Creationist abuse of cuttlefish chitin

A few weeks ago, PLoS One published a paper on the observation of preserved chitin in 34 million year old cuttlebones. Now the Institute for Creation Research has twisted the science to support their belief that the earth is less than ten thousand years old. It was all so predictable. It’s a game they play, the same game they played with the soft tissue preserved in T. rex bones. Here’s how it works.

Compare the two approaches, science vs. creationism. The creationists basically insert one falsehood, generate a ludicrous conflict, and choose the dumbest of the two alternatives.

The Scientific Approach

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find traces of organic material in ancient fossils

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Cool! We have evidence of ancient biochemistry!

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Science!

The Creationist Approach

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declare it impossible for organic material to be ancient

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steal other people’s discovery of organic material in ancient fossils

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Cool! Declare that organic material must not be ancient, because of step 1, which we invented

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Throw out geology, chemistry, and physics because they say the material is old

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Profit! Souls for my Lord Arioch!

You see, the scientists are aware of the fact that organic materials degrade over time, but recognize that we don’t always know the rate of decay under all possible conditions. When we find stuff that hasn’t rotted away or been fully replaced by minerals, we’re happy because we’ve got new information about ancient organisms, and we may also be able to figure out what mechanisms promoted the preservation of the material.

The creationists start with dogma — in this case, a false statement. They declare

Chitin is a biological material found in the cuttlebones, or internal shells, of cuttlefish. It has a maximum shelf life of thousands of years…

and

Because of observed bacterial and biochemical degradation rates, researchers shouldn’t expect to find any original chitin (or any other biomolecule) in a sample that is dozens of millions of years old–and it therefore should be utterly absent from samples deposited hundreds of millions of years ago. Thus, the chitin found in these fossils refutes their millions-of-years evolutionary interpretation, just as other fossil biomolecules already have done.

But wait. How do they know that? The paper they are citing says nothing of the kind; to the contrary, it argues that while rare, other examples of preserved chitin have been described.

Detection of chitin in fossils is not frequent. There are reports of fossil chitin in pogonophora, and in insect wings from amber. Chitin has also been reported from beetles preserved in an Oligocene lacustrine deposit of Enspel, Germany and chitin-protein signatures have been found in cuticles of Pennsylvanian scorpions and Silurian eurypterids.

So the paper is actually saying that the “maximum shelf life” of chitin is several tens of millions of years. And then they go on to describe…chitin found in Oligocene cuttlefish, several tens of millions of years old. The creationists are busily setting up an imaginary conflict in the evidence, a conflict that does not exist and is fully addressed in the paper.

The creationists do try to back up their claims, inappropriately. They cite a couple of papers on crustacean taphonomy where dead lobsters were sealed up in anoxic, water- and mud-filled jars; they decayed. Then they announce that there’s only one way for these cuttlebones to be preserved, and that was by complete mineralization, and the cuttlebones in the PLoS One paper were not mineralized.

…mineralization–where tissues are replaced by minerals–is required for tissue impressions to last millions of years. And the PLoS ONE researchers verified that their cuttlebone chitin was not mineralized.

Funny, that. You can read the paper yourself. I counted 14 uses of the words “mineralized” and “demineralized”. They state over and over that they had to specifically demineralize the specimens in hydrochloric acid to expose the imbedded chitin. And of course the chitin itself hadn’t been mineralized, or it wouldn’t be chitin anymore! Did the creationists lie, or did they just not understand the paper?

The scientists also do not claim that the chitin has not been degraded over time. They actually document some specific, general properties of decay in the specimens.

β-chitin is characterized by parallel chains of chitin molecules held together with inter-chain hydrogen bonding. The OH stretching absorbance, at about 3445 cm−1 in extant chitin, is diminished in the fossil and shifted to lower wavenumbers, showing that the specimen is losing OH by an as yet undetermined mechanism. The N-H asymmetric stretching vibration is shifted to slightly lower wavenumbers, showing that it is no longer hydrogen bonding exactly as in extant specimens. Changes in the region 2800-3600 cm−1 indicate that biomolecules have been degraded via disruption of interchain hydrogen bonds.

So, yes, the creationists seem to have rather misrepresented what the paper said. Here’s another blatant example of lying about the contents of the paper.

The question they did not answer, however, is why the original organic chitin had not completely fallen apart, which it would have if the fossils with it were 34 million years old…

Actually, they did. A substantial chunk of the discussion was specifically about that question, a consideration of the factors that contributed to the preservation. It was a combination of an anoxic environment, the presence of molecules that interfered with the enzymes that break down chitin, and the structure of cuttlebone, which interleaves layers containing chitin with layers containing pre-mineralized aragonite.

In vivo inorganic-organic structure of the cuttlebone, in combination with physical and geochemical conditions within the depositional environment and favorable taphonomic factors likely contributed to preservation of organics in M. mississippiensis. Available clays within the Yazoo Clay in conjunction with suboxic depositional environment may have facilitated preservation of original organics by forming a physical and geochemical barrier to degradation. One key to the preservation of organic tissues, in particular chitin and chitosan, is cessation of bacterial degradation within environments of deposition. Bacterial breakdown of polymeric molecules is accomplished through activities of both free extracellular enzymes (those in the water column) and ektoenzymes (those on the surface of the microbial cell) such as chitinases. Chitinases function either by cleaving glycosidic bonds that bind repeating N-acetyl-D-glucosamine units within chitin molecules or by cleaving terminal N-acetyl-D-glucosamine groups. These enzymes adsorb to the surface of clay particles, which inactivates them. Strong ions in solution like iron may act in the same manner. Once bound to functional groups within these polymeric molecules, Fe2+ ions prevent specific bond configuration on the active-site cleft of specific bacterial chitinases and prevents hydrolysis, thus contributing to preservation.

Organic layers within cuttlebones are protected by mineralized layers, similar to collagen in bones, and this mineral-organic interaction may also have played a role in their preservation. Specimens of M. mississipiensis show preserved original aragonite as well as apparent original organics. These organics appear to be endogenous and not a function of exogenous fungal or microbial activity. Fungi contain the γ form of chitin not the β allomorph found in our samples. Also, SEM analyses shows there is no evidence of tunneling, microbes, or wide-spread recrystallization of the aragonite. Therefore the chitin-like molecules detected in fossil sample are most likely endogenous. Similar to collagen in bone, perhaps, organics could not be attacked by enzymes or other molecules until some inorganic matrix had been removed.

Like I always say, never ever trust a creationists’ interpretation of a science paper: they don’t understand it, and they are always filtering it through a distorting lens of biblical nonsense. They make such egregious errors of understanding that you’re always left wondering whether they are actually that stupid, or that sleazily dishonest. Or both.

But imagine if the creationists hadn’t screwed up royally in reading the paper, if they had actually found an instance of scientists being genuinely baffled by a discovery that should not be. What if there was actually good reason to believe that chitin could not last more than ten thousand years?

Then the only sensible interpretation of this observation of 34 million year old chitin would be that the prior estimation of the shelf-life of chitin was wrong, and that it could actually last tens of millions of years. What the creationists want to do is claim that that minor hypothetical is actually correct, and that instead the entirety of nuclear physics, geology, radiochemistry, and modern cosmology is wrong. On the one hand, uncertain details about the decay of one organic molecule; in the other, entire vast fields of science, already verified, and with complex modern technologies built on their operation…and which hand would the creationists reject? The trivial one, of course.

I’m leaning towards “stupid” as the explanation for their bad arguments.

Oh, after I started this dissection, I discovered someone had already beaten me to it: here’s another analysis of the creationist misinterpretations.

(Also on FtB)

Traces of a Triassic Kraken?

At first I thought this discovery was really cool, because I love the idea of ancient giant cephalopods creating art and us finding the works now. But then, reality sinks in: that’s a genuinely, flamboyantly extravagant claim, and the evidence better be really, really solid. And it’s not. It’s actually rather pathetic.

It consists of the discovery of ichthyosaur vertebrae lying in a flattened array. They look like this.

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Photo shows shonisaur vertebral disks arranged in curious linear patters with almost geometric regularity. The arranged vertebrae resemble the pattern of sucker discs on a cephalopod tentacle, with each vertebra strongly resembling a coleoid sucker.

Wait, what? That’s it?

This work was presented at a meeting of the GSA under the title “Triassic kraken: the Berlin ichthyosaur death assemblage interpreted as a giant cephalopod midden “, with this argument:

“It became very clear that something very odd was going on there,” said McMenamin. “It was a very odd configuration of bones.”

First of all, the different degrees of etching on the bones suggested that the shonisaurs were not all killed and buried at the same time. It also looked like the bones had been purposefully rearranged. That it got him thinking about a particular modern predator that is known for just this sort of intelligent manipulation of bones.

“Modern octopus will do this,” McMenamin said. What if there was an ancient, very large sort of octopus, like the kraken of mythology. “I think that these things were captured by the kraken and taken to the midden and the cephalopod would take them apart.”

In the fossil bed, some of the shonisaur vertebral disks are arranged in curious linear patterns with almost geometric regularity, McMenamin explained.The proposed Triassic kraken, which could have been the most intelligent invertebrate ever, arranged the vertebral discs in double line patterns, with individual pieces nesting in a fitted fashion as if they were part of a puzzle.

Even more creepy: The arranged vertebrae resemble the pattern of sucker discs on a cephalopod tentacle, with each vertebra strongly resembling a coleoid sucker. In other words, the vertebral disc “pavement” seen at the state park may represent the earliest known self portrait.

Let me explain something here. This “Triassic kraken” has not been found; no fossils, no remains at all, no evidence of its existence. It is postulated to have been large enough to hunt and kill ichthyosaurs, which is remarkable—comparison to modern giant squid is invalid, since they are prey, not predator. This fossil bed is being over-interpreted as a trace fossil, with the bones arranged by intent, by an intelligent cephalopod, which they have not seen. Furthermore, a line of discs is being seen as a picture of a cephalopod tentacle, classic pareidolia. This is trivial: dump a pile of Necco wafers on a table, and I’ll see a picture of squid suckers. This is a whole series of tenuous and unlikely speculations stacked together to make an ultimately ridiculous hypothesis.

After I read the abstract and realization settled in that this was nonsense, something else was nagging me. That name, McMenamin — I’d heard it somewhere before. A little search, and there it was: I’ve encountered him tangentially before. He’s the geologist who so effulgently endorsed the imaginative pattern-spotting of Stuart Pivar. He also claims “that mariners of ancient Carthage made it to America long before Eriksson and Columbus, some time around 350 BC.”

I think I would concur with the idea that Mark McMenamin is exceptionally imaginative.

(Also on FtB)

Not like a worm?

Ann Coulter is back to whining about evolution again, and this week she focuses on fossils. It’s boring predictable stuff: there are no transitional fossils, she says.

We also ought to find a colossal number of transitional organisms in the fossil record – for example, a squirrel on its way to becoming a bat, or a bear becoming a whale. (Those are actual Darwinian claims.)

Darwin postulated that whales could have evolved from bears, but he was wrong…as we now know because we found a lot of transitional fossils in whale evolution. Carl Zimmer has a summary of recent discoveries, and I wrote up a bit about the molecular genetics of whale evolution. Whales have become one of the best examples of macroevolutionary transitions in the fossil record, all in roughly the last 30 years — which gives us a minimal estimate of how out of date Ann Coulter’s sources are.

But then she writes this, which is not only wrong, but self-refuting.

To explain away the explosion of plants and animals during the Cambrian Period more than 500 million years ago, Darwiniacs asserted – without evidence – that there must have been soft-bodied creatures evolving like mad before then, but left no fossil record because of their squishy little microscopic bodies.

Then in 1984, “the dog ate our fossils” excuse collapsed, too. In a discovery the New York Times called “among the most spectacular in this century,” Chinese paleontologists discovered fossils just preceding the Cambrian era.

Despite being soft-bodied microscopic creatures – precisely the sort of animal the evolution cult claimed wouldn’t fossilize and therefore deprived them of crucial evidence – it turned out fossilization was not merely possible in the pre-Cambrian era, but positively ideal.

And yet the only thing paleontologists found there were a few worms. For 3 billion years, nothing but bacteria and worms, and then suddenly nearly all the phyla of animal life appeared within a narrow band of 5 million to 10 million years.

It’s so weird to read that: yes, people have been predicting that the precursors to the Cambrian fauna would have been small and soft-bodied (what else would you expect), and that they would be difficult to fossilize…but not impossible, and further, scientists have been out finding these fossils. Somehow this is a refutation of evolution? What we’re seeing is exactly what evolution predicted!

What we have is a good record of small shelly fossils and trace fossils from the pre-Cambrian — before there were fully armored trilobites, there were arthropod-like creatures with partial armor that decayed into scattered small fragments of shell after death, and before that there were entirely soft-bodied, unarmored creatures that left only trackways and burrows. Even in this period Coulter wants to call abrupt, we find evidence of gradual transitions in animal forms.

And then to claim that there is an absence of transitional forms because all that was found were worms! Um, if you take an animal with an armored exoskeleton or bones, and you catch it before the hard skeleton had evolved, exactly what do you think it would look like? Like a worm.

As evolution predicted. As the evidence shows.

I can’t even guess what Ann Coulter was expecting a pre-Cambrian animal to look like. Not like a worm, apparently…but like what?

(Also on FtB)

Bacterial fossil doubts resolved

I raised a few questions about those 3.4 billion year old bacterial fossils, primarily that I was bugged by the large size and that they cited a discredited source to say that they were in the appropriate range of diameters for bacteria. Now my questions have been answered by Chris Nedin, and I’m satisfied. In particular, he shows data from 0.8 and 1.9 billion year old fossils in which the bacterial sizes are in the same range. It’s also a good review of the other evidence used to infer that they actually are bacterial microfossils.

(Also on FtB)

A questions about those ancient bacterial fossils…

Both Jerry Coyne and Larry Moran have good write-ups on the recent discovery of what are purportedly the oldest fossil cells, at 3.4 billion years old. I just have to add one little comment: a small, niggling doubt and something that bugs me about them. All the smart guys are impressed with this paper, but this one little thing gives me pause.

I’m a microscopist — I look at micrographs all the time, and one of the things I always mentally do is place the size of things in context. And I was looking at the micrographs of these fossils, and what jumped out at me is how large they are. They’re not impossibly large, they’re just well out of the range I expect for prokaryotes.

Most prokaryotes have diameters in the range of 1-10µm, while typical eukaryotes are about 10 times that size. There are exceptions: Thiomargarita gets up to 500µm across, so like I say, there’s nothing impossible about these cells, it’s just that the micrographs show lots of cells with 10-30µm diameters. And the authors come right out and report that:

The size range is also typical of such assemblages, with small spheres and ellipsoids 5-25 µm in diameter, rare examples (<10) of larger cellular envelopes up to 80 µm in diameter, and tubes 7-20 µm across (see ref. 24).

How odd. When I poke into the nervous system of an embryonic insect or fish, those are the sizes of cells I often see (well, except there aren’t many tubes of that size!). When I poke into a culture or embryo contaminated with bacteria, they’re much, much smaller. So maybe paleoarchaean bacteria tended to be larger? And they do cite a source for that size range of prokaryotes…

Then here’s a new problem: the source cited, ref. 24, is the Schopf paper, the older paper that claimed to have found ancient bacterial fossils, a claim that has since been discredited! Uh-oh. What they’re calling “typical of such assemblages” is a data set that’s widely considered artifactual now. Furthermore, that’s a simplified version of what Schopf said — he actually broke the sizes down into categories, and the range was more like 1-30 µm.

  • Very small solitary, paired or clustered rods (ca 0.75 µm broad, ca 1.5 µm long), inferred to be prokaryotic (bacterial) unicells: one unit (ca 2600 Myr old), one morphotype.
  • Small, solitary, paired or clustered coccoids (average diameter ca 3 µm, range ca 2-5 µm), inferred to be prokaryotic (bacterial, perhaps cyanobacterial) unicells: three units (range 3320-2600 Myr old), three morphotypes.
  • Large solitary or colonial coccoids (average diameter ca 13 µm, range ca 5-23 µm), inferred to be prokaryotic (bacterial, perhaps cyanobacterial) unicells: three units (range 3388-2560 Myr old), four morphotypes.
  • Narrow unbranched sinuous filaments (average diameter ca 1.25 µm, range ca 0.2-3 µm), with or without discernable septations, inferred to be prokaryotic (bacterial, perhaps cyanobacterial) cellular trichomes and/or trichome-encompassing sheaths: 10 units (range 3496-2560 Myr old), 17 morphotypes.
  • Broad unbranched septate filaments (average diameter ca 8 µm, range ca 2-19.5 µm), inferred to be prokaryotic (perhaps cyanobacterial) cellular trichomes: four units (range 3496-2723 Myr old), 10 morphotypes.
  • Broad unbranched tubular or partially flattened cylinders (average diameter ca 13 µm, range ca 3-28 µm), inferred to be prokaryotic (perhaps cyanobacterial) trichome-encompassing sheaths: five units (range 3496-2516 Myr old), five morphotypes (e.g. figures 3a-e and 4l).

So Schopf was reporting larger cells in his older samples, and now Wacey et al. are describing what look like very large cells to me in their 3.4 billion year old rocks. I’m not a microbiologist so I could be way off on this, but…isn’t this just a little bit strange? Maybe there are some micro people out there who can reassure me that this isn’t a surprising result.

Wacey D, Kilburn MR, Saudners M, Cliff J, and Brasier MD (2011) Microfossils of sulphur-metabolizing cells in 3.4-billion-year-old rocks of Western Australia. Nature Geoscience Published online Aug. 21, 20110 [doi:10.1038/ngeo1238]

(Also on FtB)

Magnificent momma

This is one beautiful plesiosaur, Polycotylus latippinus.

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(Click for larger image)
(A) Photograph and (B) interpretive drawing of LACM 129639, as mounted. Adult elements are light brown, embryonic material is dark brown, and reconstructed bones are white. lc indicates left coracoid; lf, left femur; lh, left humerus; li, left ischium; lp, left pubis; rc, right coracoid; rf, right femur; rh, right humerus; ri, right ischium; and rp, right pubis.

The unique aspect of this specimen is that it’s the only pregnant plesiosaur found; the fore and hind limbs bracket a jumble of bones from a juvenile or embryonic Polycotylus. It’s thought to actually be a fetal plesiosaur, rather than an overstuffed cannibal plesiosaur, because 1) the smaller skeleton is still partially articulated, and it’s large enough that it is unlikely it could have been swallowed whole, 2) the two sets are of the same distinctive species, 3) the juvenile is incompletely ossified and doesn’t resemble a post-partum animal, 4) the bones aren’t chewed, etched by acids, or accompanied by gastroliths. I think we can now confidently say that plesiosaurs were viviparous, which is what everyone expected.

There are other surprising details. The fetus is huge relative to the parent, and there’s only one — so plesiosaurs had small brood sizes and invested heavily in their offspring.

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(Click for larger image)
Reconstructions of female P. latippinus and newborn young. Gastralia were present in both animals but have been omitted for clarity.

The authors speculate beyond this a bit, but it’s all reasonable speculation. That degree of parental investment in fetal development makes it likely that there would have been extended maternal care after birth, and rather more tenuously, that they may also have lived in larger social groups. The authors suggest that their lifestyle may have resembled that of modern social marine mammals — picture a pod of dolphins, only long-necked and lizardy.

O’Keefe FR, Chiappe LM (2011) Viviparity and K-Selected Life History in a Mesozoic Marine Plesiosaur (Reptilia, Sauropterygia) Science 333 (6044): 870-873.

(Also on FtB)

Xiaotingia zhengi

A lovely new dinosaur fossil from China is described in Nature today: it’s named Xiaotingia zhengi, and it was a small chicken-sized, feathered, Archaeopteryx-like beast that lived about 155 million years ago. It shares some features with Archaeopteryx, and also with some other feathered dinosaurs.

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(Click for larger image)
a, b, Photograph (a) and line drawing (b). Integumentary structures in b are coloured grey. cav, caudal vertebra; cv, cervical vertebra; dv, dorsal vertebra; fu, furcula; lc, left coracoid; lfe, left femur; lh, left humerus; li, left ilium; lis, left ischium; lm, left manus; lp, left pes; lpu, left pubis; lr, left radius; ls, left scapula; lu, left ulna; md, mandible; rfe, right femur; rfi, right fibula; rh, right humerus; ri, right ilium; rm, right manus; rr, right radius; rt, right tibiotarsus; ru, right ulna; sk, skull; ss, synsacrum.

Now here’s why this particular fossil has some paleontologists in a dither. Systematics uses a set of objective, computer-based tools to objectively build phylogenetic trees: you plug a set of character parameters for a set of organisms into it, and it analyzes them and determines the most likely or most parsimonious tree to describe their relationships. Plugging in data from modern birds, Archaeopteryx, and dromeosaurs, for instance, generates trees in which Archaeopteryx clusters with the birds, and not the dromeosaurs. Archaeopteryx was not a direct ancestor of modern birds, but was thought to be related to the basal avians — so it was a kind of close cousin.

When Xiaotingia‘s data is tossed into the calculation, though, the results change. Xiaotingia doesn’t cluster so tightly with birds; it’s a more distant relative. However, Archaeopteryx shares enough significant features with Xiaotingia that they now cluster together, pulling Archaeopteryx out of the basal Aves and into a new classification. It says that Archaeopteryx is now a kind of second cousin, a little less closely related to the birds than previously thought.

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Archaeopteryx has historically been regarded as the most basal bird (avialan), but the discovery of the closely related Xiaotingia led Xu et al.1 to pull these archaeopterygids out of avialans (birds) and into deinonychosaurs along with dromaeosaurids and troodontids. This new grouping better accounts for the evolution of feeding strategies among bird-like dinosaurs. Previous research suggested that herbivory was common among this group, as reflected in the tall, boxy skulls of oviraptorosaurs and basal avialans such as Epidexipteryx. The triangular, sharp-toothed skull of Archaeopteryx was incongruous among basal avialans, but fits better among the carnivorous dromaeosaurids and troodontids.

I have to say that I think it’s extremely cool that we have a new fossil from down around the roots of the bird family tree, and it does sharpen our knowledge of what was going on down there in the middle and late Jurassic. There was a whole assortment of delicate-boned, feathered, bipedal dinosaurs that were flourishing and diversifying in that window of time, and we’ve now got enough data that we can distinguish details in the family tree, which is absolutely fabulous.

However, a lot of the fuss over the specimen as somehow radically changing the importance of Archaeopteryx is a bit overblown. The relative status of Archaeopteryx and Xiaotingia is a bit of taxonomic detail — important details in working out the specific history of life — but it’s the equivalent of deciding that a fossil belongs in one pigeonhole rather than the pigeonhole next to it. Its shift in status means that there’s a bigger gap in the early history of the true birds than we thought, and it also means that there was a greater diversity of bird-like forms than we expected in the Jurassic. One other suggestion is that removing the carnivorous Archaeopteryx from the base of the bird family tree opens up the possibility that modern birds might have descended from the vegetarian side of the family — if the last common ancestor of birds was an herbivore, that has interesting implications for the paths evolution took.

But don’t worry, Archaeopteryx still represents a beautiful example of a transitional form. This new fossil is just another transitional form discovered. Creationists cannot take any consolation from it: Archaeopteryx isn’t suddenly gone, it’s become a part of a richer picture of bird evolution.

Xu X,
You H,
Du K
Han F (2011) An Archaeopteryx-like theropod from China and the origin of Avialae. Nature 475, 465-470.

The greatest science paper ever published in the history of humankind

That’s not hyperbole. I really mean it. How else could I react when I open up the latest issue of Bioessays, and see this: Cephalopod origin and evolution: A congruent picture emerging from fossils, development and molecules. Just from the title alone, I’m immediately launched into my happy place: sitting on a rocky beach on the Pacific Northwest coast, enjoying the sea breeze while the my wife serves me a big platter of bacon, and the cannula in my hypothalamus slowly drips a potent cocktail of cocain and ecstasy direct into my pleasure centers…and there’s pie for dessert. It’s like the authors know me and sat down to concoct a title where every word would push my buttons.

The content is pretty good, too. It’s not perfect; the development part is a little thin, consisting mainly of basic comparative embryology of body plans, with nothing at all really about deployment of and interactions between significant developmental genes. But that’s OK. It’s in the nature of the Greatest Science Papers Ever Written that stuff will have to be revised and some will be shown wrong next month, and next year there will be more Greatest Science Papers Ever Written — it’s part of the dynamic. But I’ll let it be known, now that apparently the scientific community is aware of my obsessions and is pandering to them, that the next instantiation needs more developmental epistasis and some in situs.

This paper, though, is a nice summary of the emerging picture of cephalopod evolution, as determined by the disciplines of paleontology, comparative embryology, and molecular phylogenetics, and that summary is internally consistent and is generating a good rough outline of the story. And here is that story, as determined by a combination of fossils, molecular evidence, and comparative anatomy and embryology.

Cephalopods evolved from monoplacophoran-like ancestors in the Cambrian, about 530 million years ago. Monoplacophorans are simple, limpet-like molluscs; they crawl about on the bottom of the ocean under a cap-like shell, foraging snail-like on a muscular foot. The early cephalopods modified this body plan to rise up off the bottom and become more active: the flattened shell elongated to become a cone-like structure, housing chambers for bouyancy. Movement was no longer by creeping, but used muscular contractions through a siphon to propel the animal horizontally. Freed from its locomotor function, the foot expanded into manipulating tentacles.

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These early cephalopods, which have shells common in the fossil record, would have spent their lives bobbing vertically in the water column, bouyed by their shells, and with their tentacles dangling downward to capture prey. They wouldn’t have been particularly mobile — that form of a cone hanging vertically in the water isn’t particularly well-streamlined for horizontal motion — so the next big innovation was a rotation of the body axis, swiveling the body axis 90° to turn a cone into a torpedo. There is evidence that many species did this independently.

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The tilting of the body axes of extant cephalopods. This was a result of a polyphyletic and repeated trend towards enhanced manoeuverability. The morphological body axes (anterior-posterior, dorso-ventral) are tilted perpendicularly against functional axes in the transition towards extant cephalopods.

We can still see vestiges of this rotation in cephalopod embryology. If you look at early embryos of cephalopods (at the bottom of the diagram below), you see the same pattern: they are roughly disc-shaped, with a shell gland on top and a ring of tentacle buds on the bottom. They subsequently extend and elongage along the embryonic dorsal-ventral axis, which becomes the anterior-posterior axis in the adult.

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In extant cephalopods the body axes of the adult stages are tilted perpendicularly versus embryonic stages. As a con- sequence, the morphological anterior-posterior body axis between mouth and anus and the dorso-ventral axis, which is marked by a dorsal shell field, is tilted 908 in the vertical direction in the adult cephalopod. Median section of A: Nautilus, B: Sepia showing the relative position of major organs (Drawings by Brian Roach). C: shared embryonic features in embryos of Nautilus (Nautiloidea) and Idiosepius (Coleoidea) (simplified from Shigeno et al. 2008 [23] Fig. 8). Orientation of the morphological body axes is marked with a compass icon (a, anterior; d, dorsal; p, posterior; v, ventral; dgl, digestive gland; gon, gonad; ngl, nidamental gland).

The next division of the cephalopods occurred in the Silurian/Devonian, about 416 million years ago, and it involved those shells. Shells are great armor, and in the cephalopods were also an organ of bouyancy, but they also greatly limit mobility. At that early Devonian boundary, we see the split into the two groups of extant cephalopods. Some retained the armored shells; those are the nautiloids. Others reduced the shell, internalizing it or even getting rid of it altogether; those are the coleoids, the most successful modern group, which includes the squids, cuttlefish, and octopuses. Presumably, one of the driving forces behind the evolution of the coleoids was competition from that other group of big metazoans, the fish.

The nautiloids…well, the nautiloids weren’t so successful, evolutionarily speaking. Only one genus, Nautilus has survived to the modern day, and all the others followed the stem-group cephalopods into extinction.

The coleoids, on the other hand, have done relatively well. The number of species have fluctuated over time, but currently there are about 800 known species, which is respectable. The fish have clearly done better, with about 30,000 extant species, but that could change — there are signs that cephalopods have been thriving a little better recently in an era of global warming and acute overfishing, so we humans may have been giving mobile molluscs a bit of a tentacle up in the long evolutionary competition.

There was another major event in coleoid history. During the Permian, about 276 million years ago, there was a major radiation event, with many new species flourishing. In particular, there was another split: between the Decabrachia, the ten-armed familiar squid, and the Vampyropoda, a group that includes the eight-armed octopus, the cirroctopodes, and Vampyroteuthis infernalis. The Vampyropoda have had another locomotor shift, away from rapid jet-propelled movement to emphasizing their fins for movement, or in the case of the benthic octopus, increasing their flexibility to allow movement through complex environments like the rocky bottom.

Time for the big picture. Here’s the tree of cephalopod evolution, using dates derived from a combination of the available fossil evidence and primarily molecular clocks. The drawings illustrate the shell shape, or in the case of the coleoids, the shape of the internal shell, or gladius, if they have one.

i-205e51c0850d23812a20e3bd6bf7010f-ceph_lineage-thumb-500x631-67114.jpeg
A molecularly calibrated time-tree of cephalopod evolution. Nodes marked in blue are molecular divergence estimates (see methods in Supplemental Material). The divergence of Spirula from other decabrachiates are from Warnke et al. [43], the remaining divergences are from analyses presented in this paper. Bold lineages indicate the fossil record of extant lineages, stippled lines are tentative relationships between modern coleoids, partly based on previous studies [41, 76, 82] and fossil relationships are based on current consensus and hypoth- eses presented herein. Shells of stem group cephalopods and Spirula in lateral view with functional anterior left. Shells of coleoids in ventral view with anterior down. The Mesozoic divergence of coleoids is relatively poorly resolved compared to the rapid evolution of Cambro- Ordovician stem group cephalopods. Many stem group cephalopod orders not discussed in the text are excluded from the diagram.

The story and the multiple lines of evidence hang together beautifully to make a robust picture of cephalopod evolution. The authors do mention one exception: Nectocaris. Nectocaris is a Cambrian organism that looks a bit like a two-tentacled, finned squid, which doesn’t fit at all into this view of coleoids evolving relatively late. The authors looked at it carefully, and invest a substantial part of the review discussing this problematic species, and decided on the basis of the morphology of its gut and of the putative siphon that there is simply no way the little beast could be ancestral to any cephalopods: it’s a distantly related lophotrochozoan with some morphological convergence. It’s internal bits simply aren’t oriented in the same way as would fit the cephalopod body plan.

So that’s the state of cephalopod evolution today. I shall be looking forward to the Next Great Paper, and in particular, I want to see more about the molecular biology of tentacles — that’s where the insights about the transition from monoplacophoran to cephalopod will come from, I suspect.

Kröger B, Vinther J, Fuchs D (2011) Cephalopod origin and evolution: A congruent picture emerging from fossils, development and molecules: Extant cephalopods are younger than previously realised and were under major selection to become agile, shell-less predators. Bioessays doi: 10.1002/bies.201100001.

Turnabout is fair play

Phil Senter has published the most deviously underhanded, sneaky, subtle undermining of the creationist position I’ve ever seen, and I applaud him for it. What he did was to take them seriously, something I could never do, and treat their various publications that ape the form of the scientific literature as if they actually were real science papers, and apply their methods consistently to an analysis of taxonomy. So on the one hand, it’s bizarre and disturbing to see the like of Ken Ham, Jerry Bergman, and Henry Morris get actual scientific citations, but on the other hand, seeing their claims refuted using their own touted methods is peculiarly satisfying.

Senter has published a paper in the Journal of Evolutionary Biology that takes their claims at face value and analyzes dinosaur morphology using their own methods. ‘Baraminologists’ have published a set of taxonomic tools that use as input a matrix of morphological characters for an array of animals, and then spits out numbers that tell whether they were similar enough to be related. You can guess what the motivation for that is: they want to claim that Noah didn’t have to carry representatives of every dinosaur species on the Ark, but only representatives of each ‘kind’, which then diversified rapidly after the big boat landed to generate all the different species found in the fossil record.

The problem for them is that Senter found that it works far too well. Using creationist techniques, all of the Dinosauria reduce to…eight kinds. That makes the boat haulage problem relatively even easier.

Here is the summary diagram, illustrating the derived creationist tree of common descent. Oops.

i-cf7aed20267bbf27bd8d0565d5df2681-creationisttree.jpeg
Summary of results of taxon correlation analyses across Dinosauria. Each boxed group of silhouettes indicates a group for which taxon correlation found within-group morphological continuity; for silhouette groups in different boxes, taxon correlation found morphological discontinuity between the groups. Dotted lines represent uncertainty as to whether morphological discontinuity is truly present. On the cladogram, triangles indicate paraphyletic groups.

At first, the results of the taxon correlation analyses appear to imply good news for the creationist world view, on several fronts. First, seven major dinosaurian groups (birdlike coelurosaurs, Tazoudasaurus + Eusauropoda, Stegosauria, Ankylosauridae, Neoceratopsia, Hadrosauridae and basal Hadrosauriformes) are separated from the rest of Dinosauria by morphological gaps (Fig. 15). Creationist inferences that variety within Eusauropoda (Morris, 1999) and Ceratopsidae (Ham, 2009) represent diversification within separately created kinds are congruent with these results. Second, each morphologically continuous group found by taxon correlation includes at least some herbivores. This is congruent with the creationist assertion that all carnivorous animals are descendants of originally herbivorous ancestors (Unfred, 1990; Gish, 1992; Ham, 1998, 2006, 2009; Larsen, 2001; McIntosh & Hodge, 2006). Third, although creationists have answered the problem of room on Noah’s ark for multiple pairs of gigantic dinosaurs by asserting that only about 50 ‘created kinds’ of dinosaurs existed (Ham, 1998, 2001, 2006, 2009; Morris, 1999), the problem is solved even better by the results of this study, in which only eight dinosaur ‘kinds’ are found.

Awww. I guess I’m going to have to become a creationist, now that the evidence shows that dinosaurs are related by common descent…oh, hey, wait. Isn’t that what evolution says? And isn’t that easier to accommodate within the idea that they did this over millions of years, rather than the freakishly unrealistic hyper-speciation within a few thousand years that the creationists insist on?

However, a second look reveals that these results are at odds with the creationist view. Whether there were eight dinosaur ‘kinds’ or 50, the diversity within each ‘kind’ is enormous. Acceptance that such diversity arose by natural means in only a few thousand years therefore stretches the imagination. The largest dinosaurian baramin recovered by this study includes Euparkeria, basal ornithodirans (Silesaurus and Marasuchus), basal saurischians, basal ornithischians, basal sauropodomorphs, basal thyreophorans, nodosaurid ankylosaurs, pachycephalosaurs, basal ceratopsians, basal ornithopods and all but the most birdlike theropods in an unbroken spectrum of morphological continuity. The creationist viewpoint allows for diversification within baramins, but the diversity within this morphologically continuous group is extreme. Also, the inclusion of the Middle Triassic non-dinosaurs Euparkeria and Marasuchus within the group is at odds with the creationist claim that fossil representatives of the predinosaurian, ancestral stock from which dinosaurs arose have never been found (DeYoung, 2000; Ham, 2006; Bergman, 2009).

So, effectively, these results, made using the creationists own tools, demonstrate a genetic relationship between a diverse group of animals that evolution predicted, and confronts young earth creationists with the problem of a kind of frantically prolific speciation that is unimaginably rapid. If species are that fluid and can change that rapidly, their own claims of fixity of species are patently wrong.

The final word:

The results of this study indicate that transitional fossils linking at least four major dinosaurian groups to the rest of Dinosauria are yet to be found. Possibly, some creationist authors will hail this finding as evidence of special creation for those four groups. However, such enthusiasm should be tempered by the finding here that the rest of Dinosauria–including basal members of all major lineages–are joined in a continuous morphological spectrum. This confirms the genetic relatedness of a very broad taxonomic collection of animals, as evolutionary theory predicts, ironically by means of a measure endorsed and used by creation science.

This is so wonderfully, evilly devious. Superficially, it seems to support creationist methods—but what it actually is is a grand reductio ad absurdam. Laugh wickedly at it now, but laugh even harder when you see creationists citing this paper in the future, as you know they will.

Senter P (2011) Using creation science to demonstrate evolution 2: morphological continuity within Dinosauria. J Evol Biol. doi: 10.1111/j.1420-9101.2011.02349.x.