Animal Physiology & Morphology Codexery

Exoskeleton

Exoskeletons are external skeletons providing support and protection.

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An exoskeleton is a hardened external skeleton that supports an animal's body and protects its internal organs, unlike an internal endoskeleton.[1] These structures serve roles in protection, respiration, excretion, sensation, feeding, courtship display, and as an osmotic barrier against desiccation.[2] Calcified exoskeletons have arisen on 18 separate evolutionary occasions.[3]

Quick Facts

Examples
  • Arthropods
  • tardigrades
  • stony corals
  • molluscs
Materials
  • Chitin
  • calcium carbonate
  • silica
  • iron sulfides
Functions
  • Protection
  • structural support
  • muscle attachment
  • osmotic barrier
  • defense against predators and parasites
Growth mechanism
Moulting (ecdysis) in panarthropods; aperture addition in molluscs

Facts from the source article.

Key facts and history

Since exoskeletons are rigid, they limit growth, and true exoskeletons must be shed via moulting when outgrown.[4] Chitin is a component of arthropod exoskeletons; when calcium carbonate is added, the exoskeleton becomes both more rigid and more massive.[5] Apodemes, which are chitinous ingrowths of the arthropod exoskeleton, provide locations for muscle attachment.[5][6] Vertebrate tendons are surpassed in strength by apodemes by a factor of about six, and in stiffness by a factor of two.[6]

Elastic energy can be stored in apodemes for jumping, as seen in locusts, analogous to the function of tendons.[6] Before the old exoskeleton is shed, a new, soft, and flexible one forms underneath it.[4] During moulting, an animal often remains in a den or burrow because it is highly susceptible to injury.[7] One proposed trigger for the Cambrian explosion of animal life is the development of mineralized exoskeletons.[8]

What the research sources say

Statements that exoskeletons help preserve fossils and that relying on them limits evolutionary understanding are supported by the Geological Society publication.[10][11][9]

References

  1. Wikipedia, "Exoskeleton" (CC BY-SA 4.0), which cites: .; .; "Archived copy" (original not read by us) en.wikipedia.org
  2. Wikipedia, "Exoskeleton" (CC BY-SA 4.0), which cites: S. Bengtson, "Early skeletal fossils", Paleontological Society Papers, 2004, p. 67–78 (original not read by us) en.wikipedia.org
  3. Wikipedia, "Exoskeleton" (CC BY-SA 4.0), which cites: Susannah M. Porter, "Seawater chemistry and early carbonate biomineralization", Science, 2007, p. 1302 (original not read by us) en.wikipedia.org
  4. Wikipedia, "Exoskeleton" (CC BY-SA 4.0), which cites: John Ewer, "How the Ecdysozoan Changed Its Coat", PLOS Biology, 2005-10-11 (original not read by us) en.wikipedia.org
  5. Wikipedia, "Exoskeleton" (CC BY-SA 4.0), which cites: Nedin, C., "Anomalocaris predation on nonmineralized and mineralized trilobites", Geology, 1999, p. 987–990 (original not read by us) en.wikipedia.org
  6. Wikipedia, "Exoskeleton" (CC BY-SA 4.0), which cites: H. C. Bennet-Clark, "The energetics of the jump of the locust, Schistocerca gregaria", Journal of Experimental Biology, 1975, p. 53–83 (original not read by us) en.wikipedia.org
  7. Wikipedia, "Exoskeleton" (CC BY-SA 4.0), which cites: Hariharan, "Indeterminate Growth: Could It Represent the Ancestral Condition?", Cold Spring Harbor Perspectives in Biology, 2016 (original not read by us) en.wikipedia.org
  8. Wikipedia, "Exoskeleton" (CC BY-SA 4.0), which cites: "The Rise and Fall of the Ediacaran Biota", Geological Society, 2007, p. 157–179; "Borings in Cloudina shells: complex predator-prey dynamics in the terminal Neoproterozoic", PALAIOS, 2003, p. 454–459; "Borings in Cloudina shells: complex predator-prey dynamics in the terminal Neoproterozoic", PALAIOS, 2003, p. 454–459 (original not read by us) en.wikipedia.org
  9. Open Library record, ISBN 9781862392335 ("The rise and fall of the Ediacaran biota"). CC0 (metadata); book content not read. openlibrary.org
  10. Wikipedia, "Exoskeleton" (CC BY-SA 4.0), which cites: "The Rise and Fall of the Ediacaran Biota", Geological Society, 2007, p. 157–179; Nicholas J. Butterfield, "Exceptional fossil preservation and the Cambrian Explosion", Integrative and Comparative Biology, 2003, p. 166–177 (original not read by us) en.wikipedia.org
  11. Wikipedia, "Exoskeleton" (CC BY-SA 4.0), which cites: "The Rise and Fall of the Ediacaran Biota", Geological Society, 2007, p. 157–179; Richard Cowen, "History of Life", Wiley-Blackwell, 2004 (we also read that source) en.wikipedia.org

Each numbered sentence above was checked against the source it cites before publication. Sentences citing Wikipedia adapt text from the English Wikipedia article Exoskeleton (contributors), used under CC BY-SA 4.0; this entry is available under the same licence. Other sources were used for facts only; no text or images are copied from them.

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Sources

Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.

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