in the Earth's oceans. Gastropods with protective shells are referred to as snails, whereas gastropods without protective shells are referred to as slugs. "A critical reappraisal of the fossil record of the bilaterian phyla". 242 Bony edit Main article: Bony fish Bony fish have jaws and skeletons made of bone rather than cartilage. 70 Microscopic life undersea is incredibly diverse and still poorly understood. "Bi-directional conversion in Turritopsis nutricula (Hydrozoa. The earliest undisputed evidence of life on Earth dates from at least.5 billion years ago, 20 21 during the Eoarchean Era after a geological crust started to solidify following the earlier molten Hadean Eon. You can provide for each group an A3 sheet of paper and glue sticks to create a group poster. There is still debate about the classification of these specimens, mainly because the diagnostic features which allow taxonomists to classify more recent organisms, such as similarities to living organisms, are generally absent in the Ediacarans. Marine molluscs edit Reconstruction of an ammonite, a highly successful early cephalopod that first appeared in the Devonian (about 400 mya ). 89 On, scientists confirmed the existence of microorganisms living 800 m (2,600 ft;.50 mi) below the ice of Antarctica. 165 In the 1970s there was already a debate about whether the emergence of the modern phyla was "explosive" or gradual but hidden by the shortage of Precambrian animal fossils.
Evidence for the appearance of the first land plants occurs in the Ordovician, around 450 million years ago, in the form of fossil spores. "Exponential decline of deep-sea ecosystem functioning linked to benthic biodiversity loss". 154 Their taxonomic affinities are presently unknown, but their mode of growth is consistent with a bilaterian affinity. Biological oceanography mostly focuses on the microorganisms within the ocean; looking at how they are affected by their environment and how that affects larger marine creatures and their ecosystem. Fossils of cnidarians that do not build mineralized structures are rare. Archived from the original on Retrieved 10 March 1 maint: Archived copy as title ( link ) Braddy, Simon.; Poschmann, Markus; Tetlie,. Kaupia - Darmstädter Beiträge zur Naturgeschichte, 2 : 77-97. "The phylogenetic definition of Reptilia". (1985 The Mollusca,. Martin, Mark.; Grazhdankin, Dmitriy.; Bowring, Samuel.;. Paleontology and neontology of Cephalopods, New York: Academic Press, isbn Black, Richard. He used this to argue that what was at the time dry land was once under the sea.