New Miocene Decapoda (Thalassinidea; Brachyura) from Tierra Del Fuego, Argentina: Paleobiogeographic Implications
ABSTRACT A decapod crustacean fauna of Tierra del Fuego, Argentina, is documented from the middle Miocene Carmen Silva Formation and the early? Miocene Cerro Águila Conglomerate of the Cabo Domingo Group. Three new genera and five new species are named: Asthenognathus australensis, new species; Miotymolus quadratus, new genus and species; Mursia fuegiana, new species; Pharkidodes agele, new genus and species; and Tierrapilumnus edseli, new genus and species. Compilation of all described species of decapods from late Oligocene to early Pliocene exposures in 18 general localities in Patagonia, southern Argentina, and Chile documents two paleobiogeographic provinces, Argentine and Chilean. Coupled with evidence from the biogeographic patterns of associated mollusks, the faunas from Tierra del Fuego have been assigned to the Argentine Paleobiogeographic Province. Comparison of the distribution of Miocene decapods with that of extant decapods (Boschi 2000) leads to the conclusion that the thermal separation of South Atlantic and South Pacific water in the Miocene was more pronounced than today, so that there is no evidence of a discrete Magellanic Biogeographic Province characterizing the high southern latitude region during the Miocene.
ADDITIONS TO THE TERTIARY DECAPOD FAUNA OF THE PACIFIC NORTHWEST OF NORTH AMERICA
Abstract Previously undescribed fossil material from the late Eocene Hoko River Formation and the Oligocene Makah Formation, Olympic Peninsula, Washington, provides new insight into the evolution and biogeography of five families of decapod crustaceans. New taxa include Homola vancouverensis, Xeinostoma? antiqua, and Daldorfia himaleorhaphis. New material makes it possible to provide a complete reconstruction of the dorsal carapace of Macrocheira teglandi, and a possible juvenile Branchioplax washingtoniana is described for the first time. The range of the genus Homola, known in modern oceans, has been extended into the late Early Cretaceous, and the occurrence of that genus in rocks of the Pacific coast of North America marks the first authentic report of the Homolidae from that region. The Cyclodorippidae is now known to have inhabited the Pacific coast of North America as early as the late Eocene. The geologic range of the genus Daldorfia now extends into the Oligocene, and its earliest known occurrence is from rocks of Washington, U.S.A.
Decapod crustaceans from the Eocene La Meseta Formation, Seymour Island, Antarctica: a model for preservation of decapods
Thirteen species of fossil decapod crustaceans collected from 43 localities in the La Meseta Formation (Eocene), Seymour Island, Antarctica, have been located precisely using global positioning system techniques and accurately placed in their stratigraphic context using an allostratigraphic scheme. Three decapod species are congeneric with extant species known from outer shelf and slope habitats documenting an onshore–offshore pattern of ecological preference. Functional morphological analysis of the decapods confirms the environmental interpretations based upon sedimentological studies. Species diversity is greatest in the lower and upper parts of the section, in the Acantilados and Submeseta allomembers, respectively. However, numerical abundance of specimens is greatest near the top of the coarsening-upward sequence in the Cucullaea I Allomember. This allomember and the underlying Campamento Allomember are overwhelmingly dominated by a single species, Lyreidus antarcticus. The relatively high diversity of decapods in the lower and upper parts of the La Meseta Formation is interpreted as resulting from favourable preservational environments in delta-front and nearshore environments where burial was rapid and sediment reworking was minimal. In the middle part of the La Meseta Formation, sediment reworking was probably high and fragile arthropod cuticular material was destroyed, except in the case of Lyreidus, which is a burrower and was probably preserved within its burrow. The pattern of diversity documented by the arthropods differs markedly from that of the molluscs, probably because of the presence of more durable shell material in the pelecypods and gastropods. The La Meseta Formation record of decapods may serve as an important model for arthropod preservation against which other occurrences can be tested.