- Email: [email protected]
Araucariaceae as indicators of climate and paleolatitudes
Review of Palaeobotany and Palynology, 26 ( 1 9 7 8 ) : 1 1 3 - - 1 2 4
113
© Elsevier Scientific Publishing C o m p a n y , A m s t e r d a m - - P r i n t e d in T h e N e t h e r l a n d s
A R A U C A R I A C E A E AS INDICATORS OF CLIMATE A N D PALEOLATITUDES
V A L E N T I N A. K R A S S I L O V
Institute of Biology and Pedology, Vladivostok 22 (U.S.S.R.) ( A c c e p t e d for p u b l i c a t i o n J a n u a r y 10, 1 9 7 8 )
ABSTRACT Krassilov, V.A., 1978. A r a u c a r i a c e a e as i n d i c a t o r s o f c l i m a t e a n d p a l e o l a t i t u d e s . Rev. P a l a e o b o t . Palynol., 26: 1 1 3 - - 1 2 4 . Mesozoic A r a u c a r i a c e a e d o m i n a t e d in t h e l o w - l a t i t u d e ( 1 5 - - 2 0 ° N) belt o f s u m m e r - d r y climate. It is suggested, t h a t a r a u c a r i a n forests were t h e m o s t t h e r m o p h i l o u s Mesozoic assemblages. T h e r e were n o e q u i v a l e n t s o f t h e m o d e r n t r o p i c a l rain forest. In t h e m i d d l e latitudes, A r a u c a r i a c e a e s h a r e d d o m i n a n c e w i t h Elatides a n d Classopollis-producing plants. T h e n o r t h e r n m o s t Triassic records o f A r a u c a r i a c e a e o n b o t h e a s t e r n a n d w e s t e r n Pacific coasts are at 35 ° N; in t h e Jurassic a n d C r e t a c e o u s t i m e t h e y are c o n s t a n t l y at a b o u t 50 ° N. These climatically c o n t r o l l e d chorological f e a t u r e s are o b l i q u e to t h e p a l e o l a t i t u d e s i n f e r r e d f r o m p a l e o m a g n e t i c data. On t h e basis of m a t e r i a l f r o m t h e Jurassic o f Mali, a n e w species o f Araucaria is described, viz. Araucaria africana sp. nov.
INTRODUCTION
I contribute this paper in appreciation of Dr. Jonker's broad interest in paleoclimatology. The usefulness of pre-Quaternary plants as climate indicators is questionable because their tolerance cannot be safely deduced backward from that of their extant relatives and because intrinsic evidence of their geographic distribution is also ambiguous due to changing position of continents. Some paleobotanists are ready to accept paleomagnetic maps, while paleomagnetologists seek arrangements compatible with paleobotanical and other biological evidence. With this in mind, I considered the distribution of Mesozoic Araucariaceae. Their absence from the temperate Arctomesozoic (Siberian) province, in contrast with fairly numerous records elsewhere, is the primary evidence of climatic control and potential utility as climate indicators. Araucarian remains in my collection came from the Jurassic and Cretaceous localities in the Far East (Tyrma, Mongolia, Primorye, Sakhalin, Amur province) and also from equatorial Africa.
114 DISTRIBUTION IN MODERN COORDINATES The most important features of paleophytogeography are in descending order (1) abundance, (2) limits of distribution, and (3) diversity. While 1 is defined objectively, 2 is biased by imperfection of record and 3 depends on taxonomic judgements. The largest Triassic locality is the famous araucarian fossil forest of Arizona. Typical cone scales were recorded as far north as Greenland (Araucarites charcotii Harris) and Taimir (A. migayi Shvedow). On the Pacific coast, araucarian woods and other remains are known from Tonkin (Araucarioxylon zeilleri Grie) and Japan (A. sidugawaense Shimakura), while they are lacking in the rich fossil-plant localities near Vladivostok (Primorye). The northern boundary of floras with Araucariaceae on both the Asiatic and the American coasts of the Pacific (South Japan and Chile) is at about 35°N. Jurassic Araucariaceae are described from many localities, but the In-Eserin locality in the variegated Jurassic beds of the Mali--Nigerian depression in Africa is unique in its abundance of araucarian remains contrasting with a scarcity of other megafossils. Plant compressions were obtained from bore holes by bulk maceration of calcareous shales with HC1 and HF. They are mostly isolated leaves (about 100 specimens), but also wood fragments, branchlets, microstrobili with pollen grains and cone scales, all attributed to a single species of Araucaria. Earlier, I published a preliminary description of this unnamed species, (Krassilov, 1977). Now I propose the new name Araucaria africana for it.
Araucaria africana sp.nov. (Plate I--III) Diagnosis: Ultimate branchlets 1--2 mm thick. Scale-leaves imbricate, appressed or spreading. Leaf cushion rhomboidal or obovate, tapering downwards, about 3--4 mm long. Free portion clearly delimited from their base cushions, much shorter than the cushions or of equal length, triangular in section, incurved, blunt or shortly pointed or linear--lanceolate, flattened, mucronate, up to 5 mm long (average length 1.5--3 mm). Cuticle thick, showing marginal zone of narrow thin-walled, slightly sinuous cells and central zone of rectanguloid thick-walled cells, about 50-60 X 24--30 pm (80--90 X 22--25 pm in longer leaves), arranged in short rows. Cells usually papillate. Stomata on both sides of the free portion and
PLATE I
Araucaria africana sp. nov. from Mali 1. 2. 3. 4. 5.
Shoot showing scale-leaves, holotype (x 25). Leaf with its leaf-base cushion (x 25). Stoma showing fine striation of subsidiary cells (x 330). Distribution of stomata, SEM (x 300). Inside view of stomatal pit and slightly sunken subsidiary cells, SEM (X 1600).
i~"~
~
~i~,~~
~
,_...
~~
~.~
~L ~L
116
on the leaf-base cushion. Average leaves show 50--60 abaxial stomata distributed all over the surface except the marginal zone. Adaxial stomata fewer, concentrated in the lower portion of a leaf. In some linear--lanceolate leaves adaxial stomata more numerous than the abaxial ones. Stomata in short rows or scattered. Those in rows mostly transverse or longitudinal, while oblique orientation predominates among scattered stomata. Subsidiary cells usually five, radially arranged, slightly sunken, finely striated, conspicuous due to their lighter colour, forming stomatal pit with thickened border. Stomata elliptical, about 60 p m long, with T-shaped polar thickenings. Microstrobili rounded, diameter about 2.5 mm, scales obcuneate, 0.8 mm long, imbricate, bearing about 10 oval pollen sacs. Pollen grains spherical, diameter about 25 t~m, exine thin, smooth, often folded. Scales of megastrobili winged, with densely papillate cuticle. Papillae conical or cylindrical in the middle part of adaxial surface, rounded near the margin. Stomata scattered, as in leaves, but subsidiary cells less conspicuous. Holotype: IE-44; Collection of the Institute of Biology and Pedology. Type locality: Mali--Nigerian depression, In-Eserin borehole, 337--339 m. Shoots of A. africana are comparable with Pagiophyllum peregrinum (Lindley et Hutton) Schenk from the British Lias as well as Brachyphyllum tropidimorphyrn Wesley, Pagiophyllum rotzoanum Wesley and P. valdassense Wesley from the Grey Limestones of Veneto. The latter species is especially similar in cuticular characters (Wesley, 1956), though papillae are lacking. I believe that close resemblance between African and Venetian conifers has some bearing on the problem of Afro-Italian land connections in the Jurassic (see Hs[i, 1971). The In-Eserin locality suggests a lowland araucarian forest. Association of shoots, leaves and cones rules out the possibility of a long-distance transportation. The facies are similar to those of the Triassic araucarian forest in Arizona. Other low-latitude Jurassic localities -- Oaxaca in Mexico (Wieland, 1914), Kutch in India (Pant and Srivastava, 1968) and Phu Kadung in Thailand (Iwai et al., 1975) -- are also found in variegated or red-bed facies. They show that the araucarian forest was a dominant plant formation in the low-latitude belt of a summer-dry climate. In middle latitudes, abundant araucarian fossils -- cone scales, shoots of
Pagiophyllum and Brachyphyllum types -- are described from the Jurassic and Early Cretaceous localities of the eastern U.S.A. (Potomac), Portugal, France, Italy, Caucasus, Middle Asia and southern Kazakhatan (Karatau). In these PLATE II
Araucaria africana sp. nov. from Mall 1. 2. 3. 4. 5.
Inside view of a stoma, SEM (x 1600). Guard cells, one of the T-shaped polar thickenings is preserved, SEM (× 1600). Leaf cuticle showing stomata (× 25). Very short leaf spreading from its leaf-base cushion (× 25). Cleared leaf showing stomata on the leaf-base cushion (× 25).
/
..........
l
,
....
....1
~'~~ ~ i ii !!~!i¸ i i:
~
L
119 localities, Araucariaceae are next in abundance to the taxodiaceous conifers of the Elatides group and Classopollis-producing plants. Assemblages of this t y p e can be traced to the east in Mongolia and Primorye. The Mongolian Mesozoic flora was hitherto scarcely k n o w n , but recently the paleontologists A.G. P o n o m a r e n k o and V.N. Yakovlev have discovered structurally preserved plant material as a b y - p r o d u c t of their search for fossil insects and fishes. The Araucaria on Plate IV, 1--4 came from the Shin-Khuduk and Bon-Tsagan localities of Early Cretaceous age. There are branching shoots with spirally arranged scale leaves which are crescent-shaped, carinate, and provided with a single adaxial band of fairly crowded, irregularly orientated stomata. Ovuliferous cones are elliptical, rather small. Split cones show seeds e m b e d d e d in the scales with relatively thick apophyses. In the Lower Cretaceous of South Primorye (near Vladivostok), Araucariaceae are represented by c o m m o n Araucarites with Brachyphyllum-type foliage and also by two genera with bifacial pluri-nerved leaves, viz. Araucariodendron and Ussuriocladus (Krassilov, 1967). In Araucariodendron, stomata are in intercostal bands, longitudinally orientated, amphicyclic. Cone scales are small, wingless, consisting of completely fused bracts and ovuliferous scales, bearing one or two e m b e d d e d ovules. Patagonian localities may represent the Southern Hemisphere c o u n t e r p a r t of the Araucariaceae--Elatides--Classopollis belt. Conifers from these localities are n o w much bet t er unde r s t ood due to the excellent work of Stockey (1975). The Jurassic Araucariaceae have been recorded from Grahamland, and the southern limit of their distribution is not known. In the Northern Hemisphere, their numerical representation decreases towards the nort hern limits of the Araucariaceae--Elatides--Classopollis belt. The Yorkshire (Araucarites estonensis Kendall) and Ukrainian records are evidently situated near the boundary, since t h e y are lacking from the Jurassic of Greenland, Bornholm and Sweden. In Asia, no araucarian remains are known from the Arctomesozoic, or Siberian province dom i nat ed by deciduous Phoenicopsis forests (fossil woods of Araucariopitys described from various nort hern localities are now transferred to Protocedroxylon). The n o r t h e r n m o s t records are from the T y r m a River, a tributary of the Bureja, at about 50 ° N. Araucaria is a new element in the T yr m i a n flora studied by Seward, Novopokrovsky, Kryshtofovich and other authors. It is represented, mostly in the products of bulk maceration, by small fragments of shoots, isolated PLATE III
Araucaria africana sp. nov. from Mali 1. 2. 3. 4. 5. 6.
Wing-like extension of a bract (x 10). Papillate bract cuticle (× 130). Microstrobilus (x 25). Several cleared pollen sacs borne on a microsporophyll (× 130). Tetrad from a pollen sac (x 660). Pollen grain, SEM (× 3500).
120
PLATE IV
121 leaves and a single cone scale (Plate IV, 5--7). There are also numerous pollen sacs, y et unassigned, but probably belonging to this plant. The scale-leaves are spreading, straight or h o o k e d , about 3.5 mm long, fringed by dense microscopic hairs. S tom at a are on the adaxial side only, scattered, orientated along the cell rows or somewhat oblique. The cone scale is sammara-like, 5 mm wide, with broad ligule and median groove. Cuticle is thickened in the median portion, where a seed was embedded. Cuticular characters are like those of the leaves. The latest Jurassic or Berriasian flora of T y r m a is ecotonal between the Phoenicopsis and Cycadeoidea provinces (Krassilov, 1972) and contains such southern plants as Klukia and Pachypteris. In the Late Cretaceous, Sequoia replaced Elatides and ot her archaic Taxodiaceae in the middle latitude coniferous forests, while Araucariaceae maintained their position and were still c o m m o n in eastern U.S.A. (Raritan), Bohemia, Caucasus and Kazakhstan. "Damrnara" or "Darnmarites" have been o f ten q u o t e d from higher latitudes (e.g., from West Greenland), but in my opinion th ey have nothing to do with the Araucariaceae (in fact, most of t h em are isolated cone scales of Sequoia). In eastern Asia, the n o r t h e r n m o s t records are from the Tsagajan beds of the Amur province (Danian) and northern Sakhalin (Senonian), bot h at about 50 ° N. Araucarites pojarkovae (Plate V, 5--7) from Tsagajan has cylindrical shoots with imbricate obovate leaves ab o u t 11--13 X 10--11 mm. Megastrobili are globose, about 20 mm in diameter, scales obcuneate, lingulate, indehiscent, with a rather long awn and vestigial wings (Krassilov, 1976a). This species is related to the section Columbea, now restricted to South America. Araucaria from Sakhalin also resembles e x t a n t species of Columbea, but the stomatal structure is very peculiar. Each stoma is provided with a stout process overhanging the stomatal pit (Plate V, 1--4). Such unique characters, together with outstanding versatility of the Early Cretaceous Araucariaceae from Primorye (see above) suggests the Pacific region as an area of primary diversity of this group. On the American coast, Araucaria is known from the Lance F o r m a t i o n and F o r t Union Group of Dakota, but not from the equivalent strata in western Canada. Thus, the n o r t h e r n b o u n d a r y roughly coincides with the line of latitude 50°N.
PLATE IV
Araucavia from the Lower Cretaceous of Mongolia 1. 2. 3. 4.
Shoot with scale-leaves (x 7). Cleared leaf showing stomatal band (× 7 ). Part of the same stomatal band, SEM (x 550). Split cone showing seeds (x 7). Araucaria from Tyrma 5. Cone scale (x 7). 6. Shoot fragment with scale-leaves (X 7). 7. Leaf margin fringed by hairs (× 146).
L~
L~
123 RELATION TO PALEOLATITUDES S m i t h et al. ( 1 9 7 3 ) p r o d u c e d a series o f w o r l d m a p s b a s e d on t o p o g r a p h i c , t e c t o n i c , and p a l e o m a g n e t i c data. In t h e i r words, t h e p e r t i n e n t t e s t is w h e t h e r d i s t r i b u t i o n s of l a t i t u d e - d e p e n d e n t s e d i m e n t o l o g i c a l and p a l e o b i o l o g i c a l f e a t u r e s are parallel or o b l i q u e to the l a t i t u d e lines on these m a p s . A m o n g t h e f e a t u r e s d e f i n e d above, the l o w - l a t i t u d e r e c o r d s ( O a x a c a , Mall, K u t c h , Phu K a d u n g , 1 5 - - 2 0 ° N) and t h e m i d d l e l a t i t u d e A r a u c a r i a c e a e - Elatides--CIassopollis belt ( o p t i m a l d e v e l o p m e n t at 4 0 - - 4 5 ° N) are displaced to t h e s o u t h and s o m e w h a t m o r e s c a t t e r e d on the Jurassic p a l e o m a g n e t i c m a p ( 0 - - 1 0 ° N and 2 0 - - 3 0 ° N , respectively). T h e n o r t h e r n b o u n d a r y o f the Triassic floras w i t h A r a u c a r i a c e a e e x t e n d s across the Pacific f r o m 5 5 ° N in the w e s t ( s o u t h e r n J a p a n ) to 2 0 ° N in the east (Arizona). On the C r e t a c e o u s m a p , the n o r t h e r n m o s t r e c o r d s of A r a u c a r i a c e a e are s c a t t e r e d b e t w e e n 25 and 70°N. T h e y are at 4 0 ° N in eastern Asia ( N o r t h Sakhalin) and 7 0 ° N in w e s t e r n N o r t h America. T h u s , b o t h Triassic and C r e t a c e o u s isoflors based o n the n o r t h e r n m o s t o c c u r r e n c e s o f A r a u c a r i a c e a e are o b l i q u e to p a l e o l a t i t u d e s , especially so in t h e Pacific region. T h e s e isoflors are parallel to the lines o f m o d e r n latitudes 35 and 50°N. CONCLUSIONS T h e m a j o r c h o n o l o g i c a l f e a t u r e s o f the Mesozoic A r a u c a r i a c e a e in t h e p r e s e n t - d a y c o o r d i n a t e s are: (1) A r a u c a r i a c e a e d o m i n a t e d in t h e l o w - l a t i t u d e ( 1 5 - - 2 0 ° N) belt o f pred o m i n a n t l y s u m m e r - d r y r e d - b e d climate. T h e r e was n o e v i d e n c e o f a p l a n t assemblage m o r e t h e r m o p h i l o u s t h a n t h e a r a u c a r i a n forests. T h u s , the t r o p i c a l z o n e was p r o b a b l y m u c h c o o l e r t h a n at present. No e q u i v a l e n t s of t h e m o d e r n t r o p i c a l rain f o r e s t have existed. (2) A r a u c a r i a c e a e were c o m m o n in the m i d d l e latitudes. A r a u c a r i a c e a e - Elatides--Classopollis forests s t r e t c h e d f r o m P o t o m a c and Portugal t o M o n g o l i a and P r i m o r y e . T h e s e forests r e a c h e d their o p t i m a l d e v e l o p m e n t at a b o u t 4 0 - - 4 5 ° N. In t h e S o u t h e r n H e m i s p h e r e , the e q u i v a l e n t p l a n t f o r m a t i o n s o c c u p i e d s y m m e t r i c a l position. (3) T h e n o r t h e r n limit o f Triassic floras w i t h A r a u c a r i a c e a e is at a b o u t 3 5 ° N on b o t h t h e Asiatic and t h e A m e r i c a n Pacific coasts. In Jurassic and PLATE V
Araucaria from the Late Cretaceous of Sakhalin 1. Stomatal pit with a hair-like process, SEM (x 1500). 2. Guard cells, the foot of a hair is seen above, SEM (x 1500). 3. Leaf cuticle showing stomata (x 12). 4. Outside view of stomatal pits (x 1000). Araucarites pojarkovae Krassilov from the Danian of the Amur province 5. Longitudinally split cone (X 2). 6. Cone scale (X 2). 7. Shoot apex (x 1).
124
Cretaceous time, their northernmost occurrences are constantly at about 50 ° N. It appears that this boundary was not sensitive to minor climatic changes. In the Southern Hemisphere, the equivalent boundary is displaced to the south, probably due to dispersal of continents. (4) Morphological versatility of Araucariaceae from eastern Asia suggests the primary centre of diversity to be in the Pacific region. The features 1--3 are parallel to the modern latitudes, while their position on paleomagnetic maps is less regular and 3 is markedly oblique to the latitudes of contemporaneous reassemblies orientated by rotation bringing their geographic poles into coincidence with the mean paleomagnetic poles. These data would be more consistent with a method of orientation assuming minimal latitudinal shift of major continents. To reconcile drift with stable latitudinal position of continents, the outsider hypotheses of an expanding Earth or flattening of the geoid must be re-evaluated. I prefer the latter hypothesis for the reasons given elsewhere (Krassilov, 1976b).
REFERENCES Hsii, K.J., 1971. Origin of the Alps and western Mediterranean. Nature, 233: 44--48. Iwai, J., Hongnusonthi, A., Asama, K., Kobayashi, F., Kon'no, E., Nakornsri, N., Veeraburas, M. and Yuyen, W., 1975. Non-marine Mesozoic formations and fossils in Thailand and Malaysia. Geol. Palaeontol. Southeast Asia, 5: 195--218. Krassilov, V.A., 1967. Early Cretaceous Flora of South Primorye and its Bearing on Stratigraphy. Nauka, Moscc=v, 364 pp. (in Russian). Krassilov, V.A., 1972. Phytogeographical classification of Mesozoic floras and their bearing on continental drift. Nature, 237: 49--50. Krassilov, V.A., 1976a. Tsagajan Flora of the Amur Province. Nauka, Moscow, 92 pp. (in Russian). Krassilov, V.A., 1976b. Plate tectonics and rotational regime of the planet. Izv. Akad. Nauk S.S.S.R., Ser. Geol., 1 : 7 4 - - 8 2 (in Russian). Krassilov, V.A., 1977. Fossil Araucaria from the Sahara. Priroda, 5 : 6 5 - - 6 8 (in Russian). Pant, D.D. and Srivastava, G.K., 1968. On the cuticular structure of Araucaria (Araucarites) cutchensis (Feistmantel) comb. nov. from the Jabalpur Series, India. J. Linn. Soc. (Bot.), 61: 201--206. Smith, A.G., Briden, J.C. and Drewry, G.E., 1973. Phanerozoic world maps. In: N.F. Hughes (Editor), Organisms and Continents Through Time. Spec. Pap. Paleontol., 12: 1--42. Stockey, R.A., 1975. Seeds and embryos of Araucaria mirabilis. Am. J. Bot., 62: 856--868. Wesley, A., 1956. Contributions to the knowledge of the flora of the Grey Limestones of Veneto. Mem. Ist. Geol. miner. Univ. Padova, 19: 1--67. Wieland, G.R., 1914. La flora liasica de la Mixteca Alta. Bol. Inst. Geol. Mexico, 31 : 165 pp.
113
© Elsevier Scientific Publishing C o m p a n y , A m s t e r d a m - - P r i n t e d in T h e N e t h e r l a n d s
A R A U C A R I A C E A E AS INDICATORS OF CLIMATE A N D PALEOLATITUDES
V A L E N T I N A. K R A S S I L O V
Institute of Biology and Pedology, Vladivostok 22 (U.S.S.R.) ( A c c e p t e d for p u b l i c a t i o n J a n u a r y 10, 1 9 7 8 )
ABSTRACT Krassilov, V.A., 1978. A r a u c a r i a c e a e as i n d i c a t o r s o f c l i m a t e a n d p a l e o l a t i t u d e s . Rev. P a l a e o b o t . Palynol., 26: 1 1 3 - - 1 2 4 . Mesozoic A r a u c a r i a c e a e d o m i n a t e d in t h e l o w - l a t i t u d e ( 1 5 - - 2 0 ° N) belt o f s u m m e r - d r y climate. It is suggested, t h a t a r a u c a r i a n forests were t h e m o s t t h e r m o p h i l o u s Mesozoic assemblages. T h e r e were n o e q u i v a l e n t s o f t h e m o d e r n t r o p i c a l rain forest. In t h e m i d d l e latitudes, A r a u c a r i a c e a e s h a r e d d o m i n a n c e w i t h Elatides a n d Classopollis-producing plants. T h e n o r t h e r n m o s t Triassic records o f A r a u c a r i a c e a e o n b o t h e a s t e r n a n d w e s t e r n Pacific coasts are at 35 ° N; in t h e Jurassic a n d C r e t a c e o u s t i m e t h e y are c o n s t a n t l y at a b o u t 50 ° N. These climatically c o n t r o l l e d chorological f e a t u r e s are o b l i q u e to t h e p a l e o l a t i t u d e s i n f e r r e d f r o m p a l e o m a g n e t i c data. On t h e basis of m a t e r i a l f r o m t h e Jurassic o f Mali, a n e w species o f Araucaria is described, viz. Araucaria africana sp. nov.
INTRODUCTION
I contribute this paper in appreciation of Dr. Jonker's broad interest in paleoclimatology. The usefulness of pre-Quaternary plants as climate indicators is questionable because their tolerance cannot be safely deduced backward from that of their extant relatives and because intrinsic evidence of their geographic distribution is also ambiguous due to changing position of continents. Some paleobotanists are ready to accept paleomagnetic maps, while paleomagnetologists seek arrangements compatible with paleobotanical and other biological evidence. With this in mind, I considered the distribution of Mesozoic Araucariaceae. Their absence from the temperate Arctomesozoic (Siberian) province, in contrast with fairly numerous records elsewhere, is the primary evidence of climatic control and potential utility as climate indicators. Araucarian remains in my collection came from the Jurassic and Cretaceous localities in the Far East (Tyrma, Mongolia, Primorye, Sakhalin, Amur province) and also from equatorial Africa.
114 DISTRIBUTION IN MODERN COORDINATES The most important features of paleophytogeography are in descending order (1) abundance, (2) limits of distribution, and (3) diversity. While 1 is defined objectively, 2 is biased by imperfection of record and 3 depends on taxonomic judgements. The largest Triassic locality is the famous araucarian fossil forest of Arizona. Typical cone scales were recorded as far north as Greenland (Araucarites charcotii Harris) and Taimir (A. migayi Shvedow). On the Pacific coast, araucarian woods and other remains are known from Tonkin (Araucarioxylon zeilleri Grie) and Japan (A. sidugawaense Shimakura), while they are lacking in the rich fossil-plant localities near Vladivostok (Primorye). The northern boundary of floras with Araucariaceae on both the Asiatic and the American coasts of the Pacific (South Japan and Chile) is at about 35°N. Jurassic Araucariaceae are described from many localities, but the In-Eserin locality in the variegated Jurassic beds of the Mali--Nigerian depression in Africa is unique in its abundance of araucarian remains contrasting with a scarcity of other megafossils. Plant compressions were obtained from bore holes by bulk maceration of calcareous shales with HC1 and HF. They are mostly isolated leaves (about 100 specimens), but also wood fragments, branchlets, microstrobili with pollen grains and cone scales, all attributed to a single species of Araucaria. Earlier, I published a preliminary description of this unnamed species, (Krassilov, 1977). Now I propose the new name Araucaria africana for it.
Araucaria africana sp.nov. (Plate I--III) Diagnosis: Ultimate branchlets 1--2 mm thick. Scale-leaves imbricate, appressed or spreading. Leaf cushion rhomboidal or obovate, tapering downwards, about 3--4 mm long. Free portion clearly delimited from their base cushions, much shorter than the cushions or of equal length, triangular in section, incurved, blunt or shortly pointed or linear--lanceolate, flattened, mucronate, up to 5 mm long (average length 1.5--3 mm). Cuticle thick, showing marginal zone of narrow thin-walled, slightly sinuous cells and central zone of rectanguloid thick-walled cells, about 50-60 X 24--30 pm (80--90 X 22--25 pm in longer leaves), arranged in short rows. Cells usually papillate. Stomata on both sides of the free portion and
PLATE I
Araucaria africana sp. nov. from Mali 1. 2. 3. 4. 5.
Shoot showing scale-leaves, holotype (x 25). Leaf with its leaf-base cushion (x 25). Stoma showing fine striation of subsidiary cells (x 330). Distribution of stomata, SEM (x 300). Inside view of stomatal pit and slightly sunken subsidiary cells, SEM (X 1600).
i~"~
~
~i~,~~
~
,_...
~~
~.~
~L ~L
116
on the leaf-base cushion. Average leaves show 50--60 abaxial stomata distributed all over the surface except the marginal zone. Adaxial stomata fewer, concentrated in the lower portion of a leaf. In some linear--lanceolate leaves adaxial stomata more numerous than the abaxial ones. Stomata in short rows or scattered. Those in rows mostly transverse or longitudinal, while oblique orientation predominates among scattered stomata. Subsidiary cells usually five, radially arranged, slightly sunken, finely striated, conspicuous due to their lighter colour, forming stomatal pit with thickened border. Stomata elliptical, about 60 p m long, with T-shaped polar thickenings. Microstrobili rounded, diameter about 2.5 mm, scales obcuneate, 0.8 mm long, imbricate, bearing about 10 oval pollen sacs. Pollen grains spherical, diameter about 25 t~m, exine thin, smooth, often folded. Scales of megastrobili winged, with densely papillate cuticle. Papillae conical or cylindrical in the middle part of adaxial surface, rounded near the margin. Stomata scattered, as in leaves, but subsidiary cells less conspicuous. Holotype: IE-44; Collection of the Institute of Biology and Pedology. Type locality: Mali--Nigerian depression, In-Eserin borehole, 337--339 m. Shoots of A. africana are comparable with Pagiophyllum peregrinum (Lindley et Hutton) Schenk from the British Lias as well as Brachyphyllum tropidimorphyrn Wesley, Pagiophyllum rotzoanum Wesley and P. valdassense Wesley from the Grey Limestones of Veneto. The latter species is especially similar in cuticular characters (Wesley, 1956), though papillae are lacking. I believe that close resemblance between African and Venetian conifers has some bearing on the problem of Afro-Italian land connections in the Jurassic (see Hs[i, 1971). The In-Eserin locality suggests a lowland araucarian forest. Association of shoots, leaves and cones rules out the possibility of a long-distance transportation. The facies are similar to those of the Triassic araucarian forest in Arizona. Other low-latitude Jurassic localities -- Oaxaca in Mexico (Wieland, 1914), Kutch in India (Pant and Srivastava, 1968) and Phu Kadung in Thailand (Iwai et al., 1975) -- are also found in variegated or red-bed facies. They show that the araucarian forest was a dominant plant formation in the low-latitude belt of a summer-dry climate. In middle latitudes, abundant araucarian fossils -- cone scales, shoots of
Pagiophyllum and Brachyphyllum types -- are described from the Jurassic and Early Cretaceous localities of the eastern U.S.A. (Potomac), Portugal, France, Italy, Caucasus, Middle Asia and southern Kazakhatan (Karatau). In these PLATE II
Araucaria africana sp. nov. from Mall 1. 2. 3. 4. 5.
Inside view of a stoma, SEM (x 1600). Guard cells, one of the T-shaped polar thickenings is preserved, SEM (× 1600). Leaf cuticle showing stomata (× 25). Very short leaf spreading from its leaf-base cushion (× 25). Cleared leaf showing stomata on the leaf-base cushion (× 25).
/
..........
l
,
....
....1
~'~~ ~ i ii !!~!i¸ i i:
~
L
119 localities, Araucariaceae are next in abundance to the taxodiaceous conifers of the Elatides group and Classopollis-producing plants. Assemblages of this t y p e can be traced to the east in Mongolia and Primorye. The Mongolian Mesozoic flora was hitherto scarcely k n o w n , but recently the paleontologists A.G. P o n o m a r e n k o and V.N. Yakovlev have discovered structurally preserved plant material as a b y - p r o d u c t of their search for fossil insects and fishes. The Araucaria on Plate IV, 1--4 came from the Shin-Khuduk and Bon-Tsagan localities of Early Cretaceous age. There are branching shoots with spirally arranged scale leaves which are crescent-shaped, carinate, and provided with a single adaxial band of fairly crowded, irregularly orientated stomata. Ovuliferous cones are elliptical, rather small. Split cones show seeds e m b e d d e d in the scales with relatively thick apophyses. In the Lower Cretaceous of South Primorye (near Vladivostok), Araucariaceae are represented by c o m m o n Araucarites with Brachyphyllum-type foliage and also by two genera with bifacial pluri-nerved leaves, viz. Araucariodendron and Ussuriocladus (Krassilov, 1967). In Araucariodendron, stomata are in intercostal bands, longitudinally orientated, amphicyclic. Cone scales are small, wingless, consisting of completely fused bracts and ovuliferous scales, bearing one or two e m b e d d e d ovules. Patagonian localities may represent the Southern Hemisphere c o u n t e r p a r t of the Araucariaceae--Elatides--Classopollis belt. Conifers from these localities are n o w much bet t er unde r s t ood due to the excellent work of Stockey (1975). The Jurassic Araucariaceae have been recorded from Grahamland, and the southern limit of their distribution is not known. In the Northern Hemisphere, their numerical representation decreases towards the nort hern limits of the Araucariaceae--Elatides--Classopollis belt. The Yorkshire (Araucarites estonensis Kendall) and Ukrainian records are evidently situated near the boundary, since t h e y are lacking from the Jurassic of Greenland, Bornholm and Sweden. In Asia, no araucarian remains are known from the Arctomesozoic, or Siberian province dom i nat ed by deciduous Phoenicopsis forests (fossil woods of Araucariopitys described from various nort hern localities are now transferred to Protocedroxylon). The n o r t h e r n m o s t records are from the T y r m a River, a tributary of the Bureja, at about 50 ° N. Araucaria is a new element in the T yr m i a n flora studied by Seward, Novopokrovsky, Kryshtofovich and other authors. It is represented, mostly in the products of bulk maceration, by small fragments of shoots, isolated PLATE III
Araucaria africana sp. nov. from Mali 1. 2. 3. 4. 5. 6.
Wing-like extension of a bract (x 10). Papillate bract cuticle (× 130). Microstrobilus (x 25). Several cleared pollen sacs borne on a microsporophyll (× 130). Tetrad from a pollen sac (x 660). Pollen grain, SEM (× 3500).
120
PLATE IV
121 leaves and a single cone scale (Plate IV, 5--7). There are also numerous pollen sacs, y et unassigned, but probably belonging to this plant. The scale-leaves are spreading, straight or h o o k e d , about 3.5 mm long, fringed by dense microscopic hairs. S tom at a are on the adaxial side only, scattered, orientated along the cell rows or somewhat oblique. The cone scale is sammara-like, 5 mm wide, with broad ligule and median groove. Cuticle is thickened in the median portion, where a seed was embedded. Cuticular characters are like those of the leaves. The latest Jurassic or Berriasian flora of T y r m a is ecotonal between the Phoenicopsis and Cycadeoidea provinces (Krassilov, 1972) and contains such southern plants as Klukia and Pachypteris. In the Late Cretaceous, Sequoia replaced Elatides and ot her archaic Taxodiaceae in the middle latitude coniferous forests, while Araucariaceae maintained their position and were still c o m m o n in eastern U.S.A. (Raritan), Bohemia, Caucasus and Kazakhstan. "Damrnara" or "Darnmarites" have been o f ten q u o t e d from higher latitudes (e.g., from West Greenland), but in my opinion th ey have nothing to do with the Araucariaceae (in fact, most of t h em are isolated cone scales of Sequoia). In eastern Asia, the n o r t h e r n m o s t records are from the Tsagajan beds of the Amur province (Danian) and northern Sakhalin (Senonian), bot h at about 50 ° N. Araucarites pojarkovae (Plate V, 5--7) from Tsagajan has cylindrical shoots with imbricate obovate leaves ab o u t 11--13 X 10--11 mm. Megastrobili are globose, about 20 mm in diameter, scales obcuneate, lingulate, indehiscent, with a rather long awn and vestigial wings (Krassilov, 1976a). This species is related to the section Columbea, now restricted to South America. Araucaria from Sakhalin also resembles e x t a n t species of Columbea, but the stomatal structure is very peculiar. Each stoma is provided with a stout process overhanging the stomatal pit (Plate V, 1--4). Such unique characters, together with outstanding versatility of the Early Cretaceous Araucariaceae from Primorye (see above) suggests the Pacific region as an area of primary diversity of this group. On the American coast, Araucaria is known from the Lance F o r m a t i o n and F o r t Union Group of Dakota, but not from the equivalent strata in western Canada. Thus, the n o r t h e r n b o u n d a r y roughly coincides with the line of latitude 50°N.
PLATE IV
Araucavia from the Lower Cretaceous of Mongolia 1. 2. 3. 4.
Shoot with scale-leaves (x 7). Cleared leaf showing stomatal band (× 7 ). Part of the same stomatal band, SEM (x 550). Split cone showing seeds (x 7). Araucaria from Tyrma 5. Cone scale (x 7). 6. Shoot fragment with scale-leaves (X 7). 7. Leaf margin fringed by hairs (× 146).
L~
L~
123 RELATION TO PALEOLATITUDES S m i t h et al. ( 1 9 7 3 ) p r o d u c e d a series o f w o r l d m a p s b a s e d on t o p o g r a p h i c , t e c t o n i c , and p a l e o m a g n e t i c data. In t h e i r words, t h e p e r t i n e n t t e s t is w h e t h e r d i s t r i b u t i o n s of l a t i t u d e - d e p e n d e n t s e d i m e n t o l o g i c a l and p a l e o b i o l o g i c a l f e a t u r e s are parallel or o b l i q u e to the l a t i t u d e lines on these m a p s . A m o n g t h e f e a t u r e s d e f i n e d above, the l o w - l a t i t u d e r e c o r d s ( O a x a c a , Mall, K u t c h , Phu K a d u n g , 1 5 - - 2 0 ° N) and t h e m i d d l e l a t i t u d e A r a u c a r i a c e a e - Elatides--CIassopollis belt ( o p t i m a l d e v e l o p m e n t at 4 0 - - 4 5 ° N) are displaced to t h e s o u t h and s o m e w h a t m o r e s c a t t e r e d on the Jurassic p a l e o m a g n e t i c m a p ( 0 - - 1 0 ° N and 2 0 - - 3 0 ° N , respectively). T h e n o r t h e r n b o u n d a r y o f the Triassic floras w i t h A r a u c a r i a c e a e e x t e n d s across the Pacific f r o m 5 5 ° N in the w e s t ( s o u t h e r n J a p a n ) to 2 0 ° N in the east (Arizona). On the C r e t a c e o u s m a p , the n o r t h e r n m o s t r e c o r d s of A r a u c a r i a c e a e are s c a t t e r e d b e t w e e n 25 and 70°N. T h e y are at 4 0 ° N in eastern Asia ( N o r t h Sakhalin) and 7 0 ° N in w e s t e r n N o r t h America. T h u s , b o t h Triassic and C r e t a c e o u s isoflors based o n the n o r t h e r n m o s t o c c u r r e n c e s o f A r a u c a r i a c e a e are o b l i q u e to p a l e o l a t i t u d e s , especially so in t h e Pacific region. T h e s e isoflors are parallel to the lines o f m o d e r n latitudes 35 and 50°N. CONCLUSIONS T h e m a j o r c h o n o l o g i c a l f e a t u r e s o f the Mesozoic A r a u c a r i a c e a e in t h e p r e s e n t - d a y c o o r d i n a t e s are: (1) A r a u c a r i a c e a e d o m i n a t e d in t h e l o w - l a t i t u d e ( 1 5 - - 2 0 ° N) belt o f pred o m i n a n t l y s u m m e r - d r y r e d - b e d climate. T h e r e was n o e v i d e n c e o f a p l a n t assemblage m o r e t h e r m o p h i l o u s t h a n t h e a r a u c a r i a n forests. T h u s , the t r o p i c a l z o n e was p r o b a b l y m u c h c o o l e r t h a n at present. No e q u i v a l e n t s of t h e m o d e r n t r o p i c a l rain f o r e s t have existed. (2) A r a u c a r i a c e a e were c o m m o n in the m i d d l e latitudes. A r a u c a r i a c e a e - Elatides--Classopollis forests s t r e t c h e d f r o m P o t o m a c and Portugal t o M o n g o l i a and P r i m o r y e . T h e s e forests r e a c h e d their o p t i m a l d e v e l o p m e n t at a b o u t 4 0 - - 4 5 ° N. In t h e S o u t h e r n H e m i s p h e r e , the e q u i v a l e n t p l a n t f o r m a t i o n s o c c u p i e d s y m m e t r i c a l position. (3) T h e n o r t h e r n limit o f Triassic floras w i t h A r a u c a r i a c e a e is at a b o u t 3 5 ° N on b o t h t h e Asiatic and t h e A m e r i c a n Pacific coasts. In Jurassic and PLATE V
Araucaria from the Late Cretaceous of Sakhalin 1. Stomatal pit with a hair-like process, SEM (x 1500). 2. Guard cells, the foot of a hair is seen above, SEM (x 1500). 3. Leaf cuticle showing stomata (x 12). 4. Outside view of stomatal pits (x 1000). Araucarites pojarkovae Krassilov from the Danian of the Amur province 5. Longitudinally split cone (X 2). 6. Cone scale (X 2). 7. Shoot apex (x 1).
124
Cretaceous time, their northernmost occurrences are constantly at about 50 ° N. It appears that this boundary was not sensitive to minor climatic changes. In the Southern Hemisphere, the equivalent boundary is displaced to the south, probably due to dispersal of continents. (4) Morphological versatility of Araucariaceae from eastern Asia suggests the primary centre of diversity to be in the Pacific region. The features 1--3 are parallel to the modern latitudes, while their position on paleomagnetic maps is less regular and 3 is markedly oblique to the latitudes of contemporaneous reassemblies orientated by rotation bringing their geographic poles into coincidence with the mean paleomagnetic poles. These data would be more consistent with a method of orientation assuming minimal latitudinal shift of major continents. To reconcile drift with stable latitudinal position of continents, the outsider hypotheses of an expanding Earth or flattening of the geoid must be re-evaluated. I prefer the latter hypothesis for the reasons given elsewhere (Krassilov, 1976b).
REFERENCES Hsii, K.J., 1971. Origin of the Alps and western Mediterranean. Nature, 233: 44--48. Iwai, J., Hongnusonthi, A., Asama, K., Kobayashi, F., Kon'no, E., Nakornsri, N., Veeraburas, M. and Yuyen, W., 1975. Non-marine Mesozoic formations and fossils in Thailand and Malaysia. Geol. Palaeontol. Southeast Asia, 5: 195--218. Krassilov, V.A., 1967. Early Cretaceous Flora of South Primorye and its Bearing on Stratigraphy. Nauka, Moscc=v, 364 pp. (in Russian). Krassilov, V.A., 1972. Phytogeographical classification of Mesozoic floras and their bearing on continental drift. Nature, 237: 49--50. Krassilov, V.A., 1976a. Tsagajan Flora of the Amur Province. Nauka, Moscow, 92 pp. (in Russian). Krassilov, V.A., 1976b. Plate tectonics and rotational regime of the planet. Izv. Akad. Nauk S.S.S.R., Ser. Geol., 1 : 7 4 - - 8 2 (in Russian). Krassilov, V.A., 1977. Fossil Araucaria from the Sahara. Priroda, 5 : 6 5 - - 6 8 (in Russian). Pant, D.D. and Srivastava, G.K., 1968. On the cuticular structure of Araucaria (Araucarites) cutchensis (Feistmantel) comb. nov. from the Jabalpur Series, India. J. Linn. Soc. (Bot.), 61: 201--206. Smith, A.G., Briden, J.C. and Drewry, G.E., 1973. Phanerozoic world maps. In: N.F. Hughes (Editor), Organisms and Continents Through Time. Spec. Pap. Paleontol., 12: 1--42. Stockey, R.A., 1975. Seeds and embryos of Araucaria mirabilis. Am. J. Bot., 62: 856--868. Wesley, A., 1956. Contributions to the knowledge of the flora of the Grey Limestones of Veneto. Mem. Ist. Geol. miner. Univ. Padova, 19: 1--67. Wieland, G.R., 1914. La flora liasica de la Mixteca Alta. Bol. Inst. Geol. Mexico, 31 : 165 pp.