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.
Cambrian Period. The Cambrian Period is the first period of the Paleozoic Era spanning from approximately 540 to 500 million years ago. It was named in 1835 by the geologist Adam Sedqwick, after the region of Cambria in Southern Wales and England, where rocks of this age were first found.ambrian Period. The Cambrian Period is the first period of the Paleozoic Era spanning from approximately 540 to 500 million years ago. It was named in 1835 by the geologist Adam Sedqwick, after the region of Cambria in Southern Wales and England, where rocks of this age were first found.