Fossils of an animal called ichthyostega shows that it had lungs and legs. it also had teeth and a tail similar to those of fish. ichthyostega is considered to be one of the first amphibians. other fossils show that amphibians lost these fish-like features. how might scientists interpret the fossil of ichthyostega?

Scientists interpret the fossil of Ichthyostega through Comparative Embryology which states that:it has been observed that a very young human embryo look very similar with young embryos of other vertebrates in their structure and appearance.
Example: the young human ambryo look very similar with young embryos of birds, frogs,fish and reptiles.This show that,at certain stage of their development all these embryos had fish like features with gill slits and a vascular system,also they posses a simple heart with a single blood circulation.