Petrascula iberica ( DRAGASTAN & TRAPPE ) , Tersella genotii BARATTOLO & BIGOZZI , and the relationships of club-shaped dasycladalean algae during Late Triassic-Early Jurassic times

New observations on abundant material from the type locality of Petrascula iberica (DRAGASTAN & TRAPPE) GRANIER et al. reveal the presence of a reproductive structure (ampulla) located on the inner-middle part of each primary lateral. This fact suggests a new interpretation of the alga and the establishment of a new genus: Granieria BARATTOLO & ROMANO, n. gen. Also, the taxonomic status of the other club-shaped specimens from both the High and Middle Atlas of Morocco and the Central Apennines of Italy is reviewed.


INTRODUCTION
This paper begins with a discussion of the taxonomic history of three dasycladalean taxa: Petrascula, Tersella and Dissocladella.It is a good example of the complexity of taxonomic work, in which the timing of the publication of a taxonomic revision and the quality of the material used to make it are of critical importance.We summarize the main steps in the last twenty years regarding changes in the attributions of these three genera.
DELOFFRE & LAADILA (1991) described a large clubshaped dasycladales from the lowermost Jurassic strata of the Middle Atlas (Morocco) and ascribed it to Palaeodasycladus mediterraneus (PIA).BARATTOLO et al. (1994) suggested that the specimens illustrated by DELOFFRE & LAADILA (1991) should be referred to the genus Tersella.
At the "6 th International Symposium on Fossil Algae" (6 th I.S.F.A.) held in Ankara (1995), GRANIER et al. (1995) reported that the Moroccan species then consequentially designated as Palaeodasycladus mediterraneus (PIA) was similar to the forms that DRAGASTAN & TRAPPE (1986) had set up as Dissocladella iberica and Dissocladella ebroensis.GRANIER et al. (1995) referred the previous cited species to the genus Petrascula and named it Petrascula iberica (DRA GASTAN & TRAPPE) while discarding Dissocladella ebroensis as a junior synonym.Unfortunately the proceedings of the Ankara meeting were never published.However these authors were invited to submit the unpublished paper to the 7th I.S.F. A. volume (Nanjing, 1999).This volume was issued four years later (GRANIER et al., 2003) so fi nally the new designation was in print.However between the fi rst proposal (GRANIER et al., 1995) and its valid publication (GRA NIER et al., 2003), a new paper (BARATTOLO & BI GOZ ZI, 1996) was issued concerning the taxonomic status of the Iberian and Moroccan specimens.In it, the authors introduced a new tax on, Tersella genotii, erected to designate an Early Jurassic alga from Central Italy.Barattolo e Bigozzi (1996) suggested the close affi nity of this new taxon with the Moroccan specimens previously attributed by DELOFFRE & LAADILA (1990) to Palaedasycladus mediterraneus PIA.Moreover, they suggest ed that all the Spanish specimens described by DRAGASTAN & TRAPPE (1986) may be but one species of Tersella.The new combination Tersella iberica is used in BARATTOLO & ROMANO (2005).
At about the same time, shortly before the Granada Symposium, Barattolo and Romano collected samples from the lowermost Jurassic strata of Prejano (Northeastern Spain), the type locality of DRAGASTAN & TRAPPE's (1986) species.The data supplied by the new Spanish material required that for its correct allocation not only the former attribution to Dissocladella be discarded, but also that the subsequent assignments to both Tersella and Petrascula be abandoned.
Well then, the peculiar characteristics observed suggest that this taxon represents a new genus.
These new data were presented at the "9 th International Symposium on Fossil Algae" (Zagreb, September 2007).The generic identity of the other Italian and Moroccan specimens was confi rmed and both were referred to Tersella.In the following section we report the conclusions derived from the study of Moroccan (High and Middle Atlas) material and describe the new genus detected in the Spanish deposits.

SPECIMENS FROM THE HIGH ATLAS, MOROCCO
In the Toundout area (Moroccan High Atlas, see BLOMEIER & REIJMER, 1999), our colleague, A. Poisson, found dasycladacean algae in Lower Jurassic oolitic deposits.The oolitic rocks are made of bioclastic-algal fl oatstones with radial-ooid grainstone matrices.Sixty-four thin sections were prepared and analyzed using a Mitutoyo measuring microscope.This study revealed that, in spite of wide variability in measurements (ranging from 25 to 59% on any one parameter), these algal remains are representatives of but one species because they are all characterised by a unique branching pattern.
In this earliest Jurassic species, the calcifi ed branches consist of a large club-shaped phloiophorous primary pore bearing a cluster of (probably six) secondary open pores with key-hole shaped longitudinal diameters, i.e. they are globular in their proximal part, show a narrowing in their median part, and widen at their distal end.This pattern is similar to the one known from the species Tersella alpina CROS & LEMOINE.Pore lengths (l) and diameters (p) range considerably in their degree of calcifi cation.Therefore the variability in the dimensions of these parameters is closely related to the variability in the thickness (e) of the calcifi ed sheet, i.e. up to about 30%.Considering outer (D) and inner (d) diameters of the thallus sections, as already mentioned, variability is even greater (up to 59 per cent).The outer diameter ranges between 1262 to 8187 µm (average: 4274 µm); the inner diameter is from 749 to 7044 µm (average: 3163 µm).A cross-plot diagram of both parameters clearly displays two linear trends (Fig. 1), suggesting that either there is a degree of segregation within a single species or there are two species, varieties or forms (e.g.fertile versus sterile forms).The fi rst option is preferred.

SPECIMENS FROM THE MIDDLE ATLAS, MOROCCO, AND THEIR GENERIC ASSIGNMENT
DELOFFRE & LAADILA (1991) described a large clubshap ed dasycladalean alga from the Lower Jurassic strata of Morocco.They ascribed it to Palaeodasycladus mediterraneus (PIA), but according to BARATTOLO et al. (1995), the illustrated specimens did not belong to this species.Additional ob servations on the branching pattern and many precise measurements lead to the conclusion that the well-preserved specimens here and the ones from the High Atlas represent the same species.The two linear trends observed on the cross-plot diagram (Fig. 1) of outer (D) and inner (d) diameters are the result of the varying degrees of calcifi cation in any one specimen.The head of this club-shaped alga is relatively less calcifi ed than its stalk (outer diameter smaller than 4500 µm).Primary and secondary branches are calcifi ed in both the stalk and the head; there is no evidence of tertiary branches.Some sections show the characteristic apical opening of the clubshaped head (Fig. 2).This species is therefore related to the genus Tersella J. MORELLET in J. MORELLET & TERS 1951.In the Middle Atlas, the dimensions of the specimens are even greater than those previously observed from the High Atlas.Here, the algae were fossilised in situ within a boundstone facies, whereas the oolitic grainstones of the High Atlas are reworked debris that underwent some mechanical sorting.
In conclusion the specimens from both the Middle and the High Atlas are referable to this single species.In addition, the general size of the biometric parameter suggests that these specimens are referable to Tersella genotii.DRAGASTAN & TRAPPE (1986) described a rich algal as semblage from the lowermost Jurassic strata of Prejano (Northeastern Spain) (Fig. 3).These algal remains were as cribed to "Dissocladella lucasi (CROS & LEMOINE)" (originally qu oted as Linoporella), "Gyroporella retica (ZANIN BURI)" (originally quoted as Macroporella), Sestrosphaera liasina PIA, and to three new species: Dissocladella ebroensis DRA GAS-T AN & TRAPPE, Dissocladella iberica DRAGASTAN & TRAPPE, and "Macroporella nov.sp.".As in the Moroccan High Atlas, this assemblage was found in grainstones of radial ooids and bioclasts often enveloped in micritized and microbialitic fi lms.New material from Spain includes a considerable number of well-preserved specimens that, using the new biometric information collected, allows a complete characterization of the shape, size and general anatomy of the entire plant body.A statistical analysis of 72 specimens showed that the ratio between the outer (D) and inner (d) diameters of the specimens clearly displays a linear trend.According to GRA -NIER et al. (1995, 2003), this linearity suggests that the dimensi on al differences between specimens can be ascribed to nor mal intraspecifi c variation.The specimens previously described as Dissocladella iberica and Dissocladella ebroensis are consequently only one species.New data from the re-sampled type locality, moreover, demonstrate that this species must be re ferred to a new genus for which we propose the taxonomic combination Granieria iberica.
Fi gu re 1: Tersella genotii (Lower Jurassic strata, Toundout, High Atlas, Morocco).Cross-plot diagrams of the calcifi cation thickness (triangles) and of the inner diameter (Y axis) versus the outer diameter (X axis).There are two discrete trend-lines: the smallest diameters (empty squares) correspond to the stalk, the largest ones (black squares) to the head.All dimensional values are provided in µm.

Origin of the name:
The genus is dedicated to our colleague and friend Bruno Granier in observance of his great contributions to the fund of knowledge on fossil dasycladales.
Diagnosis: Club-shaped simple thallus, phloiophorous primary laterals arranged in more or less close whorls (euspondyl arrangement).Short phloiophorous secondary laterals making a cortex.One ampulla is attached on the side of each primary lateral in its inner-middle part (reproduction of choristosporous type).
Comparisons: At fi rst sight the new genus closely resembles other club-shaped Early Jurassic genera like Tersella and Petrascula, and less so Palaeodasycladus and Sestrosphaera.Nevertheless Granieria differs from all these genera mainly in the apparatus of reproduction (choristosporous) rather than cladosporous or endosporous and in part in the number and shape of the laterals.With regard to verticils, Granieria differs from Palaeodasycladus and Petrascula in the orders of ramifi cation, (three in Petrascula and Palaeodasycladus rather than the two of Granieria).Moreover in Petrascula the tertiary laterals do not make a cortex.
Choristosporous rather than cladosporous reproduction is obviously the main criterion distinguishing Granieria from Tersella.The more or less differentiated club-shaped thallus, the presence of the terminal opening related to the same type of apical zone, the two order ramifi cation and the general setting of the calcareous skeleton, are all characteristics shared by Granieria and Tersella.Consequently the occurrence of the lateral ampulla on the primary lateral represents the sole diagnostic character that distinguishes the new genus from Tersella.Taking into account the importance of reproductive structures in taxonomy (e.g.BERGER & KAEVER, 1992), this fact suggests a separation of the two genera at the family level.
In any case, the main problem in the taxonomy of fossil dasycladaleans is their degree of calcifi cation.The amount of calcifi cation is extremely variable (extensive, scattered or absent).Consequently, the structure of the alga must be inter- preted only from the pores defi ned in the calcifi ed portions.The species of Tersella show incomplete calcifi cation of the inner portion of the primary laterals, in particular in the upper portion of the thallus.This incomplete calcifi cation can ob scure the presence of reproductive structures on the lower portion of the primary laterals.However, the great number of specimens of Tersella studied, although they differ in size, degree of calcifi cation and stage of development, confi rms the absence of a reproductive structure (ampulla) in the genus Tersella.
Apart from its type of reproduction, the genus Sestrophaera differs from Granieria in: 1) the presence of only one order of laterals, 2) a more differentiated club-shaped thallus, 3) a closed, well-calcifi ed apical zone rather than an open one.
Granieria's choristosporous reproduction distinguishes this new genus from that of several other genera that appeared after the Jurassic (e. g.Goniolina and Eodasycladus).
In addition, Granieria differs from Eodasycladus in ramifi cation order, (two lateral orders rather than three) and in the general shape of the thallus (club-shaped in Granieria, cylindrical in Eodasycladus).Another important difference between these genera concerns the location of the ampulla.In Eodasycladus the ampulla is at the outer end of the primary laterals, in Granieria it is positioned on one side of them.
According to BERGER & KAEVER (1992), the position of the reproductive organs with respect to the laterals is a distinctive feature, very important in the discrimination of the tribes of any one dasycladalean family.
So, position of the ampulla structure on the side of the primary laterals distinguishes Granieria n. gen.from Eodasycladus.The placement of the ampulla on the side of the primary laterals also distinguishes Granieria from the Cretaceous-Tertiary genera Neomeris and Afghanopolia, for they too are characterized by a terminal position of the ampulla on the primary laterals.
Granieria (one ampulla per lateral) is distinguishable from other choristosporous genera including Bornetella, Jodotella, Goniolina and Microsporangiella that have more than one ampulla per lateral.
The comparison of Granieria with Cylindroporella, Chinianella, and Otternstella is complicated by the taxonomic status of these taxa that in some cases demand a careful restudy of the type species.In any event, at the present state of knowledge, Otternstella and Chinianella are characterized by whorls of fertile ampulla directly connected with the central stem that alternate with whorls of sterile laterals, while Granieria does not have this organization into alternating verticils.Cylindroporella is characterized by an alternation in the same whorl of sterile laterals and ampulla, directly connected to the central stem.In this respect too, Granieria shows no alternation between sterile and fertile laterals, nor are some ampulla set directly on the main axis.
Otherwise, Bakalovaella established by BUCUR (1993) shows an ampulla aside the primary laterals, but differs from Granieria in the general shape of the thallus, (cylindrical versus club-shaped), and the order of ramifi cation (only one versus two).Granieria shows some morphological affi nity with Pseudoactinoporella CONRAD, emend.CONRAD & PEYBERNES.According to BUCUR (2000) this latter genus is characterized by a club shaped thallus, but calcifi ed only in its basal part.The structure of laterals is interpreted as a short primary lateral prolonging into a single secondary lateral and giving rise to a terminal ampulla set aside.Therefore the genus Granieria differs from Pseudoactinoporella at least for the structure of the laterals and position of the reproductive organs.Actually the ampulla of Granieria is attached to the inner part of a long primary lateral instead of terminally on a short one, and the secondary laterals are in tufts versus a single lateral.
Attribution of Granieria to family and tribe: According to the BERGER & KAEVER (1992) classifi cation of the modern dasycladalean algae, an euspondyl arrangement of laterals with choristosporous gametangia attached to the middle part of the laterals by a short stalk restricts the attribution of Granieria n. gen. to the family Dasycladaceae.The presence of an individual reproductive organ (ampulla) set on the side of the primary laterals, the presence of an external cortex, and the club-shaped thallus assign Granieria n. gen. to the tribe Bornetellae.Emended diagnosis: Club-shaped simple thallus, slightly differentiated into a sub-cylindrical lower part (stalk) and an enlarged ellipsoidal upper one (head).Primary laterals arranged in close alternating whorls.They are set almost perpendicularly to the main axis near the base of the thallus; as they approach the top of the thallus, the primary laterals incline upward more and more so they are set vertically near the apex.Primary laterals in the stalk region have a circular cross-section, are moderately long and widen outwards, in the upper part of the thallus, only the distal end of the primary laterals is preserved.Secondary laterals, 3-4 per tuft, are shorter and also widen outwards.They show the same changes in inclination as the primary laterals and form a distal cortex probably with a hexagonal mesh.Choristosporous reproductive organs are sited on the primary laterals.Each consists of a sub-spherical ampulla connected by an inclined short peduncle to the upper side of the inner-middle portion of the primary lateral.The calcareous skeleton is thicker along the stalk where it almost entirely encases the primary laterals, the reproductive

1-4
Oblique sections of the lower part of the calcareous skeleton.

3
Oblique section of the upper part of the calcareous skeleton, BA.3139.40.

4
Detail of the Fig. 2. Note the double pores vertically paired.These represent the primary laterals and the ampulla cut in their proximal part; BA. 3139.242.

5-7
Detail of the ampulla setting in the upper inner portion of the primary laterals.

4
Oblique section of the upper enlarged portion of the calcareous skeleton, BA. 3139.20.
organs and the initial portion of the secondary laterals; elsewhere the calcifi cation is thinner; in the upper part of the skeleton it envelops only the distal end of the primary laterals and the inner-middle portion of the secondaries.Close to the apex the calcareous skeleton is a little thicker, but probably does not affect the apex leaving an opening.The most signifi cant biometric values are listed in Table 1.

General features of the calcareous skeleton:
The calcareous skeleton is simple, continuous, without annulation or in tusannulation.It exhibits moderate differentiation into a sub-cylindrical lower part (stalk) and a gradually enlarged upper part (head).The term "stalk" and "head" is used in the description although the transition between these two elements is ge nerally not sharp or well defi ned (Pl.III, Fig. 1; Pl.IV, Fig. 2).

Table 1:
The most signifi cant biometric values of Granieria iberica nov.comb from sample BA.3020 are supplied.All dimensional values are in millimetres.D = outer diameter of the stalk, d = inner diameter of the stalk, e = calcifi cation thickness, pi = width inner of the primary, pd = outer width of the primary lateral, l = length of the primary lateral, p' = width of the secondary lateral, l' = length of the secondary lateral, h = height between whorls, w = number of primaries in a whorl.The stalk is cylindrical, fl aring slightly upward.It is rather strongly calcifi ed, for generally the entire length of the primary laterals is encased, or at least most of it, and occasionally the sheath extend outward to include the inner portion of the secondary laterals (Pl.I, Figs.1-6; Pl.II, Fig. 2).Calcifi cation does not usually attain the central stem because the inner surface of the calcareous skeleton is often irregular and the tapering proximal part of the primary laterals close to their junctions to the main axis is rarely observable.
The head is ellipsoidal to ovoid, somewhat elongate; calcifi cation is rather thin there, but it envelops the distal end of the primary laterals and a part of the secondaries (see forward, Fig. 4).Near the top, the amount of calcifi cation increases so thinner primary and secondary laterals are encased, but it does not seem to be present at the apex, leaving an opening as in some species of the genus Tersella (Fig. 4b-c).In any case, the rare sections of the entire head never show this opening probably because they do not precisely cut the axis of the apical zone.
The inner diameter starts at 0.70 mm in the stalk and reaches 4.3 mm in the head portion.In the same way the outer diameter ranges from 1.40 mm in the stalk to 5.0 mm in the head.Primary laterals: The primary laterals are set perpendicularly to the main axis along the greater extent of the thallus (Pl.II, Figs.4-6; Pl.III, Fig. 3), but moving up to the apical zone the inclination of the laterals increases until they probably stand roughly vertically at the apex.
The primary laterals in the lower part of the stalk are phloiophorous, club-shaped, their diameter gradually increasing in size outwards (Pl. II,.Moving from the stalk to the head, the primary laterals tend to assume a slight differentiation into a inner sub-cylindrical portion and a more globular distal portion (Pl.IV, Figs.1-2).The laterals are circular if cross sectioned and their diameter ranges from 0.01-0.10(pi) to 0.10-0.15(pd)mm, in the inner and the distal parts respectively.The junction between primary laterals and the central stem is never observed because the calcifi cation does not reach the main axis.
The primary laterals of the head are apparently short, bigger than those of the stalk (0.15-0.21 mm), and globular in shape (Pl.IV, Fig. 1).Their reduced length is combined with a large central cavity; this fact seemingly is the result of calcifi cation restricted to the distal part of the primary laterals.This assumption is strengthened by the trend of calcifi cation which tapers upward in the stalk/head transition and because the primary pores open to the inner cavity through large pores.
The primary laterals are arranged in simple euspondyl whorls.The number of primary laterals for each whorl is 20-24 mm in the stalk and reaches 40-46 mm in the head.Subsequent whorls exhibit laterals arranged in alternate position (Pl.II,Figs. 1,4).The height between whorls (h) is 0.22-0.36mm.
Secondary laterals: The secondary laterals originate from the distal part of the primary laterals.The secondary laterals are mainly observable in the middle and upper parts of the thallus, while in the lower stalked part they are rarely visible, because they are only rarely encrusted by calcifi cation.Anyway their size and number per tuft (3-4) remain constant throughout the whole thallus.
Secondary laterals are rather short and quickly fl are outwards (Pl. I,12).They display a close packed ar rangement at the outer surface of the calcareous skeleton (Pl.IV, Fig. 3).This fact allows for the argument that the uncalcifi ed distal parts were adequately widened out in order to touch laterally in order to form a cortex.
Reproductive organs: A single sub-spherical ampulla per primary lateral (0.10-0.18 mm,) is attached, through an inclined short peduncle, on the upper side, in the inner-middle portion of the lateral.Only a few well preserved longitudinal sections of the stalk (Pl.III, Figs.5-7) clearly show this characteristic.However the presence of such structures can be detected more frequently in tangential and oblique sections cut very close to the central cavity.The whorl appears to be constituted by a row of vertically paired pores (Pl.III, Figs.1-2, 4).The pores of a couple are set very close to each other and are of comparable size.On moving laterally the paired pores disappear and only a row of single pores, increasing in size, continues.Each couple of pores represents the section of the inner portion of the primary lateral and the ampulla or its oblique peduncle.
Reproductive organs are only preserved in the stalk be cause the calcifi cation almost completely encrusts the primary laterals.The fact that calcifi cation in the head is restricted to the distal part of the primary laterals means that all the inner structures are not preserved.
Reconstruction: Most elements of the thallus that are calcifi ed have been described above.Only the shape of primary laterals in the upper part of the thallus, the presence of the reproductive structure in the head and the outer end of the secondary laterals are not preserved and are therefore treated here in a prospective reconstruction of the thallus (Figs.5-6).The uncalcifi ed primary laterals in the upper part of the thallus are assumed to be similar to those in the lower part, but are comparatively longer.The reproductive structures are thought to be present in the head too because in other dasycladales it is specifi cally the upper part of the thallus that is deputed to reproduction.The position of the ampulla has been postulated as similar to that of those visible in the lower part of the thallus, but larger in comparison to the size of the lateral.
Finally the top of the thallus is believed to resemble those of other morphologically similar fossil genera such as Tersella (e.g.Tersella alpina, Tersella genotii).
Comparisons: As discussed above, Granieria displays close analogies with other club-shaped Early Jurassic genera.In particular the type species Granieria iberica (DRAGASTAN & TRAPPE) nov.comb.shows a marked resemblance to the genus Tersella.
Granted that the presence of a choristosporous type of reproductive apparatus (ampulla) is suffi ciently decisive to distinguish Granieria iberica n. comb from all not-choristosporous species of Tersella, there are other morphological differences.
Tersella genotii BARATTOLO & BIGOZZI and Tersella incompleta MORELLET are very close to Granieria iberica in that they share a slightly differentiated club shaped calcareous skeleton and a general similarity in the pattern of calcifi cation from the stalk to the head.T. genotii is larger than Granieria iberica and its secondary laterals are cylindrical to slightly widened outwards rather than short and cone shaped as in Granieria iberica.T. alpina CROS & LEMOINE shows a narrowing in the middle portion of the secondary laterals, and T. incompleta also narrows, but in the sub-terminal portion, while Granieria iberica has regularly widening short, cone-shaped, secondary laterals.
Finally, Tersella quercensis differs from Granieria iberica in that a distinction between head and thallus is well-marked in the club-shaped skeleton.
Granieria iberica shares its choristosporous type of reproduction with Cylindroporella?liasica but the thallus in this species is cylindrical, not a moderately differentiated clubshape.The fertile ampulla is larger and forms an elongated ellipsoid rather than sub-spherical globe (Granieria iberica).
Fi gu re 5: Granieria iberica nov.comb.Reconstruction of the thallus in longitudinal view.Left side: stem, primary laterals and calcifi cation (black) in axial section.Right side: longitudinal view of the thallus without calcifi cation; in the lower part a perspective view of the primary and secondary laterals, and cortex is drawn.
Fi gu re 6: Granieria iberica nov.comb.Reconstructions in transverse view.Left-side transverse section at whorl level showing primary and secondary laterals and calcifi cation (black); right-side: primary, secondary laterals and ampulla without calcifi cation.Lower -stalk region, upper -head region

CONCLUSIONS
The taxonomic relationships of several forms of dasycladales from Morocco, Italy and Spain are more complicated than previously supposed.
The Moroccan specimens initially described as Palaeodasycladus mediterraneus by DELOFFRE & LAADILA (1991) are now referred to Tersella genotii.This attribution is based on the restudy of two discrete Moroccan dasycladalean assemblages, one from the High Atlas and the other from the Middle Atlas.
The establishment of the new genus Granieria brings to light that in the Early Jurassic the genera developed, although apparently similar in aspect, are fundamentally different in reproductive strategy.The position of Cylindroporella?liasica (BARATTOLO & PARENTE 2000) should be analyzed in the light of the coincident occurrence of a structurally similar taxon, Granieria, which differs mainly in the shape of the thallus.

Fi
gu re 2: a -Thin section of the High Atlas material with Tersella genotii (Lotharingian strata, N Ribat el Khaďr, Middle Atlas, Morocco), showing some unfragmented specimens of Tersella genotii.b -Polished section (counterpart of the rock sample illustrated by DELOFFRE & LAADILA, 1990, pl.I, fi g. 3, and from which the thin section was cut) showing several specimens of Tersella genotii.Arrows point to some well preserved apical apertures.

Fi
gu re 3: a -Location of the type-locality of Granieria iberica nov.comb.b -Field photography of the Prejano outcrop.The studied sample was collected from the oolithic massive level (arrow), Field of view is approximately 0.5 km wide.c -Schematic diagram of Lower Jurassic deposits of the Prejano area, with the position of the dasycladales bearing level (modifi ed from DRAGASTAN & TRAPPE, 1986).