Question

Amphibians are one of the most ancestral-like tetrapods.

a) What evolutionary changes have occurred between fish & amphibians?

b) What features did sarcopterygii have that allowed to move to land?

c) Why/what features make people call amphibians “living fossils”?

d) What considerable changes occurred in the cardiovascular system of amphibians?

Answer 1

a.

Important evolutionary cahnge is the development of lung for respiration on land. Lung evolution has occured form airbladder of the fish which is used in buoyancy. Next exolutionary change is movement on land for which the limbs developed instead of fins in the fish.Amphibians are the first tetrapods having four limbs. Amphibians also had to adapt ways to prevent decication. Amphibians have moist skin because there are number of mucus secreting glands in the skin which keep the skin moist and that prevents the body from desication. Skin also helps frog in respiration as their lungs are not as highly efficient to absorb O2 from air. Eyelids are developed in frog to adapt for the vision in terrestrial habitat. Ear drum developed which separates the middle ear from the external ear. Tail is lost and also the fins. The frog life cycle includes reproduction in water and fish like larva which is not seen in fish. The larva is called tadpole.

b.

Most importantly, Sarcopetygii had lung like structures which were used by these organisms to absorb O2 from air as they live in waters that are less in O2. Developemnt of internal nostrils in Sarcopterygii which allowed the air to pass in to the lung like structures in these fish. Sarcopterygii also had lobed fins which they used to move in muddy waters or marshy land when the water bodies dried during the dry seasons. The present day Coelacanth fish belonging to the group Sarcopterygii have lobbed fins which they use alternately to move like how limbs are used by tetrapods. The limbs appear to be the ancestral form of the present tetrapod limbs.

c.

Any organism that has not changed for very long and resembles the organism of the prehistoric times with very few individuals presently surviving is called a living fossil. The Hula painted frog found in 2011 in Israel is considered a living fossil because it has not changed for thousands of years resembling the extict relatives most of which do not survive now. The forg also does not have any living relatives. The frog has distinctive dark belly and white spots whose features resemble that of the genus Lotonia the group which is mostly extinct now.

d.

Heart became three chambered which was 2 chambered in fish. Fish heart is venous heart which pumped only impure blood in to gills. Where as the amphibian heart is 3 chambered and it receives pure and impure blood. The blood from the lungs is brought back to heart which pumps the blood to all parts of the body. The blood (pure and impure ) mix in the single ventricle present. Mixed blood goes to all parts of the body not completely pure blood. This way of circulation though gives higher blood pressure of pumping of blood in to tissues, it causes mixing of pure and impure blood in single ventricle of amphibians. Conus arteriosus which is present in fish is not present in amphibians. Amphibians have truncus arteriosus instead which is partitioned internally.