Upwelling currents are cause by: o temperature differences between water masses
o salinity differences between water masses
O pressure differences between water masses
o Ekman spiral

the skeletons of most mammals reach a certain size and then stop growing. however, many animals, including some mammals, keep growing throughout their lives. kangaroos, for example, just keep growing and growing until they die. also, the longer an animal lives the greater the chance it might catch some deadly disease.