Dinosaurs Origin
For
15–20 million years, the comparatively little ancestors of dinosaurs had
to coexist with those more primitive organisms. Paleontologists are
reevaluating the road dinosaurs took to become dominant in light of the
fossilized bones of an ancient mammal found in the Ghost Ranch Petrified
Forest in New Mexico last year. Ecosystems have included dinosaurs as
important members for more than 200 million years. While there are a
variety of macroevolutionary theories that attempt to explain the
Triassic genesis and the rise to dominance of dinosaurs and their
closest relatives, dinosauromorphs, none of them can be conclusively
supported by a precise chronological framework that is independent of
biostratigraphy. Whether reported faunal variations change across time,
space, or both is impossible without a rigorous geochronologic age
control to compare various scenarios.
Millions of years after their origins, closer to the Triassic–Jurassic divide, dinosaurs progressively dominated mid to high-latitude terrestrial habitats. In addition to current and living birds, Class Aves, dinosaurs are a group of terrestrial vertebrates that are assumed to have contained a range of non-bird, earthbound species that existed from around 230 million years ago to 65 million years ago. Fundamentally, dinosaurs were terrestrial creatures. Birds are the only known dinosaurs to have been able to fly; even yet, these creatures have retained certain basic terrestrial traits from their non-flying dinosaur ancestors; also, there are no confirmed marine dinosaurs.