ZOO 2090 Lecture Notes - Lecture 8: Ellesmere Island, Tiktaalik, Lungfish
1 May 2018
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ZOO2090 – Early Tetrapods
Transition from water to land in a major event in vertebrate evolution
Emergent vertebrates experience extraordinary challenges to their ability of:
• Movement
• Respiration
• Sensing the environments
• Feeding, osmoregulation and reproduction
The earliest tetrapods (Late Devonian) were aquatic and many changes that were
later useful for terrestrial life were evolved primarily in the water.
Sarcoptergii (lobe finned fish)
• acinista
• dipnoi (lungfish)
• Rhipidstia
• Tetrapods
*relationships within the group are highly controversial
Possible Scenario (Clack, 2002)
• tetrapod stem lineages branches along with lung fish
• the first tetrapods (Tetrapoda) evolved in the mid-late Devonian
• Tiktaalik is a fish-like tetrapod (fossil species)
Tetrapods are vertebrates that possess a chiridium muscular limb with well
defined joints and digits
• Fore and hind limbs have similar developmental process and structure
• Humerus (Femur) – Radius – Ulna
• Digit 4 is most important (birds always retain 3 digits including #4)
Early tetrapods have characteristic teeth (Labyrinthodonts)
• Cross section of tooth displays enamel folds
Tiktaalik (extinct; first tetrapod)
• Late Devonian (375 mya) fish from Ellesmere Island displays intermediate
characteristics between fish and tetrapods
• It has limb-like pectoral fins possibly for standing support, functional wrist
joint and mobile neck allowing flexible head movement
• Loss of bony gill covering suggests increased used of lungs for respiration
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Document Summary
Transition from water to land in a major event in vertebrate evolution. Emergent vertebrates experience extraordinary challenges to their ability of: movement, respiration, sensing the environments, feeding, osmoregulation and reproduction. The earliest tetrapods (late devonian) were aquatic and many changes that were later useful for terrestrial life were evolved primarily in the water. Sarcoptergii (lobe finned fish: acinista, dipnoi (lungfish, rhipidstia, tetrapods. Possible scenario (clack, 2002) tetrapod stem lineages branches along with lung fish the first tetrapods (tetrapoda) evolved in the mid-late devonian: tiktaalik is a fish-like tetrapod (fossil species) Early tetrapods have characteristic teeth (labyrinthodonts: cross section of tooth displays enamel folds. Tiktaalik (extinct; first tetrapod: late devonian (375 mya) fish from ellesmere island displays intermediate characteristics between fish and tetrapods. It has limb-like pectoral fins possibly for standing support, functional wrist joint and mobile neck allowing flexible head movement: loss of bony gill covering suggests increased used of lungs for respiration.
