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.
First notice of the Chirostylidae (Deeapoda) in the fossil record and new Tertiary Galatheidae (Deeapoda) from the Americas
Two new species from Alaska and Washington, USA, Munida konara sp. nov., and Munida quadroblonga sp. nov., comprise the first occurrence of the Galatheinae (Galatheidae) in western North America and only the third confirmed fossil occurrence of the family and subfamily from the North Pacific Ocean. A new genus and species from Patagonia, Austromunida casadioi, documents the first occurrence of the Galatheinae (Galatheidae) from that region. The Galatheinae appear to have evolved in the North Atlantic or Europe and subsequently dispersed to the Pacific and South Atlantic oceans via a polar route and'or Atlantic ocean currents. The Munidopsinae appear to have evolved in the North Atlantic region during the Jurassic and subsequently dispersed to the southern hemisphere by Cretaceous time, as documented by occurrences of the subfamily in Cretaceous rocks of Antarctica. A new Cretaceous genus and species, Pristinaspina gelasina from Alaska, USA, consitutes the earliest known occurrence of the Chirostylidae. That new taxon, in addition to two fossil species herein reassigned to Eumunida, E. pentacantha (Miiller and Collins, 1991) and E. nishioi (Karasawa, 1993), constitute the first notice of the Chirostylidae in the fossil record. A key to the fossil Galatheoidea demonstrates that arrangement of genera within the Galatheidae, based solely upon characters of the dorsal carapace, generally conforms with subfamilial taxa defined on biologi­ cal criteria; however, the Chirostylidae are not adequately constrained. Rugafarius Bishop, 1985, previously assigned to the Galatheidae, is herein placed within the Prosopidae von Meyer, 1860.
Formation and Strength of Magnesia Whiskers
The formation of single-crystal magnesia whiskers during the compressive deformation of single crystals at room temperatures is described. These whiskers can have strengths of the order of millions of pounds per square inch. They are formed during fracture as a result of the discontinuous propagation of cracks which are mechanically relieving internal stresses resulting from plastic flow