Marine Micropaleontology, 15 (1990) 351-364 351 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Evolutionary trends and biostratigraphic potential of selected radiolarian taxa from the Early Carboniferous

of Germany

ANDREAS BRAUN Institut fi~r Geologie und Pal(mntologie im Fachbereich Geowissenschaften der Philipps-Universitiit Marburg,

Universiti~tsgebiet Lahnberge, Hans-Meerwein-Strafle, D 3550 Marburg/Lahn (West Germany)

(Received August, 1988; revised and accepted March 1989)

Abstract

Braun, A., 1990. Evolutionary trends and biostratigraphic potential of selected radiolarian taxa from the Early Car- boniferous of Germany. Mar. Micropaleontol., 15: 351-364.

A large number of well preserved radiolarian faunas have been found in Early Carboniferous rocks (Pericyclus- Alpha to Goniatites-Stufe) of the "Rheinisches Schiefergebirge" and the Frankenwald (Germany). The growing number of fossil faunas makes it possible to show evolutionary tendencies of certain taxa within these stratigraphic levels. In the course of the Early Carboniferous a continuous transformation of the general character of the radiolarian faunas took place. This transformation generally tended towards an increase of the surface area of the skeletons. We see trends within the following groups.

The Entactiniidae Riedel 1967 show two separate tendencies, one being a considerable lengthening of their spines, the other being a reduction of spine-number connected with a strong increase in size of the remaining spines.

The AlbaiUellidae Deflandre 1973 show a documentable change in the morphology of their cavea as well as their stapia.

The Latentifistulidae Nazarov and Ormiston 1983 evolve from ancestral narrow-rayed forms to broad-triradiate and triangular forms.

The "phacoid" forms of the group Sphaerodiscus Won 1983/Eostylodictya Ormiston and Lane 1976 show a pro- gressive overgrowth of the central shell by peripheral concentric rings and a simultaneous change in morphology from flat-discoidal to lensoid.

Introduction

Since the work of Won (1983) it has been known that the Early Carboniferous siliceous shales of the "Rheinisches Schiefergebirge", Germany (Fig. 1), contain unexpectedly rich radiolarian faunas some of which are very well preserved. Investigations initiated by Won, have been carried on during the last few years with the objective of investigating the evolution and biostratigraphy of Early Carboniferous radl- olarians by examining well dated faunas over a

longer stratigraphic range. Besides siliceous shales, phosphorite-concretions from several horizons as well as siliceous limestones have been processed to extract Radiolaria. In many cases phosphorite-concretions and siliceous shales contain very well preserved fossil mate- rial but the investigation of the siliceous lime- stones has yielded no radiolarian faunas.

For the following reasons the radiolarian ma- terial obtained is well suited for investigations on evolution and biostratigraphy:

(1) The faunas are very well and completely

0377-8398/90/$03.50 © 1990 Elsevier Science Publishers B.V.

352

150 km

100

50

0

Fig. 1. Geographic situation of the investigated area ( Rheinisches Schiefergebirge, Germany). 1. = Rheinisches Schiefergebirge 2. = Frankenwald.

preserved. This facilitates the determination of forms as well as the inclusion and consideration of the total faunal a~sociation in the interpre- tation of the evolutionary tendencies. This is particularly important because previous bio- stratigraphic work on Paleozoic radiolarian faunas focus on only one or few groups, ignor- ing the rest of the assemblage. The view that the consideration of the total fauna yields a far more complete picture of the evolutionary tendencies and that a far more detailed strati- graphic subdivision is possible by the combi- nation of different evolutionary lineages is also expressed by Nazarov and Ormiston (1988).

(2) The radiolarian faunas are generally cal- ibrated with known index-fossils (conodonts, calcareous Foraminifera). The conodonts are obtained with radiolarians in the HF-residue of the siliceous shales. Calcareous Foraminifera are found frequently near the base of graded beds of allodapic limestones (siliceous lime-

A. BRAUN

TABLE I

Combination of the evolutionary steps and tendencies of Early Carboniferous radiolarian taxa connected with an increa~ of the surface area of the skeleton

Taxon Increase of surface-area by

Entactiniidae Albaillellidae

Latentifistulidae

Lattice ring-forms

Enlargement and elongation of spines - Development of wing-like cavea projections - Increase in number and size of the apophyses of the stapia - Development of spines on cavea and stapia First appearance, big surface area by development of big triradiate skeletons First appearance, big surface area by development of a big discoidal skeleton

stones), which have been transported as tur- bidity currents from the shallower epicontinen- tal shelfs of the "Kohlenkalk"-platform in the NW into the depositional area of the siliceous mud. These limestones are intercalated be- tween the siliceous shales as beds of 1-10 cm thickness. The calcareous Foraminifera are particularly important in those parts of the "Kieselschiefer", in which conodonts are either absent or nondiagnostic.

(3) The radiolarian faunas come from a se- quence of sedimentary rocks which are undis- turbed over a large area and are easily distin- guished petrographically. The characteristic units are easily traced laterally and allow a rough age-determination in the field even in lo- calities lying in a relatively large distance from one another. Although it has not yet been pos- sible to get a complete sequence of faunas from one locality, the radiolarian faunas can help in- terpret evolutionary tendencies.

(4) The stratigraphic range in the Rhein- isches Schiefergebirge represented by well pre- served radiolarian faunas can be considerably extended beyond the range documented by Won (1983). It now extends in several well distin- guishable zones from the basal Pericyclus-stufe- Alpha (=base of the middle Tournaisian,

EVOLUTIONARY TRENDS OF RADIOLARIAN TAXA 353

h a Albaillella Ceraloikiscum

Pylel~tonema ~ / f~ e ~ Archoc~ rliUlU I'alacosceniditrm

J

~.-. ~ : ~

:n m inia J " ' ~ laleuiili~Luhl

Fig. 2. Combination of the most common radiolarian taxa of the Early Carboniferous; (d) redrawn from Deflandre (1963), (e) Drawn from a photograph in Nazarov, Cock- bain and Playford (1982), (g) redrawn from Nazarov and Ormiston ( 1983 ).

= upper half of the Kinderhookian) to the Vi- sean/Namurian boundary (Table II).

The investigation of radiolarian faunas from the Rheinisches Schiefergebirge allows the elimination of several gaps in fossil documen- tation and documentation of a refined morpho- logic progression in the different genera. Dur- ing the Early Carboniferous numerous morphologic groups simultaneously appear; they constitute significant faunal elements un- til at least the Late Permian period. Whether some of these groups are ancestral forms of the main groups in the Mesozoic remains an un- solved question (Nazarov and Ormiston 1985b). The origin of the innovations and tendencies mentioned in the text are unknown. Authentic ancestral or transitional forms have not been

7 a

Fin'st Albaifiellidae

b first discoidal, "latlice-ring"-ferms

c first stluraxon radiolaria

Fig. 3. Combination of the form-groups newly appearing in the Early Carboniferous; (b) redrawn from Won (1983), (c) redrawn from Nazarov and Ormiston (1983).

found (Fig. 2). The number of known and in- vestigated fossil radiolarian faunas from the Early Carboniferous is still small and accord- ingly the faunal sequence is incompletely known. Above all, the variable degree of pres- ervation, which is dependent on the lithology of the host rocks prevents any detailed strati- graphic examination. Lithological variations may result in good preservation of only one bed or concretion. Such strata provide a view of a rich community that may be overlain by many meters of strata where there is poor preserva- tion or no preservation at all. Therefore, the se- quence represented here still gives a relatively general picture. Preservation difficulties found by Riedel and Sanfilippo (1981) during the in- vestigations of evolutionary sequences in deep- sea-drilling cores, are consistent with the pres- ervational gaps in the Paleozoic. On the other hand, the possibility of an abrupt appearance of new radiolarian groups has to be taken into consideration (Fig. 3). Due to the limited knowledge of present-day reproductive pro- cesses, effects of mutations on the skeletal mor- phology, ecologic requirements and biogeo- graphic barriers, little is known about

354 A. BRAUN

evolutionary mechanisms in radiolarians. It is possible tha t new developed morphotypes could quickly spread out worldwide by ocean cur- rents. Long term changes of ecologic factors possibly facilitated the success of single mor- phologic innovations. With regard to the theo- retical predictability (reproduction, biogeog- raphy) as well as historical observability (preservational documentat ion gaps) several gaps thus remain unclosed. Many more discov- eries of new faunas are necessary to confirm or modify the evolutionary trends mentioned in this text. For the integration of the phyloge- netic trends of Early Carboniferous radiolarian faunas into the total evolution of this proto- zoan group during the Paleozoic refer to the ex- cellent presentation of evolution of Paleozoic radiolarians in Nazarov and Ormiston (1986a).

Phylogenetic Trends

Albaillellidae

The transit ional forms between the Ceratoi- kiscidae and the true albaillellids are traceable in the different species of Huasha Cheng 1986

and ProtoalbaiUella Cheng 1986 from the late Famennian to early Tournaisian of the Ouach- ita Mountains, U.S.A. The first true albaillel- lids are slender, acute conical, unsegmented forms (AlbaiUella paradoxa Deflandre Plate I, 1 ) in the range of Per icyc lus-S tu fe -Alpha of the German Kulm subdivision. This corresponds to the belgian Tn2 and the north-american late Kinderhookian/ear ly Osagean. Albaillellids subsequently constitute an important group as far as the number of individuals is concerned until the Permian. However as far as the num- ber of species is concerned, they never form a particularly significant group. Starting with the slender, early forms, the stapia as well as the cavea change their shape in a documentable way (for morphologic terms, see Won, 1983, pp. 122, 123).

In the early true albaillellids, (cf. Albaillella

paradoxa Deflandre 1952, Plate I, 1) a stapia with only one well expressed, basally directed spine-like projection is present (Fig. 4a). In younger species (Albaillella ladarezensis Gout- melon 1987 =Albaillella undulata Deflandre 1952 ) two approximately equally sized and ba-

PLATE I 1. AlbailleUaparadoxa Deflandre 1952. Upper part of the "liegende Alaunschiefer" of Am6nau (Rheinisches Schiefergebirge, Germany). Scale bar: 100 micrometers. 2. AlbailleUa indensis Won 1983. Well preserved specimen showing complete cavea and external stapia with small basal thorns. Upper anchoralis-latus-zone of Braunau (Kellerwald, Germany). Scale bar: 30 micrometers. 3. AlbaiUella cartaUa Ormiston and Lane 1976. Upper part of the Kieselschiefer (bilineatus-zone) of Wallau (Rheinisches Schiefergebirge, Germany). Scale bar: 30 micrometers. 4. Entactinia variospina Won 1983. Anchoralis-latus-zone, Frankenwald (Germany). (Braun and Schmidt-Effing 1988, Braun, 1989). 5. CaUeUa sp., showing the short, broadly pyramid-shaped spines. Upper anchoralis-latus-zone of Braunau (Kellerwald, Germany). Scale bar: 30 micrometers. 6. Entactinia tortispina ( Ormiston and Lane 1976 ). Upper anchoralis - latus-zone of Braunau (Kellerwald, Germany ). Scale bar: 100 micrometers. 7. Archocyrtium sp. showing the round pores with elevated rims. Upper anchoralis-latus-zone of Braunau (Kellerwald, Germany ). Scale bar: 30 micrometers. 8. Sphaerodiscus rota Won 1983. Upper anchoralis-latus-zone of Braunau (Kellerwald, Germany). Scale bar: 100 micrometers. 9-12. Synchronous sequence of Latentifistulidae from the higher parts of the Kieselschiefer (bilineatus-zone). 9. Latentifistula turgida (Ormiston and Lane 1976). 10. Latentifistula ruestae (Ormiston and Lane 1976). 11. Latentifistula plenospongiosa (Won 1983 ). 12. Latentifistula concentrica (Riist 1892 ). All specimens from Wallau (Rheinisches Schiefergebirge, Germany). Scale bar: 300 micrometers in fig. 9, 100 micrometers in figs. 10, 11, 12.

EVOLUTIONARY TRENDS OF RADIOLARIAN TAXA 3 5 5

P L A T E I

356 A. BRAUN

\

c \

~ b

j a Fig. 4. Chronologic combination of the stapia of different Early Carboniferous species of the genus AIbaiUella De- flandre 1952: (a) Albaillella paradoxa Deflandre 1952 (*middle Tour- naisian ); (b) AlbailleUa undulata Deflandre 1952 ( = la- darezensis Gourmelon 1987) (*middle Tournaisian, but beginning higher than AlbaiUella paradoxa); {c) Albail- leUa deflandrei Gourmelon 1987 (*Late Tournaisian ); (d,e) Albaillella indensis Won 1983 {*Late Tournaisian, but higher than AlbaiUeUa deflandrei ) ; (f) AlbaiUeUa cartalla Ormiston and Lane 1976 (*middle to Late Visean). ( * = beginning).

sally directed, spine-like apophyses are devel- oped (Fig. 4b). These apophyses, become slightly curved outwards in Albaillella deflan- drei Gourmelon 1987 (Fig. 4c). In younger forms the apophyses move upwards and side- ways on the stapia and may in extreme cases even move a distance upwards on the sides of the cavea. The number of the apophyses of the external stapia increases from 2 (AlbaiUella in- densis Won 1983, Plate I, 2) (Fig. 4d) to 7 (Al- baillella cartalla Ormiston and Lane 1976, Plate I, 3) (Fig. 4f). In well preserved specimens of AlbaiUella indensis the beginnings of such ad- ditional apophyses appear in the form of small, basal thorns between the lateral main apo-

~C

fta j Fig. 5. Chronologic combination of the caveae of different Early Carboniferous species of the genus AlbaiUella De- flandre 1952: (a) AlbailleUa paradoxa Deflandre 1952; (b) AlbaiUeUa cornuta Deflandre 1952; (c) Albaillella indensis Won 1983; (d) Albaillella furcata Won 1983; (e) AlbaiUeUa cartaUa Ormiston and Lane 1976.

physes (Fig. 4e). With Albaillella cartaUa an ex- treme-form, as far as the number and develop- ment of stapia apophyses are concerned, is finally attained. However, besides these forms, stapia types with 2 lateral apophyses still ex- isted (AlbailleUa ouachitaensis Cheng 1986) (cf. Fig. 7) and in the late Visean a reduction of the number of apophyses can more commonly be observed (Albaillella rockensis Cheng 1986) (cf. Fig. 6a).

The form of the cavea changes in the course of phylogeny from generally slender-acute con- ical to broad-triangular and bi-winged. Besides the simple unsegmented cavea of AlbailleUa paradoxa (Fig. 5a) forms with a more expressed undulation of the cavea wall (AlbaiUella undu- lata=Albaillella ladarezensis) and a lateral, spine-like projection (AlbailleUa cornuta De- flandre 1952; Fig. 5b) soon appear. AlbailleUa

EVOLUTIONARY TRENDS OF RADIOLARIAN TAXA 3 5 7

(]

Fig. 6. Different possibilities to increase the surface area in AlbaiUeUa-species from the Late Visean: l a) AlbaiUella rockensis Cheng 1986: bipennate, winged cavea, at the same time reduction of the number of basal apophyses of the stapia. I b ) AlbaiUeUa spinosa Cheng 1986: development of spines on stapia and cavea. Both specimens pyritized from phosphorite-concretions of the Upper Visean ( Goniatites-Stufe-Alpha ) of Wuppertal, Germany.

indensis also possesses this projection near the apex (Plate I, 2; Fig. 5c ). In this form however, the segmentation becomes stronger and the cavea strongly increases in width in the middle and basal part. This broad, inflated form of the cavea is also retained in younger stratigraphic levels (i.e., Albaillella furcata and AlbaiUella cartalla). In these forms a second winglike pro- jection on the opposite edge of the cavea is added to the primary one ofAlbailleUa indensis, so that the cavea becomes bipennate winged in its whole morphology (Fig. 5d, e). This bipennate form of the cavea prevails among the albaillellids during the late Visean at least until the basal Namurian [i.e., Albaillellapennata Holdsworth (1966), Albaillella rockensis Cheng (1986) ] and is also still important in the Permian (cf. Al- baiUella foremanae Cornell and Simpson 1985: Plate I, 1-3, cf. Pseudoalbaillella scalprata Holdsworth and Jones 1980 in Cornel l and Simpson 1985: Plate I, 5).

An innovation among the albaillellids of the

late Visean is the increasing of the surface area by the development of lateral spines on the cavea and stapia (Albaillella spinosa, Cheng 1986; Fig. 6b). These spine-like structures re- main important and widespread among the al- baillellids of the Permian (cf. Albaillella appor- recta Nazarov and Ormiston 1985a: pl. 6, fig. 6- 7 from the Early Permian of the South Urals; cf. AlbaiUella amplificata Nazarov and Ormis- ton 1985a: pl. 6, fig. 8, from the Late Carboni- ferous of the South Urals).

Latentifistulidae According to previous investigations three

and four rayed early forms of the mostly big and conspicuous polyaxon Radiolaria first appear in the upper part of the Scaliognathus anchoralis- Doliognathus-latus zone of the Kulm conodont subdivision. This corresponds approximately to the belgian early Visean la and the north- american middle Osagean. The radiolarians of this taxon show a quick development to a par-

358

Fig. 7. AlbaiUella ouachitaensis Cheng 1986, an example of stratigraphically younger species of AlbaiUeUa Deflandre 1952 possessing a stapia of the "indensis-type"; pyritized specimen from phosphorite-concretions of the Late Visean ( Goniatites-Stufe-Alpha ) of Wuppertal, Germany.

£ Fig. 8. Development of the external shape in the Latenti- fistulidae Nazarov and Ormiston 1983 in the higher parts of the Kieselschiefer of the Rheinisches Sehiefergebirge (Pericyclus-Stufe Delta): starting from narrow-rayed older forms (impella-group) a synchronous sequence of forms from narrow-rayed to triangular skeletons is developed.

ticularly multiform major group. The phyloge- netic and systematic connections between Early Carboniferous and Permian stauraxon Radi- olaria are still not reliably traceable, due to the rarity of Late Carboniferous material. Accord- ing to sparse evidence of Late Carboniferous

A. BRAUN

polyaxon radiolarians and many morphologi- cally similar Early Carboniferous and Permian forms, such phylogenetic connections are prob- ably present.

The initially rare early forms are followed by the conspicuous triaxon radiolarians in the lower Gnathodus texanus conodont zone. The more variable forms possessing only slightly concave to planar triangular sides are added in the upper texanus-zone (Sandberg and Gut- schick, 1984). In the higher units of the Kulm- Kieselschiefer of the Rheinisches Schieferge- birge (Pericyclus-Stufe-Delta) a synchronous sequence from narrow-triaxon to triangular forms can be found (cf. Won, 1983, Plate I, 9- 12; Fig. 8 herein). The triangular forms are considered to be the first Tormentidae Nazarov and Ormiston (1983) by Nazarov and Ormis- ton (1985b), a family playing an important role during the Permian.

Lattice-ring-forms A third important innovation among the

Early Carboniferous radiolarian faunas are the conspicuous, big and discoidal radiolarians, strongly reminiscant of the Coccodiscidae of Cenozoic radiolarian faunas in their external appearance. The first characteristic represent- ative of the lattice-ring-forms is Sphaerodiscus rota Won (1983), which first appears in sam- ples of the Scaliognathus anchoralis-Doliogna- thus-latus zone (correlation see Table II) to- gether with Albaillella indensis Won (1983) and the first latentifistulids. Starting with this still distinctly discoidal representative with a con- spicuous ring consisting of orthogonal meshes, a progressive overgrowth of the central skeletal sphere by the peripheral rings can be observed in younger forms. At the end of this phyloge- netic development are the phacoid skeleton forms of Eostylodictya Ormiston and Lane (1976) in which the overgrowth by the periph- eral rings is already relatively far advanced and in which the characteristic orthogonal mesh- structure is visible only in partly broken speci- mens. This development continues beyond the

EVOLUTIONARY TRENDS OF RADIOLARIAN TAXA 359

TABLE II

Correlation of different zonations of the Early Carboniferous as used in this paper.

u~-

o w - ,

Cephalopods 1

nasutus-

Zone

kochi-

Zone

p l i c a t i l i s -

corpolentum-

Zone

princeps-

Zone

crassa-

Zone

subinvoluta- Zone

Conodonts I

bil ineatus-

Zone

unnamed

interval

texanus- Zone

anchoralis-

latus-Zone

typicus- Upper

Zone Lower

isosticha-Upper crenulata-Zone

sandbergi-

Zone

sandbergi-

Zone

Upper duplicata- Zone

Lower

sulcata-

Zone

1After Clausen, Leuteritz and Ziegler, 1988.

Belgium 2

Warnantian

Livian

Molini~cian

Ivorian

Hastarian o

I

North America

Chesterian

Meramecian

O s a g e a n

Kinder-

hooRian

2After Paproth et al., 1983; Tournaisian-Visean boundary after Soo-in Park, 1983. 3After Sandberg and Gutschick, 1984. 4After Leuteritz, 1968.

Lithostratigr. (Germany)

Kulm-

Grauwacke

Kulm-Ton- schiefer

& k iese l ige Ober- gangsschichten

helle ( l ight )

Kiese]'sc/~efer

dunkle ( d a r k )

liegende

Alaunschiefer

Early Carboniferous at least until the Late Per- mian. Possibly, the final states of a separate trend may occur in the multishelled Entacti- niids of the Late Carboniferous and the Per- mian. These forms show a complete overgrowth of the central sphere by the peripheral rings, whereby the skeleton assumes a sphaeroidal shape (cf. Copycyntra Nazarov and Ormiston

1985a, Late Carboniferous-Early Permian; Co- pieUintra Nazarov and Ormiston 1985a, Middle Carboniferous-Early Permian and comparison of both genera with Eostylodictya in Nazarov and Ormiston 1985a). Discoidal as well as len- soid multishelled forms closely related to the Early Carboniferous taxa persisted until the Late Permian (cf. descriptions of Eostylodictya

360 A. BRAUN

t

a

Fig. 9. Progressive overgrowth of the central skeletal sphere by the peripheral rings in the genera Sphaerodiscus Won 1983 (a) Eostylodictya Ormiston and Lane 1976 (c) and Gedauia Won 1983 (b). The tendency goes from discoidal early tbrms (9a) to phacoid sceletons (9b,c). Fig. 9a-c: cross-sections, redrawn from Won (1983); Fig. 9d: three- quartier-view of a partly cut specimen of Eostylodictya Or- miston and Lane 1976, redrawn from Won ( 1983 ).

sp. A, B and Sphaerodiscus sp. in Sashida and Tonishi, 1985a, pl. 6) (Fig. 9).

Entactiniidae Compared to the radiolarian faunas of the

Middle through Late Devonian, Early Carbon- iferous Entactiniidae do not exhibit any con- spicuous innovations. The three-bladed main spines had been present as rigid weight-saving adaptations to the planktonic mode of life since the Middle Devonian and are predominant among the spine shapes of Late Devonian and Early Carboniferous sphaeroidal radiolarians. Forms with broad, massive cylindrical spines (for example see Astroentactinia? mirousi Gourmelon 1986, Plate II, 2) can rarely be found. As these massive spines are an almost exclusive characteristic of early Paleozoic ra- diolarians, the question arises in connection

with Astroentactinia? mirousi, whether these forms have retained their cylindrical spines since the early Paleozoic, or whether cylindrical spines can also arise secondarily through trans- formation of three-bladed spines. Beginning with the Late Tournaisian the entactiniids show a conspicuous tendency towards the prolonga- tion of the main spines. The long-spined forms already occur in faunas of Late Tournaisian age and dominate the entactiniid communities of the following periods in an ever increasing de- gree. In faunas of the Late Visean, long-spined forms can be found almost exclusively. These forms remain dominant during the Permian (for example Entactinia parapycnoclada Nazarov and Ormiston (1985a) (Fig. 10).

A further increase of the surface area is achieved in these long-spined forms beginning with the Late Visean, through the development of secondary spine-like apophyses extending laterally from the main spines (Fig. 11 ). Never- theless the development of such lateral apo- physes on the main spines does not appear for the first time in the Early Carboniferous. Na- zarov, Cockbain and Playford (1982) have identified such forms (described as Entactinia additiva? Foreman 1963 in Nazarov et al. (1982)) in the Frasnian of Australia. Between the occurrences in the Frasnian of Australia and the Late Visean of Wuppertal (West Germany) such lateral apophyses have not been found in any other Late Devonian or Early Carbonifer- ous faunas. It is possible that this lack is due to selective dissolution of these fine skeletal structures. However, the fact that these forms of spines are completely missing even in faunas characterized by a very complete preservation of fine skeletal elements does not favour this hypothesis. It is more probable, that this char- acteristic of additional lateral spines indepen- dently developed several times in response to ecological requirements. Such forms remain a characteristic and common faunal constituent in Late Visean through Permian faunas (for example, Entactinia pycnoclada Nazarov and

EVOLUTIONARY TRENDS OF RADIOLARIAN TAXA 361

PLATE II

1. Pylentonema sp. Stereopair. Specimen from the anchoralis-latus-zone of the Frankenwald (Germany). Scale bar: 100 micrometers. 2. Astroentactinia? mirousi Gourmelon 1986. Stereopair. Well preserved specimen from the anchoralis-latus-zone of the Frankenwald (Braun and Schmidt-Effing, 1988; Braun, 1989). Scale bar: 300 micrometers. 3. Ceratoikiscum umbraculum Won 1983. Stereopair of well preserved specimen from the anchoralis-latus-zone of the Fran- kenwald (Germany) ( Braun and Schmidt-Effing, 1988; Braun, 1989 ).

362 A. BRAUN

a Entactiniidae: 1) reduction of spine numbers enlargement of spines

2) lengthening and torsion of spines

Fig. 10. Predominant entactiniid-spine-forms in the higher parts of the Visean: ( a ) Development of few, sturdy outer spines (example: En tactinia variospina Won 1983). (b) Development of long, three-bladed outer spines, which are often twisted (example: Entactinia tortispina (Ormis- ton and Lane 1976).

Fig. 11. Lateral apophyses on the main spines of a Late Visean species of Entactinia Foreman 1963; pyritized speci- men from phosphorite-concretions of the Upper Visean (Goniatites-Stufe-Alpha) of Wuppertal, Germany ).

Ormiston 1985a: pl. 1, fig. 3, 5-6; Lower Per- mian of the South Urals) .

Broad, pyramid-shaped, short spines such as those of CaUella Won 1983 (Plate I, 5) seem to have been a comparatively short te rmed inno- vation. They are restricted to the lithologic units of the Pericyclus-Stufe-Beta. In the higher units of the "Kieselschiefer" no trace of them can be found. It is obvious, that such short spined forms could not succeed in a time in which, presum-

ably due to ecological changes, an increase of the surface area was necessary and advantageous.

G e n e r a l c o n c l u s i o n s

In the above mentioned trends in individual groups a general t rend in the morphologic de- velopment within the total Early Carbonifer- ous faunas can be seen: The tendency in the Albaillellidae and the Entactiniidae is dis- t inctly and almost exclusively towards a pro- longation of apophyses on the skeleton (spines, "wings"). In the same period of time the first development of broadly flattened radiolarian skeletons is observed (Latentifistulidae, Eos- tylodictya). These trends and innovations re- main significant in Permian faunas. The changes mentioned occur gradually and are not exactly simultaneous in all groups: - Long-spined Entactiniidae (genus tortispina- morphotype ) are already common in the upper Siphonodella crenulata-Siphonodella isosticha conodont zone of the Rheinisches Schieferge- birge, before the first lattice-rings forms and Latentifistulidae occur. - The first lattice-ring forms and Latentifistu- lidae in the Rheinisches Schiefergebirge occur somewhere in the upper par t of the Scaliogna- thus anchoralis-Doliognathus latus conodont zone. - Many of the observed changes in the Albail- lella skeleton (development of "wings", in- crease in number of apophyses on the external stapia, lateral spines on cavea) do not occur be- fore the bilineatus conodont zone. - The strong increase in abundance and diver- sity of Latentifistulidae in the Rheinisches Schiefergebirge is observed in sediments of the b ilineatus- zo n e.

However most of the above mentioned mor- phologic changes and their accelerated evolu- tion began within a relatively short time span in the Early Carboniferous. Origin and rate of evolution of such trends vary in different sys- tematic groups within certain limits. The con-

EVOLUTIONARY TRENDS OF RADIOLARIAN TAXA 363

spicuous difference in morphology between Middle Tournaisian and Late Visean radiolar- ian faunas is remarkable. In general morpho- logy the Late Visean faunas show a stronger similarity to Permian than to Tournaisian faunas.

Geologic observat ions

It is conspicuous in the sequence of the Kie- selschiefer of the Rheinisches Schiefergebirge that a change in predominant rock colours is observed in those units in which most of the morphologic changes and innovations take place. In contrast to the dark-grey to black col- ours due to finely disseminated pyrite and or- ganic substance in the lower part of the se- quence ["Alum shale", black Kieselschiefer (="Lydi tes" ) ], light green and red colours predominate in the higher units of the Kiesel- schiefer. Both colours reflect smaller contents of organic substances and pyrite in comparison to the lydites. Thus, due to this deficiency of organic substance, the production of H2S and consequently the production of pyrite did not appear even during continuous reducing con- ditions (green colours).

Discussion

The new developments of morphological characters among radiolarians in the Early Carboniferous along with the geologic obser- vations may point towards a widespread change of ecologic factors, which favoured the evolu- tion of skeletons possessing larger surface areas. The hypothesis of Nazarov and Ormiston (1985b), that ecologic variations accelerated the seemingly abrupt evolution of the polyaxon ra- diolarians of the Early Carboniferous, there- fore gets further support by the morphologic trends in other radiolarian groups. However very little is known about the nature of these processes.

It is possible, that the scarcity of food (phyto- and zooplankton) to some extent necessitated

an increase in the surface area of the radiolar- ian skeletons to aid the capture of organisms. The possibility of a general warming of the water also has to be taken into consideration in this connection. The viscosity of the water de- creases with increasing temperature which, for passively floating organisms, necessitates the increased development of floating projections. Such a general warming may be due to a change in seawater currents, which, by an intensified circulation and aeration may equally cause a change in rock colours. The tendencies and in- novations described above are observed world- wide at least in the equatorial climatic zone (faunas from higher latitudes are not known at present). Thus, in the search for reasons for this supra-regionally effective, long-term changes have to be considered.

Acknowledgments

The current project is supported by a grant from the Konrad-Adenauer-Stiftung. I wish to acknowledge the help of Prof. Dr. R. Schmidt- Effing (Marburg) and Dr. H.-J. Gursky (Mar- burg), as well as P. Noble, J. Aitchson and B. Murchey, who made helpful comments and cor- rections on the early version of the paper. Prof. Dr. R. Huckriede (Marburg), Dr. E. Paproth (Krefeld), Dr. D. Stoppel (Hannover) and E. Thomas (Wuppertal) kindly provided well pre- served material to study. The construction of the plates would have been impossible without the help of K. Fecher, B. Gehringer, J. Kitsch and K.-H. Petrat (all Marburg).

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