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Index fossils must have a short vertical range, wide geographic distribution and rapid evolutionary trends. Another term, "zone fossil", is used when the fossil has all the characters stated above except wide geographical distribution; thus, they correlate the surrounding rock to a biozone rather than a specific time period.
Oppel's zones are named after a particular distinctive fossil species, called an index fossil. Index fossils are one of the species from the assemblage of species that characterize the zone. Biostratigraphy uses zones for the most fundamental unit of measurement. The thickness and range of these zones can be a few meters, up to hundreds of meters.
Stages are primarily defined by a consistent set of fossils (biostratigraphy) or a consistent magnetic polarity (see paleomagnetism) in the rock. Usually one or more index fossils that are common, found worldwide, easily recognized, and limited to a single, or at most a few, stages are used to define the stage's bottom.
After 1.5 million years ago (extinction of Paranthropus), all fossils shown are human (genus Homo). After 11,500 years ago (11.5 ka, beginning of the Holocene), all fossils shown are Homo sapiens (anatomically modern humans), illustrating recent divergence in the formation of modern human sub-populations.
Mammoths appear in the fossil record. 4.5 Ma Marine iguanas diverge from land iguanas. 4 Ma Australopithecus evolves. Stupendemys appears in the fossil record as the largest freshwater turtle, first modern elephants, giraffes, zebras, lions, rhinoceros and gazelles appear in the fossil record 3.6 Ma Blue whales grow to modern size. 3 Ma ...
List of fossil species in the La Brea Tar Pits, California, United States; List of fossil species in the London Clay, England; List of White Sea biota species by phylum, Russia; Paleobiota of the Hell Creek Formation, northern United States; Paleobiota of the Morrison Formation, western United States
Due to their widespread abundance, planktonic lifestyle, and well-traced evolutionary trends, graptoloids in particular are useful index fossils for the Ordovician and Silurian periods. [4] The name graptolite comes from the Greek graptos meaning "written", and lithos meaning "rock", as many graptolite fossils resemble hieroglyphs written on ...
Fossilised Orthoceras orthocones.. An orthocone is the long, cone-shaped shell belonging to several species of ancient nautiloid cephalopod—the prehistoric ancestors of today's marine cephalopod mollusks, including the cuttlefishes, nautiluses, octopuses and squids. [1]