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Tiktaalik and Fellow Fish Fossils

Tiktaalik and Fellow Fish Fossils

Intermediate

In April 2006 Neil Shubin and others published an account of Tiktaalik, a fish fossil from Ellesmere Island in Canada’s north. More recently, scientists and the media alike have hailed this fossil as incontrovertible proof that the creationists are wrong. This fossil supposedly demonstrates that some fish developed legs in place of fins and left their watery habitat to “invade the land”.

tiktaalikThe interpretation of Tiktaalik as an ancestor of land animals (tetrapods or 4-footed animals) is based on the shape of the face (snout) rather than a comparison of anatomy in the pelvic region where hind legs would have to develop. The same thing applies to other supposed ancestors such as the fishes Panderichthys and Eusthenopteron. While the pelvic region of Tiktaalik and Panderichthys is a disaster as far as appearance of legs is concerned, the pectoral (front) fins provide more potential for some not very convincing arguments. The bottom line remains however that all these specimens are true fish with no legs, no feet, just fins and no potential for invading the land.

Eusthenopteron was a fish. We know about it from fossil specimens collected at Miguasha, Quebec. Despite the fact that Eusthenopteron was definitely a fish, its claim to fame is as an ancestor of animals that walked on land. Scientists like Prof. Erik Jarvik believed that some features of the fish conveyed hints of tetrapod (4-footed) features yet to appear. While all the fins in Eusthenopteron were true fins, this fish did have one feature which seemed suggestive of land animals. That suggestive feature was “strange features in the snout, indicating a close relationship to one group of recent amphibian, the Anura [like frogs].” (Jarvik in H-P Schultze and R. Cloutier (eds) 1996. Devonian Fishes and Plants of Miguasha, Quebec, Canada. p. 288).

Evidently Eusthenopteron‘s characteristics suggestive of a relationship to land animals, lay in the head region and not in the body. Obviously this is not a very convincing similarity to land animals. The characteristic which defines land animals is the possession of four limbs (legs). Biology is full of organisms with superficial similarities which indicate nothing at all about biological relationships. The snout of an organism is not where we look to identify a land animal. Eusthenopteron did have bones connecting the rear fins to the backbone, but this was true for the upper side of the body as well as the lower side. Legs developing from the upper side, as well as the lower side, would definitely not be good news for any creature.

Another promising fish fossil was collected in 1972 at a quarry in Latvia. This fish, Panderichthys, is also considered to be an important ancestor of the land animals, closer to the tetrapods than Eusthenopteron. On the positive side (from an evolutionary point of view), this fish possessed only 2 paired fins at the front end (pectoral fins) and 2 paired fins at the back end (pelvic fins) and none on the upper body. The pectoral and pelvic areas, of course, are where one would look for legs on tetrapods. In this fish however, the fins were merely fins, with no connection to the back bone. The pelvic (hind) fins in Panderichthys moreover were even less tetrapod-like than those in Eusthenopteron, which had a distinctively fish-like arrangement of fins.

As far as Panderichthys is concerned, its pelvic fins (hind end) were particularly small and weak. The front fins (pectoral) however were somewhat more robust. Indeed, scientists suggest that Panderichthys might have been able to prop itself up by its front fins and thus drag itself along in the manner of the modern walking catfish Clarias (Nature Dec. 22/29/05 p. 1147). We should note, of course, that the catfish, whatever its talents, is still a fish and nobody suggests it is developing into anything else.

Of course there is still Tiktaalik, concerning which some evolutionists claim to be so excited. The fact is however that this fish is even less promising as an ancestor of land animals than are Eusthenopteron and Panderichthys. It is true that the front fins are quite robust. Nevertheless they are still fins. The bad news however is that the backbone is very weak at the hind (pelvic) end and the pelvic fin is extremely small. The only features in which Tiktaalik seems more tetrapod-like are its breathing and feeding anatomy. In the rest of its body, it is much like Panderichthys. (Nature April 6/06 p. 748).

Thus once again we see that the similarities to the tetrapods (land animals) are in the head region. Heads do not define a 4-footed animal, the legs do. As we all know, biology is full of superficial similarities like head shape, which mean nothing.

So newspaper accounts may refer to Tiktaalik as an “evolutionary icon”, a “fishapod” and an “extinct fish with foot-like fins” which may convince some of the reality of evolution. However it is evident that this fish signifies nothing concerning the “invasion of the land.” The media and the scientific literature may portray Tiktaalik as ancestral to tetrapods, but one look at the technical literature demonstrates that this is not true.


Margaret Helder
April 2008

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