Lecture 30 Tetrapods Flashcards
what are tetrapods?
1 of 3 surviving lineages of lobe-fins
- vertebrates with two pairs of sturdy, skeleton supported supporting limbs with digits
- four limbs
- evolved from lungfish-like ancestors in the late devonian period
- last common ancestor of amphib, reptiles, mammals
what is one of the most significant events in vertebrate history?
fins of some lobe fins evolved into limbs and feet of tetrapods
why transition to life on land?
- continental drift
- plants, anthropods, and other invertebrates colonized land — lots of food initially; diversification of land plants
- competition and predation few competitors
- new terrestrial niches
how did animals evolve for life on land
- Waterproof external layers, internal gas exchange systems, ways of reproducing that did not involve water, and strong support systems (endoskeletons) on land.
- Not all animal taxa equally successful in solving these problems
what challenges did terrestrial life for organisms adapted to aquatic life face?
Water conservation, gas exchange, reproduction and dispersal, and gravity, temp, senses, locomotion.
what challenges did terrestrial life for organisms adapted to aquatic life face?
Water conservation, gas exchange, reproduction and dispersal, and gravity, temp, senses, locomotion.
what was the evolution of tetrapods
- transitional tetrapods had legs and both lungs and gills, but were still primarily aquatic and unsuited to life on land
- limbs and joints too weak to bear its own weight
- ribs too short to prevent lungs being crushed under own weight
- fish-like tail fin would have been damaged by dragging on the ground
- most traits critical to the move on land evolved PRIOR to tetrapods : SIMPLE LUNGS & INTERNAL NOSTRILS
what are simple lungs?
outgrowth of the gut, forming a gas-filled bladder above the digestive system
what are internal nostrils?
opening from the nasal sac into the roof of the mouth
- nostrils fxn for smelling in bony fish – paired nostrils not connected to mouth or gills
- tetrapod evolution – posterior nostrils displacement internally (connect to external/anterior nostrils) – aid in respiration
what is a transitional tetrapods?
- tiktaalik
- fish features: scales, fins without digits, gills and lungs
- tetrapod features: neck, ribs, fin skeleton, eyes on top of head
- shoulder (pectoral girdle) not fused to skull – neck
- allows tetrapod to move head independently of body, up-down and side to side
- loss of the operculum – contribute neck mobility
- “fishapod” 1/2 fish, 1/2 tetrapod - limb bones and joint - shoulder, elbow, proto-wrist, but fish-like fins instead of digits
- tiktaalik could most likely prop itself on its fins, but not walk
what is a transitional tetrapods?
- tiktaalik
- fish features: scales, fins without digits, gills and lungs
- tetrapod features: neck, ribs, fin skeleton, eyes on top of head
- shoulder (pectoral girdle) not fused to skull – neck
- allows tetrapod to move head independently of body, up-down and side to side
- loss of the operculum – contribute neck mobility
- “fishapod” 1/2 fish, 1/2 tetrapod - limb bones and joint - shoulder, elbow, proto-wrist, but fish-like fins instead of digits
- tiktaalik could most likely prop itself on its fins, but not walk
- shape and size of the hip socket (pelvis) reveal that fins were capable of a wide range of movements – swimming to support weight
- evolved their feet for uses in water, only later became land-going
what is the overall structure of the tetrapod
- pelvis is still more fish-like
- pelvis is still made of one bone (tetrapods pelvis made of three parts).
- pelvis not attached to vertebrae.
what is another intermediate forms?
- acanthostega - 4 limbs with numerous bony digits
- pelvis weakly attached to vertebrate – support, weight-bearing
- long fin rays around the tail
- no true elbows, knees, wrists r ankles
- internal gills and lungs, but ribs were too short to give support chest cavity out of water
- fully aquatic
what were limbs used for?
- suitable for padding (digits webbed) or for holding on to aquatic plants
what are derived characters of tetrapods?
- tetrapods have some specific adaptations
- four limbs, feet with digits
- a neck which allows separate movement of the head
- fusion of pelvic girdle to backbone
- absence of gills (except some aquatic species)
- ears for detecting airborne sounds
