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.
Implications of Deep-Marine Miocene Deposits on the Evolution of the North Patagonian Andes
The North Patagonian Andes (38°–43°30′S) present topographic and geologic characteristics distinct from those of the Central Andes to the north, including a lower altitude, a predominance of plutonic rocks, and the presence of a major N-S-trending, dextral strike-slip, intra-arc discontinuity known as the Liquiñe-Ofqui Fault Zone (LOFZ). The timing for the uplift of the North Patagonian Andes remains poorly constrained principally because high exhumation rates resulted in the erosion of most of its volcano-sedimentary cover during the late Cenozoic. The strongly deformed Cenozoic marine deposits ascribed to the Ayacara Formation, which crop out on the western flank of this range at ∼42°S, can provide for a better understanding of the recent geologic evolution of this range. To discern this formation’s age and sedimentary environment, we have integrated sedimentology, ichnology, foraminiferal paleontology, and geochronology. Our results indicate that this unit was deposited in a deep-marine environment during the Early-Middle Miocene. Correlation of the Ayacara Formation with coeval deep-marine deposits in the forearc to the west indicate that deposition was caused by a major regional event of tectonic subsidence probably related to subduction erosion. An Early-Middle Miocene age for the Ayacara Formation is a reliable maximum age for the deformation and uplift of the western flank of the North Patagonian Andes as well as for the commencement of transpressional deformation associated with the LOFZ.
Hill country sheep production. I. The influence of age, flock, and year on some components of reproduction rate in Romney and Border Leicester × Romney ewes.
Data from 7,091 straightbred Romney and Border Leicester × Romney ewes grazed at the Whatawhata Hill Country Research Station over the period 1959 to 1967 have been used to obtain estimates of flock and age-of-ewe effects on reproduction rate and its components and of year-to-year variation. The ewes were from six groups: a Romney control (RCR) flock, a Romney flock in which ewes were mated either to Romney (RER) or to Border Leicester rams (REB), and flocks of first-cross (F1), second-cross (F2), and third-cross (F3) Border Leicester × Romney ewes mated to first-cross Border Leicester × Romney rams. The ewes' ages at lambing varied from 2 to 5 years and no selection was practised. The ratio of number of lambs weaned per ewe present at lambing increased from the RCR (0.84) to the F1 (1.07), then declined with interbreeding to the F2 (0.92) and further to the F3 (0.87) ewes. Similar changes were evident for the percentage of ewes lambing, of multiple births, and of lambs surviving to weaning. Over...