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Do Amphibian-Like Fish Necessarily Confirm Darwinian Evolution? Not at All


Recently an e-mail correspondent wrote to me, commenting on how “Evolutionists point to early amphibians with fishlike characteristics and fish with amphibian-like characteristics,” and asking if this provides some kind of special evidence for evolution. I replied by noting that sure, there are amphibians with fish-like qualities, and fish with amphibian-like qualities, known from both the fossil record and living forms.

This isn’t surprising: after all, if amphibians are designed to spend time in water, and many fish are designed to spend time out-of-water, then we might expect to see certain similarities between them. But if we claim that only “early” amphibians share similarities with fish, we might be guilty of cherry-picking evidence for evolution.

Now, a new article in Science Daily has bolstered my point. Titled “A Small Step for Lungfish, a Big Step for the Evolution of Walking,” the article states:

Extensive video analysis, published in the Proceedings of the National Academy of Sciences, reveal that the African lungfish can use its thin pelvic limbs to not only lift its body off the bottom surface but also propel itself forward. Both abilities were previously thought to originate in early tetrapods, the limbed original land-dwellers that appeared later than the lungfish’s ancestors.

In other words, living lungfish have certain walking abilities that were previously thought to be unique to the fish that allegedly led to tetrapods (i.e. 4-legged vertebrates) some 370-400 million years ago. Apparently up till now no one had taken the time to carefully study the walking abilities of lungfish:

While anecdotes and rumors circulated within the scientific community about the alleged walking behavior of these strange fish, nobody looked systematically at the biomechanics of their locomotion. An African lungfish (Protopterus annectens) kept in the laboratory of study co-author Michael Coates inspired [lead author Heather] King to study the species’ ability to walk on its unusually thin limbs.

Now obviously living “walking” lungfish in 2011 aren’t in the process of evolving into tetrapods. According to neo-Darwinian theory, that transition supposedly took place about 370 million years ago. Living lungfish are supposedly descended from lungfish that have remained lungfish for hundreds of millions of years. So again, the fact that a fish shares certain similarities with amphibians doesn’t necessarily mean it’s a direct transitional form between fish and tetrapods.

My point has nothing to do with the facile and incorrect “if we evolved from monkeys, why are there still monkeys?” argument. Rather, I’m rebutting those who cite specific similarities between fish and amphibians at specific periods as providing special evidence for evolution. Perhaps we shouldn’t mistake 370 my old fish with amphibian-like characteristics as necessarily providing some kind of special evidence of a transition between fish and amphibians.

Evolutionary paleontologist Neil Shubin, quoted in the article, spins it this way:

What we’re seeing in lungfish is a very nice example of how bottom-walking in fish living in water can easily come about in a very tetrapod-like pattern.

What we’re also seeing is a very nice example of how fish with tetrapod-like walking behavior need not have anything to do with a transition from fish to tetrapods.

Why is Neil Shubin Suddenly So Interested in Walking Lungfish?
Few scientists were previously interested in carefully investigating the walking abilities of lungfish. Why is Shubin suddenly interested in them now? Shubin’s motivation is revealed at the end of this Yahoo.com article:

These findings might also make us rethink whether recently discovered approximately 380-million-year-old tracks were in fact made by early tetrapods. They could have been created by other kinds of fish instead.

Ah, now it all makes sense. Last year on ENV we talked about how tetrapod tracks in Poland from 397 million years ago challenged Shubin’s claims (and the claims of many others) that the discovery of Tiktaalik in “rocks of just the right age” fulfilled “specific predictions” of evolutionary biology. (See here or here for those discussions.) To be more specific, the tracks implied that tetrapods lived about 20 million years before Tiktaalik, meaning that Tiktaalik‘s placement in the fossil record was no longer “just the right age” for it to be a direct transitional form between fish and amphibians.

This is why Shubin is interested now in studying lungfish to see how they might also produce walking tracks. He’s hoping to show that perhaps these Polish tracks were made by fish (and not tetrapods), and thus don’t prove tetrapods predated Tiktaalik after all. So Shubin’s motive for this research has everything to do with preserving the status of Tiktaalik — a fossil he discovered, wrote books about, and from which he won much of his fame — as a direct transitional form between fish and amphibians. It’s an ad hoc auxiliary argument intended to prevent his “specific prediction” of evolutionary biology from falling apart.

But there’s one big problem with Shubin’s new argument. When the Polish tracks were originally found, reports stated things like:

  • “They report the stunning discovery of tetrapod trackways with distinct digit imprints from Zache?mie, Poland, that are unambiguously dated to the lowermost Eifelian (397 Myr ago).” (Philippe Janvier & Gaël Clément, “Muddy tetrapod origins,” Nature, Vol. 463:40-41 (January 7, 2010) (emphasis added).)
  • “Some prints, showing individual digits, were found in limestone slabs unearthed in a quarry near Zache?mie, Poland, dated to about 395 million years ago — more than 18 million years before tetrapods were thought to have evolved.” (Rex Dalton, “Discovery pushes back date of first four-legged animal,” Nature News (January 6, 2010) (emphasis added).)
  • “The tracks were made by several individuals of a four-limbed species that had digits, or toes, on each foot, according to the research.” (John Roach, “Oldest Land-Walker Tracks Found–Pushes Back Evolution,” National Geographic (January 6, 2010) (emphasis added).)

These Polish tracks from 397 million years ago showed “distinct digit imprints” — but fish don’t have digits, tetrapods do. This inconvenient fact could make it very difficult for Shubin to explain how fish, and not tetrapods, made these specific tracks discovered in Poland from 397 mya. Seems like tetrapods might predate Tiktaalik after all.

Casey Luskin

Associate Director and Senior Fellow, Center for Science and Culture
Casey Luskin is a geologist and an attorney with graduate degrees in science and law, giving him expertise in both the scientific and legal dimensions of the debate over evolution. He earned his PhD in Geology from the University of Johannesburg, and BS and MS degrees in Earth Sciences from the University of California, San Diego, where he studied evolution extensively at both the graduate and undergraduate levels. His law degree is from the University of San Diego, where he focused his studies on First Amendment law, education law, and environmental law.



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