Tetrapoda and Amphibians Flashcards
How did tetrapods evolve? What is the 3-part limb structure?
- evolved from lung-fish-like ancestors
- fins evolved into limbs and feet
1) Upper, single longbone hinged to
2) A pair of parallel long bones with
3) Terminal hand/foot with jointed digits
What 3 factors made colonization of land favourable?
1) Early colonization by other organisms offered abundant food sources
- extensive terrestrial and shallow water vegetation
2) Environmental changes such as formation of Pangea turned coastal regions into land-locked, shallow habitats
3) Ecological pressures such as competition and predation drove need to escape and exploit new ecological niches
What were 7 challenges of terrestrial life?
- Gravity - lack supporting tissue and endoskeletons
- Water conservation - lacked protective skin
- Reproduction - spawning and external fertilization was not suitable
- Gas exchange - gills dessicate
- Locomotion - lateral, side-side movement was inefficient
- Sensory perception - light, sound, smell transmit differently in air and electrical sense and lateral line system are useless
- Temperature regulation - lack thermoregulation
What were the characteristics of transitional tetrapods?
- had limbs
- both lungs and gills
- limbs and ankles unable to support body weight
- ribs too short to protect lungs from compression by weight
- fish-like tail fin with fin rays
What 5 adaptations for transition to land emerged before land colonization?
1) Vertebral column development (Vertebrata)
2) Skeleton mineralization andemergence of 2 pairs of lateral appendages (Gnasthostomes)
3) Simple lungs (Osteichthyans)
4) Bony, muscular pectoral/pelvic fins (Lobe-fins)
5) Internal nostrils which opened from nasal sac into roof of mouth
What was the significance of internal nostrils?
- posterior nostrils shifted internally, connecting anterior nostril to the buccal cavity in the mouth
- facilitated breathing at water surface without opening the mouth
What were the fish traits and tetrapod traits of Tiktaalik?
Fish: scales, lobe-fins without digits but with fin rays, gills and lungs
Tetrapod: neck structure, rib configuration, limb skeleton, flattened skull and eyes on the top of the head
What anatomical features of Tiktaalik revealed its transitionary nature?
- lack of fusion between pectoral girdle and skull allowing for distinct neck and enabling movement of head in different directions
- loss of operculum but retention of gills contributing to neck mobility
- head, shoulder, elbow and proto-wrist joints but no digits and had fish fins
- pelvis supported swimming and limited weight support but consisted of one bone and was not attached to vertebral column
Aconthestega characteristics?
- limbs with bony digits and no fin rays
- weak attachment of pelvis to vertebral column facilitating weight-bearing
- knee and ankle joint structures suggest limited weight bearing
- internal gills and lungs but short ribs
What are the 5 shared, derived traits of tetrapods?
4 limbs with feet possessing digits
- facilitate locomotion and weight-bearing
Distinct neck allowing independent neck movement
- enhance sensory perception
Fusion of pelvic girdle to vertebral column
- stability and support for locomotion
No gills
- reliance of air for respiration
Ears that detect airborne sounds
What are the two groups of tetrapods?
Amphibians and Amniotes
Ichthyostega fish traits and tetrapod traits?
Fish: tail with fin rays, gills, > 5 digits
Tetrapod: amphibian skull, pelvic girdle attached to vertebral column, 3 part pelvis, weight-bearing knee and ankle joints, relied primarily on lungs, limbs for locomotion and tail for balance
What are the 3 clades of Amphibians?
Frogs, salamanders, caecilians
Skin traits and structure of amphibians?
- thin, water and gas permeable, moist
- no scales, little keratin
- absorb and lose water directly, prone to dessication
- mucous glands produce secretions to maintain moisture
- may secrete distasteful/toxic substances for defense
- supplementary respiratory surface complementing lung gas exchange
How do amphibians thermoregulate and what are the consequences?
- ectothermic - rely on external heat sources
- low metabolic rate, reduced food and energy requirements
- require stable environment or exhibit behavioural thermoregulation
