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.
Animal Life. The beginning of the Paleozoic era is marked by a sudden explosion of invertebrate animals, over 900 recorded species in the Cambrian period. It was only a few million years later that vertebrates appeared during the Ordovician period. The Devonian period showed an uprising in fish and other marine life. By the end of the Paleozoic era evolution had caused complex land and marine animals to exist.