Testudines

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Turtle Anatomy

  • solid and inflexible skeleton, with bones growing in concert with the scutes
    • carapace: the hard upper shell of a tortoise
    • plastron: the underside part of a tortoise's or turtle's shell
  • heart is essentially the same as that of squamates
  • some testudines use cloacal respiration
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Turtle Reproduction

  • all testudines are oviparous, with clutched numbering 1 to >100 eggs
  • use internal fertilisation
  • testudines display multiples modes of sex determination:
    • genetics sex determination, with both sexes known to be heterogametic
    • temperature sex determination (type 1a and type 2)
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Turtle Diet and Mycophagy

  • mycophagy: fungus-feeding, which is common in mammals but also seen in testudines
    • the movement of Madagascan tortoises suggests that fungi play an important role in their diet
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Testudine Diversity - Introduction

  • 351 species in 14 families 
  • primary divergence occurred around 205 million years ago
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Testudine Diversity - Pleurodira

  • Pleurodira: the side-necked turtles, a suborder of turtles which withdraw the head into the shell by bending the neck sideways
  • contains three extant families:
    • Chelidae: the snake-necked turtles, also known as the Austro-American side-necked turtles
    • Pelomedusidaethe African side-necked turtles
    • Podocnemidaethe Madagascan and South American river turtles
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Testudine Diversity - Cryptodira

  • CRYPTODIRA: the hidden-necked turtles 
  • contains 11 extant families, with 75 genera and around 250 species
    • Dermochelyidae:  a monospecific family comprising the largest marine turtle, the leatherback (Dermochelys coriacea)
    • Cheloniidae: the marine turtles, containing 6 species with cosmopolitan distribution in warm seas
    • Emydidae: the box turtle and terrapins, a family of turtles that bask on land and enter slow-moving water to feed
    • Geoemydidae: the pond turtles, terrapins, and sliders 
    • Platystenidae: the big-headed turtle, a monospecific family (Platysternon megacephalum)
    • Testudinidae: the tortoises
    • Dermatemydidae: a monospecific family containing only the tabasco turtle (Dermatemys mawi)
    • Kinsternidaemud and musk turtles
    • Chelydridaethe snapping turtles
    • Carettochelyidaethe pig-nosed turtle, a monospecific family (Carettochelys insculpta) 
    • Trionychidaethe softshell turtles
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Testudine Migration and Magnetic Sense

  • sea turtles use different navigate methods depending on where they are
    • when on the beach they use visual cues to get the sea (e.g., moonlight)
    • when in the wave refraction zone the hatchlings will use wave orientation to go into the open ocean
    •  when in the open ocean they use magnetic orientation
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Testudine Threats and Conservation

  • approximately 61% of turtle species are threatened or have become extinct in modern times
  • threatened by habitat destruction, unsustainable exploitation for food and the commercial pet trade, and climate change
    • leatherback sea turtles are often attacked when they come onto land to lay their eggs
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