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A Review of the World Distribution of Oribatid Mites [Acari: Cryptostigmata) in Relation to Continental Drift By MARIE HAMMER and JOHN A. WALLWORK Det Kongelige Danske Videnskabernes Selskab Biologiske Skrifter 22:4 Kommissionær: Munksgaard København 1979 D et K ongelige D anske V idenskabernes Selskab udgiver følgende publikationsrækker: T he R oyal D anish Academy of Sciences and Letters issues the following series of publications: Bibliographical Abbreviation Oversigt over Selskabets Virksomhed (8°) Overs. Dan. Vid. Selsk. (Annual in Danish) Historisk-filosofiske Meddelelser (8°) Hist. Filos. Medd. Dan. Vid. Selsk. Historisk-filosofiske Skrifter (4°) Hist. Filos. Skr. Dan. Vid. Selsk. (History, Philology, Philosophy, Archeology, Art History) Matematisk-fysiske Meddelelser (8°) Mat. Fys. Medd. Dan. Vid. Selsk. (Mathematics, Physics, Chemistry, Astronomy, Geology) Biologiske Skrifter (4°) Biol. Skr. Dan. Vid. Selsk. (Botany, Zoology, General Biology) Selskabets sekretariat og postadresse The address of the Academy is: Det Kongelige Danske Videnskabernes Selskab, Dantes Plads 5, DK-1556 Copenhagen V. Denmark. Selskabets kommissionær The publications are sold by the agent of the Academy: M unksgaards boghandel, 6, Norregade, DK-1165 Copenhagen K. Denmark. A Review of the World Distribution of Oribatid Mites (Acari: Cryptostigmata) in Relation to Continental Drift By MARIE HAMMER and JOHN A. WALLWORK Det Kongelige Danske Videnskabernes Selskab Biologiske Skrifter 22:4 Kommissionær : Munksgaard København 1979 Synopsis A survey is presented of the patterns of world distribution of oribatid mites, mainly at the generic level. Evidence is presented to show that the oribatids are an ancient group, and recent genera have an evolutionary history extending back to the Jurassic and probably earlier. Sixteen percent of recent genera are cosmopolitan in distribution, and this element in the world fauna can be identified with that which was present in Pangaea. With the gradual break-up of Pangaea, genera arose with a more restricted distribution — firstly in Gondwanaland and Laurasia — and subsequently in the main continental masses as we know them today. All of these elements can be identified in the recent oribatid fauna of the world. Circum-polar and pan-tropical distribu­ tion patterns provide evidence of previous Gondwanan and Laurasian connexions, and eviden­ ces of faunal intermixing at the boundaries of these two former super-continents are found in the faunas of India, north-west Pakistan and Japan. The origin of the oribatid fauna of oceanic islands is discussed and it is suggested that the source area for the fauna of the South Pacific is probably South-east Asia and that dispersal has occurred over seas, via island “stepping stones”. MARIE HAMMER JOHN A. WALLWORK dr. phil. dr. phil. Langstrupvej 1 Westfield College DK-3480 Fredensborg London NW 3 7 S. © Det Kongelige Danske Videnskabernes Selskab 1979 Printed in Denmark by Bianco Lunos Bogtrykkeri. ISSN 0366-3612. ISBN 87-7304-065-7 22:4 3 Contents Page Introduction ........................................................................................ 5 The Antiquity of Oribatids.............................................................................................................. 6 Global Patterns of Distribution..................................................................................................... 6 The Cosmopolitan F a u n a ................................................................................................................ 7 The Gondwanan E lem ent................................................................................................................. 8 New Zealand Oribatids............................................................................................................ 8 South American and African Oribatids .............................................................................. 13 Oribatids of South-east A sia ................................................................................................... 14 The Laurasian E lem ent.................................................................................................................... 17 Greenland Oribatids ................................................................................................................ 18 Arctic-alpine Oribatids ............................................................................................................ 19 Palaearctic O ribatids................................................................................................................ 19 North American Oribatids...................................................................................................... 20 Oribatid Fauna of Oceanic Islands............................................................................................... 20 SubAntarctic O ribatids............................................................................................................ 20 Pacific O ribatids........................................................................................................................ 21 Concluding R em arks......................................................................................................................... 22 Bibliography......................................................................................................................................... 24 Appendix: Lists of G enera............................................................................................................... 27 22:4 5 Introduction The moss mites, or oribatids, are small arachnids commonly outside these regions. Similarly, a Laur- which live a free existence, mainly in soils but not asian fauna would have a distribution which essen­ infrequently in wet biotopes. They are widely distri­ tially encompassed North America, Greenland and buted around the world, although little attention Eurasia. Evidence for such patterns would be prov­ has been paid so far to any patterns that may occur ided by the existence of harmonic faunas (see page on a global scale and, more particularly, to how 10) in two or more regions which are now geo­ such patterns have arisen. If we believe, for instan­ graphically isolated. ce, that the oribatids are a very ancient group of Alternatively, we must also consider the possibili­ animals, with an evolutionary history extending ty that the present distribution patterns of oribatid back many millions of years into geological time, mites are recent phenomena — the products of we must consider the possibility that the global dispersal agencies which have been operating, per­ distribution of this fauna has been influenced by haps, since the Pleistocene. Such dispersal must changes in world climate and topography which have taken place across the wide expanses of ocean have occurred during this time. Such changes have which now separate the continents of the world, been brought about principally by the movements and the agencies involved could be air currents, of continents which have been occurring at least water currents, transport by birds, or introduction since the Jurassic, 150 million years ago. At this by Man. Such agencies are essentially random ones, time, the earth’s major land masses were much and result in unbalanced, dysharmonic faunas (see closer together than they are today, forming the p. 7). supercontinent of Pangaea. The faunal continuities The evidence for continental drift is, in our that existed then would have been disrupted by the opinion, overwhelming (see readings from Scientific subsequent break-up of Pangaea and, eventually, American, entitled ‘Continents Adrift’, introduced the separation of Laurasia and Gondwanaland into by J. Tuzo Wilson 1971). We will also present eastern and western components. If oribatid stocks evidence that the oribatids are a very ancient group persisted and continued to evolve while these events of terrestrial animals. The main purpose of this re­ were occurring, even up to the present day, we view is to examine the extent to which present-day might expect to find evidence for the effects of con­ distribution patterns of these arachnids may be in­ tinental drift in the global patterns of distribution terpreted within the context of continental drift. that we can observe today. For example, stocks It is recognized at the outset that the oribatid which were widely distributed across Pangaea, if fauna of certain parts of the world, notably China, they have persisted to the present day, would be ex­ India and Australia, is very incompletely known, pected to show a cosmopolitan distribution, or a and our analyses have been limited, sometimes relict of such. Stocks which evolved in Gondwana­ severely, by this fact. However, we believe that land could be expected to be widely distributed enough information is available from many parts across the southern hemisphere today, in South of the world to allow a broad framework to be America, Africa, India and Australasia — but not developed, even though subsequent discoveries of 6 22:4 new taxa and new distribution records will un­ baeremaeidae and Plateremaeidae which have a doubtedly modify the ideas presented in this paper. cosmopolitan distribution today. The validity of Some of these ideas have already been developed these finds has recently been confirmed by the dis­ by Hammer in her works on the oribatid fauna of covery of a member of the cosmopolitan aquatic South America, North America, Greenland,

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