AMPHIBIAN "DESIGN"

Do fossil amphibans display a design?

EVOLUTIONARY MODEL

If evolution is correct, then an ancestral body plan can be significantly modified to adapt to a new environment.

CREATIONISM MODEL

If the creationism model is correct, it is not expected that the modifications which develop within a group exceed the modifications needed to produce the lineage from an ancestral group of a different "kind". The most significant adaptations should be a created feature of the kind rather than a novelty within a kind.

INTELLIGENT DESIGN

If intelligent design is correct, each group was designed for a specific way of life. If the design was truly intelligent, it is not expected that it would need to be continually reworked for survival.


Fossil amphibians share a number of anatomical features which justify their classification into a group which excludes other vertebrates. Were fossil amphibians intelligently designed? If so, the variation within fossil amphibians makes it difficult to determine what they were designed for. While some were extremely similar to rhipidistian fish (so similar that there is disagreement over the classification of some fossils), others were extremely similar to reptiles (so similar that there is disagreement over the classification of some fossils). Some were so small that their skulls measured about a centimeter while others reached lengths of 3 and even 4 meters.
mastodontosaurus

They varied in their skull bones, their vertebrae, their teeth, and many other features. In some, the relative size of the head was larger than in most amphibians.

cacops

Amphibian skulls have varied greatly in the bones they possessed. A large number of the bones in the skulls of the earliest amphibians apparently weren't absolute requirements for an amphibian design given that modern amphibians lack them.

skull

While some seemed to be primarily aquatic because they still retained primitive features of their fish ancestors,

acanthostega

others seem to represent lineages which were secondarily adapted to aquatic life.

metoposaurus

aquatic

Even the anthracosaurs, a group which included species which became better adapted to land and more reptile-like,
also included lineages which became secondarily adapted for aquatic life.

aquatic

Aquatic forms also evolved in other amphibian lineages, such as the nectridians.

How should amphibian "design" be judged? If amphibians were "designed" for terrestrial adaptations, why did the first amphibians lack important elements of this design? Why did other groups which were modified for better terrestrial adaptations subsequently modified again for an aquatic lifestyle? Why did modifications for an aquatic design occur separately in distinct groups?

If the modifications of reptiles were required because of limitations of amphibian design, why did extinct groups of amphibians become so similar to reptiles?

anthracosaur

anthracosaur


Aistopods developed long, slender bodies, reduced their limbs, and some species completely lacked legs, limb girdles, and possessed up to 230 vertebrae.

amphibians

If ancestral amphibians required an intelligent design, why did this design need to be reworked so frequently? If legs were designed for terrestrial life, why did some amphibians lose theirs?

Nectrideans were a group of amphibians in which some developed extensions of the skull (including Diploceraspis with its distinct V-shaped head).
diploceraspis

skull

Some anthracosaurs, such as the chroniosuchids, evolved dermal armor consisting of large plates (Carroll, 1988).

The earliest amphibians evolved in a world without reptiles and they reached their greatest diversity prior to the great radiation of the reptiles which succeeded them. Rather than display an intelligent design, they demonstrate the adaptability of their ancestral form.