Question

Terrestrial vertebrates face very different challenges than vertebrates living in water. Explain several adaptations of terrestrial vertebrates in order to handle these challenges. Which do you think are the most important; why?

Answer 1

Evolution studies show that first vertebrates were water animals. They had no jaws as they sucked the food stuff directly, no limbs, no lungs and were exothermic.

Land vertebrates evolved from this - but for survival on land, many other adaptations were mandatory.

1. Limbs : Limbs were essential as movement on land was impossible without them. Fins present on aquatic animals developed into limbs and helped in development of motile vertebrate land forms.

2. Lungs : Respiratory structure in aquatic forms were gills. Gills require water. As an alternate method of respiration, the land vertebrates evolved lungs in place of gills. These were first seen in an older fish group - the lung fishes, through which they were transferred into amphibians.

3. Water tight skin : Land has scarcity of water. An animal living on land has to conserve water. So, an adaptation to live on land was the evolution ofbskin which prevented loss of water. This mechanism is also supported by excretion of urea in place of ammonia. Excretion of urea requires less water as it is less toxic.

4. Endothermy : The temperature of a large water body is more or less constant throughout the day, but on land, the temperature varies considerably. So, to counter this, terrestrial vertebrates had to evolve a method of maintaining body temperature by intrinsic methods instead of relying on environmental factors.

Other changes :
5. Larval development was taken over by metamorphosis due to higher success rate.

6. Eggs changed into shelled forms to prevent loss of water.

Lungs and jaws are the most important changes as they fulfill two most important functions - nutrition and respiration.