A fish, a rabbit -- same thing, to a creationist

JBS Haldane is said to have responded to a question about how evolution could be disproved by saying, "A Precambrian rabbit". What was meant by this, of course, is any substantial discovery that greatly disrupted the evidence for the chronological pattern of descent observed in Earth's life. That pattern of descent is one of the central lines of evidence for evolution, so creationists would dearly love to find something that wrecked it -- this is why they send expeditions to Africa to find a living dinosaur, Mok'ele-mbembe, or more conveniently, to Canada in search of a plesiosaur, Manipogo.

The Discovery Institute has it easy. They don't mount expeditions, they just sit around, read scientific papers, and misinterpret them. Their latest abuse is to claim to have discovered the equivalent of a Precambrian rabbit.

A vertebrate swimming fish with camera eyes, blood vessels, digestive system, muscular swimming, and gills in the Lower Cambrian: for Darwinists, it should hardly be more surprising to find than a Precambrian rabbit.

Only it's not in the Precambrian, it's Cambrian. And it's not a mammal, it's a very primitive fish, unlike anything extant. Is anyone surprised to find ancient fish-like creatures in the Cambrian? Anyone who has been paying the slightest attention to publications about the fossils of the Burgess Shale or the Chengjian fauna in the last century?

Here's a reconstruction of the animal that Conway Morris and Caron analyzed in a recent issue of Nature. It's called Metaspriggina.

Just for comparison, here's Pikaia, a familiar chordate (although it's classification is somewhat controversial) from the Cambrian. The fossil was first described in 1911.

Here's another Cambrian beast, Haikouichthys, described in 2002.

Here is a rabbit.

One of these things is not like the others. Which one would surprise you, boys and girls, if it were found swimming in the shallow, silty seas beneath the relatively hypoxic skies of planet Earth, 500 million years ago? Which ones look similar, as if they are related, yet don't look like any modern organisms?

If you can answer those two questions, you're smarter than a creationist. There is no prize, I'm afraid that's a rather low bar to hurdle.

What also surprises is how much the Discovery Institute press release mangles the story. For instance, they want to claim that it is more advanced than modern forms.

All these traits show that Metaspriggina was not a primitive chordate intermediate to lampreys or other extinct Cambrian swimmers, but was in fact more "derived" (advanced) in some respects than some of the alleged descendants.

They then quote a section of an article that explains that lampreys have derived structures -- that their branchial anatomy is extensively specialized. What Conway Morris and Caron actually say in the paper is the opposite -- that Metaspriggina had primitive or ancestral branchial structures, that they possessed two-part bars in their branchial arches, which was the ancestral condition.

A striking feature is the branchial area with an array of bipartite bars. Apart from the anterior-most bar, which appears to be slightly thicker, each is associated with externally located gills, possibly housed in pouches. Phylogenetic analysis places Metaspriggina as a basal vertebrate, apparently close to the Chengjiang taxa Haikouichthys and Myllokunmingia, demonstrating also that this primitive group of fish was cosmopolitan during Lower–Middle Cambrian times (Series 2–3). However, the arrangement of the branchial region in Metaspriggina has wider implications for reconstructing the morphology of the primitive vetebrate. Each bipartite bar is identified as being respectively equivalent to an epibranchial and ceratobranchial. This configuration suggests that a bipartite arrangement is primitive and reinforces the view that the branchial basket of lampreys is probably derived.

Notice that Conway Morris and Caron have identified Metaspriggina as a "basal vertebrate", and that they note it's affinities to other Cambrian forms. This is not a fish out of water; there is no evolution defying anachronism here.

The creationists even comment on the cladogram included in the paper, rather obliviously. Do they even realize that this diagram places Metaspriggina in an evolutionary context, and that it is clearly an intermediate form, more advanced than Pikaia, comparable to its rough contemporary Haikouichthys, and less derived than lampreys?

Cladogram with backbone constraint for cyclostome monophyly, and using rescaled consistency indices, showing the position of Metaspriggina as part of basal stem-group soft-bodied vertebrates. The origin and potential loss of key vertebrate structures is indicated.

Seriously, what part of "basal stem-group soft-bodied vertebrate" did they fail to comprehend? Metaspriggina is an unsurprising resident of the Cambrian era…and no rabbit at all.

Morris SC, Caron JB2 (2014) A primitive fish from the Cambrian of North America. Nature 512(7515):419-22.