Britain

The other major European occurrence of Late Triassic-Early Jurassic mammals is in southern England and Wales, from sites on either side of the Bristol Channel (figure 2.3). We have drawn from the excellent review of Evans and Kermack (1994) in summarizing these occurrences. During the Late Triassic and Early Jurassic, shallow seas covered parts of the British Isles, transgressing through time, so that major islands transformed into an archipelago. Karst topography developed on the subaerially exposed Carboniferous limestone, and vertebrate remains were carried into the systems of fissures and caves together with clastic sediments. The age of these fissure deposits was long uncertain, with the result that they were simply termed Rhaeto-Liassic in age (e.g., Kermack et al., 1973). Palynological and other evidence, including reference to rocks marking the transgression that defines the beginning of the Rhaetian (Fraser et al., 1985), has led to general agreement on the ages of most of the mammal-yielding localities. One grouping of sites occurs in Glamorgan, near Brigend, Wales. The principal mammal-yielding sites (Ewenny, Pontalun, Duchy, and Pant Quarries) are part of an assemblage of localities called St. Bride's Island. They are closely grouped geographically, probably representing the same small paleoisland (Robinson, 1957), and are considered to be of Early Jurassic age. The other

figure 2.3. Mesozoic mammals of Britain. Asterisks, Late Triassic-Early Jurassic (black; localities 1-3), Middle Jurassic (gray; localities 4-11), and Late Jurassic (white; locality 12). Diamonds, Early Cretaceous (?Berriasian, localities 13, 14; Valan-ginian and ?Valanginian, localities 15-20). Localities or local faunas: 1, Holwell (?late Norian or Rhaetian, fissure filling); 2, Em-borough (Norian, fissure filling); 3, St. Bride's Island (Ewenny, Pontalun, Duchy, and Pant quarries; fissure fillings, Liassic); 4, Hornsleasow (Chipping North Formation; early Bathonian); 5, Kirtlington (Forest Marble; late Bathonian); 6, Woodeaton (Hampen Marly Formation; middle Bathonian); 7, Stonesfield (Stonesfield Member, Sharps Hill Formation; early middle Bathonian); 8, Tarlton Clay Pit; 9, Swyre; 10, Watton Cliff (Forest Marble; late Bathonian); 11, Loch Scavaig and Elgol, Isle of Skye (Ostracod Limestone; middle Bathonian); 12, Chicksgrove (Portland Stone Formation, Tithonian); 13, Durlston Bay; 14, Sunnydown Farm (Lulworth Formation, Purbeck Limestone Group; Berriasian); 15, Belle Vue; 16, Acton (Durlston Formation, Purbeck Limestone Group; Berriasian); 17, Tighe Farm (Wadhurst Formation, Wealden Group; early Valanginian); 18, Paddockhurst Park (Grinstead Clay, Wealden Group; middle Valanginian); 19, Cliff End (Wadhurst Formation, Wealden Group; early Valanginian); 20, Isle of Wight (Wealden Group, ?Valanginian).

major grouping of sites is to the east of the Bristol Channel, in the Bristol-Mendip region of southern England. Two of these sites, Emborough and Holwell, have yielded mammals; both are considered to be of Late Triassic age; and Emborough, at least, is placed in the Norian (Fraser et al., 1985).

The first mammals to be recovered from the Late Triassic-Early Jurassic fissures of Britain were isolated haramiyid teeth found by Charles Moore in 1858 at the Holwell site (Simpson, 1928a). Commercial mining of the Carboniferous limestone resulted in development of quarries and exposure of the contained fissures (Evans and Kermack, 1994). These quarries were exploited with great success by paleontologists beginning in 1939, when Walter Kühne visited Holwell. Kühne washed the clays (as had Moore before him) and, without optical aid, recovered two morganucodontid teeth and twelve belonging to haramiyids (Kermack, 1988). He later discovered mammalian specimens at one of the quarries (Duchy) on St. Bride's Island. From the early 1950s onward, work in the fissures on both sides of the Bristol Channel was continued by researchers from University College, London, including Kenneth A. Kermack, Pamela L. Robinson, Frances Mussett, Susan Evans, and their students and successors. This long-term research program led to the discovery of many additional sites and to the recovery of an extraordinary wealth of specimens (mainly from St. Bride's Island) that have provided key insights into the early history of mammals.

The haramiyids from Holwell have been studied in detail (Butler and MacIntyre, 1994). Perhaps as many as three species may be present—Thomasia antiqua, T. moorei, and T. sp. Two morganucodontid teeth from this quarry were originally described as representing distinct species, Eozostrodon parvus and E. problematicus (see Par-rington, 1941), but these were later synonymized (Par-rington, 1971). In the meantime, Kühne (1949) had described the rather similar Morganucodon watsoni from one of the St. Bride's quarries (Duchy). Confusion arose in the 1970s because of an extended controversy as to whether E. parvus and M. watsoni are synonymous (e.g., Parrington, 1971, 1973), a complicating factor being that the type of the former is not generally considered to be diagnostic (e.g., Kermack et al., 1973). Here we follow Clemens's (1979b) suggestion that the name Eozostrodon be restricted to the specimens from Holwell and that the name Morganucodon be applied to material from Wales (chapter 4).

Only one mammal has been reported from Em-borough, also in the Bristol-Mendip region. The occurrence is an important one, however: the fissure can be dated as Norian in age because of overlying basal Rhaet-

ian transgression deposits and the mammal is Kuehneo-therium (Fraser et al., 1985). Kuehneotherium has a "sym-metrodontan" molar pattern and was long considered to be the oldest therian sensu lato (see, e.g., Crompton and Jenkins, 1967; Kermack et al., 1968); however, the affinities of "symmetrodontans" are problematic (chapter 9). Regardless, Kuehneotherium is also known from the Liassic of St. Bride's Island and hence had a wide temporal range.

The fissures of St. Bride's Island, Wales, have yielded truly enormous collections of Early Jurassic mammals, including not just the usual isolated teeth, but jaws and skeletal elements as well. The bones are disassociated but are well preserved and show no evidence of reworking. Some fissure-fill matrix, which varies from clay to marl, is so fossiliferous that it might well be described as a bone coquina. For the most part (see later), the quarries on St. Bride's Island have yielded a consistent assemblage, termed the Hirmeriella association for the abundant conifer of that name. Curiously, this plant is not known from the other fissure deposits of the region. The vertebrate fauna of this assemblage includes only three principal taxa: the lepidosaur Gephyrosaurus bridensis and the mammals Morganucodon watsoni and Kuehneotherium sp. Morganucodon is the larger and by far the more abundant of the two mammals. Almost every element of the skeleton is represented in existing collections, and as a result Morganucodon is incomparably the best known of Late Triassic-Early Jurassic mammals (e.g., Kermack et al., 1973, 1981; Jenkins and Parrington, 1976). Except for one pocket in Pontalun Quarry (Kermack et al., 1968), Kuehneotherium is rather rare, and is known mainly by isolated teeth and jaws. K. praecursoris is the described species of the genus; there is evidently another kuehneo-theriid represented (Kermack et al., 1968; Mills, 1984) in the fauna, and we list this simply as Kuehneotherium sp. Whether either of these is the same as Kuhneon duchyense, from Duchy Quarry, cannot be determined because the type and only specimen of this species, an isolated molar, has been lost.

Because it typically includes only three vertebrates, the fauna of the Hirmeriella association has been characterized as depauperate (Fraser, 1989). One exception to this is found in a single fissure at Pant Quarry, which has yielded a diverse assemblage of reptiles and mammals, the latter including the haramiyid Thomasia, Morganucodon watsoni, Kuehneotherium, and an undescribed large mor-ganucodontid (Evans and Kermack, 1994). Both the incredible volume of vertebrate remains and the fact that only three taxa are generally present in the assemblages of St. Bride's Island could be explained by accumulation through action of a selective predator—perhaps the large morganucodontid from Pant (Evans and Kermack, 1994).

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