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.
Earthâs History 371 Early Paleozoic Life Life in early Paleozoic time wasrestricted to the seas. Ve rtebrates had not yet evolved,so life consistedof several invertebrate groups. The Cambrian period was the goldenage of trilobites. More than 600 types of these mud-burrowing scav-engers flourished worldwide.arly Paleozoic History During the Cambrian,Ordovician,and Silurian periods,the vast southern continent of Gondwana encom-passed ï¬ve continents (South America, Africa, Australia, Antarctica,India, and perhaps China). North America and several other landmasses were not part ofGondwana.