J. B. Richardson

A new plant assemblage (microfossil and megafossil) from the Lower Old Red Sandstone of the Anglo-Welsh Basin: its implications for the palaeoecology of early terrestrial ecosystems.

Lower Old Red Sandstone deposits penetrated by a series of cored boreholes near Newport (South Wales) have been sedimentologically logged, and recovered plant assemblages (microfossil and megafossil) investigated. Sedimentological logging indicates that the deposits are typical of the extensive terrestrial-fluviatile floodplain deposits of the Anglo-Welsh Basin. Palynomorph assemblages have been recovered from a number of horizons and comprise entirely terrestrial forms (spores and phytodebris). They essentially represent a single assemblage, belonging to the middle subzone of the micrornatus-newportensis sporomorph assemblage biozone, and indicate an Early Devonian (mid-Lochkovian) age. The new biostratigraphical data enables correlation with other Lower Old Red Sandstone deposits of the Anglo-Welsh Basin, and the deposits are assigned to the lower part of the St. Maughans Group. A plant megafossil/mesofossil assemblage recovered from one of the spore-bearing horizons includes a zosterophyll assigned to Zosterophyllum cf. fertile. This is the earliest reported zosterophyll from the Anglo-Welsh Basin. The new palynological/palaeobotanical data provide important information on the palaeoecology and palaeobiogeography of the vegetation of the southeastern margin of the Old Red Sandstone continent during Lochkovian times. Palaeogeographical variation in the distribution of plant microfossils and megafossils is interpreted as reflecting differences between the flora of the lowland floodplain and inland intermontaine basins, although this is to a certain extent overprinted by variation due to localized differences in environmental conditions.

Progress in reconstructing vegetation on the Old Red Sandstone Continent: two Emphanisporites producers from the Lochkovian sequence of the Welsh Borderland

Abstract Small coalified fossils (mesofossils) have yielded new insights into vegetation of the Old Red Sandstone Continent in early Devonian times. Particularly useful are those containing spores that can be placed in dispersed spore taxa, although patinate and emphanoid spores have not hitherto been found in situ. Emphanisporites cf. micrornatus Richardson & Lister is described in a bifurcating cylindrical sporangium preserved as a cuticular sheath. A terminal dehiscence feature is compared with that in Horneophyton. The sporangium is encased in amorphous detritus with some tubular fragments. Similar associations occur on other sporangia, e.g. Tortilicaulis and axes at this North Brown Clee Hill locality, and they are interpreted as remains of a microbial or fungal film. Fragmentary cuticles, interpreted as isolated sporangial valves, bear an undescribed species of Emphanisporites with fine interdigitating proximal muri and laevigate distal surfaces referred to Emphanisporites sp. A Richardson & Lister. Analysis of dispersed spore assemblages from the locality and others in the Welsh Borderland indicate that the two emphanoid taxa were not common components of the spore ‘rain’. This evidence, coupled with the dearth of mesofossils of the producers, suggests that the plants grew at the upper reaches of the drainage basin of the river that deposited the sediment, although the paucity of sporangia may also be attributed to their low fossilization potential.

The advantages and frustrations of a plant Lagerstätte as illustrated by a new taxon from the Lower Devonian of the Welsh Borderland, UK.

Abstract A Lagerstatte of fragmentary charcoalified plants from a siltstone horizon in the Welsh Borderland, UK, provides remarkable insights into Early Devonian vegetation, in the form of anatomical data on basal embryophytes (tracheophytes, cryptophytes), nematophytes, lichens, and plant–animal interactions. Investigations continue and here we describe a new taxon to add to the list of presumed tracheophytes. It possesses unusual reproductive complexes. A terminal, discoidal sporangium, containing trilete spores, is attached centrally and expands distally into an overlying planar structure that extends into large peripheral triangular projections. Short subtending stems and distal surfaces of the planar structure bear occasional stomata. This unique sporangial organisation raises questions of function, including photosynthesis and spore dispersal, and of affinity (although the sporangia themselves would be described as cooksonioid). However, the study of these fossils is not without challenges and frustrations. These in part could be mitigated by the use of new technological advances in visualization and geochemistry in future research.