Anatomically preserved Dicroidium from the Transantarctic Mountains
Dow, W.G. 1977. Kerogen studies and geological interpretations. Journal of Geochemical Exploration, 7, 79-99.
Griffin, J . , H. Windom, and E.D. Goldberg. 1968. The distribution of clay minerals in the world ocean. Deep Sea Research, 15, 433-459. Guthrie, J.M., D.W. Houseknecht, and W.D. Johns. 1986. Relationships among vitrinite reflectance, illite crystallinity, and organic geochemistry in Carboniferous strata, Ouachita Mountains, Oklahoma and Arkansas. American Association of Petroleum Geologists Bulletin, 70, 26-33. Keller, W.D. 1970. Environmental aspects of clay minerals. Journal of Sedimentary Petrology, 48, 788-854.
Anatomically preserved Dicroidium from the Transantarctic Mountains
Krissek, L.A., and T.C. Homer. 1986. Sedimentology of fine-grained Permian clastics, central Transantarctic Mountains. Antarctic Journal of the U.S., 21(5), 30-32. Maxwell, D.T., and J. Hower. 1967. High-grade diagenesis and lowgrade metamorphism of illite in the Precambrian Belt series. American Mineralogist, 52, 843-857. Nesbitt, H.W., and G.M. Young. 1982. Early Proterozoic climates and plate motions inferred from major element chemistry of lutites. Nature, 299, 715-717. Weaver, C.E. 1960. Possible uses of clay minerals in search for oil. American Association of Petroleum Geologists Bulletin, 44, 1508-1515.
pinnules are up to 5.0 millimeters long and 3.0 millimeters wide. Within the pinna rachis, the midrib is noticeably more prominent than lateral veins (figure 1). Internally, Dicroidiurn pinnules are characterized by prominent vascular bundles, each
KATHLEEN B. PIGG and THOMAS N. TAYLOR
Department of Botany
and Byrd Polar Research Center Ohio State University Columbus, Ohio 43210-1293
The genus Dicroidium represents a major component of the Triassic Gondwana flora, with 20-30 species described from throughout the Southern Hemisphere (e.g., Retallack 1977; Anderson and Anderson 1983). This foliage genus is represented by a dichotomizing frond with morphologica lly variable pinnules arranged pinnately. Leaves assignable to Dicroidium are thought to represent the vegetative leaves of the Corystospermales, an enigmatic group of Mesozoic pteridosperms. Despite the fact that taxa are well known from a number of localities and certain species have been important as biostratigraphic indicators (e.g., Anderson and Anderson 1983), little is known about the anatomy, ecology, plant habit, phylogenetic relationships, and other biological aspects of these plants. Although frond morphology and cuticular features have been described for most species from compression/impression specimens, nothing is known of the internal anatomical features of this leaf form. Permineralized peat from the Fremouw Peak locality in the central Transantarctic Mountains of Antarctica (Smoot, Taylor, and Delevoryas 1985) contains three-dimensionally preserved Dicroidiuin fronds, and provides the first opportunity to describe the anatomic features of this form. A combination of weathered surfaces revealing leaves in paradermal surface view (figure 1), closely spaced serial peels of transverse sections (figure 2), and macerated cuticle fragments (figure 3) has been studied to reconstruct the frond anatomy and morphology of the Dicroidium leaf. This approach allows for the direct comparison of this permineralized material with previously described compression/impression specimens. Surfaces reveal fronds of at least bipinnate organization with odontopteroid pinnules (figure 1). Pinnules are bluntly lobed and contain several sets of dichotomizing veins each. Individual 28
T: 41
1
•. A .
Figure 1. Weathered surface of silicified peat block showing characteristic Dicroidium pinnules. 10,200 C3 Side. (x 2.7)
Figure 2. Transverse section of Dicroidium pinnule. Note prominent vascular bundles surrounded by bundle sheath, and well-differentiated mesophyll. 580 C Bot. #la. (x 27) ANTARCTIC JOURNAL
abaxial surface. The cuticle is thin but resistant, and shows dicyclic stomata with incomplete rings of subsidiary cells (figure 3), a feature characteristic of many species of Dicroidium (e.g., Anderson and Anderson 1983). Specimens from the Fremouw Peak locality provide the first evidence of the anatomical features of Dicroidium fronds and show well-organized mesophyll, thin but resistant, amphistomatic cuticles, and a frond-like organization. Descriptions of this sort are invaluable in providing detailed information about the Triassic flora that in turn can be used as a data base for subsequent studies regarding climatologic and ecologic parameters of the Triassic Gondwana landscape. Moreover, the Fremouw Peak specimens afford the opportunity to reconstruct an important group of Mesozoic gymnosperms that some believe may provide clues to angiosperm origins. The research was supported by National Science Foundation grants DPP 86-11884 and BSR 84-10399. Logistical support was provided by members of U.S. Navy squadron VXE-6. References
Figure 3. Portion of macerated curicle showing structure and arrangement of stomata, subsidiary and epidermal cells. (x 400)
surrounded by a bundle sheath and a well-differentiated mesophyll showing both palisade and spongy layers (figure 2). The foliage contains numerous scattered resinous cells throughout. Leaves are amphistomatic with more stomata occurring on the
An unusual gymnospermous reproductive organ of Triassic age THOMAS
Anderson, J.M., and H.M. Anderson. 1983. Paleoflora of southern Africa Molteno Formation (Triassic), Volume I. Rotterdam: A.A. Balkema. Retallack, C. 1977. Triassic vegetation: Microfiche supplement; reconstructing Triassic vegetation of eastern Australasia: A new approach for the biostratigraphy of Gondwanaland. Alcheringa, 1, 253-283. Smoot, E.L., T.N. Taylor, and T. Delevoryas. 1985. Structurally preserved fossil plants from Antarctica. I. Antarcticycas, gen. nov., a Triassic cycad stem from the Beardmore Glacier area. American journal of Botany, 72, 1410-1423.
site has yielded a diverse array of well-preserved plant organs including several reproductive structures. One of the most interesting gymnospermous reproductive organs is a cupule-like structure containing several seeds (figure 1). In transverse section the seed-bearing unit is oval mea-
N. TAYLOR and EDITH L. TAYLOR Byrd Polar Research Center
and Department of Botany Ohio State University Columbus, Ohio 43210-1293
One of the least-known periods in geologic time relative to plant evolution is the Triassic. Although Triassic plant remains have been documented, almost all are preserved as impression/ compression specimens in which critical information about the internal tissues is lacking. Thus, to date our understanding about Triassic plants has had to rely on morphological features of predominantly two-dimensional fossils. For this reason the discovery of Triassic plants that are three-dimensionally preserved in silica is particularly significant because it provides the opportunity to detail the anatomy of plants of this time period. The material was collected during the 1985-1986 field season from a col north of Fremouw Peak (84°16'S 164'21'E, Buckley Island Quadrangle) and occurs as blocks of allochthonous peat in the upper Fremouw Formation. This early/middle Triassic 1987 REVIEW
I
Figure 1. Section of gymnospermous reproductive organ containing three seeds showing nature of enclosing laminar unit. (x 31.25)
29
Griffin, J . , H. Windom, and E.D. Goldberg. 1968. The distribution of clay minerals in the world ocean. Deep Sea Research, 15, 433-459. Guthrie, J.M., D.W. Houseknecht, and W.D. Johns. 1986. Relationships among vitrinite reflectance, illite crystallinity, and organic geochemistry in Carboniferous strata, Ouachita Mountains, Oklahoma and Arkansas. American Association of Petroleum Geologists Bulletin, 70, 26-33. Keller, W.D. 1970. Environmental aspects of clay minerals. Journal of Sedimentary Petrology, 48, 788-854.
Anatomically preserved Dicroidium from the Transantarctic Mountains
Krissek, L.A., and T.C. Homer. 1986. Sedimentology of fine-grained Permian clastics, central Transantarctic Mountains. Antarctic Journal of the U.S., 21(5), 30-32. Maxwell, D.T., and J. Hower. 1967. High-grade diagenesis and lowgrade metamorphism of illite in the Precambrian Belt series. American Mineralogist, 52, 843-857. Nesbitt, H.W., and G.M. Young. 1982. Early Proterozoic climates and plate motions inferred from major element chemistry of lutites. Nature, 299, 715-717. Weaver, C.E. 1960. Possible uses of clay minerals in search for oil. American Association of Petroleum Geologists Bulletin, 44, 1508-1515.
pinnules are up to 5.0 millimeters long and 3.0 millimeters wide. Within the pinna rachis, the midrib is noticeably more prominent than lateral veins (figure 1). Internally, Dicroidiurn pinnules are characterized by prominent vascular bundles, each
KATHLEEN B. PIGG and THOMAS N. TAYLOR
Department of Botany
and Byrd Polar Research Center Ohio State University Columbus, Ohio 43210-1293
The genus Dicroidium represents a major component of the Triassic Gondwana flora, with 20-30 species described from throughout the Southern Hemisphere (e.g., Retallack 1977; Anderson and Anderson 1983). This foliage genus is represented by a dichotomizing frond with morphologica lly variable pinnules arranged pinnately. Leaves assignable to Dicroidium are thought to represent the vegetative leaves of the Corystospermales, an enigmatic group of Mesozoic pteridosperms. Despite the fact that taxa are well known from a number of localities and certain species have been important as biostratigraphic indicators (e.g., Anderson and Anderson 1983), little is known about the anatomy, ecology, plant habit, phylogenetic relationships, and other biological aspects of these plants. Although frond morphology and cuticular features have been described for most species from compression/impression specimens, nothing is known of the internal anatomical features of this leaf form. Permineralized peat from the Fremouw Peak locality in the central Transantarctic Mountains of Antarctica (Smoot, Taylor, and Delevoryas 1985) contains three-dimensionally preserved Dicroidiuin fronds, and provides the first opportunity to describe the anatomic features of this form. A combination of weathered surfaces revealing leaves in paradermal surface view (figure 1), closely spaced serial peels of transverse sections (figure 2), and macerated cuticle fragments (figure 3) has been studied to reconstruct the frond anatomy and morphology of the Dicroidium leaf. This approach allows for the direct comparison of this permineralized material with previously described compression/impression specimens. Surfaces reveal fronds of at least bipinnate organization with odontopteroid pinnules (figure 1). Pinnules are bluntly lobed and contain several sets of dichotomizing veins each. Individual 28
T: 41
1
•. A .
Figure 1. Weathered surface of silicified peat block showing characteristic Dicroidium pinnules. 10,200 C3 Side. (x 2.7)
Figure 2. Transverse section of Dicroidium pinnule. Note prominent vascular bundles surrounded by bundle sheath, and well-differentiated mesophyll. 580 C Bot. #la. (x 27) ANTARCTIC JOURNAL
abaxial surface. The cuticle is thin but resistant, and shows dicyclic stomata with incomplete rings of subsidiary cells (figure 3), a feature characteristic of many species of Dicroidium (e.g., Anderson and Anderson 1983). Specimens from the Fremouw Peak locality provide the first evidence of the anatomical features of Dicroidium fronds and show well-organized mesophyll, thin but resistant, amphistomatic cuticles, and a frond-like organization. Descriptions of this sort are invaluable in providing detailed information about the Triassic flora that in turn can be used as a data base for subsequent studies regarding climatologic and ecologic parameters of the Triassic Gondwana landscape. Moreover, the Fremouw Peak specimens afford the opportunity to reconstruct an important group of Mesozoic gymnosperms that some believe may provide clues to angiosperm origins. The research was supported by National Science Foundation grants DPP 86-11884 and BSR 84-10399. Logistical support was provided by members of U.S. Navy squadron VXE-6. References
Figure 3. Portion of macerated curicle showing structure and arrangement of stomata, subsidiary and epidermal cells. (x 400)
surrounded by a bundle sheath and a well-differentiated mesophyll showing both palisade and spongy layers (figure 2). The foliage contains numerous scattered resinous cells throughout. Leaves are amphistomatic with more stomata occurring on the
An unusual gymnospermous reproductive organ of Triassic age THOMAS
Anderson, J.M., and H.M. Anderson. 1983. Paleoflora of southern Africa Molteno Formation (Triassic), Volume I. Rotterdam: A.A. Balkema. Retallack, C. 1977. Triassic vegetation: Microfiche supplement; reconstructing Triassic vegetation of eastern Australasia: A new approach for the biostratigraphy of Gondwanaland. Alcheringa, 1, 253-283. Smoot, E.L., T.N. Taylor, and T. Delevoryas. 1985. Structurally preserved fossil plants from Antarctica. I. Antarcticycas, gen. nov., a Triassic cycad stem from the Beardmore Glacier area. American journal of Botany, 72, 1410-1423.
site has yielded a diverse array of well-preserved plant organs including several reproductive structures. One of the most interesting gymnospermous reproductive organs is a cupule-like structure containing several seeds (figure 1). In transverse section the seed-bearing unit is oval mea-
N. TAYLOR and EDITH L. TAYLOR Byrd Polar Research Center
and Department of Botany Ohio State University Columbus, Ohio 43210-1293
One of the least-known periods in geologic time relative to plant evolution is the Triassic. Although Triassic plant remains have been documented, almost all are preserved as impression/ compression specimens in which critical information about the internal tissues is lacking. Thus, to date our understanding about Triassic plants has had to rely on morphological features of predominantly two-dimensional fossils. For this reason the discovery of Triassic plants that are three-dimensionally preserved in silica is particularly significant because it provides the opportunity to detail the anatomy of plants of this time period. The material was collected during the 1985-1986 field season from a col north of Fremouw Peak (84°16'S 164'21'E, Buckley Island Quadrangle) and occurs as blocks of allochthonous peat in the upper Fremouw Formation. This early/middle Triassic 1987 REVIEW
I
Figure 1. Section of gymnospermous reproductive organ containing three seeds showing nature of enclosing laminar unit. (x 31.25)
29
