ABSTRACT
Mammalian fossils from the Cromer Forest Bed Formation (CF-bF) have been collected from exposures on the Norfolk and Suffolk coasts over a period of rriore than 160 years. In situ faunas are available from West Runton and a few other localities, but much of the material in museum collections lacks stratigraphic information. However, by comparison both with the in situ CF-bF finds and with the record from continental Europe, many of the unstratified fossils can be assigned to one of two groups, widely separated in time; the older representing parts of the Early Pleistocene and the younger of early Middle Pleistocene age.
At the Cromerian interglacial Stage type site at West Runton, Norfolk, fluviatile organic muds of the West Runton Freshwater Bed (assigned to substages Cr Ib-IIb by R.G. West) have yielded a rich vertebrate fauna, with 45 species of mammals, 8 fishes, 5 amphibians, 3 reptiles and several birds recorded so far. Stratigraphically significant species include: Mimomys savini (the only species of Mimomys present), Microtus arvalis, M. oeconomus, Pitymys arvaloides, P gregaloides, Pliomys episcopalis, Sorex savini, Beremendia fissidens, Mammuthus trogontherii, Dicerorhinus etruscus, Megaloceros verticornis, and Megaloceros savini. No artefacts are known from here or elsewhere in the CF-bF. The fauna is largely consistent with the pollen and plant macrofossil evidence for regional temperate forest, reedswamp and fen, and local areas of dry grassland.
The large mammal fossils from the Suffolk CF-bF sites of Corton, Pakefield and Kessingland are entirely of early Middle Pleistocene taxa. The molluscan fauna confirms the palaeobotanical evidence for a Cromerian (s.s.) age for the ‘Rootlet Bed’ and associated deposits, and M. savini is now recorded from Kessingland. A vertebrate fauna, generally similar to West Runton and also with Mimomys savini, is known from Sugworth, Berkshire, associated with substage IIIb. The non-marine molluscs again indicate correlation with the Cromerian (s.s.). However, at Little Oakley, Essex, malacological evidence suggests that a post-Cromerian interglacial is represented, although the vertebrate fauna is again similar to that from West Runton, including M. savini. Moreover, M. savini is present in the sparse small vertebrate fauna from the Sidestrand Unio Bed, which has a molluscan fauna which also differs significantly from West Runton.
None of the numerous CF-bF finds of Hippopotamus was recorded in situ, but the sediment matrix from 3 museum specimens yielded pollen assemblages assigned to substages substages IIIb and IV of an early Middle Pleistocene interglacial.
Pollen assemblages obtained from the sediment matrix of Arvicola cantiana, from Ostend, Norfolk, were correlated with Cromerian substage Cr IV, implying that the M. savini/A. cantiana transition occurred within the later part of the Cromerian Stage. However, the presence of A. cantiana at Westbury-sub-Mendip, Somerset, Boxgrove, Sussex, and at continental sites such as Mosbach, Mauer (Germany) and Noordbergum (Netherlands), together with other faunal differences, suggests that they belong to a distinct temperate event, younger than the Cromerian interglacial of West Runton, but pre-dating the Anglian/Elsterian Stage.
