This period started about 419 million years ago and ended 358.9 million years ago. Marine faunas continued to be dominated by bryozoa, diverse and abundant brachiopods, the enigmatic hederellids, microconchids and corals. [41], By the Devonian Period, life was well underway in its colonization of the land. The southern continents of today were united into the supercontinent of Gondwana during the Devonian approximately along the lines of their present-day continental shelf boundaries. The placoderms began dominating almost every known aquatic environment. The close of the Devonian Period is considered to be the second of the "big five" mass extinction events of Earth's history. The rocks corresponding to those epochs are referred to as belonging to the Lower, Middle and Upper parts of the Devonian System. (Image credit: Zina Deretsky, National Science Foundation), Precambrian: Facts About the Beginning of Time, Silurian Period: Climate, Animals & Plants, 30 of the world's most valuable treasures that are still missing, Painful 'cross-shaped incision' in medieval woman's skull didn't kill her, but second surgery did, Human brain looks years 'older' after just one night without sleep, small study shows. These include Chilenia, Cuyania, and Chaitenia, which now form much of Chile and Patagonia. Most trilobite groups, bivalves, and echinoderms were still present. [62][63][64][65] Canadian paleontologist Digby McLaren suggested in 1969 that the Devonian extinction events were caused by an asteroid impact. Oceanic conditions and biological richness resulted in the greatest production of carbonate during the Paleozoic Era. Lily-like crinoids (animals, their resemblance to flowers notwithstanding) were abundant, and trilobites were still fairly common. Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. The Devonian* saw the peak of marine faunal diversity during the Paleozoic Era. By the end of the Devonian, progymnosperms such as Archaeopteris were the first successful trees. The geological history of North America comprises the history of geological occurrences and emergence of life in North America during the interval of time spanning from the formation of the Earth through to the emergence of humanity and the start of prehistory. Corrections? [27][28][32], Sea levels in the Devonian were generally high. Of these, Siberia and Kazakhstania began fusing during the late Devonian and later joined Laurussia, forming the Ural Mountains along the junction. The Euramerican and Gondwana plates began their collision that would lead to the eventual formation of Pangea. The most important group to be affected by this extinction event were the reef-builders of the great Devonian reef systems.[59]. Sponges (ToL: Porifera