Bridge animals (mosaic form / transitional form)

Fossil and recent bridgeheads ...

A bridging animal (often a mosaic) is understood in biology to be an animal that combines the characteristics of two different groups of animals (for example, mammals, fish, amphibians, birds). For the theory of evolution, the existence of mosaic forms is an important fact, because it proves the relationship of two groups of animals to each other and can therefore be assumed that species have not developed side by side, but apart.

One differentiates between fossil, thus already extinct bridge forms (for example the Archeopteryx) and recent, today still alive mosaic forms (for example the platypus). Recent bridge animals are usually living fossils as well.

Fossil Bridge Animals - The Archeopteryx

The Archeopteryx is due to its characteristics of two animal classes as a bridgehead between reptiles and birds. Features of the older form of the reptiles include the teeth, a long tail spine and an unfused metacarpal bone. Among the typical bird features include the plumage, the back toe, and the overgrown clavicles (fork leg).

Recent bridgeheads - The Platypus

The platypus seems to be one of the most bizarre creatures of the animal kingdom. With the characteristics of a reptile (lays eggs, possesses a cloaca and venom glands) as well as a mammal (suckling his cubs over the mammary glands, possesses a fur) equipped, by recent genetic engineering even the relation to the group of the birds has become (among other things it shows in the hatching of eggs a bird-like behavior).

Summary

Bridge animals have characteristics of different groups of animals.
There is a distinction between fossil and recent bridge forms
Examples of bridle animals are: Archeopteryx, Platypus or Ichthyiostega