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Cephalopod evolution: A new perspective –
Implications from two Early Cretaceous ammonoid
suborders (Northern Calcareous Alps, Upper Austria)
A. LUKENEDER
Abstract:ThestatusoftwoEarlyCretaceousammonoidgroupsfromUpperAustria(NorthernCalcareousAlps)isexaminedwith
respecttotheevolutionoftheirshapeaswellastotheirmorphologyandenvironmentalpreference.TheValanginianOlcoste-
phanusguebhardi(VerrucosumZone,137mya)showstheevolutionaryseparationofsexintwodifferentenvironmentsandhas
adapteditsshapetothesomewhatdifferentenvironmentalconditions.TheheteromorphBarremianammonoidKarstenicerastern-
bergense(CoronitesZone,124mya)isshowntohaveevolvedduringtimeswithintermittentoxygen-depletedconditionsassocia-
tedwithstable,salinity-stratifiedwatermasses.Basedonlithologicalandgeochemicalanalysiscombinedwithinvestigationsof
tracefossils,microfossilsandmacrofossils,aninvasionofanopportunistic(r-strategist)Karstenicerasbiocoenosisduringunfavou-
rableconditionsisassumed.BothexamplesarechosentodemonstrateevolutionarytrendsintheEarlyCretaceouswhichcanbe
observedinthecephalopodgroupasawhole.
Keywords:Evolution,ammonoids,palaeobiology,NorthernCalcareousAlps,EarlyCretaceous.
Introduction phologicalchangeandthereforeappearsasanewevo-
lutionary trend. Radial or linear evolutions are the
ABEL (1916) was the first to show a strong corres- mainevolutionarydirectionsandpathways,butareon-
pondence and interaction between the environment
lydescriptivemirrorsformoreimportantprocessesthat
andthenewlyevolvingshapes,morphologiesandstruc-
morecephalopodworkersshouldrecognize(seeHOUSE
tures of cephalopods. That seminal paper on the
& SENIOR 1980). Spectacular evolutionary radiation
palaeobiologyofcephalopodsunderlinedthatcephalo-
andstepsforwardmostlytookplacewhentheenviron-
podevolutionistypicallycloselyrelatedwithchanging
mentchangeddrastically.Thepresentpaperexamines
environmentalconditionsinthesea.Itisevidenttoday
theproblemofammonoidevolutionfromapalaeobio-
thatthedifferentfieldstreatedbycephalopodworkers
logicalpointofview,usingtwocephalopodcasestudies
like evolution, biodiversity, ecology and palaeobiology
from the Early Cretaceous of Upper Austria. These
are blending into one another. Evolution moulds the
showstrikingevidencefortheevolutionofnewforms
geneticprogrammingofcephalopodsand,indoingso,
due to environmental changes or due to adaption of
alsomouldsthepotentialforadaptation(YOUNGetal.
habittothepreferredhabitat.Theadaptivestrategyis
1998;YACOBUCCI1999).Adaptationisthemajormo-
clearlyprovenbythechangeofmorphologyinthefos-
torforevolution,asituationrecognizedbyABEL(1916)
silrecordandtheembeddingfauna.
whenheerectedthenewfieldknownaspalaeobiology.
Palaeobiology shows how important the animal-envi- Casestudy1showstheEarlyCretaceousmass-occur-
ronmentinteractionisforpromotingevolution. rence(KB1A=Klausrieglerbach1,sectionA,Ternberg
Nappe,oftheNorthernCalcareousAlps-NCA;Upper
Do ammonoids speciate profusely because internal
Austria)withdominatingOlcostephanus(Olcostephanus)
factors enhance variability and reproductive success?
guebhardi KILIAN morph. querolensis BULOT, from the
Or do ammonoids respond passively to environmental
Saynoceras verrucosum Zone (Late Valanginian)
changes and therefore react after changes of the envi-
(LUKENEDER2004;LUKENEDER&HARZHAUSER2003).
ronment?Thesequestionsgobeyondthescopeofthis
paper,buttheproblemsassociatedwiththesemajoris- Casestudy2showsanEarlyCretaceousmass-occur-
Denisia20,
sues in cephalopod research can be highlighted by di- renceofammonoidsintheTernbergNappeoftheNCA zugleichKatalogeder
oberösterreichischen
verse papers expressing different points of views. The (Upper Austria), which is described for the first time. Landesmuseen
adoptionofnewhabitsinteractswithlong-lastingmor- Themass-occurrence(sectionKB1B=Klausrieglerbach NeueSerie66(2007):
395-404
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Fig.1:LocalitymapofUpperAustria
showingtheoutcropofLowerCretaceous
sediments(black)aroundthesection
investigatedwithintheNorthern
CalcareousAlps.Positionsofthesynclines
aregiveninthetectonicmapontheleft.
(1)LosensteinSyncline,(2)Schneeberg
Syncline,(3)AnzenbachSyncline,(4)
EbenforstSyncline.ThepositionoftheKB1
A(blue)andKB1B(yellow)sectionis
markedbyacross(x).
1, section B) dominated by Karsteniceras ternbergense logical, palaeoecological and sedimentological investi-
LUKENEDER is of Early Barremian age (Coronite darsi gations,combinedwithstudiesoflithofaciesinthinsec-
Zone)(LUKENEDER2003;LUKENEDER&TANABE2002). tions,peelsfrompolishedrocksurfacesandgeochemical
investigations (CaCO, TOC, S), yielded information
The main aim of this contribution is to show the 3
abouttheenvironmentalconditionsintheareaofdep-
significanteffectofsynecologicalstress,causedeitherby
osition.Inparticular,‘parameters’suchasoxygen-level
environmentalchangesofabioticfactorssuchasoxygen
(deduced not measured), total organic carbon (TOC)
content,salinityanddepth,orbyautecologicalstressas-
content and sulphide contents help to solve the ques-
sociatedwithbioticcompetitorsoccupyingthesameen-
tionofautochthonousversusallochthonousdeposition
vironment.
oftheammoniteshells.Sulphuranalysesconfirmthere-
sults of many other methods used to test for anoxic or
Material and methods oxic conditions (e.g. TOC, HI). Thus, the sulphur
Section KB1 A.Theolcostephanid-dominatedma- analysismethodsdevelopedbyKOMA(1978)andothers
appeartobeapplicableforthestudyofanoxic-dysoxic
terial originates from section KB1 A in the Losenstein
eventbedselsewhere.
Syncline. Ammonoids represent almost the totality of
the macrofauna (98 per cent). The very abundant but Thetotalsulphurcontent(weightpercent)ofsam-
generallypoorlypreservedLateValanginianassemblages plesfromtheKB1sectionwasanalysedusingX-rayflu-
consist of 9 genera. About 200 specimens of Ol- orescence and wet methods. All the chemical analyses
costephanusguebhardi(BULOT)between10and102mm were carried out in the Laboratory of the Institute of
in maximum diameter were investigated. Many of the Forest Ecology at the University of Vienna. Calcium
specimensarefragmented.Twogroupsofvaryingmaxi- carbonatecontentwasdeterminedusingthecarbonate
mumsizeanddifferentaperturesaredistinguishable.The bombtechnique.Totalcarboncontentwasdetermined
smaller group represents the microconchs (up to 42 using a LECO WR-12 analyser. Total organic carbon
mm),whereasthelargerspecimensaremacroconchs(up (TOC) content was calculated as the difference be-
to102mm).Duetothelargenumberofspecimens,ex- tweentotalcarbonandcarbonatecarbon,assumingthat
traordinarily well-preserved specimens (e.g. lappets of allcarbonateispurecalcite.
microconchs)couldbecollected.Theircasts(sculpture
moulds), with perfectly preserved sculpture, are usually
Geographical setting
compressed.Nosuturelinesarevisibleonthesteinkerns.
Both occurrences are located within the same log
Section KB1 B. About 300 specimens of
KB1.ThesectionissituatedintheTernbergNappein
KarstenicerasternbergenseLUKENEDERbetween5and37
UpperAustria.Theexactpositionisabout7kmwestof
mmindiameterwereinvestigatedfromtheKB1Bsec-
Losenstein, 1 km south of Kienberg and 500 m south-
tion.Mostofthespecimensareobservableononeside
westoftheKlausrieglerinn(652m,ÖK1:50000,sheet
only;mostareentireandshownofragmentation.Juve-
69 Großraming, Fig. 1). The stream outcrop fixed by
nilestagesandtheventralareaarevisibleinjustafew
GPS data (global positioning system: N 47°54’32“, E
specimens.Twogroupsshowingthickmainribsbutdif-
14°21’10“) crosses the western part of the east-west
ferent maximum size are distinguishable. The very
striking Losenstein Syncline at a line between the
abundantsmallheteromorphsaregenerallypoorlypre-
Kreuzmauer(853m)tothenorthandthePfaffenmauer
served. Their casts (sculpture moulds), with perfectly
(1218m)tothesouth.Fordetaileddescriptionsofthe
preservedsculpture,areusuallypyritized.
investigation area see LUKENEDER (1997, 1998, 1999).
Bed-by-bed collecting and a systematic-taxonomic Thissectionwasthestartingpointforalateralanalysis
studyprovidethebasicdataforstatisticalanalysisofthe of the distribution of the reported ammonite mass-oc-
ammonite faunas from KB1 A and KB1 B. Palaeonto- currence.
396
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The Olcostephanus occurrence (KB1 A) is situated
intheuppermostpartoftheKB1ravine(800m).The
fossiliferous limestone, comprising the Olcostephanus-
bearinginterval,islocatedontheleftwallofthegorge
(dipping080/70).TheKarstenicerasoccurrence(KB1B)
issituatedinthemiddleoftheKB1ravine(717m,dip-
ping080/70).
Geological setting
TheLosensteinSynclineissituatedinthesouthern-
mostpartoftheTernbergNappeoftheNorthernCal-
careous Alps. This is followed directly to the south by
theSchneebergSyncline,theAnzenbachSynclineand
thentheEbenforstSynclineoftheReichramingNappe
(NorthernCalcareousAlps),allofwhichareconstitut-
ed by Lower Cretaceous sediments. At the section in-
vestigated, the Early Cretaceous is represented by four
formations, from bottom to top the Steinmühl Forma-
tion (c. 20 m, Early Berriasian to late Early Valangin-
ian), the Schrambach Formation (c. 160-200 m, Late
Valanginian to Late Barremian), and the Tannheim
Formation(c.40m,EarlyAptiantoLateAptian)and
theLosensteinFormation(c.20m,Albian(Fig.2).
Theinvestigatedammonite‘mass-occurrences’,rep-
resentingtheOlcostephanusLevelandtheKarsteniceras
Level, are situated in the lowermost part (KB1 A, Ol-
costephanus,LateValanginian)andtheupperpart(KB1
B, Karsteniceras, Early Barremian) of the Schrambach
Formation(LUKENEDER1997,1998)(Fig.3).
Case study 1: KB1 A
Facies-relatedevolutionand
sexualdimorphicpairs
The mass-occurrence of Olcostephanus (Olcostepha-
nus)guebhardimorph.querolensis(Fig.4)overaninterval
ofalmost3metres(KB1A)isinterpretedtobetheresult
ofacombinationofalong-termaccumulationfromthe
watercolumn(autochthonousparts)duringafavourable
time interval and redepositonal phases (allochthonous
parts) of the Late Valanginian (S. verrucosum Zone,
LUKENEDER 2004). The abundant olcostephanids reflect
lessoffshoreinfluencesandnearnessofshallowenviron-
ments.PartsoftheOlcostephanusmass-occurrence(accu-
mulation beds) show some similarities to a ‘Kondensat-
Lagerstätte’.Anenrichmentbyredeposition,currentsor
turbiditesisproposedforonlyafewmarlylayerswithac-
cumulated fragmented olcostephanids. The ol-
costephanidsweredepositedwithinaphyllocrinid-ophi- Fig.2:PositionoftheoutcropattheKB1section(centre),situatedinthe
SchrambachFormation,withindicatedexposureoftheinvestigateddetailed
urid association. Irregular echinoids proved soft bottom
logsKB1A(topphoto)andKB1B(bottomphoto).
conditions of the secondary allochthonous depositional
environment(LUKENEDER2004).TheabundanceofOl-
costephanusattheKB1Asectionseemstoberelatedto
397
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Fig.3:Stratigraphiclogofthe REHÁKOVÁ2004).‘Faunalturnover’,‘mass-occurrence’,
investigatedsection,consistingof and‘migrations’havealwaysbeenconsideredtobecon-
theSteinmühl-,theSchrambach-
trolled by transgressive and regressive cycles in various
andtheTannheimformations,
indicatingthepositionoftheKB1A Early Cretaceous ammonite groups (RAWSON 1981,
andKB1Bsections. HOEDEMAEKER1990).
A huge rise in sea level took place in the Late
Valanginian (Verrucosum Zone) succession (HOEDE-
MAEKER1990)ofthelowermostSchrambachFormation
(KB1), containing the Olcostephanus Level, which is
dominated by the migrated genus Olcostephanus. The
presence of Olcostephanus in the Losenstein Syncline
andespeciallyattheKB1-Asectionisapparentlyrelat-
ed to transgressive facies, presumably associated with
sea-levelrises.
This was probably within the Late Valanginian
trangressionphase,whichalsoledtoaworld-wide(e.g.
Argentina, Mexico, Colombia, Spain, France, Italy,
Switzerland,N.Germany,Austria,CzechRepublic,Ro-
mania,Bulgaria,Russia,Tunisia,Algeria,SouthAfrica,
Madagascar,Pakistan)spreadingorevenexplosionand
occupation of new regions (e.g. Boreal Realm) by the
Olcostephanusgroup.Thismostlyreflectsthecreationor
renewalofsea-ways.Comparingfieldevidenceandpub-
lished data from the Vocontian Trough (e.g. BULOT
1993)supportstheproposalofafaciesdependence(e.g.
depth, outer-inner shelf) of Olcostephanus (Ol-
costephanus) guebhardi morph. querolensis also for the
Austrian KB1-A occurrence (Fig. 5). The descendants
aremostprobablyinhabitantsoftheoutershelfandre-
lated areas. It is also suggested that Olcostephanus (Ol-
costephanus) guebhardi morph. querolensis has its acme
withintheS.verrucosumZone,whereastheancientOl-
costephanus (Olcostephanus) guebhardi s. str. is most
abundant in the latest Early Valanginian (Inostranzewi
Zone)(BULOT1992;LUKENEDER2004).
Among ammonoid genera of Tethyan origin, Ol-
costephanus(whichapparentlyoriginatedinthewestern
Mediterranean area during the Early Valanginian) was
dispersed over many parts of the world by the mid-
Valanginiansea-levelrise,whenthe‘guebhardichrono-
cline’ extended to Mexico, Argentina, the Antarctic
Peninsula,SouthAfrica,Madagascar,andintotheBo-
real Realm (especially the West European Province)
(BULOT 1990), although it never penetrated into truly
borealareas(RAWSON1993).
transgressivefacies,presumablyassociatedwithsea-level
OnthenorthernmarginoftheTethystheammonite
rises.
assemblages of the outer platform areas in southern
Lithological differences observed around the Ol- SpainandProvence(southernFrance)aredominatedby
costephanus-Levelareclearlyconsequencesofanaltered Olcostephanus and by Neocomitidae (COMPANY 1987;
palaeooceanographyandthereforereflectsea-levelfluc- BULOT1993;REBOULET1996).BULOT(1993)hasshown
tuationsduringtheEarlyCretaceous,especiallywithin distinct geographic distributions in some species of the
the Berriasian and Valanginian stages (LUKENEDER & Olcostephanidaeinplatformorbasinenvironments.
398
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Studies carried out in south-east France provided bution when neocomitids (e.g. Neocomites appears in
goodevidenceofammonitedistributionlinkedtofacies. theEarlyValanginian)wererareorabsentinthesame
AmongtheAmmonitina,theOlcostephaninaeandthe area, which leads to the well-known “bottle neck“ ef-
Neocomitidaeyieldedthebestexamplesoffaunalassem- fects in the evolution of the olcostephanid group. The
blagevariationsbetweenthebasinandoutershelf(BU- olcostephanids may have inhabited more shallow seas
LOT1993;REBOULET1996;REBOULET&ATROPS1997). thantheneocomitids.Incontrast,theneocomitidswere
DuringmostoftheValanginian,Olcostephanuswassplit able to live in deeper areas. The living realm of both
into two different ‘lineages’: Olcostephanus (Ol- ammonoid groups were therefore shifted against each
costephanus) guebhardi (KILIAN) and related species are other. Due to the ecological stress caused by the other
restricted to the outer shelf facies, while Olcostephanus ammonoidgenus,thedifferentammonoidsevolvedin-
(Olcostephanus) tenuituberculatus (BULOT) and its de- tofreenichesoftheshallowerordeepersea.Thelatter
scendantscorrespondtothebasinfacies(BULOT1993). fact most probably explains why we can observe only
one genus (Olcostephanus) in the shallowest facies, al-
The splitting into two facies-linked olcostephanid
thoughthissituationrequiresfurtherinvestigation.
lineagesduringtheValanginianclearlyshowstheevo-
lution within the olcostephanids. Starting from the Sexual dimorphism in ammonoid cephalopods is
Berriasianuni-facial,deeper-watergenusSpiticeras(e.g. discussed in detail for example by DAVIS et al. (1996)
S. multiforme DJANÉLIDZÉ), followed by the still uni-fa- and COOPER (1981). The latter author precisely de-
cialolcostephanidancestorOlcostephanus(O.)drumen- scribed sexual dimorphism in Olcostephanus. In Ol-
sisKILIANintheearlymostValanginian,thekeyevolu- costephanus,asinotherammonoids,theontogeneticde-
tionary point follows in the middle Early Valanginian. velopment of the shell is similar in both antidimorphs
The evolutionarily important split into a deep-water (sensuDAVIS1972)untiltheonsetofmaturity.
lineageandamoreshallow-waterlineagewithintheol-
Within the KB1-A olcostephanid fauna, sexual di-
costephanids markedly changes the picture of ol-
morphism is very apparent due to the unusually large
costephaniddistributionandsystematics.
size attained by the macroconch forms (M; measured
One lineage evolved the shelf forms from Early specimens=adultsize),someofwhichexceed102mm
ValanginianOlcostephanusguebhardis.str.,overtheLate
in diameter. In contrast, the largest confirmed micro-
Valanginian Olcostephanus guebhardi morph. type
conch(m)sofarrecordedfromthesebedsmeasureson-
querolensisuptoHauterivianspecieslikeOlcostephanus
lyslightlymorethan42mmindiameter,withtheaver-
densicostatus(WEGNER). agebeingfarless(LUKENEDER2004).Themacroconchs
Thesecondlineageinhabitedthebasinsandevolved range in size from 82 to 100 mm and the microconchs
fromOlcostephnausdrumensis,continuingovertheEarly 20to42mm,indicatingasizeoverlapbetweenantidi-
Valanginian Olcostepanus stephanophorus (MATHERON) morphs of approximately 20 % of the total combined
intotheLateValanginianspeciesofOlcostephanustenu- size range of the two antidimorphs. The microconchs
ituberculatus (BULOT), Olcostephanus balestrai (RODI- show at the aperture a final constriction coupled with
GHIERO)andOlcostephanusnicklesiWIEDMANN&DIENI. laterallappets,whereasthemacroconchshaveonlyafi-
ThislineageendswiththeendoftheValanginian. nal constriction. In Olcostephanus guebhardi, sexual di-
morphism is expressed by differences not only in adult
This differentation in Olcostephanus ended in the
shape, size and ornament but also in the form of the
EarlyHauterivianwithevolvingspecieslinkedtoboth
aperturalmargin(Fig.4).
basin and shelf facies. These are Olcostephanus densi-
costatus and its descendants Olcostephanus astierianus
(ORBIGNY), Olcostpephanus sayni KILIAN and Jeanno- Case study 2: KB1 B
ticeeas jeannoti (ORBIGNY) for the Early Hauterivian. Oxygenasimpulseforevolutionin
Other data from various places of the western Tethys
heteromorphr-strategists
confirm this facies-linked distribution of Olcostephanus
About300specimensofKarstenicerasternbergensebe-
(NorthernCaucasus,KVANTALIANI&SAKHAROV1986; tween5mmand37mmindiameterwereinvestigated.
Spain,COMPANY1987;Switzerland,BULOT1989,1992) Juveniles, adults, including micro- and macroconchs,
and therefore underline a general trend for the entire
couldbeseparated.AsexualdimorphisminKarsteniceras
TethysRealm(BULOT&COMPANY1990). canbeobserved.Anenrichmentbyredepositionthrough
Various evidence points to the fact that the evolu- currents or turbidites can be clearly ruled out based on
tionoftheEarlyCretaceousolcostephanidswasclosely theautochthonouscharacterofthenearlymonospecific
linked to the evolution and concurrent appearance of benthic macrofauna (e.g. Inoceramus, Propeamussium),
theneocomitids.Olcostephanidshadtheirwidestdistri- the preservation of fragile parts and the extraordinary
399
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Fig.4:Karsteniceras light-greybioturbated,organic-depletedlimestonessug-
ternbergense gests that the oxic and dysoxic conditions episodically
specimensfromcase
changed.Ahighlydynamicenvironment,controlledby
study2(KB1B):(A)
short-andlong-termfluctuationsinoxygenlevels,and
NHMW
2001z0170/0002,x1; poorcirculationofbottom-watercurrentswithinaniso-
(B)holotype,NHMW lated,basin-likeregion,ledtotheaccumulationofthe
2001z0170/0001,x1;
KarstenicerasLevel.Thelaminationgenerallyindicates
(C)NHMW
a very quiet depositional environment, which was not
2001z0170/0004,x1;
(D)NHMW disturbedbycurrents(LUKENEDER2003).
2001z0170/0003,x1;
WithintheSchrambachFormation,dysaerobic(not
(E)NHMW
2001z0170/0005,x1; anaerobic) conditions prevailed, allowing endobenthic
(F)NHMW colonization of the incompletely bioturbated sediment
2001z0170/0007,x1.
byChondrites(accompaniedbyPlanolitesinsomebeds).
Olcostephanus
(Olcostephanus) Increasing levels of dissolved oxygen in bottom waters
guebhardimorph.type over time are suggested by well-bioturbated, pale grey
querolensisspecimens limestone beds, whereas dysaerobic conditions are ex-
fromcasestudy1(KB1
pressed through thin, black, laminated limestones
A):(G)macroconch,
2002z0070/0001,x1; (‘black shales’). The Karsteniceras mass-occurrence is
(H)microconch, situated in the laminated horizons. The following fea-
2002z0070/0002,x1, tures are observable: (1) high TOC, (2) high sulphur
(I)macro-and
content,(3)concentrationsofpyrite,(4)phosphaticsi-
microconch
2002z0070/0003,x1. phunclestructures,(5)indistinctlamination,(6)almost
monospecific trace fossil community (e.g. Chondrites),
(7)fishremains,(8)extremelyrarebenthos(e.g.inoce-
ramids, ‘paper pectens’), (9) rare microfauna, (10)
‘mass-mortality’ of Karsteniceras, very abundant and
smallinsize,(11)nearly‘monospecific’faunalspectrum
and(12)insituaptychi.
It is assumed that, based on the described features
fromKB1Bandliteraturedata,Karstenicerasmostprob-
ablyhadanopportunistic(r-strategist)modeoflifeand
was adapted to dysaerobic sea-water. These ancylocer-
atidsmostlikelyinhabitedregionsreachingfromthesea
floortoatleastafewtensofmetersintotheoverlying
water-column, based on the in situ aptychi and the
nearlymonospecificfaunalassemblageofsmallhetero-
morphs. Most of the associated other ammonoids (e.g.
Barremitescf.difficilis)showdifferentovergrowthstages
(serpulids).Thesecanbeexplainedasareflectionoflife
in the upper, oxygenated water-column, with subse-
quent sinking to the sea floor or drifting after death.
Karsteniceras probably inhabited areas of water stagna-
tion with low dissolved oxygen, showing abundance
peaksduringtimesofoxygendepletion,whichhindered
otherinvertebratesfromcolonisingsuchenvironments.
ThedescribedautochthonousKarstenicerasmass-occur-
rence features fit well into the scheme of a ‘Konservat
preservationofinsituaptychiwithinthebodychambers Lagerstätte’(LUKENEDER2003).
ofKarstenicerasternbergense(Fig.4).
Interbeddingofsedimentsalternatelyrichandpoor
The geochemical results indicate that the assem- inorganicmattercanbetheresultofeitherdifferential
blage was deposited under conditions of intermittent preservationoforganicmatter,differentialratesofsup-
oxygen-depletion associated with stable water masses. ply of organic matter, different sources of primary pro-
The rhythmicity of laminated black shale layers and duction,and/ordifferentialsedimentationrates.Differ-
400
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entpreservationcanresultifbottomwatersattheaccu-
mulationsitearealternatelyoxicanddysoxic(ornear-
anoxic).Cyclicvariationintheamountoforganicmat-
ter accumulating at a continental margin site may be
explainedbycyclicfluctuationsinthethicknessandin-
tensityofamidwateroxygen-minimumlayer.Bothde-
positional models (basin deoxygenation as well as ex-
pansionandestablishmentofanoxygen-minimumlay-
er)havebeenproposedtoexplaintheaccumulationof
organiccarbon-richstrata.
Oxygenisabio-limitingelementformetazoansand
is among the key factors influencing species diversity
and abundance in the marine realm. Reduced concen-
trationsofdissolvedoxygencanhavedisastrousconse-
quencesformarinelife,reducingdiversityandultimate-
lyleadingtomass-mortality.
Factors associated with low diversity include high
stress and ecological immaturity. Most opportunists (r-
strategists) are characterized by small size and a short
lifespan.Thelatterfactsalsohintatpositivemutations.
The small-sized leptoceratids seem to be resistant
against oxygen depletion in the sea water. The robust
small-sized forms evolved morphologies and evolution-
ary adaptations which allowed them to inhabit such
hostileenvironments.Theybecameaccustomedtosuch
conditions, occurring in masses and becoming geo-
graphically widespread (LUKENEDER 2003). The body
size of the leptoceratids was therefore reduced to give
risetootherfeaturesimportantforlivinginoxygen-de-
pletedwaters,andtheopportunistic(r-strategist)mode
of life was perfectly adapted to dysaerobic sea-water.
This was the sense in which the word “Paläobiologie“
wasoriginallymeantbyitsfounderO.ABEL(1916).He
Fig.5:ThestratigraphicpositionofthecasestudiesKB1A(blue)andKB1B
noticed almost 100 years ago for the cephalopods in
(yellow)withintheEarlyCretaceous(Valanginian–Barremian)oftheKB11
general the same relation shown for the special cases faunaintheLosensteinSyncline.TableafterHOEDEMAEKERetal.(2003,with
presentedherein.Thechangeinbodysizeandmorphol- modifications).
ogyinKarstenicerasisaccompaniedcausallybythespe-
cialisationoftheanimalduringenvironmentalchanges.
differentmorphologiesandsizes.Theyalloriginatefrom
This phenomenon can be detected through the the Late Hauterivian genus Veveysiceras VA Í EK &
ŠČ
whole Early Cretaceous. The phylogenetically totally WIEDMANN (VA Í EK & WIEDMANN 1994). The three
ŠČ
separated Berriasian Leptoceratoides (THIEULOY 1966) important lineages are: 1) Karsteniceras (criocone), 2)
show the same facies-linked distribution as that of the Hamulinites (ancylocne) and 3) Eoheteroceras (ancylo-
muchyoungerBarremianVeveysicerasdescendants.The cone)togetherwithManoloviceras(slightlycurved).All
favoured sediments are clayey, dark to laminated marls ofthesearoseintheEarlyBarremian.Eoheterocerasmost
withincreasingcontentoforganicmatterandpyrite. probablywastheancestoroftheLateBarremianHete-
roceras.Karstenicerasformsthecentralstock,withmost
A typical group of such opportunistic small-sized
descendantsupintotheearlyLateBarremian.
hetermorph ammonoids is the monophyletic subfamily
LeptoceratoidinaeTHIEULOY.Thelattersubfamilyisas- Thephylogeneticallyandstratigraphicallyseparated
signedtothefamilyAncyloceratidaeGILL.Withinthe group around UHLIG’S (1883) type species Leptoceras
latter,threeevolutionarylinesarerecognized;thehere- brunneri belongs to an unrelated earlier group from the
in-described Karsteniceras ternbergense is a member of BerriasiantoValanginian(THIEULOY1966).Noleptocer-
oneoftheselines.Theselineagesareseparatedthrough atidtransitionalformsareknownfromtheHauterivian.
401
© Biologiezentrum Linz, download unter www.biologiezentrum.at
Fig.6:Cretaceous The ancestral stock of the second and totally separated
shapeexamplesfor later micromorph Barremian group the Leptoceratoid-
“normal“coiledam-
inae(beforeVeveysiceras),isstillobscure.Notransitional
monoids:(A)phos-
forms can be observed and the ancestor is unknown.
phatizedPlacenticeras
meeki(BOEHM)with Veveysiceras occurred first with Pseudothurmannia in the
shellpreservation, latestHauterivian.Theevolutionarycentreexpandsina
Campanian,Alberta,
longitudinal east-west region from central/southeastern
Canada,NHMW-
2006z0260/0001and EuropetoJapan(VA Í EK&WIEDMANN1994).
ŠČ
(B)Placenticeraspla-
In the field, researchers should therefore look for
centa(DEKAY)showing
sutureline,South thin, relatively widespread (but isochronous) horizons
Dakota,USA,NHMW- dominated by one species of body or trace fossil. The
2002z0066/0001. thin, black laminated layers with mass-occurrences of
Heteromorpham-
Karstenicerasareacaseinpoint.The‘normal-accumula-
monoidsare:(C)Dis-
tion’ofKarsteniceraswithinsuchblack,laminatedsedi-
coscaphitesgulosus
(MORTON)withshell mentsisinterpretedtobetheresultofspecialpalaeoen-
preservation,Maas- vironmental conditions (e.g. poor oxygen, low to no
trichtian,SouthDako-
currents).Here,Karsteniceras,asamemberofanoppor-
ta,USA,NHMW-
tunistic (r-strategist) ammonite group, sought the un-
2006z0260/0002,and
(D)Didymocerasne- favourable, oxygen-limited environmental conditions
brascense(MEEK& thatotherammonitegroupswereunabletotolerate.
HAYDEN)withshell
preservation,Campan- Takingintoaccountthespeculationsonammonoid
ian,SouthDakota, life-habitats, the demersal forms, feeding on the sea
USA,NHMW
floor, should be very rare or even absent in the anoxic
1980/0023/0000.
levels (BATT 1993). VA Í EK & WIEDMANN (1994) al-
ŠČ
readynotedthepossibilitythatthebiotopeoftheLepto-
ceratoidinae was close to stagnant, poorly oxygenated
environments,wheretheyusuallyoccurredconcentrated
in‘nests’dominatingthefaunalspectrum.Thishasbeen
recentlyinterpretedtoreflectopportunisticbehaviourof
some taxa (Bochianitidae and leptoceratoids) in un-
favourable environments (CECCA 1998). Leptoceratoid
andspiroceratidecology,palaeobiologyandlife-habitats
were discussed by UHLIG (1883), NIKOLOV (1960),
THIEULOY (1966), DIETL (1973, 1978), RIEBER (1977),
VA Í EK (1977), WESTERMANN (1990), VA Í EK &
ŠČ ŠČ
WIEDMANN (1994), CECCA (1997) and AVRAM (1999).
Summarizingthevariousopinionsonleptoceratoidecol-
ogy, clear differences are evident between those of
THIEULOY (1966; autochthonous life assemblage),
RIEBER (1977; nektonic above anoxic bottom) and
LUKENEDER (2003, nektonic in dysoxic water column),
WESTERMANN(1990,1996;distalshelf),andVA Í EK&
ŠČ
WIEDMANN(1994;autochthonousbetweenturbidites).
Concluding remarks
This contribution shows the significant effect that
synecological stress – caused either by environmental
changes of abiotic factors as oxygen content, salinity
and depth or by autecological stress from biotic com-
petitorsoccupyingthesameenvironment–hasonthe
shape and morphology of Cretaceous ammonoids. Ex-
amples for different Cretaceous ammonoid shapes are
giveninFigure6.
402
© Biologiezentrum Linz, download unter www.biologiezentrum.at
Two contrary examples (Olcostephanus and Acknowledgements
Karsteniceras)wereselectedtoshowevolutionarytrends
Thanks are due to the Austrian Science Fund
inammonoids.Theoldercasestudy(Valanginian)deals
(FWF) for financial support (project P16100-Geo.).
with “normal“ coiled Olcostephanus. A number of facts
The author is grateful to Herbert Summesberger and
show that the evolution of the Early Cretaceous ol-
MathiasHarzhauser(bothNaturalHistoryMuseum,Vi-
costephanids was closely linked to the evolution and
enna)fortheirthoughtfulandvaluablecomments.Pho-
concurrent appearance of the neocomitids. Due to the
tographs were taken by Alice Schumacher (Natural
ecological stress generated by the neocomitids, the ol-
HistoryMuseum,Vienna).
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deeper sea. The split into two facies-linked ol-
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Addressoftheauthor:
munity (Valanginian, Northern Calcareous Alps, Austria).
—Cret.Research24:477-485. Dr.Mag.AlexanderLUKENEDER
LUKENEDERA.&D.REHÁKOVÁ(2004):LowerCretaceoussectionof Geological-PalaeontologicalDepartment
theTernbergNappe(NorthernCalcareousAlps,UpperAus- NaturalHistoryMuseumVienna
tria):Facies-changes,biostratigraphyandpaleoecology.—
Burgring7
Geol.Carpathica55(3):227-237.
1010Vienna,Austria
LUKENEDERA.&K.TANABE(2002):Insitufindsofaptychiinthe
E-Mail:[email protected]
Barremian of the Alpine Lower Cretaceous (Barremian,
404
