Europe

An excellent review of the Middle Jurassic microverte-brates of Britain and their geologic context was given by Evans and Milner (1994), and we have drawn from their account in summarizing mammal occurrences (table 2.5) there. During the Middle Jurassic, most of Britain was covered by an epicontinental sea. A brief regression during the Bathonian provided estuarine, lagoonal, and deltaic depositional environments suitable for the preservation of terrestrial vertebrate fossils, including mammals. For the most part, the age of these occurrences can be determined with some precision through reference to nearby marine units and their contained molluscs. The first specimens to be discovered, those from the Stonesfield Slate, were recovered in situ during the course of quarrying. These provide a wealth of information, but unfortunately they represent only a few species. In recent years, bulk processing and concentration techniques (Freeman, 1982; Ward, 1984; Kermack et al., 1987) have been employed on un-consolidated clays and marls. Though virtually all of the mammalian fossils recovered are isolated teeth, the result of this effort has been a far larger, more diverse sample of mammals and other microvertebrates. We review the Middle Jurassic sites of Britain (figure 2.3) in approximate stratigraphic order.

The geologically oldest occurrence of mammals in the Middle Jurassic of Britain is in the Hornsleasow Quarry, which is in the Chipping Norton Formation and is of early Bathonian age (figure 2.3). Microvertebrates, including unspecified mammals, have been collected from a clay-stone within the Chipping Norton limestone.

The first mammals to be found and described from any rocks of Meosozic age are those of the Stonesfield Slate, from the Stonesfield quarries (figure 2.3). Rock from these quarries is actually a calcareous sandstone, not a slate, and has long been valued for construction purposes because it splits well along bedding planes. A mammalian specimen was evidently found by a stonemason working at Stones-field as early as 1764, but the occurrence did not receive scientific attention until decades later when Buckland (1824), encouraged by the great Georges Cuvier, mentioned them. Hitherto, mammals had not been known table 2.5. Middle Jurassic Mammals of Britain (see figure 2.3; locality numbers do not correspond between figure and table). Localities: 1, Hornsleasow Quarry (Chipping Norton Limestone, early Bathonian); 2, Loch Scavaig and Elgol, Isle of Skye (Ostracod Limestone, middle Bathonian); 3, Stonesfield (Stonesfield Member of the Sharps Hill Formation, middle Bathonian); 4, Woodeaton (Hampen Marly Formation, middle Bathonian); 5, Tarlton Clay Pit; 6, Swyre; 7, Watton Cliff; 8, Kirtlington (all Forest Marble Formation, late Bathonian)

Mammalia incertae sedis (1, 4, 5, 6, 7) Morganucodonta

Family incertae sedis (7) Morganucodontidae Wareolestes rex (8) ?Wareolestes sp. (5) Docodonta

Family incertae sedis

Gen. et sp. indet. (5, 7) Cyrtlatherium canei (8) Docodontidae

Borealestes serendipitus (2) Simpsonodon oxfordensis (8) Simpsonodon sp. (7) Shuotheridia Shuotheriidae

Shuotherium dongi (8) Shuotherium kermacki (8) Shuotherium sp. (8) Eutriconodonta "Amphilestidae"

Amphilestes broderipii (3, 7) Phascolotherium bucklandi (3) Haramiyida

Eleutherodontidae

Eleutherodon oxfordensis (7, 8) Stem Cladotheria ("eupantotherians") Family incertae sedis (2, 7, 8) ?Amphitheriidae

? Amphitherium sp. (8) Amphitheriidae

Amphitherium prevostii (3, 7) Amphitherium rixoni (3) Dryolestidae indet. (8) Peramuridae

Palaeoxonodon ooliticus (8) Palaeoxonodon sp. (7)

from the Mesozoic and the announcement caused considerable controversy (see Simpson, 1928a; Desmond, 1984). The quarries lie in the Stonesfield Member of the Sharps Hill Formation, which overlies the Chipping Norton Formation, and are of early middle Bathonian age. The fauna includes marine elements, and the depositional setting is thought to have been nearshore marine or estuarine. Four mammals are known from Stonesfield, each represented by several comparatively good specimens consisting of dentulous jaws generally preserved in slabs. Two, Am-philestes broderipii and Phascolotherium bucklandi, are "am-philestid triconodonts"; the others, Amphitherium pre-vostii and A. rixoni (see Butler and Clemens, 2001), are "eupantotherians" that may be stem members of the lineage that ultimately gave rise to boreosphenidan mammals (chapter 11). A footprint from Stonesfield that possibly belongs to a mammal, Pooleyichnus burfordensis, was described by Sarjeant (1975).

Continuing stratigraphically upward, mammals have been reported from Woodeaton, in the "Monster Bed" of the Hampen Marly Formation (middle Bathonian). Details on the fauna are contradictory. Clemens et al. (1979) list seven taxa, including an allotherian, a morganu-codontid, a docodontan, a "symmetrodontan" similar to Kuehneotherium, and at least three "eupantotherians." A more recent compendium (Evans and Milner, 1994) mentions only a possible mammal incisor.

Two mammal localities, Loch Scavaig and Elgol, are known from the Isle of Skye, western Scotland (figure 2.3). They are in the Ostracod Limestone, also considered to be middle Bathonian. Two taxa, the docodontan Borealestes serendipitus and an unidentified "eupantotherian," have been reported from the Isle of Skye (Waldman and Savage, 1972; Savage, 1984).

By far the greatest diversity of Middle Jurassic mammals comes from the Forest Marble, which is upper Bathonian and thus represents the youngest in Britain's sequence of Middle Jurassic assemblages. To date, four localities in the Forest Marble have yielded mammals: Swyre, Tarlton Clay Pit, Watton Cliff, and Kirtlington (figure 2.3). The paleoenvironments of Kirtlington and Tarlton Clay Pit are believed to be similar and to represent a swampy inshore brackish or freshwater lagoon, perhaps similar to the Florida Everglades (Evans and Milner, 1994). E. F. Freeman (1979) suggested that the bone accumulation at Kirtlington may have been the result of predator activity, through "coprocoenosis"—concentration in feces or regurgitata (see also Mellett, 1974). Watton Cliff and Swyre are believed to have had a higher-energy depo-sitional environment. Though the fossils are often abraded, the fauna is similar in known respects to that of the other mammal-bearing sites in the Forest Marble. Swyre has yielded one unidentified mammal; three taxa are known from Tarlton Clay Pit, including a morganucodontid and a docodontan. The assemblages of Watton Cliff and, especially, Kirtlington are much more diverse. Two taxa, the aforementioned eutriconodontan Amphilestes and the "eupantotherian" Amphitherium (both also known from the Stonesfield Slate), are present at Watton Cliff but not Kirtlington (but see E. F. Freeman, 1979). Otherwise, the fauna of Kirtlington is considerably better sampled and thus deserves special mention.

Microvertebrates were discovered in the Old Cement Works Quarry at Kirtlington by Eric Freeman in the 1970s (E. F. Freeman, 1976a,b, 1979). The productive horizon, termed the Mammal Bed, is a thin marly clay that is astonishingly fossiliferous. The quarry was later worked by Kermack and associates; the total collection includes some 700 mammal teeth, together with skeletal elements (Kermack et al., 1998). Some of the information has been published, but much of the mammalian fauna remains un-described at this writing. The collection is currently under study by Denise Sigogneau-Russell.

Whereas the eutriconodontans of the Stonesfield Slate (Amphilestes and Phascolotherium) are advanced, particularly with respect to their jaw structure, the presence of Wareolestes rex at Kirtlington documents the survival of morganucodontids at least into the Bathonian (E. F. Freeman, 1979). "Amphilestids," curiously, have not yet been reported from Kirtlington. Early reports (e.g., E. F. Freeman, 1979) suggested the presence of true multitubercu-lates in the Forest Marble, based on fragmentary teeth. The occurrence is notable because undoubted multi-tuberculates do not otherwise appear in the fossil record until the Late Jurassic. Kermack et al. (1998) referred all allotherian teeth (13 specimens) from Kirtlington and Watton Cliff to Eleutherodon oxfordensis. The authors referred Eleutherodon to a new higher category of Allo-theria, Eleutherodontida (see chapter 8). However, Butler (2000) reportedly has identified a few teeth from Kirtling-ton that he considers referable to the Multituberculata. On this basis, we tentatively retain multituberculates in the faunal list for the Forest Marble. The docodontans Cyrt-latherium canei (originally described as a kuehneotheriid "symmetrodontan," see E. F. Freeman, 1979; Sigogneau-Russell, 2001) and Simpsonodon oxfordensis (see Kermack et al., 1987) have also been described from Kirtlington; Simpsonodon is also known from Watton Cliff. Perhaps the most remarkable mammalian occurrence at Kirtlington is that of Shuotherium, represented by as many as three species (Sigogneau-Russell, 1998). Shuotherium is characterized by lower molars that have a "talonid" developed anterior to the trigonid and upper molars with a cusp pattern similar to (but evidently evolved separately from) that of tribosphenic mammals (Sigogneau-Russell, 1998; Wang, Clemens, et al., 1998; Kielan-Jaworowska et al., 2002, see chapter 6). The genus is otherwise known only from the Late Jurassic of China (Chow and Rich, 1982); one of the taxa from Kirtlington is so similar to the Chinese form that it is placed in the same species, S. dongi (see

Sigogneau-Russell, 1998). "Eupantotherians" of Kirtling-ton are noteworthy for their diversity: five or more taxa, not all yet described, may be represented (E. F. Freeman, 1979; Evans and Milner, 1994), as compared to the single species, Amphitherium prevostii, known from Stonesfield. Palaeoxonodon oolithicus is referred to the "eupantother-ian" family Peramuridae, a group that is widely believed to be closely related to northern tribosphenic mammals (Kraus, 1979). Its occurrence at Kirtlington is the oldest for the family. Another oldest record for the site is that of Dryolestidae, represented by an unnamed taxon. Dry-olestids later became abundant, diverse elements of the mammalian faunas of the Late Jurassic and earliest Cretaceous (Simpson, 1928a, 1929a).

A final occurrence of a Middle Jurassic (late Bathon-ian) mammal from this region is that of an isolated femur from a fissure-fill deposit at the Peski Quarry, Kolomensk District, Russia, about 100 km southeast of Moscow (figure 2.11). The specimen is well preserved and was referred to Morganucodontidae by Gambaryan and Averianov (2001). Given the poor state of knowledge of the skeleton in most groups of stem mammals, we follow the referral with question.

0 0

Post a comment