Where do the hagfish fit in?

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Hagfish are wonderful, beautiful, interesting animals. They are particularly attractive to evolutionary biologists because they have some very suggestive features that look primitive: they have no jaws, and they have no pectoral girdle or paired pectoral fins. They have very poorly developed eyes, no epiphysis, and only one semicircular canal; lampreys, while also lacking jaws, at least have good eyes and two semicircular canals. How hagfish fit into the evolutionary tree is still an open question, however.

Continue reading "Where do the hagfish fit in?" (on Pharyngula)

9 Comments

The hagfish debate is hardly over, and more is soon to be published about the conflict of the molecular phylogenetic analysis. I wish to bet otherwise than PZ: lampreys and gnathotomes are closer to each other than to hagfish. I am quiet more respectful when uncontroversial, robust results are retrieved within morphological phylogenetic analysis. Morphology CLEARLY indicates lampreys as closer to gnthostomes than to hagfish. So, even if he molecular data may retrieve a monophyletic cyclostomata, this would imply a massive loss of several traits in hagfish, a truly huge morphological transformation.

In other words: KNOW when you are wiping your ass with the most parsimonious interpretation of the evolution of morphology. KNOW what you are doing when you just take the molecular evidence over the morphological.

Something very similar has happened with the position of the urochordates; a few questionable molecular studies, a “sacralized” observation of an apparently more similar migratory neural crest… and everyone seems to have bought that they must be sister group to vertebrates. They should at least KNOW all the morphology this implies has been simply erased along the urochordate lineage.

Keep your eyes peeled: There is going to be further major clashes between molecular and morphological phylogenies. Indeed, the morphological transformations implied by mindlessly adopting molecular phylogenies may be just too ridiculous to be believed.

I wonder what social clique will be victorious in this debate? This reminds me of the discussion about the arthritic bones ancient men classified as the ape-man transitional form called “Neanderthals” were really our ancestors. However, due to the influence of the Leaky family in the Darwinian establishment their own discovery–the collection of monkey bones called “Lucy” was christened instead.

It is worth pointing out that generally, there is much more agreement than disagreement between morphological and molecular phylogenetic analysis. Each case is examined according to the available information; normally, the most parsimonious morphological history IS consistent with the molecular signal. For instance, the fact that crocodylia are closer to aves than to other reptiles. Or that whales are ungulates. When there is an apparent conflict (there is, after all, only one true tree) it usually reflects the scrappiness of one or both of the sources of information, morphological, or molecular. Several of the more famous “clashes” of the past have been resolved as a result of better taxon sampling. Long-branching in specific clades (urochordates, for instance) can also retrieve artifactual phylogenetic relationships in molecular studies. All I’m saying is: morphologically, these relationships are well-resolved.

Pole Greaser:

I wonder what social clique will be victorious in this debate? This reminds me of the discussion about the arthritic bones ancient men classified as the ape-man transitional form called “Neanderthals” were really our ancestors. However, due to the influence of the Leaky family in the Darwinian establishment their own discovery–the collection of monkey bones called “Lucy” was christened instead.

Neandertals were never considered “ape-men”. They were thought of as odd-looking modern men, until they were unambiguously associated with fossil mammals.

The specimen to which you refer is the “Old man of La Chapelle-aux-Saintes”, discovered in 1908. While you mention arthritis, that of course was from one of the nice things about science– that the work of science is self-correcting. The diagnosis of arthritis was made in the reanalysis of Marcellin Boule’s distorted and biased original description of the remains. That reanalysis effectively demolished the “Ally Oop” caveman caricature that Boule’s work had fostered.(1)

Despite the attempts to marginalize Neandertals, (which says more for the unfortunate retention of prejudices than Paleoanthropologists would like to admit, but has also led to a great deal of analysis and advancement of knowledge of human origins), the evidence show that Neandertals were great hunters, treated their infirm, aged and dead with respect, used language, and were likely interbreeding with “modern” humans (1,2,3,4).

Of course afarensis/Neandertal is not an either/or proposition. They are separated by 3-4 million years–indeed Neandertals are afarensis descendants.

BTW, “Lucy” was not a Leakey family discovery, the remains were found by Don Johanson and Tom Gray. (5,6,7)

Pole Greaser Grade: D-

1. http://anthro.palomar.edu/homo2/mod_homo_2.htm 2. http://news.nationalgeographic.com/[…]derthal.html 3. http://news.nationalgeographic.com/[…]al-gene.html 4. http://www.sciencedaily.com/release[…]03083616.htm 5. http://www.anthro4n6.net/lucy/ 6. http://lucyexhibition.com/lucys-discovery.aspx 7. http://www.pbs.org/wgbh/aso/tryit/e[…]on/lucy.html

DPR

D-? Grade inflation. There is not a single correct item in that post by Pole Greaser. F.

mplavcan:

D-? Grade inflation. There is not a single correct item in that post by Pole Greaser. F.

I hate to flunk someone on the first assignment.

DPR

So, if the hagfish do form a monophyletic clade with the lampreys, would this mean that the hagfish, too, are descendants of the Anaspids, or, would the hagfish be considered the sister group of (Anaspida + lampreys)+Osteostraci+Thelodonti+Galeaspida?

if cyclostomes are monophyletic, hagfish would be fairly derived craniates that have become secondarily simplified in their morphology. However, morphologically, they are likely to be even more basal than conodonts, splitting off before the ostracoderms. Anybody correct me if I am wrong

This thread is a fascinating example of a true conflict in evolutionary studies versus the conflict between all evolutionary theory and the bogus claptrap spouted by creationists.

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This page contains a single entry by PZ Myers published on January 15, 2008 12:54 PM.

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