15+16

• Tiktaalik


  A significant transitional form, often referred to as a "fishapod," which exhibits both fish and tetrapod characteristics
• Seymouria


  A diadectomorph, an extinct group of reptile-like amphibians, which are important for understanding the evolution of terrestrial adaptations
• Branches leading to


  • Lepospondyli (an extinct subclass of primitive tetrapods)
  • Amniota (the group that includes all modern mammals, reptiles, and birds)
• Amniota


  Characterized by their ability to lay eggs on land or retain the fertilized egg within the mother
• Groups leading towards amniotes

  • Anthracosauria
  • Lissamphibians (the group that encompasses modern amphibians like frogs, toads, salamanders, and caecilians)
• The timeline at the bottom indicates geological periods from the Devonian to the Cenozoic, showing when these groups emerged
• Synapsida


  Leading to mammals
• Diapsida


  Leading to reptiles, including dinosaurs, and birds
• Synapsids


  • Have a single temporal opening in the skull
• Diapsids


  • Have two temporal openings in the skull
• Reptilian groups


  • Lepidosaurs (including squamates like snakes and lizards)
  • Testudines (turtles)
  • Archosaurs (including crocodiles and birds)
• Turtles have lost skull openings, and birds have unique skull characteristics
• Amniotes evolved features like the shedding of skin in one piece and the presence of extraembryonic membranes such as the amnion, which are crucial for terrestrial reproduction
• Amniotic egg


  A key adaptation that enabled amniotes to become fully terrestrial, containing four membranes (the amnion, chorion, allantois, and yolk sac) that protect and nourish the embryo on land
• Water-resistant skin


  • Amniotes evolved keratinized skin, which is less permeable to water and helps prevent desiccation in a terrestrial environment
• Claws


  • The presence of keratin extends to the development of claws, which aid in defense, movement, and various behaviors
• Enhanced neck mobility


  • Evolution of a more mobile neck, often through the development of specialized cervical vertebrae such as the atlas and axis, allowed greater head movement and enhanced interaction with the environment
• Limb articulation


  • Improved articulation of the limbs, particularly the hip and shoulder joints, allowed for better support and movement on land
• Efficient kidneys


  • The evolution of metanephric kidneys in amniotes allows for more efficient water conservation and waste filtration
• Efficient respiratory system


  • Amniotes typically have more efficient lungs compared to their aquatic ancestors, allowing for better gas exchange in air
• Amnion


  A fluid-filled cavity that cushions the embryo
• Chorion


  Facilitates gas exchange
• Allantois


  Deals with waste and also participates in gas exchange
• Yolk sac


  Provides nourishment from the stored yolk
• Amniotic egg shell


  • Can be either hard, like in birds and some reptiles, or leathery, as seen in many reptiles
• Atlas and axis vertebrae

  • Provide a range of motion for the skull, which is critical for predation, feeding, and sensory perception in many amniotes
• Additional skeletal adaptations of amniotes for life on land

  • Highly ossified skeleton
  • Dermal elements (e.g. turtle shells)
  • Secondary palate
  • Modifications to ribs and sacral vertebrae
  • Skull fenestrae
• Anapsid skulls


  Have no temporal openings, making the skull more rigid and protective but limiting jaw muscle size
• Diapsid skulls


  Have two sets of temporal openings, allowing for larger jaw muscles and a more powerful bite
• Synapsid skulls


  Have one lower temporal opening per side, allowing for strong jaw muscles, ancestral to mammals
• Reptilian kidneys


  • Are metanephric, an advanced form that is efficient at concentrating urine to preserve water
  • Excrete uric acid, which is less toxic and can be excreted as a semi-solid paste, requiring less water than urea
• Reptilian cloaca and urinary bladder


  • Allow for storage and reabsorption of water from uric acid wastes
• Reptilian respiratory system


  • Has rigid, cartilaginous rings supporting the trachea
  • Most reptiles lack a diaphragm, using rib and body wall movement to create negative pressure for breathing
  • Crocodilians and mammals have a diaphragm for more efficient breathing
• Reptilian lungs have a larger surface area of alveoli for more efficient gas exchange
• Sphenodontia (tuatara)


  A unique reptile species
• Tuatara


  • Akinetic skull - skull bones are fused, little to no movement between them
  • Acrodont teeth - not set in sockets, fused to top of jaw bones, do not replace throughout life
  • Parietal eye - photosensitive 'third eye' involved in regulating circadian rhythms and hormone production
• Tuataras are a relict group, survivors of a once diverse assemblage of reptiles from the Mesozoic era
• Tuataras are limited to two species, found only in New Zealand, which indicates a significant contraction in their diversity and distribution over time
• Reptile Diversity - Sphenodontia (tuatara)


  • Formerly diverse lineage throughout Mesozoic
  • Akinetic skull
  • Acrodont teeth (rootless)
  • Parietal eye
  • Two species restricted to isolated New Zealand islands
• Tuatara


  • Akinetic skull (skull bones fused, little to no movement)
  • Acrodont teeth (not set in sockets, fused to jaw bones, do not replace)
  • Parietal eye (photosensitive 'third eye')