparison with (1) bituminous plant remains from a shale slab with Austrotrachyceras shells, (2) black substance from an orthoconic cephalopod shell from the Ordovician in Sweden, (3) industrial asphalt, (4) dried ink from recent squid Loligo, (5) fossilized mantle, ink sac and ink in Jurassic "fossil teuthid" Loligosepia and ink substance in Teudopsis, (6) fossilized mantle in belemnoids Belemnoteuthis and Megateuthis, (7) ink from fossilized ink sacs of Aptian and Late Carboniferous coleoids. In the mantle of Austrotrachyceras the fibers show a granular replacement, and the C-content is approximately 65 per cents of the total weight (EDAX data). This indicates that the soft body tissues probably have been reworked by carbon-accumulating bacteria. Bacteria and fungi are abundantly preserved on the surface of the black substance. The external mantle surface shows a regular honey-comb pattern with the diameter of the cells about 3-4 um. Their size and shape are similar to those of the nacreous tablets of the nacreous layer on the inner surface of the body chamber. The mantle has a fine lamellar ultrastructure and a fibrous ultrastructure of each lamella. It lacks alternating circular and radial muscular bundles, and a criss-cross pattern of the mantle tunic typical for living and fossil coleoids. This is interpreted as an evidence of a "primitive" structure of a less muscular mantle in Austrotrachyceras and in ammonoids in general. The idea that the ammonoids secreted an ink substance (Lehmann, 1967, Mazur, 1971) is supported by new observations.
One of the most intriguing paleobiological problems in ammonoids is to interpret the organization of their muscular system in order to obtain a better understanding of their locomotion and, ultimately, their mode of life. Despite the effects of diagenesis, many ammonoid shells have surprisingly retained visible muscle, ligament, and mantle attachment scars. These scars have been extensively investigated over the last 30 years; in fact, during the quarter of a century that has passed since the classical paper by Jordan (1968), the number of genera exhibiting preserved attachment scars has doubled and is now approximately 80.
The position of the Ammonoidea within the Cephalopoda is no longer in much dispute. Almost all those who study cephalopods agree that the Ammonoidea are more closely related to the Coleoidea than to the other ectocochleate cephalopods, i.e., the Nautiloidea (Jacobs and Landman, 1994). There also can be no serious doubts that the Ammonoidea were derived from bactritids (Jacobs and Landman, 1994). However, it is still worth the effort to state more precisely the position of the Ammonoidea within the Coleoidea clade (= Neocephalopoda) using a cladistic approach. Berthold and Engeser (1987) and Engeser (1990b) discussed the position of the Ammonoidea only in general.