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Origins and of the Antarctic biota: an introduction

J. A. CRAME British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK

Within the last 25 there has been a dra- in this volume L. R. M. Cocks provides a brief matic increase in our knowledge of the but succinct review of 's place within record of Antarctica. Improved access to the to Gondwana. It is perhaps remotest parts of the continent, the advent of not generally appreciated that the greater part offshore drilling and intensive study of early of Antarctica's extensive Early and Middle expedition collections have all led to the ac- Cambrian sedimentary record was laid down cumulation of a vast amount of data that under tropical conditions. The extensive stretches back nearly 600 Ma to the beginning of Shackleton of the Transantarctic the Cambrian period. No longer can Antarctica Mountains, and its correlatives, contains abun- be dismissed from our view of the history of life dant shelly faunas with Australian and Chinese on earth simply because so little is known about affinities, and part of the margin of what we it; it is fast becoming another crucial reference now know as the Gondwana supercontinent point for global palaeontological syntheses. formed a reef belt that protruded 10~ ~ into If, today we have an image of Antarctica as a the Northern Hemisphere. The most abundant remote, inhospitable continent that supports and characteristic early Palaeozoic of little life, we now know that such a view cannot Antarctica are in fact archaeocyaths and F. be projected back indefinitely through time. Debrenne & P. D. Kruse show how, in con- Abundant plant and animal fossils from a variety junction with certain skeletal cyanobacteria and of periods point to much more benign climates algae, these primitive coral-like organisms were and immediately raise a series of interconnected the primary framework-builders of the reefs. questions: where did such organisms come from, Taxonomic revisions presented by these authors how long did they persist, and precisely when confirm the particularly strong faunal links be- (and how) did they become extinct? Can our tween Antarctica and South Australia in the most southerly continent throw further light on Early Cambrian. the long-term role of climate in driving evol- Amongst the inarticulate brachiopods, tri- utionary trends (e.g. Valentine 1967; Vrba lobites, primitive molluscs and other marine 1985)7 invertebrates that inhabited the Early Cambrian It was with points such as these in mind that a reefs and carbonate platforms, a particularly mixed group of palaeontologists, biologists, ge- important series of monoplacophorans and gas- ologists and geophysicists gathered together tropods has been identified by G. F. Webers & for an international discussion meeting on the E. Yoeheison. These occur in the Late 'Origins and evolution of the Antarctic biota' at Cambrian (Dresbachian) of the Geological Society, London on 24 and 25 the Ellsworth Mountains and comprise some 20 May 1988. A further workshop day (26 May taxa. The most important of these is the mono- 1988) was held at the British Antarctic Survey, placophoran, Knightoconus antarcticus, which Cambridge and altogether over 100 scientists could well have been a direct ancestor of the from some 15 different countries took part in cephalopods. Its 7cm long, curving, cap-like the discussions. shell bears multiple internal septa along at least Obviously, in such a short space of time, it one-third of its length and these are perforated was not possible to cover all aspects of Antarctic by a rudimentary connecting tube (siphuncle). palaeontology, and some subjects were necess- The stratigraphic position of this species can be arily reviewed in greater detail than others. As demonstrated to be slightly beneath that of Palaeozoic biotas and biogeography were to be Plectronoceras, the first true cephalopod (from the subject of a complementary symposium China). ('Palaeozoic biogeography and palaeogeogra- In his review, Cocks points out that there is a phy'; Oxford, 14-19 August 1988), they were very limited and sedimen- not examined exhaustively here. Nevertheless it tary and palaeontological record in Antarctica; was felt to be important to spend some time it is likely that this was a time of extensive up- considering Antarctica's first macrofossils, and lift and erosion. However, it is apparent that,

From Crame, J. A. (ed.), 1989, Origins and Evolution of the Antarctic Biota, Geological Society Special Publication No. 47, pp. 1-8. Downloaded from http://sp.lyellcollection.org/ by guest on September 24, 2021

2 J.A. CRAME during the later part of early Palaeozoic time, phyllolepid placoderms, xenacanth sharks and profound changes were occurring in the dis- bothriolepid antiarchs. tribution of supercontinents and the large Collision of the Gondwana and Baltica/ Gondwana plate slid progressively over the con- Laurentia blocks in the latest Devonian to form temporary south pole. By the early Middle the single supercontinent of Pangea radically Devonian the pole lay under either S. Africa or alters our view of the subsequent evolution of S. America, and Antarctica came to occupy a life in the southern high latitudes. It has tra- mid- to high-latitude position (35~176 de- ditionally been felt that the classic 'Gondwana' pending on the reconstruction used). It has sequences in these regions, comprising Permo- essentially maintained this ever since. non-marine glacial facies Although palynomorphs of probable Early overlain by coal measure facies containing a Devonian age are known from the Beacon Glossopteris flora and non-marine facies Supergroup of southern Victoria Land (Kyle with a Lystrosauras fauna and Dicroidium flora, 1977), the most characteristic fossils of this were the product of supercontinent isolation. age comprise a series of marine invertebrates However, viewed in terms of the single super- from the Horlick Mountains, Ohio Range, continent model, it would now appear that . These clearly have these classic sedimentary facies and biotas can Malvinokaffric Province (i.e. cool-water) af- be re-interpreted as austral components of a finities (Doumani et al. 1965) and testify to Pangean super-sequence (Veevers 1988). The the comparatively high-latitude position of basal glacial successions reflect the mid- to high Antarctica in the Early Devonian. Some Lower southern latitudes and succeeding beds contain Devonian fish fossils have been recorded from a provincial biota separated from boreal Pangea both the Horlick and Ellsworth mountain ranges on the east by the Tethyan gulf and on the west and Middle-Late Devonian plant remains are by a tropical land zone (Veevers 1988, fig. 2c). known from the Ruppert Coast of Marie Byrd Although Veevers dates the coalescence of Land (Grindley et al. 1980); however, these are Gondwana and Euramerica slightly later (mid- overshadowed in both stratigraphical and bio- Carboniferous, c. 320 Ma), it is clear from his geographical importance by the Givetian (late reconstruction that the classic Glossopter& flora Middle Devonian) Aztec Siltstone fish fauna now has a distinctly austral aspect. from southern Victoria Land. Dicynodonts, a widespread, morphologically In a comprehensive review, G. C. Young diverse group of mammal-like reptiles prevalent shows that the Aztec fauna comprises not only during the and Triassic, are the subject the oldest but also one of the most diverse fossil of a comprehensive review by S. L. De Fauw. vertebrate assemblages yet found in Antarctica. Essentially composed of herbivores, this group Over 30 taxa have so far been identified and appears to have undergone two significant these belong to four major groups of jawed adaptive radiations: one in the Late Permian fishes -- the placoderms (armoured fishes), (Tatarian) and the other in the early Middle acanthodians (spiney-finned fishes), chon- Triassic (Anisian). Both radiations were un- drichthyans (sharks and their relatives) and doubtedly aided by the development of homo- osteichthyans (boney fish) -- and one group of geneous Gondwana floras (the Glossopteris and agnathans (primitive jawless vertebrates; the Dicroidium floras, respectively), but it is import- thelodontids). The fauna has its strongest bio- ant to emphasize that many genera achieved geographic links with eastern Australia and very widespread distributions in Pangea. The indicates that a distinctive East Gondwana ver- equatorial barrier does not appear to have been tebrate faunal province persisted until at least impenetrable to terrestrial vertebrates (see also the end of the Middle Devonian (Young 1981). Chatterjee 1987), and of the 35 known dicyno- By the latest Devonian the vertebrate faunas of dont genera approximately 11 are known from Euramerica and East Gondwana are much more two or more cratonic regions. Lystrosaurus, the similar, particularly in the composition of their famous dicynodont from the Fremouw For- respective freshwater assemblages. Young links mation of Antarctica, is now known to have this change to major palaeogeographic recon- been particularly widely dispersed. Semi- structions and suggests that this may have been aquatic and probably able to forage for a variety the time when the ocean separating these two of food types, it may have been the most suc- supercontinents disappeared. The presence cessful mammal-like reptile of all time. of a significant number of primitive taxa (or One of the most significant palaeontological paraphyletic stem groups) in Antarctica and discoveries yet made in Antarctica is that of a Australia suggests that this extensive continental series of fossil forests. Characterized by both region was the site of origin of major groups of petrified logs and in situ stumps bearing clearly- Downloaded from http://sp.lyellcollection.org/ by guest on September 24, 2021

INTRODUCTION 3 defined annual growth rings, they are now occurs in later beds) and northwards known from the Permian and Lower Triassic through South America. Similarly, the gymno- of the Transantarctic Mountains, the Lower sperm Dacrydium balansae/D, bidwillii alliance Cretaceous of Alexander Island and the Upper is now distributed from South America, through Cretaceous-lower Tertiary of the nothern New Zealand, to certain Pacific islands and Antarctic Peninsula region (e.g. Creber & Malaysia. Its history can be traced by the pollen Chaloner 1984). So striking is their abundance genus Lygistepollenites and the oldest occur- and diversity, and so mild the climatic deduc- rences (Coniacian-Santonian) shown to be tions made from them, that it was thought at on the Antarctic Peninsula and in southeast one time that they may indicate periods of Australia. fundamental change in the growing conditions Particularly important in confirming the high- in polar regions (perhaps related to shifts in the latitude origins of a number of angiosperm tilt of the earth's axis; e.g. Jefferson 1983). lineages has been the elucidation of the However, W. G. Chaloner & G. T. Creber Cretaceous-Tertiary boundary section on have been interested in this problem for some Seymour Island by R. A. Askin. Data from time, and in their review of the phenomenon of here are important in confirming that species forest growth in Antarctica they suggest that from a range of families, which includes the only factor which inhibits tree growth in the the Fagaceae, Myrtaceae, Proteaceae, highest latitudes at the present day is tempera- Winteraceae, Casuarinaceae, Gunneraceae, ture. It is now apparent that the annual input of Bombacaceae and Loranthaceae, have late solar energy to the polar regions is sufficient to Cretaceous-early Tertiary first appearances produce large annual growth rings and it has somewhere along the southern Gondwana mar- been demonstrated that many evergreen trees gins. It should be emphasized, however, that can tolerate long, dark winters. Studies on the not all these families necessarily originated in composition of both living and fossil forests this region. Myrtaceous pollen, for example, is have shown that the low angle of sunlight does known from early Campanian and Maastrichtian not cause excessive mutual shading of trees. sediments on the Antarctic Peninsula; this oc- It has long been suspected that many of the currence clearly predates records in key elements of today's Southern Hemisphere Australia and New Zealand, but postdates those humid and perhumid forests could be traced from undifferentiated 'lower Senonian' in well back into the Mesozoic period. This is Borneo and Santonian in Gabon. In her paper, particularly so for certain lycopods, ferns, Dettmann speculates that a number of austral araucarians and podocarps which may belong to angiosperm taxa may actually have had northern lineages originating as early as the early , Gondwanan or even Laurasian origins and then or even the (Fleming 1963, 1975). migrated via a South America-Antarctica- Certainly, elements of the extensive Late Australia route. Jurassic evergreen coniferous rainforests that It seems to be possible to conclude that covered much of the southern Gondwana mar- Antarctica was both an important source gins have persisted to the present day (Jefferson area and dispersal corridor (during the early 1983; Dettman 1986). Cretaceous-early Tertiary period) for austral If much of the early evidence for the antiquity plants now living at mid- to low latitudes. Quite of austral forest floras came from macro- why a number of major groups should either palaeobotany, much of the latest information originate in, or disperse through, the highest stems from a proliferation of palynological in- southern latitudes is not readily apparent, but, vestigations. Utilizing both on- and offshore as Askin points out, the climate during this successions, and a wide variety of palynoflora period was for the most part mild and equable. taxa, it is now possible to establish at least Indeed, it could well be that an unusual com- the Cretaceous ancestry of a number of living bination of climatic conditions (comprising a groups. M. E. Dettmann, for example, shows polar winter/summer light cycle, low light angles how the fern Lophosoria, which is restricted to and relatively mild and wet weather at the South and central America, had a much wider poles) provided an unique stress impetus for distribution in the Cretaceous and Tertiary. diversification of a wide variety of taxa. We Traced by its unique spore, Cyatheacidites will return to polar origination events and the annulatus (Dettman 1986), this genus can time-discrepancy of high- and lower-latitude be shown to have its earliest stratigraphic oc- occurrences of taxa (often referred to as currence (in basal Cretaceous strata) in the heterochroneity) below. Antarctic Peninsula-South America region; it We know that for much of the Cretaceous then migrated eastwards to Australia (where it Antarctica was covered by thick forests, Downloaded from http://sp.lyellcollection.org/ by guest on September 24, 2021

4 J.A. CRAME

but which animals may have inhabited them? New Caledonia, Papua New Guinea and South Although the Cretaceous terrestrial and fresh- America. However in the Jurassic, eastern water faunal record from the continent is still Gondwana rotated in a direction away from poor, T. H. Rich, P. V. Rich, B. Wagstaff, the South Pole and this led directly to a sub- J. McEwen-Mason, C. B. Douthitt & R. T. stantial improvement in global climates. Gregory maintain that it is possible to specu- Simultaneously, new shallow-water migration late on the composition of at least the Early routes were established around the southern Cretaceous biotas by close comparison with Gondwana margins and by the southeastern Australia. At this time the two warm-temperate Tethyan faunas were able continents were of course still joined and it is to spread to Australia, New Caledonia, New estimated that the terrestrial vertebrates pre- Zealand and West Antarctica. Such a scenario served within the Otway and Gippsland basins is certainly borne out by the belemnite as- could have lived at as high a palaeolatitude as semblages described by P. Doyle & P. J. 85~ Hypsilophodont dinosaurs are particularly Howlett, for in the Middle- a common in these Victoria coast assemblages, distinctive Belemnopsis- Hibolithes- Duvalia and there is at least one theropod, Allosaurus fauna can be traced southwards from European sp.. Turtles are common too, although they Tethys to the Gondwana margins. Local en- seem to belong to primitive types, and there is a demic centres can be identified at this time, variety of fish (including ceratodont lungfish such as in the embryonic trans-Gondwana sea- and the unique Australian koonwarrids), lepido- way, but they are only discernible at the species saurs, pterosaurs, plesiosaurs (presumably level. freshwater) and birds, together with a possible By the , extensive rifting labyrinthodont amphibian. That dinosaurs had occurred across Gondwana and the proto- could have lived in southeastern Australia (and Indian and South Atlantic oceans were begin- thus Antarctica too) is not altogether surprising ning to form. This in turn led to a reversal of the for they have been known for some time from rotation of the eastern Gondwana block and the deposits on the North Slope of re-introduction of its southern margins into Alaska. Rich et al. believe it unlikely that the the highest latitudes. Here, a cool-temperate herbivorous hypsilophodontids would have molluscan fauna developed, with one of its most migrated vast distances to areas of winter day- important components being the endemic light and suggest instead that a large brain and belemnite family, the Dimitobelidae. Further eyes may have pre-adapted them to the low opening of the Atlantic and Indian oceans oc- light conditions of polar habitats. curred throughout the Late Cretaceous and it By comparing assemblages from both was at this time that New Zealand's land links Australia and southern South America, R. E. with the rest of Gondwana were severed by Molnar has suggested that the one dinosaur the formation of the Tasman Sea. However, known from the Late Cretaceous of Antarctica as Stevens points out, there were still good (an ankylosaur from James Ross Island; Olivero Late Cretaceous shallow-marine connections et al. in press) was part of a terrestrial fauna between New Zealand, West Antarctica and that included hypsilophodontids, pterosaurs, South America. A cool-temperate Weddellian ratites, sphenodontians, leiopelmatid frogs and Province can be established between these local- ceratodontid lungfish. In reviewing austral ities until well into the Paleogene (Zinsmeister Mesozoic terrestrial vertebrate faunas, he was 1982). struck by the fact that three of the fifteen The abundant early Campanian-late known genera from the Jurassic-Cretaceous marine invertebrate faunas of the James Ross of Australia (Allosaurus, Austrosaurus and Island region have been investigated by R. M. Siderops) seem to have been relicts. Coupled Feldmann & D. M. Tschudy. They are particu- with the occurrence of the apparent labyrinth- larly interested in an unusually rich decapod odontid amphibian, this could be taken to indi- crustacean fauna which occurs in association cate one of two things: either there was some with ammonites, bivalves, gastropods, echino- form of geographical barrier protecting the derms and brachiopods. Concentrating on the Australian region (and Antarctica too?), or macrurous decapods (lobsters), they have been certain taxa may have preferentially survived in able to identify four species in the shallow-water polar regions (cf. Vermeij 1987). Campanian-Paleocene Lopez de Bertodano Returning to the marine realm, G. R. Stevens Formation. Hoploparia stokesi is extremely indicates that a distinctive cool-temperate abundant, but shows no clear-cut evolutionary Maorian province can be detected within the trends in shape over a 20 Ma period. Metane- Triassic invertebrate assemblages known from phrops jenkinsi, a probable derivative of H. Downloaded from http://sp.lyellcollection.org/ by guest on September 24, 2021

INTRODUCTION 5

stokesi, is particularly noteworthy as it extends until suitable conditions develop for their the range of the genus back from the dispersal. to the Campanian. Metanephrops today is in It is this second aspect of heterochron- fact only known from outer shelf/slope habitats eity which may have been crucial here, with at lower latitudes, and Feldmann & Tsehudy Australian marsupial radiation being closely believe that this may be another example of a linked to habitat diversification. New stem marine invertebrate taxon that originated in the taxa are held to have evolved in the latest Late Cretaceous-early Tertiary of the James Cretaceous-early Tertiary Weddellian Prov- Ross Island region and then dispersed slowly to ince but these could not proliferate in the lower latitudes through the Cenozoic. So far, uniform cool-temperate closed rainforests. at least five bivalve, one gastropod, three However, by the mid- to late Eocene, Australia echinoderm, seven decapod and two brachiopod had separated sufficiently from Antarctica to genera known previously from either the late generate much more diverse open-forest habi- Cenozoic or Recent of mid- to low-latitude tats and this provided the trigger for extensive regions can be shown to have their earliest family-level cladogenesis to occur. stratigraphic occurrences at this Antarctic Although it is generally assumed that the best locality (Zinsmeister & Feldmann 1984; Crame record of the deterioration of Cenozoic climates 1986; Wiedman et al. 1988). This is and onset of glaciation in Antarctica is contained another striking example of high-latitude in marine cores (e.g. Leg 113 scientific party heterochroneity. 1987; Leg 119 scientific party 1988), there are Marine vertebrates from the Lopez de also some important terrestrial sequences to be Bertodano Formation include teleost fish, considered. K. Birkenmajer & E. Zastawniak sharks, mosasaurs and plesiosaurs. The last two indicate that a long sequence of late Mesozoic- groups have been studied by S. Chatterjee & B. Tertiary floras is contained within the volcanic- J. Small as they almost certainly occupied the lastic sediments interbedded with a thick top-predator niches filled at the present day by volcanic pile on King George Island, South seals and whales. Material belonging to two Shetland Islands. Radiometric dating of the separate plesiosaur families, the Plesiosauridae volcanics has enabled the plants to be grouped and Cryptoclididae, has now been identified, into a series of discrete assemblages, which can and a new species within the latter taxon is then be analysed palaeoecologically. The results described (Turneria seymourensis sp. nov.). of this study, in conjunction with sedimen- Interestingly enough, it would appear that cryp- tological investigations of intercalated glacial toclidids fed by sieving food particles through a deposits, have been used to construct a 'climato- mesh formed by their slim, delicate, interlocking stratigraphy' for the South Shetland Islands. teeth. Chatterjee & Small speculate that they Warm phases are identified in the Late may even have fed on Hoploparia, in a manner Cretaceous- Paleocene, middle Eocene- early analogous to that of crabeater seals feeding on , late Oligocene (in part) and at the krill. Oligocene- boundary; intervening In a stimulating new hypothesis to account cold ones are identified in the early Eocene for the origin of the Australian marsupials, J. (the Krakow Glaciation) and late Oligocene A. Case suggests that Zinsmeister's (1982) (Polonez and Legru glaciations, separated by Weddellian Province can also be identified in the Wesele Interglacial). the terrestrial realm. Here it is characterised, in In a review of the evolution of the Antarctic the Paleocene and Eocene of South America, fish fauna, J. T. Eastman & L. Grande demon- south-east Australia and Antarctica (Seymour strate that the dominant living group, the noto- Island), by two key elements: Nothofagus and thenioids, have no fossil record. Their rise to marsupials. Case points out that, just as the prominence seems to have been a consequence concept of high-latitude heterochroneity can be of the thermal isolation of Antarctica, which used to account for the origin of certain plant was partially achieved after the final (deep and marine invertebrate taxa within the prov- water) separation of Australia in the late ince, so it may also be applicable to terrestrial Eocene-early Oligocene (38Ma) and com- vertebrates too. In its original formulation pleted on the formation of the Drake Passage at (Zinsmeister & Feldmann 1984), the concept the Oligocene-Miocene boundary (23Ma) was split into two distinct components: first, the (e.g. Kennett 1977). With the formation of high latitudes may serve as centres of origin for the Antarctic Convergence, it is likely that the taxa which can 'escape' under existing climatic southward migration/colonization by most conditions, and second, they may serve as 'hold- pelagic fishes would have been prohibited; the ing tanks' for new taxa which remain isolated ancestral notothenioid stocks could then de- Downloaded from http://sp.lyellcollection.org/ by guest on September 24, 2021

6 J.A. CRAME

velop unchallenged in the vast Southern Ocean. Fossil evidence from both Antarctica (Seymour Eastman & Grande point out that the most Island) and New Zealand supports the con- logical explanation for the replacement of the clusion that, within the Cetacea (whales and Seymour Island Tertiary fish fauna by a rela- dolphins), the filter-feeding Mysticeti and echo- tively depauperate Recent one is the 15~ de- locating Odontoceti arose from the primitive cline in temperature over a 50Ma period. Archeoceti in the latest Eocene-earliest Nevertheless this should not have been an Oligocene interval. Both groups certainly ap- insurmountable evolutionary problem, for this pear to have then proliferated in the mid- to averages out to a decrease of only 0.03~ per high southern latitudes through the Oligocene. 100000 years. Adaptation to low temperature Lobodontine phocids (true seals) radiated in as such presents few major biological obstacles the Southern Ocean region in approximately and literally thousands of species have ac- the late Miocene, and perhaps excluded cer- complished it (Dunbar 1968; Clarke 1988). tain otariids (fur seals and sea lions), such as Other ecological restraints, such as limited Arctocephalus, from high-latitude pagophilic habitat space and trophic resources, are far lifestyles. more likely to have inhibited the development E. Thomas considers the fact that polar cool- of the Antarctic fish fauna. ing had major effects on the formation of bottom A more general survey of the Southern Ocean water, and this in turn is reflected in the compo- marine fauna by A. Clarke & J. A. Crame sition of benthic foraminiferal assemblages. She reveals that a substantial part of it may have describes a new sequence of Late Cretaceous evolved in situ over a long period of time. A (Maastrichtian) to late Miocene taxa that were number of living invertebrate groups, such as obtained during ODP Leg 113 drilling on Maud the pycnogonids, certain gastropods (trochids, Rise. They are all lower bathyal to upper abyssal littorinids, trichotropids and buccinaceans), types and analysis of them reveals distinct com- echinoderms (ophiuroids, ctenocidarid cid- positional shifts at seven levels (early/late Paleo- aroids and schizasterid spatangoids) and as- cene boundary, latest Paleocene, early Eocene, cidians, appear to be the products of adaptive early middle Eocene, miJdle middle Eocene, radiations that began in the Cenozoic, or even, earliest Oligocene, middle Miocene). At two in some instances, the late Mesozoic. Far greater of these, the early Eocene and early middle areas of shallow-water habitats were available Eocene, the changes are particularly striking for colonisation in the geological past; even and suggest that the formation of bottom water after the onset of the main ice caps, substantial may have been very different from preceding de-glaciations occurred in interglacial periods. and succeeding periods. The marked lack of Turning to more physiological matters, spiral forms and dominance of buliminids can Clarke & Crame consider the slow growth rates, be linked to lower oxygen levels and higher extended development times and low metabolic nutrient supply. These may have been times rates of cold-water ectotherms (cold-blooded when deep waters were formed by evaporation organisms). Low temperature is of course the at low latitudes (to form warm saline bottom traditional explanation for all these phenomena, water) rather than in polar regions. but it seems somewhat paradoxical to suggest Finally, L. E. Watling & M. H. Thurston that it should hinder some processes such as consider a method of investigating the origins growth, but not others such as locomotion. and evolution of an Antarctic amphipod family, There is in fact a great energetic benefit to be the Iphimediidae, without recourse to the fossil derived from living in cold water, because basic record. Using a combination of phylogenetic maintenance costs are so low (Clarke 1988). (cladistic) and biogeographic data, they show The real problem for organisms in polar waters that the most primitive members of the family seems to be adapting to a severely pulsed food are distributed primarily outside Antarctica; supply. these are inferred to be the relicts of a former Using evidence gleaned from both the austral global distribution. The evolution of the family fossil record and the adaptations and distri- is then marked by a basic reorganization of the bution of living organisms, R. E. Fordyce mouth field appendages which led directly to a suggests that the formation of the Southern major radiation of taxa. It is suggested that this Ocean may have had a seminal influence on occurred in the Antarctic region at approxi- the development of certain groups of mar- mately the Eocene-Oligocene boundary, with ine mammals. The formation of the circum- the cool waters of the embryonic Southern Antarctic current, psychrosphere and Atlantic Ocean acting as an incubator for the evol- Convergence almost certainly provided the utionary advance. With the possession of a new stimulus to develop new feeding strategies. scissors-like mandible, the family spread swiftly Downloaded from http://sp.lyellcollection.org/ by guest on September 24, 2021

INTRODUCTION 7

outwards from the Antarctic (principally Antarctica (and Gondwana) seem to have been through the genus Iphimedia; approximately 35 particularly important dispersal routes and species worldwide) and successfully colonised undoubtedly served as a major corridor for the thermally changing global ocean. floral and faunal interchange between the high and low southern latitudes. Summary What is perhaps more surprising is to find that a number of plant and animal groups seem The new, but still fragmentary, fossil record to have both originated in, and then radiated that we have from Antarctica indicates that a from, the high southern latitudes. Even after surprisingly wide variety of organisms has lived the marked deterioration of climates and loss of on or around our southermost continent. Since habitats through the Cenozoic, there still appear the early Middle Devonian (385 Ma ago), when to have been adaptive radiations (especially in Antarctica (within Gondwana) reached approxi- the marine realm). mately its present position, it has been colonized Could it be that temperate, cool-temperate by a succession of plants and animals that shows and even cold-temperate regions of the world signs of being as complex as those on any other have been more effective in the process of continent. species diversification than hitherto recognized? Vast habitat areas available for occupation The improved fossil record from Antarctica by both terrestrial and marine organisms, coup- may be crucial in determining the contribution led with equable climates for very long periods of high-latitude regions to the global species of time, certainly contributed towards this pro- pool. liferation of life. The southern margins of

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