Enterobacter is a genus of common Gram-negative, facultatively anaerobic, rod-shaped, non-spore-forming bacteria of the family Enterobacteriaceae.nterobacter is a genus of common Gram-negative, facultatively anaerobic, rod-shaped, non-spore-forming bacteria of the family Enterobacteriaceae.
Trilobite fossil from the Cambrian Period. Photo Credit: Archbob. The first period in the Paleozoic Era is known as the Cambrian Period. Many of the ancestors of the species that have evolved into what we know today first came into existence during the Cambrian Explosion in the early Cambrian Period.
The Silurian period (443-416 million years ago) was the shortest period of the Paleozoic Era. This is when the very first terrestrial plants and invertebrates (i.e., bugs) appeared, while the most important development in vertebrate life was the evolution of jawed fish.he Silurian period (443-416 million years ago) was the shortest period of the Paleozoic Era. This is when the very first terrestrial plants and invertebrates (i.e., bugs) appeared, while the most important development in vertebrate life was the evolution of jawed fish.