Mapping of Phanerozoic rocks at 1:250,000 scale by joint teams from the Saudi Arabian Deputy Ministry for Mineral Resources and the Bureau de Recherches Géologiques et Minières since 1980 has covered most of the Jurassic outcrops in central Saudi Arabia. Stratigraphic, sedimentologic and paleogeographic studies provided a precise framework for collected gastropod faunas that could be calibrated against ammonite zones and sequence-stratigraphic zones. Of more than 600 samples collected, about 440 gastropod specimens could be determined on at least a generic level. Their age range is from Bajocian to Oxfordian–Kimmeridgian. They correspond to 26 genera and 35 species from the Euomphalidae, Ataphridae, Pseudomelaniidae, Coelostylinidae, Procerithiidae, Nerineidae, Purpurinidae, Aporrhaidae, Naticidae, Acteonidae, Retusidae, and Akeridae families. Twelve species are new, and three (Kosmomphalus and Bifidobasis in the Euomphalidae, and Striatoonia in the Pseudomelaniidae) were proposed for new taxa of generic or subgeneric rank. Most of the identified species are of Middle Jurassic age, mainly Bathonian and Callovian and only six are Late Jurassic. All species are typical of an internal platform environment (upper infralittoral), in a lagoonal to back-reef setting, but some also colonized the external platform in the lower infralittoral fore-reef zone. Paleogeographically, most of the species are related to European and Sinai faunas; only seven are equivalent to North African or East African faunas, and one only was reported from Madagascar.
The gastropod faunas studied were collected by joint field teams from the Saudi Arabian Deputy Ministry for Mineral Resources (DMMR) and the Bureau de Recherches Géologiques et Minières (BRGM). The collections were made during 1:250,000-scale field mapping of the Phanerozoic Cover Rock Program from 1980 to 1987. These are the first gastropod faunas from the Jurassic of central Saudi Arabia to be described and analyzed in detail, since the very limited data published by Newton and Crick (1908) and Newton (1921).
The fossils are from the Shaqra Group of Toarcian to Kimmeridgian age. They were collected during mapping of the 1:250,00-scale quadrangles shown on Figure 1. From north to south they are: Qibah (Robelin et al., 1994), Buraydah (Manivit et al., 1986), Al Faydah (Vaslet et al., 1985a), Shaqra (Vaslet et al., 1988), Ar Riyad (Vaslet et al., 1991), Darma (Manivit et al., 1985b), Wadi ar Rayn (Vaslet et al., 1983), Wadi al Mulayh (Manivit et al., 1985a), Sulayyimah (Vaslet et al., 1985b). In addition, reconnaissance field trips were made in the As Sulayyil, Wadi al Faw and Al Mudafin quadrangles.
GEOGRAPHIC AND GEOLOGIC DATA
(Y.-M. Le Nindre, J. Manivit and D. Vaslet)
The stratigraphic framework used for this study comes from papers by Le Nindre et al. (1990a, 1990b) and Manivit et al. (1990), supplemented with global bathymetric indicators (Le Nindre et al., 1988), and for eustasy (Le Nindre et al., 1990c). Many specialized papers have been published on the paleontology and biostratigraphy of these deposits: ammonites (Enay et al., 1986, 1987; Enay and Mangold, 1994); nautiloids (Tintant, 1987); brachiopods of Dogger age (Alméras, 1987); ostracods (Dépêche et al., 1987); calcareous nannofossils (Manivit, 1987); and dasycladacean algae (Bernier, 1987).
The gastropod faunas were collected from the Jurassic deposits that crop out along 1,000 km of the Tuwayq escarpment, between latitudes 28°N. and 18°N. It is around Riyadh (lat. 24°00′N) that the outcrops of Jurassic deposits are the widest (85 km) and thickest (over 1,000 m).
The Jurassic rocks are deposits of the Arabian platform on the southern margin of the Tethys Ocean bordering Gondwana. The open-sea domain during Jurassic times was over the area of the present Arabian Gulf (Dercourt et al., 1993; Al-Husseini, 1997).
Lithostratigraphic and Biostratigraphic Setting
The Shaqra Group is named after the town of Shaqra (Manivit et al., 1990), and comprises all Late Jurassic deposits in central Saudi Arabia. The group overlies the Late Permian to Late Triassic Buraydah Group (Le Nindre et al., 1990a) with a disconformable contact (erosion surface). The upper boundary of the Shaqra Group, corresponding to a pre-Early Cretaceous erosion surface, is overlain by the Early Cretaceous Thamama Group (Powers et al., 1966). These two erosion surfaces correspond to regional disconformities that are locally conformable at outcrop scale.
The Shaqra Group mainly consists of carbonates and claystone, with locally terrigenous deposits in the south and the northwest that correspond to margins of the platform. The Shaqra Group is divided into seven lithostratigraphic units mappable at 1:250,000 scale as defined by Powers et al. (1966) and Powers (1968), and revised by Manivit et al. (1990) (Figure2).
The abundant fossils sampled in the Shaqra Group permit a precise definition of the stratigraphy of Jurassic deposits in central Arabia. The biostratigraphic framework was based on ammonites (Enay et al., 1987). From the late Toarcian to the early Kimmeridgian, this Jurassic succession is divided into 16 ammonite biozones and 2 subzones. This biozonation is complemented by zonation based on other fauna (nautiloids, echinoderms, brachiopods, bivalves, gastropods, and hexacorals) and on microfauna (foraminifers, ostracods) and nannoflora. An Arabian ammonite zonation was later proposed by Enay and Mangold (1994). Reference is made to the West European and Mediterranean ammonite zonation (Groupe Français d’Etude du Jurassique, 1997) for the correlation of Arabian and European gastropod faunas, and a correlation between European and Arabian ammonite zonations is proposed in Figure 2.
From bottom to top, the Shaqra Group is subdivided into the following formations:
The Marrat Formation (126 m thick in the type section at Khashm adh Dhibi) is informally subdivided into lower (47 m), middle (40 m) and upper Marrat (39 m). It consists of interbedded marine sandstone, carbonate and claystone deposits that are Toarcian to older in age. According to the faunal contents, the upper part of the lower Marrat and the middle Marrat belong to the early Toarcian (Serpentinum zone). The basal part of the upper Marrat yielded a Nejdia fauna assigned to the middle Toarcian (Bifrons zone). The middle and upper parts of the upper Marrat deposits did not provide any paleontologic markers. A possible Aalenian hiatus exists between the Marrat and Dhruma formations.
The Dhruma Formation (450 m thick in the type section at Khashm adh Dhibi) comprises units D1 to D7 (Manivit et al., 1990). These are lower Dhruma (D1–D2: 143 m), middle Dhruma (D3–D6: 193 m) and upper Dhruma (D7: 111 m, type section at Khashm al Mashriq). The Dhruma Formation is mainly composed of limestone and claystone in the central part of the outcrop area. In the north and the south of this area, the formation is composed of detrital rocks. The age of the Dhruma Formation is early Bajocian to middle Callovian.
D1 The basal part of the lower Dhruma yielded an Euhoploceras and Hyperlioceras fauna of early Bajocian age (upper part of the Discites zone). The Shirbuirnia fauna found in the upper part of D1 is also dated as early Bajocian (lower part of the Laeviuscula zone).
D2 The basal part of D2 yielded a Dorsetensia, Normannites and Stephanoceras fauna together with the first primitive forms of Ermoceras dated as late early Bajocian (lower part of the Humphriesianum zone). The upper part of D2, the Dhibi Limestone Member, contains the main Ermoceras fauna of the late Bajocian Niortense zone.
D3 The basal and middle parts of D3 yielded late Bajocian ammonite faunas of the Garantiana zone (Ermoceras mogharense fauna) and the Parkinsoni zone (Thambites fauna). The Zigzagiceras fauna discovered at the top of D3 is early Bathonian in age (Zigzag zone).
D4 Yielded a Tulites fauna assigned to the early Bathonian Zigzag zone.
D5 Characterized by a Micromphalites fauna of early Bathonian age (Aurigerus zone).
D6 Yielded an endemic fauna with Dhrumaites and two species of nautiloids (Tinant, 1987) that suggest an early Bathonian age. The early Bathonian age is retained here and accords with a major break in sedimentation observed at the top of the middle Dhruma. However, this age is brought into question by the brachiopod faunas that could suggest a late Bathonian age for D6 (Almeras, 1987).
D7 The upper Dhruma is divided into two members, from bottom to top, the Atash Member and the Hisyan Member.
The Atash Member contains a carbonate nannofossil fauna typical of the middle Callovian in the Middle East (Manivit, 1987). As an ammonite fauna is missing, this middle Callovian age remains questionable. However, a stratigraphic hiatus is suggested at the D6–D7 (middle–upper Dhruma) boundary. At its maximum, this hiatus could represent the middle and late Bathonian, the early Callovian, and the base of the middle Callovian.
The Hisyan Member yielded a Grossouvria fauna in its lower part (possible Kuntzi Horizon according to Enay and Mangold, 1994) and a Pachyerymnoceras fauna in its upper part, both being assigned to a middle Callovian (Coronatum zone). This age is confirmed by the faunal associations of nautiloids (Tintant, 1987), brachiopods (Almeras, 1987), and nannoflora (Manivit, 1987).
The Tuwaiq Mountain Limestone (184 m in the type section near Riyadh) is composed of units T1 (32 m), T2 (56 m) and T3 (96 m) and is middle to late Callovian in age. It is locally clayey at the base but consists mostly of shallow-marine infralittoral to reefal-related limestone that creates the cuesta of Jabal Tuwayq, the main topographic feature of central Arabia.
T1, T2, and the bottom of T3, yielded (as for D7) a Pachyerymnoceras fauna attributed to the late middle Callovian (Coronatum zone).
Middle and upper parts of T3 yielded Peltoceras (El Asa’ad, 1989) and Pachyceras faunas assigned a late Callovian age (Athleta zone). A late Callovian age is also supported by nannoflora from the topmost beds of T3 (Manivit, 1987).
The Hanifa Formation (126 m thick in the type section south of Riyadh) comprises, from bottom to top, the units H1 (Hawtah Member) and H2 (Ulayyah Member) that are Oxfordian to early Kimmeridgian in age. The lower part of the formation is composed of carbonates and claystone, and the upper part is mainly carbonate rock, locally reefal.
The Hawtah Member is early Oxfordian (?Cordatum zone) at the base, based on brachiopods (Boullier, in Manivit et al., 1990). The middle and upper parts of the Member are middle Oxfordian (Plicatilis zone) according to the Euaspidoceras ammonite fauna (Enay et al., 1987), nautiloids (Tintant, 1987) and nannoflora (Manivit, 1987).
The Ulayyah Member is late Oxfordian in its basal part, based on the occurrence of foraminifera Alveosepta jaccardi (Andreieff, in Manivit, 1990), and brachiopods (Boullier, in Manivit, 1990). The upper part of the Member yielded echinid faunas (Clavel, in Manivit et al., 1990) that suggest an early Kimmeridgian age (?Hypselocyclum zone).
The Jubaila Limestone consists of units J1 (50 m) and J2 (35 m) that are early Kimmeridgian in age. It is composed of limestone with some sandstone on the southern and northwestern margins of the platform. In the Al Jubaylah type section north of Riyadh, these two units are considered as early Kimmeridgian in age because of nautiloids (Tintant, 1987) and affinities of the endemic ammonites with early Kimmeridgian ammonite faunas (Enay et al., 1987).
The Arab Formation consists of four superposed carbonate-evaporite sequences (Arab-D to Arab-A members) and is about 54m thick in outcr op. Microfaunal associations suggest a Kimmeridgian to Tithonian age.
The Hith Anhydrite, 90 m thick at Dahl Hit, corresponds to the evaporite sequence of the Arab-A Member (Powers et al., 1966). This unit has not yet yielded any fauna, but is considered as late Tithonian in age (Powers, 1968).
This stratigraphic framework shows a relatively precise biozonation of the Jurassic sequence of central Saudi Arabia, even if some uncertainties remain in details. The biozonation succession is interrupted by two major hiatuses:
The probable late Toarcian and Aalenian hiatus, between the Marrat and Dhruma formations.
The probable hiatus of the middle Bathonian to the base of the middle Callovian, between the middle and upper Dhruma.
Paleogeographic and Sedimentologic Setting
The Shaqra Group corresponds to a complete sedimentary cycle. This started in the early Toarcian, with the Liassic transgression on to the Arabian platform, and lasted until the Kimmeridgian/Tithonian evaporites at the top of the Group that correspond to a maximum confined environment.
The Marrat Formation first shows a mesotidal, then a lagoonal, and, finally, an infralittoral environment. Sequences are regressive, corresponding to a rapid subsidence at the base followed by a slow aggradation.
The Dhruma Formation recorded the highest tectonic activity of the Middle Jurassic, corresponding to deformation of the Arabian platform. Three domains are recognized from outcrop observations:
South of latitude 22°N., a deltaic zone of Bathonian to early Callovian age is traceable in the northern marine deposits of the Riyadh area, by a hiatus during the middle-late Bathonian to early Callovian period.
Between latitudes 22°N and 25°N., a carbonate platform was opened to the northeast.
Between latitudes 25°N and 28°N., a relatively deep platform-border zone received terrigenous deposits.
The maximum transgressive phases were roughly contemporaneous in these three domains. The first is clearest in central Arabia (Laeviuscula and Humphriesianum zones); the other phases extended more widely into the southern and northern border areas (Zigzag and Coronatum zones).
The Tuwaiq Mountain Limestone shows reef-related platform deposits in its upper part. The extension of these facies during the middle and late Callovian was the result of repeated transgressive reef sequences. Condensed beds, south of latitude 22°N. at the base of the T3 unit, mark one of the maximum Jurassic marine transgressions over the Arabian platform (Le Nindre et al., 1990b).
The Hanifa Formation, in its lower middle part, corresponds to a more confined environment, with well-bedded sand bodies. This indicates a cessation of the transgression that restarted during the Callovian (upper Dhruma). The upper Hanifa Formation corresponds to a new transgressive trend identified by the appearance of the benthic foraminifer Alveosepta jaccardi and of reef facies with bioherms.
The Jubaila Limestone is a marine carbonate formation characterized by high-energy reworked terrigenous deposits. The abundant presence of rolled and crusted fossils and lithoclasts suggests episodic causes, such as violent storms or faulting.
The Arab Formation and the Hith Anhydrite show a rapid succession of four carbonate sequences with, for each, a confined environment at the top with gypsum, salt and anhydrite deposits. The carbonates include reworked, altered, and cumulative coastal deposits. Mud-deposits and post-mortem crusts are typical of inner platform environments, from mediolittoral to very proximal infralittoral. Deposits indicate a very flat, shallow-marine topography, similar to that prevailing in the Jubaila Limestone north of latitude 25°N, with crusts and hardgrounds.
The diagenesis of these rocks is seen in the clay content (kaolinite), local dolomitization of limestone, the formation of ferruginous oolites during transgressive periods, and the development of siliceous joint-fills. Compaction was high in the Jubaila Limestone, and supergene alteration (dissolution breccia) is found in the uppermost evaporite units.
STUDY OF THE GASTROPODS
Detailed sampling of fossils in the field provided a precise view of the in situ distribution of the gastropods, which contributed to a more precise paleogeographic interpretation of the Jurassic deposits that contain them. The main gastropod sites (Figure 3), as plotted on the sampled sections, show that the greatest fossil abundance occurred during the Bajocian, Bathonian and Callovian, within the Dhruma Formation (D1 to D7 units) and the Tuwaiq Mountain Limestone (T1 to T3 units). This concerns in particular the area covered by the Shaqra, Darma, Wadi Ar Rayn, and Wadi Al Mulayh quadrangles in central Saudi Arabia, where the deposits reach their maximum thickness. Gastropods, as well as other faunal elements, are less common in the north (Qibah) and south (quadrangles south of Wadi al Mulayh) of the platform.
The fauna is very rich in specimens of euomphalids, pseudomelaniids, nerineids, aporrhaids, naticids, and probable acteonids, all families that lived from Bajocian to Kimmeridgian times. However, most samples are internal molds, more or less deformed and impossible to identify specifically, even for the genus. Nevertheless, some internal molds were recognized of Callovian pleurotomariids and trochids, and two molds of a Portlandian neritid species.
About 600 samples were taken, corresponding to about 1,000 specimens. Less than half of these, however, were sufficiently well preserved to be of use in systematics.
The species descriptions below are followed by paleoecologic and paleoenvironmental comments that forms the basis for a discussion of the paleogeographic distribution of the studied faunas.
Description of Species
This study only describes those samples that provided a species determination with certainty; that is, 120 samples representing about 440 specimens. This paper presents the systematic study of 35 species, from Euomphalidae, Ataphridae, Pseudomelaniidae, Coelostylinidae, Procerithiidae, Nerineidae, Purpurinidae, Aporrhaidae, Naticidae, Acteonidae, Retusidae and Akeridae. Fourteen species are new and three, from the Euomphalidae and Pseudomelaniidae, required the proposal of new taxa, of genus or sub-genus rank.
Cleaning of the samples was difficult because of the extreme hardness of the host limestone and the relative fragility of the tests that were also composed of calcium carbonate. It was particularly so for species with fine or spiny ornaments that are easily destroyed by needles or microvibrator tools.
Species are described following the systematic order, by families and genus. Precise geographic locations of each sample are given for each quadrangle by alphanumerical values corresponding to the sampling site as it was numbered by the joint DMMR/BRGM field team. The identification numbers consist of the initials of the geologists responsible for the geological mapping of the relevant 1:250,000-scale quadrangle, the year of sampling, and the sequential sample number that corresponds to the site locality. For example: JMA82-34 for Jacques Manivit, year 1982, sample (site) no. 34; VD80-424 for Denis Vaslet, year 1983, sample (site) no. 424.
The samples collected, including the type specimens, are the property of the Saudi Arabian Deputy Ministry for Mineral Resources (now the Saudi Geological Survey) and are held in Jiddah, Saudi Arabia. Plastic molds of the studied samples are kept in the Laboratory of Paleontology, French National Museum of Natural History, Paris, were they can be examined. The Museum reference collection numbers of the molds are given with the description or illustration of each species.
Origin of name: from Latin, “with reticulate structure”.
Material. Two specimens. One is a test (holotype, no. IPM-B.74204) from the middle Callovian (higher part of unit D7, Coronatum zone), Buraydah quadrangle (site JMA.83-195). The other is an internal mold of the middle Callovian (base of unit T3, Coronatum zone), Shaqra quadrangle (site VD.82-532).
Dimensions. Holotype: preserved height 6.5mm; r econstituted height 7.5mm; pr eserved width 11.5mm; r econstituted width 13mm. The other specimen (internal mold) is 9.5mm high and 17mm wide.
Description. Shell perfectly planispiral, making four convex turns, separated by a hollow suture, the last whorl occupying all the height. The test is thick. The surface is ornamented by regularly spaced spiral cords, about twenty for the last whorl, that are crossed by collabral opisthocyrt ribs. These ribs remain alone at the end of growth, where they spread out and form small ridges. The last whorl is rounded on the edge, which lies at one-third of its height. The base is occupied by a deep umbilicus, non-circumscribed but well limited, where both costal and spiral ornaments continue. The aperture is higher than wide, somewhat smaller downward, holostomatous, with a slightly enlarged lip at the end of growth that is closely applied to the columellar side.
Observations. This species shows strong analogies with the genus Coelodiscus Brösamlen, 1909, and Colpomphalus Cossmann, 1916, both Early and Middle Jurassic, and usually assigned to the Euomphalidae family. However, it differs from them because of its flat spire and thick columellar ridge. It also differs from Coelodiscus by its costal and spiral ornament and from Colpomphalus by the absence of turberculous ornaments. These differences explain the creation of the new genus Kosmomphalus [from Greek kosmeo, ornamented, and omphalos, umbilicus, (m)] with K. reticulatus as the type species. Its diagnostic characteristics are a euomphaloid shell of modest size, planispiral with convex whorls, with both spiral and collabral ornaments, a non-circumscript umbilicus, an aperture higher than wide, and a thick columellar ridge.
Kosmomphalus reticulatus also shows some analogies with Klebyella striatocostataGründel (1998, p. 3, pl. 1, figs. 4-7), Callovian, Poland, that is a genus and species based on a single specimen less than one millimeter in size. This species is identified by an outline close to that of K. reticulatus and with the same spiral and axial ornaments. Gründel (1975, p.778, fig.2 in text and figs.15 and 16 on plate) had previously placed this fossil in the genus Coelodiscus sp. before proposing the new genus Klebyella in the Turbinidae (sub-family Liotiinae). However, K. reticulatus, with its euomphaloid-type character, differs from Klebyella striatocostata by its higher and clearly less discoid shape, its periphery situated at the upper third of the last whorl (sub-median in the species described by Gründel), its non-circular aperture that becomes smaller downward, and by its narrower umbilicus that is limited by a bulge and is clearly less enlarged.
Origin of name: from Jabal Tuwayq.
Material. Four specimens of the early Bathonian (unit D4, Zigzag zone), Shaqra quadrangle (sites JMA.82-354A and VD.82-630).
Holotype. specimen no. IPM-B.74201, site VD.82-630.
Dimensions. Holotype (juvenile): total height 10.5mm; aperture height 7mm; width 16.3mm; umbilicus diameter 5.5mm; incr easing angle of the first whorls 90°. The species can grow up to 15 mm high and 24 mm wide.
Description. The shell is of medium size, with five whorls, first of regular growth, then more or less strongly coeloconoid. The protoconch is slightly depressed, looking smooth. The first whorls are slightly bulged and are separated by a deep suture and ornamented by 8 to 10 granular cords crossed by prosoclinal ribs, first regular and closely spaced, then becoming wider spaced and stronger until the fourth whorl where they start forming nodes. The spiral cords persist until the last whorl where 15 nodes have become subspiny at end of growth. The periphery of the last whorl is smoothly convex and bi-keeled. The base, slightly bulged, is ornamented by 20 to 25 concentric granulated cords that are crossed by more or less irregular collabral ribs. A large umbilicus with excavated walls is limited by 10 to 15 strong nodosities. The end of the last whorl is detached and inclined downward from a width of about 20 mm. The subcircular aperture with continuous lip is initially slightly oblique, but, by the end of growth at the last whorl, forms an angle of 50° to 60° with the spiral axis.
Observations. This species resembles both Colpomphalus polygonoides (Hudleston, 1892, p.323, pl. XXVI, fig. 9), late Bajocian, Great Britain (see also Cossmann, 1916, p.137, pl.VI, figs.13–15), and C. coronatus (Terquem and Jourdy, 1871, p.60, pl.III, figs.1–3), early Bathonian, France. However, it is different from the latter because of its higher spiral, and from both by the greater height of its last whorl, and its bi-keeled curve.
This species could be related to Colpomphalus altus nov. sp. (Delpey, 1948, p.8, pl.I, fig.1), Bathonian, northwest Madagascar, which was sketchily described and drawn, but seems different by its apparently higher spiral and its clearly less open umbilicus. The taxon proposed by Delpey is in any case invalid as it is homonymous with Colpomphalus altus (d’Orbigny, 1853), a distinct Bathonian species from France (see Fischer and Weber, 1997, p.124, pl.22, figs. 5a–c).
Material. Six specimens of the middle Callovian (middle and upper parts of unit D7, Coronatum zone), Buraydah quadrangle (sites JMA.83-194, -195, -199) and Shaqra quadrangle (sites VD.82-487, -607).
Dimensions. The largest specimen collected is 5.1mm high and 21.5mm wide, with an apertur e 5.1mm high and 7 mm wide.
Observations. These specimens present all morphologic and ornamental characteristics of Discohelix tenuisiensisCox (1969, p. 245, pl. I, figs. 1a–d), a species based on only one specimen from southeast Tunisia of early Callovian age. The upper face is planispiral or slightly excavated and ornamented on each whorl by about 15 spiral cords crossed by collabral and slightly prosoclinal ribs. The ribs are spaced regularly in two rows of crenulations, one on the suture limit and the other more developed at the periphery. The periphery of the last whorl is three-keeled, the upper and lower keels being crenulated and framing a middle one with fine oblique ribs. The lower face, largely umbilicated, is slightly bulged and ornamented by five to eight spiral cords that are crossed by very small collabral orthoclinal ribs. These ribs form also two rows of crenulations, one at the periphery and the other on the edge of the scaliform umbilicus. A sub-quadrangular aperture is clearly wider than high.
This species was attributed by Cox to the genus Discohelix but belongs in fact to the genus Asterohelix Szabó, 1984 (p. 67, fig. 2) in presenting all its characteristics.
Schröder (1995, p. 10) introduced a new family Discohelicidae (including the genera Discohelix, Nummocalcar, Platybasis, and Asterohelix) assigned to the Trochacea because of the homeostrophic details of the protoconch, but without consideration for the most important characteristics of the teleoconch. However, the homeostrophic feature of the protoconch is almost the same in both Trochacea and Euomphalacea, whereas the characteristics of the teleoconch are very different in these two superfamilies. Consequently, the genera Asterohelix and Nummocalcar are here assigned classically to the family Euomphalidae of which they have the main characteristics in common.
Material. Nine specimens of early Bathonian age (top of unit D3, and units D4 to D6, Zigzag and Aurigerus zones), Shaqra quadrangle (sites JMA.82-354, -354A, VD.82-482, -629), Darma quadrangle (site JMA.82-1), and Wadi ar Rayn quadrangle (site VD.80-424).
Dimensions. Specimen shown pl.1, figs.6a,b: height 9mm; total width 30mm; apertur e width 11mm. Specimens shown pl. 1, figs 5a–c: height 5.3mm; total width 20mm; apertur e width 7mm. This species can grow up to 40 mm wide, excluding spines.
Description. Shell sub-planispiral, made of six whorls with moderately depressed spirals. The upper face of the whorls is ornamented by five to seven weakly granulated spiral cords that are crossed by sharp prosoclinal ribs regularly spaced between the two keels. In young specimens, these are sharp, strongly protruding and subspiny, becoming rounded and nodular with growth. The periphery of the last whorl is marked by a sharp keel, at first subspiny, which is armed progressively by massive conical spines that can be over 5 mm long when fully grown. The lower face is ornamented by numerous small spiral cords and collabral ribs that in young forms develop into two grainy protruding keels. These keels become nodular and rounded separated by a deep median depression. A large umbilicus limited by the sutural keel, is subscaliform in young forms, becoming increasingly flared in adult forms. The aperture is subovoid, a bit wider than high, with a continuous lip, smooth and thick inside, that is inclined by 55° from the spiral axis.
Observations. These specimens, because of their shape and proportions as well as their ornamentation, undoubtedly belong to the species described and sketchily drawn by Delpey (1948, p. 8, pl. I, figs. 2–4) as Nummocalcar hourcqi, from the Bathonian at Tongobory, northwest Madagascar.
This species, with its particular characteristics, is evidently not a Nummocalcar and can be assigned to the genus Asterohelix Szabó, 1984. It has the same type of shape and ornaments during the first stages of growth, but differs by the development of strong peripheral spines that appear after 3 cm width of the last whorl. Also, its base is spirally excavated out of a large circum-umbilical depression framed by two nodular keels, and its umbilicus is much more flaring but not really scaliform. These relatively important differences justify the proposal of the new subgenus Bifidobasis [from Latin bifida, divided into two, and basis, base (f)], with A. (B) hourcqi as the type species. The characteristics of the new subgenus are as follows: euomphalid subplanispiraled, close to Asterohelix; spiral and axial ornaments; a peripheral keel strongly spiny at end of growth; a wide flaring umbilicus circumscribed by a double keel, and a strongly slanting and subovoid aperture.
Origin of name: adjective from the Latin verb deflectere, “swerve off its direction”.
Material. Five specimens with tests of late Bajocian age (upper part of unit D2: Dhibi Limestone Member, Niortense zone), Shaqra quadrangle (sites VD.82-478B, 651 and -651A).
Holotype. Specimen no. IPM-B.74203, site VD.82-651.
Dimensions. Height 5.5 mm; width18.5 mm.
Description. The shell is a flat spiral composed of six to seven whorls with regular growth, the last slightly detached and lowered at end of growth. The whorls are ornamented on the upper face by eight to ten spiral cords, more or less grainy and prominent and variously disposed, that are crossed by radial ribs, oblique and irregular. The periphery of the last whorl is marked by irregularly nodular subrounded keels. One keel is at the upper angle, the second at the periphery. The base is slightly bulging, hollowed by a large umbilicus limited by a weak nodular keel that tends to smooth out at the end of growth. In addition, the entire basal surface is ornamented by fine concentric cords (until into the umbilicus), crossed by irregular collabral ribs. The aperture is subcircular, strongly oblique, on a plane, with non-thickened lips directed downward towards the end of growth at an angle of 55° to 75° with respect to the spiral axis.
Observations. This species shows all the characteristics of the genus Nummocalcar sensu stricto, that was not clearly identified before the early Bathonian. It is clearly lower than N. polygonium (d’Archiac, 1843), of the Western European Bathonian, from which it is also distinct by its keel, its less pronounced peripheral nodosities, and the slightly different ornaments of the base. This species cannot be confused with N. bussoniCox, 1969, of the Tunisian early Callovian, that has a different shape and ornaments.
Material. Twenty-one specimens from the early Bathonian (top of unit D3, units D4 and D5, Zigzag and Aurigerus zones), Shaqra quadrangle (sites JMA.82-350, VD.82-482, -484A, -561, -630), and one middle Callovian specimen (unit T1, Coronatum zone), Shaqra quadrangle (site VD.82-212).
Dimensions. Height 15 to 16mm; last whorl height 1 1 to 12mm; apertur e height 8mm; width 16mm; growth angle 65° to 75°.
Observations. Cossmann (in Douvillé, 1925, p.319, pl.VII, figs.8a,b) based this species on only one specimen from the Callovian in northern Sinai. As shown by him, the center of the base is occupied by an umbilical depression of variable size, in places subkeeled, but shallow and not easy to see.
It is the same species that was mistakenly described by Cox (1969, p.247, pl.I, figs.4a,b, 5a-d,) from the Callovian of southeast Tunisia as Ataphrus labadyei (d’Archiac), a European Bathonian species that is quite different (see Fischer, 1969, p.131, fig.31, pl.XV, figs. 1-6).
It is different from Ataphrus asiaticusDouvillé (1916, p.48, pl.V, figs.31-33), north Sinai, Bathonian-Callovian, because its whorls are more bulged and the growth angle is more open.
The species A. douvillei, as wide as it is high, seems to have evolved from A. acmon (d’Orbigny, 1853), Europe, late Bajocian (see Fischer and Weber, 1997, p.109, pl.20, fig. 14), from which it differs by its whorls being clearly more prominent.
Material. Four adult specimens: two of early Bathonian age (unit D4, Zigzag zone), Shaqra quadrangle (site VD.82-561), and two of middle Callovian age (upper part of unit D7, Coronatum zone), Buraydah (site JMA.83-195) and Shaqra quadrangles (site VD.82-608).
Dimensions. Preserved height 18mm; r econstituted total height 22 mm; width 6.5mm; gr owth angle 20°.
Observations. These specimens are typically from Pseudomelania trochiformis (Piette, 1857) (see Fischer, 1969, p.147, pl.XVI, figs.15–17). It is a species that is easy to identify and well known from the Bathonian and early Callovian of France (Zigzag zone to Herveyi zone, ex Macrocephalus zone). It is the same species that was named Eulima calloviensis by Hébert and Eudes-Deslongchamps (1860, p.187, pl.VII, figs. 8a,b), as it is possible to check with the dir ect comparison between its holotype (no. IPM-J.1361), and good-quality topotypes (no. IPM-R.372) of Piette’s species.
It was described from the Callovian of Sinai by Reiner (1968, p.173, pl.I, figs.4, 5), by the name Pseudomelania cf. calloviensis and from the middle Callovian of the same area by Hirsch (1980, p. 140, pl. 9, figs. 13–16), by the name Pseudomelania cf. trochiformis.
Origin of name: from Shaqra quadrangle.
Material. Three specimens of early Bathonian age (unit D4, Zigzag zone), Shaqra quadrangle (sites JMA.82-354, VD.82-561, -629), and nine specimens of middle Callovian age (upper part of unit D7, Coronatum zone), Shaqra quadrangle (sites VD.82-514, -524, -607). All specimens have partly preserved tests.
Holotype. Specimen no. IPM-B.74207, site JMA.82-354.
Dimensions. Holotype: preserved height 53mm; r econstituted total height 80 mm; last whorl height 27mm; apertur e height 16.5mm; width 13.8mm; gr owth angle 12°.
The growth angle can vary from 11° to 15° in a population. Based on internal molds of early Callovian age that seem to be from the same species, the height could be up to 155mm and the width from 25 to 30 mm.
Description. Shell with regular growth. Young whorls are plane, but become slightly bulging at the end of growth, with a height close to 80 percent of the width, separated by a linear suture without a rim. Completely smooth surface marked only by a few collabral opisthocyrt striations. The periphery of the last whorl is regularly rounded; the aperture is perfectly holostomatous with a fine labrum and an almost straight and only slightly thickened columellar edge.
Observations. The early Callovian specimen from Sinai described by Hirsch (1980, p.140, pl.9, fig. 23) under the name “?Pseudomelania sp. II”, apparently is the same species.
It is clearly narrower than P.lonsdalei (Morris and Lycett, 1851), Bajocian and Bathonian, Western Europe that has a growth angle of 16° to 20° and clearly depressed whorls in the middle (see synonymy in Cox and Arkell, 1950, p. 61). It is also narrower than P.niortensis (d’Orbigny, 1851), Bathonian, France that has non-depressed whorls but a growth angle of 16° to 17° (see Fischer and Weber, 1997, p.22, fig.3 and pl.2, figs.10, 11).
This species is also quite different from the late Bathonian to Callovian spiral fragments (lot no. IPM-R.7563) from southwest Madagascar, described and shown by Nicolaï (1951, p. 54, pl. VI, figs. 1–4) under the name Pseudomelania sp. This has a similar growth angle (11–13°) but its whorls are clearly higher and with a pronounced infrasutural bulge.
Material. One incomplete specimen, with test, of late Oxfordian or early Kimmeridgian age (unitH2), Shaqra quadrangle (site JMA.82-391).
Dimensions. Preserved height 18 mm; reconstructed height 20 mm; width (after compensating for deformation) 10.5 mm; growth angle from 66° (first whorls) to 45° (last whorls).
Observations. Though relatively small, this specimen belongs to the recently redefined species cornelia (see Fischer and Weber, 1997, p. 27 and 31, pl.1, figs.17–19), that is known in France from the middle Oxfordian to early Kimmeridgian.
Material. Three specimens of middle Callovian age (upper part of unit D7, Coronatum zone). Two of the specimens, with tests deformed through compaction, are from the Buraydah quadrangle (site JMA.83-195) and Darma quadrangle (site JMA.82-402). The third is a strongly weathered specimen from the Wadi al Mulayh quadrangle (site JMA.80-561).
Dimensions. After compensation for deformation: preserved heights 35.5, 24 and 20mm; r econstructed heights 65, 40 and 23mm; width 12.5, 8.5 and 7.5mm; gr owth angle 13°.
Observations. These specimens are all similar in shape and ornamentation (fine spiral ribbons crossed by opisthoclinal growth ridges), with the Callovian specimen from Sinai on which Reiner (1968, p.174, pl. I, fig. 9) based his species. This is also true for the Callovian specimen from Sinai that was mistakenly recorded as Pseudomelanlia scarburgensis (Morris and Lycett) by Cossmann (in Douvillé, 1925, p.306, pl.5, fig. 2).
Origin of name: from Gondwana paleo-continent.
Material. Eight specimens of middle Callovian age (middle and upper parts of unit D7, Coronatum zone), Shaqra quadrangle (sites VD.82- 604, -606 and -607).
Holotype and paratype. Respectively specimens no. IPM-B.74210 A and B, site VD.82-607.
Dimensions. Holotype: total height 38mm; last whorl height 30mm; apertur e height 22.5mm; width 22.5mm; gr owth angle from 85° (first whorls) to 45° (last whorls). For the narrower specimens, the growth angle is only 70° for the first whorls.
Description. Cyrtoconoid shell with low variation in proportions composed of seven slightly bulging whorls separated by a well-marked suture. The entire surface is ornamented until the base by fine, regularly disposed spiral cords (25 to 30 for the next-to-last whorl), that are crossed by fine, weakly opisthocyrtic collabral striations that are mainly visible on the last whorl. The aperture, much higher than wide, is perfectly holostomatous with a fine labrum and a variably callous columellar edge that has a narrow umbilical slit in its lower quarter.
Observations. If this species did not have well-marked spiral ornaments it could have been attributed to the subgenus Oonia that it resembles, including the sub-umbilicated and thin columella. In fact, it relates to Oonia (a stocky-shaped Pseudomelania), in the same manner as the sub-genus Rhabdoconcha (also with spiral striations) relates to elongated Pseudomelania shapes. This means that a new subgenus Striatoonia [from latin striatus, striated, and Oonia, (f)] has to be created, with P.(S.) gondwanea as type species and with the following diagnostic description: pseudomelaniform cyrtoconoid shell, with spiral striations on surface, collabral opisthocyrt lines, a perfect holostomatous aperture, and a lower subumbilicated callous columellar edge.
Cox (1969, p.266, pl.III, figs.1a,b) described and showed under the name Ovactaeonina custodiorum, a middle Callovian specimen from southeast Tunisia that is certainly not an Acteonidae but could represent a species of the genus and sub-genus Pseudomelania (Striatoonia) that has less dense spiral ornaments than P.(S.) gondwanea. This could also be true for the late Callovian specimen from Sinai shown by Hirsch (1980, p. 144, pl. 12, figs. 20, 21) under the name Ovactaeonina sp.
The subgenus Striatoonia must be compared to the subgenus GardetiaDubar, 1948 (late Pliensbachian, Morocco), that also has a spiral ornament, but which differs in its more trochiform shape (not cyrtoconoid) and by the ribbon aspect of its spiral ornaments.
Material. Two specimens (internal molds, one with traces of test) of late Bajocian age (upper part of unit D2: Dhibi Limestone Member, Niortense zone), Darma quadrangle (site JMA.82-290).
Observations. The shape and proportions of these specimens (the largest is 47mm high and 25mm wide with a 45° growth angle), and the regular spiral striations that are preserved on the surface of one of the specimens are, without doubt, typical of Bourguetia saemanni. This is a common species of the early Bajocian to late Oxfordian in Europe (Fischer and Weber, 1997, p.127, pl.3, fig.1). In addition, it is listed from the Callovian of Sinai (Reiner, 1968, p.175, pl.1, figs.12, 13) and from the Callovian to Kimmeridgian of East Africa (Stefanini, 1939, p.105; Joubert, 1960, pl.12, figs.2a,b; Cox, 1965, p.152, pl.25, figs.8, 9).
Material. Eight adult specimens with at least partly preserved tests, some quite deformed, of early Bathonian age (unit D4, Zigzag zone), Shaqra quadrangle (site VD.82-482).
Dimensions. For this set of specimens, the maximum dimensions (after compensation for deformation) are: total height 38mm; last whorl height 28mm; total width 26mm; apertur e width 19mm; gr owth angle from 65° to 70°, depending on the specimen.
Observations. These specimens are similar to those from Western Europe, with the same fine test and the same proportions and shape. They have strongly convex whorls and a well-marked suture, and the same umbilicus and perfectly holostomatous and subcircular aperture, with a fine and weakly opistocyrte labrum.
This species is known from the “Great Estuarine Series” (middle Bathonian, Subcontractus zone) of Great Britain (Anderson and Cox, 1948, p.1 15, pl.III, figs. 13a,b, 14; Cox and Arkell, 1950, p.89), from the middle Bathonian in France (Fischer, 1961, p.81; 1964, p.44), and from the Bathonian of eastern Sardinia (Dieni et al., 1983, p.127, pl.I, figs. 3-la,b, 2a,b).
Origin of name: from Tethys.
Material. Two specimens with test (holotype and paratype, no. IPM-B.74213 A and B) of middle Callovian age (upper part of unit D7, Coronatum zone), Buraydah quadrangle (site JMA.83-195).
Dimensions. Holotype: preserved height 19mm; r econstructed height 20mm; width 5mm; gr owth angle 12°.
Description. Spire showing regular growth. Whorls slightly convex separated by an indistinct suture and ornamented by six smooth or slightly granular spiral threads, the second from the top being possibly larger, more prominent, and more granular than the others. This spiral ornament is not trellised by any axial ornament. The last whorl is subkeeled at the periphery of the base, where the spiral ornament continues. The aperture is procerithiform with a well-developed columellar channel.
Comment. This species has strongly different characteristics from all other known examples of the genus Procerithium sensu stricto.
Origin of name: from Arabian Peninsula.
Material. Nine specimens with tests of middle Callovian age (upper part of unit D7, Coronatum zone), Qibah quadrangle (site VD.84-125) and Buraydah quadrangle (site JMA.83-195).
Holotype. Specimen no. IPM-B.74214, site VD.84-125.
Dimensions. Holotype: preserved height 23 mm; total reconstructed height 35mm; width 9mm; growth angle 16°.
Description. Spire with regular growth. Whorls weakly convex with a slight submedian spiral depression, separated by a linear suture marked by a small infrasutural bulge. Ornaments are composed on each whorl, of 11 to 14 smooth or slightly granular spiral threads. The upper fifth to seventh ones are crossed by an infrasutural crown of 25 more-or-less marked axial costules that stops at the mid height of the whorl. The last whorl is subkeeled at the periphery of the base, where the spiral ornament is continued. The aperture is procerithiform, with a well-formed columellar channel.
Comments. Our specimens cannot be referred to any known species. They are clearly different from P.(C.)dorvali (Cossmann, 1900), Bathonian, France (see Cossmann, 1913, p.65, pl.III, figs. 63, 64). This has a growth angle of 20° to 22° (not 25° as was mistakenly written by Cossmann), and only seven to nine spiral threads for each whorl. Cossmann (in Douvillé, 1925, p.319, pl. VI, fig. 6), based on a single Callovian specimen from southern Sinai, introduced the taxon evanescens as a “race” of the species dorvali, because of the less pronounced costal ornaments. Reiner (1968, p.183, pl.1, figs.16, 17), apparently correctly attributed to the species dorvali sensu stricto Callovian specimens from Sinai in which the costal ornaments are, on the contrary, strongly developed. Cox (1969, p.256, pl.1, figs.17a,b) also mentioned the species dorvali from the early Callovian of southeast Tunisia. Parnes (1981, p.42, pl.6, figs.23–27), although distinguishing it from the species dorvali, expressed his doubt that specimens from Sinai (dated by him as Bajocian), belonged to the evanescens form (with moderate costal ornaments and 7 to 9 spiral cords on the last whorls).
Our specimens cannot be attributed to P.(C.) picardiHirsch, 1980 (see below), because of a more open growth angle (16° compared to 10°) and a smaller number of spiral threads.
Procerithium deserti Douvillé (1916, p.44, pl. V, fig.9), of the Bathonian-Callovian in north Sinai, has only six to nine spiral cords that are more-or-less pearled.
Material and observations. Of the samples collected, about 10 specimens are of good size as internal or external molds, with partial traces of ornaments or tests. They are of middle Callovian age (upper part of unit D7, units T1 and T2 and base of unit T3, corresponding to the Coronatum zone), Shaqra quadrangle (sites VD.82-522,-532), Wadi ar Rayn quadrangle (site VD.80-284) and W adi Al Mulayh quadrangle (site JMA.80-550).
Their growth angle is 10° on average and the largest specimen is 17 mm wide.
They show the typical characteristics of the species picardi as described by Hirsch (1980, p. 150, pl. 11, fig. 1) for specimens from the middle to late Callovian of Sinai. This is particularly so in respect of the growth angle, the low elevation of the whorls, and the ornament details. On the last whorls, the ornaments are composed of about 15 spiral threads, half of which are crossed by a crown of 15 to 20 infrasutural axial costules; the base is entirely ornamented by spiral threads.
Origin of name: from Latin, “shaped as a small tower”.
Material. Three specimens of middle Callovian age (upper part of unit D7, Coronatum zone). Two are from the Buraydah quadrangle (site JMA.83-195) and one is from the Shaqra quadrangle (site VD.82-514).
Holotype. Specimen no. IPM-B.74217, site JMA.83-195.
Dimensions. Holotype: preserved height 19 mm; reconstructed total height 65 mm; width 6mm. Specimen of site VD.82-514: preserved height 18 mm; reconstructed total height 65 mm; width 5.5 mm. Growth angle 5°; sutural angle 11°.
Description. Sub-baculiform shell. Whorls scarcely excavated and sutured between two very small ledges. Ornaments are seven to nine unequal spiral cords, irregularly distributed, that are crossed by fine opisthoclinal growth striations going back to the upper suture. The last whorl is angular in its periphery. The base is slightly excavated and apparently smooth. The aperture is subquadrangular, with a thin labrum and an almost straight columella, notched in the lower part. The axial section shows total absence of internal folds, whether columellar, labial, or parietal.
Observations. The slender shape and complete absence of internal folds indicate that this species is part of the genus Aptyxiella P. Fischer, 1885. It is known in North Africa from the Pliensbachian (Dubar, 1948, p. 52), but in Europe only from the middle Oxfordian.
Material. Twenty specimens of early Kimmeridgian age (upper part of unit H2, ?Hypselocyclum zone), most of them reduced to internal molds; Buraydah quadrangle (sites VD.82-303, -305), Shaqra quadrangle (site VD.82-662), and Wadi al Mulayh quadrangle (site JMA.80-74).
Observations. The specimens constitute a rather homogeneous population. They have average dimensions of about 300 mm total height, 45 mm width, 50 mm for the height of the last whorl, 6° to 10° of growth angle for the last whorls, and 100° for the sutural angle.
They are conformable with the European species C. desvoidyi (d’Orbigny). They present exactly the same growth angle, the same slightly excavated whorls with a suture below a strong peripheral ridge, and the same almost smooth surface (only marked on some by collabral growth striations crossed by nearly imperceptible spiral ribbons). In addition, they have the same aperture and internal folds that are composed of a columellar bulge and a simple labial fold, without a parietal fold.
Newton and Crick (1908, p. 9, pl. I, fig. 10) and Newton (1921, p. 391, pl. XI, fig. 1), had doubtfully attributed to this species internal molds from the Late Jurassic in the “Nobat” area (about 80 km north of Aden), and from “Bachain” (close to “Sadus”, central Saudi Arabia).
This species was clearly identified by Delpey (1939, p. 165, fig. 128, and pl. II, figs. 1 and 2) in the Kimmeridgian of Lebanon.
Early Oxfordian internal molds from Sinai, described by Hirsch (1980, p. 152, pl. 12, fig. 3) as Cossmannea sp. aff. desvoidyi (d’Orbigny), seem to be co-specific with those from Saudi Arabia.
Jaboli (1959, p. 83, pl. X, fig. 12; pl. XI, figs. 1, 2a,b), using the variety name aethiopica, had mentioned its existence in East Africa from where it had been previously cited by Stefanini (1939, p. 105).
This species is widespread in the West European north-Tethys area, from the Atlantic to Poland. It ranges in age from middle Oxfordian to early Tithonian (see Cossmann, 1898, p. 56, pl. V, figs. 14–21; Fischer and Weber, 1997, p. 42, pl. 11, figs. 1–3).
Origin of name: from Riyadh area.
Material. Fifteen specimens of early Bathonian age (unit D4, Zigzag zone, and unit D6, possible early Bathonian): Shaqra quadrangle (sites VD.82-561, -629) and Darma quadrangle (site JMA.82-198).
Holotype and paratype. Specimens no. IPM-B.74216 A and B, site VD.82-561.
Dimensions. Holotype: preserved height 26 mm; reconstructed height 85 mm; width 9 mm. Specimen of site VD-82-629: preserved height 30 mm; reconstructed height 110 mm; width 11.2 mm. Growth angle 5° to 6°; sutural angle 99°.
Description. Spire with regular growth made of whorls twice as wide as they are high, more-or-less excavated and separated by a linear suture between two bulges. Surface entirely smooth except for fine opisthoclinal growth lines that are retrocurrent close to the upper suture. Last whorl has an angular periphery. Sloping base slightly excavated; square aperture; very thick non-perforated columella. Five internal folds: one very large bifid or threefid parietal; two columellar, the lower triangular; and two on the internal labral face, the lower bi-angular.
Observations. This species can be compared to Bactroptyxis trachaea (Eudes-Deslongchamps, 1843) (see Fischer, 1969, p. 178, fig.39; Fischer and W eber, 1997, p. 33, 34 and 36), a widespread species in the northwest European Bathonian. However, it clearly differs because of a few more open growth angles, much lower whorls, a clearly smaller sutural angle, and a surface without any spiral ornaments.
Reiner (1968, p.191, pl. III, fig. 6) considered one specimen from the Callovian of Sinai as “Bactroptyxis? sp.”, but this was later correctly attributed by Hirsch (1980, p. 156, pl. 12, fig. 15, and pl. 13, fig. 6) to the new species Nerinella reineri.
The genus Bactroptyxis Cossmann, 1896, is here identified with certainty for the first time from the Jurassic of the Arabian Peninsula.
Material and observations. The presence of this species is attested by a specimen of early Bathonian age (top of unit D3, Zigzag zone), Wadi ar Rayn quadrangle (site VD.80-409). Although it is a slightly deformed internal mold with remnants of test, it shows exactly its shape and characteristics. The surface is smooth and ornamented only by a crown of 10 to 12 nodosities on the upper part of the last whorls. It is about 100 mm high (reconstructed) and 70 mm wide, with a growth angle of 67°.
The species is well represented in the Bathonian of Great Britain and France (see Cossmann, 1913, p. 178, pl. VII, figs. 8-10). It was doubtfully attributed by Jaboli (1959, p. 85, pl. X, fig. 14) to an internal mold collected in Ethiopia that is too fragmented to be of much value.
Material. Sixty specimens of early Bathonian age (unit D4, Zigzag zone) from the Shaqra quadrangle (sites VD.82-333, -482, -562, -629, -630) and Darma quadrangle (sites JMA.82-188, -189, -284, -285, -288). In addition, three specimens of middle Callovian age (upper part of unit D7, Coronatum zone), Shaqra quadrangle (site VD.82-514) and Darma quadrangle (site JMA.82-21, -402). Only the specimens with a test were considered, in order to be certain of the determination.
Dimensions. Height 45 mm; last whorl height 35 mm; aperture height 25 mm; width 27 mm; growth angle 62°. These dimensions are from the specimen in figure 6a,b, pl. 2, which is the largest known. The height and width rarely exceed 33 mm and 24 mm, respectively. The growth angle can reach 75° for the stockiest specimens.
Observations. This species was described by Cossmann (in Douvillé, 1925, p. 316, pl. VII, fig. 5) from a Callovian specimen of Sinai, and reused by Reiner (1968, p. 177, pl. I, figs. 10 and 11) and Parnes (1981, p. 42, pl. 6, figs. 19–22), based on Callovian to Bathonian specimens from Sinai. It is apparently abundant in central Arabia, which makes it possible to refine its characteristics.
The first whorls appear smooth, the fourth is ornamented by six to seven spiral ribbons that are progressively double, until forming about 20 subequal spiral cords in the middle of the sixth whorl. At this stage in the growth, short oblique ribs form that are more-or-less marked and limited upward by a shoulder 2 mm below the suture. The last whorl bears 10 to 15 ribs and is entirely ornamented by subequal spiral cords. The aperture is semi-circular, with a thin labrum, pseudo-notched at the linking point with the sub-straight and strongly callous columella. The callus covers most of the narrow umbilical slit.
Material and observations. This species was previously known only from the early to middle Oxfordian (Cordatum-Plicatilis zones) of France (see Cossmann, 1913, p. 180, pl. VII, fig. 17). It has now been found in the middle Oxfordian (top of unit H1, Plicatilis zone) of the Darma quadrangle (sites JMA.82-269, -276) and in the Wadi Al Mulayh quadrangle (site JMA.80-149). The seven specimens are internal molds but are so preserved as to show all the characteristics of this species. The largest specimens are 80 mm high and 60 to 65 mm wide (growth angle 75°). The least weathered have a crown of about 10 prominent nodosities on the upper part of the whorls, and the impression of a fine spiral ornamentation over the entire surface. These characteristics clearly differentiate this species from P. deserti Douvillé, 1925 (Callovian of north Sinai) that has a much more open growth angle (90°) and more strongly developed nodosities.
Material. Three incomplete specimens (aperture missing) from the base of the late Bajocian (upper part of unit D2: Dhibi Limestone Member, Niortense zone), Shaqra quadrangle (site VD.82-651).
Dimensions. Preserved heights, respectively, 23, 22 and 19 mm; preserved widths, respectivly, 13, 12 and 11 mm; growth angle (of the three specimens) 55° (first whorls) to 40° (last preserved whorls).
Comments.Parnes (1981, p. 44, pl. 6, figs. 34–37) described this species from incomplete specimens of the Bajocian in the Sinai Peninsula. The three Saudi Arabian specimens, although without labrum and smaller in size, seem to be follow Parnes’ definition. Their proportions, the cyrtoconoid shape of the spire, and the bulges on their whorls are the same. In addition, they have exactly the same ornamentation. This consists of two to four spiral cords intercalated between the suture and the upper digital keel, three main threads with intercalated threads between the two keels of the last whorl, and about 10 main spiral threads doubled by intercalated threads below the lower digital keel. A spiny nodosity is found slightly before the middle part of the last whorl, on the upper digital keel, and the columellar edge shows a smooth and excavated callosity that is clearly limited on the outside.
Material. Fourteen specimens, mostly internal molds, of early and late Bajocian age (lower and upper parts of unit D2, Humphriesianum-Niortense zones and unit D3, Garantiana-Parkinsoni zones) collected from Shaqra (site VD.82-651), Darma (sites JMA.82-169, -170, -279, -280), Wadi ar Rayn (site VD.80-547), and Wadi al Mulayh (sites JMA.80-80, -553) quadrangles.
Dimensions. The largest specimens are 80 mm high and 40 to 50 mm wide, excluding the channel and the digitations. The growth angle varies from 40° to 55°.
Observations. The specimens have characteristics that demonstrate their cospecific nature. These are a regularly growing spire composed of seven to eight weakly bulging whorls separated by a slightly sunken linear suture and ornamented (for the specimen with a well-preserved test), by about 15 narrow spiral grooves that continue on the base of the whorls of the spire (no axial ornament and no growth-line traces). The ninth and last whorl is well developed and occupies, not counting the channel, almost 60 percent of the total height. The ornamentation of the last whorl is unknown, but it is regularly rounded at the periphery of the base, without traces of keel nodosity. The start of a narrow columellar channel indicates it would be long. The labrum is unknown, but its upper digitation, partially preserved in two of the larger internal molds, climbs along the spire and sticks to it, at least at the beginning.
Because of the missing characteristics of the channel and the digitations, it is impossible to describe this species as new, or even to attribute it with certainty to the genus Cuphosolenus. It is comparable to Cuphosolenus sphinxPiette, 1882 (p. 379, pl. 73, figs. 2–5) from the Bathonian of France. However, it differs from C. sphinx by having a more open growth angle, less bulging spire whorls, and a last whorl that is more ample being both higher and wider.
It is very different from the Callovian species of Sinai that Hirsch (1980, p.142, pl.10, figs.7, 8), without description, assigned to the genus Cuphosolenus (spelling by Hirsch Cyphosolenus).
Origin of name: from Bajocian.
Material. Four specimens of internal mold with a few traces of test, of early Bajocian age (unit D1, Discites zone, and base of unit D2, Humphriesianum zone), from the Darma quadrangle (site JMA.82-170) and W adi ar Rayn quadrangle (sites VD.80-527, -528, -545).
Holotype. Specimen no. IPM-B.74226, site VD.80-545.
Dimensions. Holotype: total height 78 mm; height of last whorl 63 mm; aperture height 50 mm; width 62 mm; growth angle 93°.
The growth angle can vary according to the specimens from 80° to 98°. The largest specimen has a total height of as much as 95 mm, a last-whorl height of 75 mm and a width of 70 mm.
Description. Shell growth along a regular angle, consisting of four to five regularly bulging whorls, separated by a linear suture. The surface is entirely smooth. The last globular whorl occupies 80 percent of the total height and is regularly rounded at the periphery. The aperture is almost semicircular and perfectly holostomatous, with the columellar edge excavated and a thin callus that fully covers all the umbilicus area.
Observations. This species is remarkable for its large size and its globular shape and cannot be confused with others known from the Middle Jurassic. It is similar in shape to G. rupellensis (d’Orbigny, 1852), Oxfordian and Kimmeridgian over a large geographic area (see Fischer and Weber, 1997, p. 77, 79 and 83, pl. 16, figs. 1–5). However, the test does not show a punctuated structure, the spire is shorter, and the height of the last whorl is smaller in proportion.
Material and observations. One specimen 55 mm high and 50 mm wide, slightly deformed but with a partially preserved test, from the Oxfordian-Kimmeridgian boundary (upper part of unit H2) in the Shaqra quadrangle (site JMA.82-391). It shows exactly the shape, proportions, and characteristics of Globularla rupellensis and has the typical punctuation of the test that appears on the fourth whorl.
It is a Western European species of early Oxfordian (Cordatum zone) to late Kimmeridgian (Eudoxus zone) age, mentioned by Delpey (1939, p. 84, figs. 59, 60) from the “Lusitanian” of Lebanon, and by Cox (1969, p. 262, pl. III, fig. 2) from the Oxfordian of southeast Tunisia, with the name Globularia aff. millepora.Fischer and Weber (1997, p.77, 79 and 83, pl. 16, figs. 1–5) established that Natica milleporaBuvignier, 1852, is only a specifically synonymous variant of Natica rupellensis d’Orbigny, 1852.
The internal mold from the Upper Jurassic (Oxfordian?) of Bihendula near Berbera (Somalia) that Stefanini (1925, p. 157, figs. 3 and 4) showed as “Natica sp.” perhaps belongs to this species.
Material. One specimen with test from the Oxfordian-Kimmeridgian boundary (upper part of unit H2), in the Shaqra quadrangle (site JMA.82-391).
Dimensions. Preserved height 52 mm; reconstituted total height 60 mm; reconstituted height of last whorl 44 mm; reconstituted width 41 mm; growth angle 80° (first whorls) to 55° (last whorls).
Observations. The single specimen found is characteristic of Globularia elea from the late Kimmeridgian (Eudoxus zone) and early Portlandian (Tithonian, Gigas zone) of France (see Fischer and Weber, 1997, p. 81, 82 and 84, pl. 17, figs. 1a,b, 2, 3, 4a,b). Under the synonym G.phasianelloides (d’Orbigny, 1852), it was cited by Joubert (1960, pl. 12, fig. 5) and Cox (1965, p. 166, pl. 29, figs. 1a,b) from the late Oxfordian and late Kimmeridgian of East Africa, and by Reiner (1968, p. 188, pl. II, figs. 10, 11) and Hirsch (1980, p. 144) from the Callovian of Sinai.
Material. Two specimens (deformed internal molds) of early Kimmeridgian age (upper part of unit H2, ?Hypselocyclum zone) from the Wadi al Mulayh quadrangle (sites JMA.80-159 and -175).
Observations. Although poorly preserved, these two specimens, about 30 mm high and wide, can be attributed without doubt to Roemer’s species with its typical shape. It is known in Europe from the middle Oxfordian to early Kimmeridgian (see Fischer and Weber, 1997, p. 77, 78 and 83, pl. 16, figs. 6–9), and was identified in the late Kimmeridigian of East Africa (Stefanini, 1939, p. 105; Jaboli, 1959, p. 78, pl. X, fig. 4; Joubert, 1960, pl. 12, figs. 4a,b; Cox, 1965, p. 166, pl. 28, fig. 9). It was also r ecorded from the Callovian to Kimmeridgian of the Near East (Reiner, 1968, p. 189, pl. II, figs. 16,17; Hirsch, 1980, p. 144).
Origin of name: from Latin brevis, short, and spira, spire.
Material. Forty-three specimens of early Bathonian age (unit D4, Zigzag zone), Shaqra quadrangle (sites JMA.82-354, VD.82-482, -561, -630). In addition, 16 specimens of middle Callovian age (upper part of unit D7 and unit T2, Coronatum zone) from the Buraydah (site JMA.83-195, 196), Shaqra (sites VD.82-514, -604, -608) and Darma (site JMA.82-34) quadrangles.
Holotype. Specimen no. IPM-B.74233 A, site VD.82-482.
Dimensions. Holotype: preserved height 24 mm; reconstructed height 28 mm; width 22.5 mm; growth angle 95°.
The largest specimen is as much as 27 mm high and 24 mm wide. The growth angle can vary in a same population from 95° to 115°, depending on the specimens.
Description. Globular shell, regularly growing spire, consisting of five whorls that are strongly convex because of a non-excavated infrasutural ramp, well defined but without angulation. Suture well marked. Last whorl very high, regularly rounded at its periphery. Smooth surface showing only a few orthoclinal growth striations. Aperture holostomatous, semi-circular, with weakly excavated columellar edge, of which the callus, not overturned, covers almost all of the umbilicus slit, and with a thin labrum.
Observations. This species is characteristic of the genus and subgenus Ampullospira G.F. Harris, 1897. Its columellar characteristics are well presented: the columellar edge, although slightly thickened, does not extend to the base forming a “limbus” (callus limited by a crest on the outside). It is distinguished from all other co-generic species known from the Jurassic by both its short spire and the bulge of its whorls.
It is perhaps the same species that was shown by Cox (1969, p.263, pl.III, figs.8a-c, 9a,b) from the Bathonian-Callovian of southeast Tunisia. This had the inaccurate name of Ampullospira stricklandi (Morris and Lycett), a taxon that is, in fact, synonymous with Globularia formosa (Morris and Lycett, 1851) (see Fischer, 1969, p. 186, with synonymy).
Because of its shape and proportions, it resembles an East African Middle Jurassic species shown by Cox (1935, p.155, pl.XIV, figs.3, 4) with the name of Globularia sp. It was then named by Stefanini (1939, p.150, pl.XVIII, figs.6a,b) as Ampullina coxi and reused by Jaboli (1959, p.76, pl.X, fig.2), but without genus and species characters being clearly established. It may belong to the genus Globularia. However, if it is an Ampullospira, the taxon coxi Stefanini cannot be retained as it has already been used to designate a Bathonian species in France (Ampullospira coxiFischer, 1953, p. 20, pl. II, figs.16-18).
Thévenin (1908, p.124, pl.III, fig.7) showed an incomplete Liassic specimen (no. IPM-B.10082) named “Natica cf. Palops d’Orb.” from Nossi-Bé Island north of Madagascar, that resembles A.brevispira except for its growth angle of only 45° and its subangulated infrasutural flat.
Origin of name: from Orient.
Material. Four specimens of middle Callovian age (upper part of unit D7, and base of unit T3, Coronatum zone). Two specimens are from the Buraydah quadrangle (site JMA. 83-196), and two from the Shaqra quadrangle (sites VD. 82-514 and 532).
Holotype. Specimen no. IPM-B.74231, site VD.82-514.
Dimensions. Holotype: preserved height 25 mm; reconstructed height 28 mm; width 20 mm; growth angle 79°. The largest specimen is 35 mm high and 25 mm wide.
Description. Shell with regular growth, consisting of five slightly bulging whorls separated by a well-marked suture. Last whorl very developed, regularly rounded at the periphery. Smooth surface. Elongated-oval holostomatous aperture with a columellar edge, the callus (not overturned) covers most of the umbilical slit.
Observations. These specimens are in all aspects the same as the middle Callovian specimen from Sinai attributed by Hirsch (1980, p. 144, pl. 11, figs. 6–8) to Globularla subumbilicata (d’Archiac, 1843), a Bathonian species from the Paris Basin. However, this species is always smaller, it has a proportionally shorter spire, the last whorl is more globular, and the columellar callus is different (see Fischer, 1969, p. 189, figs. 53–58, with synonymy).
Material. Twenty-four specimens of early Bathonian age (unit D4, Zigzag zone) from the Shaqra quadrangle (sites JMA.82-352, VD.82-482), and one specimen of middle Callovian age (upper part of unit D7, Coronatum zone) from the Buraydah quadrangle (site JMA.83-196).
Dimensions. The largest specimens are 20 mm in total height, have a last-whorl height of 13 to 15 mm, a 2.5 mm aperture height, and a width of 13 to 15 mm. Depending on the specimen, the growth angle can vary from 72° to 85°.
Observations. These specimens are indistinguishable from A.(P.) lorierei, Bathonian species of France (see Fischer, 1969, p. 191, pl. XVIII, figs. 29-31; Fischer and Weber, 1997, p. 70, pl. 17, fig. 9). They have exactly the same shape of whorls and a narrow, deeply channelled suture; the same growth angle; and the same columellar edge that may, or may not, show a narrow umbilical slit.
This species was tentatively recognized by Reiner (1968, p. 187, pl. II, fig. 9) from the Callovian of Sinai.
Material and Comments. Two fragmental specimens of middle Callovian age (upper part of unit D7, Coronatum zone), from the Qibah (site VD.84-125) and Shaqra (site VD.82-607) quadrangles.
Notwithstanding their poor preservation, these two specimens (15 to 18 mm wide), show apparently the same proportions and characteristics (particularly the infrasutural ramp, the aspect of the columellar bourellet, and the umbilical position) as the species of Morris and Lycett, from the middle and late Bathonian of Great Britain and France (see Fischer, 1969, p. 191, pl. XVIII, figs. 23a,b, with synonymy; Fischer and Weber, 1997, p. 72, pl. 17, fig. 12).
Natica actaea d’Orbigny, 1852, which is synonymous with Naricopsina subcanaliculata, was doubtfully cited by Nicolaï (1951, p. 56) from the “Late Bathonian–Callovian” of southwest Madagascar.
Origin of name: from Dogger.
Material. Twelve specimens with test, of early Bathonian age (unit D4, Zigzag zone), Shaqra quadrangle site VD.82-482).
Holotype and paratype. Specimens shown here, numbers IPM-B.74236 A and B.
Dimensions. Holotype: total height 20.5 mm; last-whorl height 15 mm; aperture height 10 mm; width 8.5 mm; growth angle from 55° (first whorls) to 38° (last whorls). Paratype: preserved height 17.2 mm; reconstructed total height 20.5 mm; last-whorl height 14 mm; aperture height 11mm; width 8 mm; growth angle 48°.
Description. Shell of somewhat variable proportions. It is composed of seven to eight whorls organized in tiers, separated by a well-marked suture accompanied by a flat or slightly inclined infrasutural ramp, more or less keeled, and with a spiral groove just under the keel. The last whorl is sub-cylindrical. Except for a smooth band under the infrasutural keel, the surface is covered by spiral threads of which there are about 30 to 35 on the last whorl. The aperture is perfectly holostomatous, very narrow at the upper part, with a thin prosocyrtal labrum strongly overturned towards the suture, and a smooth weakly callous columellar edge without teeth.
Observations. It is apparently the same species that was described and shown by Parnes (1981, p. 45, pl. VI, figs. 46–49) under the name Acteonina (Striactaeonina?) sp., based on specimens from Sinai, assigned by him to the Bajocian. It is the most recent species of the subgenus Striactaeonina, that, except for the doubtful species Striactaeonina? sarthacensis (d’Orbigny, 1852) (see Fischer and Weber, 1997, p. 64), was previously known only from the Early Jurassic, mainly from the Hettangian to Sinemurian of France (Cossmann, 1895, p. 25 and following).
This new species can be compared to A.(S.) supraliasicaCox (1965, p. 173, pl. 29, figs. 4a–c), of the Toarcian of Kenya, but which differs by its clearly higher spire.
Origin of name: from Saudi Arabia.
Material. Forty-eight specimens of early Bathonian age (unit D4, Zigzag zone, and unit D5, Aurigerus zone), of the Buraydah (site JMA. 83-236), Shaqra (sites VD.82-482 and -561) and Darma (site JMA.82-398) quadrangles. Also included are over 20 specimens of middle Callovian age (lower and upper parts of unit D7, Coronatum zone), of the Shaqra (sites VD.82-600, -604, -607 and 608) and Darma (site JMA.82-208) quadrangles. Only specimens with tests were used for definite determinations.
Holotype. Specimen no. IPM-B.74238, site VD.82-482.
Dimensions. Holotype: total height 25mm; last-whorl height 24.5mm; apertur e height 22mm; width 11.2 mm.
This species can grow up to 35 mm high and 17 mm wide.
Description. The protoconch is weakly mucronated. The shell composed of six to seven whorls. The spire is not prominent and when young it can be totally planispiral. In older specimens, the spire is at most one-seventh of the total height. The infrasutural ramp is keeled and canaliculated. The subcylindrical last whorl is ornamented at the top by fine costules that are turned back on the infrasutural ramp, and by about 30 spiral threads on its lower half. It is smooth on the rest of the surface. The aperture is perfectly holostomatous, very narrow in its upper part and strongly enlarged abapically. A thin protocyrtal labrum is present, briefly turned back on the infrasutural ramp. The excavated columella is slightly callous in its lower part and totally without plications.
Observations. The Bathonian internal molds of northern Sinai shown by Hirsch (1980, p.144, pl.12, figs.18, 19) and named “ Cylindrites? sp. cf. C.striatus (Lissajous)”, may probably be assigned to this species.
The species described here differs from Retusa mirabilis Cossmann (1896, p.119, pl.V, figs.28, 29) from the early Bathonian of France, in its more prominent spire and its keeled infrasutural ramp. The spire is much less acuminate than on Retusa scalaris (Lycett, 1863), middle Bathonian, Great Britain (see Cox and Arkell, 1950, p.89). Cylindrites plicifer Cossmann (in Douvillé, 1925, p.311, pl.VI, figs.5a,b) from the Callovian of northern Sinai that was attributed by Reiner (1968, p.192, pl.III, figs.12–14) to the genus Retusa (genus attribution discarded by Hirsch, 1980, p.144) has, on the contrary, a clearly involute spire.
Material and observations. The samples contain two middle Callovian internal molds (upper part of unit D7, Coronatum zone) from the Darma (site JMA.82-212) and Wadi al Mulayh (site JMA.80-561) quadrangles. Their sizes are, respectively, height/width = 38/22 and 30/21 mm, with flat or weakly involute spires. These specimens are attributed to the genus Akera Muller, 1776 even though their shape is much more bulging than in all other known species of this genus. For example, A. mediojurensis Cossmann (1896, p.128, pl.VI, figs.8, 9) from the Callovian of France, and A. tanganyicensisCox (1965, p.174, pl.29, figs.5a,b) from the Callovian of East Africa. However, their state of preservation is too poor to create a new species taxon for them.
Comments on Paleoecology
Gastropods with tests represent an unfortunately relatively low proportion (one third) of the collected samples, most of which are internal molds. This shows that the aragonitic shells were dissolved without diagenetic substitution by secondary calcite. Furthermore, many of the samples are deformed, which indicates synsedimentary compaction.
However, the tests show no evidence of fragmentation or signs of primary clastic erosion, indicating a relatively low-hydrodynamic-energy sedimentary environment. The common traces of alteration of the fossils can all be attributed to recent weathering of the deposits in outcrop.
Some of the gastropod shells, particularly those of early Bathonian (unit D4) and middle Callovian (upper part of unit D7) age, show spires that are partially encrusted by serpulids of the genus Spirorbis. Examples are the tests of Asterohelix (Bifidobasis) hourcqi (sites VD.82-354 and -354A) and Aptyxiella turriculata (site VD.82-514). Some other tests of late Bajocian (Dhibi Limestone Member), early Bathonian (unit D4), and Oxfordian-Kimmeridgian ages, such as Nummocalcar deflectum, Purpuroidea perstriata and Dicroloma triseriatum (sites VD.82-629, -651 and -651A), and Globularia elea (site JMA.82-391), are encrusted with left valves of small ostreacea. The existence of such epizoa (perhaps more correctly named epiliths) signifies only that the gastropod shells were lying free for some time on the paleosubstratum without being subjected to erosion, before being covered by sediment. This could have happened before or after the death of the animal.
The open-marine environment and the location of deposits, whether lagoonal, back-reef or fore-reef, have been described by Le Nindre et al. (1990a). Table 1 shows the sedimentary environment of the gastropods and their stratigraphic distribution. Identified gastropods of at least genus rank are from the infralittoral open-marine domain. All were deposited in an inner-platform zone or shallow-water lagoon, probably less than 50m deep, which may have corr esponded to the upper infralittoral domain. However, six of the studied species (Asterohelix tenuisiensis, Pseudomelania shaqrahensis, Pseudomelania (Rhabdoconcha) raabi, Pseudomelania (Striatoonia) gondwanea, Naricopsina cf. subcanaliculata and Retusa saoudica) were also found in a fore-reef zone corresponding to a deeper (lower infralittoral) environment.
The faunal assemblages that include these gastropods mostly consist of strongly diversified populations of benthic invertebrates, such as anthozoa, bivalves commonly associated with brachiopods and echinoderms, and rare nautiloid and ammonoid shells. However, four exceptions occur. Cossmannea desvoidyi (late Oxfordian) and Akera sp. (middle Callovian) are associated only with bivalves and other gastropods and Purpuroidea lapierrea (middle Oxfordian) and Globularia bajociana (early Bajocian) were found in association only with ammonoid shells and rare other gastropods.
Comments on Paleobiogeography
A peculiar feature of the central Saudi Arabian gastropod faunas is the complete absence in all samples of trochotomids, fissurellids, acmeids, paraturbinids, cirrids, amberleyids, nododelphinulids, turbinids, neritopsids, zygopleurids, ceritellids, rissoids and lamelliphorids. These families are generally common in the Jurassic carbonate-platform deposits of Western Europe and North Africa, but are also absent from Sinai. Their absence from the Jurassic basins of the Arabian Plate indicates a well-marked faunal particularity.
Other Tethyan domains that had known, preferential, faunal relationships with the Arabian platform during the Jurassic are, mainly Western Europe (southern margin of Laurasia), and Lebanon, Sinai, Africa, India and Madagascar (northern margin of Gondwana) (table 2).
With regard to the paleogeographic relationship with the particularly well known and highly diversified Western European Jurassic gastropod faunas, at least 12 species are found on the Arabian platform. They are Bourguetia saemanni (Bajocian); Pseudomelania trochiformis, Bathonella scotica, Purpuroidea glabra, Ampullospira (Pictavia) lorierei and Naricopsina cf. subcanaliculata (Bathonian); Pseudomelania (Oonia) cornelia, Cossmannea desvoidyi, Purpuroidea lapierrea, Globularia rupellensis and G. hemisphaerica (Oxfordian); and Globularia elea (Kimmeridgian).
Species in common with the rest of the Arabian platform (in particular Lebanon and Sinai), are Dicroloma triseriatum (Bajocian), Ataphrus douvillei, Pseudomelania trochiformis, P. shaqrahensis, P. (Rhabdoconcha) raabi, P. (Striatoonia) gondwanea, Procerithium (Cosmocerithium) arabicum, Purpuroidea perstriata and Ampullospira orientalis (Callovian), and Cossmannea desvoidyi, Globularia rupellensis and G. hemisphaerica (Oxfordian).
In the case of North Africa, two Callovian species (Asterohelix tenuisiensis and Ataphrus douvillei) and an Oxfordian one (Globularia rupellensis) are in common. The faunal relationship with East Africa is restricted to Bourguetia saemanni and three determinable species of Oxfordian to Kimmeridgian age, namely, Cossmannea desvoidyi, Globularia elea, and G. hemisphaerica.
India, particularly the Kutch (Kachh) region, had faunal connections with the Arabian platform during the Jurassic, but almost nothing is known concerning its gastropod faunas. The apparently rather poor Jurassic gastropod faunas in Madagascar, even though not studied in much detail (Newton, 1895; Thévenin, 1908; Delpey, 1948; Nicolaï, 1950–51), has yielded at least one Arabian platform species of Bathonian age (Asterohelix (Bifidobasis) hourcqi). In the case of the Bathonian-Callovian Naricopsina subcanaliculata, the determination needs to be confirmed.
Douvillé (1925, p.303), Reiner (1968, p.195), and Hirsch (1976, p.550; 1980, p.157f f.), had already insisted that the middle Bathonian to Callovian molluscan fauna of Sinai had clear affinities with the Bathonian faunas of Europe, particularly gastropods.
Even though they are not very diversified when compared with European faunas, the Bathonian to Callovian gastropods of central Saudi Arabia, whatever their peculiarities, have affinities with Bathonian European gastropod faunas. Table 2 shows that the affinities of central Arabian gastropods with Western European faunas became even stronger in the Upper Jurassic with six species in common.
Particular attention should be paid to Middle Jurassic nerineids. First, the genus Aptyxiella that is identified in North Africa from the Pliensbachian, appears in Europe only in the middle Oxfordian, but is represented in central Saudi Arabia by a well-identified Callovian species. Second, Hirsch (1976, p.550) has pointed out that the “African-Arabian nerineids, deriving from the Bathonian nereids of Europe, provided the populations of the European ‘Rauracian’ ecologic niches”. It is true that if nerineids are unknown in the Callovian deposits of Western Europe, they were common from the Hettangian to the Bathonian and in the Oxfordian. In contrast, they were diversified in the Middle East during Callovian times where at least nine species are known of the genera Nerinella, Aptyxiella, Cossmannea, and Bactroptyxis, and where, for a time, they found favorable living conditions.
This first study of Jurassic gastropods from Saudi Arabia is a new and major contribution to the knowledge of the Gondwana faunas from the southern Tethyan margin. The value of the results has been greatly improved by the abundant fossil samples from Bajocian to Kimmeridgian age that cover a wide range of sedimentary domains and provide a good stratigraphic and paleoenvironmental framework.
The study shows that this class of molluscs was rather poorly diversified in central Arabia. Only a dozen families were identified, with 25 genera or subgenera and 35 identifiable species. Remarkable is the total absence of many groups that are generally well represented in Jurassic carbonate-platform deposits of Europe and North Africa. The relatively high proportion of new taxa further accentuates this faunal peculiarity. Of the new taxa, three are of genus rank and 14 are species.
Of the 35 species found, less than 25 exist in other Tethyan domains; for example, a dozen in Europe, six in North and East Africa, and one in Madagascar. It is frustrating that no comparison is possible with the Kutch region (India) where the Jurassic gastropod fauna has not yet been described.
The faunas studied here constitute a major paleo-biogeographic benchmark on the southern margin of Tethys, between the North African basins and the Indian-Malagasy domains. However, because the gastropod faunas of the Indian-Malagasy region are insufficiently known, it is impossible to trace the propagation directions of the faunas, or their possible endemism.
From a paleoecologic point of view, most of the Saudi Arabian Jurassic gastropod faunas preferentially occupied the inner platform in lagoonal and back-reef environments (the upper infralittoral domain). Only a few also colonized the outer (lower infralittoral) platform in the fore-reef domain.
This study was carried out within the framework of an agreement between the Saudi Arabian Deputy Ministry for Mineral Resources (now Saudi Geological Survey) and the French Bureau de Recherches Géologique et Minières, during geologic mapping activities in central Arabia. Publication of these results was made possible thanks to the support and authorization of Dr. M.A. Tawfiq, then Assistant Deputy Minister for Survey and Exploration, Deputy Ministry for Mineral Resources, now Acting Director, Saudi Geological Survey.
ABOUT THE AUTHORS
Jean-Claude Fischer is Emeritus Professor of Paleontology at the Musum national dHistoire naturelle (Paris), which he entered in 1962 as a Research Assistant. He received his Scientific Doctorate in 1969 from the University of Paris. He was, respectively, between 197891 and 198589, responsible for the Invertebrate Paleontological Department of the Musum national dHistoire naturelle (Paris), and President of the Collections and Data Banks section of the Scientific Council of the Museum. His geological investigations (more than one hundred papers) have dealt mostly with the invertebrate communities and sedimentary marine environments of Jurassic basins. At present, he is a guest editor of the Revision critique de la Palontologie franaise dAlcide d Orbigny (Masson and MnHn, Paris).
Yves-Michel Le Nindre has more than 10 years experience in the geological mapping of the Phanerozoic rocks of Saudi Arabia. He received his Doctorate of Sciences from the University of Paris in 1987, on sedimentation and geodynamics of central Arabia from the Permian to the Cretaceous. Yves-Michel is currently working in the French Geological Survey on sedimentary basin analysis and modeling, particularly in hydrogeology. He is also involved in present-day littoral modeling.
Jacques Manivits career was as a mapping geologist and stratigrapher in the French Geological Survey and with the Bureau de Recherches Gologiques et Minires. He was involved in the Cover Rocks mapping project of the Saudi Arabian Deputy Ministry for Mineral Resources from 1980 to 1988. Jacques received his Doctorate of Sciences on the bviostratigraphy of Permian to Late Jurassic rocks of central Arabia, from the University of Paris in 1987. He is now retired but is still involved in the geology of the Paris Basin.
Denis Vaslet has 20 years of experience in the geology of Saudi Arabia. He was responsible for the Cover Rocks mapping project of the Saudi Arabian Deputy Ministry for Mineral Resources from 1979 to 1991. Denis has been involved in the complete lithostratigraphic revision of the Phanerozoic rocks of central Saudi Arabia, for which he received his Doctorate of Sciences from the University of Paris in 1987. Denis is currently in charge of the basic geology and mapping at the French Geological Survey.