Example 3: Egg laying mammals: Egg laying mammals are the connecting link between reptiles and mammals. For example, duck-billed platypus. They have few mammalian characters such as hair, mammary glands, diapharm whereas it lays eggs with yolk and egg shell similar to reptiles (Figure 5.7).

Figure 5.7 : Duck-billed platypus.

Few other examples of connecting lins are as follows:
Neopalina: it is a connecting link between annelids and the mollusks.
Balanoglossus: it is a connecting link between non-chordates and chordates.
Chimaera: it is a connecting link between cartilaginous and bony fishes.
Coelocanth: it is a connecting link between bony fishes and amphibians.
Sphenodon: it is a connecting link between amphibians and reptiles.
Connecting link clearly highlight the fact that different organisms are evolved together from a common ancester.

2. Embryological evidences: Comparative study of the embryology of different organisms shows stricking similarities between them. To explain this phenomenon, biogenetic law was proposed by Ernst Haeckel. This theory states that an organism in its individual development follow different developmental stages through which its ancesters have passed in the course of their evolution. In another words, “ontogeny repeats phylogeny”.  The embryological stages of selected organism is given in the Figure 5.8. Lets take the example of development of frog from it. In its development stages, it forms fish like tadpole larva with tail, fin, gills for breathing in water. It indicaes that frog is evolved from fish like ancestor.