Morphostructure and Systematics of Linderina Brugesi - Eocene Foraminifera

MORPHOSTRUCTURE AND SYSTEMATICS OF L I N D E R I N A BR UGESI SCHLUMBERGER, 1893

(FORAMINIFERA, EOCENE)

CARLES FERR/iA~DEZ-CAI~ADELL & JOSEP SERRA-KIEL

FERR/kNDEZ-CAI~ADELL & SERRA-KIEL J. 1999. Morphostructure and Systematics of Linderina brugesi SeHLUMBERGER, 1893 (Foraminifera, Eocene). [Morphostructure et syst~matique de Linderina brugesi SeHLUMBERGER, 1893 (Foraminifere, Eocene)]. GEOBIOS, 32, 4: 525-537. Villeurbanne, le 31.10.1999.

Manuscrit d~pos~ le 23.12.1997; accept~ d~finitivement le 11.07.1998.

ABSTRACT - The morphostructure of the genus Linderina SCHLUMBERGER, 1893 is revised relying on a structural study of the type species L. bruguesi, SCHLUMBERGER. Its test is lamellar-involute, with annular-cyclic growth of orbitoidal type. It has only one kind of stolons which are crosswise-oblique, alternately arranged in axial rows, and correspond with the apertures in the last chamber. The lateral thickenings of the test are formed by the superposition of the successive involute outer lamellae of the different chambers, lacking piles and granules, and the irregularity of the lateral surfaces is due to the lateral rounded reliefs of the alternate chamberlets. The embryonic apparatus is quadrilocular, with three subspherical initial chambers forming a triconch, and a fourth larger, arcuate chamber with rows of apertures in both sides from which the orbitoidal growth starts. An explanation is given for the morphogenesis of embryos in triconch, observed in a number of foraminiferal genera. L. brugesi shows a close similarity to American Eocene species Caudriella ospinae (CAUDRI), which differs from Linderina in that it has lateral chamberlets. Because of this affinity, Caudriella is included in the Linderinidae. A redefinition of the genus Linderina and of the family Linderinidae is performed. The genera Eoannularia and Epiannularia, previously classified into the Linderinidae, do not fit into the new characterization of the family and are thus grouped into a new family, named Eoannularidae.

KEYWORDS: LINDERINA, FORAMINIFERA, MORPHOSTRUCTURE, EOCENE, SYSTEMATICS.

RI~SUMt~ - La morphostructure du genre Linderina SCHLUMBERGER, 1893 est rSvis~e ~ part ir de l'~tude structurale de l'esp~ce-type, L. brugesi. Le test de Linderina est annulaire-cyclique, de croissance orbitoYdale, et lamellaire-involute. I1 ne poss~de qu'un seul type de stolons qui sent entrecrois~s et disposes en rang6es axiales alternantes. Ces stolons correspondent aux ouvertures dans la derni~re loge. Les ~paissements lat~raux du test sent form,s par la superposition de lamelles externes involutes successives, il n'existe ni piliers ni granules. Les irr~gularit~s de la surface externe sent produites par les reliefs arrondis des logettes alternantes. L'appareil embryonnaire est quadrilo- culaire, avec trois loges subsphSriques initiales formant une triade et une quatri~me Ioge arqu~e, plus grande, avec des rang~es d'ouvertures de chaque c5t5. A part ir de cette loge commence la croissance orbito~dale. L. brugesi res- semble beaucoup ~ l'esp~ce ~oc~ne am~ricaine Caudriella ospinae qui se distingue notamment de Linderina par la presence de logettes lat~rales. En raison de cette affinitY, Caudriella est rattachSe aux Linderinidae. Une redefinition du genre Linderina et de la famille Linderinidae est propos~e. Les genres Eoannularia et Epiannularia, jus- qu'ici classes parmi les Linderinidae, n 'entrent plus dans la nouvelle d~finition de la famille et sent, par consequent, regroup~s en une nouvelle famille, celle des Annularidae.

MOTS-CL]~S: LINDERINA, FORAMINIFERA, MORPHOSTRUCTURE, I~OCI~NE, SYSTEMATIQUE.

INTRODUCTION

Since i ts def ini t ion (Sch lumberge r 1893) the genus Linderina has been described, or s imp ly repor ted f rom the Te r t i a ry of Europe , Africa, Amer ica , Asia and Aus t r a l i a , u n d e r abou t 15 dif ferent species a s s ignmen t s . Never the le s s , the descr ip t ions of this genus a re insuff ic ient and contradictory. The re is no a g r e e m e n t on f u n d a m e n t a l ques t ions such as the shape of the embryo or the stolon sys tem. Here , a rev is ion of the m o r p h o s t r u c t u r e of the genus is m a d e b a s e d on the type species, Linde- rina bruguesi SCHLUMBERGER, 1893, bas ica l ly on the l a m e l l a r cons t ruc t ion and the p a t t e r n and

a r r a n g e m e n t of i ts m e g a l o s p h e r i c e m b r y o n i c a p p a r a t u s , c h a m b e r s and chamber l e t s , s tolons and aper tu res . This s t r uc tu r a l s t udy a l lowed us to cla- r i fy some p rob lema t i c points dea l ing wi th the s t ruc ture , such as the s tolon sys tem, or the s t ruc- tu re of the embryonic a p p a r a t u s . The r e su l t s of th is s t udy imply a revis ion of the s y s t e m a t i c s of the group at genus and fami ly level.

PREVIOUS WORK

The genus Linderina was def ined by S c h l u m b e r g e r (1893) f rom Eocene core m a t e r i a l f rom Bruges (Gironde, s o u t h w e s t e r n France) w i th Linderina

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brugesi as the type species. According to Freu- denthal (1969), the material probably came from the "Calcaires de Blaye", with an stimated Lutetian age according to data in Schoeller (1949) and Roman & Cahuzac (1992). Since then about 15 species have been assigned to this genus (Tabl. 1). Specific assignation has often been justified exclu- sively basing on external features (e.g. Le Calvez 1970; Colom 1971; Ferrer 1971). Descriptions of the internal features vary between species, and even within species,, depending on different authors.

The genus Linderina has been reported from Eocene beds in Europe (England, France, Spain, Italy, Switzerland, Hungary, Romania), Turkey, Somalia, Qatar, Oman, Iran, Iraq, Afghanistan, Pakistan, India, Burma, Borneo, Celebes, Aus- tralia, New Guinea, Bismarck Islands (W Pacific), Jamaica, Florida, St. Barthelemy (French Antilles), and Venezuela. Some references to Cretaceous Lin- derina (Douvilld, 1906; Silvestri 1910; Visser 1951; Hofker 1958) were later identified as Hellenocy- clina (MacGillavry 1963), Monolepidorbis (Astre 1927) or Orbitoides tissoti (ScHLUMBERGER, 1902) lacking lateral chambers (Neumann 1958), later assigned to a new species, O. hottingeri, by van Hinte (1966). Some reports of Miocene Linderina

were reassigned to Miogypsina or Planorbulina (Nuttall & Brighton 1931). Finally, L. chapmani HALKYARD, 1919 was assigned to Halkyardia (Neumann 1958; Freudenthal 1969), and L. ovata HALKYARD, 1919 was chosen as type species for a new genus, Droogerinella (Popescu & Brotea 1995).

Freudenthal (1969) made a revision of the genus Linderina based on the biometry of the internal characters. He studied material from England, France (Paris and Aquitanian basins), Somalia (including topotypes of L. buranensis NUTTALL & BRIGHTON, 1931), Qatar, Celebes (including types ofL. paronai OSIMO, 1909), and Borneo, and consi- derably reduced the number of species by establi- shing synonymies (Tabl. i). For example, he reduced to one the four Indian species described by Singh (1953). Freudenthal (1969) stated that the species of Linderina had mainly been based on "slight differences of the external characteristics in comparison with the type species L. brugesi"; moreover he affirmed that the species he recognized could be "a junior synonym of L. brugesi, the internal characteristics of which are completely unknown". The aim of this work is to provide a better characterization of the type species and, thus, of the genus, based on a structural study.

SPECIES AUTHOR LOCALITY AGE COMMENTS

L. brugesi Schlumberger 1893 France Middle Eocene Type species

L. paronai Osimo 1909 Celebes Upper Eocene Recognized by Freudenthal (1969) in the Paris Basin

L. chapmani Halkyard 1919 France Bartonian = Halkyardia (Neumann1958; Freudenthal 1969)

L. ovata Halkyard 1919 France Bartonian = Droogerinella (Popescu & Brotea1992)

L. buranensis Nuttall & Somalia Middle Eocene Recognized also in Qatar (Freudenthal, 1969)

Brighton 1931

L. floridensis Cole 1942 Florida Late Middle Eocene Possibly = L. paronai (Freudendhal 1969)

L. bihilensis Silvestri 1948 Somalia Middle Eocene = L. buranensis (Azzaroli 1952; Freudenthal 1969)

L. nuttalli Silvestri 1948 Somalia Middle Eocene = L. buranensis (Azzaroli 1952; Freudenthal 1969)

L. rajasthanensis

L. bikanerensis

L. keyalatensis

Singh 1953 India Lutetian The four species of Singh can be reduced to

one = L. rajasthanensis (Freudenthal 1969)

L. kirtharensis L. visserae Hoiker 1958 Netherlands Maastrichtian = Hellenocyclina (MacGillavry 1963; Freudenthal 1969

L. douvillei Silvestri 1910 France Originally described as Monolepidorbis douvillei (Astre

Visser 1961 Netherlands Campanian 1927) = Orbitoides (Neumann 1958; van Hinte 1966)

L. baldaci Preyer 1912 Italy Eocene-Miocene "status completely obscure" (Freudenthal 1969)

L. glaessneri McGowran & Australia Late Eocene Not figured, not described.

Beecroft 1986

TABLE 1 - Species of L i n d e r i n a found in the l i terature, wi th reference to the original description, area and age of type locality and comments on synonymies . Some species ass igned to Linder ina were later identified as Hellenocycl ina, Orbitoides, Ha lkyard ia , Miogyps ina or Planorbu l ina , or included into a new genus, Droogerinella. The res t of species, were reduced by F r e u d e n t h a l (1969) to four: L. buranens i s , NUTTALL & BRIGHTON, L. ra jas thanens i s SINGH, L. parona i OSIMO and L. f lor idens is COLE, t hough he s ta ted t ha t the la t te r species might be a jun io r synonim of L paronai , and tha t one of the species may be a jun ior synonim of L. brugesi. Esp~ces de Linder ina trouvdes clans la l i t tdrature compor tan t la descript ion originale, la rdgion et l'Ctge de la localitd type et des com- menta i res sur les synonymies . Quelques esp~ces a t t r ibu tes au genre Linder ina ont dtd iden t i f i&s pos t~r ieurement cornme Hellenocyclina, Orbitoides, Halkyardia , Miogypsina ou Planorbufina, ou classifi~es dans un nouveau genre, Droogerinella. Les autres esp~ces ont ~tg r~duites & quatre p a r Freuden tha l (1969): L. bu ranens i s NUTTALL & BRIGHTON, L. r a j a s t h a n e n s i s SINGH, L. paronai 08IMo et L. f lorindensis COLE, bien qu'il air d&larg qu 'une de ces esp&ies pourra i t ~tre un s ynonymic du L. brugesi .

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MATERIAL AND METHODS

Our morphostructural study was carried out on specimens of Linderina brugesi SCHLUMBERGER, 1893, from level IV (Douvillfi & O'Gorman 1929) of the Tuilerie of Biron (Gave du Pau region, Southern France; see Fig. 37 in Schaub 1981 for the location of the site), collected by one of us (Serra-Kiel) in 1979. These beds contain Num- mulites praeaturicus SeHAUB, 1962, N. benehar- mensis DE LA HARPE IN ROZLOZSNIK, 1926, N. bous- saci ROZLOZSNIK, 1924, Assilina spira spira (DE RoISS¥, 1805) and A. exponens (SowERBY, 1840), that correspond to the middle Lutetian (Schaub 1981), or to Shallow Benthic Zone SBZ14 (Middle Lutetian 1) of Serra-Kiel et al. (1998). The tuilerie was abandoned many years ago and the outcrop is nowadays completely covered by vegetation.

Only 8 specimens were found in the sample, but they were well preserved and empty of cement and sediment, facilitating their study by SEM. Obser- rations were performed using a Hitachi 2300 Scanning Electronic Microscope of the Serveis Cientifico-T~cnics of the University of Barcelona.

Because of the probable loss of the type material ofL. brugesi (Neumann 1954; Freudenthal 1969), the assignment of our specimens to this species is based on the original description by Schlum- berger, and on both geographic and stratigraphic relationships of the respective samples. According to Freudenthal (1969), the species of Linderina from the Aquitanian basin differs from that from the Paris basin. The specimens described from Gironde-Aquitania (Sclumberger 1893; Welch in Schoeller 1949; Neumann 1954; this work) would belong to L. brugesi whereas those from the Paris basin were assigned to L. sp. cf. paronai by Freudenthal (1969), though he stated that they "might be named L. paronai (or L. floridensis) on the basis of our present knowledge".

REVISION OF THE DESCRIPTIONS OF LINDERINA

As stated above, the descriptions of the different species of Linderina are insufficient and contradictorious. We'll summarize here the main features of the descriptions found in the literature, taking into consideration only those species which have not been posteriorly reassigned to other genera.

EXTERNAL MORPHOLOGY

Most authors agree in the description of the external features of the test of Linderina: discoidal shape, more or less convex; lobulate outline; and perforate lateral surface. Most descriptions also mention numerous small pustules, granules or papillae on the lateral surfaces of the test (Nuttall

& Brighton 1931; Singh 1953; Neumann 1954; Smout 1954; Bombita & Popescu 1977; Loeblich & Tappan 1987). In his original description, Schlum- berger (1893) only mentioned small prominences between the perforations that give the test a rugo- se surface. Schlumberger (1893) and Nuttall & Brighton (1931) also point out the absence of "pillars" (piles sensu Hottinger et al. 1993).

EMBRYONIC APPARATUS

Various different descriptions and interpretations of the embryonic apparatus and the early growth stages in Linderina have been published. Schlumberger (1893) described a large, spherical central chamber in L. brugesi. According to Nuttall & Brighton (1931), the new species L. buranensis they described from Somalia had a "large, central, subcircular chamber" with at least five smaller and compressed chamber's around it in equatorial section. Smout (1954), on the other hand, speaks of the small "nucleoconch" in L. 5ru- gesi from Qatar, without specifying number and arrangement of the embryonic chambers.

A bilocular embryonic apparatus have been described in L. brugesi (e.g. Neumann 1954; Dupeuble et al. 1972; Bombita & Popescu 1977), and in the original descriptions of other species such as L. bikaren- sis SINGH, 1953, L. kirtharhensis StNGH, 1953. L. ko- layatensis SINGH, 1953 and L. floridensis COLE, 1942.

Finally, the initial chambers of L. brugesi were described as "trocospiral" by Horv~Lth-Koll~nyi (1988), yet she did not specify if the specimens she described were micro- or megalospheric forms.

LAMELLAR CONSTRUCTION

Schlumberger (1983) stated that the lamellae show continuity in both equatorial section "where they form rings" and axial section "where they form the lateral thickenings" (see figs 3 and 4 in Schlumber- get 1893). The continuity of the lamina "of each whorl" had also been described by Nuttall & Brighton (1931).

Neumann (1954) and Dupeuble et al. (1972) claimed that such an interpretation was erroneous, and that the wall is not continuous in equatorial section. However, attached figures show continuous annular walls (see fig. 7a,b in Dupeuble et aI. 1972). According to these authors, the lateral thickenings of the test correspond to a "more or less thickened calcareous wall" (Neumann 1954) or to a covering formed by several lamellae (Du- peuble eta]. 1972; and also in Loeblich & Tappan 1987).

The only explicite reference to the lamellar structure of Linderina is that of Freudenthal (1969) who regards the genus as monolamellar.

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CHAMBERS AND CHAMBERLETS

Most authors (Schlumberger 1893; Smout 1954; Neumann 1954; Freudenthal 1969; Dupeuble et al. 1972; Loeblich & Tappan 1987) use the term chamber when referring to each compartment of the test. The term chamberlet is used indiscriminately with chamber, only to reflect the size (e.g. Horv~ith- Koll~nyi 1988).

When referring to chamber arrangement, several terms are used: "circles" (Schlumberger 1893); "rings" (anneau) (Dupeuble et al. 1972; Horv~th- Koll~nyi 1988); "rounds" or "whorls" (tour) (Nuttall & Brighton 1931; Neumann 1954); and "cycles" or "series" (Schlumberger 1893; Loeblich & Tappan 1987). Horv~ith-KolMnyi (1988) described chambers as arranged "in annular rings, in planospiral succession".

STOLONS

Descriptions of stolons in Linderina are very variable too. Schlumberger (1893) only described stolons connecting adjacent chambers of the same circle. On the contrary, Dupeuble et al. (1972) describe three types of stolons: "annular" stolons connecting chambers of the same ring; stolons connecting chambers of adjacent rings (placed proximally, at the base of the "chambers"), and a third kind of stolons, placed in the distal end of the "chambers" connecting "chambers" of alternate rings (see figs. 7 and 8 in Dupeuble et al. 1972).

APERTURES

Neumann (1954) described the apertures ofL. brugesi as rounded depressions, of 50 ~am in diameter, surrounded by a thin annular wall. She regarded the pat tern of apertures in Linderina as similar to that of stolons in Orbitoides sensu stricto. Such a comparison was also utilized by Loeblich & Tappan (1964). According to Freudenthal (1969), Linderina has apertures arranged in rows between periphe- ral "chambers", with 3 to 5 apertures in each row. Horv~ith-Koll~nyi (1988) and Loeblich & Tappan (1987) describe apertures at the base of the "cham- bets", but without specifying their number. Finally, after describing four new species from India, Singh (1953) stated that the absence of"lipped apertures at the border" was a generic character for Linde- rina and differentiated it from Planorbullinella.

MICROSPHERIC FORMS

There is few information about microspheric forms ofLinderina. Schlumberger (1893) differen- t iated microspheric forms in L. brugesi by the size of their initial chamber, but he made no reference to the kind of growth or to the arrangement of the initial chambers. Nuttal l & Brighton (1931) only stated that "a spiral arrangement of the earliest

chambers was observed" in L. buranensis. A photograph of a microspheric form of L. brugesi was published in Bombita & Popescu (1977) but with no description. Its magnification does not allov¢ to distinguish the arrangement of the initial chain- bets, though no spiral is visible. According to Loeblich & Tappan (1987), the early chambers of microspheric forms are arranged "in an irregular cluster, ra ther than in a distinct spire".

In the original description of L. rajasthanensis SINGH, 1953, the author describes a microspheric form with "two subequal chambers partially surrounded by three auxiliary chambers in a trochoid spire". Such a description and the size of the initial chambers (30-40 l~m) seem to correspond to a megalospheric form. Both Horv~th-Koll~inyi (1988) and Freudenthal (1969) claimed that the initial growth was trochospiral in some specimens, but without specifying if they were or not microspheric forms. Freudenthal also stated that the "lenght of the initial spiral" ranged from 8 to 15 chambers in microspheric specimens.

It is plain that previous descriptions of Linderina given by different authors are inconsistent: Some of them describe the megalospheric embryonic apparatus as monolocular, others as bilocular; up to three different stolon types have been described; with regard to chamber arrangement, both isolated chambers and rings of "chambers" have been described. Other sources of contradiction are the presence of granules in the lateral surfaces and the absence of "pillars". Finally, the early chamber arrangement in microspheric forms is not clear.

MORPHOSTRUCTURE OF LINDERINA

From the SEM study ofLinderina brugesi several structural features of the genus could be clarified. However, the limited number of available specimens has left some unsolved problems, mainly the kind of growth of the initial chambers of microspheric forms, as all the studied specimens were megalospheric forms. A redescription of the main structural features of the genus, based on the megalospheric forms of the type species, follows.

EXTERNAL MORPHOLOGY

The test is discoidal to lenticular, thickened in the central par t and lobulate in outline. The shape of the test varies through ontogeny, having the younger specimens a more pronounced central thickening (Fig. 2.2). Test size in studied specimens is up to 1,5 mm in diameter and 0.8 mm in thickness. Lateral surfaces show visible pores of 4-6 ilm in diameter (Fig. 2.1-3).

CHAMBERS AND LAMELLAR CONSTRUCTION

Linderina has a bilamellar test, with walls made up by an outer lamella and an inner lamella. The

529

FIGUR~ 1 - Block-diagram showing the lamellar construction of the test in Linderina brugesi SCHLUM- BERGER. Pores, stolons and apertures have been omited for clarity. Note the continuity of the outer lamella in each annulus, the involute superposition of outer lamellae in the lateral parts giving the test its lenticular shape, and the arrangement of inner lamellae in each chamberlet. Bloc-diagramme de la construction lamellaire du test de Linderina brugesi SCHLUM- BERGER. Les pores, les stolons et les ouvertures ont dtd omis pour plus de clartd. Notez la continuitd de la lamelle extdrieure dans chaque anneau, la superposition involute des Iamelles externes dans les par- ties Iatdrales, qui donne au test sa forme lenticul~e, et [a disposition des lamelles intdrieures dans chaque logette.

inner lameila ~ I Outer lamella --~

~ :i':i:i ,~..::,~,:.,. Lateral Surfac e

Section ~ ~ . . ~

growth is lamellar-involute, meaning that each outer lamel la completely covers all previous chambers. The lamellar-involute character is best reflected in axial section, where the superposition of the successive outer lamellae produces the lateral thickenings of the test (Fig. 1; Fig. 2.4).

There is a mis taken idea of annular-cyclic growth in some orbitoidiform foraminifers, including Linderina and also some other forms such as the Orbi toclypeidae (e.g. N e u m a n n 1954, 1972; Dupeuble et al. 1972; Loeblich & Tappan 1987), implying that the equatorial annuli are formed by true, independent chambers arranged in "cycles". This idea is incompatible with a three-dimensional construction of the foraminiferal tes t as shown by the lamellar construction.

Taking the definition of chamber as "all the structures formed in a growth step" (Hottinger 1978; Ferr~ndez-Cafiadell & Serra-Kiel 1992), in Linderina a chamber is the sum of all the chain- berlets limited by the same outer lamella. Neanic chambers are made up of a number of arcuate chamberlets arranged in an equatorial annulus. The chamberlets of the same annulus are somewhat separated one from another, so that the undu- late septum comes into contact with the previous one between chamberlets (Fig. 3.1,2) The chamberlets are rounded, both in equatorial and axial section, thus producing rounded reliefs on the lateral surfaces of the test. Due to the lamellar-involute character, these reliefs are mitigated towards the centre of the test, where the number of superposed IamelIae is higher (Fig. 2.1) There are no imperforate sectors or piles in the lateral thickenings (Fig. 2.4). The inner lamella covers the entire inner surface of the chamberlets (Fig. 2.8), including the pre-

vious apertural face (thus forming a septal flap). The septa are thus trilamellar, consisting of an outer lamella between two inner iamellae, except for the last chamber, which has a bilamellar septum as it lacks the septal flap. The lamellar construction of the Linderina test is represented in figure 1.

Lamellar-involute character may be difficult to see in equatorial section, as the continuity of the lamellae is obscured by the stolons, and there is a superposition of only two outer lamellae in neanic (annular) chambers, and only between chamberlets. In axial section, however, the lamellar-involute character can easily be seen, due to the absence of stolons and the higher number of superposed outer lamellae (Fig. 2.4). In equatorial section, the lameL lar-involute character can be inferred by the local thickenings of walls, mainly in the early stages because each chamber only has a few chamberlets. Thus, species with a first chamber (after the embryo) consisting of one or two chamberlets (cal- led auxiliary "chambers") have embryo walls often showing a variable thickness through its perimeter in equatorial section. Thus different thickness and stolon arrangement allow to reconstruct the onto- genetic succession of chambers and chamberlets.

PORES

Pores, about 4-6 pm in diameter, are located at the lateral walls of chamberlets, crossing the super~ posed involute outer lamellae until they reach the outer surface of the test (Fig. 2.4,10). Only the zones between two successive chamberlets (where stolons are) and the apertural face are imperforate, although a few pores were observed in the distal wall of the chamberlets of the last annulus (Fig. 2.7,6).

530

STOLONS AND APERTURES

Chamberlets are connected by means of a crosswise-oblique stolon system, connecting each chamberlet with two chamberlets of the previous chamber and two of the following one, and forming spiral ali- gnments in two opposite directions. The stolons are placed proximally, at each side of the chamberlets, m imperforate depressions between chamberlets of the same chamber (Fig. 2.9,10). Each chamberlet has 2-3 stolons in each side, in alternate arrangement with the stolons of the adjacent chamberlet of the same chamber. Due to this alternate arrangement, often only stolons in one direction are seen in an equatorial section (Fig. 3.1).

There is no communication between chamberlets of the same chamber. The annular stolons cited by some authors (e.g. Schlumberger 1893; Neumann 1954; Dupeuble et al. 1972) are actually the crosswise-oblique stolons as they appear in axial section (compare Fig. 2.4 with Fig. 8 in Dupeuble et al. 1972). There is no other kind of stolons.

The stolon ar rangement can clearly be seen in the aper tural face, as the stolon system corresponds there to the apertures. Up to six apertures can be seen in the axial inflection between two chamberlets of the same chamber (Fig. 2.3,5-7). The apertures show a well-developed peristome forming a continuous S-shaped rim through the rows of aper tures s i tuated between each chamberlet of the last annulus (Fig. 2.6,7). In older chambers the peristomes are either absent or a t tenuated by the inner lamella of the septal flap (Fig. 2.9,10). The recovering by inner lamella could also account for the different diameter of apertures (10-12 ~m) and of stolons (5-9 om).

There are no aper tures or stolons neither in the distal edge of the chamberlets "where Dupeuble et al. (1972) described stolons connecting chamberlets of al ternate annuli" nor in the lateral surfaces of the test. All apertures are si tuated in the imperforate depressed zones of the periphery of the test. The stolon-aperture system of Linderina closely resembles tha t of the first chambers of

Lepidocyclina as described by Br6nnimann (1947) and Eames et al. (1962).

MEGALOSPHERIC EMBRYONIC APPARATUS

When studied in thin section (see Fig. 2.1 as a comparison), the megalospheric embryonic apparatus seems to be bilocular, with a protoconch and a deuteroconch in isodilepidine configuration followed by a first chamber with two chamberlets, one at each side of the embryo. However, three- dimensional images provided by SEM reveal further complexities in the embryonic apparatus of Linderina. The embryonic appara tus is quadrilocular, with three initial subspherical chambers of about 60 ~m in diameter and an arcuate, larger fourth chamber (Fig. 3.3-7). The maximum diameter of the embryonic apparatus (triconch plus fourth chamber) is of 200 ~m. The first three chambers are bounded by thin f lat tened walls (Fig. 3.4,6), and they are connected one to another by a single stolon (Fig. 3.3-7, arrows). The fourth, larger chamber shows one row of apertures in each side, from which two separate chamber]ets are formed in the first chamber after the embryo. Each chamberlet of this chamber also has rows of apertures in each side, start ing the crosswise- oblique stolon system and the orbitoidal growth.

CHAMBERS, CHAMBERLETS, AND GROWTH PLAN

The test of Linderina has a typical orbitoidal growth, with chambers made up of an increasing number of separate arcuate chamberlets arranged in annular-cyclic growth and connected by a crosswise-oblique stolon system. The appropriate ter- minology for an accurate description would include the words: chamberlet, as a par t of a chamber, referring to each arcuate compartment of the test; chamber, referring to all the compartments (i.e., chamberlets) formed in the same growth step, and surrounded by the same outer lamella; and annulus (instead of "cycle", "whorl", "series", etc.) referring to all the chamberlets of one chamber in annular arrangement. As Linderina lacks lateral

FIGURE 2 - 1-10. Linderina brugesi SCHLUMBERGER, 1893. Middle Lutet ian, Biron. 1,2, external view of two megalospheric specimens. Note the lobulate outline of the test, the pores, and the relief of the lateral surfaces. 3, detail of fig. 1 in oblique view. 4, axial section. Note the la teral thickenings due to the superposition of successive outer lamellae (lamellar-involute character), the absence of piles, the pores, and the stolons. 5-7, periphery of the test showing the aper tura l face with the apertures. Note the peristome and the a l te rna te a r r angemen t of the apertures, and the presence of several pores in the last septum. 8, i r regular equatorial sec- t ion showing the inner lamella (arrows) covering the entire inner surface of each chamberlet. 9, proximal side of the last chamber in a specimen in which the last septum is broken. Note the a t tenua t ion of the peristomes by the covering inner lamella (septaI flap). 10, tangent ia l section showing the stolons. Note the reduced peristome. 1-10. Linder ina brugesi SCHLUMBERGER, 1893. Lutdtien Moyen, Biron. 1,2, rue externe de deux spdcimens mdgalosphdriques. Observez le profil lobd du test~ les pores et le relief des surfaces latdrales. 3, ddtail de la figure 1 en rue oblique. 4, coupe axiale. Observez les dpaississements latdraux produits par la superposition des lamelles externes suceessives (caract~re lamellaire-involutd) et l'absence des piles, des pores et des stolons. 5-7, pdriphdrie du test montrant la face orale. Observez le pdristome, la disposition alternde des ouvertures, et la prdsence de quelques pores clans le dernier septum. 8, coupe dquatoriale irrdguli~re montrant la lamelle interne (indiqude par les fl~ehes) couvrant route la surface intdrieure de chaque logette. 9, cotd proximal de la derni~re loge d'un spdcimen dans lequel le dernier septum est cassd. Observez l'attdnuation des pdristomes par la lamelle intdrieure qui forme une couverture (septal flap). 10, coupe tangentielle montrant les stolons. Observez le pdristome rdduit..

500/am

531

Z

4

200 ~m 5

7

6 100 pm

9

chamberlets, in the neanic stage the terms chamber and annulus, would be synonyms

D I S C U S S I O N

THE SHAPE OF THE EMBRYO

As stated above, the walls dividing the three initial, subspherical embryonic chambers are fiat and thin, probably consisting solely of inner lamella (Fig. 3.4,6). Hott inger and Scheuring (in press) suggested to call triconch this type of embryo, which is found in several other foraminifers, such as PlanorbuIinella (e.g. Freudenthal 1969: pls. 1-3; Hottinger et al. 1993: P1. 158, fig. 11), or Hellenocyclina (Mac Gillavry 1963: P1. VII, figs la,2a,2b). The tr iconch in Linderina is somewhat oblique to the other embryonic chamber, that 's why in equatorial section usually only two chambers of the triconch are cut.

Flat walls between two chambers point out to a s imultanei ty in their formation (Smout 1954). The walls between the triconch's chambers are not exactly flat, tha t would indicate a trilocular chamber. Nei ther they are rounded walls as if chambers would have formed in sequence. In reality, they are something intermediate: flattened walls separa t ing rounded chambers. How can this shape be interpreted and relationed with the formation of the chambers?

An explanation for embryonic apparatus in triconchs can be found in the study of schizogony in Planorbulina mediterranensis D'ORBI~NY, 1826 by Le Calvez (1938). In this species, the gamonts leave the mother's test having seven chambers. Following Le Calvez's detailed description of the formation of the gamont, the first chamber does not calcify until the fourth chamber is forming. That means that initially, the walls of the three first chambers consist of a flexible organic membrane. Afterwards they adopt a more stable shape by flattening the membranes between the chambers. When these initial chambers calcicify, the mineral walls adopt a flattened shape, so forming a triconch. The same explanation can be applied to other genera with similar embryos in triconchs, and also to some bilocular embryos with a protoconch and deuteroconch bounded by a flattened wall, such as lepidocycli- nids. A characteristic of the embryonic apparatus of L. brugesi is the unusual large size of the chamber

532

immediat ly following the triconch. Embryonic apparatus in triconch in other Linderina species can be seen in Freudenthal (1969: L. sp. cf. paronai from the Paris Basin, pl. 10, fig. 7; L. paronai from Celebes and Borneo, pl. 15, figs 1, 2).

MICROSPHERIC FORMS

As stated above, no clear descriptions of the initial growth of microspheric forms of Linderina can be found in the literature. On the other hand, the available descriptions are contradictorious: the initial chambers would have a "spiral arrangement" according to Nuttall & Brighton (1931); would be arranged in an "irregular cluster" according to Loeblich & Tappan (1987) or would show "two subequal chambers partially surrounded by three auxiliary chambers in a trochoid spire" according to Singh (1953). Curiously, the authors that provide descriptions of microspheric forms (e.g. Nuttall & Brighton 1931; Singh 1953) do not figure them, whereas those who figure microspheric forms do not include a description (e.g. Bombita & Popescu 1977). Unfortunately, we did not find any microspheric specimen in our material. Best source of information about microspheric forms of Linderina is probably Freudenthal (1969). Freudenthal stated the lenght of the initial spire of microspheric forms in 8 to 15 chambers, though he did not specify how many microspheric specimens he studied, nor the species they belonged to. On the other hand, he provided the only clear photograph of an equatorial section of a microspheric form of Linde- rina we found in the l i terature (Freudenthal 1969: pl. 10, fig. 6). This microspheric specimen comes from Bois de Ronquerolles (Paris Basin) and it was assigned by Freudenthal to L. sp. cf. L. paronai. As stated above, the species from the Paris Basin is different from the Aquitanian basin one, identified as L. brugesi by Neumann (1954). Nevertheless, the species from the Paris basin has an embryonic apparatus in triconch too (see Freudenthal 1969: pl. 10, fig. 7) and can be undoubtely assigned to Linderina. From the photograph in Freudenthal 's work, the initial microspheric chambers of Linde- rina are arranged in a spire, similar to that of PlanorbulineUa, but with a thinner spiral wall, and they are connected by basal stolons.

L I N D E R I N A A N D C A U D R I E L L A

Linderina brugesi shows a striking structural similarity with the American genus Caudriella (Caudri

FIGURE 3 - 1-7. Linderina brugesi SCHLUMBERGER, 1893. Middle Lutetian, Biron. 1,3-5, same specimen. 2,5-7, same specimen. 1,2, equatorial sections. Note the bilocular appearance of the embryo. 3-7, details of 1 and 2 showing the structure of the embryo. It consists of three chambers in a triconch (a, b, c), and a fourth larger chamber (d). The embryonic chambers are connected by a single stolon (arrows). The fourth, larger chamber has one row of stolons at each side connecting it with the two chamberlets of the first chamber. 1-7. Linderina brugesi SCHLUMBERGER, 1893. Lutdtien moyen, Biron. 1,3-5, m~me spdcimen. 2,5-7, m~rne spdcimen. 1,2, coupes dquatoriales. Observez l'aspect biloculaire de l'embryon. 3-7, ddtails de 1 et 2 montrant la structure de l'embryon, consistant en trois loges dans un triconque (a, b, c) et une quatri~me loge plus grande (d). Les loges embryonnaires sont relides par un seul stolon (fl~ches). La quatri~me loge, plus grande, a une ligne de stolons de chaque cStd relige avec les deux logettes de la premiere loge.

533

500 l~rr,

1 2 3

534

1974; Haman & Huddleston 1988), only known from one species, C. ospinae (CAUDRI, 1974), from the Middle Eocene of the Punta Mosquito Fro. (Margarita, Venezuela). This species, originally described as Margaritella ospinae (see P1.7, figs. 1-9 in Caudri 1974), has a quadrilocular embryo too, with three subspherical initial chambers in a triconch and a fourth larger chamber with apertures at both sides. The diameter of the embryonic chambers is similar too: about 60 ~m for the three triconchal chambers and about 200 ~m for the maximum diameter of the whole embryonic apparatus. The neanic chambers are orbitoidal, as in L. brugesi, and shape and size of the test look alike too. The two species seem to differ only by the presence of lateral chamberlets in C. ospinae. Caudri (1974) stated a "certain resemblance" of CaudrieIla with Linde- rina though she did not include the former genus within any systematic group. Loeblich & Tappan (1987) included Caudriella into the Lepidocyclini- nae. Nevertheless, the structure of the embryo of Caudriella can only be compared with that of L. brugesi here described. Because of the structural similarity of their embryos, and of the main test features to Linderina, Caudriella should be included in the family Linderinidae, as a genus with lateral chamberlets. The study of the microspheric forms of Caudriella will provide further criteria for its systematic position.

IMPLICATIONS FOR THE SYSTEMATICS

As stated above, the genus Linderina has been reported in the Tertiary of all continents, assigned to many different species. Nevertheless, in most cases determinations are made on the basis of external features or of a few axial thin sections. The study of the structure of "Linderina" ovata permit- ted to find several characters (bilateral symmetry, canals) which justified its assignment to a new genus, Droogerinella, and its placing into a new family, Droogerinellidae (Popescu & Brotea 1995).

The present s tructural s tudy of L brugesi also revealed new characters and questioned the classification at family level. Though partially explai- ned by the complexity of the embryonic apparatus, the disagreements in the descriptions of Linderina species, as well as its wide geographical distribution, may be due to the existence of different genera with similar general test features. Possibly, new structural studies will show that several different forms with similar external appearance or axial section, but different structural characters, have been classified into the same genus. Only s tructural analysis of the different species can clarify this point. On the other hand, our research demonstrated that some structural features, such as the structure of the embryonic appara tus or the arrangement of stolon systems,

can be misinterpreted when studied in thin section only. Empty, loose material is rare to find, but is not always studied in detail. For instance, Horv~th-Koll~nyi (1988) found empty specimens of both Linderina and Epiannularia in the Lutet ian of Dudar (Hungary). Although she used SEM to photograph the specimens (Horv~th- Koll~nyi 1988: P1.23, figs. 1-3), she described the internal features only observing it by t ransparen- cy, without sectioning the test. Even if no empty material is available, s tructural studies can be performed from thin sections.

Structural studies are needed to stablish a solid systematic classification. The characters to be used in classification above species level must be qualitative, of presence/absence, not quanti tat ive (Hottinger 1978); special relevance must be given to the microspheric initial chambers to stablish phylogenetic relationships and their reflection in systematics.

SYSTEMATICS

The results of this study call for a revision of the systematics. The species L. brugesi must be redefined in order to include the new characters here described, basically the megalospheric embryo in triconch. According to this redefinition, a revision of the species up to date assigned to Linderina is needed, basically checking the structure of the embryo.

However, the redefinition ofL. brugesi implies further changes in systematics. Firstly, being L. brugesi the type species, its redefinition implies the redefinition of the genus. Secondly, as Linderina is the nominative genus of the family, Linderinidae, the family has to be redefined as well. A redefinition of the family including a megalospheric embryo in triconch in the diagnosis, as it is found in the type species of the nominative genus, leads to a number of problems. According to the classification in Loeblich and Tappan (1987), the Linderi- nidae include two Eocene Car ibbean genera, Eoannularia and Epiannularia, From the photo- graphs in the original descriptions of Eoannularia (Cole & Bermudez 1944) and Epiannularia (Cau- dri 1974), both genera seem to have true bilocular megalospheric embryos, so they can not be grouped with Linderina into the family Linderinidae. Moreover, the chambers of EoannuIaria and Epiannularia are annular instead of orbitoidal as in Linderina. The microspheric initial growth of Epiannularia pollonaise CAUDRI, 1974 (the type species), has a initial peneroplid-like spire (see Caudri 1974: PI. 3, figs 6,9; reproduced in Loeblich and Tappan, 1987: PI. 729, fig. 1), very different from the spire found in Linderina. On the other hand, as discussed above, the genus Caudriella should be included into the Linderinidae because of its similarity with L. brugesi.

Taking into account the above statements, the species, the genus and the family are redefined as follows:

• Family LINDERINIDAE Loeblich & Tappan, 1974 LINDERINIDAE Freudenthal , 1969, p. 138, nora.

n u d . LINDERINIDAE Loeblich & Tappan, 1974, p. 54

E m e n d e d d e s c r i p t i o n - Test bilamellar and perforate, discoidal to lenticular with lobate outline. Megalospheric embryo in triconch, with three initial chambers separate by flattened walls, and a fourth larger, arcuate chamber, with apertures at both sides. Later chambers in orbitoidal growth, with crosswise-oblique stolons arranged in an equatorial layer. Massive lateral thickenings due to involute-lamellar growth or lateral chamberlets at both sides of the equatorial layer giving the test a lenticular shape• Microspheric initial chambers arranged in a Planorbulina-like spire.

Remarks - As here defined, the family includes the genera Linderina (without la teral chamberlets) and Caudriella (with la teral chamberlets) , both of Middle Eocene-age• The microspheric ini t ial growth of Caudriella should be studied in order to confirm the relat ionships between the genera. The species

LINDERINIDAE

Diagnosis - Embryonic apparatus tetralocular, with a triconch followed by a large fourth chamber

- Orbitoidal growth

Linderina Without lateral chamberlets

Caudriella With lateral chamberlets

~ . ~ . - - 5~.,.~." , . : " - - - - ~ ~ "~"L~.,~:

535

up to date assigned to Linderina (Tabl. 1) should be restudied to check the s t ructure of the megalospheric embryo as well as the microspheric j uvena r ium and the s tolon/apertures system.

The genera Eoannularia and Epiannularia, previously included into the Linderinidae (Loeblich & Tappan 1987), mus t be classified in a different family because of the i r bilocular n-mga- lospheric embryo, thei r annu la r chambers, the absence of lateral thickenings or lateral chamberlets, and the i r different microspheric init ial growth.

Genus L i n d e r i n a SCLU•BSRGER, 1893 T y p e s p e c i e s - Linderina brugesi SCHLUMBERGER 1893, p. 120.

E m e n d e d d e s c r i p t i o n - Bilamellar involute test with orbitoidal growth in annular cyclic arrangement. Lateral thickenings of the test formed by the superposition of the successive involute outer lamellae, piles absent. Orbitoidal chambers consisting of arcuate chamberlets alternately arranged in successive annuli. Crosswise-oblique stolon system with stolons in the proximal part of chamberlets arranged in axial rows of alternating stolons. There are no annular stolons, nor stolons in the distal wall of chamberlets. The apertures correspond to the stolon system, with rows of apertures between chamberlets in the last chamber. Quadri- locular megalospheric embryo, with three chain-

EOANNULARIDAE

Diagnosis - Bilocular embryo - Initial orbitoidal growth chaging to

annular growth

Eoannularia Annular chambers subdivised

Epiannularia Annular chambers unsubdivided

FIGURE 4 - Character iza t ion of the families Linderinidae and Eoannular idae nov. faro. wi th the genera Linderina, Caudriella, Eoannularia and Epiannularia. Caractgrisation des familles Linderinidae et Eoannularidae nov. faro. avec les genres Linderina, Caudriella, Eoannula r ia et Epiannular ia .

536

bers in a triconch and a fourth larger arcuate chamber with rows of apertures in each side, from which the orbitoidal growth starts. Microspheric initial chambers arranged in a Planorbulina-like spire. Middle Eocene, cosmopolitan.

Genus Caudr ie l la HAMAN & HUDDLESTON, 1988

Type s p e c i e s - Margaritella ospinae CAUDRI, 1974, p. 307.

Caudriella seems to differ from Linderina only in the presence of well-developed lateral chamberlets, though a revision of the genus is needed. Up to date, only one species, Caudriella ospinae (CAUDRI, 1974), from the Middle Eocene of Marga- ri ta Island (Venezuela), is known.

R e m a r k s - Caudri (1974) discussed the systematic place of her new genus. After considering and discarting the relationship with Linderina and with Pseudolepidina, she decided to leave it "standing alone and isolated from all other groups and evolutionary lineages". Loeblich & Tappan (1987) included Caudriella into the Lepidocyclininae (together with Astrolepi- dina, Eulepidina, Lepidocyclina and Pseudolepidina, all of them with a bilocular megalospheric embryo), a classification which in our opinion, is not sufficiently justified. The embryonic apparatus of Caudriella, with a triconch followed by a large fourth chamber only resembles that of Linderina, and both genera should be classified in the same group.

Family EOANNULARIDAE Ferrhndez-Cafiadell & Serra-Kiel, nov. fam.

Test bilamellar perforate, discoidal, flat or slightly concavo-convex. Bilocular megalospheric embryo followed first by orbitoidal chamberlets and by annular chambers later. Annular chambers subdi- vided into rectangular chamberlets or unsubdivided. Microspheric initial chambers arranged in a peneroplid-like spire that changes into annular chambers by a progressive increase in chamber width.

R e m a r k s - Includes the genera Eoanularia (Cole & Bermudez 1944) and Epiannularia (Caudri 1974), both of Middle Eocene age. Epiannularia is known only from Venezuela (Caudri 1974), whereas Eoannularia has been reported from Vene- zuela, Cuba, Hungary, Turkey and Australia.

S U M M A R Y A N D C O N C L U S I O N S

The s tudy of empty specimens of the type species of Linderina brugesi demonstrated that it has a complex megalospheric embryo, with three initial chambers in a triconch and a fourth larger arcuate chamber with apertures at both sides from which the orbitoidal growth starts. The study also revealed other features, such as the presence of inner lamella in the chamberlets, and clarified some controversial points, such as the absence of piles or granules, and the absence of annular stolons and of stolons connecting chamberlets of al ternating annuli. The American genus Cau-

driella seems to differ from Linderina, as here described, only by the presence of lateral chamberlets.

As L. brugesi is the type species of the genus a redefinition of Linderina including the new characters is at tempted. Being Linderina the nominative genus of the Linderinidae, a redefinition of the family is a t tempted too, including the triconch embryo as a family diagnostic character, as well as the possible presence of lateral chamberlets so to include the American genus Caudriella.

The genera Eoannularia and Epiannularia, previously included into the Linderinidae, differ from Linderina in several characters (basically, they have a bilocular megalospheric embryo and annular growth), and consequently they are included into a new family, Eoannularidae.

Finally, we want to stress the necessi ty to revise all Tertiary simple orbitodiform foraminiferal species in order to elaborate a solid systematic classification. Most specific and generic assignments are justified by the observation of external characters only, and they are often contradicted by the, otherwise few, structural studies.

A revision of the species assigned to Linderina should be under taken to check the s tructure of their megalospheric embryo and, thus, their taxo- nomic position. The s tudy of the microspheric form of Linderina and Caudriella would clarify their phylogenetic relationship.

A c k n o w l e d g e m e n t s - This research was supported by the DGICYT project PB95-0883 and a F.P.U. grant of the Ministerio de Educacidn y Cultura of the Spanish Goverment, and is a contribution to the IGCP Project n °. 393. We thank K. Drobne and M. B. Hart for their suggestions to improve the manuscript.

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SILWSTRI A. 1910 - Lepidocicline sannoisiane di Antonimina in Calabria. Memorie della Pontificia Accademia Romana dei Nuovi Lincei, 28: 103-163.

SILWSTRI A. 1948 - Foraminiferi dell'Eocene della Somalia. Parte III, 2. Paleontographia Italica, 32, 6: 277-331.

SINGH S.N. 1953 - Species of the genus Linderina from the Kirthars of Kolayat, Bikaner, India. Proceedings of the Natural Academy of Sciences, India, 23, 1-3: 21-28.

SMOUT A.H. 1954 - Lower Tertiary Foraminifera of the Qatar peninsula. Publications of the British Museum, Natural History, London, 96 p.

VISSER A.M. 1951 - Monograph of the foraminifera of the type- localities of the Maestrichtian (South-Limburg, Nether- lands). Leidsche Geologische Mededelinge, 16: 197-359.

C. F E R ~ E Z - C A N A D E L L & J. SERRA-KIEL Departament d'Estratigrafia i Paleontologia

Facultat de Geologia, Universi tat de Barcelona Zana Universit~ria de Pedralbes

E-08071, Barcelona Tel. (34) (3) 402 13 83 Fax. (34) (3) 402 13 83

e-mail: [email protected] e-mail: [email protected].

Documents

Morphostructure and Systematics of Linderina Brugesi - Eocene Foraminifera