Review of Palaeobotany and Palynology, 53 (1987): 163-173 Elsevier Science Publishers B.V., Amsterdam — Printed in The Netherlands

A NEW ARCHAEOPTERIDALIEAN PLANT FROM THE DEVONIAN OF PAVLOVSK, U.S.S.R.

V.A. KRASSILOV, MARINA G. RASKATOVA and ALLA A. ISTCHENKO

Institute of Biology and Pedology, Vladivostok 690022 (U.S.S.R.) Voronezh University, Voronezh, 394693 (U.S.S.R.) Institute of Geological Sciences, Kiev, 252054 (U.S.S.R.)

(Received March 25, 1986; revised and accepted January 21, 1987)

Abstract

Krassilov, V.A., Raskatova, M.G. and Istchenko, A.A., 1987. A new archaeopteridalean plant from the Devonian of Pavlovsk, U.S.S.R. Rev. Palaeobot. Palynol., 53: 163-173.

Tanaitis furcihasta, gen. et sp. nov. is described from the lower Frasnian (lower Upper Devonian) of Pavlovsk in the upper reaches of the Don River (U.S.S.R.). Its fertile appendages and spores are similar to those of Archaeopteris while the sterile appendages are unwebbed as in aneurophytes. This plant might form a link between the Aneurophytales and Archaeopteridales.

Introduction Frasnian stages. There is a local unconformity between these stages, and the uppermost Give- It has been known for many years that tian is missing. The basal horizon resting on Devonian rocks of the Voronezh basin in the the Precambrian granitoids consists of sand- central part of the East-European platform are stones and sandy clays with abundant Oresto- rich in fossil plants. However, it is only very via and a few lycophytes and sphenophytes. recently that modern paleobotanical tech- The Frasnian sandstones above contain re- niques were applied to this material. A. Ist- mains suggestive of aneurophytes as well as chenko and T. Istchenko (1981) have described fragments of Orestovia. These beds grade thalloid spongiophytes, and the present paper upward into light-gray siltstones containing is the first account of a new vascular plant. Tanaitis, the taxon described here. Our material was collected in the large Pavlovsk Quarry near Pavlovsk — a small Tanaitis Krassilov, Raskatova et Ist- town in the upper reaches of the Don River chenko, gen. nov. south of Voronezh. The general stratigraphy of the area is given in Raskatova (1968). The Etymology, from Tanais, ancient greek name Devonian rocks are subdivided into a number for the Don River; tanaitis — an inhabitant of of horizons (lateral series of formations in the the Tanais banks, an amazon. Soviet stratigraphical classification) recogniz- able chiefly by their sporomorph contents. The Type species Tanaitis furcihasta, sp. nov. plant-bearing rocks exposed in the quarry are assigned to the upper Givetian and lower Diagnosis: Three-ranked branching system.

0034-6667/87/$03.50 © 1987 Elsevier Science Publishers B.V. spiral, three-dimensional. Proximal and distal at an acute angle, directed upward. Their axes parts of the branch system bearing sterile are 2 mm thick. In the available fragments of ultimate appendages, middle region with 5-6 the branch systems, probably distal, they pairs of fertile appendages. Sterile branchlets attain 40 mm in length, but there are unat- unwebbed, forking twice (once toward the tached sterile secondary branches, probably penultimate apex), showing no signs of dorsi- proximal which are more than 85 mm long ventral differentiation in epidermal charac- (Plate II, 3). Axes of the first and second order ters. Epidermis consists of fusiform inter- show longitudinal striation and transverse digitate cells, stomata widely scattered, bars perhaps caused by collapse of subepider- surrounded by weakly specialized subsidiary mal tissues. and encircling cells. Fertile appendages with Sterile and fertile penultimate branches do erect sporangia singly or in pairs except at the not differ in length. In the holotype (Plate I, 1) base and on the apical dichotomy. Fully sterile secondary branches occur above the developed fertile appendages fork unequally at fertile axes. At the same time there are larger the base giving off a short acroscopic arm sterile branches, seemingly proximal to the which dichotomize once or twice ending in fertile. Therefore it appears that both basal and sporangia. Mega- and microsporangia mixed apical parts of a branching system were sterile, on a fertile branchlet with the latter tending to while the sporangia-bearing branches were arise more distally. Megasporangia larger than confined to the middle region. Neither of the microsporangia. Micro- and megaspores are penultimate branches can be defined as com- homomorphous but related about 1:10 in diam- pletely fertile because even those of them which eter and dimensions of the sculptural elements. bear fertile ultimate branchlets have also a few pairs of sterile ultimate branchlets at the base. Tanaitis furcihasta Krassilov, Raskatova et In the middle region of a branching system Istchenko, sp. nov. where the penultimate branches are about 40 mm long they bear two pairs of proximal Etymology: from furca — a fore and hasta — a sterile branchlets followed by five or six pairs of spear, referring to the shape of appendages, as fertile branchlets including an apical fork of the in Plate III, 4. penultimate axis. The branchlets are helically Holotype: Repository of the Institute of Biology arranged at an acute angle to the axis, alternate and Pedology, NDP1-1 (Plate I, 1). or subopposite, more crowded toward the apical Locality: The Pavlovsk Quarry near Pavlovsk, fork. Many branchlets overlap each other and upper reaches of the Don River, U.S.S.R. some are directed at an angle to the bedding Age: Lower Frasnian (lower Upper Devonian). plane piercing the rock matrix and/or showing Description: Remains of Tanaitis are confined the base twisting. Based on these observations to a siltstone bed few centimeters thick. They it is suggested that the penultimate branch are fragmentary compressions which easily system was three-dimensional. break into small blocks. The matrix is fragile The sterile branchlets are oblique to the and it is difficult to obtain fragments more than secondary axis, decurrent, 11-15 mm long, 15 cm long. The most complete specimens are 1 mm thick at the base, typically forking twice three-ranked branching systems (Plate I, 1). into thin pointed lobes. In the distal part of a The axis designated as primary is 3 mm thick secondary branch the branchlets fork once or

PLATE I

Tanaitis furcihasta 1. Sterile three-ranked branching system, x 2. 2. Three-ranked branching system showing sterile (above) and fertile penultimate branches, holotype, x 2.

Tanaitis furcihasta 1, 2. Penultimate branches bearing fertile appendages and a few sterile ones at the base, x 3. 3. Sterile penultimate branches, x 1. 4. Tattered sterile appendages, x 3. Tanaitis furcihasta 1, 2. Fertile appendages showing two kinds of sporangia, the bulkier ones are megasporangia, x 7. 3. A fertile appendage showing dichotomy of a short basal arm, x 7. 4. Lobes of a sterile appendage, x 7. one of the arms may fork again. Two apical a characteristic interdigitate pattern (Plate VI, pairs of branchlets seen in one of the penulti- 2) which is often met in modern ferns, but mate axes on Plate II, 3 are simple. Some sterile virtually unknown in gymnosperms. Stomata branchlets appear tattered as in Plate II, 4. are widely scattered, longitudinal, elliptical, The cuticle of the sterile branchlets is about 50 /urn long. The guard cells are not delicate and shows distinctly marked fusiform, sunken, nor thickened around the aperture. often kneed cells about 100 fim long which form Guard cells are surrounded by 5-6 fusiform cells the lateral of which (or only one of them) size differences are rather slight, they permit surround the stoma. Lateral cells of up to three predictions of the sporangial contents. There adjacent rows are vaguely encircling. Apart are about seven sporangia per fertile axis of from the bending, a peculiar specialization of which a few basal ones are megasporangia the subsidiary and occasional encircling cells while the proximal can be either mega- or is manifested in cuticular features: in SEM microsporangia. these cells appear smooth while the ordinary Macerated sporangia show narrow fusiform cells are coarsely pitted (Plate IV, 1). There are cells in longitudinal rows. No specializations no signs of dorsiventral differentiation in the for dehiscence were observed. Mega- and epidermal structure while strong folds on the microspores never mix in one sporangium. cuticle suggest flattening by compression. The Megaspores are about 16 per sporangium, cuticle of the terminal lobes is delicate, some- 200-350 /.im in diameter, with an inner body what stronger on one side than on the other — about one half of the diameter. The amb is a differrence most probably related to preser- rounded-triangular, the trilete rays extend vation. Stomata are scarce on both sides. almost to diameter. They are simple, raised, Vascular elements with spiral thickenings straight, slightly expanded when crossing cur- were occasionally macerated from the sterile vaturae and on the ends (Plate VI, 1, 2). appendages so that there is little doubt about Contact areas are bound by curvaturae which them being vascularized (compare with the more or less coincide with the contour of the situation in Aneurophyton described in Serlin inner body. The sculpture consists of thin, and Banks, 1978). partially fused baculi on contact areas and of Fertile branchlets are attached at a some- much stouter coni about 10 /im long on curva- what more open angle than the sterile. They turae and the rest of the surface. Endexospo- are recurved at the base and incurved at the rium, exposed by peeling off the outer layer apex, typically 12 mm long. They bear sporan- (Plate VII, 1, 2), is similarly sculptured. gia acroscopically along two thirds their Microspores are rounded, about 37-42 ¿mi in length, while a basal portion and the apical diameter. Trilete rays are simple, straight, fork are sterile. Sporangia are upright except slightly raised, extended to about 4/5 of the on the apical pair of branchlets where they spore radius (Plate V, 3). Contact areas are point downward — a possible joint effect of the smooth or slightly scabrate. The rest of the branchlet twisting and compression. surface is sculptured with dense cones and Arrangement of sporangia on the fertile axis granules. poses a problem because most of them overlap each other as well as sporangia of the adjacent Discussion fertile axes. After much scrutiny we became convinced that sporangia attached by a short Fertile branchlets of this new plant show a stalk arise singly or in pairs (Plate III, 1-3). In general archaeopteridalean aspect (Phillips more developed fertile branchlets a short etal., 1972) while its sterile branches are acroscopic arm is produced by unequal basal unwebbed, isolateral as to the distribution of dichotomy. This basal arm forks once or stomata, and less leaf-like than in Archaeop- occasionally twice, ending in two or occasion- teris. They are more like the ultimate appen- ally three sporangia (Plate III, 3). dages in the Aneurophytales. Hence we sug- Sporangia are elliptical, pointed, about 2 mm gest for Tanaitis an intermediate position long including a stalk about 0.3 mm long. Two between the progymnospermous orders of modes of their width are 1 mm and 0.6 mm. It Aneurophytales and Archaeopteridales. This was ascertained by maceration that the larger plant shows also a mosaic evolutionary devel- sporangia contain megaspores while the nar- opment of organs: while its putative leaf rower ones are microsporangia. Though the percursors were still in primitive state, the Tanaitis furcihasta 1. Stomatal apparatus showing smooth cells in contrast to the coarsely pitted outer walls of the surrounding cells, SEM, x 1000. 2. Interdigitate pattern of epidermal cells, SEM, x 300. Tanaitis furcihasta 1, 2. Spore contents of the micro- and megasporangia, SEM, x 100. 3, 4. Microspores from fig.l, one of them in proximal view, SEM, x 400 and 1500. Tanaitis furcihasta 1. 2. Megaspore, smaller than average, showing inner body (mesosporium) and the inner layer (endexosporium) of the outer wall exposed by peeling off the outer layer (ectexosporium) seen in Plate VII, SEM, x400 and 600. Tanaitis furcihasta 1. Outer layer (ectexosporium) peeled off a megaspore shown in Plate V, SEM, x 600. 2. The same, sculpture in the region of a curvature, x 2000. fertile parts have reached the most advanced from the Upper Devonian of Uralo-Volgian state known among archaeopterids. area as Archaeopteris acuta Tschirkova-Zaless- There are also some noteworthy deviations kaya (1957). It differs from T. furcihasta in from the archaeopteridalean archetype in the somewhat broader sterile appendages and construction of fertile appendages. At least much larger sporangia. This plant may belong some of them fork unequally at the base in Tanaitis, but neither the arrangement of its producing a short acroscopic arm reminiscent sporangia nor their spore contents are known. of the fertile branchlets of Milleria (Protopteri- The same is true for some other branching dium), Tetraxylopteris (Bonamo and Banks, systems with terete terminal lobes described by 1967) and other aneurophytes, while a pair of Kryshtofovich (1939) and Schmalhausen (1984). apical fertile appendages are almost lyre- Fossil wood fragments up to 5 cm in diameter shaped and resemble those of Aneurophyton, found in association with Tanaitis may suggest especially the "atypical" form (with inverted a small tree or shrub. It seems to be a dominant sporangia) discussed in detail by Serlin and plant on swampy lowlands in the earliest Late Banks (1978). The alternation of sterile and Devonian time. fertile regions in Tanaitis is like in Psilophyton dawsoni (Banks et al., 1975) although the References branching of fertile appendages is much re- Andrews, H.N. and Gensel, P.G., 1975. A new fossil plant of duced in comparison with trimerophytes and probable intermediate affinities (Trimerophyte — even Oocampsa, which is considered intermedi- Progymnosperm). Can. J. Bot., 53: 1719-1728. ate between trimerophytes and progymno- Andrews, H.W., Gensel, P.G. and Forbes, W.H., 1974. An sperms (Andrews and Gensel, 1975). apparently heterosporous plant from the Middle Devo- nian of New Brunswick. Palaeontology, 17: 387-408. Heterospory is not confined to Archaeopteri- Banks, H.P., Leclerq, S. and Hueber, F.M., 1975. Anatomy and morphology of Psilophyton dawsonii, sp.n. from the dales (Andrews et al., 1974) but is more common Late Devonian of Quebec (Gaspe'), and Ontario, Canada. in this order than in more primitive groups. The Palaeontogr. Am., 8: 77-127. heterospory of adjacent sporangia character- Bonamo, P. and Banks. H.P., 1967. Tetraxylopteris schmid- istic of Tanaitis was hitherto demonstrated in a tii: its fertile parts and its relationships within the Aneurophytales. Am. J. Bot., 54: 755-768. single specimen provisionally assigned to Ar- Istchenko, T.A. and Istchenko, A.A., 1981. Middle Devo- chaeopteris cf. jacksonii (Pettit, 1965). Size nian flora of the Voronezh anticlise. Naukova Dumka, differences have been noted between the mega- Kiev, 1981, 110 pp. (in Russian). and microsporangia found in association with Kryshtofovich, A.N., 1939. Upper Devonian plants from the Timan Tundra. Sci. Mem. Leningrad Univ., Ser. Soil- A. latifolia, but not in the supposedly con- Geol., 5: 203-205 (in Russian). specific A. hibernica. Phillips et al. (1972) have Pettit, J.M., 1965. Two heterosporous plants from the found no reliable correlation between the Upper Devonian of North America. Bull. Br. Mus. Nat. dimensions of sporangia and their spore con- Hist. (Geol.), 10: 83-92. Phillips, T.L., Andrews, H.N. and Gensel, P.G., 1972. Two tents in several heterosporous Archaeopteris. hetero-sporous species of Archaeopteris from the Upper Micro- and megaspores of Tanaitis furci- Devonian of West Virginia. Palaeontographica, 139B: 47-71. hasta are essentially similar to those of Raskatova, L.G., 1968. Spore-pollen complexes from the Archaeopteris (Phillips et al., 1972). The mega- Middle and Upper Devonian in the south-eastern part of spores correspond to the form-genus Bihari- the Central Devonian Field. Voronezh Univ., Voronezh, sporites Potonie. They show an inner body, or 166 pp. (in Russian). mesosporium and their outer wall, or exospo- Schmalhausen, J., 1984. Uber Devonische Pflanzen aus dem Donetz-Becken. Mem. Comm. Geol. St-Petersb., 8: 1-36. rium is easily separable into two layers — Serlin, B.S. and Banks, H.P., 1978. Morphology and anatomy ectexosporium and endexosporium (which of Aneurophyton, a progymnosperm from the Late Devo- shows incidentally that mesosporium is not nian of New York. Palaeontogr. Am., 8: 343-359. formed of nexine in this case), similarly Tschirkova-Zalesskaya, E.F., 1957. Division of the terrige- nous Devonian in the Uralo-Volgian area based on fossil sculptured and marked by curvaturae. plants. Acad. Sci. U.S.S.R. Press, Moscow, 136 pp. (in A plant of the Tanaitis aspect was described Russian).