GEOLOGIJA 37, 38, 87-121 (1994/95), Ljubljana
The development of the mollusc fauna in the Cenomanian
of the stratigraphie sequence of Visogliano
(Karst of Ћ-ieste, Italy)
Favnistični razvoj mehkužcev v cenomanìjskem stratigrafskem
zaporedju pri Mžovljah (Tržaški Kras, Italija)
Mauro Caffau & Nevio Pugliese
Dipartimento di Scienze Geologiche Ambientali e Marine,
Università degli Studi di Trieste, Via Eduardo Weiss 2 CAP 34127 Trieste
Mario Pleničar
Katedra za geologijo in paleontologijo.
Univerza v Ljubljani, Aškerčeva 2, 1000 Ljubljana, Slovenija
Abstract
The stratigraphie sequence of Visogliano (Karst of Trieste) belongs to low-
er part of the Zolla Member of the still informal and provisional "Trieste Karst
Limestone Formation" and has been attributed to Middle-Late Cenomanian. This
sequence records an environmental evolution of more or less restricted settings,
where a rich mollusc fauna is present.
Among the molluscs, six radiolitid species occur {Radiolites carsicus n. sp.,
Radiolites peroni, Praeradiolites acutilamellosus n. sp., Praeradiolites cf. P.
fleuriausus, Sauvagesia sharpei, and Durania acuticostata n. sp.). Of these,
three species are described as new (Radiolites carsicus n. sp., Praeradiolites
acutilamellosus n. sp., and Durania acuticostata n. sp.). In addition, attention
has been focussed on the link between radiolitids and environmental changes to
refine the previously described environmental evolution. In this regard, a hier-
archy of tolerability to environmental changes can be also suggested. The most
tolerant radiolitids species are Praeradiolites cf. P. ßeuriausus and Sauvage-
sia sharpei, meanwhile the least tolerant ones are Radiolites carsicus n. sp.,
Radiolites peroni, Praeradiolites acutilamellosus n. sp., and Durania acuti-
costata.
Kratka vsebina
Stratigrafsko zaporedje plasti pri Vižovljah (Tržaški Kras) pripada spodnje-
mu delu »člena Col« (Membro di Colla), še neformalne in začasno določene
»apnenčeve formacije Tržaškega Krasa«, ki ga štejemo v srednji do zgornji del
cenomanijske stopnje. To zaporedje kaže na razvoj okolja na bolj ali manj ome-
jenih območjih z bogato favno moluskov.
Med moluski smo ugotovili šest radiolitidnih vrst {Radiolites carsicus n. sp.,
Radiolites peroni, Praeradiolites acutilamellosus n. sp., Praeradiolites cf. P.
ßeuriausus, Sauvagesia sharpei in Durania acuticostata n. sp. Od teh so bile
tri vrste opisane kot nove {Radiollites carsicus n. sp., Praeradiolites acutila-
88	Mauro Caffau, Nevio Pugliese & Mario Pleiiičar
mellosus n. sp. iri Durania acuticostata n. sp.). Razen tega smo posvetili po-
zornost na zvezo med radiolitidi in spremembami okolja. Radiolitidi imajo različno
stopnjo prilagodljivosti na spremembe okolja. Najbolj prilagodljivi radiolitidni vrsti
sta Praeradiolites cf. P. ßeuriausus in Sauvagesia sharpei, medtem ko so
najmanj prilagodljive vrste Radiolites carsicus n. sp., Radiolites peroni, Praera-
diolites acutilamellosus n. sp. in Durania acuticostata n. sp.
Introduction
In agreement with Cucchi et al. (1987), the lithotypes outcropping in the Karst of
Trieste pertain to the stiH informal and provisional Trieste Karst Limestones Formation w^hich
ranges from early Cretaceous to early Eocene. Within this formation, the low^er part of the
Zolla Member, w^hich has been up to now attributed to Cenomanian-early Turonian, corre-
sponds to the begirming of a clear development of the mollusc fauna and, particularly, of
the radiolitids. Thus, the paleontological study concerning this member can be considered
very useful to increase the knowledge of the stratigraphy and palaeoenvironmental evolu-
tion of the Karst of the Trieste.
This research focuses on the outcrops of Visogliano, near Sistiana (western Trieste Karst,
F°40 111 NE of the IGM; Fig. 1), where the geological survey highlights a thick sequence
with very fossiliferous beds wdthin the lower part of the ZoUa Member. The fossils here found
mainly consist of bivalves and, particularly, of radiolitids.
Purposes of this work are 1) the chronological and palaeoenvironmental study of the
stratigraphie sequence of Visogliano, and 2) the identification of the mollusc fauna and, parti-
cularly, of the radiolitids here found in order to refine the interpretation of the environ-
mental evolution.
Historical setting
Cucchi et al. (1987) include the ZoUa Member between the underlying dolomitic Rupin-
grande Member (Albian p.p.-Cenomanian p.p.) and the overlying Borgo Grotta Gigante
Member (early Turonian p.p.-Senonian p.p.). They subdivide it into two parts: the lower
part, which is mainly characterized by blackish limestones, sometimes with a very rich
radiolitid fauna and, at the basis, interbedded dolostones; the upper part, which is charac-
terized by grey limestones, with rudist fragments and Pithonella specimens. The fossils of
the lower part consist of radiolitids, such as Sauvagesia nicaisei and Sauvagesia sharpei,
and microfossils, such as Nubeculariidae, Miliolidae, and ostracods. Because of these radio-
litids, and of the lack of the microfossils, which are significant from the chronological point
of view, these authors attribute the lower part of this member to an undefined time-span
from Cenomanian to early Turonian. Besides, they attribute the upper part of this member
to early Turonian for the finding of the Pithonella specimens, in agreement v^ith Polšak
(1979).
Other papers concerning the outcrops of the Zolla Member are due to Cucchi et al.
(1986) and C o lizza et al. (1987), who studied the stratigraphy of localities of the Karst of
Trieste, such as Zolla-Monrupino and San Pelagio, respectively. These papers confirmed the
stratigraphie data already presented in the above cited studies.
The development of the mollusc fauna in the Cenomanian...	89
Fig. 1. Location map; the studied area is delimitated by a rectangle. The as-
terisk shows the location of interval 6 of the Visogliano stratigraphie sequence,
where all the studied mollusc species were represented. Visogliano
SI. L Situacijska karta; raziskano območje je omejeno s pravokotnikom. Zvezdica
kaže lego šestega intervala stratigrafskega zaporedja pri Vižovljah, iz katere-
ga so vse predstavljene vrste moluskov. Vižovlje
The stratigraphie sequence
In the Visogliano area the lithotypes of the Zolla Member shovv^ a monoclinal asset with
WNW-ESE main axial direction and southward main dip of 22°. In detail, on the basis of the
mollusc fauna and the microfacies analyses, the stratigraphie sequence here recognized can
be subdivided into nine intervals (Fig. 2). For each interval, data regarding lithology, palae-
ontology, microfacies, thickness, and palaeoenvironment are reported. The nine intervals
are described below, from bottom to top.
Interval 1
This interval consists of foetid very fossiliferous black limestones and interbedded dark
greyish dolostones, both with bedding of decimetric period.
In the limestones, the fossils mainly consist of radiolitids (Praeradiolites cf. P. ßeuri-
ausus and Sauvagesia sharpei), which are present in lenses of isooriented displaced shells.
90	Mauro Caffau, Nevio Pugliese & Mario Pleiiičar
The development of the mollusc fauna in the Cenomanian...	91
These lenses are horded by isolated specimens, w^hich seem to be in situ. On the contrary,
the dolostones are devoid of fossils, save for some rare gastropod ghosts.
The limestones are characterized by microfacies such as bioclastic (rudist) w^ackestones
and packstones with very common Nubeculariidae, Miliolidae, and subordinate algae (Thau-
matoporella parvovesiculifera, Cayeuxia sp.), Textulariidae, Chrysalidina gradata,
Cuneolina sp., Nezzazata simplex, and ostracods. The dolostones show a subeuhedral
dolomitic mosaic with gastropod ghosts only.
This interval overlies the dolostones of the Rupingrande Member and is 71 m thick. From
the palaeoenvironmental point of view, it testifies very restricted settings, sometimes
characterized by local biostromes (lenses of displaced radiolitids) and the first isolated
radiolitid specimens. The latter are probably able to colonize such restricted settings tak-
ing advantage of temporary permissive conditions for benthic life. These conditions degradate
in correspondence with very restricted environment, as testified by the almost unfossiliferous
dolostones.
Interval 2
This interval is characterized by dark-grey fossiliferous limestones, with bedding of deci-
metric period. The fossils consist of rare fragmented radiolitid specimens pertaining to
Praeradiolites cf. P. ßeuriausus and Sauvagesia sharpei, together with Neitheaßeuri-
ausiana.
The corresponding microfacies are represented by wackestones and packstones with
bioclasts (radiolitids) and very common Nubeculariidae, Miliolidae, and subordinate algae
{Thaumatoporella parvovesiculifera, Cayeuxia sp.), Chrysalidina gradata, Broecki-
na balcanica, Cuneolina sp., Nezzazata simplex, and ostracods. This interval is 12m thick.
It indicates episodes of an increased bottom energy in a restricted environment, as demon-
strated by the presence of very abundant radiolitid fragments.
Interval 3
This interval is characterized by interbeddings of grey dolostones and blackish fossilif-
erous limestones, with bedding of decimetric period. The dolostones are devoid of fossils,
meanwhile the limestones include fossils such as Chondrodontajoannae, Neitheaßeuri-
ausiana, and scattered fragments of Praeradiolites acutilamellosus n. sp. and Radiolites
carsicus n. sp.
The corresponding microfacies are respectively represented by euehedral/subeuehedral
dolomitic mosaic, wàth gastropod ghosts, and bioclastic mudstones or wackestones with rare
intraclasts and pellets; the microfossils are represented by very common Nubeculariidae
Fig. 2. The stratigraphie sequence of Visogliano within the Zolla Member, showing the age,
lithology, sampling-stations of the 9 intervals. The real thickness of intervals 1 and 3 is reported
in the text. The interval 1 overlie the dolostones of the Rupingrande Member. In addition, the
mollusc fauna and the microfossils, significant from the chronostratigraphic point of view, are
reported. For the latter the first occurrence (F. 0.) is indicated. The numbers 1-15 indicate
the sampling-stations
SI. 2. Stratigrafsko zaporedje pri Vižovljah, ki predstavlja »člen Col« (»Zolla Member«). Na stolpcu
vidimo geološko starost, litologijo in lego vzetih vzorcev iz devetih intervalov. Resnična debelina
prvega in tretjega intervala je navedena v besedilu. Prvi interval leži na dolomitu »člena Veli-
ki Repen« (»Rupingrande Member«). Razen tega je podana favna moluskov in mikrofosilov,
pomembnih za kronostratigrafijo. Slednji so bih najdeni prvič. Številke 1-15 označujejo lego
vzetih vzorcev
92	Mauro Caffau, Nevio Pugliese & Mario Pleiiičar
and Miliolidae, and subordinate Thaumatoporellaparvovesiculifera, Cuneolina sp., Bro-
eckina balcanica, Chrysalidina gradata, Pseudorhapydionina dubia, Textulariidae,
Nezzazata conica, and ostracods.
This interval, vi^hich is 65m thick, indicates very restricted settings (dolostones) with a
moderately increased bottom energy (bioclastic limestones), where lamellar shells of Chond-
rodonta joannae colonize the substrate, also in correspondence with a low rate of sedi-
mentation.
Interval 4
This interval is constituted by grey, sometimes dolomitic, limestones, with a fossilifer-
ous level (in the basal part), which is from 1.80 to 3m thick and characterized by shells of
Chondrodonta joannae and rare fragments of radioHtids.
The corresponding microfacies are represented both by bioclastic floatstones and bound-
stones (in the lower part), and wackestones or packstones (in the mid-upper part) with
very common Miliolidae, and, subordinately, Aeolisaccus kotori, Thaumatoporella parvo-
vesiculifera, Broeckina balcanica, Chrysalidina gradata, Textulariidae, Nubeculariidae,
and thin carapaces of ostracods.
This interval is 18m thick. In the lower part, it records the colonization of the substrate
due to the specimens of Chondrodonta joannae. Because of the lamellar morphology of
the shell of Chondrodonta joannae, this colonization probably occurs in correspondence
v^dth episodes of moderate-high bottom energy and low sedimentation rate. In the mid-up-
per part of the interval, the mollusc fauna is substituted by a large number of microorgan-
isms, probably in relation to environmental conditions shovvdng a decreased bottom energy
and an increasing sedimentation rate.
Interval 5
This interval is characterized by brovm dolomitic limestones with not evident bedding.
The corresponding microfacies are characterized by very abundant euhedral dolomitic
crystals included in a carbonatic mud, wdth rare Miliolidae and fragments of Chrysalidina
gradata.
The thickness of this interval is 5m. It testifies very restricted settings, which become
adverse for the benthic life.
Interval 6
This interval consists of grey-brovm very fossiliferous limestones with bedding of deci-
metric period. The fossils are represented by requienids, and very common specimens of
thickshelled radiolitids (Radiolites carsicus n. sp., Radiolites peroni, Praeradiolites acuti-
lamellosus n. sp., Praeradiolites cf. P. ßeuriausus, Sauvagesia sharpei, and Durania
acuticostata n. sp.), very and Chondrodonta joannae; in addition, rare specimens of
Neithea ßeuriausiana are also present. Among the molluscs, the radiolitids are often
present in clusters consisting of from 2 to 10 specimens in situ.
The main microfacies are represented by boundstones (clusters of radiolitids) and
bioclastic wackestones, with abundant microfossils. These latter consist of very common
Chrysalidina gradata, Nubeculariidae, Miliolidae, and subordinate specimens of Bacinella
irregularis, Cayeuxia sp., Thaumatoporella parvovesiculifera, Cuneolina sp. Textu-
lariidae, Broeckina balcanica, and Nezzazata simplex.
This interval is 8.5m thick. It records restricted settings characterized by favourable
environmental conditions for the benthic life, for both the growth of the build-ups and the
The development of the mollusc fauna in the Cenomanian...	93
increased specific diversity of the microfossils. This episode can correspond to a dicreased
bottom energy and an increased sedimentation rate.
Interval 7
This interval is characterized by grey limestones vvith bedding of decimetric period. The
fossils are rare and consist of fragments of radiolitids, such as Radiolites carsicus n. sp.
The main microfacies are represented by bioclastic wackestones with Chrysalidina
gradata, and rare Textulariidae, Broeckina balcanica, MiìioMae, Nezzazata simplex, and
thick carapaces of ostracods.
This interval is 6m thick. It shows a decreased specific diversity for both the radiolitids
and the microfossils. The radiolitids are represented by rare small specimens and, over all,
by fragments. The latter also testify episodes of high bottom energy in a restricted setting.
Interval 8
This interval consists of from light grey to grey-brovm dolomitic limestones, wdth bed-
ding of decimetric period.
The corresponding microfacies are characterized by very abundant euhedral dolomitic
crystals included in a carbonatic mud, with rare Miliolidae.
This interval is 6m thick and indicates very restricted settings, which are adverse for
the benthic life.
Interval 9
This interval is characterized by from dark-grey to blackish foetid limestones, with rare
fragments of radiolitids and bedding of centimetric period.
The corresponding microfacies are represented by muddy plane-parallel laminations
including rare microfossils, such as Thaumatoporella parvovesiculifera, Chrysalidina
gradata, Cuneolina sp., Nubeculariidae, Miliolidae, Nezzazata sp., and ostracods.
This interval tops the sequence studied and it has been analysed in the first meters
only. It indicates restricted settings affected by episodes of increased bottom energy, prob-
ably linked to tractive currents, as demonstrated by the plane-parallel laminations.
The mollusc fauna
Mauro Cqffau and Mario Pleničar
The Visogliano sequence shows the occurrence of a rich mollusc fauna, characterized
by Chondrodonta joannae, Neithea ßeuriausiana, requienids (Requienia sp.), and, over
all, radiolitids. The radiolitid fauna consist of six species: Praeradiolites acutilamellosus
n. sp., Praeradiolites cf P. ßeuriausus, Radiolites carsicus n. sp., Radiolites peroni,
Sauvagesia sharpei, Durania acuticostata n. sp.
Chondrodonta joannae, Neithea ßeuriausiana, and requienids have been already
signalled in the Karst of Trieste by several Authors in beds which are Cenomanian and/or
Turonian in age, as reported by Forti and Mas oli (1969). Recently, Chondrodonta joan-
nae and Neithea ßeuriausiana are reported as Chondrodonta and Neithea, respectively,
and occur in the limestones of Borgo Grotta Gigante Member (Cucchi et al., 1987), mean-
while requienids have been signalled by M as o li and Ulcigrai (1969) and Cucchi et al.
(1987) in black limestones of Aptian-Albian age.
94	Mauro Caffau, Nevio Pugliese & Mario Pleiiičar
Among the radiolitids, Praeradiolites acutilamellosus, Radiolites carsicits, and Dura-
nia acuticostata are considered new. Thus, these species have been signalled for the first
time in the Karst of Trieste, meanwhile Radiolites peroni and Sauvagesia sharpei had
already been signalled in the Turonian beds by Par ona (1932) and in the Zolla Member
by Cucchi et al. (1987), respectively. In addition, Praeradiolites cf. P. ßeuriausus and
Radiolites carsicus are also present in the Cenomanian of the Archi locality (Karst of
Gorizia) by Caffau and Pleničar (1991).
All the radiolitid species are described in the following sections, where data concern-
ing their morphology, stratigraphie distribution, and geographical diffusion are reported. Ba-
sic source for the stratigraphie and geographic data is Sanchéz' catalogue (1981).
Family Radiolitidae Gray, 1848
Subfamily Radiolitinae Gray, 1848
Genus Praeradiolites Douvillé, 1902
Praeradiolites acutilamellosus n. sp.
PI. 1, figs. 1, 2, 3, 4; PI. 2. figs. 1, 2, 3; PI. 7, fig. 1
Derivation of name: The specific name acutilamellosus is due to large and strongly
dissociated lamellae.
Type-series: Holotype, MCV 104 (PL 1, fig. 1). Paratype, MCV 105 (PI. 1, fig. 2),
deposited in the rudist collection of the Institute of Geology and Paleontology, University
of Trieste.
Examined material: Lower valves of 15 specimens from MCV 104 to MCV 118,
deposited in the rudist collection of the Institute of Geology and Paleontology, University
of Trieste.
Type-locality: Visogliano (Vižovlje) near Sistiana (Sesljan).
Diagnosis: The right valve shows strong external lamellae turned towards the com-
missure and proyecting outwards in correspondence of the cardinal zone (PI. 2, fig. 2). A
considerable variability characterizes the siphonal ridges which are protruding, flat (PI. 1,
figs. 1, 2) or rounded (PI. 1, fig. 4; PI. 2, fig. 1). The ridge "E" is wider than ridge "S". The
interband is slightly concave; in its middle part it shows a weak rib, which does not appear
in all the specimens. Where present, the rib is differently pronounced, mostly in the lower
part of the valve. (PI. 1, fig. 2; PI. 2, fig. 2). The ligament ridge is thin. The valve layer is
considerably broader in the cardinal zone than in the siphonal one.
Description: The valves are from 25 to 90mm long, with a commissural diameter of
30-60mm. The structure of the layer is characterized by parallel rows of rectangular prisms
along the entire valve periphery, save for the siphonal zone where the rows of prisms bend
and form a syncline-like arrangement (PI. 7, fig. 1). External lamellae are both almost hori-
zontal in correspondence of the cardinal side, and erected in the siphonal one.
Similarities and differences: Prœradiolites acutilarmllosusmseTcib\es\hesY>Q-
cies Praeradiolites ßeuriausus (d'Orbigny), but it differs from the latter for the lack of
foot fold "V".
Praeradiolites cf. P. ßeuriausus (d'Orbigny, 1842)
PI. 4, fig. 4; PI. 7, fig. 2
Examined material: Lower valves of 6 specimens; from MCV 120 to 125, depos-
ited in the rudist collection of the Institute of Geology and Paleontology, University of Trieste.
The development of the mollusc fauna in the Cenomanian...	95
Description: The lower valves are cylindrical-conical, from 40 to 70mm long, with
commissural diamater of 30-39mm. The lower valve has strong and protruding lamellae. In
the lower part of the valve, in correspondence with the foot fold "V", the lamellae are
pronouncedly inverted (PI. 4, fig. 4). The siphonal zone is not entirely preserved in each
valve examined. This part is damaged in all the specimens, and as a consequence, the spe-
cies could not be exactly determined. Because of this, a dubitative taxonomic attribution is
to be preferred. The celluloprismatic structure of the layer is very evident in eros section
(PI. 7, fig. 2). The layer is 1-2 mm thick in the siphonal side, and 3-4mm in the cardinal
one.
Stratigraphie distribution and geographic diffusion: Even if this spe-
cies is dubitatively determined, we recall that Praeradiolites ßeuriausus (d'Orbigny) is
characteristic of Cenomanian. It may be found in Italy, Istria (Croatia), France and Roma-
nia.
Genus Radiolites Lamarck, 1801
Radiolites carsicus n. sp.
PI. 3, figs. 1, 2, 3; PI. 4, figs. 1, 2; PI. 8, figs. 1, 2, 3
Derivation of name: The specific name carsicus is due to Karst of Trieste.
Type-series: Holotype, MCV 126 (PL 3, fig. 2). Paratype MCV 127 (PL 4, fig. 1); MCV
128 (PI. 4, fig. 2), deposited in the rudist collection of the Institute of Geology and Paleon-
tology, University of Trieste.
Examined material: Lower valves of 20 specimens; from MCV 126 to MCV 145, de-
posited in the rudist collection of the Institute of Geology and Paleontology, University of
Trieste.
Type-locality: Visogliano (Vižovlje) near Sistiana (Sesljan).
Diagnosis: The lower valve is from 41 to 110mm long, abruptly narrowing towards
the basis, ornamented with fine longitudinal ribs. The external lamellae are numerous and
well expressed. They also pass through the siphonal region. The latter consists of two pro-
truding siphonal ridges. In some specimens, the ridge "E" is slightly stronger than ridge "S".
The intersiphonal area is characterized by two different types of ornamentation. The most
frequent ornamentation is constituted by three longitudinal ribs, which run along the shell,
or by V-shaped protruding lamellae.
Description: Twenty lower valves have been studied. They are 40 to 112mm long,
with a commissural diameter of 25-50mm. The shell is traversed by rounded and well ex-
pressed ribs interrupted by weU developed neighbouring megacycles. The "E" siphonal band
is rounded, protruding and similar to the "S" band. The interband consists of both three
ribs, very similar to the others of the shell (PL 3, fig. 2) and by "V"-shaped lamellae (PL 4,
figs. 1, 2). In a transversal section of the lower valve the siphonal zone shows a structure of
pseudopillars. The "E" siphonal zone shows two small different-sized lobes, meanwhile the
"S" zone presents only one prominent lobe (PL 8, figs. 1, 2). In cross section the cellular
structure of the shell is evident (PL 8, figs. 1, 2, 3) The ligament ridge is triangular.
Similarities and differences: Radiolites carsicus n. sp. differs ivom Radiolites
lusitanicus (Bayle) and Radiolites trigeri (Coquand) because of the siphonal area mor-
phology. "E-S" bands are very protruding and rounded in Radiolites carsicus n. sp., while
in the other mentioned species these bands are slightly pronounced and flattened.
96	Mauro Caffau, Nevio Pugliese & Mario Pleiiičar
Radiolites peroni (Choffat, 1886)
PI. 4, fig. 3
1981 Radiolites peroni (Choffat) - Sánchez, p. 182 сшп syn.
Examined material: Lov^^er valves of 3 specimens, from MCV29 to MCV 31, depos-
ited in the rudist collection of the Geology and Paleontology Institute of Trieste university.
Description: The low^er valves examined are from 30 to 45nun long with a conical
shape. The outer part of the shell consists of a series of protruding and neighbouring mega-
cycles. The lamellae are traversed by wdde longitudinal ribs which determine an undulating
outline. The "E-S" bands are flattened, slightly protruding, and have similar sizes. The
interband is concave and traversed by a pleat which vanishes towards the basis of the shell.
The ligament ridge is small and triangular. The inner part of the layer shows a poligonal
structure, which is sometimes seen as a quadrangular network. This effect should be due
to oblique sections as reported byAlencaster and Pons (1992).
Stratigraphie distribution and geographic diffusion: Radiolites peroni
(Choffat) is characteristic of Cenomanian. It may be found in Italy, Istria (Croatia), Portu-
gal, France, Greece, Romania, Albania, Liban and Iran.
Subfamily Sauvagesiinae Douvillé, 1908
Genus Sauvagesia Bayle, 1887
Sauvagesia sharpei (Bayle, 1857)
PL 5, fig. 1; PL 9, fig. 1.
1981 Sauvagesia sharpei (Bayle) - Sánchez, p. 202 cum syn.
Examined material: Lower valves of 6 specimens, from MCV 20 to MCV 25, depos-
ited in the rudist collection of the Institute of Geology and Paleontology, University of Trieste.
Description: The lower valves are cylindrical-conical and slightly curved, crossed by
thin longitudinal ribs. The valves are from 45 to 100mm long wdth a commissural diameter
of 25-50mm. The "E" siphonal band is three times wdder than the "S" one. Along the "E"
band there are 17 thin ribs, and other 7 can be seen in the "8" band. The interband is con-
cave. The triangular ligament ridge is weUpronounced. The shell structure is prismatic,
consisting of hexagonal prisms (PL 9, fig. 1).
Stratigraphie distribution and geographic diiixxsion-. Sauvagesia sharpei
(Bayle) is characteristic of late Cenomanian-early Turonian. It may be found in Italy, Croatia,
Portugal, Spain, France and Algeria.
Genus Durania Douvillé, 1908
Durania acuticostata n. sp.
PL 5, figs. 2, 3; PL 6, figs. 1, 2; PL 9, fig. 2
Derivation of name: The specific name acuticostata is to due to its ornamenta-
tion, characterized by strong and longitudinal costae.
Type-series: Holotype, MCV 4 (PL 6, figs. 1, 2). Paratype, MCV 5. (PL 5, fig. 3),
deposited in the rudist collection of the Institute of Geology and Paleontology, Uruversity
of Trieste.
Examined material: Lower valves of 15 specimens from MCVI to MCV 15, depos-
ited in the rudist collection of the Institute of Geology and Paleontology, University of Trieste.
The development of the mollusc fauna in the Cenomanian...	97
Type-locality: Visogliano (Vižovlje) near Sistiana (Sesljan).
Diagnosis: The low^er valve is conical-cylindrical and characterized by a commissural
diameter which is 0.5-1 times longer than the shell. 13-16 triangular and well pronounced
costae run longitudinally along the thick shell. The "E" siphonal band area is flattened and
traversed by 9-11 thin ribs while the "S" area shows 5-7 ones. A concave interband, as wide
as the "S" band, is traversed by a protruding thin rib.
Description: These specimens are characterized by graceless lower valves, v^th a
development in length once or twice the commissural diameter. In the correspondence with
the commissure, the thickness of the layer varies from 6 to 10mm, in the dorsal zone, and
from 1 to 2.5mm, in the ventral one (PI. 9, fig. 2). The "E" and "S" siphonal band areas are
flattened, slightly protruding, and located in the thinner part of the shell (ventral zone).
The "E" band is three times wdder than the "S" band. Both are separated by a concave 1.8mm
deep and 4mm vvide interband, traversed by a thin 0.4mm wide and 0.6mm high rib (PI. 6,
figs. 1-2). Thin sections of lower valves show the celluloprismatic structure of the shell. In
addition, a great difference in thickness between the dorsal and ventral areas is evident.
The former is thicker than the latter. The shell ornamentation consists of triangular and
well pronounced ribs, wáth wide basis and acute apex. The distance between the ribs cor-
responds to the width of each rib.
Similarities and differences: Durania acuticostata n. sp. presents significant
differences wdth respect to all the species of this genus so far described in literature, mainly
for the morphology of siphonal area (presence of a concave interband) and the shell orna-
mentation (strong and longitudinal costae).
Discussion
Save for the interval 1, which should be generically attributed to middle-late Cenomanian
for the presence of Chrysalidina gradata (PL 10, fig. 1), in agreement vdth De Castro (in
Schroeder & Neumann, 1985), the Visogliano sequence can be entirely attributed to
late Cenomanian p.p. This chronological attribution is due to Broeckina balcanica (PL 10,
figs. 2, and 3), which is present in all the Visogliano sequence, and over all to Chondrodonta
joannae and Neithea fleuriausiana. Really, the foraminiferal species is considered as
middle-late Cenomanian in age by Cherchi and Schroeder (in Schroeder & Neumann,
1985), meanwhile the molluscs are considered as late Cenomanian in age by Dhondt and
Die ni (1993). In agreement with the above described data, it is possible to refine the pre-
vious chronological attribution of the majority of the lower part of the ZoUa Member by dating
back it from Cenomanian-Turonian to late Cenomanian p.p.
Thus, the previously described environmental evolution mainly occurs during the late
Cenomanian p.p. Within a frame of an evolution of restricted settings, it is possible to record
a very important biological event: the development of the mollusc fauna and, particularly,
of the radiolitids. Really, after a first very brief appearance of requienids within the Aptian-
Albian limestones of the Monte Coste Member, the moUuscs found in the Visogliano sequence
are able to colonize the substrates.
In the Visogliano sequence, the development of the mollusc fauna begins with the oc-
currence of two radiolitid species, such as Praeradiolites cf. P. ßeuriausus and Sauvagesia
sharpei, in the interval 1. This colonization is interrupted several times, as recorded in the
dolostones of the interval 1, the bioclastic high bottom energy limestones of the interval 2,
and in the dolostones and bioclastic limestones of the interval 3. Thus, the above cited
radiolitid species are able to colonize the substrate in the scattered way, only in correspon-
98	Mauro Caffau, Nevio Pugliese & Mario Pleiiičar
dence with the favourable environmental conditions, probably linked to restricted rather
than very restricted settings. In the intervals 3 and 4, the specimens of Chondrodonta
joannae begin colonizing the substrate with their lamellar shells. The succession of several
generations of shells of Chondrodonta joannae is recorded in the thick build-up of the
interval 4 and testifies their builders' activity. This action is again interrupted in the inter-
val 5, in correspondence with the dolomitic limestones of very restricted environment. In
the interval 6, several radiolitid species (Radiolites carsicus n. sp., Radiolites peroni,
Praeradiolites acutilamellosus n. sp., Praeradiolites cf P. ßeuriausus, Sauvagesia
sharpei, oxiá Durania acuticostata n. sp.), Chondrodonta joannae, and rare specimens
of Neithea ßeuriausiana occur probably in relation to a change from very restricted to
restricted environment. Such molluscs take advantage of this situation and begin again colo-
nizing the substrate with specimens of Chondrodonta joannae and radiolitid elevators (PI.
11, fig. 1; sensu Skelton, 1978,1985). As soon as these forms have prepared a sufficiently
coherent substrate, successive radiolitids, i.e. the encrusters (PI. 11, fig. 2; sensu Skelton,
1978, 1985), appear and settle on the previous shells.
Among the radiolitids, the elevators are more frequent with respect to the encrusters.
The elevators are able to aggregate in monospecific clusters mainly consisting oi Radiolites
carsicus n. sp. or Praeradiolites acutilamellosus n. sp. These clusters consist of up to 10
specimens, which present thick, well ornamented, cylindric-conical, straight, more or less
equal in size shells, with neighbouring megacycles. This shell morphology corresponds to
an increased sedimentation and a decreased bottom energy. Other elevators present an
individual development; they are characterized by very flattened ornamentations, such the
megacycles in Praeradiolites acutilamellosus n. sp., or by conical shapes with broad ba-
sis in correspondence with the commissure, as present in Sauvagesia sharpei. These or-
namentations and shapes represent adaptive strategies to avoid the burial. The encrusters
always show an individual development and are represented by small specimens from 29 to
40 mm in size.
The following intervals show a probably local decline of the radiolitid fauna, probably
due to an increased bottom energy (limestones of the intervals 7, and 9), with an interbedded
period of very restricted conditions (dolomitic limestones of the interval 8).
In conclusion, the molluscs found in the Visogliano sequence are represented by a num-
ber of species, which is the highest of all the outcrops hitherto examined within the Zolla
Member. Among them, three radiolitid species are described as new (Praeradiolites
acutilamellosus, Radiolites carsicus, and Durania acuticostata.
It is also possible to underline the role of both Chondrodonta joannae and the eleva-
tors in preparing the substrate for the life of successive molluscs and for their builders'
activity. In addition, among the radiolitids, it is also possible to consider Praeradiolites cf.
P. ßeuriausus and Sauvagesia sharpei, which are able to tolerate a continuous shifting
from restricted to very restricted environment (interval 1), as pionier species in colonizing
the environment. Thus, they can be considered as opportunistic species. Other radiolitids
species (Radiolites carsicus n. sp., Radiolites peroni, Praeradiolites acutilamellosus
n. sp., and Durania acuticostata n. sp.) appear successively and probably indicate stabler
environmental conditions with respect to the previous ones. With respect to the tolerance
of environmental changes, this can suggest a possible hierarchy of radiolitids from the most
tolerant (Praeradiolites cf. P. ßeuriausus and Sauvagesia sharpei) to the least tolerant
(Radiolites carsicus n. Radiolites peroni, Praeradiolites acutilamellosus n. sp., and
Durania acuticostata). This hierarchy wiU have to be tested and, if verified, enlarged in
further studies on rudist communities of the Karst area.
The development of the mollusc fauna in the Cenomanian...	99
Acknowledgements
We gratefully acknow^ledge geom. Marino Caffau for finding the fossiliferous area. We
also thank Marjan Grm for the photographic job and Dr. Maria Ines Gutierrez and Dr. Simon
Pire for helping with the translation of the text. Research is supported by 40 % and 60 %
MURST Programs (1992), directed by G. Longo Salvador and N. Pugliese, respectively, and
with the grant of the Ministry for Science and Technology of the Rep. Slovenia and of the
Slovene Academy of Sciences and Arts.
References
Alencaster, G. & Pons, J. M. 1992: New observation on the Upper Cretaceous rud-
ist of Chiapas. - Comparison between american and european fauna and taxonomic impUca-
tions 28, 327-339, 1 fig., 2 pis., Roma.
Caffau, M. & Pleničar, M. 1991: Rudistid fauna from Turonian deposits of the local-
ity Archi/Moščenice in the surroundings of Duino (Karst of Triest). - Razprave SAZU 4. razreda
32 (8), 259-315, 4 figs., 16 pis., Ljubljana.
Colizza, E., Costa, R., Cucchi, F.. Knezaurek, G., Pirini Radrizzani, C.,
Pugliese, N., Ulcigrai, F. & Zucchi Stolfa, M. L. 1987: The geology of the San Pela-
gio area (Karst of Trieste, Italy). - Mem. Soc. Geol. It. 40, 45-51, 6 figs., Trieste.
Cucchi, F., Melis, R., Pallini, M., Pirini Radrizzani, C., Pugliese, N. & Ul-
cigrai, F. 1986: 11 passaggio Cenomaniano-Turoniano nell'area di Monrupino (Carso Triesti-
no). - Quad. Mus. Geol. Paleont. Monfalcone, num. spec. 13-24, 11 figs., Monfalcone.
Cucchi, F., Pirini Radrizzani, C. & Pugliese, N. 1987: The carbonate stratigraphie
sequence of the Karst of Trieste (Italy). - Mem. Soc. Geol. It. 40, 35-44, 1 fig., 2 tabs., Tri-
este.
Dhondt, A. V. & Dieni, 1. 1993: Non-rudistid bivalves from late Cretaceous rudist
limestones of NE Italy (Col dei Schiosi and Lago di S. Croce areas). - Mem. Sc. geol. 45, 165-
241, 18 text-figs., 20 pis., 1 tab., Padova.
Forti, F. & M as oli, M. 1969: Comparazioni cronostratigrafiche delle formazioni car-
bonatiche del Carso Triestino. - Boll. Bibl. e dei Mus. Civ. e delle Biennali d'arte antica, 1-23,
Udine.
Masoli, M. & Ulcigrai, F 1969: Termini Albiani della serie stratigrafica del Carso
Triestini. - St. Trent. Sc. Nat., Sez. A 46, 65-91, Trento.
Parona, C. F. 1932: Fauna cretacica di Aurisina (Trieste). - Giornale di Geologia, ser.
2, vol. 7, 405-421, Bologna.
Polšak, A. 1979: Upper Cretaceous beds of the Northwestern part of Outer Dinarides
(Lika, Croatian littoral and Istria). - 16th Europ. Micropaleont. Coll., 101-106, Ljubljana.
Schroeder, R. & Neumann, M. 1985: Les grands foraminifères du Crétacé moyen de
la région méditerranénne. - Geobios, Mém. 7 spécial, 1-161, 68 pis., Lyon.
Sánchez, M. V. 1981: Hippuritidae y Radiolitidae (Bivalvia). - Catalogo de especies. -
Univ. aut. Barcelona, pub. de geologia 15, 1-228, Barcelona.
Skelton, P. W. 1978: The evolution of functional design in rudist (Hippuritacea) and
its taxonomic impUcation. - Phil. Trans. R. Soc. London. 284a., 305-318, 1 pl., 8 figs., London.
Skelton, P. W. 1985: Preadaptation and evolutionary innovation in rudist bivalves. - Spec.
Pap. Paleont. 33, 159-173, 2 pis., 3 figs., London.
100	Mauro Caffau, Nevio Pugliese & Mario Pleiiičar
Plate 1 - Tabla 1
i, 2 Praeradiolites acutilamellosus n. sp.
Ventral side view of holotype (fig. i) and paratype (fig. 2). The straight and protruding
E-S siphonal bands can be seen (x 1). Visogliano. Samples MCV 104 (holotype) and MCV
105 (paratype)
Pogled na ventralno stran holotipa (si. i) in paratipa (si. 2). Vidimo ravni in štrleči si-
fonalni progi E-S(x 1). Vižovlje. Primerka MCV 104 (holotip) in MCV 105 (paratip)
3	Praeradiolites acutilamellosus n. sp.
Lateral view (x 1). Visogliano. Sample MCV 111
Pogled od strani (x 1). Vižovlje. Primerek MCV 111
4	Praeradiolites acutilamellosus n. sp.
Ventral side view. The E-S siphonal bands are rounded and protruding (x 1). Visogliano.
Sample MCV 112
Ventralna stran. Sifonalni progi E-S sta zaobljeni in štrleči (x 1). Vižovlje. Primerek MCV
112
The development of the mollusc fauna in the Cenomanian...	101
102	Mauro Caffau, Nevio Pugliese & Mario Pleiiičar
Plate 2 - Tabla 2
1	Praeradiolites acutilamellosus n. sp.
Ventral side view. The rounded E-S siphonal bands can be seen (x 1). Visogliano. Sample
MCV 113
Ventralna stran. Vidni sta zaobljeni sifonalni progi E-S (x 1). Vižovlje. Primerek MCV 113
2	Praeradiolites acutilamellosus n. sp.
Protruding and flattened E-S siphonal bands (x 1). Visogliano. Sample MCV 114
Štrleči in sploščeni sifonalni progi E-S (x 1).Vižovlje. Primerek MCV 114
3	Praeradiolites acutilamellosus n. sp.
Lateral view. The neighbouring megacycles can be seen (x 1). Visogliano. Sample MCV 107
Pogled od strani. Vidijo se sosednji megacikli na lupini (x 1). Vižovlje. Primerek MCV 107
The development of the mollusc fauna in the Cenomanian...	103
104	Mauro Caffau, Nevio Pugliese & Mario Pleiiičar
Plate 3 - Tabla 3
1, 2 Radiolites carsicus n. sp.
Ventral side view of holotype (fig. 2) and paratype (fig. i). The E-S siphonal bands are
seen as rounded and protruding ribs. The interband is traversed by three ribs (x 1). Vi-
sogliano. Samples MCV 127 and MCV 128
Ventralna stran holotipa (si. 2) in paratipa (si. i). Sifonalni progi E-S sta zaobljeni štrleči
rebri. V medsifonalni coni potekajo tri podolžna rebra (x 1). Vižovlje. Primerka MCV 127
in MCV 128
3 Radiolites carsicus n. sp.
Ventral side view (x 1). Visogliano. Sample MCV 131
Ventralna stran (x 1). Vižovlje. Primerek MCV 131
The development of the mollusc fauna in the Cenomanian...	105
106	Mauro Caffau, Nevio Pugliese & Mario Pleiiičar
Plate 4 - Tabla 4
1, 2 Radiolites carsicus n. sp.
Ventral side view of two specimens. The protruding and rounded E-S siphonal bands, and
the V - shaped interband can be seen (x 1). Visogliano. Samples MCV 129 and MCV 130
Ventralna stran dveh vzorcev. Vidimo štrleči in zaobljeni sifonalni progi E-S in medsifonalno
cono v obliki črke V (x 1). Vižovlje. Primerka MCV 129 in MCV 130
3	Radiolites peroni (Choffat)
Ventral side view. The E-S siphonal bands are flattened and protruding. The interband
is traversed by a rib (x 1). Visogliano. Sample MCV 24
Ventralna stran. Sifonalni progi sta sploščeni in štrleči. Na medsifonalni coni je podolžno
rebro (x 1). Vižovlje. Primerek MCV 24
4	Praeradiolites cf. P. fleuriausus (d'Orbingny)
Lateral view of foot fold V (x 1). Visogliano. Sample MCV 121
Lateralna stran z nožno gubo V (x 1). Vižovlje. Primerek MCV 121
The development of the mollusc fauna in the Cenomanian...	107
108	Mauro Caffau, Nevio Pugliese & Mario Pleiiičar
Plate 5 - Tabla 5
1 Sauvagesia sharpei (Bayle)
Ventral side view (x 1). Visogliano. Sample MCV 21
Ventralna stran (x 1). Vižovlje. Primerek MCV 21
ê Durania acuticostata n. sp.
Ventral side view. The E and S siphonal areas are wide, flattened and slightly protruding
(x 1). Visogliano. Sample MCV 2
Ventralna stran. Sifonalni progi E in S sta široki, sploščeni in rahlo štrleči (x 1). Vižovlje.
Primerek MCV 2
3 Durania acuticostata n. sp.
Lateral view. The ornamentation characterized by strong and triangular costae can be seen
(x 1). Visogliano. Sample MCV 5
Lateralna stran. Značilna ornamentacija so močna trikotna rebra (x 1). Vižovlje. Primerek
MCV 5
The development of the mollusc fauna in the Cenomanian...	109
110	Mauro Caffau, Nevio Pugliese & Mario Pleiiičar
Plate 6 - Tabla 6
2	Durania acuticostata n. sp.
Holotype. Ventral (fig. i) and dorsal view (fig. 2) of the same specimen. The E-S sipho-
nal areas traversed by thin ribs, and the concave interband with a thin rib (fig. i) and
longitudinal costae (fig. 2) can be seen (x 1). Visogliano. Sample MCV 12
Holotip. Ventralna (si. i) in dorzalna (si. 2) stran istega primerka. Čez sifonalni progi E-S
potekajo tenka rebra, vidimo pa tudi konkavno medsifonalno cono s tenkim rebrom (si.
i) in še z več drobnimi rebri (x 1). Vižovlje. Primerek MCV 12
3	Neithea ßeuriausiana (d'Orbigny)
Left valve (x 1). Visogliano. Sample MCV 22b
Leva lupina (x 1). Vižovlje. Primerek MCV 22b
The development of the mollusc fauna in the Cenomanian...	Ill
112	Mauro Caffau, Nevio Pugliese & Mario Pleiiičar
Plate 7 - Tabla 7
1 Praeradiolites acutilamellosus n. sp.
Transversai thin section showing the celluloprismatic structure. In the siphonal area, the prisms
form a syncline-like arrangement. Visogliano. The length of the bar at the bottom of the table
corresponds to 10mm
Prečni presek (zbrusek) kaže celuloprizmatično strukturo lupine. V sifonalni coni so prizme
razporejene v obliki sinklinale. Vižovlje. Dolžina črtice spodaj ustreza dolžini lOmm
S Praeradiolites cf. P. ßeuriausus (d'Orbigny)
Transversal thin section showing the celluloprismatic structure. Visogliano. The length of the
bar at the bottom of the table corresponds to 10 mm
Prečni presek (zbrusek) kaže celuloprizmatično strukturo lupine. Vižovlje. Dolžina črtice spodaj
ustreza dolžini 10 mm
The development of the mollusc fauna in the Cenomanian...	113
114	Mauro Caffau, Nevio Pugliese & Mario Pleiiičar
Plate 8 - Tabla 8
1, 2 Radiolites carsicus n. sp.
Transversai thin section of three specimens showing the celluloprismatic structure. The
siphonal structure E is seen as a double radial band and S structure as one radial band
(magnification of fig. 1 - x 2.5, and fig. 2 - x 3.5). Visogliano
Prečni preseki (zbruski) treh primerkov kažejo celuloprizmatično strukturo. Struktura lupine
v sifonalni coni E je podobna dvojni radialni progi, v sifonalni coni S pa enojni radialni
progi (povečava si. 1 - x 2,5 in si. - x 3,5). Vižovlje
3 Radiolites carsicus n. sp.
Transversal thin section showing a celluloprismatic structure. The structures of E-S si-
phonal bands differs from those of figs. 1, 2 because the section is not perfectly trans-
versal to the development of the specimen. Visogliano. The length of the bar at the bot-
tom corresponds to 10 mm
Prečni presek (zbrysek) spodnje lupine kaže celuloprizmatično strukturo. Strukturi sifonakiih
prog E-S se ločita od struktur na slikah 1, 2, ker presek na sliki 3 ni popolnoma pravokoten
na glavno os primerka. Vižovlje. Dolžina črtice spodaj ustreza dolžini lOmm
The development of the mollusc fauna in the Cenomanian...	115
116	Mauro Caffau, Nevio Pugliese & Mario Pleiiičar
Plate 9 - Tabla 9
Sauvagesia sharpei (Bayle)
Transversai thin section showing the celluloprismatic structure (x 2). Visogliano
Prečni presek (zbrusek) spodnje lupine kaže celuloprizmatično strukturo (x 2). Vižovlje
Durania acuticostata n. sp.
Transversal thin section the lower valve showing the celluloprismatic structure (x 2). Visogliano
Prečni presek (zbrusek) spodnje lupine kaže celuloprizmatično strukturo (x 2). Vižovlje
The development of the mollusc fauna in the Cenomanian...	117
118	Mauro Caffau, Nevio Pugliese & Mario Pleiiičar
Plate 10 - Tabla 10
1 Chrysalidina gradata (x 38)
Interval 6 of the Visogliano sequence
Interval 6 stratigrafskega zaporedja pri Vižovljah
2, 3 Some sections of Broeckina balcanica (x 58)
Interval 6 of the Visogliano sequence
Nekaj presekov vrste Broeckina balcanica (x 58)
Interval 6 stratigrafskega zaporedja pri Vižovljah
The development of the mollusc fauna in the Cenomanian...	119
120	Mauro Caffau, Nevio Pugliese & Mario Pleiiičar
Plate 11 - Tabla 11
1	Monospecific cluster of Praeradiolites acutilamellosus n. sp. consisting of specimens
developped as elevators (x 1). Visogliano
Monospecifični skupek rudistov vrste Praeradiolites acutilamellosus n. sp., razvit kot
elevator (x 1). Vižovlje
2	Specimens of Praeradiolites acutilamellosus n. sp. (signet by the arrow) encrusted on
the shell of a shell of Radiolites carsicus n. sp. (x 1). Visogliano
Primerki vrste Praeradiolites acutilamellosus n. sp. (označeni s puščico), prirasli
(inkrustirani) na lupini vrste Radiolites carsicus n. sp. (x 1). Vižovlje
The development of the mollusc fauna in the Cenomanian...	121