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AMMONOID SHELL STRUCTURES OF PRIMARY
ORGANIC COMPOSITION
by CHRISTIAN KLUG*, THOMAS BRUHWILER*, DIETER KORN,
GUNTER SCHWEIGERT, ARNAUD BRAYARD* and JOHN TILSLEY*Palaontologisches Institut und Museum der Universitat Zurich, Karl Schmid-Str. 4, CH-8006 Zurich, Switzerland;
e-mails: [email protected]; [email protected]; [email protected]
Museum fur Naturkunde der Humboldt-Universitat zu Berlin, Invalidenstr. 43, D-10115 Berlin, Germany; e-mail: [email protected]
Staatliches Museum fur Naturkunde, Rosenstein 1, D-70191 Stuttgart, Germany; e-mail: [email protected]
UMR-CNRS 5125, Paleoenvironnements et Paleobiosphere, Universite Claude Bernard Lyon 1, 2 rue Dubois, F-69622 Villeurbanne Cedex, France;
e-mail: [email protected]
Ansell Road, Sheffield S11 7PE, UK; e-mail: [email protected]
Typescript received 18 May 2006; accepted in revised form 30 November 2006
Abstract: Palaeozoic and Mesozoic cephalopod conchs
occasionally reveal dark organic coatings at the aperture. A
number of these coatings, including still unrecorded exam-ples, are described, figured and interpreted herein. On the
basis of elemental analysis, actualistic comparison and a
comparison with Triassic bivalves, some of these coatings are
shown to consist of apatite and primarily probably of
conchiolin (and also probably melanin). In several Mesozoic
ammonoid genera such as Paranannites, Psiloceras, Lytoceras,
Phylloceras, Harpocerasand Chondroceras, some of these coat-
ings (recorded herein for most of these taxa for the first
time) are interpreted as a structure similar to the black band,
which was previously known only from Recent Allonautilus
and Nautilus. In contrast to these nautilid genera, however,
the organic material of some Mesozoic ammonoids was notdeposited on the inside of the shell but externally, albeit
positioned at the terminal aperture as in Recent nautilids.
Some ammonoids of Carboniferous and Triassic age show
several such bands at more or less regular angular distances
on the ultimate whorls and at the aperture, e.g. Nomismo-
ceras, Gatherites, Owenites, Paranannites, Juvenites and Mel-agathiceratidae gen. et sp. nov. Triassic material from Oman
shows that the black coating was probably secreted from the
inside, because the position of this organic deposit changes
from interior to exterior in an anterior direction (i.e. adaper-
turally). This structure has previously been referred to as a
false colour pattern and is here interpreted as having been
formed at an interim aperture or megastria (alter Mund-
rand). All structures discussed in the paper are considered
to have been secreted by a single organ and to have been ini-
tiated by some form of stress or adverse conditions. Thus,
certain environmental parameters and growth anomalies
appear to have influenced their formation.
Key words: Ammonoidea, mature modifications, body
chamber, growth, taphonomy.
Among fossil invertebrates, molluscs probably represent
the most useful group for studying ontogeny and growth.
Growth changes are recorded in most molluscan shells
and usually are preserved even on internal moulds. In
some cases, these growth changes permit interpretations
with respect to changes in mode of life and habitat (e.g.
Nutzel and Fryda 2003; Klug and Korn 2004). A fascinat-ing topic is the morphogenetic countdown (Seilacher
and Gunji 1993; Seilacher and LaBarbera 1995) that has
been postulated for some ammonoids. Terminal growth
of ammonoids is remarkable because it is occasionally
associated with drastic changes in shell morphology (e.g.
the ultimate whorl of many heteromorph taxa; see Davis
et al. 1996 and references therein).
Among Recent nautilids (compare Collins and Ward
1987; Ward 1987; Text-fig. 1), mature specimens show
(1) a shell growth band (shell thickening at the apertural
edge, up to 25 mm wide and 1 mm thick); (2) a black
band at the aperture (this character is not expressed in all
adults according to Ward 1987); (3) a deepening of the
ocular sinuses; (4) a reduction of whorl height by a
decrease in whorl expansion rate; (5) a reduction of
whorl width by a decrease in whorl width expansion rateand a simultaneous formation of a more rounded venter;
(6) septal thickening (the last septum is up to 30 per cent
thicker than the penultimate septum); (7) septal crowd-
ing; (8) a distinct maximum shell diameter (a poor char-
acter because of variability); (9) a white ventral area; (10)
an increase in body chamber length (caused by narrowing
of the whorl section); and (11) a reduction of cameral
liquid (probably to compensate for additional shell mate-
rial at the aperture and a longer body chamber). Among
[Palaeontology, Vol. 50, Part 6, 2007, pp. 14631478]
The Palae ont ological Associa tion doi: 10 .1 11 1/j.1475 -4983 .200 7.007 22.x 1463
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these modifications, septal crowding is probably the most
widely known phenomenon that has also been described
for many fossil chambered ectocochleate cephalopods.
Except for 9 and 11, all the phenomena listed (although
often slightly differing in one aspect or another) are also
known in ammonoids (compare Sun 1928; Davis 1972;
Davis et al. 1996). Some of these, however, are quite rare.
For example, questionable fossil remains of the black
band have, to our knowledge, been documented just once
(Klug 2004). For it to be fossilized, organic matter needs
to be preserved because originally it consisted of conchio-
lin and melanin. Conchiolin (or conchin) is made up of a
chitinous albuminoid and, as such, has a moderately low
preservation potential (Allison 1988; Briggs et al. 1993;
Kear et al. 1995; Briggs and Wilby 1996).
In specimens described by Klug (2004), remains of the
black band and black aperture had transformed to apatite.
The black band was first described for Recent nautilids
(Saunders and Spinosa 1978; Doguzhaeva and Mutvei
1986; Collins and Ward 1987; Ward 1987; Mutvei et al.1993; Mutvei and Doguzhaeva 1997). It is usually repre-
sented by a dark line of varying width (15 mm) and
thickness (< 1 mm) that surrounds the inside of the aper-
ture in mature specimens. In most of the ammonoids
described below, this dark material apparently lies on the
outside of the conch, leading to the question as to
whether this structure is really the same as in Recent nau-
tilids.
Here we describe and illustrate some examples of am-
monoids from the Carboniferous of Great Britain, the
Triassic of Oman, Nevada, South China and Germany,
and the Jurassic of Germany that preserve black bands
and related structures. The origin and formation of these
structures are discussed and interpreted.
T E R M I N O L O G Y
The black band
The black band (Saunders and Spinosa 1978; Collins and
Ward 1987; Ward 1987; black border of Stenzel
1964) is a structure at the terminal aperture in Recent
nautilids consisting of conchiolin and melanin (Comfort
1950). It surrounds the adult aperture in a band of vary-
ing width and thickness and passes gradually into the
black layer (Stenzel 1964). Although most of the organic
matter is found in the interior of nautilids and externally
in several ammonoids, this structure is here referred to
as the black band for simplicity. In Recent nautilids, itdoes not display the dark coating in all adult specimens
(Ward 1987), which might in part account for the fact
that this structure is rare among ammonoids. We may
speculate that a combination of terminal growth and
environmental stress is required for the formation of this
structure.
The function of the mantle adhesive layer in Recent
nautilids has been discussed by Mutvei et al. (1993) and
Mutvei and Doguzhaeva (1997). According to these
authors, the anterior mantle margin was attached to the
apertural mantle attachment layer with vertical pores
(Mutvei and Doguzhaeva 1997, text-fig. 10); the latter
contained finger-like epithelial extensions. Apparently,
the apertural mantle attachment is rather weak in Recent
nautilids and appeared to function in preventing water
from entering between the mantle and shell, particularly
during swimming (Mutvei et al. 1993, p. 11).
The black layer
The black layer (Ward 1987; Keupp 2000; Kulicki et al.
2001; Klug and Lehmkuhl 2004; Klug et al. 2004; black
film of Stenzel 1964 and black deposit of Mutvei and
Doguzhaeva 1997) is an organic part of the dorsal shell.In Recent nautilids and in some ammonoids, it projects
dorsally out of the body chamber. Behind the aperture,
increasingly thick layers of lustrous shell cover the organic
material, causing an increasingly light colour. In Recent
nautilids, the mantle margin secretes both the black layer
and the black band. According to Pruvot-Fol (1937),
these black structures represent excretions of metabolic
waste like cephalopod ink which all contain melanins
(Comfort 1950). This fact also questions the interpreta-
T E X T - F I G . 1 . Nautilus pompilius (Linnaeus, 1758), in section
PIMUZ 7806; Recent; locality unknown; with black band
(photograph Heinz Lanz, Zurich).
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tion of organic matter in the body chamber of a Triassic
ammonoid as fossil ink by Doguzhaeva et al. (2004). This
material might equally represent remains of the black
layer.
Adverse life conditions as well as injuries may also
cause deposition of conchiolin, darkening the conch more
or less locally or at an interim or terminal aperture
(Landman and Cochran 1987; Saunders et al. 1987; Ward
1987; Keupp and Riedel 1995; Rein 2000, 2002; Klug and
Lehmkuhl 2004). On the basis of shape, Klug (2004)
referred to these structures as black stripes (a spiral
stripe caused by a punctiform injury) or black apertures
(superficially resembling a black band, but much wider).
The black aperture
The black aperture (Klug 2004) is a black line of varying
width formed at an interim aperture caused by adverse
conditions or injuries (see, e.g. Keupp and Riedel 1995).Like the black band, it encircles the aperture, yet not
necessarily the terminal one, and also consists of conchi-
olin.
The black stripe
The black stripe (Klug 2004) is a black spiral band, start-
ing at a minor shell injury which occurred at a former
apertural edge. For this structure, the terms Rippensche-
itelung, forma verticata, forma pseudocarinata and
forma semiverticata have been introduced for ammo-
noids (Holder 1956, 1977; Keupp 1979, 2000; Hengsbach
1996), although the black deposits that occasionally
accompany these injuries are rarely preserved. These
structures represent the regenerative reaction of molluscs
to a punctiform injury of the apertural epithelium, often
caused by arthropod attacks (see Keupp 2000 and refer-
ences therein). It is very likely that at least some of these
healed injuries were originally accompanied by a black
line now no longer preserved.
False colour patterns
False colour patterns (Mapes and Davis 1996) include
more or less regular transverse patterns that can be asso-
ciated with constrictions, megastriae and pseudoconstric-
tions, as well as with spiral lines formed by the umbilical
seam of a missing subsequent whorl which cross the false
colour patterns. Normally, they are parallel to growth-
related structures such as those listed above (see Mapes
and Sneck 1987). Usually, more than one such line occurs
within a single whorl.
True colour patterns
Colour patterns have been recorded from numerous fossil
cephalopod shells including various Palaeozoic nautiloids
and CarboniferousCretaceous ammonoids (Mapes and
Davis 1996). Presumably, these patterns consisted of pig-
ments (mainly melanin and porphyrins) stored in eitherthe periostracum or the outer part of the shell as in
Recent molluscs (Hollingworth and Baker 1991). These
structures are not discussed herein as numerous articles
on this subject are available (for references, see Mapes
and Davis 1996).
Siphuncle
As the connecting rings of ammonoids are also of organic
composition, these have to be listed here, too. This part
has also been examined and discussed frequently (for a
review and references, see Tanabe and Landman 1996).Remarkably, details of soft-tissues within the siphuncle,
including blood vessels, have been discovered and
described by Tanabe et al. (2000).
Institutional abbreviations: MHI, Muschelkalkmuseum Hagdorn,
Ingelfingen; PIMUZ, Palaontologisches Institut und Museum,
Zurich University; SMNS, Staatliches Museum fur Naturkunde,
Stuttgart; Zx, British Geological Survey, Nottingham.
D E S C R I P T I O N O F S P E C I M E N S
Carboniferous
Carboniferous strata have yielded surprisingly well-pre-
served ammonoid specimens which often show highly
unusual details. For instance, the first radulae to be dis-
covered were in specimens of Eoasianites from the Car-
boniferous of Uruguay (Closs and Gordon 1966; Closs
1967; Bandel 1988) and the oldest aragonitic goniatitids
come from the Pennsylvanian (Desmoinesian) Buckhorn
Shale of Oklahoma (Smith 1938; Kulicki et al. 2002).
Two specimens of Nomismoceras vittiger (Phillips,
1836) with coarsely recrystallized shells of Asbian (Early
Carboniferous) age from Derbyshire are available(Zx2212, 2288; Text-fig. 2), measuring 19 and 26 mm in
diameter and collected at Treak Cliff near Castleton
(Korn and Tilsley 2006). Both display roughly equidistant
dark lines that are clearly symmetric, and which can
be traced back on two to three younger whorls in the
umbilicus. In both specimens, the dark bands lie within
zones of thickened shell. It is important to note that the
anterior edge of each of these dark bands is more clearly
defined than the posterior one. This is because shell
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thickness between the black material and shell exterior
increases posteriorly. About two to three such bands can
be seen per whorl; they form a little projection on the
umbilical edge, followed by a strongly asymmetrical sinus
and an adjacent parabolic ventrolateral projection. On the
venter, the bands form moderately deep U-shaped
sinuses. EDAX analyses have yielded no data on the
origin of the black material; possibly it is still covered by
a very thin layer of calcite.
Triassic
Remarkably, Triassic deposits worldwide have yielded
ammonoids with organic remains preserved. Much that
is currently known about ammonoid palaeobiology was
gained from Triassic material. One of the most specta-
cular examples are the phosphatized ammonoids from
Spitsbergen which preserve, in addition to delicate
remains of septa, significant portions of the digestivetract, beaks with radula and even gill remains (Leh-
mann and Weitschat 1973; Lehmann 1985; Weitschat
1986; Weitschat and Bandel 1991, 1992). Diversity, and
preservation of colour patterns and black layers in part
account for the fame of Triassic ammonoids from Fos-
sil Hill or Crittenden Springs in Nevada (Smith 1932;
Kummel and Steele 1962; Mapes and Davis 1996;
Keupp 2000). Some specimens collected there also show
the black band. In Oman, Early Triassic ammonoids
occur in exotic blocks of Hallstatt facies in deep-water
strata of the Hawasina unit (Blendinger 1991, 1995;
Tozer and Calon 1990). Although most of these are
difficult to extract and prepare, preservation is some-
times excellent. In rare cases, remains of false colour
patterns have been found. In contrast, Early Triassic
ammonoids from South China are numerous and easily
collected. However, so far no colour patterns have been
documented, except for some rare, recently discovered,
specimens that display intriguing false colour patterns
and other kinds of black structures.
Finally, ammonoids from the Muschelkalk (Middle Tri-
assic) of the Germanic Basin have received some atten-
tion, not just in view of their utility as stratigraphical
tools but also for their superficially poor preservation,
which make them interesting study objects for tapho-
nomic analyses (e.g. Kumm 1927; Seilacher 1963, 1966,
1968, 1971; Mayer 1968; Mundlos 1970; Aigner 1975; Du-
ringer 1982; Hagdorn and Mundlos 1983; Mundlos and
Urlichs 1990; Maeda and Seilacher 1996; Klug 2001; Zeeh
and Hagdorn 2002; Klug et al. 2004, 2005a, b). These am-
monoids have not been fully appreciated previously,
which is demonstrated by the fact that in recent years,
several specimens that preserve originally organic struc-
tures such as the black layer, the black band, black aper-tures, organic membranes in the phragmocone and
elsewhere have been found and described (Rein 1993,
1995, 2005; Klug 2004; Klug et al. 2004, in press). These
are structures that are rarely preserved otherwise (e.g.
Weitschat and Bandel 1992).
From the Early Triassic Thaynes Formation of
Nevada, USA, two well-preserved specimens of Paranan-
nites slossi (Kummel and Steele, 1962) (Jenks Coll. nos.
269C, 499C) and one of Juvenites septentrionalis Smith,
1932 (Jenks Coll. no. 499C; see Text-fig. 3) were put at
our disposal by J. Jenks (Salt Lake City), who collected
them from the Euflemingites romunderi Zone at Critten-
den Springs (Elko County, Nevada). The Paranannites
specimens measure 27 mm (No. 499C) and 31 mm
A
B
C
T E X T - F I G . 2 . The Early Carboniferous ammonoid Nomismoceras vittiger (Phillips, 1836) from Treak Cliff near Castleton, Derbyshire
(UK). A, Zx2212. BC, Zx2288. Note the black lines on the outer whorls visible at irregular distances.
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(No. 269C) in diameter. All three retain calcitic replace-
ment shell and display more or less regular radial, dark
bands. On account of the densely spaced growth lines
and apertural shell thickening, the two specimens of
Paranannites were apparently adult. These two also have
remains of the black layer and wrinkle layer (Runzel-
schicht; Walliser 1970; Bayer 1974). One of these speci-
mens (499C) shows a darkened terminal aperture
(Text-fig. 3A).
Well-preserved Early Triassic ammonoids are also avail-
able from Oman from an exotic block of Hallstatt facies
at Wadi Musjah (75 km SSW of Musqat). Two specimens
of Paranannites sp. with false colour patterns (Text-
fig. 4AE) were collected from a bed also yielding Owe-
nites koeneni Hyatt and Smith, 1905 and Inyoites oweni
Hyatt and Smith, 1905 of Smithian age. They measure
19 mm (PIMUZ 26262) and 20 mm (PIMUZ 26263) in
diameter. Because of the relatively dense spacing of
growth lines and constrictions near the aperture, PIMUZ
26262 was apparently adult; most representatives of thisspecies are roughly the same size and thus most of them
were probably adult too (including PIMUZ 26263). Both
specimens have remains of the wrinkle layer. They show
several black lines that extend symmetrically from the
umbilical shoulders around the venter and coincide with
shell thickenings posterior of constrictions. The width of
these lines does not increase towards the venter but
remains constant. The anterior edge of the lines follows
the shell constrictions. The posterior edge is more or less
parallel to the anterior one and therefore crosses growth
lines. As in the Carboniferous material, the anterior edge
of these dark bands is more clearly delimited than the
posterior edge. Posterior of the constrictions, the dark
material is located internally in the thickened shell, and
the outermost shell layer is not coloured (Text-fig. 4E).
Towards the aperture, the dark material crosses the shell
from within and surfaces so that the entire shell is col-
oured at the constrictions.
A well-preserved Early Triassic representative of the
Melagathiceratidae (gen. et sp. nov.; PIMUZ 25900) from
Jinya (Guangxi, South China; Flemingites rursiradiatus
beds) also displays intriguing remains of dark material
(Text-fig. 4FJ). Interpretations of these are ambiguous.
Indeed, the specimen clearly displays symmetrical black
lines extending from the umbilicus to the venter, coincid-ing with constrictions as in the Omani specimens of
Paranannites. The dark material of the lines is also con-
centrated only at the constrictions. At the aperture, prob-
able equivalents of the black band and black layer are
visible on the inside of the shell. A more questionable
dark pattern is seen on the umbilical wall, which gener-
ates a black spiral line. It is difficult to identify the origin
of this structure, which rather appears as a dark calcitic
crust covering the umbilical wall.
Only three cephalopod specimens from the German
Upper Muschelkalk of northern Baden-Wurttemberg
(southern Germany) that display remains of the black band
or black aperture are available. One of these (SMNS 65424)
is a specimen ofCeratites postspinosus Riedel, 1916 measur-
ing 139 mm in diameter and thus more or less adult, which
is corroborated by a slight increase in umbilical width char-
acteristic of adultCeratites. It was collected from the Schon
and Hippelein quarry at Neidenfels from Upper Muschel-
kalk marls (postspinosus Zone, Ladinian). This specimen
displays irregular and poorly preserved black remains,
which extend radially over 48 mm and spirally over
176 mm. As in the following specimen, the black material
does not surround the entire aperture, demonstrating
incomplete preservation, partial sediment filling only and
pressure solution. This and the next two specimens have
previously been discussed by Klug (2004).
Ceratites meissnerianus Penndorf, 1951 (SMNS 25397-3;
leg. A. Lehmkuhl and M. Urlichs) shows remains of the
black layer. Collected from a quarry near Unterohrn(northern Baden-Wurttemberg, Germany) in the Upper
Muschelkalk (semipartitus Zone, Ladinian), it probably
represents a more or less adult individual; this is indi-
cated by its large diameter (309 mm), septal crowding
and the eccentric shape of the umbilicus. At its aperture,
it preserves black remains that measure over 52 mm radi-
ally and 33 mm in maximum width. These black remains
do not surround the whole aperture and thus probably
represent only a small portion of the entire structure,
which suffered from pressure solution as well as mechani-
cal wear and breakage. As seen in the black band of
Recent Nautilus, these dark layers become lighter col-
oured posteriorly (adapically).
A specimen of the nautilid Germanonautilus bidorsatus
(von Schlotheim, 1820) showing a black line at a former
aperture was collected by H. Hagdorn at a quarry near
Garnberg (northern Baden-Wurttemberg; compressus
Zone, Anisian; MHI 919). This specimen was described
and figured by Klug and Lehmkuhl (2004; it displays the
large muscle attachment scar of the cephalic retractor as
well as faint traces of the black layer). It is mentioned
here for comparison because it preserves a narrow black
line surrounding a former aperture (not a megastria or
alter Mundrand; see also the discussion of false colour
patterns below). Judging by the abnormal depth of thehyponomic sinus, this aperture probably formed following
injury. Additionally, it continued to grow after the forma-
tion of the black line and thus, this was not the terminal
aperture. Growth increments within the hyponomic sinus,
however, display a faint but widely spaced ribbing proba-
bly reflecting a high growth rate. The data obtained from
EDAX analyses performed on the black substance of the
black line were quite interesting. Both silica and probably
apatite occur (Klug 2004), which is additionally corrobo-
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A
B
C
D
E
F
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rated by comparable analyses of a coating of ceratitid
muscle attachment structures which also revealed apatite
(Klug et al. in press).
Jurassic
A number of Jurassic ammonoids from Germany, Great
Britain and Switzerland display black lines at the aper-
tures. Most of these are of Early Jurassic age, which is not
surprising as the conditions of preservation were occa-
sionally excellent at this stratigraphic interval, for instance
in some Fossillagerstatten (for reviews, see Bottjer et al.
2002 and Selden and Nudds 2004).
1. The oldest material is of the index of the basal ammo-
noid zone of the Early Jurassic, Psiloceras planorbis (J. de
C. Sowerby, 1824). Two crushed specimens on a slab of
claystone from early Hettangian sediments at Blue Anchor
T E X T - F I G . 3 . Triassic ammonoids from southern Germany and the USA with black band and false colour patterns. AC,
Paranannites slossi(Kummel and Steele, 1962) and Juvenites septentrionalisSmith, 1932 (Jenks Coll. no. 499C); Euflemingites romunderi
Zone (Thaynes Formation, Early Triassic), Crittenden Springs (Elko County, Nevada). A, detail of C, aperture with black band, dorsal
shell and false colour patterns. B, lateral view. C, ventral and apertural view. D, Ceratites postspinosusRiedel, 1916 (SMNS 65424);
postspinosus Zone (Ladinian, Upper Muschelkalk), Neidenfels, northern Baden-Wurttemberg; note remains of the black band
(photograph Wolfgang Gerber, Tubingen); modified after Klug (2004). EF,Ceratites meissnerianus (Penndorf, 1951) (SMNS 25397-3);
semipartitus Zone (Ladinian, Upper Muschelkalk); Unterohrn, northern Baden-Wurttemberg; note remains of a questionable black
band and septal crowding. E, detail of F showing remains of the black band. F, lateral view of entire specimen with the black band
(photograph Wolfgang Gerber, Tubingen). DF modified after Klug (2004).
AB
G H
I J
F
E
DC
T E X T - F I G . 4 . Early Triassic
ammonoids from Oman and South
China with false colour patterns and
other possible organic remains. AE,
Paranannitessp., Owenites koeneni beds
(Smithian), from Wadi Musjah (75 km
SSW of Musqat, Oman). AB, PIMUZ
26262, lateral and ventral views. CE,PIMUZ 26263. C, lateral view. D, ventral
view. E, detail of D showing cross-
section of shell with two dark stripes at
constrictions; note that the dark material
crosses the shell in an anterior direction.
FJ, Melagathiceratidae gen. et sp. nov.
(PIMUZ 25900),Flemingites
rursiradiatus beds (Smithian), Jinya
(Guangxi, South China). F, lateral view.
GH, apertural view. IJ, view of umbo
showing black material on umbilical wall
forming a spiral; note that Paranannites
clearly displays false colour patterns;
in contrast, dark remains ofMelagathiceratidae gen. et sp. nov. are
more difficult to interpret in terms of
organic deposits.
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(Watchet, Somerset, UK; PIMUZ 6519; Text-fig. 5) were
collected by G. Kahn (Zurich); one is nearly complete
and measures 49 mm in diameter. Both preserve the ara-
gonitic shell and the terminal aperture. Anterior to the
aperture, the black layer is clearly visible on the venter of
the penultimate whorl of specimen A. Additionally, the
other specimen (B) shows a trace of the black layer at the
umbilical seam. The most interesting structure, however,
is the black band, which is well preserved in both speci-
mens. Its colour is slightly lighter than that of the black
layer and its position is 12 mm behind the aperture in
PIMUZ 6519 (leaving a narrow white stripe) and directly
at the aperture in other specimens (e.g. PIMUZ 12581;
same locality and strata). This structure was found in
many specimens from this locality.
A poorly preserved individual that also showed this
black band was subjected to EDAX analyses at Tubingen
University. These element analyses, however, did not yield
any sign of preservation of originally organic material.
Elements identified indicate the presence of calcium car-bonate and clay minerals.
2. An additional lot of three specimens collected from the
Posidonienschiefer Formation (Posidonia Shale, Toar-
cian, Early Jurassic) of southern Germany are on display
in museums, which is why we did not take samples for
elemental analyses. Phosphatized, originally organic,
structures are well known from this stratigraphic unit;
thus, we assume the black structures seen in these speci-
mens to be phosphatized as well. This conclusion is sup-
ported by the similar appearance of associated, primarily
chitinous, ammonoid beaks.
The first specimen, identified as Phylloceras(Phylloceras)
heterophyllum (J. Sowerby, 1820), and collected at Ohm-
den from the Fleins Bed (tenuicostatum Zone, semicelatum
Subzone), is on exhibit at Stuttgart (SMNS 26462; Text-
fig. 6). It measures 87 cm in diameter and was thus most
likely adult at death, which is also evident from coarser
growth lines, large size and presence of the black band. At
its terminal aperture, it displays a black line of varying
width (almost 10 mm). In addition to this, it preserves the
lower and upper beak in the body chamber. This is of
interest because the beaks and the black band apparently
show the same type of preservation, indicating a similar,
originally chitinous composition. Usually, only the perios-
tracum of the ammonoid shell was left, as demonstrated
by Seilacher et al. (1976). From this it might be concluded
that the black band was part of the periostracum, and thus
probably external as in specimens from other localities.
Another large, and most likely adult, specimen (SMNS
26465; Text-fig. 7) from the Posidonienschiefer Forma-
tion, assigned to Lytoceras ceratophagum (Quenstedt,1885), is also from Ohmden, having been collected from
the Unterer Schiefer Bed (falciferum Zone, elegantulum
Subzone). It measures 41 cm in diameter, and shows the
black line very clearly, delimited posteriorly by an alter
Mundrand (megastria) and anteriorly by the terminal
aperture. The distance between these two is 30 mm;
nearly 20 irregular growth lines or lirae are seen therein.
This black band was probably part of the periostracum.
The third specimen is an adult Harpoceras (Harpoceras)
falciferum (J. Sowerby, 1820) from Holzmaden (falcife-
rumbifrons zone, falciferumlower commune subzones),
T E X T - F I G . 5 . Psiloceras planorbis (J. de C. Sowerby, 1824) (PIMUZ 6519); planorbis Subzone (planorbis Zone, Hettangian, Early
Jurassic), Blue Anchor (Watchet, Somerset, UK). Note the black band, black layer and the trace it leaves at the umbilical seam.
Natural size (photograph Thomas Galfetti, Zurich).
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housed at the Urweltmuseum Hauff and previously fig-
ured by Selden and Nudds (2004, text-fig. 150). At an
overall diameter of 24 cm, it shows narrowly crowded
ribs and a black band whose width does not exceed
5 mm at its aperture (Text-fig. 8). In addition to the
crowded ribs and its large size, the slightly widened umbi-
licus indicates that this was a mature individual.
3. The only specimen from the Middle Jurassic (Bajocian)
is a Chondroceras sp. (PIMUZ 16339) from Lupfen near
Talheim (south-west Germany; Text-fig. 9). Among seven
specimens from a small collection it is the single one that
preserves a black structure and a complete terminal aper-
ture. In this specimen, adulthood is indicated by eccentric
coiling of the last whorl; a radial constriction; a strong,prorsiradiate rib; a triangular constriction which is
restricted to the umbilical wall, and three short anterior
projections (one on each flank and one on the venter).
Remains of the black band are preserved only on the left
side, being at a very low angle to the crest of the strong
rib on the anterior flank of it and sweeping forwards on
the venter, forming part of a ventral projection. As in the
above-mentioned Psiloceras, there is a light-coloured shell
portion between the black band and the actual aperture.
It appears certain, however, that it is part of the terminal
apertural modification.
4. The last fossil (PIMUZ 7527) is of Late Jurassic (Ox-
fordian) age; it represents the only specimen in which the
black structure is probably secondary, i.e. not a true black
band (Text-fig. 9D). This specimen probably belongs to
the microconchiate genus Glochiceras. Collected at the
Lagern, a mountain ridge north of Zurich, this internal
mould measures 23 mm in diameter, which is characteris-
tic of adult specimens of this taxon. It also displays typi-
cally adult apertural modifications, a constriction and
lateral apertural apophyses. The deeper portion of this
apertural modification, i.e. the constriction and the med-
ian furrow of the right apertural apophysis, contains darkgrey matter that resembles some dendritic deposits well
known from Late Jurassic deposits in southern Germany;
magnesium oxide secondarily filled the void which was
originally occupied by shell. It differs from the true
black bands described above in composition and colour.
The presence of such secondary deposits can easily be
explained by increased shell thickness within the constric-
tion: after dissolution of the aragonitic shell, the fairly
broad void often witnessed secondary mineral deposition.
T E X T - F I G . 6 . Phylloceras (Phylloceras) heterophyllum (J. Sowerby, 1820), SMNS 26462, Posidonienschiefer Formation (Fleins Bed,
tenuicostatumZone, semicelatum Subzone; Toarcian, Early Jurassic), Ohmden (Baden-Wurttemberg, Germany). Note the upper and
lower beak in the body chamber and the black band.
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We suggest referring to this feature as a pseudo-black
band.
Recent
For comparison, a shell of Recent Nautilus pompilius
(Linnaeus, 1758) PIMUZ 7806 was examined (Text-
fig. 1). At a diameter of 183 mm, it shows the black band
directly behind the aperture. Especially the posterior mar-
gin is very irregular and the black matter fades out over
approximately 10 mm. The exact distribution of the black
material at the apertural margin is somewhat unclear
because in many museum specimens of this taxon, the
apertural edge was removed, polished or damaged during
post-mortem transport. It turned out that the black mate-rial is thickest near the umbilical plug (c. 1 mm) and
thins towards the venter to approximately 03 mm. On
the venter and in the umbilical plug, the black material
actually covers part of the surface. The black band passes
into the black layer without interruption. This feature is
not visible in fossils available to us, but we expect that
there are no differences between ammonoids and nauti-
lids in this respect. As described by Mutvei and Doguzh-
aeva (1997), the area of the black band also displays the
irregularly distributed pore canals which have not been
documented in the fossil specimens.
T E R M I N A L A P E R T U R E
All structures described here undoubtedly are related to
growth processes, except for the pseudo-black band in
Glochiceras. In other Jurassic specimens, and in Paranan-
nites from Nevada, the formation of a black band at the
aperture is clearly linked to terminal growth. Some details
of the growth patterns, however, appear to differ from
those of terminal growth in Recent nautilids (Text-
fig. 10). The main difference between the terminal
aperture and the distribution of the conchiolin in Jurassic
ammonoids and Recent nautilids is the fact that in severalammonoids the organic material is present mainly on the
shell exterior, perhaps as part of the periostracum as in
the Posidonia Shale material (compare Seilacher et al.
1976; Text-fig. 10) whereas in nautilids it can be found
mainly internally. In all of the studied ammonoids, the
black band rather represents a thickened organic coating
(like a thickened periostracum) on the outer shell surface.
Similar black lines occur behind the aperture in juvenile
ammonites (annulare Linie; Richter 2002, pp. 1314, pl.
T E X T - F I G . 7 . Lytoceras ceratophagum (Quenstedt, 1885), SMNS 26465; Posidonienschiefer Formation (Unterer Schiefer Bed,
falciferumZone, elegantulum Subzone; Toarcian, Early Jurassic), Ohmden (Baden-Wurttemberg, Germany). Note the black band.
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11, fig. 1; pl. 21, figs 4, 11), which possibly represent
interim or black apertures. In nautilids, it appears very
likely that the black band is somehow related to the aper-
tural mantle attachment, which served to prevent water
from entering between shell and mantle (Mutvei et al.
1993). Since the black band appears to be external in am-
A
B
C
D
T E X T - F I G . 9 . AC, Chondroceras sp. (PIMUZ 16339); Middle Jurassic (Bajocian), Lupfen near Talheim (Germany); note the black
band on the last rib. D, ventral view ofGlochiceras sp. (PIMUZ 7527), Oxfordian, Lagern (north of Zurich, Switzerland); note the
pseudo-black band.
black band
1 cm
T E X T - F I G . 8 . Harpoceras (Harpoceras) falciferum (J. Sowerby, 1820), photograph courtesy of Urweltmuseum Hauff;
Posidonienschiefer Formation (Posidonia Shale, falciferumbifrons zones, falciferumlowercommune subzones; Toarcian, Early
Jurassic), Holzmaden (Baden-Wurttemberg, Germany).
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monoids, it might either have resulted from gerontic
growth lacking a soft-tissue attachment function or, alter-
natively, it might be explained by the mantle that
extended out of the aperture.
F A L S E C O L O U R P A T T E R N S A N D
M E G A S T R I A E
In Carboniferous and Early Triassic material from
Nevada, Oman and South China, black lines are formed
at irregular and, apparently aperiodic, angular distances
(cf. e.g. Bucher 1997). In all of these specimens, the ante-
rior edge of these black lines is clearly delimited whereas
the lines fade out posteriorly. A specimen from Oman
(PIMUZ 26262) has helped us to understand this phe-
nomenon. A piece of shell had broken off and enabled
the study of shell cross-section at two of these bands. It
turned out that the black material covered the inside of a
former aperture, because it traverses the shell from theinside to the outside with an adoral tilt. Possibly the
structures thus formed were identical to the black band
in Recent nautilids, at least in its distribution and forma-
tion. This shows that these black lines were formed dur-
ing a growth halt. Mapes and Davis (1996) included these
structures in their category of false colour patterns, and
stated that, in many cases, these correlated with the for-
mation of constrictions, pseudo-constrictions, varices and
megastriae. The distribution of the black material in the
Omani specimen demonstrates that these lines were
formed at a growth interruption and, thus, can be inter-
preted as megastriae, previously also referred to as, for
example, alte Mundrander, demarcation lines or tran-
sitional mouth borders (Pompeckj 1884; von Mojsisovics
1886; Wahner 1894; Diener 1895; Matsumoto et al. 1972;
Bucher and Guex 1990; Matsumoto 1991; Tozer 1991; for
a review of this structure and additional references, see
Bucher et al. 1996). It is quite conceivable that this struc-
ture was also related to a temporary apertural soft-tissue
attachment as in the terminal aperture of Recent nauti-
lids. As a secondary effect, these false colour patterns
may have had similar functions (e.g. camouflage) as true
colour patterns, which are confined to the surface of the
ammonoid shell.
B L A C K A P E R T U R E
The Middle Triassic cephalopod remains of Germany donot allow an unequivocal interpretation. The smaller of
the two ammonoid specimens (Ceratites postspinosus) is
not of a size typical of adults of the species. It is unclear,
however, whether this falls within the intraspecific vari-
ability. Septal crowding is seen in this specimen but this
can easily be produced under environmental stress, as can
a black band (see Arnold 1985; Ward 1987 for Recent
nautilids). The irregular distribution of the black sub-
stance within the black line at the aperture might be some
A
B
C
D
E
F
G
T E X T - F I G . 1 0 . Schematic cross-sections through the shell; in BG at the adult aperture, in A roughly half a whorl prior to the
terminal aperture. Towards the aperture is on the right, towards the outside is to the top of the illustration. In BF the shell thickness
is estimated because the aragonitic shell is either not preserved or potentially incomplete. A, cross-sections through megastriae in
Paranannites sp. (PIMUZ 26263) containing conchiolin at an alte Mundrand. B, cross-section through terminal aperture of
Paranannites slossi(Kummel and Steele, 1962) (Jenks Coll. no. 499C), displaying a thin dark layer immediately at the aperture on the
shell surface. CD, two specimens ofPsiloceras planorbis (J. de C. Sowerby, 1824) (PIMUZ 6519 and 12581); in these specimens, the
black band is in one case (C) immediately behind, and in the other (D) directly in front of the terminal shell thickening. E, several
ammonite species from the Toarcian Posidonia Shale at Ohmden (Germany) displaying the thin, dark black band. Since only the
periostracum is preserved, the band appears to be part of the periostracum and thus, this structure was probably on the outside of the
shell. F, Chondroceras sp. (PIMUZ 16339); note the black band on the surface of the last rib. G, terminal aperture ofNautilus
pompilius(Linnaeus, 1758) (PIMUZ 7812) with the thickness relationship of the aragonitic shell and the conchiolin of the black band.
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kind of artefact. The fact that it wedges out posteriorly is
reminiscent of the state of the black band in Recent nau-
tilids. For this specimen, it appears reasonable to assume
that the black structure represents a combination of
mature modification and a structure formed under
adverse environmental conditions. In contrast, the black
line found in Germanonautilus can definitely be inter-
preted as a black aperture.
In addition to terminal growth itself, the rarity of pres-
ervation of this structure invites a discussion on the age
pyramid of an ordinary ammonoid. When studying
ammonoid taphocoenosis, usually two cases are encoun-
tered. Either only more or less adult ammonoids of
approximately the same size are found and juveniles are
exceedingly rare, or representatives of almost all growth
stages are preserved, although only very rarely represent-
ing the actual age pyramid. This phenomenon can be
explained to a large extent by taphonomic bias, i.e. early
dissolution andor breakage of fragile shells of small spec-
imens or sorting by currents, respectively (e.g. Maeda1991). Remarkably, the black band is rarely preserved
even in ammonoid taphocoenoses of the first type. This
can probably be explained mainly by the organic nature
of this structure and its poor preservation potential.
Additionally, it shows that truly fully grown ammonoids
are rare for many taxa. Furthermore, not every mature
ammonoid will have secreted a black band; after all, some
mature Recent nautilids also lack this feature (Ward
1987). This fits the interpretation of ammonoids as r-
strategists, which would correspond to a type III survi-
vorship curve.
C O N C L U S I O N S
As all of the above structures primarily consisted of
conchiolin and are located at the terminal or at a for-
mer aperture, and as they are preserved in several spec-
imens from the German Posidonia Shale (where most
ammonoids display periostracum preservation), it is
reasonable to assume that most of these structures were
formed by the mantle fold, which also secreted the
periostracum. Terminal growth of the specimens, like
any kind of environmental stress or injury, might have
represented internal stress. Thus, we suggest that allthese structures were formed under adverse conditions
in a broad sense which perturbed the regular formation
of periostracum and shell. Therefore, the formation of
all of the structures presented herein has the same
underlying cause, i.e. some kind of stress, but with
varying results: injury (black stripe), adverse conditions
at any growth stage (black aperture), interim growth
stops (megastriae; false colour bands) and terminal
growth (black band).
As the black bands of the ammonoids depicted herein
are located on the external shell surface, they clearly differ
from the state in Recent nautilids, in which the area of
the black band serves the attachment of the apertural
mantle. This functional interpretation appears unlikely for
ammonoids. In ammonoids, the black band might simply
be a gerontic artefact.
Acknowledgements. This work benefited from a research stay in
Berlin (DE-TAF) in July 2006, supported by Synthesys, where
the Carboniferous material was examined. It is a contribution to
Swiss National Science Foundation project no. 200020-113554 to
Hugo Bucher (Zurich). For providing material and photographs
of specimens we thank Jim Jenks (Salt Lake City), Gilbert M.
Kahn (Zurich), Hans Hagdorn (Ingelfingen) and Rolf Bernhard
Hauff (Holzmaden). Some of the photographs were taken by
Heinz Lanz, Thomas Galfetti and Rosemarie Roth (all Zurich),
and by Wolfgang Gerber (Tubingen). We acknowledge the
EDAX analyses run by Michael Montenari and Hartmut Schulz
(both Tubingen), and appreciate the thorough revision of the
manuscript by John W. M. Jagt (Maastricht) as well as the con-structive reviews of Ryoji Wani (Tokyo) and an anonymous
referee.
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