1. A connecting link is an intermediate or transitional state between two systematic groups of organisms.
2. It bears characters common to both these groups on either side of its position. Thus it represents an evolutionary line.
3. Connecting links are also called a missing link.
E.g. Archaeopteryx, the extinct bird is a connecting link between Reptiles and Aves.
4. Seymouria is a connecting link between Amphibia and Reptilia.
5. Ichthyostega is a connecting link between Pisces and Amphibia.
