Megalospheric forms of Priabonian Spiroclypeus of the Western Tethys were morphometrically investigated. Based on the reduction of the average number of undivided, post-embryonic chambers, the investigated populations are grouped into two successive, phylogenetically linked species, S. sirottii sp. nov. and S. carpaticus. The evolution is also demonstrated by the increase of the number of secondary chamberlets in particular chambers, by the increase of the diameter of the first two whorls and by that of the size of the proloculus, although the latter turned out to be also ecologically controlled. This evolution is supported by the stratigraphic succession of populations in the Mossano section (N Italy) and by the change of accompanying fossils. Lacking in upper Bartonian beds, the first appearance of genus Spiroclypeus seems to be synchronous with the beginning of the late Eocene. The newly described S. sirottii is associated with Heterostegina reticulata mossanensis and orthophragmines containing forms of middle Eocene acme, both marking the lower part of the Priabonian. Meanwhile S. carpaticus co-occurs with H. gracilis and/or with orthophragmines characteristic of the upper part of the Priabonian. We suppose that the Spiroclypeus sirottii-carpaticus lineage is restricted to the Priabonian. Thus, Spiroclypeus sirottii is a zonal marker for the Shallow Benthic Zone (SBZ) 19 (early Priabonian) while S. carpaticus indicates the SBZ 20 (late Priabonian).
The representatives of genus Spiroclypeus can be very frequently found in the upper Eocene larger foraminiferal assemblages of the Western Tethys. Two species, “Spiroclypeus carpaticus” and “S. granulosus” are mentioned alternatively; however, their relationship to each other is not clear.
The aim of this study is to elucidate the stratigraphic significance of species belonging to this genus within the Western Tethyan Eocene. This includes the comparative investigation of populations collected from different localities to determine whether they form a single evolutionary lineage and to recognize the stratigraphically controlled evolutionary trends that can lead to a more detailed subdivision of the genus and then, in turn, to a more well-established subdivision of the time-interval spanned by the studied samples. Based on joint occurrences with Spiroclypeus, the results of the paper by Less et al. (2008) on involute Heterostegina are widely used in this process in two respects. On the one hand, relying on their morphological similarity, the same methods used to investigate Heterostegina are applied to Spiroclypeus; on the other hand, the high-resolution heterosteginid scale serves for stratigraphical calibration of the spiroclypeid evolution.
No Spiroclypeus has been found in upper Bartonian localities containing Heterostegina armenica or the less ad vanced representatives of the H. reticulata-lineage with more than three undivided post-embryonic chambers in average. In four localities (Mossano, Verona—Castel San Felice, Úrhida, and Şarköy) the first occurrence of Spiroclypeus is linked to the presence of H. reticulata mossanensis marking the basal Priabonian. Thus, we can reasonably conclude that they appeared in the late Eocene. Data, seemingly contradicting this statement are discussed below. Because either involute Eocene Heterostegina or orthophragmines (both having become extinct at the end of the Eocene) are present in all the studied localities, our review is restricted to the Priabonian. The relationship between Priabonian and Oligocene—Miocene Spiroclypeus is discussed below.
The Indo-Pacific (e.g., Krijnen 1931; Tan 1937; Matsumaru 1996) and Caribbean (Vaughan and Cole 1941) representatives of the genus Spiroclypeus are beyond the scope of our study, since they can be distinguished from the Western Tethyan late Eocene forms by their much looser spire and, therefore, no direct phylogenetic relationship can be reasonably supposed between them.
ITU O, Istanbul Technical University, Özcan collection of the Geology Department;
MÁFIE and O, Geological Institute of Hungary (Budapest), Eocene (E) and Oligocene (O) collection.
Abbreviations for biozones.
NP, Paleogene calcareous nannoplankton zones by Martini (1971);
OZ, orthophragminid zones for the Mediterranean Paleocene and Eocene by Less (1998) with correlation to the SBZ zones;
SBZ, shallow benthic foraminiferal zones for the Tethyan Paleocene and Eocene (SBZ 1–20) by Serra-Kiel et al. (1998) and for the Oligocene and Miocene (SBZ 21–26) by Cahuzac and Poignant (1997) with correlation to the planktic and magnetic polarity zones.
Uhlig (1886) was the first to describe and figure identifiable Spiroclypeus under the name of Heterostegina carpatica from the flysch deposits of the Woła Łużańska (Polish Carpathians). The two drawings illustrating the equatorial section of A-forms give reliable information not only on the tightness of the spire (significant for Western Tethyan late Eocene Spiroclypeus) but also on the number of undivided neanic chambers that allow to quantify the evolutionary stage of the taxon. He listed also the associated fossils, among which the presence of orthophragmines assures the Eocene age of the type locality. At the same time Nummulites tchihatcheffi (corresponding to the megalospheric form of the N. millecaput-group) was also listed. This suggests a reworking of fossils in the type locality of Spiroclypeus carpaticus.
Douvillé (1905) introduced the genus Spiroclypeus from the Aquitanian beds of Borneo with a differential diagnosis that stresses the completely embracing nature of subsequent whorls as distinction from Heterostegina. Boussac (1906) emended the generic diagnosis by recognizing the presence of lateral chamberlets in not only the forms from Borneo but also in the material from Priabona. He introduced the name Spiroclypeus granulosus for these latter forms. In contrary to the good figures of the axial section, the equatorial section was rather poorly illustrated, a fact that hampers the recognition of the evolutionary stage of this species. Boussac (1906) distinguished his new species from Uhlig's (1886) “carpatica” by external features like the presence of the thin, undulated flange and also by the larger dimension and density of granules.
Bieda (1957, 1963) considered the presence of granules on the surface of Spiroclypeus as a generic feature and followed Boussac (1906) in distinguishing S. carpaticus and S. granulosus from each other by the quality of granulation. Internally, however, the two forms are quite different in the character of the spire; the one of S. granulosus being much more open. In our opinion these forms correspond to Heterostegina gracilis (more details see below).
Roveda's (1961) work from Priabona is very important in two respects. His published equatorial section of Spiroclypeus granulosus from the type-locality bears the same tight spire as S. carpaticus and it is very different from the spire characteristic for Bieda's (1957) S. granulosus (= H. gracilis, see above). Roveda (1961) declared the presence of the lateral chamberlets to be the most diagnostic feature of Spiroclypeus.
Hottinger (1977) provided the currently used definition of the genus and after a preliminary study (Hottinger 1964) proposed a single evolutionary lineage for the genus starting in the late Eocene with Spiroclypeus granulosus followed by the early Oligocene (?) S. carpaticus, by the late Oligocene S. tidoenganensis and terminating with the early Miocene S. anghiarensis. He also recognized the main evolutionary trends, the size increase of the proloculus, the opening of the spiral and the flattening of the test. By comparing the Eocene and post-Eocene forms, however, we do not suppose a direct phylogenetic continuity between them.
Herb (1978) introduced H. gracilis from Possagno (Italy), a taxon with granules on the surface but with no lateral chamberlets. Its internal features are practically identical with those of Bieda's (1957, 1963) and Grigoryan's (1986) S. granulosus, therefore these forms are not discussed below (see also in Less et al. 2008).
Fermont and Troelstra (1983) and Schiavinotto (1986) were the first to investigate Spiroclypeus populations and to characterize them biometrically. In our paper we adopt their system with some additions. Based on Schiavinotto's (1986) data on S. granulosus from Priabona, the type locality, this taxon in our opinion is a junior synonym of Uhlig's (1886) S. carpaticus.
Some figures of Spiroclypeus are presented in the works of Papazzoni (1994), Papazzoni and Sirotti (1995), Less (1999) and Özcan et al. (2007). These forms are described and discussed in more details below.
Terminology and concepts
The general architecture of Spiroclypeus.—According to Hottinger (1977), Spiroclypeus is a planispiral, lamellar, finely perforated, involute foraminifer belonging to the subfamily Nummulitinae. Its chambers become secondarily subdivided into regularly arranged secondary chamberlets (of very slightly hexagonal shape as seen in equatorial sections) by well-developed, complete secondary septa at different moments of their ontogeny. The spiral chambers never develop into annular ones as do those of Cycloclypeus or Heterocyclina. The diagnostic feature of Spiroclypeus that distinguishes it from Heterostegina is the presence of lateral chamberlets (Fig. 1), symmetrically on both sides of the spiral, formed by folding the walls of the alar prolongations and by piling the cavities between the folds from successive chambers to a chessboard-patterned construction. Externally (Fig. 1), the test is biconvex with a very slightly eccentric outline. Most of the surface is covered by granules; the network of chamberlets can be frequently seen on its very edge.
Banner and Hodgkinson's (1991) interpretation of lateral chamberlets is somewhat different from that of Hottinger (1977, 2006). They mean by “true” lateral chamberlets in heterosteginids their alar prolongations subdivided into chamberlets. Hottinger (2006) suspects these “lateral chamberlets” to be undivided alar prolongations cut at an oblique angle in respect to the median line of the alae. Banner and Hodgkison (1991) introduced the term “cubicula” for lateral chamberlets in our and Hottinger's (2006) interpretation. In order to avoid misunderstandings, in this work we follow Hottinger's (2006) concept on lateral chamberlets.
Spiroclypeus are assumed to have been symbiont-bearing. No particular size-difference of the adult shells between stratigraphically older and younger or between megalo- (A) and microspheric (B) forms can be observed. B-forms are rare, A-forms predominate. Axial sections are to be studied further. Therefore, we concentrate our investigations on the equatorial section of megalospheric forms.
Taxonomical concept.—We adopt the taxonomical concept and morphometric method based on Drooger (1993) and described in Less et al. (2008). Spiroclypeus from each sample appeared to form one single population both typologically and biometrically. Contrary to Heterostegina reticulata and H. armenica which were segmented into subspecies by Less et al. (2008), the supposed single lineage of Western Tethyan late Eocene Spiroclypeus is subdivided into (two) species because not only their populations but in most cases also their specimens can be distinguished from each other. The quite well recognizable differences in the axial sections of the two taxa also support their distinction in the specific level (see below).
Morphometry.—To apply the morphometric method, Eocene Spiroclypeus is described by nearly the same quantitative parameters that are measured and counted in the equatorial section of A-forms of Heterostegina by Less et al. (2008). One difference is the measurement of parameter D in the first two whorls. Five measurements and counts were executed as follows (see also Fig. 2):
P: The inner cross-diameter of the proloculus in µn. Wallthickness is not measured.
X: the degree of “operculinid reduction” as reflected in the number of undivided, “operculinid” chambers before the appearance of the first subdivided, heterosteginid chamber, excluding the embryon (the first two initial chambers of megalospheric forms, see Hottinger 2006). Undivided chambers, reappearing after the first heterosteginid chamber, are not counted. In Fig. 2, X = 2.
S: the density of secondary chamberlets (“heterosteginid escalation”) as reflected in the number of chamberlets in the fourteenth chamber (including the embryon). In Fig. 2: S = 6.
Statistical data of Spiroclypeus populations. Abbreviations: n, number of measured specimens; aff. c., Spiroclypeus aff. carpaticus. * For D and K n = 18, for S n = 13. ** For S n = 7.
Most important characteristics of the localities investigated. * based on Less et al. (2008); ** orthophragmines and their zones are based on Less (1998) for Mossano, Less (1999) for Kisgyr, Less et al. (2000) for Úrhida, Özcan et al. (2007) for Şarköy, and on GL 's unpublished data in the case of Verona and Priabona. Abbreviations: ↑ and ↓: above and below; ?: very rare occurrence.
d: The maximum diameter of the first whorl measured along the common symmetry axis of the first two chambers (in urn). This parameter is not tabulated in Table 1, but is used for calculating parameter K.
D: The maximum diameter of the first two whorls (in µm) measured in the same way as d. From these direct parameters:
K: the index of spiral opening (independent from the size of the proloculus), is computed as:
Five parameters (P, X, S, D and K) are evaluated statistically by standard methods per population. The results are summarized in Table 1. Bivariate plots and 95.44% confidence ellipses are generated in the same way as given in Less et al. (2008). For microspheric forms see the discussion in “Evaluation of parameters”.
Material and methods
We tried to investigate material from a wide geographical (Fig. 3) and stratigraphical range. In describing our samples we start with Northern Italy where the most important paleontological sites are located. The most significant characteristics of the samples are summarized in Table 2 (the nomenclature of spiroclypeid populations is discussed later, specific names are listed here for the completeness of data). The information on the localities and the source of information on their fossil contents for Mossano, Verona, Possagno, Úrhida, Benidorm, Biarritz, and Şarköy are discussed in detail in Less et al. (2008). Additional comments on the samples are given below.
Northern Italy, Veneto area
Priabona.—The historical background of the Priabonian type section was extensively described recently by Bassi et al. (2000). Our sample was collected from the upper part of Via Centra (figured in Setiawan 1983) corresponding to about the boundary of the “Discocyclina beds” and “Blue claystone” of Hardenbol (1968) and Sirotti (1978). Relying on the description of the locality and on the similar faunal assemblage our sample has been taken very probably from the bed of sample Pr.55 by Setiawan (1983). This bed should be very close to the layers from where Boussac (1906), Roveda (1961) and Schiavinotto (1986) took their samples containing Spiroclypeus, since based on Sirotti (1978) and Setiawan (1983), the vertical range of the genus is rather restricted in the Priabona profile. Moreover, morphometrically our population (see Table 1) is very similar to that of Schiavinotto (1986), therefore it can be considered as topotypical for Spiroclypeus granulosus described by Boussac (1906) from here. At the same time in our opinion, its characteristics correspond to those of Uhlig's (1886) S. carpaticus, and therefore this latter name has to be used for specimens found at this site (more details see in the systematical part).
Sirotti's (1978) and Setiawan's (1983) orthophragminid materials were revised in Modena and Utrecht by GL (still unpublished). Nummulitids are listed based on Roveda (1961) and Sirotti (1978). Planktic foraminiferal and calcareous nannoplankton data are based on Barbin (1986, see in Brinkhuis 1994) and on Verhallen and Romein (1983), respectively.
Possagno.—Since Spiroclypeus are rather rare and morphometrically similar in the two samples (see Table 1), they are discussed together.
Mossano.—Spiroclypeus specimens occur only in the lower part of the Marne di Priabona starting immediately at the base. Samples Mossano 5 and 6 were taken from the two outcrops both representing the base of the Priabonian (see details in Less et al. 2008), and therefore, they are discussed together. In sample Mossano 7 Spiroclypeus is rather rare and poorly preserved. In sample Mossano 8 they are quite common, though again poorly preserved.
Population Mossano 8 differs from Mossano 5+6 (see also Table 1) in having (i) a somewhat smaller number of operculinid chambers (parameter X), (ii) a somewhat larger proloculus and (iii) some more chamberlets in chamber 14 (S). This trend is the same as observed in the case of the Heterostegina reticulata lineage in the same samples (Less et al. 2008). It is in accord with the stratigraphic position of the two populations and also with their slightly different accompanying fossils (Table 2). At the same time all the three parameters are much less advanced in both populations than for Spiroclypeus carpaticus in Priabona and Possagno. Therefore, a new species, S. sirottii is introduced in this paper for them with the type locality of the basal part of the Priabona marls in Mossano (sample Mossano 6).
Verona.—Since the morphometrical data from the three samples of Castel San Felice (Villa Le Are, Villa Devoto, and hairpin bend) in which the genus is present are rather similar (see Table 1), the populations are discussed jointly below.
Benidorm.—One specimen of Spiroclypeus was found in the sample and another one has been measured based on Hottinger's (1964) pl. 7: 6.
France, SW Aquitaine
Biarritz, Lou Cachaou.—The biometrical data of the spiroclypeid population (see Table 1) show an intermediate position between those of typical S. carpaticus from Priabona and those of typical S. sirottii from population Mossano 5+6. Since the average number of post-embryonic pre-heterosteginid chambers (Xmean = 2.38) is closer to the value defining S. carpaticus (Xmean <2.7) than to that of S. sirottii (Xmean >2.7), the population is determined as S. aff. carpaticus, taking into account also the relatively small size of the proloculus.
Úrhida (W Hungary).—Spiroclypeus only appear in the uppermost sample (Urhida 10) associated to Heterostegina reticulata mossanensis, the most advanced representative of this lineage in this locality.
Kisgyr, Remete-kút (NE Hungary).—Only one (Remete-kút 3) of the four samples described and figured in detail by Less (1999) and Less et al. (2000) from Kisgyr contains a fairly rich population of well preserved Spiroclypeus carpaticus (S. granulosus in the two papers listed above). Planktic foraminifers have not been found in any of the four samples yet; however calcareous nannoplankton (determined by Mária Báldi-Beke) could be studied from samples Remete-kút 2 and 4. More details and the fossil list can be found in Less (1999) and Less et al. (2000) where other larger foraminifers (determined by GL) are also listed. According to our recent studies (unpublished data) Nummulites retiatus of the above two papers from Kisgyr corresponds to N. fabianii.
Turkey (Thrace Basin)
Şarköy.—The genus Spiroclypeus was identified in all samples (Şarköy 2, 4, 9, and A) studied by Özcan et al. (2007) and Less et al. (2008); however, they are statistically investigated only from Şarköy 4.
We have studied isolated specimens mostly from marls and marly limestones. The axial sections from all localities and most equatorial sections from §arköy have been exposed by thin-sectioning. In all the other cases we opened the equatorial section by splitting. In some cases (Priabona, Possagno) tests were heated before splitting. In other cases (Mossano, Verona, Úrhida, Kisgyr) shells have been stained by violet chemical ink. For the comparison of the splitting and the thin-sectioning see Less et al. (2008).
Evaluation of parameters
Contrary to genus Heterostegina (Less et al. 2008), Western Tethyan late Eocene Spiroclypeus seems to be nearly homogenous in their qualitative features like the surface of the test and the arrangement and shape of secondary chamberlets. Differences, however, may appear in the development of lateral chamberlets as observed in the axial sections. In specimens from samples with orthophragmines of middle Eocene acme (Discocyclina pratti, Nemkovella strophiolata, Asterocyclina alticostata, A. kecskemetii) lateral chamberlets are poorly developed (in Mossano, Verona, and Şarköy), whereas in specimens from samples containing Heterostegina gracilis but no orthophragmines of middle Eocene acme (Priabona, Kisgyr) they are quite well-developed.
The statistical summary of quantitative features per population is given in Table 1. The greatest differences between populations are to be seen in the parameters X and S. Their mean values at the 95% confidence level are plotted in Fig. 4 (with the exception of the Benidorm population, which had too few specimens) from which the following conclusions can be drawn:
(i) The Spiroclypeus populations cluster in two groups. The upper left group corresponds to Spiroclypeus sirottii, the lower right group to S. carpaticus. The population from Biarritz, Lou Cachaou (S. aff. carpaticus) takes an intermediate position between them.
(ii) The populations are arranged in the plot according to their associated, age-determining larger foraminiferal fauna. Those without orthophragmines of middle Eocene acme or with Heterostegina gracilis are concentrated in the centre and in the bottom right whereas those with orthophragmines of middle Eocene acme in the upper left. It is worth noting that in this latter group not only the parameters of Spiroclypeus from particular populations but also those of Heterostegina are very similar to each other.
(iii) The stratigraphic superposition of the population Mossano 8 in respect to Mossano 5+6 that was directly observed in the field, is reflected also in their position in the plot.
(iv) The decrease of the number of undivided neanic chambers (X) and the increase of the number of chamberlets in chamber 14 (S) have a great stratigraphic significance. The strong negative correlation between the two parameters can also be read from Fig. 4.
Almost the same conclusions can be drawn from Fig. 5 where the mean values of the size of the proloculus (P) per population are plotted against those of X at the 95% confidence level. However, in this case the population from Biarritz, Lou Cachaou is closer to the group of Spiroclypeus sirottii associated with orthophragmines of middle Eocene acme. This means that the general increase of the size of the proloculus is not only a far less rapid evolutionary trend than the change of X and S, but also far less reliable, probably because it is under an additional ecological control (for more details see Beavington-Penney and Racey 2004).
The diameter of the second whorl (D) is also quite useful in distinguishing the two species as shown in Fig. 6 where this parameter is plotted against X, once again at the 95% confidence level. From this plot the same consequences can be extracted as from the former two figures, almost with the same resolution power. The population from Biarritz, Lou Cachaou is again intermediate between the group of Spiroclypeus carpaticus and that of S. sirottii, as in Fig. 4.
The least diagnostic numerical parameter is K, the index of spiral opening that shows a very slow and rather uncertain increase, i.e., the spiral becomes generally looser in time. In general, there is a slight positive correlation between the size of the proloculus (P) and the laxity of the spiral.
As seen from the photos of Fig. 7, no real increase in the size of the test can be observed during the evolution of Spiroclypeus in the late Eocene. Moreover, no difference in the test size could be observed between the A- and B-forms, although the latter were rare. Parameter X (with the same meaning as in the A-forms) could be counted in four specimens. In sample Mossano 6, the X values were 18 and 22, in sample Mossano 7 it was 17 whereas in sample Kisgyr, Remete-kút 3 it was reduced to about 14. These data suggest that a reduction in the number of undivided neanic chambers also occurs in the microspheric forms, although the number of observations is too low to reach any firm conclusions.
Order Foraminiferida Eichwald, 1830
Family Nummulitidae de Blainville, 1827
Genus Spiroclypeus Douvillé, 1905
Type species: Spiroclypeus orbitoideus Douvillé, 1905, late Aquitanian, river Tabalong, close to Tandjong (Borneo)
Remarks.—Based on the parameters evaluated above, Western Tethyan late Eocene Spiroclypeus can be grouped into two species. They can be discriminated using the number of the undivided neanic chambers (X). Based on our data (Table 1) Xmean = 2.7 is the most suitable value to separate Spiroclypeus sirottii with more undivided chambers from S. carpaticus with fewer. The classification of particular populations in the different taxa is reported in Table 1. Stratigraphical ranges of particular taxa are given in advance.
Spiroclypeus sirottii sp. nov.
Fig. 7A-N, P, Q, T.
2004 Spiroclypeus sirottii sp. nov.; Less and Gyalog 2004: pl. (black and white) 2: 4.
2007 Spiroclypeus sirottii sp. nov.; Özcan et al. 2007: pl. 1: 20.
Derivation of the name: In honor of the late Professor Achille Sirotti (Modena), an expert on larger Foraminifera.
Holotype: MÁFI E. 9591 (Fig. 7K), a megalospheric specimen split along the equatorial plane.
Type locality: Mossano (N Italy, Colli Berici), Marne di Priabona, sample Mossano 6.
Type horizon: Basal Priabonian, SBZ 19 A.
Material.—18 well-preserved megalospheric specimens split along the equatorial plane.
Diagnosis.—Involute, lense-shaped test with poorly developed lateral chamberlets. Most of the surface is covered by granules except at the shell's margin where usually a rectangular suturai network can be seen. The proloculus is small; the coiling of the spiral is rather tight. The number of undivided postembryonic chambers (parameter X) is usually 2–7; its mean value exceeds 2.7 which distinguishes it from Spiroclypeus carpaticus (Uhlig, 1886). The secondary chamberlets are more or less regularly arranged, somewhat sparsely spaced and of very slightly hexagonal shape.
External features (Fig. 7B, D, G).—The test is small (1.5 to 4 mm in diameter), involute, biconvex, lense-shaped with a very slightly inflated, broad umbonal part occupying 70–90% of the test's diameter. It is covered by granules, which are very slightly larger in the centre than towards the shell's periphery where they are absent and where a regular, rectangular network of primary and secondary septa can sometimes be seen. No significant difference in size was recognized between A- and B-forms.
Internal features.—The equatorial section of A-forms: The proloculus is small (P = 50–150 urn, Pmean of different populations varies between 80 and 115 µm) and (after a kidneyshaped deuteroconch of similar size) is followed by a rather tightly coiled spiral comprising 2.5 to 4 whorls (d = 350–720 µm, dmean = 490–650 µm; D = 700–1350 µm, Dmean = 920– 1160 µm; K = 38–61, Kmean = 49–56). The chambers are very high; the primary septa are very strongly curved backward. After a few undivided (operculinid) postembryonic chambers (X = 2–7, very rarely 1 or 8 to 10; Xmean = 2.7–5.5) all the successive chambers are subdivided into secondary chamberlets that are rather regularly arranged, somewhat sparsely spaced (S = 2–5, very rarely 6 or 7; Smean = 2.3–4.3) and of very slightly hexagonal shape.
The equatorial section of B-forms (Fig. 7N): Based on three specimens from samples Mossano 6 and 7, the size of the proloculus is 10–15 µm. It is followed by 17–22 undivided (operculinid) chambers before the appearance of the first subdivided chamber after which some undivided chambers may reappear in a few specimens. The arrangement and shape of chamberlets in the adult stage do not differ from those of the A-forms.
Axial section (Fig. 7H, I): The test is inflated, involute and biconvex. Piles are well visible, lateral chamberlets are visible but poorly developed.
Remarks.—The name Spiroclypeus sirottii was informally used by Less and Gyalog (2004) for the population from sample Úrhida 10 and by Özcan et al. (2007) for the population from sample Şarköy 4, although no description was provided, so the taxon is introduced formally herein. The figures of Papazzoni (1994) and Papazzoni and Sirotti (1995) cited in the synonymy list illustrate specimens from nearby samples Mossano 5 to 7. These populations were re-evaluated in this paper and placed in synonymy with the present species.
Spiroclypeus sirottii can be confused only with S. carpaticus, however, the mean value of the post-embryonic pre-heterosteginid chambers (parameter X) for the A-forms is above 2.7 for S. sirottii. The other discriminative parameters are the mean value of the number of chamberlets in chamber 14 (parameter S) which is below 4.3 and that of the diameter of the first two whorls which is below 1160 µm. In axial section the rather poorly developed lateral chamberlets also help discriminate the two taxa.
In accord with Hottinger (1977) we suppose that Spiroclypeus (and consequently S. sirottii, the first representative of the genus known so far) evolved from involute Heterostegina, very probably from H. reticulata since it has a similar structure in equatorial section, but lacks lateral chamberlets and appeared in stratigraphically lower horizons. At the same time there can be little doubt on the derivation of S. carpaticus from S. sirottii. The identical structure of their equatorial sections, the more advanced numerical characteristics of S. carpaticus compared to S. sirottii (see Table 1 and Figs. 4–6), and the presence of well-developed lateral chamberlets at S. carpaticus and of course the relative stratigraphic position of the two taxa suggests S. carpaticus evolved from S. sirottii.
Geographic and stratigraphic distribution.—Early Priabonian (SBZ 19) of N Italy (Mossano, samples 5, 6 and 8; Verona, Castel San Felice: Villa Le Are, Villa Devoto and the outcrop of the hairpin bend), W Hungary (Úrhida, sample 10), NW Turkey (Şarköy).
Spiroclypeus carpaticus (Uhlig, 1886)
Fig. 7R, S, U-Z, AA-AD.
1886 Heterostegina carpatica sp. nov.; Uhlig 1886: 201–202, pl. 2: 14–15; text-fig. 10.
1906 Spiroclypeus granulosus sp. nov.; Boussac 1906: 96–97, pl. 2: 15–18; pl. 3: 19.
Diagnosis.—Involute, disc-shaped test with well-developed lateral chamberlets. Most of the surface is covered by granules except the peripheries where usually a rectangular septal network can be seen. The proloculus is small to mediumsized; the coiling of the spiral is moderately tight. The number of pre-heterosteginid postembryonic chambers (parameter X) is usually 1–2, rarely 3; its mean value is less than 2.7, which distinguishes it from Spiroclypeus sirottii sp. nov. The secondary chamberlets are quite regularly arranged and densely spaced and of nearly rectangular shape.
External features (Fig. 7R, S).—The test is small (1.5 to 4 mm in diameter), involute, biconvex, disc-shaped with a very slightly inflated, broad umbonal part occupying 60–90% of the test's diameter. It is covered by granules, which are slightly larger in the centre than towards the shell's periphery where they are absent and where a regular, rectangular network of primary and secondary septal sutures may often develop. No significant difference in adult shell size can be recognized between A- and B-forms.
Internal features.—The equatorial section of A-forms: The proloculus is small to medium-sized (P = 100–200 µm, Pmean = 115–155 µm) and (after a kidney-shaped second chamber of similar size) followed by a moderately tightly coiled spiral with 2.5 to 4 whorls (d = 450–950 µm, dmean = 600–750 µm; D = 950–1700 µm, Dmean = 1150–1550 µm; K = 40–63, Kmean = 51–60). The chambers are very high; the primary septa are very strongly curved backwards. After a very few undivided (operculinid) postembryonic chambers (X = 1–3, very rarely 4; Xmean = 1.2–2.7) all the successive chambers are subdivided into chamberlets that are quite regularly arranged and densely spaced (S = 4–9, very rarely 3; Smean = 4.3–7) and of nearly rectangular shape.
The equatorial section of B-forms (Fig. 7AD): The single specimen from sample Kisgyr, Remete-kút 3, exhibits a microsphere of 15 µm in diameter. It is followed by about 14 undivided (operculinid) chambers before the appearance of the first subdivided chamber after which undivided chambers can rarely reappear. The arrangement and shape of chamberlets in the adult stage do not differ from those of the A-forms.
Axial section (Fig. 7W, Y): Relying also on Boussac's (1906: pl. 3: 19) and Roveda's (1961: pl. 17: 1–3; pl. 19: 12, 13) figures and descriptions, the test is slightly inflated, involute and biconvex. Lateral chamberlets are well developed, piles are well visible.
Remarks.—Uhlig (1886: text-fig. 10) provided two good figures of the equatorial section of A-forms when introducing the name “carpatica” for specimens from Woła Łużańska (Poland). In both sections the number of post-embryonic undivided chambers (parameter X) is 2 and in the upper figure the number of chamberlets in chamber 14 (parameter S) is 7. These parameters correspond well to our material, therefore the name Spiroclypeus carpaticus can be applied to them. Based on Roveda's (1961), Schiavinotto's (1986) and our data and the figures of Boussac's (1906) S. granulosus from Priabona we conclude that Uhlig's (1886) S. carpatica is synonymous but has priority making S. granulosus invalid. Moreover, the name “granulosus” was confusingly used previously for Heterostegina gracilis (see Less et al. 2008).
The figures of Boussac (1906), Roveda (1961), Hottinger (1977) and Schiavinotto (1986) cited in the synonymy illustrate specimens from the very close vicinity of our sample from Priabona, while Hottinger's (1964) form from Benidorm and Less' (1999) specimens from Kisgyr come from the same samples which we have studied.
The distinction between S. sirottii and S. carpaticus is discussed under the description of the former. According to the figures of Western Tethyan upper Oligocene and lowermost Miocene Spiroclypeus by Henson (1937), Cahuzac and Poignant (1997), and also based on our unpublished data, it seems that they differ from S. carpaticus in having a much looser spire, and a larger proloculus (compare them also in Figs. 7 and 8). Since no Spiroclypeus have been found in the Western Tethyan lower Oligocene and also because the above differences between S. carpaticus and the upper Oligocene and lowermost Miocene forms do not allow to directly link them phylogenetically, we suppose that S. carpaticus became extinct with no successors at the very end of the Priabonian.
Geographic and stratigraphic distribution.—Late Priabonian (SBZ 20) of the Polish (Wola Łużańska, Bukowiec) and Slovakian (Raslavice) Carpathians, of N Italy (Priabona, blue claystone; Possagno, Calcare di Santa Giustina, samples Possagno 1 and 2), NE Hungary (Kisgyr, sample Remetekút 3), SE Spain (Benidorm).
Spiroclypeus aff. carpaticus (Uhlig, 1886)
The few specimens found in the sample from Biarritz, Lou Cachaou have intermediate numerical characteristics between those of Spiroclypeus sirottii and S. carpaticus (see Table 1 and Figs. 4–6). Because of the scarcity of the material the axial section could not be investigated. Based on the associated Heterostegina gracilis marking the late Priabonian and according to the average number of undivided chambers (Xmean = 2.38) that is closer to the value defining S. carpaticus than to that of S. sirottii, the population from Biarritz is determined as S. aff. carpaticus, taking into account also the relatively small size of the proloculus.
Correlation with other fossil groups.—In Table 3 we summarize the age data based on the various fossil groups and discuss them in detail under the description of the various localities.
The boundary between the P 15 and 16 Planktic Foraminiferal Zones falls within the range of Spiroclypeus sirottii. The P16 Zone extends into the range of S. carpaticus. The P 16/17 boundary cannot be detected in our material.
The basal beds of the Priabona marl in Mossano (samples 5 and 6) with S. sirottii belong to the NP 18 Calcareous Nannoplankton Zone, however, the range of the species extends into the NP 19–20 Zone. S. carpaticus can also be found in this latter zone as well as in NP 21, marking the very top of the whole Eocene, since according to Berggren et al. (1995) the Eocene/ Oligocene boundary is located within this latter zone.
The representatives of the Nummulites fabianii-group were found only in very few samples. Typical Nummulites fabianii occurs with both Eocene spiroclypeid species whilst the flatter form (= N. “retiatus”) was found only with S. carpaticus. Based on Serra-Kiel et al. (1998) N. fabianii marks the SBZ 19 Shallow Benthic Zone while N. retiatus indicates SBZ 20. Meanwhile Herb and Hekel (1973), Barbin (1988) and Trevisani and Papazzoni (1996) record N. fabianii with and sometimes above N. retiatus suggesting that their occurrence in upper Priabonian beds may be partly controlled by ecological factors. According to our recent studies (Less et al. 2006, unpublished data), typical N. fabianii occurs from the base of the Priabonian into the lower Oligocene. Meanwhile the flatter N. fabianii (formerly N. retiatus), having adapted to somewhat deeper marine environments, only occurs in the upper part of the Priabonian together with S. carpaticus as in the vicinity of Kisgyr, Remete-kút (Less 1999; Less et al. 2000).
Our two spiroclypeid species can be correlated with the revised Eocene involute heterosteginid taxa (Less et al. 2008). Spiroclypeus sirottii from samples Mossano 5+6, Verona— Castel San Felice, Úrhida 10 and Şarköy 4 occurs with Heterostegina reticulata mossanensis marking the basal Priabonian (SBZ 19 A) and with H. reticulata italica (SBZ 19 B-20) in the more upper part of the Mossano profile (sample Mossano 8). Spiroclypeus carpaticus associates with H. gracilis indicating SBZ 20, in Possagno also with the simultaneously existing H. reticulata italica.
Spiroclypeus sirottii is found with orthophragmines of middle Eocene acme (Discocyclina pratti, Nemkovella strophiolata, Asterocyclina alticostata, and A. kecskemetii) whose last occurrence indicates the OZ 14 Orthophragminid Zone. The level of sample Mossano 8, where only rare A. alticostata was found, is placed at the limit of OZ 14/15. Spiroclypeus carpaticus does not associate with the above listed forms of middle Eocene acme, the orthophragminid fauna in the Priabona sample indicates OZ 15 while in Kisgyr OZ 16 (the highest orthophragminid zone) is recorded.
Assemblages of different fossil groups co-occurring with Spiroclypeus from particular localities that are ranged among shallow benthic subdivisions. Abbreviations: aff. c., aff. carpaticus; ↓ below; ? very rare occurrence.
Chronostratigraphic correlation.—The placement of the middle/late Eocene (= Bartonian/ Priabonian) boundary is discussed in detail in Less et al. (2008). The base of the Priabona marls in the Mossano section is suggested to be the most suitable level for fixing this boundary. In this case the base of the Priabonian coincides with the first occurrence of three quite widespread larger Foraminifera: Nummulites fabianii, Heterostegina reticulata mossanensis, and Spiroclypeus sirottii, the latter also being the first representative of the genus itself, since it has not been found with the less advanced members of the H. reticulata lineage from the latest Bartonian (Less et al. 2008). The co-occurrence of Spiroclypeus with large-sized Nummulites (with test diameter of the B-forms exceeding 15 mm, belonging to the N. perforatus—biedai-, N. millecaput—maximus-, and N. gizehensis—lyelli-groups) having become extinct at the very end of the middle Eocene is unknown as well. However, the co-occurrence of S. sirottii with H. reticulata mossanensis in four different localities from three quite remote areas (North Italy: Mossano and Verona; Hungary: Úrhida; NW Turkey: Şarköy) suggests that the first appearance of the genus Spiroclypeus was synchronous.
Bibliographic data on the presence of Spiroclypeus in the late middle Eocene can be disproved as follows: (i) The case of Schweighauser (1953) is discussed in the description of the Mossano locality in Less et al. (2008). (ii) Racey (1995: 81) indicates Spiroclypeus from one sample of the “Auversian” of Oman based on the presence of Silvestriella tetrahedra, Fabiania cassis, Borelis vonderschmitti, and Calcarina and on the absence of Nummulites fabianii. In our opinion, this accompanying assemblage may indicate both the late Bartonian and the Priabonian. (iii) Finally, Mohiuddin (2004) mentions Spiroclypeus vermicularis from the upper middle Eocene of Bangladesh that is in our opinion an erroneous determination according to his fig. 4B, which illustrates rather a Nummulites.
It is clear from Table 3 that the fossil assemblages associating with S. sirottii indicate the lower part of the Priabonian whereas those co-occurring with S. carpaticus indicate its upper part. Therefore, S. sirottii may be used as a zonal marker for the SBZ 19 Zone (early Priabonian) while S. carpaticus defines SBZ 20 (for details see also Table 8 in Less et al. 2008).
The further evolution of the genus in the early Oligocene is not recorded in the Western Tethys. Based on this and on the reasons discussed at the end of the chapter “Remarks” to the description of S. carpaticus, we can reasonably suppose that the S. sirottii—carpaticus lineage is restricted to the Priabonian.
In almost all the investigated localities (with the exception of Benidorm from where we have no information), orthophragmines have been found in great quantity. They mark outer shelf conditions (Papazzoni 1994), thus we can reasonably suppose that Spiroclypeus are characteristic also for this environment, indicating a narrower paleoecological niche as compared to Heterostegina (Less et al. 2008). Nevertheless, their distribution from Spain to at least Oman (Racey 1995) provides potential for using Spiroclypeus in Western Tethyan stratigraphical correlation.
Based on the morphometrical study (especially on the statistical evaluation of the equatorial section of A-forms) of Spiroclypeus from ten European localities (extending from Spain to Turkey and covering the whole Priabonian) and also on the critical evaluation of bibliographic data we conclude that:
(i) Based on the reduction of the average number of undivided, post-embryonic chambers (parameter X), populations can be grouped into two successive, phylogenetically linked species, Spiroclypeus sirottii sp. nov. and Spiroclypeus carpaticus (Uhlig, 1886). Xmean above 2.7 is diagnostic for the populations of the first species, whilst Xmean below 2.7 for those of the second one.
(ii) The evolution is also proven by the increase of the number of chamberlets in particular chambers (parameter S), by the increase of the diameter of the first two whorls (parameter D) and by that of the size of the proloculus (parameter P), although the latter turned out to be also ecologically controlled. Meanwhile the spire becomes only slightly looser (although this change—characterized by parameter K—is very uncertain) and the size of the test does not really increase in time. The morphological changes of the lateral chamberlets are to be studied further.
(iii) The evolution is supported by the stratigraphical succession of populations in the Mossano section (N Italy) and also by the change of the accompanying planktic foraminifera, the calcareous nannoplankton, the nummulitids (Nummulites fabianii-group and Heterostegina) and the orthophragmines.
(iv) Lacking in upper Bartonian beds, the first appearance of the genus Spiroclypeus in the Western Tethys seems to be synchronous with the beginning of the late Eocene.
(v) Based on the absence of the genus Spiroclypeus in the Western Tethyan lower Oligocene and on the significant morphological differences between the upper Eocene and upper Oligocene to lowermost Miocene forms, we suppose that the Spiroclypeus sirottii—carpaticus lineage is restricted to the Priabonian.
(vi) The newly described Spiroclypeus sirottii sp. nov. is associated with Heterostegina reticulata mossanensis and with orthophragmines containing still forms of middle Eocene acme, both marking the lower part of the Priabonian, thus it is a zonal marker for the SBZ 19 Zone.
(vii) Because Spiroclypeus carpaticus (Uhlig, 1886) co-occurs with Heterostegina gracilis but with no orthophragmines of middle Eocene acme (both phenomena characteristic for the upper part of the Priabonian), it characterizes the SBZ 20 Zone.
This work was completed under I.G.C.P. project n° 393 which also financed some of GL' travels. The final phase of the work was financed for GL by the National Scientific Fund of Hungary (OTKA, grants n° T 032370, 037619, 042799, and 060645), for EÖ by TÜBİTAK (project n° YDABAG-101Y060). We are grateful to the late Achille Sirottii and Cesare A. Papazzoni (University of Modena, Italy) for guiding through the Italian localities in 1990 and to Lukas Hottinger (Natural History Museum of Basel, Switzerland) for discussions, for the critical remarks including terminological and linguistic improvements and for providing material from Benidorm and Biarritz. The critical remarks of Pamela Hallock (University of South Florida, St. Petersburg, USA, special thanks also for the linguistic improvements) and of Simon Beavington-Penney (University of Cardiff, Great Britain) are highly appreciated.