Cooksonia; early land plant; Early Devonian; heteromorphic life cycle; eutracheophytes
Abstract :
[en] An exceptionally large specimen of the early land plant Cooksonia paranensis Gerrienne et al. has been discovered from the type locality (Jackson de Figueiredo, Parana Basin, Brazil; early Lochkovian, Early Devonian). This nearly complete specimen consists of five dichotomous axes attached at their base to a small thalloid(?) structure. Each terminal axis segment ends in an expanded, cup-like, empty tip. Three interpretations of the specimen are proposed. (1) The whole specimen is a gametophyte of the Sciadopkyton-type, with a central area from which five axes depart; under this interpretation, the terminal cups are gametangiophores. (2) The basal structure represents the remains of a rhizome bearing five upright aerial axes, in which case the whole plant is a sporophyte. (3; our favoured hypothesis) The specimen is a cluster of five individual sporophytes still attached to the remains of a small female or bisexual gametophyte. In the latter case, this fossil is evidence that reduced thalloid gametophytes and branched axial sporophytes are plesiomorphic among the earliest eutracheophytes. We suggest that a major difference in life cycle defines a basal dichotomy in tracheophytes. Eutracheophyta, including all living vascular plants, have a heteromorphic, sporophyte dominant alternation of generations, whereas their extinct sister-group Rhymopsida (renamed here Paratracheophyta) is characterised by a more or less isomorphic alternations of generations. (c) 2006 Elsevier B.V. All rights reserved.
Edwards D.S. Aglaophyton major, a non-vascular land-plant from the Devonian Rhynie Chert. Bot. J. Linn. Soc. 93 (1986) 173-204
Edwards D. Xylem in early tracheophytes. Plant Cell Environ. 26 (2003) 57-72
Edwards D. Embryophytic sporophytes in the Rhynie and Windyfield cherts. Trans. R. Soc. Edinb. Earth Sci. 94 (2004) 397-410
Edwards D., and Feehan J. Record of Cooksonia-type sporangia from late Wenlock strata in Ireland. Nature 287 (1980) 41-42
Edwards D., Davies K.L., and Axe L. A vascular conducting strand in the early land plant Cooksonia. Nature 357 (1992) 683-685
Edwards D., Morel E.M., Paredes F., Ganuza D., and Zúñiga A. Plant assemblages from the Silurian of southern Bolivia and their palaeogeographic significance. Bot. J. Linn. Soc. 135 (2001) 220-250
Edwards D., Axe L., and Duckett J.G. Diversity in conducting cells in early land plants and comparisons with extant bryophytes. Bot. J. Linn. Soc. 141 (2003) 297-347
Fairon-Demaret M., Hilton J., and Berry C.M. Surface preparation of macrofossils (dégagement). In: Jones T.P., and Rowe N.P. (Eds). Fossil Plants and Spores. Modern Techniques (1999), The Geological Society, London 33-35
Fanning U., Richardson J.B., and Edwards B. Cryptic evolution in an early land plant. Evol. Trends Plants 2 (1988) 13-24
Gensel P.G., Kotyk M.E., and Basinger J.F. Morphology of above- and below-ground structures in Early Devonian (Pragian-Emsian) plants. In: Gensel P.G., and Edwards D. (Eds). Plants Invade the Land: Evolutionary and Environmental Perspectives (2001), Columbia University Press, New York 83-102
Gerrienne P., Bergamashi S., Pereira E., Rodrigues M.A.C., and Steemans P. An Early Devonian flora, including Cooksonia, from the Paraná Basin (Brazil). Rev. Palaeobot. Palynol. 116 (2001) 19-38
Gerrienne P., Meyer-Berthaud B., Fairon-Demaret M., Streel M., and Steemans P. Runcaria, a Middle Devonian seed plant precursor. Science 306 (2004) 856-858
Gradstein F.M., Ogg J.G., Smith A.G., Bleeker W., and Lourens L.J. A new geologic time scale, with special reference to Precambrian and Neogene. Episodes 27 (2004) 83-100
Graham L.E., and Wilcox L.W. The origin of alternation of generations in land plants: a focus on matrotrophy and hexose transport. Philos. Trans.-R. Soc. Lond., Phys. Sci. Eng. B355 (2000) 755-767
Habgood K.S., Edwards D., and Axe L. New perspectives on Cooksonia from the Lower Devonian of the Welsh Borderland. Bot. J. Linn. Soc. 139 (2002) 339-359
Karol K.S., McCourt R.M., Cimino M.T., and Delwiche C.F. The closest living relatives of land plants. Science 294 (2001) 2351-2353
Kenrick P. Alternation of generations in land plants: new phylogenetic and palaeobotanical evidence. Biol. Rev. 69 (1994) 293-330
Kenrick P. The relationships of vascular plants. Philos. Trans. R. Soc. Lond., Phys. Sci. Eng. B355 (2000) 847-855
Kenrick P., and Crane P.R. Water-conducting cells in early fossil land plants: implications for the early evolution of tracheophytes. Bot. Gaz. 152 (1991) 335-356
Kenrick P., and Crane P.R. The origin and early evolution of plants on land. Nature 389 (1997) 33-39
Kenrick P., and Crane P.R. The origin and early diversification of land plants. A Cladistic Study (1997), Smithsonian Institution Press, Washington DC 441 pp.
Kenrick P., Remy W., and Crane P.R. The structure of water-conducting cells in the enigmatic early land plants Stockmansella langii Fairon-Demaret, Huvenia kleui Hass et Remy and Sciadophyton sp. Remy et al. 1980. Arg. Palaeobot. 8 (1991) 179-191
Kerp H., Trewin N.H., and Hass H. Rhynie Chert gametophytes. Trans. R. Soc. Edinb. Earth Sci. 94 (2004) 411-428
Raven P.H., Evert R.E., and Eichhorn S.E. Biology of Plants. Sixth Ed. (1999), Freeman, New York 944 pp.
Remy W. Lower Devonian gametophytes: relation to the phylogeny of land plants. Science 215 (1982) 1625-1627
Remy W., and Hass H. Kidstonophyton discoides nov. gen. nov. spec., ein Gametophyt aus dem Chert von Rhynie (Unterdevon, Schottland). Arg. Palaeobot. 8 (1991) 29-45
Remy W., and Hass H. Langiophyton mackiei nov. gen., nov. spec., ein Gametophyt mit Archegoniophoren aus dem Chert von Rhynie (Unterdevon Schottland). Arg. Palaeobot. 8 (1991) 69-117
Remy W., and Remy R. Devonian gametophytes with anatomically preserved gametangia. Science 208 (1980) 295-296
Remy W., Schultka S., and Hass H. Calyculiphyton blanai, nov. gen., nov. Ps., ein Gametophyt aus dem Ems. Arg. Palaeobot. 8 (1991) 119-140
Remy W., Gensel P.G., and Hass H. The gametophyte generation of some Early Devonian plants. Int. J. Plant Sci. 154 (1993) 35-58
Schultka S. Cooksonia-Zur Morphologie einer frühen Landpflanze aus dem Unterdevon der Eifel. Cour. Forsch.-Inst. Senck. 241 (2003) 7-17
Schweitzer H.-J. Der Generationwechsel der Psilophyten. Bonn. Paläobot. Mitt. 5 (1981) 1-38
Schweitzer H.-J. Planzen erobern das Land. Kleine Senckenb.-Rh. 18 (1990) 1-75
Strother P.K., Al-Hajri S., and Traverse A. New evidence for land plants from the lower Middle Ordovician of Saudi Arabia. Geology 24 (1996) 55-58
Taylor T.N., Kerp H., and Hass H. Life history biology of early land plants: deciphering the gametophyte phase. Proc. Natl. Acad. Sci. U. S. A. 102 (2005) 5892-5897
Wellman C.H., Osterloff P.L., and Mohiuddin U. Fragments of the earliest land plants. Nature 425 (2003) 282-285
