Reptiles

• Nonavian reptiles


  Reptiles that are not birds
• Nonavian reptiles


  • Include lizards, snakes, turtles
  • Occupy a great variety of terrestrial habitats such as deserts
  • First truly terrestrial vertebrates
• First reptiles appeared, 50 MY after the appearance of the first amphibians


  310 MY ago

  
• Cleidoic egg


  Self-contained egg capable of storing water, allowed the evolution of reptiles, birds & mammals
• By 225 (end of Permian) most amphibians of the time had become extinct
• Reptiles began diversifying onto land at the time of variable climate tending to get drier and diversification of plants including flowering plants creating numerous habitats
• Amniote


  Vertebrate that lays cleidoic eggs
• Largest living reptiles


  • Komodo dragon
  • Australian saltwater crocodile
  • Leatherback sea turtle

  
• Largest reptile ever


  • Diplodocus hallorum, a giant sauropod

  
• Smallest living reptiles


  • Caribbean gecko
  • Thread snake
  • Brookesia nana

  
• Reptile skin


  • Consists of epidermis and dermis
  • Epidermis much thicker than amphibians
  • Contains lipids and waxy keratin
  • Scales in the epidermis, not the dermis
• Scutes


  Modified scales of turtles

  
• Structures made completely of keratin are often referred to as "horny"
• Reptile scales are homologous to feathers and fur of birds and mammals
• Reptile skin


  • Outer layer of epidermis is shed periodically
  • Dermal plates (equivalent to fish scales) under their scales producing large rigid scales
• Chromatophores


  Structures in the thick dermis that allow reptiles to change color
• Reptile skeleton and support

  • Fewer skull bones
  • Nasal cavity separated from mouth by a shelf of bone (palate)
  • Limbs stronger, more flexible & closer to body; toes with claws

  
• Reptile movement


  • More powerful muscles than amphibians
  • Millions of adhesive fibers on the feet of geckos allow them to climb walls and hang from ceilings
  • Some reptiles can glide or burrow into mud
  • Most reptiles swim with ease
  • Some use their scales to grip the ground and move forward with rib muscles
• Basilisk lizards can run on water
• Reptile feeding and digestion

  • Most are carnivores with jaws efficient for crushing and gripping prey
  • Tongue is muscular and mobile, used to help catch prey
  • Most have teeth, some have modified salivary/venom glands as poison glands
• Protrusibile


  Able to be thrust out or extended
• Scientists propose that birds should be grouped with reptiles because they evolved from the archosaur branch of the reptilian lineage

  
• The synapsid branch of the amniote lineage evolved into mammals