Stereom: Difference between revisions

{{biomineralization sidebar|exoskeletons}}

'''Stereom''' is a [[calcium carbonate]] material that makes up the internal skeletons found in all [[echinoderm]]s, both living and fossilized forms. It is a sponge-like porous structure which, in a sea urchin may be 50% by volume living cells, and the rest being a matrix of [[calcite]] crystals. The size of openings in stereom varies in different species and in different places within the same organism.<ref name=Baeuerlein2007/> When an echinoderm becomes a [[fossil]], microscopic examinationisused to reveal the structure and such examination is often an important tool to classify the fossil as an echinoderm or related creature.<ref name=Taylor2007/>

==Evolution==

Stereom was the first form of biomineralization to evolve in deuterostomes, predating the evolution of spicules in tunicates and [[bone]] in vertebrates.<ref name=Kouchinsky2011/> Stereom likely evolved before other distinctive traits of echinoderms, such as [[radial symmetry]], as it is present in basal echinoderms with bilaterally symmetric or asymmetric body plans.<ref name=Zamora2012/> Stereom may have evolved alongside a transition in [[ocean chemistry]] from an [[aragonite sea]] to a [[calcite sea]], which occurred late in [[Cambrian Stage 2]].<ref name=Zamora2015/><ref name=Kouchinsky2011/>

In the largely falsified<ref name=Lefebvre2019/> [[calcichordate hypothesis]], stereom was believed to have been present in the common ancestor of echinoderms and [[vertebrates]]. However, the [[genes]] which code for stereom are unique to echinoderms, indicating that it is likely that stereom is a [[synapomorphy]] of echinoderms, and that all stereom-bearing fossil taxa belong to the echinoderm [[total group]].<ref name=Bottjer2006/><ref name=Rahman2009/>

{{Reflist|refs=

<ref name=Baeuerlein2007>Edmund Bäeuerlein, ''Handbook of Biomineralization: . Biomimetic and bioinspired chemistry'', Wiley-VCH, 2007 {{ISBN|3-527-31805-4}}, page 393</ref>

<ref name=Bottjer2006>{{Cite journal| doi = 10.1126/science.1132310 | volume = 314| issue = 5801| pages = 956–960| last1 = Bottjer| first1 = D. J.| last2 = Davidson| first2 = E. H.| last3 = Peterson| first3 = K. J.| last4 = Cameron| first4 = R. A.| title = Paleogenomics of Echinoderms| journal = Science| date = 2006-11-10| pmid = 17095693| bibcode = 2006Sci...314..956B| doi-access = | s2cid = 12789370}}</ref>

<ref name=Kouchinsky2011>{{Cite journal| doi = 10.1017/S0016756811000720| volume = 149| issue = 2| pages = 221–251| last1 = Kouchinsky| first1 = Artem| last2 = Bengtson| first2 = Stefan| last3 = Runnegar| first3 = Bruce| last4 = Skovsted| first4 = Christian| last5 = Steiner| first5 = Michael| last6 = Vendrasco| first6 = Michael| title = Chronology of early Cambrian biomineralization| journal = Geological Magazine| date = 2011| doi-access = free}}</ref>

<ref name=Lefebvre2019>{{Cite journal| doi = 10.1016/j.geobios.2018.11.001| issn = 0016-6995| volume = 52| pages = 27–36| last1 = Lefebvre| first1 = Bertrand| last2 = Guensburg| first2 = Thomas E.| last3 = Martin| first3 = Emmanuel L.O.| last4 = Mooi| first4 = Rich| last5 = Nardin| first5 = Elise| last6 = Nohejlová| first6 = Martina| last7 = Saleh| first7 = Farid| last8 = Kouraïss| first8 = Khaoula| last9 = El Hariri| first9 = Khadija| last10 = David| first10 = Bruno| title = Exceptionally preserved soft parts in fossils from the Lower Ordovician of Morocco clarify stylophoran affinities within basal deuterostomes| journal = Geobios| date = 2019 | doi-access = free| bibcode = 2019Geobi..52...27L}}</ref>

<ref name=Rahman2009>{{Cite journal| doi = 10.1111/j.1365-2451.2009.00703.x| volume = 25| issue = 1| pages = 34–38| last = Rahman| first = Imran A.| title = Making sense of carpoids| journal = Geology Today| date = 2009| bibcode = 2009GeolT..25...34R| s2cid = 129493134}}</ref>

<ref name=Taylor2007>Paul D. Taylor, David N. Lewis ''Fossil Invertebrates'' Harvard University Press, 2007 {{ISBN|0-674-02574-1}} pages 163-164</ref>

<ref name=Zamora2012>{{Cite journal| doi = 10.1371/journal.pone.0038296| issn = 1932-6203| volume = 7| issue = 6| pages = –38296| last1 = Zamora| first1 = Samuel| last2 = Rahman| first2 = Imran A.| last3 = Smith| first3 = Andrew B.| others = Keith A. Crandall (ed.)| title = Plated Cambrian bilaterians reveal the earliest stages of echinoderm evolution| journal = PLOS ONE| date = 2012-06-06| pmid = 22701623| pmc = 3368939| bibcode = 2012PLoSO...738296Z| doi-access = free}}</ref>

<ref name=Zamora2015>{{Cite journal| doi = 10.1111/pala.12138| issn = 0031-0239| volume = 57| issue = 6| pages = 1105–1119| last1 = Zamora| first1 = Samuel| last2 = Rahman| first2 = Imran A. | title = Deciphering the early evolution of echinoderms with Cambrian fossils| journal = Palaeontology| date = 2015| url = https://research-information.bris.ac.uk/en/publications/deciphering-the-early-evolution-of-echinoderms-with-cambrian-fossils(951cc086-7ed1-469b-98ac-2cc338c4e823).html| doi-access = free| hdl = 1983/951cc086-7ed1-469b-98ac-2cc338c4e823| hdl-access = free}}</ref>

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[[Category:Calcium minerals]]

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