2007 Klug Et Al. Shell

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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).

1464 P A L A E O N T O L OG Y , V O LU M E 50


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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

K L U G E T A L . : A M M O N O I D S H E L L S T R U C T U R E S 1465


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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).



9/16

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.



10/16

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.



11/16

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).



12/16

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.



13/16

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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