Downloaded from http://sp.lyellcollection.org/ by guest on September 24, 2021 Origins and evolution 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 years there has been a dra- in this volume L. R. M. Cocks provides a brief matic increase in our knowledge of the fossil but succinct review of Antarctica's place within record of Antarctica. Improved access to the Cambrian to Devonian 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 Limestone 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 fossils 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) Minaret Formation 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 Ordovician and Silurian 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. Carboniferous 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 Triassic 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 Transantarctic Mountains. 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 Permian 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