They're very good at making statements with no evidence to back them up.

Laughing at someone's position and saying "that's silly" or "that's totally absurd" unfortunately doesn't prove anything.

They still can't explain why radiometric dating (done in a variety of ways, by many different labs which compare results) tells us that the earth is over 4 billion years old, or why God would have sorted the fossil record in the geological column in order to presumably deceive us into thinking evolution happens and the earth is old (or maybe they think it was Satan, who knows).

The Case of the ‘Fish-ibian’

A common argument of creationism is that no transitional forms between major organismal groups (e.g. the classes of the vertebrates: fish, birds, mammals etc.) are seen in the fossil record. However, paleontologists have uncovered a great wealth of fossils that are clearly transitional forms. In this essay, I will specifically address the transition from aquatic fish to terrestrial amphibian. First, let’s review what a ‘transitional’ form is and how we might recognize it.

All vertebrates are united by having a spinal column. The red lines are the evolutionary relationships among various groups of vertebrates. As one moves upward along any of these evolutionary lines, one moves forward in time, toward more ‘modern’ or ‘advanced’ species (see my discussion of the term ‘advanced’ in my previous column here). The splits between groups occurred among ‘primitive’ members of the groups. For example, the first amphibians lie on the phylogeny at the point labeled “2” which represents the origin of terrestrial locomotion. These first amphibians, while classified as amphibians, are quite different from modern frogs and salamanders we see today. These first amphibians evolved from primitive fishes, which are also unlike any fish we have today.



Shown above are the positions on the phylogeny where the intermediate forms between the major classes would reside. Note that these are not at the tips of the evolutionary lines (modern forms) but lower on the phylogeny.

The transition from fishes to amphibians

Is (or was) there such a thing as a “fish-ibian?” (The term ‘fishibian’ is borrowed from Huse, 1993, p. 60.) If so, what would it look like? How would you know the “fish-ibian” was neither a fish nor an amphibian or that it was both? If we were to look at the most familiar modern fish and amphibians, we might envision the transitional form to be half frog, half trout:

But the reality is that the transition did not occur between modern fish and amphibians, but rather between some very ancient vertebrates some 375 million years ago. Back then, the distinction between fish and amphibians was not as immediately clear as it is today.

To put this on a phylogram, it would might something like this:



What is a “Fish?”

Definition: In the simplest sense, a fish is an aquatic vertebrate that depends upon water as its primary environment for day-to-day living and reproduction. Fishes breathe oxygen dissolved in water through gills. Fish have limbs adapted as fins for swimming, with no ‘fingers’ or ‘toes.’ Fishes typically have bony scales covering their entire body.

What is an “Amphibian?”

Definition: Amphibians are semi-aquatic vertebrates which divide their time between water and land for day-to-day living. Amphibians are dependent upon water for reproduction. Amphibians typically have paired limbs (arms and legs) that include ‘fingers’ and ‘toes’ for moving about on land. Amphibians also have strengthened pectoral and pelvic girdles adapted for walking on land. Amphibians begin life in water breathing through gills and later in life transition to being able to breathe air through lungs. Amphibians typically do not have bony scales on their bodies.

Which Distinctive Characteristics Will Fossilize?

These definitions depend a great deal on processes, behaviors and features that would not fossilize. As paleontologists, what are we left with? What is readily evident in the fossil record? And which of these characteristics allow us to distinguish between Fishes and Amphibians?

Based upon this, we see that the primary distinctions that may be made between fish and amphibians are with the breathing apparatus and skull (in adults especially), in the structure of the skin and scales, and in the structure of the limbs.

The Fish-ibian

Based upon the above characters, what would we predict the ‘fish-ibian’ to look like?

• Fish-ibians had backbones.
• Fish-ibians were cold-blooded.
• Fish-ibians breathed with gills, but may have used lungs in adults.
• Fish-ibians layed eggs in water.
• Fish-ibians may or may not have had scales.
• Fish-ibians had limbs adapted in part for swimming and in part for moving about on land.

Limb Structure

Perhaps one of the most striking differences between fishes and amphibians – at least in the Devonian – was in the structure of the limbs. This makes sense because a fin used to paddle a neutrally-buoyant fish about in water is not capable of lifting and hauling this same fish about on dry land.



One character that makes a fish a FISH is the presence of fin rays or lepidotrichia. These are the tiny bones that support the flexible, almost clothlike, membrane of the fin itself. The lepidotrichia are movable, allowing the fish to alter the shape of the fin in behavioral displays or in locomotion. Lepidotrichia are “dermal bones,” meaning that they develop embryologically directly from the dermal layers of skin. Land-dwelling vertebrates lack lepidotrichia, as the fin membrane is lost, to be replaced with bony fingers. Finger bones, as well as all wrist and arm bones, are termed “endochondral bones,” which are bones that develop from a cartilage precursor. Thus, lepidotrichia and phalanges arise from different embryological origins, despite occupying a similar position on the limb.

The Diagnosis of Tiktaalik – Cladistics style.

Below is a more detailed listing of the various characteristics used to distinguish Tiktaalik from other fish and amphibians (Data from Daeschler et al., 2006; Shubin et al., 2006). Based upon this, Tiktaalik appears to be more amphibian-like than fish-like.

Let’s return to the definitions of ‘fish’ and ‘amphibians’ and the characteristics of each that can fossilize.

Breathing: Fish have gills – therefore they also have the opercular bones. Amphibians (adults anyway) lack opercular bones. Tiktalik also lacks opercular bones, therefore it is more like an AMPHIBIAN.

Scales: Fish have scales covering their bodies. Modern amphibians lack scales. Tiktaalik has scales along its back, making it more like a FISH. However, it is not certain that early amphibians lacked scales, and the presence or absence of scales is not considered definitive.

Limb structure: Fish have fins with lepidotrichia used for swimming. The most ‘primitive’ fish lack the limb bones characteristic of terrestrial vertebrates. However, some lobe-finned fishes have characteristic limb bones like (in the arm) the humerus, radius, and ulna, as well as some of the carpal bones. The finger bones (metacarpals and phalanges) are lacking in lobe-finned fish, which instead have lepidotrichia. Amphibians have the complete suite of limb bones required for terrestrial locomotion (humeri to phalanges), and no lepidotrichia. Tiktaalik has lepidotrichia, which is more like a FISH. However, it also has elaborations of the bones in the limb which may have been precursors of metacarpals and phalanges, making it more like an AMPHIBIAN.

It appears that Tiktaalik is both FISH and AMPHIBIAN. It is a transitional form between fish and amphibians.

"It had an overall amphibian gestalt. … You know, kind of a froggy slamander-y sort of look," said Jason Anderson, a comparative biologist at the University of Calgary, Canada, who led a new analysis of the fossil.

"But also I recognized some of the archaic features too, and I thought that this would be a critical piece of evidence in trying to work out the origins of modern amphibians."

Dubbed Gerobatrachus hottoni, the animal looked somewhat like a salamander with a stubby tail and froglike ears.

Gerobatrachus fits into a noted gap in the fossil record of amphibians—between one of the groups hypothesized to be ancestors of modern amphibians, called temnospondyls, and the earliest frogs and salamanders.

The origin of extant amphibians (Lissamphibia: frogs, salamanders and caecilians) is one of the most controversial questions in vertebrate evolution, owing to large morphological and temporal gaps in the fossil record1, 2, 3. Current discussions focus on three competing hypotheses: a monophyletic origin within either Temnospondyli4, 5, 6, 7 or Lepospondyli8, 9, 10, or a polyphyletic origin with frogs and salamanders arising among temnospondyls and caecilians among the lepospondyls11, 12, 13, 14, 15, 16. Recent molecular analyses are also controversial, with estimations for the batrachian (frog–salamander) divergence significantly older than the palaeontological evidence supports17, 18. Here we report the discovery of an amphibamid temnospondyl from the Early Permian of Texas that bridges the gap between other Palaeozoic amphibians and the earliest known salientians19, 20 and caudatans21 from the Mesozoic. The presence of a mosaic of salientian and caudatan characters in this small fossil makes it a key taxon close to the batrachian (frog and salamander) divergence. Phylogenetic analysis suggests that the batrachian divergence occurred in the Middle Permian, rather than the late Carboniferous as recently estimated using molecular clocks18, 22, but the divergence with caecilians corresponds to the deep split between temnospondyls and lepospondyls, which is congruent with the molecular estimates.

The Gerobatrachus fossil provides a much fuller understanding of the origin and evolution of modern amphibians. The skull, backbone and teeth of Gerobatrachus have a mixture of frog and salamander features--the fossil has two fused bones in the ankle, which is normally only seen in salamanders, and a very large tympanic ear (ear drum). It also has a lightly built and wide skull similar to that of a frog. Its backbone is exactly intermediate in number between the modern frogs and salamanders and more primitive amphibians.

The new fossil also addresses a controversy over molecular clock estimates, or the general time salamanders and frogs evolved into two distinct groups.