The Mesozoic Era lasted more than 180 million years and was marked by a generally tropical climate where plants and animals -- especially dinosaurs -- thrived. Today, Colorado retains evidence of its Mesozoic history in fossils, geographic formations and natural history landmarks.
The Mesozoic Era
The Mesozoic (meaning "middle life") Era, or the Age of Dinosaurs, occurred 248 to 65 million years ago at the end of the Paleozoic Era. At that time, the Colorado Plateau separated from Pangea, the supercontinent. The Mesozoic is divided into three time periods: Triassic, Jurassic and Cretaceous. Dinosaurs evolved and early mammals first appeared during the Mesozoic Era.
Colorado During the Mesozoic
Colorado was desert-like for a good portion of the Mesozoic, although it was also above and below water many times. Volcanic mountain ranges to the east erupted and coated what is modern-day Colorado beneath layers of ash. Later, lakes, rivers and inland seas developed, evidence of which can still be seen in the earth's sediment. These bodies of water created massive geological formations that still can be seen today, like the Chinle and Kayenta in Arizona, Utah and Colorado. Uplift -- or the collision of two continents -- in the Colorado Plateau was created by orogenies (or mountain-building events), and there are a series of sandstone cliffs in the central Colorado Plateau.
During the mid-Mesozoic Era, Colorado got cooler and more damp, and plant life increased. Dinosaurs and small lizards moved in. Most of today's oil and coal deposits are from the Mesozoic. At the end of the Mesozoic, Colorado was covered by a shallow sea. This sea receded slowly to the east, and left behind a swampland that was rich with vegetation and ideal for dinosaurs.
Plants
During the late Mesozoic, subtropical forests covered parts of Colorado. Plants in these areas included palms, ferns, cedar trees, cycads, horsetails, gingkos, figs, magnolias and oaks.
Animals
During the Mesozoic, large amphibians, small early mammals (most no larger than a cat) and dinosaurs roamed the lands of Colorado. Some of the more well-known dinosaurs of the Mesozoic were Stegosaurus, Riojasaurus, Triceratops, Ichthyodectes, and Tyrannosaurus rex. There were also turtles, fish, snails, frogs, lizards, crocodiles, early sharks, marine invertebrates, and insects, including termites.
Preservation of the Mesozoic Era in Colorado Today
One of the most famous Mesozoic fossil locations in Colorado is Dinosaur Ridge in Morrison, Colo. Apatosaurus, Diplodocus, Stegosaurus and Allosaurus remains were found there in 1877 by geologist Arthur Lakes. Visitors can still see bones and tracks of different Mesozoic creatures. The area was designated Morrison Fossil Area National Natural Landmark by the National Park Service in 1973.
Another popular site is Dinosaur National Monument, located between Colorado and Utah where the Green and Yampa rivers meet. Paleontologist Earl Douglass first discovered fossils there in 1909. Eleven different kinds of dinosaurs have since been discovered in the area.
In a tribute to its Mesozoic past, Colorado's state fossil is a Stegosaurus, designated in 1982.
Tags: Mesozoic Colorado, Colorado Plateau, early mammals, Mesozoic Mesozoic, million years, still seen
