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For instance, the conodont Eoplacognathus pseudoplanus has a short range in the Middle Ordovician period. [62] If rocks of unknown age have traces of E. pseudoplanus, they have a mid-Ordovician age. Such index fossils must be distinctive, be globally distributed and occupy a short time range to be useful.
Fossils of organisms' bodies are usually the most informative type of evidence. The most common types are wood, bones, and shells. [59] Fossilisation is a rare event, and most fossils are destroyed by erosion or metamorphism before they can be observed. Hence the fossil record is very incomplete, increasingly so further back in time.
Pyrite disks or spindles are sometimes mistaken for fossils of sand dollars or other forms (see marcasite). Cracks, bumps, gas bubbles, and such can be difficult to distinguish from true fossils. Specimens that cannot be attributed with certainty to either fossils or pseudofossils are treated as dubiofossils. Debates on whether specific forms ...
This includes groups that are significant in paleontological contexts, abundant in the fossil record, or have a high proportion of extinct species. Special notations are explained below: [ ! ]: Indicates clades that are important as fossils or abundant in the fossil record. [ – ]: Indicates clades that contain a large proportion of extinct ...
Abatocrinus † Abatocrinus grandis † Acanthocrania † Acantholaminatus † Acantholaminatus multistylus † Acantholaminatus typicus † Acodus † Actinoceras † Actinoceras capitolinum † Actinoceras cuvieri † Actinoceras tenuifilum † Actinocrinites † Adinocrinus † Agaricocrinus Fossilized calyx of the Carboniferous crinoid ("sea lily") Agaricocrinus americanus, or the mushroom ...
Fossil orthoconic nautiloid from the Ordovician of Kentucky; an internal mold showing siphuncle and half-filled camerae, both encrusted. Understanding of early cephalopod origins is by necessity biased by the available fossil material, which on the whole consists of shelly fossils.
Planolites is an ichnogenus found throughout the Ediacaran and the Phanerozoic that is made during the feeding process of worm-like animals.The traces are generally small, 1–5 mm (0.039–0.197 in), unlined, and rarely branched, with fill that differs from the host rock.
tr This is a list of stratigraphic units from which dinosaur body fossils have been recovered. Although Dinosauria is a clade which includes modern birds, this article covers only Mesozoic stratigraphic units. Units listed are all either formation rank or higher (e.g. group).