Evidence from comparative anatomy and morphology - Connecting link

 

There are various existing animal and also fossil of animals that show various combination of character. These are called connecting link.

On the  other hand , if any animal is classified as connecting link , it means it has combination of characters. The connecting link between the two  small group are not easily detectable but it can easily identified between the two larger group. These connecting link play an important role to understand the process of evolution in a hirechy. Some important connecting link are as follow - 

Euglena - It is considered the connecting link between Plant and animal because it can synthesize its own food through the photosynthesis. When sun light is not available than it depend on other organism for food and behave as animal like heterotrophs.

Proterospongia- It is a Protozoan having combine feature of flagellated protozoan and Choanocyte bearing Sponges. Hence it is connecting link between Protozoa and Porifera.

Neoplina - It is a primitive Mollusc . It has shell Mantle and muscular foot  like mollusc but it also has various features of Annelids like segmented gill , nephredia and circular and longitudnal muscles. Neoplina is a connecting link of Mollusc and Annelids.

Peripatus - It is a caterpillar like Arthropods having combine character of Annelids and Arthropods. The arthropods characters in Peripatus are jointed legs, compound eye and trachea whereas Worm like bodies , segmental nephredia and non chitinous cuticle are Annelids character.

Balanoglossus - It is considered as connecting link between chordates and non chordates. It has the features of both phylum. The chordates characters in Balanoglossus are  no to chord , pharyngeal gills slit and dorsal heart like non chordates.

Protopterus - It is an African lung fish and considered as connecting link between Fish and Amphibea. It can respire by gill in water if aquatic environment is dried up than it can use their reduced lung for respiration. 

Seymoria - It is a  connecting link between amphibea and reptiles. Its  skull looks like an amphibian skull, but the rest of the anatomy of the body and the formation of the skeleton is more like a normal reptile.

Acheoptaryx - It was a primitive bird with feathers but its skeleton looks more like that of a small reptiles. Therefore it is considered as connecting link between reptiles and birds. 

Ornithorhynchus - It is commonly called Duck billed platypus. It has mammalian characters like mammary gland and  hair. It is an egg laying mammal but egg laying features belong to reptiles. Therefore it is considered as connecting link between reptiles and mammals .