a b Gu, H.; Kirsch, M.; Zinßmeister, C.; Söhner, S.; Meier, K.J.S.; Liu, T.; Gottschling, M. (2013). "Waking the dead: Morphological and molecular characterization of extant † Posoniella tricarinelloides (Thoracosphaeraceae, Dinophyceae)". Protist. 164 (5): 583–597. doi: 10.1016/j.protis.2013.06.001. PMID 23850812. Mayr, Gerald, and Vanesa L. De Pietri. " Earliest And First Northern Hemispheric Hoatzin Fossils Substantiate Old World Origin Of A ‘Neotropic Endemic’". Naturwissenschaften, vol 101, no. 2, 2014, pp. 143-148. Springer Science And Business Media LLC, doi:10.1007/s00114-014-1144-8

Any of the first three definitions, but the clade also has a low taxonomic diversity (low diversity lineages). [ citation needed]Kin, Adrian; Błażejowski, Błażej (2014-10-02). "The Horseshoe Crab of the Genus Limulus: Living Fossil or Stabilomorph?". PLOS ONE. 9 (10): e108036. Bibcode: 2014PLoSO...9j8036K. doi: 10.1371/journal.pone.0108036. ISSN 1932-6203. PMC 4183490. PMID 25275563. Discocone – Intermediate between oxycones and spherocones: involute and moderately broad. The modern Nautilus is an example of a discocone cephalopod. Doguzhaeva, Larisa A.; Royal H. Mapes; Herbert Summesberger; Harry Mutvei (2007). "The Preservation of Body Tissues, Shell, and Mandibles in the Ceratitid Ammonoid Austrotrachyceras (Late Triassic), Austria". In N. H. Landman; etal. (eds.). Cephalopods Present and Past: New Insights and Fresh Perspectives. Dordrecht: Springer. pp. 221–238. doi: 10.1007/978-1-4020-6806-5_11. ISBN 978-1-4020-6806-5. Others believed ammonites, which they referred to as "salagrana" were composed of fossilized worm dung, and could be used to ward off witches. [35]

a b Herrera-Flores, Jorge A.; Stubbs, Thomas L.; Benton, Michael J. (2017). "Macroevolutionary patterns in Rhynchocephalia: is the tuatara (Sphenodon punctatus) a living fossil?". Palaeontology. 60 (3): 319–328. doi: 10.1111/pala.12284. Some genera of ammonites had shells that were coiled in more bizarre ways than the usual spiral. These are known as heteromorphs, from the Greek heteros meaning ‘different’ and morphe meaning ‘form or shape’. Creationists seize upon the phrase in its most rigid form, pointing to species that have apparently not evolved for a great deal of time as evidence that evolution does not exist. This, of course, is where the very literal definition of a living fossil gets us into trouble—no species alive today has followed a flat line of evolution since it first appeared however many millions of years ago. Not even the famed coelacanth is the same now as it was when it arrived in the fossil record 410 million years ago.But by applying a standard technique for dating commercial fish, French scientists calculated they actually live close to a century, according to a study in the journal Current Biology released on Thursday.

The plates are collectively termed the aptychus or aptychi in the case of a pair of plates, and anaptychus in the case of a single plate. The paired aptychi were symmetric to one another and equal in size and appearance. See also: List of ammonite genera An ammonite shell viewed in section, revealing the internal chambers and septa. Large polished examples are prized for both their aesthetic and scientific value. However, it is estimated that over 10,000 species of ammonite - possibly even over 20,000- have been discovered. Oxycone – Strongly involute and very narrow, with sharp ventral keels and a streamlined, lenticular ( lens-shaped) cross-section. These ammonoids are estimated to be nektonic (well-adapted to rapid active swimming), as their shell form incurs very little drag and allows for efficient, stable coasting even in turbulent flow regimes. [10]Permineralization is a process of fossilization that occurs when an organism is buried. The empty spaces within an organism (spaces filled with liquid or gas during life) become filled with mineral-rich groundwater. Minerals precipitate from the groundwater, occupying the empty spaces. This process can occur in very small spaces, such as within the cell wall of a plant cell. Small scale permineralization can produce very detailed fossils. [13] For permineralization to occur, the organism must become covered by sediment soon after death, otherwise the remains are destroyed by scavengers or decomposition. [14] The degree to which the remains are decayed when covered determines the later details of the fossil. Some fossils consist only of skeletal remains or teeth; other fossils contain traces of skin, feathers or even soft tissues. [15] This is a form of diagenesis.