The First 40 Million Years of Planktonic Foraminifera

: We provide a biochronology of Jurassic planktonic foramininfera, using ﬁrst order linkage to ammonite and nannofossil stratigraphy and geochronology. This enigmatic and understudied group of microfossils occurred from middle Toarcian through Tithonian time, from ~180 to ~143 Ma; its origin is unknown. There are three genera: Globuligerina , Conoglobigerina and Petaloglobigerina . The genus Globuligerina, with a smooth to pustulose test surface texture appeared in Toarcian (late Early Jurassic) and Conoglobigerina, with a rough reticulate test surface texture in Oxfordian (early Late Jurassic) time. The genus Petaloglobigerina , having a petaloid last whorl with one or more claviform and twisted chambers evolved in early Kimmeridgian time from Globuligerina balakhmatovae . Biochronologic events for Jurassic planktonic foraminifera are most like First Common Appearance or Last Common Appearance events. The very ﬁrst or very last appearance levels of taxa are not easily sampled and detected. We recognize stratigraphic events from eleven species across four postulated evolutionary lineages, calibrated to Geologic Time Scale 2020. A faunal change, which is not well documented led to the survival of only one taxon, most likely Gobuligerina oxfordiana in the Tithonian.


Introduction
We provide a tentative biochronology of Jurassic planktonic foramininfera, using their taxonomy, stratigraphy, paleoecology and paleogeography with first order linkage to ammonite and nannofossil stratigraphy and geochronology. The study uses biochronostratigraphic information summarized in the section called 'Stratigraphic Inventory' on this enigmatic and understudied group of microorganisms. For one, studies on the earliest (Toarcian) record in this group are wanting, and there is no information on evolutionary transition in Tithonian time to Cretaceous planktonic foraminifera.
The summary below takes from our recent studies [1,2]. For details, including the formal taxonomy, the interested reader is referred to the monograph on this group of microfossils in [1,3]. The formal taxonomy also is provided in the Mikrotax internet site at http://www.mikrotax.org. The Jurassic planktonic foraminifera were microperforate and probably all aragonitic in test composition, in equilibrium with Jurassic high-magnesium calcite seawater. The aragonitic test limits fossilization and may partially account for the scattered stratigraphic and paleogeographic distribution. We have not found evidence for dimorphism and asume reproduction was sexual as in recent planktonic foraminifera. The group occurred from middle Toarcian through Tithonian time, from~180 to~143 Ma; its origin is unknown. The earliest record is from one locality in Turkey only, suggestive of the isolated population concept in evolution. The literature record since 1881 counts fewer than 100 publications [4].
Coiling mode, chamber configuration in the last whorl, test surface features and intraspecific variation in aperture shape are key taxonomic features; it precludes use of

Principles of Biochronology
Biostratigraphic correlation is not necessarily time correlation. It may approximate time-correlation, or it may be the identification of the same biofacies and potentially be diachronous, because comparable fossil record in samples some distance apart, does not imply synchronicity of deposition.
The above conservative statement comes from the International Stratigraphic Guide [6]. The Guide recognizes (and sparsely defines) units and principles of biostratigraphy, but does not recognize and define biochronology. The most likely reason is that the latter is a predictive interpretation, and not an observation and description of fossil correlation. In its formal stratigraphic presentation the Guide has no place for biochronology, since the latter resolutely bypasses zones, stages and chronostratigraphy on its way to geochronology.
Biochronology avoids the classical concept of zones (and stages), in favour of 'the organisation of geologic time according to the irreversible process of evolution in the organic continuum' [7]. The authors lament that the essential desire to extend correlation in time, mistakenly is an activity in stratigraphy, whereas it properly is an exercise in geochronology: "Biochronology attempts to rank, order and scale fossil events and fossil ranges in linear time, and scale regional stratigraphies with isochrons".
Despite not being honoured by the International Stratigraphic Guide, biochronology is really what a great many paleontologists and stratigraphers are after. Many studies aim to generate an optimum network of fossil correlations, thought to embody a reliable and high-resolution isochronous time (lines) framework. Linking such a network with magnetochrons, stable and unstable isotope determinations, and cyclothems, albeit in danger of inviting circular reasoning, creates a geochronologic correlation framework.

Paleontologic Events
The key to biochronology and its building blocks are fossil events. A fossil or paleontological event is the presence of a taxon in its time context, derived from its position in a rock sequence. Most commonly used are First Appearance and Last Appearance Datum's (FAD and LAD). Since the first or last appearance datums may be difficult to recognize or distinguish where specimen numbers dwindle or get obscured by 'noise' (like reworking of fossil tests), it can be advantageous to substitute with first and last consistent (or common) appearances. A first or last appearance datum is consistent when such stratigraphic range endpoints are part of an observed continuous stratigraphic range ( First consisten Occurrence (FCO) Figure 1. Terminology of biostratigraphic events along the total stratigraphic range of a single taxon. The first and last consistent occurrence may coincide with the first and last common occurrence; the rapid increase and rapid decrease encapsulate the acme of the taxon. Instead of First or Last Occurrence, First or Last Appearance is frequently used. The former is a chronostratigraphic term, and the latter a geochronologic one.
If the fossil record encountered in stratigraphic sections that we want to correlate and calibrate in time would be ubiquitous and perfect, i.e., if only time would control the appearance, range and disappearance of taxa, then biostratigraphy would be a straightforward exercise. The science of biochronology, as developed for the evolutionary first and last occurrence datums of ocean plankton, in conjunction with geomagnetic reversals in Deep Sea Drilling Sites, would be a matter of systematic book keeping on a worldwide scale, only constrained by taxonomic deliberations. Unfortunately, the paleontological record is highly imperfect, and its noise may call for more intricate, or even murky biostratigraphic decision making (for example when absence of occurrence is an argument) that detracts from the validity of a potential biochronologic framework.
Factors bearing on the quality of the fossil record are in Figure 2. Together, these uncertainty factors are as follows: (1) Quality and quantity of sampling (2) Specimen frequency of fossil taxa (3) Confidence of taxonomic identification (4) Influence of environmental change on the stratigraphic range of taxa (5) Differential rate of taxon evolution in different parts of the world (6) Time lag in migration of taxa, where correlation is over large distances, or across major environmental barriers. A more extensive description of these factors is in Gradstein et al. (1985). If significant diachroneity is observed for bioevents, e.g., by plotting them against magnetochrons or time calibrated stable isotope spikes in two or more sections, than a numerical method or graphic illustration should be devised to quantify the error bar on bioevent correlations. As a matter of routine latitudinal or environmental shifts in event calibrations should be taken into account.
An important lesson from these factors bearing on the quality of the fossil record is that biochronologic events for Jurassic planktonic foraminifera are most like First Common Appearance or Last Common Appearance events, or even the acme. The very first or very last appearance levels are not easily sampled sampled and detected.

Material and Methods
The Polish, Dagestan and Portuguese outcrop sections and offshore eastern Canada well sections were described with great stratigraphic detail and with complete geographic notations in [1].
In addition to standard Leica (M205C with PLANAPO 1.0× and 1.6× objectives and Nikon stereo microscopes, good use was made for wall surface texture determination of the Leica DM 750M biological microscope with polarizer/analyser and Epi 10×/0.25 and N Plan L 20×/0.35 and Plan L50×/0.50 objectives. Both objectives have long distances between objective and specimen and allow optimum incident light illumination. Digital optical images were acquired efficiently with a Deltapix M12ZS digital microscope with 1.25, 2.5 and 4.16 objectives and Insight stacking software. SEM images were obtained with a QUANTA 200 FEG scanning microscope at the Laboratory of Phase, Structural, Textural and Geochemical Analyses of the Faculty Geology, Geophysics and Environmental Protection at AGH (Krakow, Poland).

Stratigraphic Inventory
Below we describe in stratigraphic order, from Toarcian through Berriasian-early Valanginian our sample material with planktonic foraminifera as free tests from washed sample residues. The listing of these 25 localities worldwide also includes critical literature references with planktonic assemblages from which we do not have specimens or sample material (indicated with a small x). Figure 3, in an approximate manner shows the majority of localities from which Jurassic planktonic foraminifera are known [3] including the key ones on which the current analysis is based. The zonal and age assignments, as derived from ammonite or nannofossil zonations follow the chronostratigraphic subdivisions of the Jurassic and earliest Cretaceous stages in [8][9][10]. Note that the early, middle and late subdivision of stages is not formalized and open to change. Zones and age: Humphriesianum and Niortense Zones, middle Bajocian. Assemblage: The planktonic assemblage is diverse and dominated by large specimens, often reaching 400 µm in diameter, including Globuligerina aff. dagestanica, Globuligerina oxfordiana (medium and large forms), Globuligerina aff. bathoniana (large form), and Globuligerina avariformis.
Reference: Wernli and Görög (1999) [14]. Middle Bajocian, France (x) Study and locality: Find of Jurassic planktonic foraminifera in the type section of the Bajocian Stage, France.
Zone: Humphriesianum Zone, middle Bajocian. Assemblage: Poorly preserved Globuligerina oxfordiana in a biomicrite with ferriginous oolites, attesting to the shallow marine nature of the sediment.

Late Bajocian, Azerbijan (x)
In 1984 Kasimova and Aliyeva [16] briefly described Conoglobigerina avariformis Kasimova from the Bajocian of Azerbaijan. The holotype drawings provide no wall sculpture information, but a metatype specimen illustrated in [17]  Through the courtesy and cooperation of Temirbekova Umuhayabat Temirbekovna (Makhachkala, Dagestan, Russia) we obtained Jurassic planktonic specimens from the type sections near Gunib and Chokh in Central Dagestan. This allowed us to study topotype specimens. Through the courtesy of Ludmila Kopaevich we also obtained micropaleontology slides with planktonic foraminifera of the Gunib and Chokh sections from the Gorbachik collection in Moscow.
References: Morozova and Moskalenko (1961) [18];   [1]. Late Bajocian-Early Bathonian, Dagestan (Russia) Study and locality: Co-author L.G. participated in 2015 in a field trip to a nearby and stratigraphically identical section (42 • 9 23 N, 47 • 7 60 E) to Gunib and Chokh. This means that the Jurassic planktonic foraminifera in it are essentially topotypes of those described first by Morozova and Moskalenko [18]. The stratigraphic levels in this new section XУPУKPA (Khouroukra) were studied and sampled together with specialists in ammonite and belemnites. The studied part of the Khouroukra section includes the lower and middle subformation of the Tsudakhar Formation.
The lower subformation shows interbedded light gray siltstones and sandstones. The middle subformation consists of a dark gray claystones, with interbeds of siltstones, rare sandstones, with siderite concretions. There are rare and thin (0.10-0.15 m) interbeds of calcareous rocks.

Middle Bathonian, Portugal
Rare specimens of Globuligerina bathoniana occur in the shallow marine sedimens of middle Bathonian age in the Brenha Road section, Mondego area, Portugal [20].
Middle Bathonian, Poland Study and locality: In 1969, Pazdrowa published 'Bathonian Globigerina from Poland' [21]. The taxon Globigerina bathoniana was described with about 150 well-preserved specimens from the ore-bearing clays of Ogrodzieniec, Zawiercie County, Southern Poland at 50 • 27 N and 19 • 31 E. Author F.G. received from Pazdrowa a foraminiferal assemblage from Ogrodzieniec, including the globigerinid taxon. Later, he undertook self micropaleontological sampling of the strata in the Ogrodzieniec claypit; these samples were used in the Ph.D. study by Stam [20]. Now, the Ogrodzieniec quarry has been partly filled in and made inaccessible (but see below).
References: Pazdrowa (1969) [21]; Stam (1986) [20]; Gradstein et al. (2017) [1]. Middle Bathonian, Poland Study and locality: After the Ogrodzienie quarry became non-existent (see above), co-author AW undertook fieldwork and sampling of the same Morissi ammonite Zone in the Gnaszyn iron ore quarry in the southern part of Kraków-Silesia. The Gnaszyn (Gnaszyńscy) quarry (coordinates: 50 • 48 11.4 N, 19 • 02 31.9 E) is located in the S.W. Częstochowa city area of the Gnaszyn district. The 25 m thick section of dark shales represents the higher part of the Częstochowa ore-bearing clay formation being locally 140 m thick. The monotonous, strongly bioturbated black or dark greyish siltstones and claystones are rich in bioclasts, occasionally with different amount of sandy admixture. It contains seven levels of sphaerosideritic concentrations (N-T horizons).
The Jurassic planktonic foraminifera bearing GN-6 sample was taken in the lower part of the Gnaszyn section. This is a grey and slightly sandy claystone with numerous bioclasts, mainly of mollusks shells. The sample is rich in very well preserved, aragonitic planktonic foraminifera with Globuligerina oxfordiana and fewer Globuligerina bathoniana, Globuligerina glinskhikae and Globuligerina waskowskae.
Middle Callovian, Portugal Study and locality: Along the Mareta Beach section in southern Portugal, thick and well bedded calcareous shales crop out, locally with thin sand layers with ripple marks, load and flute casts, and upwards in the beach section with more marls and limestones. The shales and marls have common Bositria.
Zone and Age: Bordalo da Rocha (1976) [24] assigned a late Bajocian through Callovian age to the lithological unit, using a detailed ammonite zonation.
Middle Oxfordian, Switzerland Study: In April 2016, author Gradstein visited the Natural History Museum in Basel, Switzerland to study type slides listed to contain Globigerina helvetojurassica Haeusler, and also sample the nearby Eisengraben Section to obtain fresh microfossil material containing this species. The museum type slides did not contain suitably preserved specimens of this taxon, and are unrecognizable, but topotypes of this taxon were successfully sampled, under the expert guidance of Etter and Knappertsbusch.
Zone-stage: Transversarium Zone, middle Oxfordian. Microfossil assemblage: Directly below level 4 in the Eisengraben Section, samples with common and well-preserved specimens were obtained that we consider to be topotypes of Conoglobigerina helvetojurassica (Haeusler). Also, rare specimens were obtained of small sized Globuligerina bathoniana and G.oxfordiana. Level 4 top has many agglutinated taxa, but hardly any planktonic specimens. Sample 4 mid, at the level of Stam's sample with 'helvetojurassica' has best preserved specimens, and also includes well-preserved benthics belonging in Bigenerina, Textularia, Ophthalmidium, Ammodiscus, Glomospira, Trochammina, Haplophragmoides, Dentalina, Nodosaria, Lenticulina plus some indeterminate taxa. Micro gastropods also occur. Small limonitic concretions are common; small glauconite lumps also occur, testifying to a likely neritic mode of deposition. There are no epistominid benthic taxa.  Micropaleontology slides of Oesterle (1968) [27] in the Basel Museum from the Birmenstorfer type section contain 50+ of many more (often broken) specimens which we studied that show the same test moulds of crystallized carbonate fragments. The peculiar preservation is the result of a rigorous processing technique (likely a form of acetolysis). At least five morphotypes may be distinguished, which, despite poor preservation, can easily be assigned to the species Globuligerina aff. oxfordiana, Globuligerina aff. bathoniana, Globuligerina aff. jurassica (with an elongated, high spired and irregularly trochospiral test), Globuligerina aff. balakhmatovae, Globuligerina aff. tojeiraensis (with slightly elongated last chamber) and Conoglobigerina aff. grigelisi. However, the latter might be Globuligerina aff. avariformis, since we cannot determine wall texture. For sampling details and plates with SEM illustrations of all planktonic taxa, including the topotypes of Conoglobigerina helvetojurassica see [28].
References Oesterle (1968)  In Central Russia, well preserved specimens of this taxon (as assigned by Grigelis) also occur in sample 801 in the Shatriche-2 outcrop at the Nikitino settlement on the river Oka, Ryazan District. The actual outcrop is on high right bank of River Oka, ca 2.5 km below the confluence with River Pronya, at outskirt of village Shatriche, in a river washout called "Durnyanki". The sampled sediments are assigned to the middle to late Oxfordian, but no specific fossil information is provided. Type specimens of this species provided by A.Grigelis on Plate 12 in [1].
References: Grigelis (1958)  References: Birkenmajer (1977Birkenmajer ( , 1986 [30,31] [37]. Middle Kimmeridgian, Portugal Study and locality: In 1978, as part of the extensive Tojeira Formation sampling (see above), Rogerio Bordalo da Rocha (Lisbon) kindly guided author F.G. and students to two dark shales outcrops, one along the road just outside Villa Verde dos Francos and another one outside Pereiro, both in the Montejunto area. The fossiliferous shales with ammonites and Bositria are of the Abadia Formation, that overly the Tojeira Formation and underly thick-bedded conglomeratic sands. In the Montejunto area, the Abadia Formation, with shales, sands, conglomerates and olistolithic limestone blocks reach a thickness of over 1 km.
Zone and age: Middle Kimmeridgian, according ammonite studies of the Portugese Geological Survey.
Micropaleontologic assemblage: Our samples 4/1 and 25/1 have large size benthic foraminifera with Epistomina stellicostata, E.volgensis and E.uhligi. The first two taxa do not occur in the underlying Tojeira Formation, and have their first, regional stratigraphic occurrence in these two samples. In correlation with eastern Canada, this benthic foraminiferal assemblage is Kimmeridgian-Tithonian in age.
Planktonic foraminifera include Globuligerina bathoniana (abundant), common Globuligerina oxfordiana, rare Globuligerina tojeiraensis, rare Petaloglobigerina simmonsi and rare Conoglobigerina grigelisi. No Conoglobigerina helvetojurassica was observed, a species common in the upper part of the underlying Tojeira Formation. Some Globuligerina oxfordiana specimens have a reticulate wall texture, a feature taken up in the section on Evolution.
References: Ascoli et al. (1984) [38]; Stam (1986) [20]; Williamson and Stam (1988) [39]. Tithonian, Hungary (x) Study: Co-author A.W. and colleagues in 2019 visited the Paprét-árok profile in the Gerecse mountains of Hungary. This locality is described with outcrop details and a Tithonian planktonic foraminiferal assemblage in [40]. It turns out the locality does not exist, and its publication and description are based solely on archival data. The locality originally was a railway cut.

Lithology and Zone-Age:
In the Paprét-árok profile the succession begins with red radiolarite (Lókút Radiolarite Formation) of Middle Jurassic-Kimmeridgian age. It is followed upwards with a massive and hard bank about 75 cm in thickness, grey, pink and purple in colour. This massive bank is subdivided in five beds numbered 6 to 2, from the base to the top: Beds 6-7 belong to the Beckeri and the Hybonotum Zones, Bed 5 questionably to the Darwini Zone and Bed 4 questionably to the Fallauxi Zone, all considered early Tithonian in age. Limestone Beds 3 and 2 are not zoned, but considered as probably late Tithonian in age. Above this massive limestone bank occur grey marl and breccia layers, belonging to the Lower Cretaceous Bersek Marl Formation.
Microfossil assemblage: 'Protoglobigerinids' are described from bed 5? Darwini Zone using thin sections and free specimens obtained with weak acetic acid. The authors consider the planktonic foraminiferal assemblage to be monospecific, with a species transitional between Globuligerina oxfordiana and Favusella hoterivica, but no pore features and wall texture can be determined, making the interpretation tentative. Stratigraphically higher-up, it states that the same section might yield Berriasian planktonic foraminifera, but none are listed.

Tithonian-Valanginian, North Africa
Other localities: There is a meagre record of unspecified planktonic foraminifera in thin sections from Tethyan limestones of Tithonian through Valanginian age in N. Africa and Central Europe [40].
Early Berriasian, Crimea Study: For our study of Mesozoic planktonic foraminifera, Ludmila Kopaevich (Moscow) obtained samples from the Tonas River Basin in E. Crimea, Russia. The hard marly sediment interval is assigned to the Jacobi ammonite Zone, early Berriasian, not far above the Jurassic-Cretaceous boundary. The Tonas River Basin is a locality from which Gorbachik and Poroshina [41]  Sample Cr1 contains about 100 specimens of planktonic foraminifera taxa, all microperforate, including with frequent specimens Favusella hoterivica, with common specimens Clavihedbergella eocretacea and Conoglobigerina gulekhensis and with less than 10 specimens each of the taxa Hedbergella aff. similis, ?Favusella sp., Hedbergella aff. handousi and ? Globuligerina sp.
Only Conoglobigerina gulekhensis was previously known from Berriasian strata, and this only from two regions, Crimea and Azerbaijan. Favusella hoterivica (Subbotina) with certainty only is known from Valanginian through Aptian marine strata, and the other taxa only from Valanginian, Hauterivian or even younger stratigraphic intervals. All taxa are of Tethyan or sub-Tethyan origin.
Note: As outlined in some detail in the geological history study by Nikishin et al. (2017) [42], the Crimea region underwent late Berriasian vertical movements, leading to a regional unconformity with erosion and karstification of underlying strata. The Krasnoselivka section preserves non-karstified Berriasian limestones, subject of our study.
References Zone, stage: Using dinoflagellates and benthic foraminifera, the studied interval is assigned a Berrisian-early Valanginian age.
Microfossil assemblage: In total about 50 specimens of Favusella hoterivica were obtained, many pyritized and with good wall texture details. Some questionable Conoglobuligerina aff. gulekhensis were found, but preservation is insufficient to provide reliable identification. Benthic foraminifera include Lenticulina busnardoi, Epistomina minireticulata, E.stellicostata, Neobulimina sp, Discorbis aff. valdendisensis, Discorbis sp., agglutinated indet. Micro gastropods are common to abundant, as they are in the Kimmeridgian Tojeira Formation in Portugal.
Globuligerina, with a smooth to pustulose test surface texture appeared in Toarcian (late Early Jurassic) time, and Conoglobigerina, with a rough reticulate test surface texture in Oxfordian (early Late Jurassic) time. Petaloglobigerina, with a petaloid last whorl and one or more twisted and claviform chambers evolved in early Kimmeridgian time from Globuligerina balakhmatovae. Table 1 list the oldest age level of formally described Jurassic planktonic foraminifera species, and Figure 4 depicts the FAD of genera and species in a simple stratigraphic column, calibrated to ammonite and nannofossil stratigraphy, as outlined below. The biochronology uses the GTS2020 geochronologic scale. Event age uncertainty beyond the duration of the ammonite zone(s) in which FAD's were determined is not touched upon on in this study.From older to younger the FAD's in Ma of the genera are: The study of Wernli [11] on thin sections from Toarcian limestone samples in the Domuz Dag mountain chain of SE Turkey provided by. Poisson (Paris) from his thesis [49] documents the oldest known occurrence of planktonic foraminifera. Curiously, this is the only record in the whole world of this oldest known assemblage. Hence, planktonic foraminifera appeared in the Toarcian around 180 Ma ago. The youngest Jurassic occur-rence of this group is documented by Görög and Wernli [40] describing a single taxon of planktonic foraminifera (extracted with acetic acid) in Tithonian age samples from Hungary. Hence, Jurassic planktonic foraminifera range from Late Toarcian (Bifrons-Variabilis ammonite Zones) through Late Tithonian (C. alpina calpionellid Zone).
Unfortunately, the Toarcian through Aalenian record is only known from thin-sections, but we consider that an often larger and higher spired form similar to Gobuligerina bathoniana and a smaller, lower spired form similar to Globuligerina oxfordiana occur in these thin-sections. This needs better documentation with well-preserved free specimens. Test size difference in itself may not be a taxonomic feature, and often has more to do with growth conditions in optimal or sub-optimal environments, selective sediment sorting, water masses and vertical biota distribution, and other hard to evaluate factors in fossil material.
The LAD's of these taxa is not known, but all Jurassic species have disappeared before Cretaceous (143 Ma).
From the stratigraphic record outlined in the 'Stratigraphic inventory' chapter it is clear that Globuligerina oxfordiana, Globuligerina bathoniana and Globuligerina balakhmatovae have a long stratigraphic range, spanning several stages for 20 myr or more. Conoglobigerina helvetojurassica has a much shorter stratigraphic range, spanning two stages for 10 myr or more. The single observation that the regionally restricted Conoglobigerina grigelisi appears in Callovian -Oxfordian strata on the Grand Banks means its common presence in the Kimmeridgian of Portugal is not an FAD event. The regionally restricted species Globuligerina dagestanica, Globuligerina glinskikhae, Globuligerina avariformis and Globuligerina waskowskae may have been stratigraphically short-lived. A special case is Globuligerina tojeiraensis, first described by us from the Kimmeridgian of central Portugal. Here it is consistently present in long series of consecutive samples, with a stable and unique test morphology and with frequent specimens. Comparable tests occur with few specimens in Middle Jurassic samples from Dagestan and Poland, hence Globuligerina tojeiraensis might have appeared earlier than shown here (cf. Gradstein, 2017 [28]).

Tentative Evolutionary Lineages
As outlined in Figure 5 (which updates Figure 3G.1 in [50]) we postulate that within the Jurassic and earliest Cretaceous four lineages of planktonic foraminifera occur, which for graphic clarity are shown with green, brown, blue and red stratigraphic lines. We stress that these lineages are hypothetical and need more stratigraphic data. Two taxa, Petaloglobigerina simmonsi and Globuligerina oxfordiana are postulated to be ancestral to Cretaceous taxa as indicated in Figure 5 and discussed in some detail in [31]. This study of the planktonic foraminifera of the lower Berriasian in Crimea also determined Conoglobuligerina gulekhensis and Hedbergella aff. similis, for both of which no potential Jurassic ancestral link is established.
The 'green group' is monotypic and consists of Globuligerina balakhmatovae evolving during Kimmeridgian time in Petaloglobigerina simmonsi.
The ancestry of Globuligerina balakhmatovae is not clear. A possible morphological transition exists to Oberhauserella aff. parocula described by Wernli and Görög [51] from SE France, but this requires refinement of our knowledge on the stratigraphic appearance and test morphology of both taxa. A detailed study of wall textures should be undertaken. An issue is that the holotype of Globuligerina balakhmatovae falls outside the common Globuligerina balakhmatovae morphology as we observe it in our rich topotype material from Dagestan; the holotype test is more inflated and chambers are not petaloide or ovate.
There is no stratigraphic record of the low-spired, and often claviform chambered Petaloglobigerina simmonsi in post (early) Kimmeridgian strata. Based on a general similarity in test morphology, Gradstein et al. [44] proposed that this taxon might have evolved in Clavihedbergella eocretacea in early Berriasian time.
The 'brown group' includes Globuligerina dagestanica (Morozova) and the common species Globuligerina bathoniana, all higher spired trochoid morphotypes with an arch to looped aperture and commonly a bulla. Essentially, we can distinguish one taxon with a more symmetrical and regular trochospire with four chambers in the last whorl (bathoniana type), and another taxon with more irregular (or sometimes triangular) trochospire with 3, 3-4 or 4 chambers in the last whorl (dagestanica type). In our opinion, Globuligerina jurassica (Hofman) might be a local and often aberrant variant of Globuligerina dagestanica.
The 'blue group' consists of Globuligerina avariformis (Kasimova) and Conoglobigerina grigelisi (Gradstein), both of which do not have a geographically widespread record. The two species typically have a last whorl that strongly embraces earlier ones, such that the test almost appears involute. A possible evolutionary line age is postulated from the compact Globuligerina avariformis into the equally, or even more compact Conoglobigerina grigelisi. The latter acquires a reticulate wall sculpture. Its youngest record is middle Kimmeridgian. One issue, common to other Jurassic planktonic foraminiferal species is that we do not have a stratigraphic and sampling record leading from one species to the other species. We refrain to speculate on the ancestry of Globuligerina avariformis.
The 'red group' includes Globuligerina oxfordiana, Globuligerina glinskikhae, Globuligerina tojeiraensis and the inferred lineage from Globuligerina waskowskae to Conoglobigerina helvetojurassica. These are low-to medium high-spired morphotypes, with spherical-globular or radially somewhat elongated chambers, narrow to wide umbilicus, large last whorl and arch to looped aperture with lip. In well-preserved and typical Globuligerina oxfordiana the looped aperture is very slightly offset from the umbilicus. A stratigraphic trend exists in this taxon to a more reticulate wall texture with the umbilicus opening up.
Gorbachik [52] showed the onset of reticulation on older chamber of a specimen of this species; this is clearly an ontogenetic feature in rare specimens of some assemblages. If ontogeny recapitulates evolution, this wall texture change strengthens our postulation that Jurassic Globuligerina oxfordiana is ancestral to Cretaceous Favusella hoterivica. The close morphological comparison and overlap in wall texture features, makes it viable to consider Globuligerina oxfordiana to be the ancestor of Favusella hoterivica. Both taxa are illustrated in Figure 5. It is interesting, as listed above that reticulate Globuligerina oxfordiana occur in the Middle Kimmeridgian of Portugal.
The species Globuligerina tojeiraensis, with elongated chambers and wide-open umbilicus is frequent in the Kimmeridgian of Portugal. Its overlap in morphology with Globuligerina oxfordiana suggests the latter to be ancestral. Figure 5 tentatively shows that the taxon might have originated earlier and a special study should be undertaken of Globuligerina with elongated chambers. The origin of Globuligerina oxfordiana is shrouded in mystery.
The discovery and description in Gradstein and Waskowska [2] of well-preserved Globuligerina waskowskae with a test morphology much alike Conoglobigerina helvetojurassica makes it attractive to consider the former taxon to be ancestral, although this likely is a case of broad morphological resemblance due to the strongly embracing last whorl. The principal new feature is the distinctive reticulate wall surface texture of Conoglobigerina helvetojurassica, appearing in Middle Oxfordian.
In summary, and as illustrated in Figure 5 the planktonic foraminifera appeared during Toarcian time (but no free specimens record) and occurred with at least eight taxa of one genus in Bajocian-Bathonian. The Oxfordian-Kimmeridgian planktonic foraminiferal record consists of six taxa in four genera. A faunal change-over, which is not well documented led to the survival of only one taxon, most likely Gobuligerina oxfordiana in the Tithonian.       6 from Plate II in [47] with permission from the authors). Clavihedbergella eocretacea (Neagu). Subfigures 7-12, sample Cr1 of Berriasian age, Krasnoselivka section, Crimea, Russia.