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Heol Senni Quarry

The quarry contains fossils that define the first significant colonisation of terrestrial habitats by vascular plants and fossil chordates.

Natural Resources Wales is responsible for it and this is their description of it:

National grid reference: SN 914222, Site area: 3.4 hectares
The site is of special geological interest on two scores:
(i) Non-marine Devonian: the site has cliff exposures of the Brownstones (the upper part of the Welsh Lower Old Red Sandstone). The Brownstones here consist of pebbly, cross-bedded sands, which formed in a large braided river system. The cliffs allow reconstruction of bar morphologies and river size, and show the way channels were stacked vertically to build up the sequence. The well developed stream topography between bars and channels that is seen in the deposits here is typical of the eastern outcrops of the Brownstones, and contrasts with the deposits of the western Brownstones in south Wales. This locality is the best of the eastern Brownstone outcrops, showing a distinct form of river alluvium.
(ii) Vertebrate palaeontology: the type and only locality for Althaspis senniensis. Chordates are extremely rare in the Senni Beds and are know only from two other sites. Althaspis senniensis is a typical pteraspid of the ‘Dittonian’ and is very similar to, and might even be conspecific with Althaspis leachi, a form known throughout north-west Europe at the top of the Gedinnian Stage. Another Senni Beds quarry locally yields Rhinopteraspis dunensis, which occurs in the type area of the Siegenian Stage. Taken together these two quarries show that the Gedinnian/Siegenian boundary lies somewhere within the Senni Beds between these two fossil-bearing horizons. At present, work is being concentrated on these two species, and future research potential lies in determining the stratigraphical and facies controls on their distribution in Europe.

See also the entry in Wikekpedia

In 2010 a site was found in Argentina showing that a diversity of land plants had evolved by 472 million years ago. The earliest recognized land plants are liverworts, that are likely to be the ancestors of all land plants. These findings suggest that the first colonisation of land by plants could have occurred during the early Ordovician period (488 to 472 million years ago) or even during the late Cambrian period (499 to 488 million years ago).

Updated 20/02/2022