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New floral structure from the Lower Cretaceous of Lake Baikal area
Review of Palaeobotany and Palynology, 47 (1986): 9--16 Elsevier Science Publishers B.V., Amsterdam --Printed in The Netherlands
9
NEW FLORAL STRUCTURE FROM THE LOWER CRETACEOUS OF LAKE BAIKAL AREA
V.A. KRASSILOV Institute of Biology and Pedology, 690022, Vladivostok-22 (U.S.S.R.) (Received December 6, 1984; revised and accepted September 10, 1985)
ABSTRACT
Krassilov, V.A., 1986. New floral structure from the Lower Cretaceous of Lake Baikal area. Rev. Palaeobot. Palynol., 47 : 9--16. A new floral structure from the Balsa locality in the upper reaches of the Vitim River in Lake Baikal area is described as a gynoecium consisting of four ovulate appendages ("carpels") each bearing a single orthotropons ovule. It is supported and covered by linear-lanceolate bracts. The ovules contain Ephedripites pollen grains in the pollen chambers. This structure is compared with floral organs of gnetophytes and protoangiosperms. INTRODUCTION A l t h o u g h Baisa, a well k n o w n locality o f Early C r e t a c e o u s p l a n t s a n d i n v e r t e b r a t e s in t h e u p p e r r e a c h e s o f t h e V i t i m R i v e r east o f L a k e Baikal was e x p l o r e d r e p e a t e d l y , it is still c a p a b l e o f giving surprises. In 1 9 6 2 it y i e l d e d an a n g i o s p e r m - l i k e leaf, D i c o t y l o p h y l l u m p u s i l l u m V a c h r a m e e v ( V a c h r a m e e v a n d K o t o v a , 1 9 7 7 ) , in 1 9 7 9 p r o t o a n g i o s p e r m o u s Baisia (Krassilov a n d B u g d a e v a , 1 9 8 2 ) a n d in 1 9 8 3 a f a s c i n a t i n g floral s t r u c t u r e d e s c r i b e d below. T h e l a t t e r was f o u n d b y Dr. V.V. Z h e r i k h i n , a p a l a e o e n t o m o l o g i s t w h o c o n t r i b u t e d i m m e n s e l y t o o u r k n o w l e d g e o f t h e Baisian f a u n a a n d flora. A general d e s c r i p t i o n o f t h e locality is given in Krassilov a n d B u g d a e v a ( 1 9 8 2 ) . T h e n e w p l a n t fossil c a m e f r o m a m a r l b e d in t h e m i d d l e p a r t o f t h e section. SYSTEMATICS
Eoantha K r a s s i l o v g e n . n o v . N a m e : f r o m cos -- d a w n a n d a n t h o s -- f l o w e r (Gr.). T y p e species: E o a n t h a z h e r i k h i n i i Krassilov, sp. nov. Diagnosis: Floral s t r u c t u r e consisting o f f o u r o v u l a t e a p p e n d a g e s radial o n t h e axis w h i c h bears also linear-lanceolate b r a c t s b e l o w a n d a b o v e t h e
0034-6667/86/$03.50
© 1986 Elsevier Science Publishers B.V.
10 g y n o e c i u m . T h e ovulate appendages are wedge-shaped, showing a strong midrib and a n a s t o m o s i n g transverse ribs. The ovules are o r t h o t r o p o u s , o n e per appendage, showing a t h i n l y cutinised i n t e g u m e n t , free nucellus, and c o n s p i c u o u s l y granular megaspore m e m b r a n e . Polyplicate pollen grains o f the form-genus Ephedripites o c c u r systematically in the pollen chambers.
Eoantha zherikhinii Krassilov sp. nov. (Plate I, Plate II). Name: a f t e r Dr. V.V. Zherikhin. Diagnosis: as f o r t h e genus. Holotype: R e p o s i t o r y o f the Institute o f Biology and P e d o l o g y , N TB 15-600 (Plate I, 3).
Description: T h e r e are t w o impressions and their c o u n t e r p a r t s . In the h o l o t y p e (Plate I, 3, 4) the f o u r - p a r t e d g y n o e c i u m is spread rosette-like o n the bedding plane. It is a b o u t 4 m m wide. The appendages are wedgeshaped, a b o u t 1.6 m m long, 1.8--2 m m wide, slightly concave, b r o a d l y r o u n d e d at the distal end, t o u c h i n g or slightly overlapping their margins. T h e y seem flashy with a strong midrib appearing as a d e e p m e d i a n groove filled with coaly crumbs. Transverse ribs arise f r o m the m i d r i b at right angle, diverge slightly. T h e y are s o m e w h a t sinuous, showing i n f r e q u e n t forking and anastomosing. Grooves b e t w e e n the transverse ribs are sharp and narrow. Delicate longitudinal striation is seen u n d e r magnification. An ovule compression occurs o n one o f the appendages o c c u p y i n g its w h o l e width. It is s h o w n in Plate I, 4 intact and in Plate II, 1 cleared. A n o t h e r a p p e n d a g e retained a half o f t h e ovule split longitudinally (Plate II, 2). On t h e remaining t w o appendages, m i c r o p y l a r p o r t i o n s were f o u n d o n l y near the apices. Bracts spread radially a r o u n d the g y n o e c i u m . T h e y are linear-lanceolate, a b o u t 6 m m long, 0.8 m m wide at t h e base, a t t e n u a t i n g to the apex. Large p o l y g o n a l cells are seen on t h e bract impressions u n d e r low magnification. The bracts seem to underlie and overlap the g y n o e c i u m as if t h e y arised below as well as above it. The latter suggestion is c o n f i r m e d by a n o t h e r specimen in which the axis lies along the bedding plane (Plate I, 1, 2). T h e axis is relatively massive, 1 m m thick, with partially permineralised vascular tissue showing in SEM t r a c h e a r y elements with occasionally preserved p o r e s (Plate I, 6). The axis rises above the gynoecial n o d e at which o n l y o n e a p p e n d a g e is seen intact, PLATE I
Eoantha zherikhinii sp. nov. 1, 2. Side view showing a relatively thick axis, one of the gynoecial appendages and spirally arranged bracts, x 3 and x 8. 3, 4. Front view aspect showing narrow bracts and four gynoecial appendages, one of them (left) with an intact ovule, x 3 and x 8. 5. Same, after the ovule was removed. 6. Vascular tissue from the axis of the specimen shown in Fig.2 with tracheary elements showing vestiges of the pores (arrow), SEM, x 1200.
I
j~
Z
-?
MI
13
\\
~,,~
n~~
~ ~ ' "
"..:.~.'~. ~ , . , ~ . : ~ . ) < , •
:'~ ....... . , d ~
~,,_~; ~ '
Fig.1. E o a n t h a zherikhinii, spread on the bedding plane (above) and in side view. Large polygonal cells are seen on the lower bracts. Top right: rib pattern on the fertile appendages. Bottom right: pollen grains from the pollen chamber.
while the positions of the others are marked by lateral vascular bundles from the axis. Bracts arise obliquely below and above the gynoecial node giving the specimen a bushy appearance. The ovules are broadly obovate, obtuse, slightly concave at the chalazal PLATE II 1.
Macerated ovule from the specimen shown in Plate I, 3 (left appendage) showing a broad nucellus and a micropylar tube, x 70. 2. A half of the ovule from another appendage with ovules in the pollen chamber, × 70. 3. Pollen chamber and the nucellar beak of the same specimen, x 165. 4, 5. Pollen grains in the pollen chamber, different focuses, × 600. 6. Granular membrane within the nucellus, X 165.
14
Fig.2. Eoantha zherikhinii, reconstruction. end. Cleared ovule compressions show a single integument hardly more than 2 cells thick, thinly cutinised, forming a short micropylar tube about 112 #m long. The nucellus is broad, free to the base, showing elongate cells. Inside the nucellus there is a conspicuously granular megaspore membrane which extends up to the pollen chamber. The latter is low dome-shaped, with a vestigial beak. Pollen grains occur in the pollen chambers of two ovules scattered or in small clusters, seen in equatorial as well as polar aspects. All of them are of the same type, elongate-elliptical, about 50 X 25 mm, obtusely pointed, polyplicate with 7--8 distinct ribs converging at the poles. The exoexine appears clefted between the ribs (Plate II, 4, 5). DISCUSSION Though this plant is obviously gymnospermous as far as the mode of pollination is concerned, the gynoecial rosette surrounded by radially spreading bracts is flower-like. At the same time, projection of the bractbearing floral axis above the gynoecium suggests reduction from some kind of strobilar structure. The gynoecium consists of four appendages which can be compared with the bracts of Welwitschia supporting seed-scale complexes which look like
15
Fig.3. Eoantha zherikhinii, 1000.
pollen grains in the pollen chamber,
different
foci, ~800 and
winged seeds. However, in Welwitschia the bracts are strongly concave and the striation pattern is longitudinal and slightly divergent. It is very unlike the deep median groove and anastomosing transverse ribs of the fossil floral appendages. Due to the latter features they resemble opened follicles of some ranunculaceous angiosperms showing relief venation of the locule wall. This being the case, the ovules should be held within the opened follicles by their funicles as in some members of the Magnoliaceae. The pollen grain morphology indicates some relationships with gnetophytes. They correspond to the current concept of the pollen-genus Ephedripites which, according to Balme (1970), is distinguishable from Gnetaceaepollenites by better defined regular ribs and a generally denser exoexine which appears structureless or faintly granulate. Longitudinal clefts in the exoexine are described in Gnetaceaepollenites and extant Welwitschia. Hitherto pollen grains of this kind were not attributed to any macrofossils. They might have been produced by some Paleozoic pteridosperms and retained in extant gnetophytes as well as in the Mesozoic transitional forms. Gnetophytes of extant morphology are not known from the Mesozoic, though, in the present author’s opinion (Krassilov, 1982) the samaras of Hirmeriella bearing ovules enclosed within the cuticle-lined locules resemble corresponding organs of Welwitschia rather than any coniferous seed-scales with which they were conventionally compared. Plants with the Hirmeriellatype ovulate organs and Corollina (Classopollis) pollen grains might represent an extinct order of the gnetophytes. Eoantha is another candidate but its follicle-like gynoecial appendages suggest affinities with protoangiosperms or some transitional forms between them and gnetophytes. ACKNOWLEDGEMENTS
I thank Mrs. Claudia Novikova and Miss Svetlana Volotovskaya for technical help.
16 REFERENCES Balme, B.E., 1970. Palynology of Permian and Triassic strata in the Salt Range and Surghar Range, West Pakistan. In: B. Kummel and C. Teichert (Editors), Stratigraphic Boundary Problems: Permian and Triassic of West Pakistan. University Press of Kansas, Lawrence, Kans., pp. 305--453. Krassilov, V.A., 1982. On ovuliferous organ of HirmerieUa. In: D.D. Nautiyal (Editor), Studies on Living and Fossil Plants, Pant Comm. Vol. Phyta: 141--144. Krassilov, V.A. and Bugdaeva, E.V., 1982. Achene-like fossils from the Lower Cretaceous of the Lake Baikal area. Rev. Palaeobot. Palynol., 36: 279--295. Vachrameev, V.A. and Kotova, J.Z., 1977. Earliest angiosperms and associated plants from the Lower Cretaceous of Transbaikalia. Palaeontol. Zh., 4 : 1 0 1 - - 1 0 9 (in Russian ).
9
NEW FLORAL STRUCTURE FROM THE LOWER CRETACEOUS OF LAKE BAIKAL AREA
V.A. KRASSILOV Institute of Biology and Pedology, 690022, Vladivostok-22 (U.S.S.R.) (Received December 6, 1984; revised and accepted September 10, 1985)
ABSTRACT
Krassilov, V.A., 1986. New floral structure from the Lower Cretaceous of Lake Baikal area. Rev. Palaeobot. Palynol., 47 : 9--16. A new floral structure from the Balsa locality in the upper reaches of the Vitim River in Lake Baikal area is described as a gynoecium consisting of four ovulate appendages ("carpels") each bearing a single orthotropons ovule. It is supported and covered by linear-lanceolate bracts. The ovules contain Ephedripites pollen grains in the pollen chambers. This structure is compared with floral organs of gnetophytes and protoangiosperms. INTRODUCTION A l t h o u g h Baisa, a well k n o w n locality o f Early C r e t a c e o u s p l a n t s a n d i n v e r t e b r a t e s in t h e u p p e r r e a c h e s o f t h e V i t i m R i v e r east o f L a k e Baikal was e x p l o r e d r e p e a t e d l y , it is still c a p a b l e o f giving surprises. In 1 9 6 2 it y i e l d e d an a n g i o s p e r m - l i k e leaf, D i c o t y l o p h y l l u m p u s i l l u m V a c h r a m e e v ( V a c h r a m e e v a n d K o t o v a , 1 9 7 7 ) , in 1 9 7 9 p r o t o a n g i o s p e r m o u s Baisia (Krassilov a n d B u g d a e v a , 1 9 8 2 ) a n d in 1 9 8 3 a f a s c i n a t i n g floral s t r u c t u r e d e s c r i b e d below. T h e l a t t e r was f o u n d b y Dr. V.V. Z h e r i k h i n , a p a l a e o e n t o m o l o g i s t w h o c o n t r i b u t e d i m m e n s e l y t o o u r k n o w l e d g e o f t h e Baisian f a u n a a n d flora. A general d e s c r i p t i o n o f t h e locality is given in Krassilov a n d B u g d a e v a ( 1 9 8 2 ) . T h e n e w p l a n t fossil c a m e f r o m a m a r l b e d in t h e m i d d l e p a r t o f t h e section. SYSTEMATICS
Eoantha K r a s s i l o v g e n . n o v . N a m e : f r o m cos -- d a w n a n d a n t h o s -- f l o w e r (Gr.). T y p e species: E o a n t h a z h e r i k h i n i i Krassilov, sp. nov. Diagnosis: Floral s t r u c t u r e consisting o f f o u r o v u l a t e a p p e n d a g e s radial o n t h e axis w h i c h bears also linear-lanceolate b r a c t s b e l o w a n d a b o v e t h e
0034-6667/86/$03.50
© 1986 Elsevier Science Publishers B.V.
10 g y n o e c i u m . T h e ovulate appendages are wedge-shaped, showing a strong midrib and a n a s t o m o s i n g transverse ribs. The ovules are o r t h o t r o p o u s , o n e per appendage, showing a t h i n l y cutinised i n t e g u m e n t , free nucellus, and c o n s p i c u o u s l y granular megaspore m e m b r a n e . Polyplicate pollen grains o f the form-genus Ephedripites o c c u r systematically in the pollen chambers.
Eoantha zherikhinii Krassilov sp. nov. (Plate I, Plate II). Name: a f t e r Dr. V.V. Zherikhin. Diagnosis: as f o r t h e genus. Holotype: R e p o s i t o r y o f the Institute o f Biology and P e d o l o g y , N TB 15-600 (Plate I, 3).
Description: T h e r e are t w o impressions and their c o u n t e r p a r t s . In the h o l o t y p e (Plate I, 3, 4) the f o u r - p a r t e d g y n o e c i u m is spread rosette-like o n the bedding plane. It is a b o u t 4 m m wide. The appendages are wedgeshaped, a b o u t 1.6 m m long, 1.8--2 m m wide, slightly concave, b r o a d l y r o u n d e d at the distal end, t o u c h i n g or slightly overlapping their margins. T h e y seem flashy with a strong midrib appearing as a d e e p m e d i a n groove filled with coaly crumbs. Transverse ribs arise f r o m the m i d r i b at right angle, diverge slightly. T h e y are s o m e w h a t sinuous, showing i n f r e q u e n t forking and anastomosing. Grooves b e t w e e n the transverse ribs are sharp and narrow. Delicate longitudinal striation is seen u n d e r magnification. An ovule compression occurs o n one o f the appendages o c c u p y i n g its w h o l e width. It is s h o w n in Plate I, 4 intact and in Plate II, 1 cleared. A n o t h e r a p p e n d a g e retained a half o f t h e ovule split longitudinally (Plate II, 2). On t h e remaining t w o appendages, m i c r o p y l a r p o r t i o n s were f o u n d o n l y near the apices. Bracts spread radially a r o u n d the g y n o e c i u m . T h e y are linear-lanceolate, a b o u t 6 m m long, 0.8 m m wide at t h e base, a t t e n u a t i n g to the apex. Large p o l y g o n a l cells are seen on t h e bract impressions u n d e r low magnification. The bracts seem to underlie and overlap the g y n o e c i u m as if t h e y arised below as well as above it. The latter suggestion is c o n f i r m e d by a n o t h e r specimen in which the axis lies along the bedding plane (Plate I, 1, 2). T h e axis is relatively massive, 1 m m thick, with partially permineralised vascular tissue showing in SEM t r a c h e a r y elements with occasionally preserved p o r e s (Plate I, 6). The axis rises above the gynoecial n o d e at which o n l y o n e a p p e n d a g e is seen intact, PLATE I
Eoantha zherikhinii sp. nov. 1, 2. Side view showing a relatively thick axis, one of the gynoecial appendages and spirally arranged bracts, x 3 and x 8. 3, 4. Front view aspect showing narrow bracts and four gynoecial appendages, one of them (left) with an intact ovule, x 3 and x 8. 5. Same, after the ovule was removed. 6. Vascular tissue from the axis of the specimen shown in Fig.2 with tracheary elements showing vestiges of the pores (arrow), SEM, x 1200.
I
j~
Z
-?
MI
13
\\
~,,~
n~~
~ ~ ' "
"..:.~.'~. ~ , . , ~ . : ~ . ) < , •
:'~ ....... . , d ~
~,,_~; ~ '
Fig.1. E o a n t h a zherikhinii, spread on the bedding plane (above) and in side view. Large polygonal cells are seen on the lower bracts. Top right: rib pattern on the fertile appendages. Bottom right: pollen grains from the pollen chamber.
while the positions of the others are marked by lateral vascular bundles from the axis. Bracts arise obliquely below and above the gynoecial node giving the specimen a bushy appearance. The ovules are broadly obovate, obtuse, slightly concave at the chalazal PLATE II 1.
Macerated ovule from the specimen shown in Plate I, 3 (left appendage) showing a broad nucellus and a micropylar tube, x 70. 2. A half of the ovule from another appendage with ovules in the pollen chamber, × 70. 3. Pollen chamber and the nucellar beak of the same specimen, x 165. 4, 5. Pollen grains in the pollen chamber, different focuses, × 600. 6. Granular membrane within the nucellus, X 165.
14
Fig.2. Eoantha zherikhinii, reconstruction. end. Cleared ovule compressions show a single integument hardly more than 2 cells thick, thinly cutinised, forming a short micropylar tube about 112 #m long. The nucellus is broad, free to the base, showing elongate cells. Inside the nucellus there is a conspicuously granular megaspore membrane which extends up to the pollen chamber. The latter is low dome-shaped, with a vestigial beak. Pollen grains occur in the pollen chambers of two ovules scattered or in small clusters, seen in equatorial as well as polar aspects. All of them are of the same type, elongate-elliptical, about 50 X 25 mm, obtusely pointed, polyplicate with 7--8 distinct ribs converging at the poles. The exoexine appears clefted between the ribs (Plate II, 4, 5). DISCUSSION Though this plant is obviously gymnospermous as far as the mode of pollination is concerned, the gynoecial rosette surrounded by radially spreading bracts is flower-like. At the same time, projection of the bractbearing floral axis above the gynoecium suggests reduction from some kind of strobilar structure. The gynoecium consists of four appendages which can be compared with the bracts of Welwitschia supporting seed-scale complexes which look like
15
Fig.3. Eoantha zherikhinii, 1000.
pollen grains in the pollen chamber,
different
foci, ~800 and
winged seeds. However, in Welwitschia the bracts are strongly concave and the striation pattern is longitudinal and slightly divergent. It is very unlike the deep median groove and anastomosing transverse ribs of the fossil floral appendages. Due to the latter features they resemble opened follicles of some ranunculaceous angiosperms showing relief venation of the locule wall. This being the case, the ovules should be held within the opened follicles by their funicles as in some members of the Magnoliaceae. The pollen grain morphology indicates some relationships with gnetophytes. They correspond to the current concept of the pollen-genus Ephedripites which, according to Balme (1970), is distinguishable from Gnetaceaepollenites by better defined regular ribs and a generally denser exoexine which appears structureless or faintly granulate. Longitudinal clefts in the exoexine are described in Gnetaceaepollenites and extant Welwitschia. Hitherto pollen grains of this kind were not attributed to any macrofossils. They might have been produced by some Paleozoic pteridosperms and retained in extant gnetophytes as well as in the Mesozoic transitional forms. Gnetophytes of extant morphology are not known from the Mesozoic, though, in the present author’s opinion (Krassilov, 1982) the samaras of Hirmeriella bearing ovules enclosed within the cuticle-lined locules resemble corresponding organs of Welwitschia rather than any coniferous seed-scales with which they were conventionally compared. Plants with the Hirmeriellatype ovulate organs and Corollina (Classopollis) pollen grains might represent an extinct order of the gnetophytes. Eoantha is another candidate but its follicle-like gynoecial appendages suggest affinities with protoangiosperms or some transitional forms between them and gnetophytes. ACKNOWLEDGEMENTS
I thank Mrs. Claudia Novikova and Miss Svetlana Volotovskaya for technical help.
16 REFERENCES Balme, B.E., 1970. Palynology of Permian and Triassic strata in the Salt Range and Surghar Range, West Pakistan. In: B. Kummel and C. Teichert (Editors), Stratigraphic Boundary Problems: Permian and Triassic of West Pakistan. University Press of Kansas, Lawrence, Kans., pp. 305--453. Krassilov, V.A., 1982. On ovuliferous organ of HirmerieUa. In: D.D. Nautiyal (Editor), Studies on Living and Fossil Plants, Pant Comm. Vol. Phyta: 141--144. Krassilov, V.A. and Bugdaeva, E.V., 1982. Achene-like fossils from the Lower Cretaceous of the Lake Baikal area. Rev. Palaeobot. Palynol., 36: 279--295. Vachrameev, V.A. and Kotova, J.Z., 1977. Earliest angiosperms and associated plants from the Lower Cretaceous of Transbaikalia. Palaeontol. Zh., 4 : 1 0 1 - - 1 0 9 (in Russian ).