(Jasper is out! It's time for a paddlin'! This post is in two sections. Recognizing the potential for it to drag on into lengthy details and scare readers away, I have chosen to put the main points up front and add a supplementary section at the end for those of you who are interested in some of the additional details of biology related to this post)
Dr. David Menton of Answers in Genesis has written the latest reaction to Tiktaalik roseae. Interestingly, the article makes almost no reference to the Tiktaalik fossils themselves, except where facts are made up.
In the article, Menton's only claims about the anatomy of Tiktaalik relate to the pelvic fins and girdles (i.e. the hips and legs) of Tiktaalik. There is no disucssion of the skull or shoulder girdle, and only tacit reference to the fin skeleton. Menton explains in relation to fishes and tetrapods that:
[t]he hind limbs [of tetrapods] in particular have a robust pelvic girdle securely attached to the vertebral column. This differs radically from that of any fish including Tiktaalik. Essentially all fish (including Tiktaalik) have small pelvic fins relative to their pectoral fins.Menton is a liar. He cannot possibly know anything about the pelvic fins of Tiktaalik. The two papers describing Tiktaalik offer absolutely no descriptions of the pelvic fin skeletons or girdle. I've seen the material first-hand and there are no such details of the pelvic fin.
I took the time to go one step further. I emailed Ted Daeschler (of Colbert Report fame) who is one of the authors of the papers to drive this point home. Here's his reply which I got this morning [emphasis added]:
Regarding Tiktaalik pelvic fins . . . no pelvic fin material has been reported. Less for him to misrepresent!I know this is like taking a whizz in the ocean, but chalk up another lie for AiG.
The article is replete with misinformation, and I will only take up a few of them here. There is a "supplement" below for those who are interested in the finer details of biology or the particularly vapid claims that Menton makes. The article has some subtle ways of using definitions as though they were arguments. For instance, Menton claims that "no fish (including Tiktaalik) has true finger or toe bones." This is a "truth by definition". Tetrapods, by definition, have digited limbs. In other words, only tetrapods have true finger or toe bones by definition. If it has fingers, it ain't a fish! Menton's claim isn't even an argument, but it sure is misleading.
Edited to add. It gets worse and I can't believe I forgot to add it. Nevermind the rhetoric, Menton (who is an anatomy professor! states: "Finally, no fish (including Tiktaalik) has true finger or toe bones. Instead, fish have slender bony fin rays, which even evolutionists concede are not homologous or related in any way to digits". Rays are not in the place of digits. Rays are dermal bone, they develop in the skin like scales and skull bones. Thus, they are in the skin and form a "sandwich" over the internal, or endochonrdral/cartilage, skeleton. Digits are part of this internal skeleton. You cannot have "rays instead of digits". You may have one and not the other, but neither takes the other's anatomical place. Coming from an anatomist, this statement demonstrates first-rate incompetence. Tiktaalik does have jointed radials, a feature which is typically only in lobe-finned fishes. These are endochondral bones. Whether or not they are homologous to digits is a question of ongoing investigation which will require more fossils and involves gene expression work in lungishes.End of edit
The real problem is not even whether or not Tiktaalik has a tetrapod-like pelvic girdle. It's that Menton's attempt to discredit the claims of the authors is based on listing the fish-like aspects of Tiktaalik and ignoring the tetrapod-like aspects. An animal that is a fish-tetrapod transitional would be expected to have some properties of a fish, no?
Menton's use of quotations is also appallingly dishonest. In a section titled "So Is Tiktaalik a Missing Link?", he quotes the News and Views article by Ahlberg and Clack and states that it concedes a point he is trying to make.
In their review article on Tiktaalik, Ahlberg and Clack (Nature 440(7085):747–749) tell us that “the concept of ‘missing links’ has a powerful grasp on the imagination: the rare transitional fossils that apparently capture the origins of major groups of organisms are uniquely evocative.” The authors concede that the whole concept of “missing links” has been loaded with “unfounded notions of evolutionary ‘progress’ and with a mistaken emphasis on the single intermediate fossil as the key to understanding evolutionary transition.”But the whole quote reveals that Menton's own choice of word's ("missing link") is a loaded question (a particularly dishonest rhetorical trick such as asking somebody "Have you stopped beating your wife yet?").
The concept of 'missing links' has a powerful grasp on the imagination: the rare transitional fossils that apparently capture the origins of major groups of organisms are uniquely evocative. But the concept has become freighted with unfounded notions of evolutionary 'progress' and with a mistaken emphasis on the single intermediate fossil as the key to understanding evolutionary transitions. Much of the importance of transitional fossils actually lies in how they resemble and differ from their nearest neighbours in the phylogenetic tree, and in the picture of change that emerges from this pattern.Ahlberg and Clack were saying nothing like Menton's implication.
What I don't understand is why this article had to be written by a professor of anatomy. There is no cogent discussion of anatomy that is relevant to the issue of Tiktaalik. There's a heck of a lot of really bad zoology (see the supplementary section), but not even a discussion of the anatomy of of Tiktaalik. Instead, the attack is a shameful distortion of definitions, quote mining, and outright lies. To give you an impression of what Ahlberg and Clack actually think about Tiktaalik here is the figure from their article. Compare especially the skull roofs along the left-hand side of the figure, an aspect which Menton completely ignores.
Figure caption: The lineage leading to modern tetrapods includes several fossil animals that form a morphological bridge between fishes and tetrapods. Five of the most completely known are the osteolepiform Eusthenopteron16; the transitional forms Panderichthys17 and Tiktaalik1; and the primitive tetrapods Acanthostega and Ichthyostega. The vertebral column of Panderichthys is poorly known and not shown. The skull roofs (left) show the loss of the gill cover (blue), reduction in size of the postparietal bones (green) and gradual reshaping of the skull. The transitional zone (red) bounded by Panderichthys and Tiktaalik can now be characterized in detail. These drawings are not to scale, but all animals are between 75 cm and 1.5 m in length. They are all Middle–Late Devonian in age, ranging from 385 million years (Panderichthys) to 365 million years (Acanthostega, Ichthyostega). The Devonian–Carboniferous boundary is dated to 359 million years ago18.
I suspect I know why this article was written and where these comments stem from. When Tiktaalik was first reported in Nature nearly a year prior to this writing, Answers in Genesis published a screed co-authored by Menton. In response, I called out the authors for botching Vertebrate Anatomy 101. They seem to be clarifying their mistake, but I already covered that base:
On the other hand, if they're talking about the pelvic limbs, then Menton and Looy are just blowing smoke, because there is no report on the pelvic girdle here.The problem that the creationists are facing here, and what Menton's reaction is symptomatic of, is that fossils like Tiktaalik are stunningly beautiful, articulated, their implications immediately obvious even at a glance, and information about them can be disseminated widely through the world wide web. Anybody with a computer can get high-res pictures of Tikaalik and see it for themselves. In response, big-money creationists like AiG have to go through extraordinary rhetorical acrobatics to keep fleecing the flock.
Here I outline some detailed responses to claims in Menton's article but aren't necessarily related to Tiktaalik.
Part I: Fish breathing and circulation
Menton briefly discusses a number of teleost fishes that have specialized types of air breathing: mudskippers and climbing perch. Teleosts are ray-finned fishes and to put things in creationists terms: "Evolutionists" believe that all ray-finned fishes are more closely related to than they are to tetrapods. In other words, they form a clade. Conversely, there are lobe-finned or sarcopterygian fishes which "evolutionists" believe are closer to tetrapods than they are to any other fishes. Thus, they are said to form a clade with tetrapods. (Digression: It makes sense that Tikaalik is a bona fide lobe-finned fish. If it had been a teleost, that would have been a problem.) In discssing air-breathing teleosts, Menton concludes:
none of these curious fish are considered by evolutionists to be ancestors of tetrapods—they are simply interesting and specialized fish.Isn't there a glaring omission here? Has Menton not heard of lungfishes? Lungfishes are, indeed, sarcopterygian fishes. They breathe air (hence lungfishes). In fact, not only do they breath air, but their circulatory system is connected to their lung in the same way as it is in amphibians. A review of vertebrate circulatory systems can be found here, and a particular reference to the lungfishes can be found here.
Here's a little review. Vertebrates have two main types of circulation: single and double (or undivided and divided). Fishes have the single (undivided) system, and the heart is relatively simple: it's basically a muscular series of chambers. Blood is pumped through the gills where it is oxygenated and passed through the body, collected back to a major vein (common cardinal vein) and delivered back to the heart. Repeat. In tetrapods, it gets complicated where the system is double or divided. In reptiles, birds, and mammals, the blood is first sent to the lungs where it is oxygenated, then back to the heart where it goes out to the body and back. Repeat.
Amphibians and lungfishes have a system that is somewhere in between. A pulmonary artery is linked to the lung from the systemic (or gill) arches and leads to the lung where it is oxygenated. A pulmonary vein then carries blood from the lung to the heart and it is pumped back to the body. However, the heart remains largely a simple structure like in fishes. The key difference is that the atrium, the chamber that receives the blood, is partly divided to separate the flows of oxygenated blood from the lung and deoxygenated blood from the body coming back to the heart (i.e. there is some mixing, but this is also controlled a bit). This partly divided system is lacking the air-breathing fishes he talked about. It is only known in lungfishes and amphibians.
Why was this information not important enough to be included and discussed by Menton?
Part II: Air breathing "crossopterygians"?":
It gets even more deceptive where Menton notes:
Most evolutionists look to crossopterygian fish for the ancestors of tetrapods—even though unlike many living fish, none of these fish are known to be capable of either walking or breathing out of water. [Original emphasis]Very clever. "Crossopterygian" is a dated term showing that Menton has read nothing about the study of tetrapod origins or lobe-finned fish systematics from the past 20 years. Although I have a particular affection for the term, nobody uses "crossopterygian" anymore. It's Menton's convenient use of an outdated typological term that excludes lungfishes by it's definition that is particularly misleading. The term "crossopterygian" referes to a sub-group of lobe-finned fishes that included coelacanths and "osteolepiforms", the latter including the iconic Eusthenopteron frequently seen crawling out of the water in children's dinosaur books (though few scientists think it actually did this). The term is largely discarded today because it assumes that lungfishes and tetrapods are not simply modified "crossopterygians". By using this term, Menton can safely ignore lungfishes, even though most palaeontologists (and a significant number of molecular biologists) now think lungfishes are a closer living cousin than is the only living "crossopterygian", the coelacanth Latimeria. I hesitate to comment as to whether this was done on purpose by Menton, but it is rather convenient that he should choose to dig up such an old term that specifically excludes lungfishes whilst simultaneously neglecting them in a discussion of air-breathing fishes.
However, let's accept Menton's use of "crossopterygian" for the moment. Coelacanths are the only living crossopterygians. They do not have a lung, but rather an oily swim bladder. This swim bladder has a little trachea (the tube that connects the lung to the throat) and a very small version of a vein that corresponds to the pulmonary vein.
What's even more deceptive is Menton's comment that there are no crossopterygians known to breathe air when, in fact, most things that are called "crossopterygians" are extinct. While there is one living genus of coelacanth, hundreds of other genera of "crossopterygian" are extinct. Rhizodontids, "osteolepiforms", porolepiforms, onychodonts, are all "crossopterygians" and have very distinct from coelacanths and may have anywhere from half a dozen to hundreds of sub-taxa with different adaptations and, presumably, different modes of life. Of these, it is impossible to observe air-breathing. At best, some functional and/or bone histological studies might give clues to different respiratory physiology. But, at best, conclusions about air-breathing would be inferential, and thus excluded from phylogenetic analysis (i.e. interpretations of how organisms are related to each other). That said, it is yet another truism that Menton should claim that no crossopterygians are known to breathe air.
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