Dinosaur ancestors developed during the Paleozoic Era.
While the Paleozoic Era contained many new plant and animal species, dinosaurs were not among them. During the Paleozoic, plants and animals adapted to life on land resulting in the greatest proliferation of organisms ever to occur on Earth. It also experienced the greatest extinction of life. No dinosaurs lived in the Paleozoic Period, instead animals went through a number of evolutionary changes leading to dinosaurs in the Mesozoic Period.
Paleozoic Era – Periods
Trilobites thrived during the Cambrian Period.
The Paleozoic Era lasted about 300 million years, and ran from about 542 to 251 million years ago. It started with the Cambrian Period, and ended with the Permian Period. It included four other geological periods. In chronological order, they are Ordovician, Silurian, Devonian and Carboniferous. Thirty-five animal phyla came into existence during the Cambrian explosion of life. On the other hand, 90 to 95 percent of plants, and 70 percent of animals became extinct during the Permian Period.
Animals with a Back Bone – Vertebrates
The evolution from amorphous living blobs to animals with internal skeletons occurred during the Cambrian Period.
During the Cambrian Period animals developed vertebrae or back bones. Fish appeared on the evolutionary scene. The first ones may have had cartilage instead of bone; their bodies were covered with armor plates, and they had a vertebrae. This was an important step in the evolution of higher organisms, including dinosaurs.
Devonian Period – Vertebrates Move to Land
Amphibians began the movement of vertebrates to land during the Devonian Period.
The Devonian Period occurred between 416 and 359 million years ago. During this period vertebrates moved onto land as amphibians. They could breath air, but still needed water environments to survive. In the meantime, land-based plants continued to adapt, and the amount of oxygen in the atmosphere began to increase. In addition to plants and amphibians, wingless insects and spiders inhabited land.
Reptiles appeared during the Carboniferous Period.
Abundant plant life characterized the Carboniferous Period. The plant life from this period provided the material that eventually became the coal beds of today. Also during the Carboniferous, insects developed the ability to fly, an important evolutionary development. In regards to dinosaurs, during this period the first reptiles inhabited the Earth.
Permian Period – Archosaurs
During the Permian Period, reptiles adapted to living in a dryer, warmer climate.
The Permian Period ended about 251 million years ago. During this period the climate changed, temperatures increased and rainfall decreased. Swampland turned into coniferous forests. The Earth experienced its greatest mass extinction. The die off of plants and animals made room for the evolution of new life forms. Reptiles evolved into several new branches including archosaurs, dinosaur ancestors.
Mesozoic Era – The First Dinosaurs
The earliest dinosaurs evolved about 230 million years ago during the early Mesozoic Era.
Dinosaurs first appeared during the Triassic Period of the Mesozoic Era about 230 million years ago. The oldest fossil records of dinosaurs come from South America. Eoraptor evolved about 230 million years ago. Initially, scientists considered Eoraptor a predator, but according to Scientific American magazine, paleontologists are considering reclassifying it as an herbivore. Another early dinosaur, Herrerasaurus also evolved during the Triassic Period. Although these are the earliest known dinosaur fossils, it does not mean older ones will not be found.