Crocodylia

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Crocodylia Anatomy

  • largest living reptiles
  • form similar among all crocodylomorphs
  • diapsid skull with robust secondary palate
    • allows eating and breathing at the same time
    • have thecodont, polyphyodont teeth
  • have three eyelids, with the third being referred to as the nictating membrane
    • cleans the eye on land, and protect the eye whilst underwater
  • osteoderms covered in thick keratinous skin provide armour to the neck, trunk, and tail
  • crocodilian hearts possess four-chambers
    • completely divided ventricle with two pumping chambers 
    • lung circulation and body circulation are separated
    • foramen of panizza allows the mixing of blood from outside the ventricles
    • allows for enhanced oxygen transport whilst underwater
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Crocodylia Reproduction

  • all crocodilians are oviparous, with clutches averaged between 12 and 48 eggs
    • clutch size increases with female size both between species and within species
  • all crocodilians use internal fertilisation
  • all crocodilians use temperature-based sex determination
    • two types used in Crocodylia: type 1b and type 2
  • eggs deposited either in mounds, on floating vegetation in shallow water, or in burrows
  • all crocodilians display parental care, but the level varies
    • common trait among archosaurs
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Crocodylia Lifespan

  • can live long periods (up to 120 years), but do stop growing
  • lose their power in old age like other animals, so not immortal as some reports claim 
    • can repair parts of their body, e.g., their tail
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Ecology & Behaviour of Crocodylia

  • predators that ambush prey in shallow waters or at waterside
  • semiaquatic and spend much of their life in the water, but do spend time out of the water
    • regularly bask on the shoreline
    • construct territorial nests for incubation of eggs 
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Crocodylia Diversity

  • GAVIALIDAE: a family containing the Indian gharial and the false/Malayan gharial
    • contains two species in two genera
    • genera split 20 million years ago
  • CROCODYLIDAEa family of crocodilians in which the fourth tooth of the lower jaw fits into a notch in the upper jaw, being visible when the mouth is closed
    • CROCODYLINAE: subfamily of true crocodiles, containing all species except the dwarf and slender-snouted crocodiles 
    • OSTEOLAEMINAE: subfamily of true crocodiles, containing the dwarf and slender-snouted crocodiles 
  • ALLIGATORIDAEfamily of crocodilians that have a broad, flat snout in which the fourth tooth of the lower jaw fits into a pit in the upper jaw and cannot be seen when the mouth is closed
    • ALLIGATORINAEsubfamily of Alligatoridae which contains the alligators and their closest extinct relatives, consisting of one genus (Alligator)
    • CAIMANINAE: subfamily of Alligatoridae which contains the caimans and their closest extinct relatives,consisting of three genera
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Crocodylia Conservation

  • status reports show that crocodilians are in serious decline globally
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