Evolution: Palaeontology

Overview: Intermediate forms - transitional forms

Definition of mosaic and transitional forms

If macro-evolution actually did occur, then there would have been many transitional forms of life through the past. In order to discuss such transitional forms, we must clarify what is understood by such forms. For instance the pair of terms mosaic form and intermediate form are particularly important.

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Cambrian Explosion

The fossil record of multicellular animals begins in the Lower Cambrian with an almost sudden emergence of animals having a wide variety of different physical structures or building plans. This phenomenon is known today as the "Cambrian Explosion". The comparatively few fossils in the uppermost Precambrian are unlikely to be the forerunners of the Cambrian phyla.

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Origin of tetrapods

The origin of tetrapods - the step out of the aquatic environment onto the terrestrial ground in case of the vertrebrates - is one of the best-known examples for evolutionary transitions. In this regard the concepts of evolutionary theory have significantly changed during the last years. Yet substantial questions about this transition remain unanswered.

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Origin of birds

The evolutionary transition from reptiles to birds is meanwhile considered well supported due to the finding of numerous fossils over the past years. The famous "Urvogel" Archaeopteryx is joined by further fossil species (particularly small carnivore dinosaurs) which are placed in the transition area reptles-birds. It still remains unclear how both the characteristic bird feature i.e. the feathers and the ability to fly have developed. According to the inconsistence of features the evolutionary transition is also controversial.

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