north america and south america divide at the isthmus of panama.
north america and south america divide at the isthmus of panama.
where does north america and south america divide?
the isthmus of panama
this is a list of the native wild mammal species recorded in south america. south america's terrestrial mammals fall into three distinct groups: "old-timers", african immigrants and recent north american immigrants. the marsupials and xenarthrans are "old-timers", their ancestors having been present on the continent since at least the very early cenozoic era. during the early cenozoic, south america's only land connection was to antarctica, so it was effectively cut off from most of the world; as the fragments of gondwana continued to separate, this connection was lost, leaving south america an island continent. caviomorph rodents and monkeys arrived as "waif dispersers" by rafting across the atlantic from africa in the eocene epoch, 35 million or more years ago. all the remaining nonflying mammals of south america are recent arrivals, having migrated from north america via central america during the past seven million years as part of the great american interchange; this invasion, which peaked around three million years ago, was made possible when the formation of the volcanic isthmus of panama bridged north and south america. the newcomers out-competed and drove to extinction many mammals that had evolved during south america's long period of isolation, as well as some species from other classes (e.g., terror birds).
list of mammals of south america
candidate galaxies around redshift "z" = 3 can then be selected by looking for galaxies which appear in optical images (which are sensitive to wavelengths greater than 3600 å), but do not appear in ultraviolet images (which are sensitive to light at wavelengths shorter than 3600 å). the technique may be adapted to look for galaxies at other redshifts by choosing different sets of filters—the method works as long as images may be taken through at least one filter above and below the wavelength of the redshifted lyman limit. in order to confirm the redshift estimated by the color selection, follow-up spectroscopy is performed. although spectroscopic measurements are necessary to obtain a high-precision redshift, spectroscopy is typically much more time-consuming than imaging, so the selection of candidate galaxies via the lyman-break technique greatly improves the efficiency of high-redshift galaxy surveys.
lyman-break galaxy