Cooksonia

Cooksonia
	Cooksonia , life reconstruction
Temporal occurrence
	Silurian ( Ludlow ) to Lower Devonian ( Emsium )
	423 to 397 million years
Locations
	worldwide;
Systematics
without rank:	Charophyta
without rank:	Phragmoplastophyta
without rank:	Streptophyta
Empire :	Plants (Plantae)
Department :	Rhyniophyta
Genre :	Cooksonia
Scientific name
	Cooksonia
	Long

Cooksonia is a fossil plant genus that is mainly known from the Silurian . Their representatives are among the oldest known land plants.

features

Cooksonia were only a few inches high. The bare axes were forked (dichotomous), had stomata and an outer ring of thickened cells (sterome). The sporangia were terminal, the spores were thick-walled. The axes had real vessels ( tracheids ).

Systematics

The genus Cooksonia is traditionally placed with the Rhyniophyta . However, it is highly polyphyletic : While some species are basal representatives of the eutracheophytes , Cooksonia cambrensis is close to the bear moss plants . Some types are:

Cooksonia pertonii is known from the late Silurian ( Pridolium ) of Hertfordshire , England, or the early Devonian ( Lochkovium ) of Shropshire , England, among others . The shoot axes may be unbranched, bare and have an outer layer of thick-walled cells (sterom). No water-conducting cells have been preserved. The epidermal cells of the axis are elongated, stomata are present. The epidermal cells of the sporangium are isodiametric. The sporangia are oval, broader than high. They are terminal and have no recognizable opening structures. The microspores are trilet (three-pointed scar). Like the following species, Cooksonia pertonii is right at the base of the eutrachophytes (see cladogram in vascular plants ).

Cooksonia caledonica is known from the Lochkovian of Angus , Scotland , among others . The axes are bare and evenly dichotomously branched at least four times. Anatomy or cuticle are unknown. The sporangia are oval to kidney-shaped, are terminal and possibly open into two equal valves. Spores and gametophyte are unknown.
Cooksonia cambrensis has been described from fragmentary fossils of the Lower Red Marl Group of Freshwater East Bay, Dyfed , Wales , from the late Silurian ( Pridolium ). The axes are bare and at least once evenly branched dichotomously. Anatomy, stomata or cuticle properties are unknown. The sporangia are circular to elliptical and are terminal. Opening mechanisms are not known.
Cooksonia hemisphaerica was described from the lower Old Red Sandstone of Shropshire , England, from the Lochkovian . The axes are up to 6.5 centimeters long, bare and branch evenly dichotomously at least once. The axle diameter is around 1.5 millimeters. The sporangia are hemispherical to elliptical and are terminal. The stomata are unknown. The microspores are spherical, smooth, and 23 to 35 micrometers in diameter.

Cooksonia banksii was only described in 2002 from the Lower Devonian (Lochkovian) of Shropshire, England. The spore-containing area is included here in the extended tip region of the axis. The cavity is lined with a smooth, non-cellular layer. Clearly cells are only found at the edge of the sporangia. The spores belong to Ambitisporites avitus .

Temporal and geographical distribution

Cooksonia was found in Wales in deposits from the middle Silurian ( Ludlow ) and are up to 423 million years old. Cooksonia- like sporangia from Ireland are dated to Wenlock (428 million years). The finds reach as far as the Emsium in the Lower Devonian, which ended 397 million years ago.

Fossils of the genera have been found practically worldwide, but mainly in areas of the former continent Laurasia , such as the USA, Canada, Scotland, the former Czechoslovakia, Wales, Libya and Siberia. Finds from South America, for example, are rare.

Botanical history

The genus was named by William Henry Lang after Isabel Clifton Cookson , a paleontologist.

supporting documents

Paul Kenrick, Peter R. Crane: The Origin and Early Diversification of Land Plants. A Cladistic Study . Smithsonian Institution Press, Washington DC 1997, pp. 324-326. ISBN 1-56098-729-4
Thomas N. Taylor, Edith L. Taylor: The Biology and Evolution of Fossil Plants . Prentice Hall, Englewood Cliffs 1993, pp. 191f. ISBN 0-13-651589-4

Individual evidence

↑ D. Edwards , KL Davies, L. Ax: A vascular conducting strand in the early land plant Cooksonia . In: Nature . 357, No. 6380, 1992, pp. 683-685. doi : 10.1038 / 357683a0 .
^ KS Habgood, D. Edwards, L. Ax: New perspectives on Cooksonia from the Lower Devonian of the Welsh Borderland . Botanical Journal of the Linnean Society, Volume 139, 2002, pp. 339-359. doi : 10.1046 / j.1095-8339.2002.00073.x
^ D. Edwards, J. Feehan: Records of Cooksonia-type sporangia from late Wenlock strata in Ireland . Nature, Vol. 287, 1980, pp. 41-42. doi : 10.1038 / 287041a0
^ E. Morel, D. Edwards, and M. Inigez Rodriguez: The first record of Cooksonia from South America in Silurian rocks of Bolivia . Geological Magazine, Volume 132, 1995, pp. 449-452.

Web links

Commons : Cooksonia - collection of images, videos and audio files

Cooksonia on www.palaeos.com

[Edwards1992-1] D. Edwards , KL Davies, L. Ax: A vascular conducting strand in the early land plant Cooksonia . In: Nature . 357, No. 6380, 1992, pp. 683-685. doi : 10.1038 / 357683a0 .

[2] KS Habgood, D. Edwards, L. Ax: New perspectives on Cooksonia from the Lower Devonian of the Welsh Borderland . Botanical Journal of the Linnean Society, Volume 139, 2002, pp. 339-359. doi : 10.1046 / j.1095-8339.2002.00073.x

[3] D. Edwards, J. Feehan: Records of Cooksonia-type sporangia from late Wenlock strata in Ireland . Nature, Vol. 287, 1980, pp. 41-42. doi : 10.1038 / 287041a0

[4] E. Morel, D. Edwards, and M. Inigez Rodriguez: The first record of Cooksonia from South America in Silurian rocks of Bolivia . Geological Magazine, Volume 132, 1995, pp. 449-452.