Vertebrate-bearing fissure deposits of South-West England and South Wales

Cave and fissure systems developed in the Carboniferous Limestones of the Mendips and Glamorgan (Figure 4.22) during the Late Triassic and earliest Jurassic contain abundant reptilian and other vertebrate remains. The Mendips and parts of South Wales appear to have comprised an archipelago of low limestone islands, and the fissures developed in these limestones preserve a detailed record of the diverse and often insular herpetofaunas of the time (Robinson, 1957a; Tarlo, 1962; Halstead and Nicoll, 1971; Kermack et al., 1973; Fraser, 1986, 1988b, 1994; Savage, 1993). The nature of the palaeokarst and the geology of the caves is reviewed by Simms (1990). The fossil bones, although isolated and disarticulated, are often well preserved and lend themselves to detailed anatomical studies involving a large number of individuals, for example Whiteside (1986) on Diphydontosaurus avonis and Fraser (1988c) on Clevosaurus. The main Late Triassic (1–8) and Early Jurassic (9–13) fissures of south-west England and Wales (Figure 4.22), and their reptile faunas see (Figure 4.24), are listed below:

1. Slickstones (Cromhall) Quarry, Avon [ST 704 916]. Seven species of sphenodontid, including the types of Clevosaurus budsoni Swinton, 1935, C. minor Fraser (1988c), Planocephalosaurus robinsonae Fraser (1982), Sigmala sigmala Fraser (1986) and Pelecymala robustus Fraser (1986), as well as two unnamed sphenodontids, a procolophonid, the gliding diapsid Kuebneosaurus, an ?aetosaur, a ?scleromochlid, a terrestrial crocodilomorph, a ?sphenosuchid, a rhamphorhynchoid pterosaur, the dinosaur Thecodontosaurus, the enigmatic diapsid/ procolophonid Variodens and various unidentified diapsids.
2. Tytherington Quarry, Avon [ST 660 890]. Type of the sphenodontid Diphydontosaurus avonis Whiteside (1986), as well as the sphenodontids Clevosaurus, Planocephalosaurus, a crocodilomorph, the dinosaur Thecodontosaurus, a 'coelurosaue dinosaur, and unidentified sphenodontids and archosaurs.
3. Durdham Down, Avon [ST 572 747]. Types of the prosauropod dinosaur Thecodontosaurus antiquus Morris (1843) and the (?) phytosaur Rileya platyodon (Riley and Stutchbury, 1840). Also Diphydontosaurus.
4. Batscombe Quarry, Somerset [ST 460 550]. Type of the gliding diapsid Kuebneosuchus (?= Kuebneosaurus) latissimus (Robinson, 1962).
5. Emborough Quarry, Somerset [ST 623 505]. Types of the gliding diapsid Kuebneosaurus latus Robinson (1962) and the enigmatic diapsid Variodens inopinatus Robinson (1957b), as well as an archosaur, a sphenodontid and the mammal Kuebneotherium sp.
6. Highcroft Quarry, near Gurney Slade, Somerset [ST 623 499]. A reptile jaw (Robinson, 1957a), ?Clevosaurus (Fraser, 1994).
7. Pant-y-ffynon Quarry, South Glamorgan [ST 047 741]. Type of the terrestrial crocodilomorph Terrestrisuchus gracilis Crush (1984), as well as the gliding diapsid Kuehneosaurus, the sphenodontid Clevosaurus, a scleromochlid, the dinosaurs Thecodontosaurus cf. antiquus (Kermack, 1984) and Syntarsus, and lepidosaurs.
8. Ruthin Quarry, South Glamorgan [SS 975 796]. Type of Tricuspisaurus thomasi Robinson (1957), as well as pleurodont reptiles, the sphenodontids Clevosaurus and Planocephalosaurus and archosaurs (Fraser, 1986, 1994).
9. Windsor Hill Quarry, near Shepton Mallet, Somerset [ST 615 452]. Types of the tritylodont mammal-like reptiles Oligokyphus major Kühne (1956) and O. minor Kühne (1956).
10. Holwell Southern Quarry, near Frome, Somerset [ST 727 452]. Types of the early mammals Haramiya moorei (Owen, 1871), H. fissurae (Simpson, 1928), Thomasia anglica Simpson (1928), Eozostrodon parvus Parrington (1941) and E. problematicus Parrington (1941), as well as teeth of crocodilians, and other reptiles (Robinson, 1957a), a tritylodont (Savage and Waldman, 1966) and Clevosaurus (Fraser, pers. comm., 1993).
11. Duchy Quarry, South Glamorgan [SS 906 757]. Type of Morganucodon watsoni Kühne (1949), as well as other triconodont teeth and a symmetrodont mammal.
12. Pont Alun Quarry, South Glamorgan [SS 899 765]. Types of the sphenodontian Gephyrosaurus bridensis (Evans, 1980, 1981) and Kuhneosaurus praecursori Kermack et al. (1968), as well as Morganucodon/Eozostrodon.
13. Pant Quarry, South Glamorgan [SS 896 760]. The sphenodontian Gephyrosaurus, three sphenodontids, one or more archosaurs, the tritylodont Oltgokyphus and the mammals Thomasia, Kuehneotherium and Morganucodon watsoni.

The dating of the fissures is difficult. Robinson (1957a) regarded all the reptile-dominated ('sauropsid') faunas as being Norian in age, and those dominated by tritylodonts and mammals ('theropsid' faunas) as Rhaetian or Early Jurassic. Fraser (1986, 1994) argued that the sauropsid/theropsid, Norian/Rhaeto-Jurassic correlation was not clear-cut: it could just as readily be a taphonomic division of faunas. Independent palynological evidence has established a Rhaetian age for some Tytherington fissures (Marshall and Whiteside, 1980) and a Hettangian–Sinemurian age for Duchy, Pant and Pont Alun Quarries, based on the occurrence of Hirmerella (Cheirolepis) spores in the last three sites. The division into sauropsid/theropsid assemblages was further challenged by the discovery of a mammal tooth, Kuehneotherium sp., at Emborough Quarry in a fissure otherwise clearly placed in the 'sauropsid' Triassic group (Fraser et al., 1985).

In the absence of further palynological evidence, some indication of the ages of individual fissure faunas may be obtained by comparisons of reptiles and mammals with more securely dated localities elsewhere. For example, the crocodylomorph Terrestrisuchus is most like Saltoposuchus (and may be congeneric) from the middle Norian Mittlerer Stubensandstein of south-west Germany. Thecodontosaurus is a basal prosauropod, like forms of Late Carnian to Norian age in North America, central Europe and southern Africa. Procolophonids, aetosaurs and scleromochlids all died out before the end of the Triassic elsewhere, and aetosaurs are exclusively Late Carnian to Rhaetian in age. Scleromochlus is known otherwise only from the Late Carnian of Scotland. Kuehneosaurus is most like Icarosaurus from the Late Carnian of North America. All the evidence, therefore, confirms a Late Triassic age for the fissures nos. 1–8 in the above list, and probably a range of ages from Late Carnian to Rhaetian. There is no reason why all should be regarded as contemporaneous, but all should postdate the Mid Carnian pluvial episode of Simms and Ruffell (1989, 1990), if those authors are correct that most of the fissures were excavated at that time.

Four fissure localities of scientific and historic importance are selected as GCR sites, while Windsor Hill Quarry has been scheduled for its tritylodont remains as a mammal site (see GCR Fossil Mammals and Birds volume):

1. Slickstones (Cromhall) Quarry, Avon [ST 704 916]. Late Triassic (Carnian/Norian), fissure fill.
2. Durdham Down, Avon [ST 572 747]. Late Triassic (Carnian/Norian), fissure fill.
3. Emborough Quarry, Somerset [ST 623 505]. Late Triassic (Carnian/Norian), fissure fill.
4. Tytherington Quarry, Avon [ST 660 890]. Late Triassic (Carnian/Norian), fissure fill.

References