The observation that certain fossils were associated with certain rock strata led early geologists to recognize a geological timescale in the 19th century.The development of radiometric dating techniques in the early 20th century allowed geologists to determine the numerical or "absolute" age of the various strata and thereby the included fossils.
This article deals primarily with non-avian dinosaurs.
Dinosaurs are a varied group of animals from taxonomic, morphological and ecological standpoints.
Like other tyrannosaurids, Tyrannosaurus was a bipedal carnivore with a massive skull balanced by a long, heavy tail.
Relative to the large and powerful hindlimbs, Tyrannosaurus forelimbs were small and they retained only two digits. rex have been found in North American rock formations dating to the last three million years of the Cretaceous Period at the end of the Maastrichtian stage, approximately 68.5 to 65.5 million years ago; it was among the last dinosaurs to exist prior to the Cretaceous-Tertiary extinction event. rex have been identified, some of which are nearly complete skeletons.
From the Quagga --half zebra, half horse-- to the Irish Deer --the largest deer that ever lived--, an impressive list with pictures of amazing animals we will never see.
Tyrannosaurus rex was one of the largest land carnivores of all time, measuring up to 43.3 feet long, and 16.6 ft tall, with an estimated mass that goes up to 7 tons.
Birds, at over 10,000 living species, Through the first half of the 20th century, before birds were recognized to be dinosaurs, most of the scientific community believed dinosaurs to have been sluggish and cold-blooded.
Most research conducted since the 1970s, however, has indicated that all dinosaurs were active animals with elevated metabolisms and numerous adaptations for social interaction. Evidence suggests that egg laying and nest building are additional traits shared by all dinosaurs.
Usually, atoms have an equal number of protons and neutrons.