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Transmission Electron Microscopy of Mesozoic Terrestrial Microfossils

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Transmission Electron Microscopy of Mesozoic Terrestrial Microfossils Asociación Paleontológica Argentina. Publicación Especial 7 ISSN 0328-347X VII International Symposium on Mesozoic Terrestrial Ecosystems: 113-116. Buenos Aires, 30-6-2001 TRaNSMission elecTRON microscopy of Mesozoic TeRrestriaL microfossils Miklós KEDVES1 Abstract. From the evolutionary point of view the most important ultrastructural characteristic features of the terrestrial microfossils are presented in this contribution. During the Mesozoic Era important innova- tions happened in the ultrastructure of the gyrnnosperm pollen grains. The earliest saccate elements rep- resent the alveolar infratectal ultrastructure, which appeared in the Carboniferous, and remains in the pre- sent day gymnosperm species iPinus, Picea). New events during the Mesozoic: 1.Appearance of the mod- ern ultrastructure type in several inaperturate and monosulcate pollen grains (Arallcariacites Cookson, Cycadopites (Wodehouse) Wilson and Webster). 2. Exclusively Mesozoic gyrnnosperm types with peculiar LM morphology and exine ultrastructure. The pollen grains of the Operculati (Circuiina Malyavkina, Classopo/lis Pflug, Classoidites Amerom) are very isolated by their LM morphology, the wall ultrastructure is very cornplicated, similar to some angiosperm taxa. 3. Angiosperm-like exine ultrastructure appeared at the LM rnorphologically gyrnnosperrn pollen grains of the Spheripollenites Couper fgen. 4. The gym- nosperrnous Eucommiidites Erdtman has sorne angiosperm characteristics with the granular infratectallay- er. Concerning the evolution of the vegetation the appearance of the angiosperms was the most important event. Regarding the ultrastructure of the pollen grains, the most important evolutionary alterations may be followed by the alterations in the ultrastructure of the infratectal layer. In the earliest Longaxones (Lower Cretaceous) the colurnellar infratectal layer is characteristic, this may be followed in some Brevaxones by the granular one, during the Senonian. Keywords. Palynology.Mesozoic.Ultrastructureevolution. IntroductioN The earliest ultrastructure characteRistic features The evolution of the Plant Kingdom may be fol- lowed at different levels of organization. The starting Based on TEM data from Silurian (Hemsley, 1992, level is the molecular, this is followed by different 1994)the lamellar ultrastructure is the earliest. At the biopolymer structures and the ultrastructure of the Devonian spores outer spongy and inner lamellar organic remains. The concept of the "ultrastructure wall were established. But the evolved homogeneous evolution" of the plant cell wall was introduced by wall appeared also in microspores of some het- Ehrlich and Hall (1959)based on the first TEM data erasporous Pteridophyta during the Paleozoic Era. of fossil pollen grains frorn the Eocene layers of Earliest and evolved ultrastructural characteristic South Mayfield Kentucky, U.S.A. Several TEM re- features were described at the first saccate pollen grain sults were published from different kinds of spores (Archaeoperisaccus (Naumova) Potonié) by Meyer and and pollen grains from different ages. Raskatova (1984)isolated from Devonian sediments. Monographical works were also published by the The endexine is lamellar, the saccus alveolar. writer of the angiosperm (1990),gyrnnosperm (1994) pollen grains and spores (1996).After these volumes several new data appeared and a new synthesis of The MOST important alteratiONS during the the ultrastructure phylogeny seems necessary. Mesozoic time The aim of this contribution is to synthetise from an evolutionary point of view the most important al- 1. Differenciation of evolved Pteridophyta. terations in the ultrastructural features of different 2. Differenciation of gyrnnosperms. 2.1. Evolution of the earliest disaccate types. taxa of the Mesozoic terrestrial ecosystems. 2.2. Appearance and extinction of peculiar gym- nosperm types; Operculati (Circulina Malyavkina, 'Cell Biological and Evolutionary Micropaleontological Laboratory of the Department of Botany of the University of Classopollis Pflug. Classoidites Ameram), Eucomiidites Szeged.H-6701,Szeged,P.O.Box993,Hungary. Erdtman. ©Asociación Paleontológica Argentina 0328-347X/01$OO.OO+50 114 M. Kedves 2.3.Appearance of pollen grains which are impor- Parvisaccites radia tus Couper may be pointed out, by tant for the evolution of angiosperms. the small sacci and radially oriented alveolar system. 3. Appearance and early differentiation of the 2. The ultrastructure of the inaperturate pollen primitive angiosperms. types represents three great types from an evolution- ary point of view: EvOLUtionary lineages in the sporoderm 2.1. Early spongy ectexine composed of irregular rods of sporopollenin and lamellar endexine at the ultrastructure of the Mesozoic Cormophyta Balmeiopsis pollen grains (Kedves and Párdutz, 1974, Pteridophyta Archangelsky, 1994), and at some taxa of Araueariaeites Cookson (e.g.: A. hungarieus Deák; In general, in heterosporous fems, the ultrastruc- Kedves, 1985). ture of the megaspore wall represents the early type, 2.2. Granular ectexine which may represent the in contrast to the evolved (homogeneous) exospore three layered ectexine, and lamellar endexine is at the of the microspore. The microspore wall of evolved Araueariaeites Cookson pollen grains. This is Nathorsisporites hoplitieus Jung from the Triassic is a the modem inaperturate exine ultrastructure type modem homogeneous exospore with perispore. Wall which also occurs at several recent pollen taxa ultrastructure of miospores of the Jurassic time is in (Taxaceae,Taxodiaceae, Cupressaceae, etc.). general homogeneous sometimes transversed with 2.3. Angiosperm ectexine (tectum, columellar in- radially oriented channels (Paraeoneavisporites Klaus). fratectallayer and foot layer) is characteristic for the Perispore remains were observed at the surface of the pollen grains of the Spheripollenites Couper form- homogeneous exospore of Saadisporites (Kedves, genus (probably extinct type of Taxaceae) pollen 1986). During the Early Cretaceous homogeneous grain (ef Kedves and Párdutz, 1973, Batten and spore ultrastructure was described for several Dutta, 1997).This pollen group is also of Mesozoic miospores [Rujjordiaspora australiensis (Cookson) type. Dettmann and Cookson, Ruffordia goepperti (Dunker) 2.4. The exine ultrastructure of Eueommiidites Seward in situ spores, Plieatella distoearinata Erdtman is also of angiosperm character, but with (Dettmann and Playford) Davies, Cyatheaeidites tec- granular infratectal layer (Doyle et al., 1975, Batten tijera Archangelsky and Gamerro]. Spongy perispore and Dutta, 1997).There are a number of publications and more or less compact exospore were observed in on this subject. The taxonomy and the botanical affin- spores of the form-genus Crybelosporites Li Wen-ben ity were discussed for example by Batten and Dutta and Batten. In the megaspore ultrastructure three (1997).Worth mentioning is the Eueommiitheea hirsu- types may be distinguished: ta Friis and Pedersen (1996b), from the early 1. The early: spongy perispore, and lamellar ex- Cretaceous of Portugal. TEM and SEMinvestigations ospore. were made on the associated pollen grains also. The 2. The intermediate: spongy outer layer, and fila- electron dense endexine may be emphasized at this mentous inner one. material. 3. The evolved types are represented by a spongy 2.5. Similar is the ultrastructure of the polyplicate perispore and an homogeneous exospore. gymnosperm pollen grains (Ephedripites Bolkho- The wall ultrastructure of Upper Cretaceous vitina). spores presents mostly modem and intermediate 2.6. The Operculati group (Cireulina Malyavkina, types, particularly in the megaspores. In several Classopollis Pflug, Classoidites Amerom) which repre- Upper Cretaceous miospores homogeneous wall was sents the Cheirolepidaceae (Pagiophyllum, Braehy- described, but in the Lycopodiaceous Zlivisporis phyllum, Cheirolepis) is an important constituent of Pacltová lamellar perispore and exospore were estab- the Mesozoic vegetation. Circulin« Malyavkina is the lished. The wall of the Hydrosporis Krutzsch form- earliest, Classoidites Amerom the most evolved type. genus (microspore of fossil Azolla) is homogeneous, The LM morphology is completely isolated without but the spores are embedded in a unit-membrane like relation to other fossil and recent gymnosperm epispore. pollen grains. The exine ultrastructure as Pettitt and Chaloner (1964) pointed out "complexity is un- Gyrnnosperrnophyta matched even among living angiosperms". There are several papers conceming the exine ultrastructure of 1. The disaccate gymnosperm pollen type with this group, the most important are as follows: alveolar infratectal layer is represented by different Circulina Malyavkina fspp. 1-3 (Médus, 1977), types during the Mesozoic. This pollen type is pre- Classopollis classoides (Pflug) Pocock and Jansonius sent from the Paleozoic until the present day vegeta- 1961(Kedves, 1990),Classoidites glandis Amerom 1965 tion (Pinus, Picea, etc.). The peculiar Mesozoic type (Kedves and Párdutz, 1973).The pollen grains of the A.P.A.PublicaciónEspecial7,2001 Transmissionelectronmicroscopyof Mesozoicterrestrialmicrofossils 115 last two form-genera can be well distinguished by 3.5. In a further stage of evolution the columellar ectexine ultrastructure, infratectallayer is columellar infratectal layer and the endexine appear, but at a in Classopollis Pflug, and irregular in Classoidites higher level. Amerom form-genus. Based on the concept of 3.6. It is necessary
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