Topic 19 Flashcards
What were the evolutionary steps from sea to land?
internal nostrils (opening from the nasal sac into the roof of the mouth): first component of the tetrapod body plan to evolve (well before the origin of limbs)
origin: displacement of posterior external nostril
tetrapods: only one pair of external/anterior nostrils
posterior –> internal nostrils
evolved independently in two lineages
Why transition to life on land?
continental drift –> pangaea: coastal regions became land-locked
plants (esp. seed-bearing) beginning to colonize land –> forests
anthropods and other invertebrates colonizing land –> lots of food
most predators still aquatic
fewer competitors on land
What were the challenges of terrestrial life for aquatic organisms?
gravity desiccation respiration reproduction locomotion temperature regulation
How is gravity a challenge for aquatic organisms adapting to terrestrial life?
aquatic life is buoyed by water, air is not
so terrestrial animals need some sort of supporting tissue
How is desiccation a challenge for aquatic organisms adapting to terrestrial life?
air is drier than water
so terrestrial organisms need some form of skin or coat to keep all their precious bodily fluids from leaking out and to protect the embryo
How is respiration a challenge for aquatic organisms adapting to terrestrial life?
aquatic organisms exchange oxygen and carbon dioxide dissolved in water
in air, these substances are gases, so new structures are needed to breath
How is respiration a challenge for aquatic organisms adapting to terrestrial life?
aquatic organisms often release their eggs, sperm, etc., directly into the water
this approach is much less effective in air, so other solutions evolve
How is locomotion a challenge for aquatic organisms adapting to terrestrial life?
aquatic animals can swim, or otherwise move through the water
these motions have to be modified in the terrestrial realm
How is temperature a challenge for aquatic organisms adapting to terrestrial life?
fluctuate more in air than in water
terrestrial animals have to evolve adaptations to deal with these fluctuations (homeostasis)
What was tiktaalik?
fishy features: scales, fins without digits, and gills + lungs
tetrapod features: neck, ribs, fins with skeleton, eyes on top of head
neck: allows tetrapod to move head independently of body, up-down and side-to-side
shape and size of the hip socket (pelvis) reveal that fins were capable of a wide range of movements
overall structure of the pelvis is still more fish-like
What was Acanthostega?
primitive traits: gills, lateral line, long fin rays around the tail, no true elbows, knees, wrists or ankles
derived traits: 4 limbs with bony digits, pelvis weakly attached to vertebrate
primarily aquatic
features are more different from ancestral condition when compared to Tiktaalik
What was ichthyostega?
terrestial vertebrates were, until recently, thought to be descended from ancestors that had 5 digits per limb
closer examination of fossil taxa ichthyostega revealed that ancient semi-terrestial vertebrates had 5+ digits
primitive traits: gills, lateral lines
derived traits: limbs attached to vertebrates, weight bearing joints
What are some characteristics of tetrapoda?
terrestrial vertebrates with four legs with digits
limbs with carpals, tarsals and digits
vertebral column with regional differentiation, vertebrae with zygapophyses
What is the class amphibia?
monophyletic group: frogs, salamanders, caecilians
thin, permeable skin (sole site of gas exchange for some lungless salamanders)
buccal pump (similar to lungfish) to inflate lungs air drawn into the oral/throat cavity through nostrils or mouth mouth and nostrils then sealed and oral/throat cavity contracted to force air into lungs
What is the life cycle of amphibians?
amphi = both, bios = life, hence “Amphibia”
aquatic larvae (tadpole) and terrestrial adults
tadpoles: gills, lateral line system, tail, no legs
adults: legs, lungs, eardrums
external fertilization
eggs lack shell, subject to desiccation, laid in water in most species
not fully adapted to life on land
