East america fossil dating
When one thinks about dinosaur fossils, Western North America usually comes to mind, and it's no wonder.The Western United States is world famous for its dinosaur fossils in quantity, quality, and diversity in all three dinosaur ages.After traditional and well accepted direct-dating methods failed because the bones were mineralized from long emersion in warm salty water within this limestone cave system, they worked closely with colleagues to build a geochronological framework for Naia using a unique combination of techniques to constrain the age of the skeleton to the end of the ice age.To build the case for a late Pleistocene age they collaborated with Yemane Asmerom and Victor Polyak from the University of New Mexico using global sea level rise data to determine when the cave system, which at the time Naia and the extinct animals entered was dry, filled with water.Orrorin lived about 6 million years ago, while Ardipithecus remains have been dated to 5.8-4.4 million years ago.At present, the vote is still out as to whether any of these three primates were in fact true hominins and if they were our ancestors.The fossils have been tentatively classified as members of three distinct genera-- .Sahelanthropus was the earliest, dating 7-6 million years ago.
A variety of dates has been proposed and some are in dispute.
Here, nearly complete specimens of Coelophysis from the Late Triassic are found.
The Jurassic Morrison Formation preserves numerous Stegosaurs, a wide range of Sauropods, and the famous theropod, Allosaurus.
The primate fossil record for this crucial transitional period leading to australopithecines is still scanty and somewhat confusing.
However, by about 4.2 million years ago, unquestionable australopithecines were present.
The classification of Sahelanthropus has been the most in question.