Prescott Corner

[SJ 6636 8118]

Highlights

Prescott Corner near Farlow in south Shropshire has been the source of at least five species of fossil fishes, including Bothriolepis macrocephala Egerton and Eusthenopteron farloviensis White, both forms otherwise recorded only from Farlow. These fishes form a particular assemblage, typical of the 'Farlovian' Stage, correlated with the Frasnian Stage of the Late Devonian.

Introduction

At Prescott Corner a small roadside exposure of Upper Devonian conglomerates lies within a series of yellow sandstones that are seen in cliffs nearby. This site has yielded an assemblage of Upper Devonian fishes which, although restricted and fragmentary, is equivalent to the assemblage that was discovered from a similar horizon from a quarry in Farlow in 1856 (Morris and Roberts, 1862). The geology of the vicinity has been described by King (1925), Ball and Dineley (1961), Allen (1965) and Greig et al. (1968).

Description

The distinctive pale sandstones of this part of the Clee Hills area were named the Farlow Sandstones by WW King (1925). They unconformably overlie Ditton Group (Early Devonian) red sandstones and siltstones and there is a faulted contact with the Lower Carboniferous. Ball and Dineley (1961) divided the Farlow Group into a lower Yellow Farlow Sandstone Formation, consisting of about 60 m of fine- to coarse-grained yellow sandstones and pebbly sandstones, with rare red or green mudstones, above a basal conglomerate, and an overlying upper Grey Farlow Sandstone Formation, 12–90 m of pebbly calcareous sandstones with subordinate red mudstones and nodular mudstones.

Both units of the Farlow Group contain fragments of fossil fishes. The Yellow Sandstones are rather more fossiliferous and have been the source of a few complete plates; the Grey Sandstones have yielded only fragments. The site at Prescott was the only site that Ball and Dineley (1961, p. 208) found to be relatively prolific, and they described the occurrence of 'the fragments …concentrated in a small lens of gritty sandstone, obviously representing a winnowed deposit… as at Farlow, other plates occur scattered randomly in finer sandstones'.

Fauna

Placodermi: Antiarchi: Bothriolepidae

Bothriolepis macrocephala Egerton, 1862

B. sp.

Osteichthyes: Porolepiformes: Holoptychidae

Holoptychius sp.

Pseudosauripteris anglicus (Woodward, 1891a)

Osteichthyes: Osteolepiformes: Eusthenopteridae

?Eusthenopteron farloviensis White, 1961

Dipnoi and other indeterminate sarcopterygians

Bothriolepis macrocephala is only recorded from Farlow, its description by Egerton (1862) having been based on material collected from Church Quarry. The specimens represent a small, or juvenile, Bothriolepis with a relatively large head, closely related to the larger Bothriolepis hydrophilia (Agassiz) from Dura Den, Scotland (Woodward, 1891a; Stensiö, 1948). No larger specimens were recorded from Church Quarry in the original descriptions, but White (1961) suggests that one specimen in the collection may be of the latter species. Taken together with the occurrence of fragments of a larger form from Prescott Corner, this led him to concludes that B. macrocephala is likely to be a young form of B. hydrophila or some similar large Bothriolepis, but Miles (1968) and Denison (1978) maintained the distinction between the two species.

Eusthenopteron farloviensis is based mainly on several fragments from the Church Quarry collections, plus a jaw-bone with teeth from Prescott (White, 1961; (Figure 7.7)B). They belong to a fish that would have been about 0.8 m long, and which was similar to the E. foordi Whiteaves from Canada, and to the Scottish E. traquairi Woodward.

The genus Pseudosauripteris is relatively new. Sauripteris anglicus was described by Woodward (1891a), based on fragmentary material of scales and teeth from the Church Quarry collection. The ornament of the scales is well preserved. Sauripteris is a genus of rhizodont from the Catskill red beds of eastern North America. In redescribing the Farlow material, including newly collected specimens from Prescott Corner, White (1961) identified it as holoptychiid because of radiating lines of tubercles on the overlapped part of the scales, which are characteristic of the group. He erected the new genus Pseudosauripterus for the single species from Farlow (Figure 7.7) A. White (1961) also described from Church Quarry a previously unknown entopterygoid which is probably from this species, plus some other imperfect fragmentary remains from Prescott.

Interpretation

The Farlow Group is interpreted as of fluvial origin, deposited by episodic floods of elastic detritus discharging through shallow channels across a coastal plain. Water flow was predominantly southwards from uplands in Wales and central England (Allen, 1965, 1979). The vertebrate fossils, largely known from very fragmentary material, probably originated in local small faunules occupying the river system and periodically flushed downstream by episodic floods.

The Farlow Group has a limited outcrop in the Farlow area to the east of Titterstone Clee Hill, and because of uncertain stratigraphical relationships was termed the 'Farlovian' by King (1934) who used this stratigraphical term to include all Upper Old Red Sandstones in the Welsh Borders. This was regarded as a single biostratigraphical stage (Ball and Dineley, 1961; Allen, 1965) based on the fish assemblage best seen in the Farlow area. Fossils are rare in the continental Anglo-Welsh Upper Old Red Sandstones, but the Farlow assemblage may be compared with specimens of Holoptychius from sites in Pembrokeshire and the Black Mountains of South Wales, and of larger Upper Old Red assemblages from the Forest of Dean and the Bristol area. The Farlovian Stage is equated roughly with the Famennian Stage (Allen, in House et al., 1977).

Comparison with other localities

No other localities in southern Britain have yielded an Upper Devonian vertebrate fauna as extensive as that at Prescott Corner. Devonian localities in Scotland have provided the nearest comparable fish assemblages (Chapter 8).

Conclusion

The Farlovian fish assemblage from Prescott Corner is a localized fauna, containing some unique species. The assemblage has been important in characterizing a stage in the continental Devonian of the Welsh Borders, but many of the original quarries are no longer accessible. The conservation value of Prescott Corner lies in its potential for future collection of the unusual fish assemblage.

References