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Recent Antarctic and Subantarctic Brachiopods

Recent Antarctic and Subantarctic Brachiopods

Merrill W. Foster (Editor)

ISBN: 978-1-118-66465-0 April 2013 American Geophysical Union 189 Pages



Published by the American Geophysical Union as part of the Antarctic Research Series, Volume 21.

The Recent brachiopod faunas from southernmost South America, Antarctica, and the Subantarctic consisting of 21 genera and 37 species are described from new material. New taxa include the genera Manithyris and Bathynanus. Also new are 11 species: Compsothyris ballenyi, Hispanirhynchia? chiliensis, Manithyris rossi, Liothyrella multiporosa, Liothyrella scotti, Bathynanus tenuicostatus, Eucalathis macrorhynchus, Amphithyris hallettensis, Dallina eltanini, Fallax antarcticus, and Magellania? spinosa.

Factor analysis was used to study relationships among morphological characters and environmental parameters. In Liothyrella, negative associations were found between beak height and water depth. The size of the pedicle opening within this genus is associated with the width of the hinge plate and the loop; apparently, these associations are related to increased dorsal adjustor muscle size with increased pedicle size. Similar relationships are found in the terebratellids, although here all of the characters are also negatively associated with water depth. Characters negatively associated with water depth may relate to the differing current strength at various depths. Puncta density is positively correlated with water temperature.

Examples of brachiopod variation are discussed. Synonyms have resulted from former failure to study large samples and to appreciate the extent of brachiopod variation. A priori valuation of certain characters as being specific is unwarranted, since sibling species may be more similar than different subspecies of the same species.

Many Recent and fossil brachiopod genera are too narrow in definition owing to oversplitting or to a narrow conception of monophyly. I advocate somewhat broader and more practical genera for obtaining the maximal information value from such taxa.

Brachiopods, contrary to popular belief, are an abundant and viable group in the southern hemisphere faunas. Most brachiopods in the Ross Sea appear to have definite niches and habitats but may overlap geographically where population densities are low. Brachiopods here can be divided roughly into a slope and a shelf assemblage. The greatest species diversity occurs at the seaward edge of the Ross Sea shelf, interpreted as an ecotone effect where two different water types meet.

Only South America and Antarctica appear to have or have had direct communication between some elements of their brachiopod faunas. Other similarities between separate southern continents are related to retention of common pre-Cenozoic elements or to chance dispersal of larvae across barriers.

Events related to cooling during the late Pliocene or Pleistocene caused reduction of puncta density, shell thickness, and spiculation in the Recent fauna and apparently influenced the present species structure, at least in Liothyrella uva, Gyrothyris mawsoni, and Macandrevia.

Frontispiece iv

The Antarctic Research Series
Morton J. Rubin vii

Abstract ix

Introduction 1

Techniques  5

List of described taxa  7

Variation and taxonomy  9

Intraspecific variation  9

Species taxonomy  10

Generic taxonom  11

Quantitative analyses  13

Terebratulidee ndopunctation  17

Ecology  23

General observations  23

Ross Sea region 24

Distribution 33

Recent brachiopod distribution 33

Cenozoic brachiopods and their distribution 33

Conclusions  34

General conclusions  37

Systematic discussion  39

Key to brachiopod families of far southern waters  39

Family Discinidae 39

Family Craniidae 40

Family Basiliolidae  47

Family Hemithyrididae  49

Family Frieleiidae  50

Family Terebratulidae 56

Family Dyscoliidae  79

Family Cancellothyrididae 79

Family Platidiidae  84

Family Dallinidae 85

Family Terebratellidae 97

Appendix 1. Station list 149

Appendix 2. Statistical determinations 165

References  177

Acknowledgments 182

Systematicin dex  183