Tetrapods Flashcards
What are the closest ancestors of Tetrapods?
Sarcopterygian Fish e.g. Coelcanths, Lungfish (Dipnoi)
What were the advantages of moving to land?
Increase in range of habitats and food, avoidance of aquatic predators/competitors, abundant oxygen and to raise body temperature to accelerate metabolism.
What were the disadvantages of leaving water?
Gravity; need support for body locomotion/prevention of lung collapse, need adaption of respiratory system, skin resistant to desiccation, greater fluctuations in temperature, blood circulation more difficult, different food and methods of capture, adjust sense to new stimuli in air.
How did the skeletal body plan change to support the body on land?
Longer ribs, interlocking vertebrae, loss of soul bones freeing shoulder for flexible neck, larger pelvis attached to spine, modification of paired fins to form limbs with feet with digits, strengthening of musculature.
What term is given to the acquisition of hands and feet?
Autopodia.
What characteristics arose with the evolution of the tetrapod skull?
First cervical vertebra modified to allow skull movement, Hyomandibular bone becomes stapes conducting sound to ear, pectoral girdle separated from skull to form mobile neck.
What characteristics defined the Eusthenopteron (lobe finned fish) skull?
Short snout with many bones, opercular bones covering gills and throat.
What characteristics defined the Acanthostega (Early Tetrapod) skull?
Longer snout with fewer bones, absence of opercular bones.
How did vision change to aid the emergence of tetrapods on lands?
Eyes moved to the top of the head, eyes have flatter lens than fish as vision is easier in air.
How did circulation evolve to accommodate the change from water to land?
Changed from a uni-directional single circulatory system with only 2 heart chambers to a double circulatory system with 4 heart chambers, no mixing of the blood.
How was Tiktaalik an intermediate organism?
Possessed fins, scales, primitive jaws, gills and lungs like a lobe-finned fish, but also possessed a neck, wrists, a flat skull with eyes on top and expanded ribs like land-living animals.
What were the three major events in the evolution of land organisms?
Origin of limbs with digits, origin of walking and origin of terrestriality.
What two species where the earliest known tetrapods but where still aquatic and unsuited for land?
Acanthostega, Ichthyostega; no wrists or ankles, paddle-like limbs, internal gills, not enough spinal support, however possessed digits.
How did the changes in the lower jaw aid respiration?
Fusing of bones of the lower jaws to form the buccal pump meant the mouth cavity could move in an action that meant air was gulped and forced into the lungs.
Name the structures of the mammalian forelimbs?
Humerus, Radius, Ulna, Carpals, Metacarpals, Phalanges
