Benton, M.J., Cook, E. and Hooker, J.J. 2005. Mesozoic and Tertiary Fossil Mammals and Birds of Great Britain. Geological Conservation Review Series No. 32, JNCC, Peterborough.
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J.J.Hooker, E. Cook and M. J. Benton
The term 'Tertiary', although replaced in current global chronostratigraphical parlance by the Paleogene Period and earlier parts of the Neogene Period, spans an important interval of Earth history between the end of the Mesozoic Era and the beginning of the Quaternary Sub-era (Gradstein et al., 2004). As such, it is only the name that is archaic, not the concept. In the GCR Series, the Tertiary is accorded the rank of sub-era like the Quaternary and ends two thirds of the way through the Pliocene Epoch at the beginning of the Gelasian Stage (see Balson in Daley and Balson, 1999, pp. 237–9). The youngest mammaliferous Tertiary deposit is accordingly the Red Crag of late Piacenzian (Middle Pliocene) age and is succeeded by the early Quaternary Norwich Crag of Gelasian (Late Pliocene) age. Quaternary mammals, including those from Gelasian sediments are described in a separate volume of the GCR series (Schreve, in prep.).
During the latest part of the Cretaceous Period, Britain experienced an episode of tectonic uplift. This resulted in slight deformation (folding) of the chalk sediments and exposure of most of the British Isles as land (Anderton et al., 1979). The modern tectonic context of the British Isles developed at this time: uplift in the north-west and subsidence in the south-east, and this pattern of exposure continued throughout most of the Tertiary Sub-era. By late Paleocene times the basic shape of the modem coastline had evolved (Murray, 1992) and it differed from that of today mainly in that the North Sea incorporated much of south-east England from Dorset to Norfolk. Moreover, late in the Paleocene Epoch and early in the Eocene Epoch there was an intermittent land bridge to North America via Greenland, the North Atlantic being at an early stage of rifting.
Early Tertiary (Paleogene) sediments accumulated in one large depositional basin that is now divided by folding into the London and Hampshire tectonic basins
The sediments of the London and Hampshire basins have proved to be rich in vertebrate, especially mammal, fossils (Hooker, 1989b) in latest Paleocene, Eocene and early Oligocene strata, with less abundant specimens (mainly reworked) from the Miocene and Pliocene sediments in East Anglia. The vertebrate record for the earlier Paleocene and later Oligocene intervals is missing, along with the sediments. The British mammal sites include good representatives of the Mammal Paleogene Reference Levels MP7–9 and MP16–21 (Schmidt-Kitder, 1987) and reference localities for biozones of Early, late Mid and Late Eocene age (Hooker, 1986, 1987, 1996a).
Earliest Paleocene sediments in continental Europe include marine chalks and biodastic limestones. If such sediments were ever deposited in Britain, they were subsequently removed by erosion. The first preserved sediments (the Thanet Formation) of late Paleocene (Thanetian) age in Britain are restricted to eastern parts of the London Basin, and the fullest sequence occurs in eastern Kent. These sediments are marine in origin and comprise fine-grained sands, silts and clays (Murray, 1992). Further transgression during the youngest part of the Paleocene Epoch led to the short-term spread of shallow marine environments across the entire London and Hampshire basins. The resulting thin unit is the Upnor Formation (formerly known as the WoolwichlReading Bottom Bed; Ellison et al., 1994). A single mammal specimen is known from the Upnor Formation, indicative of the Cernaysian European Land Mammal Age (Hooker and Millbank, 2001.)
There has been much past discussion on where best to place the Paleocene–Eocene epoch boundary. This debate reached its peak during the last decade with International Geological Correlation Programme Project 308. Previously, most workers distributed those strata between the Upnor Formation and division A2 of the London Clay Formation to either the Paleocene or the Eocene epochs or some to each. Some workers, however, preferred to regard these strata as belonging to the 'Paleocene–Eocene boundary interval' in anticipation of a final decision on placement by the International Union of Geological Sciences (IUGS). The latter standpoint was taken for the purposes of one earlier published GCR volume on fossil plants (Cleat et al., 2001), whereas in another (Daley and Batson, 1999) the boundary was placed between the Woolwich and Reading formations below and the 'Harwich Formation' above. The IUGS has now ratified the global position of the Paleocene–Eocene boundary as being marked by the beginning of the Carbon Isotope Excursion (CIE) and fixed the Global Standard Stratotype-section and Point (GSSP) at Dababiya, Egypt. Recognition of the Paleocene–Eocene boundary in Britain relies on recognition of the CIE and/or the associated biotic proxies. The CIE marks an abrupt 200 thousand-year long warming event that coincided with, and was apparently the cause of, widespread extinction of deep marine benthos, especially foraminifera, known as the 'Benthic Foram Extinction' (BFE); a near global acme in marine dinofiagellates of the genus Apectodinium; and the Mammalian Dispersal Event (MDE) that saw the sudden appearance of many modern mammalian groups in the Northern Hemisphere and which represented their earliest global records (Berggren et al., 1995). In Britain, the CIE has been recognized in soil nodules in the lower part of the Reading Formation in the Jubilee Line borehole 404T in central London (Thiry et al., 1998) and in the Cobham Lignite Bed at Cobham, Kent (Collinson et al., 2003). Both underlie the lower shell beds of the Woolwich Formation that contain the Apectodinium acme. We can now therefore be more precise about which units in the London and Hampshire basins are the late Paleocene and which are early Eocene in age.
The latest Paleocene times in Britain (the top of the Upnor Formation) were marked by widespread regression, leading to deposition of the Woolwich and Reading formations. During the deposition of these strata all of the British Isles except the extreme south-east of England was land, although generally of low relief. It is thought that the overall pattern of fluvial drainage was towards the south-east. The Reading Formation sediments are predominantly mottled green and red clays, with local developments of sandy pebble beds. Palaeosols are present and are thought to represent deposition under fluviomarine conditions with a predominantly warm, seasonally dry climate (Murray, 1992; Newell, 2001). Low-energy, brackish-water environments are represented by the Woolwich Formation, which interdigitates with the Reading Formation. Vertebrates are very rare in the Reading Formation, but a few mammals are known from the Woolwich Formation.
The succeeding London Clay Formation crops out in the London and Hampshire basins. It represents the spread of fully marine conditions over the whole area. The sediments form a thick sequence of dark-grey muds, which shows five cyclical transgression-regression events. Arenaceous horizons are found locally at the base (Murray, 1992), namely the Oldhaven Formation, Blackheath Beds, Suffolk Pebble Beds. The London Clay Formation is extremely fossiliferous and preserves many plant (Chandler, 1978; Collinson, 1983a; Cleal et al., 2001), invertebrate and vertebrate taxa. In the London Basin the maximum water depth during the deposition of the London Clay Formation has been estimated at some 200 m. In the neighbouring Hampshire Basin the environment of deposition is thought to have been one of shal low, occasionally brackish, seas (Murray, 1992).
Towards the end of Early Eocene (late Ypresian) times, and during the early Mid Eocene (Lutetian Stage), sedimentation was more arenaceous in nature, resulting in the deposition in the eastern Hampshire Basin of the Bracklesham Group. Similar sediments in the London Basin are often referred to informally as the 'Bagshot Beds'. In the western Hampshire Basin, continental time-equivalents of the Bracklesham Group are called the 'Bournemouth Group'. The two groups interdigitate on the Isle of Wight (Murray and Wright, 1974; Edwards and Freshney, 1987).
In late Mid Eocene (Bartonian) times, renewed westerly spread of marine environments began, represented by the Barton Clay Formation, and ended with a major regression, represented by the Becton Sand Formation (Hooker, 1986). A non-marine representative of this time interval is the Creechbarrow Limestone Formation of Dorset.
The Late Eocene (Priabonian) and early Oligocene (Rupelian) strata have a restricted outcrop area: they are found only in Hampshire and on the Isle of Wight. Widespread sea-level fall at the end of Mid Eocene time (Plint, 1988) meant that Priabonian and Rupelian sediments are dominantly non-marine, with a few restricted marine intercalations.
The sequence of mammal faunas in the Late Eocene and Early Oligocene sediments of the Hampshire Basin offers a unique opportunity to erect a relatively continuous biostratigraphical scheme spanning some 4 million years. The relative continuity of deposition and the succession of mammal-bearing horizons are not matched anywhere in continental Europe, where most of the localities are more isolated (Hooker, 1987; Hooker et al., 2004).
The Miocene and Pliocene epochs are poorly represented in Great Britain by sediments. Probably the only existing Miocene deposits are the marine late Messinian Lenham Beds of Kent and possibly the continental Brassington Formation of Derbyshire. Both lack vertebrates. The pre-Gelasian Pliocene is represented only by the Coralline and Red Crags and by their shared Basement Bed, whose outcrop is restricted to north-east Essex and south-east Suffolk (Balson in Daley.and Balson, 1999). Both formations are marine. "The Coralline Crag (late Zanclean to early Piacenzian stages) has yielded only cetaceans, but the Red Crag (late Piacenzian) and the Basement Bed have yielded a diverse fauna of land and marine mammals. Most, but not all of the latter appear to occur as reworked fossils in the Basement Bed (also known as the 'Suffolk Bone Bed', 'Nodule Bed', 'Coprolite Bed', 'Boxstone Bed' and 'Sub-Crag Detritus Bed': Balson in Daley and Balson, 1999), although stratigraphical data associated with the mainly 19th Century collections are poor. The fauna was recorded in a monograph by Newton (1891) but remains largely unrevised today. It has long been recognized that fossils from the Basement Bed (and in some cases in the main mass of the Red Crag) are reworked from older deposits that have all but been removed by sub-Crag erosion. Some fossils retain matrix attributable to one deposit, which consists largely of reworked nodules. This deposit has been named the 'Tritnley Sands' (incorporating also the term 'Boxstones'). Most of the fossils, including those with 'Trimley Sands' matrix, are thought to be of early Pliocene age, whereas others may date from Miocene times (Balson, 1990; Balson in Daley and Balson, 1999). Some are even older, dating clearly from the Early Eocene, namely the dawn horses Hyracotherium leporinum and Pliolophus vulpiceps (Hooker, 1980, 1994a) and the pantodont Coryphodon, reworked from the underlying London Clay Formation. The unique enigmatic toothless cranium of Mphodon' platyceps is possibly from a later Eocene deposit now completely eroded away. Together with these reworked fossils are a few that are autochtho-nous, e.g. the proboscidean Mammuthus cf. rumanus (Lister and Van Essen, 2004) and the giant deer, Megaloceros, which have apparently been found in the main mass of the Red Crag (Spencer, 1971).
The outlines of mammal evolution have been given in Chapter 1. In summary, the time-span represented by British fossil mammal-bearing beds, from the latest Palaeocene to early Oligocene times, encompasses some major changes in mammalian faunas. This time-span documents the maximum ordinal diversity of mammals, when both archaic and modern mammalian orders were present. The archaic orders are those that arose in the Paleocene Epoch or earlier and became extinct relatively early in the Tertiary Sub-era, whereas modern orders and families were still undergoing their initial diversification. Further details of the typical mammal groups are given in Chapter 1 and in general texts such as Savage and Long (1986), Carroll (1988), Benton (2005) and Rose and Archibald (2005). Krause (1984) and Rose (1984) gave detailed accounts of the mammal groups of the Paleocene and Eocene epochs respectively, essentially based on the North American record. More up-to-date accounts of the Paleocene radiation (Alroy, 1999) and of the carnivores and hoofed mammals (Janis et al., 1998) are now available. However, there is much of relevance to Europe also, because there were several phases of faunal interchange between the two continents during these two epochs.
Major changes in habitats and in mammalian adaptations occurred during the Eocene to early Oligocene interval (Collinson and Hooker, 1987; Hooker et al., 1995, 2004). Collinson and Hooker (1987) gave an account of these changes, based on extensive study of fruits, seeds and megaspores and of mammalian bones and teeth.
Latest Paleocene and earliest Eocene floras in southern England indicate open and disturbed environments with limited wooded/forested areas but with mammalian communities that today are typical of dosed forest vegetation (few large mammals or herbivore browsers). This incongruence probably results from the plants and mammals being provenanced from different areas or local habitats.
In southern England dense forest of tropical aspect characterized the Early to early Mid Eocene environments, and mammals showed a high ratio of small to large ground-dwelling forms, a relatively high percentage of arboreal species and adaptations to eating soft fruit and low-fibre-content leaves. By early Late Eocene times many tropical taxa had been lost and the vegetation was characterized by reed marshes and swamps with patches of woodland or forest. In latest Eocene times, an extensive and persistent reed marsh developed. These changes were accompanied by extinctions of many earlier mammalian adaptive types, a reduction in arboreal species and an increase in large ground-dwelling forms, especially herbivores with specializations for a higher-fibre diet.
In more detail, Collinson and Hooker (1987) showed the evolution of dietary preferences among rodents and perissodactyls through the English Eocene to early Oligocene interval
The perissodactyls show a more dramatic one-way change, from a mixed frugivore-herbivore diet to a purely browsing herbivorous one. The Early Eocene horses and their extinct European relatives, the palaeotheres, fed on fruit as well as browsing leaves from low bushes. They belonged to the genera Pliolophus, Hyracotherium and Cymbalophus. Later relatives of Hyracotherium, species of the palaeothere genus Propalaeotherium, had teeth with longer crests that were adapted for a greater component of browsing in the diet, although these horses still ate fruits, as is confirmed by preserved stomach contents in specimens from Messel (Franzen, 2001). During Early and Mid Eocene times, new genera of larger perissodactyls with stricter adaptations to browsing became dominant. Genera such as Lophiodon and Hyrachyus were at first minor components of the faunas. With their bilophodont teeth, they were adapted to bulk feeding in an environment with a year-round supply of leaves (Hooker, 2000a). Later in the Eocene Epoch, new genera such as Palaeotherium and Plagiolophus, with teeth of a selenolophodont pattern, showed increasing crown height and molarization of their premolars, thus providing increased surface area for chewing and hence a firmer adaptation to a solely browsing diet. Several of the named perissodactyl genera became extinct in late Mid Eocene time, and Palaeotherium and Plagiolophus took over as the dominant forms until earliest Oligocene times, when the rhinoceros Ronzotherium replaced them.
These changes in generic dominance through Mid and Late Eocene times also document a major change in the dominant large browsing herbivores, from the hyrachyids and lophiodonts to the palaeotheres Palaeotherium and Plagiolophus. This switch is associated with a change in tooth type from the bilophodont to the selenolophodont type (Collinson and Hooker, 1987). The bilophodont cheek tooth bears two transverse crests (lophs), and it is seen today in the tapir Tapirus, which specializes in eating the leaves of forest trees. The bilophodont tooth shears the leaves coarsely, and they are swallowed in relatively large fragments. The selenolophodont tooth of the palaeotheres is more complex, bearing sharp-edged ridges made from upright plates of enamel, which wear against the opposing teeth to produce a series of shearing surfaces. Such teeth are seen today in the hyrax Heterohyrax, which generally is a browser and feeds on tough dry leaves, twigs and bark, which it shears, crushes and grinds into a very fine mush before swallowing. This comparison suggests a major change in browsing pattern in the British and continental European Eocene herbivorous perissodactyls, from soft to tough vegetation and to a relatively more efficient feeding mode.
The Hampshire Basin sequence of mammal-bearing sediments spans the Eocene–Oligocene boundary. The earliest Oligocene was a time of major extinctions among mammals in Europe, termed the 'Grande Coupure'. The extinction event occurs within the Hamstead Member of the Bouldnor Formation; it is marked by the loss of numerous mammalian species and followed by the origins of new taxa of lipotyphlan insectivorans, rodents and ungulates (Hooker et al., 2004). This event had been dated previously to lie precisely at the Eocene–Oligocene boundary, and to be caused perhaps by climate change or by competition with new mammal species dispersing into Europe from Asia. Close study of the sequences in the Hampshire Basin shows first that the major event happened in earliest Oligocene time, and that it was preceded by a smaller extinction event that correlated with vegetational change. The 'Grande Coupure' itself coincided with the earliest Oligocene glaciation, so it is likely that climate change, as well as competition with the new Asian mammals, combined to produce the faunal turnover (Hooker et al., 2004).
After a gap of some 25 million years, we get a glimpse of British late Tertiary mammals from the Basement Bed of the Coralline and Red Crags. Dated as early Pliocene (and/or possibly late Miocene) in age, the fauna is very different from that of the latest preserved Paleogene and much more modern in character. Land mammals are represented by large proboscideans such as the gomphothere Anancus arvernensis and the mammutid Mammut borsoni, the three-toed horse 'Hipparion', a tapir, Tapirus arvernensis?, a large rhino, deer, a bovid, a large relative of the Red Panda (Parailurus anglicus) and several other carnivorans belonging to modern families, namely a cat, a hyaena, an otter and two bears, a monkey (?Mesopithecus cf. monspessulanus), and a few large rodents (size here almost certainly resulting from a preservational bias), namely the beavers Castor and Trogontherium and the porcupine Hystrix (including evidence from gnawed bones — Sutcliffe and Collings, 1972). Marine mammals are represented by a diversity of whalebone and toothed cetaceans, identified mainly from ear bones, rostra and teeth. They belong to the modern families Balaenopteridae (rorquals), Balaenidae (right whales), Physeteridae (sperm whales), Ziphiidae (beaked whales), Delphinidae (dolphins) and the extinct Cetotheriidae and Squalodontidae. Also present are a few seals, the walrus Trichecodon huxleyi and the dugongid sea-cow 'Halitherium' canhami. The Middle Pliocene strata, represented by the main Red Crag deposition saw the appearance of the first members of the elephant family in Britain (Lister and Van Essen, 2004). These late Tertiary faunas have not been recently comprehensively revised and therefore some identifications may be unreliable (for recent reviews and some up to date identifications, see Spencer, 1971; Delson, 1974; Mayhew, 1978; Stuart, 1982; Pilleri, 1987, pp. 139–41; Van Essen and Mol, 1996; Lister, 1996, 1999; Forsten, 2002; Lister and Van Essen, 2004).
Mammals have been reported from many localities in the London and Hampshire basins (Hooker et al., 1980). Fossiliferous sites are predominantly located in extensive coastal sections, some along the northern and southern banks of the Thames Estuary and others along the south coast of Hampshire and the north and northwestern coasts of the Isle of Wight. Other sites comprised quarries or temporary construction sites. An outline of the main locations is noted here, together with the name of the fossiliferous unit. Localities are arranged according to their occurrence in the London Basin (London, Suffolk, Essex, Surrey, Sussex, Kent, Hertfordshire, Berkshire) or the Hampshire Basin (Hampshire, Isle of Wight, Dorset). Most Crag localities in Suffolk are imprecise, so grid references are mostly omitted (see Balson, 1999, for guidance).
LONDON: Dulwich (
SUFFOLK: Kyson, near Woodbridge (
ESSEX: Harwich Harbour area (
SURREY: Croydon (
SUSSEX: East Wittering, Bracklesham Bay
KENT: Studd Hill, Herne Bay (
HERTFORDSHIRE: Bignell's Corner, South Mimms (
BERKSHIRE: Burghfield, near Reading (
HAMPSHIRE: Royden, near Brockenhurst (
ISLE OF WIGHT: Totland Bay
DORSET: Hengistbury Head (
From these potential locations, eight are selected as GCR sites for their fossil mammal remains, two being Early Eocene in age (Ferry Cliff, Abbey Wood), one late Mid Eocene (Creechbarrow Hill), four Late Eocene (Hordle Cliff, Headon Hill, Lacey's Farm Quarry, Whitecliff Bay, the last site also Early Oligocene) and one Early Oligocene (Bouldnor Cliff). The Mammal Paleogene (MP) reference level numbers, Paleocene–Eocene (PE) zones and other biozonations are indicated for each site (based on Schmidt-Kittler, 1987; Hooker, 1986, 1987, 1996a).