Pleistocene Herpetological Localities

Localities in countries in the Geographic Divisions below arc numbered to correspond with those in the taxonomic accounts in Chapter 4. Figure 40 is an artists concept of some Pleistocene herpetological species and extinct mammals at the Shropham Pit Locality (Interglacial Component), Norfolk, England (Britain: Upper Pleistocene Site 10). Countries are arranged in divisions from west to cast, and from north to south when possible. Oceanic islands are listed under the country to which they belong. Malta is included with Italy because of its important Pleistocene herpetofauna and proximity to Sicily and Italy…. I. Northwest Division: Ireland and Britain, p. 130 II. French Division: France and Monaco, p. 142 III. Southwest Division: Spain, p. 149 IV. Northcentral Division: Netherlands, Belgium, Luxembourg, Germany, Austria, and Switzerland, p. 157 V. Northeast Division: Poland and the Czech Republic, p. 175 VI. Southeast Division: Italy, Hungary, Yugoslavia: (Croatia, Bosnia, Serbia), and Greece, p. 182… Pleistocene herpetofaunal records in Ireland are rare and consist mainly of records of Rana temporaria. More work needs to be done in this critical area for the study of the fragmentation of ranges of herpetological species in the Pleistocene.

The European Herpetofauna: Paleocene Through Pliocene

In both Europe and North America, modern herpetological families and genera became established quite early in the Cenozoic, and modern species occurred as early as the Miocene. Because of deteriorating climates that began late in the Eocene, a marked decrease in herpetological diversity occurred in the Oligocene in both continents. However, both areas became herpetologically enriched in the Miocene. In post-Miocene times Europe was isolated from Africa and warm areas in the east by the Mediterranean Sea and eastern mountain ranges, and a depauperate herpetofauna developed there that continued into recent times. In North America, however, with its vast, accessible southern land mass, the richness of the Miocene herpetofauna (with the exception of several archaic colubrid genera [Parmley and Holman, 1995] that became extinct in the the Miocene) persisted into modern times. The following discussion of changes in the European herpetofauna in the Cenozoic era has been synthesized from Auge (1986), Ballón (1991a), Bailon ct al. (1988), Barbadillo et al. (1997), Crochet et al. (1981), Estes (1981, 1982, 1983), Fritz (1995), Holman (1995c), Milncr (1986), Milner et al. (1982), Mlynarski (1976), Rage (1984a, 1984c, 1986, 1993), Rage and Auge (1993), Rage and Ford (1980), Roček (1994), Sanchiz. (1977b, in press), Sanchiz and Mlynarski (1979), Sanchiz and Roček (1996), Spinar (1972), Szyndlar (1984, 1991b, 1991c), and Szyndlar and Bohme (1993). Because of the high probability that herpetological fossils have been identified correctly at the family level, herpetological families arc used here to reflect the taxonomic diversity of the European herpetofauna from the Paleocene through the Pliocene. In a following section, the earliest appearance of herpetological genera and species in the European Tertiary arc discussed. Extinct families are prefixed with an asterisk (*). Families that became extinct in Europe in the Cenozoic but presently occur elsewhere are prefixed with a number sign (#). Two primitive, extinct, presumably permanently aquatic salamander families, me *Albanerpetontidae and *Batrachosauroididae (the latter also known from the Tertiary of North America) made limited appearances in the Cenozoic of Europe. The *Albanerpetontidae occurred only in the Middle Miocene (having reappeared from the Cretaceous), and the *Batrachosauroididae occurred from the Upper Paleocene to the Lower Eocene.

Pleistocene Events in the Herpetofaunas of Britain and Europe, and North America Compared

This last chapter deals with differences and similarities between British and European and North American Pleistocene herpetofaunas. Compared with North America, Britain and Europe had a depauperate Pleistocene herpetofauna, which has carried over into modern times. For instance, the large, "warm" country of Spain, which by European standards has a rich modern herpetofauna, has only 13 species of snakes and four species of nonmarine turtles (Engelmann et al., 1986). On the other hand, Michigan, a northern border state with cold winters, has 17 species of snakes and 11 species of turtles (Holman et al., 1989; Harding and Holman, 1990). Indiana, just south of Michigan, has 31 species of snakes and 15 species of turtles (Minton, 1972; Brown, 1996; Conant and Collins, 1991). The southern coastal state of Florida has 45 species of snakes and 20 species of nonmarine turtles (Conant and Collins, 1991). This is almost twice as many snakes and more than three times as many nonmarine turtles as occur in Britain and Europe. In the Pleistocene, British or European herpetofaunas are considered to be rich when they contain 10 species. In North America, Pleistocene herptofaunas with more than 20 species are common, and sites with more than 40 herpetological species are known (Holman, 1995c). The reasons for these differences are as follows. Both North America and Europe became herpetologically enriched in the Miocene. But the climatic deterioration at the end of the Miocene caused a depletion of the herpetofauna in Europe. Because Europe was mainly isolated from Africa by the Mediterranean Sea and from warm areas to the east by mountain ranges and seas, its depauperate herpetofauna persisted into modern times. Ireland and Britain have even more depauperate modern herpetofaunas than the continent because these islands were cut off from the mainland before they could be reinvaded by all of the species displaced by the last glaciation (Fig. 45). In North America, however, with a vast, accessible southern land mass, and equable Pleistocene climates south of the periglacial regions (Lundelius et al., 1983), the richness of the Miocene herpetofauna persisted into Pleistocene and modern times.

Herpetological Population Adjustments in the Pleistocene of Britain and Europe

Compared to herpetological population adjustment patterns in North America (sec Holman, 1995c), the patterns in Britain and central and northern Europe seem to be rather straightforward. Basically, (1) very few herpetological species were present in ice-free areas during full glacial times, and (2) formerly glaciated areas were reinvaded by species from the south during warming cycles. Moreover, during climatic optimal warm times, several southern species existed well north of their present ranges. The invasion of southern Europe by northern populations in cold times is taken for granted (e.g., Rocek, 1995), although, as addressed in this chapter, it is difficult to document this in the fossil record. As indicated by geological and fossil evidence, the British Islands were connected to continental Europe during much of the Pleistocene. Although sea level changes in the British late Pleistocene arc a subject of some controversy (Stuart, 1982), it is generally agreed that Britain first separated from Ireland and then from the continent early in the Holocene. The classic idea is that the very depauperate British heretofauna of the cold part of the Devensian (last glacial stage) became somewhat, but not fully enriched by herpetological species during a warming trend that began about 10,000 ybp and lasted until about 8,500 ybp. The fact that Ireland has a much poorer modern herpetofauna (Triturus vulgaris, the rare Bufo calamita, Rana temporaria, and Lacerta vivipara) than Britain, which has six native species of amphibians and six native species of reptiles (Fra/,er, 1983; Smith, 1964), is attributed to Ireland's early separation from Britain. The Irish herpetofauna suggests that this separation occurred rather soon after the final withdrawal of the Devensian (last glacial) ice sheet. One of the most common questions asked about snakes, especially near St. Patrick's Day, is, "Have there ever been any snakes in Ireland?" No fossil snakes have ever been found in Ireland. But since Ireland lacks a terrestrial fossil record during most of the time that snakes have existed, it would seem that snakes could have lived in Ireland during some part of geological time. As far as I am aware, the few Pleistocene deposits containing herpetological remains in Ireland represent very late Devensian (last glacial) times.

The Pleistocene in Britain and Europe

A general introduction to the Pleistocene with an emphasis on herpetological remains was presented in the companion volume Pleistocene Amphibians and Reptiles in North America (Holman, 1995c). For a general introduction to the Pleistocene that gives much attention to Britain and Europe, the reader is referred to Sutcliffe (1985). A detailed account of Pleistocene mammals in Britain is given by Stuart (1982), and a general account of Pleistocene mammals in Europe is given by Kurten (1968). The present chapter deals mainly with chronological divisions of the Pleistocene in Britain and Europe. Early geologists recognized that glacial deposits and land forms existed far south of existing glaciated areas, and they correctly reasoned that these features indicated not only the presence of ice sheets but the onset of cold climates, as well. As these features were mapped and stratigraphic studies were made, it was found that some sections contained weathered zones of organic soils and plant remains between layers of glacially derived sediments. It was suggested that these organic zones represented nonglacial environments and that ice sheets must have advanced and retreated several times. In Europe, before studies of deep sea sediments were made, Pleistocene chronological events were determined on the basis of piecemeal evidence from terrestrial sediments. The earliest widely accepted chronology of climatic Pleistocene intervals was the classic fourfold subdivision of Pleistocene glacial events in the Alps by Penck and Bruckner (1909). These glacial stage names, from oldest to youngest, are Gu'nz glacial, Mindcl glacial, Riss glacial, and Wiirm glacial. Between the glacial stages, intcrglacial stages were designated by compound names based on the underlying and overlying glacial stages (e.g., The Gunz-Mindel intcrglacial stage lies between the Giinz and Mindel glacial stages). These Alpine glacial stages have been widely used, and one still finds references to them (especially the younger stages) in the recent literature (e.g., Fritz, 1995).

Introductio

There is disagreement about the time of the beginning of the Pleistocene. For instance, Repenning (1987), a North American, puts the beginning date at 1.9 million ybp. On the other hand, some modern Europeans studying the subject (e.g., Gibbard et al., 1991; Kolfschoten and Meulen, 1986; Roebroeks and Kolfschoten, 1995; Zagwijn, 1985, 1992) consider the epoch to have begun about 2.3 million ybp. The system used here, however, follows Sanchiz (in press), who accepts the official usage of Harland et al. (1990), who put the beginning of the Pleistocene at 1.64 million ybp. Evidence that the Pleistocene ended about 10,000 ybp (Meltzer and Mead, 1983) is widely accepted. This ending date correlates very closely with the terminal extinction of many large land mammal species. The Pleistocene is characterized by climatic oscillations and a series of glacial and interglacial events where great continental ice sheets advanced and retreated many times. The ice sheets were massive forces, sculpting the topography of the land and carrying much sedimentary material, including huge boulders and even megablocks of land up to 4 km in diameter, as far as 250 km in the Canadian prairies (MacStalker, 1977). In Britain and Europe, as well as in North America, the advance and retreat of ice sheets had a marked effect on the distribution of plant and animal life. Huge tracts of habitat were alternately obliterated and reopened several times, but other effects perhaps arc not so well known. For instance, during glacial times, so much atmospheric water was tied up in the formation of the ice that sea levels worldwide lowered markedly. On the other hand, sea levels rose during interglacial times when water was melting off the ice sheets. The most interesting and controversial biological event that took place in the Pleistocene was the sudden, almost worldwide, extinction of large land mammals, and to a lesser extent birds, that took place by the end of the epoch 10,000 years ago. At least 200 mammalian genera became extinct, among them large herbivores, the carnivores that preyed on them, and the scavengers that fed on the remains of both groups.

Herpetological Species as Paleoenvironmental Indicators

In Chapter 5 we have seen that Pleistocene herpetofaunas are often used to suggest paleoenvironmental conditions. The present chapter discusses the validity of this use. With the exception of behavioral responses (and a few quasi-physiological adaptations in reptiles), herpetological species are poorly adapted to resist temperature changes. Or, to put it another way, amphibians and reptiles lack the complex internal physiological mechanisms that interact to regulate temperature in endotherms. This has led to the assumption by many that herpetological species, because of their supposed greater sensitivity to temperature changes, arc much better indicators of local thermal conditions than are birds and mammals. Moreover, most Quaternary amphibians and reptiles represent extant species whose ecological tolerances and habitat preferences are well known, whereas many Pleistocene endotherms, especially large mammals, are extinct species whose ecological traits and specific habitat requirements are not totally understood. This suggests that Pleistocene herpetofaunas should give more refined information about specific habitats than endothermic faunas. Also, it can be argued that most amphibian and reptile species are more spatially confined than endothermic ones (especially birds and large mammals) and that Pleistocene herpetological species indicate paleoenvironmental conditions of more restricted areas. Bailón and Rage (1992) address this subject in the light of their European experience: "They (amphibians and reptiles] arc unable to compensate for large climatic variations as endotherms (birds and mammals) can; therefore each amphibian and reptile species can live only in a definite climate." (p. 95). Moreover,… Amphibians and reptiles present another advantage: whereas endotherm vertebrates are represented in Quaternary fossiliferous localities by a not negligible percentage of extinct species, practically all fossil amphibians and reptiles of that age belong to extant species. If a species is extinct its ecological requirements cannot be known with certainty and arc open to speculation whereas living species present in fossiliferous assemblages afford accurate information, (p. 95)… They also state that the size of reptile home ranges is small, and that as these species are not the preferred prey of predaccous birds, they are probably not an admixture of species that live in a wide area around the locality. Let us examine these assumptions.

A Bestiary—Annotated Taxonomic Accounts

This chapter consists of annotated taxonomic accounts of Pleistocene amphibians and reptiles recorded from the study area (see Fig. 1). General external characters, habits, and distributional patterns of modern taxa of amphibians and reptiles that occur in the British and European Pleistocene in this and following chapters are from the author's unpublished field notes and photographs as well as the following sources: Arnold and Burton (1978), Ballasina (1984), Beebee (1983), Berger et al. (1969), Duellman (1993), Duellman and Trueb (1986), Engelmann et al. (1986), Ernst and Barbour (1989), Escriva (1987), Estes (1981, 1983), Frazer (1983), Frost (1985), Gunther (1996), Halliday and Adler (1986), Hellmich (1962), Hvass (1972), King and Burke (1989), Matz (1983), Noble (1931), Smith (1964), Sparreboom (1981), and Zug (1993). The reader is cautioned not to attempt to identify Pleistocene amphibian and reptile fossils solely on the basis of skeletal characters discussed or skeletal figures presented in this book—or in other publications. To identify Pleistocene amphibian and reptile fossils accurately, it is necessary to compare them with adequate modern and fossil skeletal material. Pleistocene locality numbers below correspond with locality numbers in Chapter 5. Pleistocene caudate amphibians are usually identified on the basis of individual trunk vertebrae (see Holman, 1995c, p. 83). Figure 3 illustrates the important features of a trunk vertebra of Triturus cristatus from the Middle Pleistocene of Cudmore Grove, Essex, England.

Extinction Patterns in the Herpetofauna of the Pleistocene of Britain and Europe

As we have seen in Chapter 4, many invalid European Pleistocene amphibian and reptile species were named on the basis of insufficient and inadequately described fossils (e.g., Estes, 1981, 1983; Rage, 1984c; Sanchiz, in press). Some of these forms have been synonymized with modern species, but others are in taxonomic limbo because of the international rules of zoological nomenclature. We now turn to a consideration of the few European Pleistocene fossil herpetological species that have been recognized as valid in recent years. These taxa fit into three catagories: (1) an extinct Pliocene anuran taxon that extended into the Pleistocene, (2) large Lacerta species that lived on oceanic islands, and (3) Pleistocene species that are probably morphological variants of living forms. All of the following taxa are addressed in Chapter 4. No extinct species of Pleistocene salamanders are currently recognized in Britain or Europe. The genus * Pliobatrachus from the Pliocene of eastern Europe extended into the Lower Pleistocene of Poland and the Middle Pleistocene of Germany in the form of * Pliobatrachus cf. Pliobatrachus langhae. The *Palaeobatrachidae, the only family in the history of the Anura that became totally extinct (Roček, 1995), represents the only extinct herpetological family known in the Pleistocene of Britain and Europe, and *Pliobalrachus represents the only extinct herpetologcal genus known in the Pleistocene of the region. Rocck (1995) suggested that the *Palaeobatrachidae did not survive the Pleistocene cooling because of their prevailingly aquatic mode of life, unlike, for instance, the Ranidac and Bufonidae that were able to withdraw from iceobliterated areas and return when climatic conditions improved. *Lacerta goliath is a Pleistocene or Holocene species that is known only from two localities in the Canary islands (see Chapters 4 and 5). It is twice the size of Lacerta lepida, the largest modern European Lacerta. *Lacerta maxima is another very large Pleistocene or Holocene Lacerta that is endemic to the Canary Islands. This species is known from a single fossil locality (see Chapters 4 and 5) and is differentiated from * Lacerta goliath on the basis of several trenchant osteological characters.