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The origin of Neornithes is the most uncertain of all three groups analysed, stretching from the end of the Cretaceous around 66 million years ago all the way until the middle Early Cretaceous, around 120 million years ago.
The reason for this uncertainty is simply due to the state of the fossil record during the Late Cretaceous, in which the taxonomy of some species is quite difficult to assess.
But this "age" was not only the result of a broken radioisotope system, it was contrived to agree with previously assigned dates for the samples.
The scientists analyzed the abundance of radioactive isotopes of certain elements that had leeched into the edges of buried dinosaur bone from the San Juan Basin in northern New Mexico and southern Colorado.
This is important for evolutionary studies as it means that we can now more accurately assess the times of important steps in the global tree of life, and apply these to our large-scale understanding of the macroevolution of life on Earth. Palaeontologist into crocodiles, dinosaurs & mass extinctions. Passionate about open science, and Communications Director for Science Open.This is fairly close to when we see the oldest potential bird fossils, and some of the oldest evidence of feathered dinosaurs.belong on the stem of this group, and can actually be considered as ‘stem birds’.This is because new sediments are always laid down on top of sediments that have already been deposited.So, when looking at the history of a cliff face, it is important to read the story it tells from the bottom layer up.