Pharyngula

Shark with legs?

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A little knowledge would short circuit a lot of strange speculation. That picture to the right is of a shark caught in Malaysia, and people are calling those odd dangly bits “legs”. Despite the fact that someone said what they actually are in a comment early on, there are people arguing both that a shark with legs is evidence for evolution, and that it is evidence for creation.

They’re both wrong.

It’s a male shark. Those are the shark’s claspers, or intromittent organs. The shark does the usual act you’d expect with a female of the species, and like many shark species, it has clasper spurs, or little poky bits that help lock the organ into the female’s cloaca while he gets happy.

They aren’t homologous to legs at all. We also wouldn’t expect to find legs on a shark — they aren’t in the lineage that led to tetrapods.

I’m actually most surprised that a worker at the Malaysian Fisheries Development Board, who found this animal, didn’t recognize that these were just ordinary claspers. Anyone who has worked with sharks for even a little while would know about these structures. I suspect someone at the board is pulling the media’s, and the public’s, leg.


You know you want to see this: here’s a photo of two sharks getting affectionate. Shark lovin’ often involves a fair amount of biting and tearing, and leaves scars that you can find in captured specimens, so I don’t recommend trying this at home. Especially since sharks don’t believe in safewords.

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Comments

  1. #1 Stanton
    July 29, 2007

    I always thought the claspers were longer.
    The claspers of ptyctodont placoderms are more hook-like, that I know.

  2. #2 Tom @Thoughtsic.com
    July 29, 2007

    And once again knowledge prevails. Hooray, knowledge!

  3. #3 Paguroidea
    July 29, 2007

    Thanks to the photo, I can see why those claspers would come in handy indeed. It looks rather tricky to do it standing on their heads.

  4. #4 Kimpatsu
    July 29, 2007

    Hot shark lovin’ involves biting and tearing? What do they think they are, Klingons?

  5. #5 arachnophilia
    July 29, 2007

    They aren’t homologous to legs at all. We also wouldn’t expect to find legs on a shark — they aren’t in the lineage that led to tetrapods.

    well, no, they’re not. but they’re not terribly far off that line, either. tetrapods come from sarcopterygiid osteichthyes — about the same level as chondrichthyes (sharks). legs come out of shark’s sister grouping.

    and the lobe-fins on sarcopterygii ARE homologous to legs, because that where legs came from. as such, it would be pectoral fins that would be the best bet to being homologous to legs, but iirc, they are quite different interally from lobe-finned fishes.

    also iirc, claspers are not bony at all, and aren’t really homologous to ANYTHING.

  6. #6 Stanton
    July 29, 2007

    Actually, sharks are pretty far from the tetrapod lineage: sharks are regarded as the sister-group of placoderms, who share a great deal of skull anatomy, and possibly the sister-group of the thelodont agnathans, who share a great deal of scale histology.

  7. #7 Stanton
    July 29, 2007

    I forgot to say that the sharks diverged from the vertebrate line that would give rise to tetrapods sometime during the Silurian/earliest Devonian.

  8. #8 uncle bob
    July 29, 2007

    I think we’re scraping the bottom of the barrel here.
    Didn’t anything else piss us off today?

  9. #9 arachnophilia
    July 29, 2007

    ah, right. placoderms.

    (not a fish person)

  10. #10 Janine
    July 29, 2007

    “Safewords are for wusses.”
    Faith

    Sorry, I had to state it. I am a huge Buffy fan and that target was just so big.

  11. #11 Odonata
    July 29, 2007

    If you’re curious how male sharks use their claspers, you can find out the nitty gritty details at http://www.elasmo-research.org/education/topics/lh_2penises.htm .

  12. #12 cyan
    July 29, 2007

    Well, you know how some guys refer to the penis as the third leg….

    It seems to me that it would have been relatively easy for someone with some knowledge of sharks to immediately dispel this notion of those claspers being legs or proto-legs.

    “Claspers” is not the best term that could have been used to identify these structures, since in most peoples’ minds it might conjure up their function as being to clasp the female’s body to the male’s during copulation – but hey: like the terms introns & exons: not immediately logical.

    Claspers usually move together just before copulation and remain together during copulation; the more closely they have moved together, the better the chances that some sperm moving in the channel formed between them will get to the oocyte in the female. (Imagine a penis that is split normally when unstimulated, but comes together when sexually stimulated – yeah, not a comfortable image, but it woiks).

    Less tightly aligned claspers result in more sperm moving out into fluid surrounding the combined claspers, instead of into the female.

    More tightly aligned claspers result in more fertilization, so it is a trait that persists.

  13. #13 donna
    July 29, 2007

    Shark porn!

  14. #14 donna
    July 29, 2007

    Shark porn!

  15. #15 rrt
    July 29, 2007

    That blog’s comment thread is simultaneously the most hilarious and depressing thing I’ve read all year.

    “You evilutionist atheists cooked this up!”
    “No we didn’t! This is clear evidence for evolution.”
    “Yeah, but which direction is it trying to go? Backwards or forwards?”
    “Dudes, those are claspers…”
    “God loves you! Burn in Hell, lol!!!111!one!”
    “Clearly this proves evolution, I mean, if fish can get legs in one generation, then anything’s possible!”
    “Idiot, sharks aren’t fish. They breathe air!”
    “Moron, everyone with half an education knows sharks are fish. And anyway, all fish breathe air!”

    *sob*
    *giggle*
    *sob*

  16. #16 Jason
    July 29, 2007

    This story certainly has legs.

    myxopterygium (mix-op-ter-ridge-ee-um): The copulatory organ or clasper of Elasmobranchii and Holocephali; rod-like extensions of the inner side of the pelvic fins. It is composed of the long stem cartilage, a shorter distal cartilage, the dorsal terminal cartilage (or rhipidion, fan-shaped for dispersing sperm in a radiating spray during copulation), the hook-shaped terminal cartilage (or claw) which has a cutting edge on its inner margin, and the narrow, sharp spur. The claw and spur serve to anchor the clasper in the female oviduct and a groove along the clasper enables the sperm to reach the oviduct. The siphon contracts to propel sperm into the oviduct.

  17. #17 arachnophilia
    July 29, 2007

    my brain hurt after reading the first few comments, and i decided to call it quits.

  18. #18 Laelaps
    July 29, 2007

    I was surprised to see this story resurface; I blogged about it in March when it first appeared in the Underwater Times, but I didn’t see anyone comment about it until people started claiming that the photo proved/disproved evolution a few days ago. I did, however, receive the following attempted refutation (if it can be called that) from someone who saw my explanation that the “feet” were really claspers;

    “yeah but the first feet probably were not “feet” either. the process of evolution involves mutations, and this is an example of a mutation could have lead to feet. it would be unintelligent to assume that the first feet were actually intended to be used in the way land animals use them. It would be even more unintelligent to think that something hand designed everything on earth..”

    At least all this was a good reason to remember the old Land Shark sketch…

  19. #19 Bourgeois Nerd
    July 30, 2007

    There are smaller species of sharks (epaullette and bamboo sharks, for instance) that use their fins to “walk,” and whom I’ve often fantasized will give rise to a new theropod lineage in about a hundred million years, but, yeah, those just look like funky claspers.

  20. #20 letters
    July 30, 2007

    Thanks for the photo at bottom. Now I know where my ex has been hanging out, and that she hasn’t changed a bit.

  21. #21 Baratos
    July 30, 2007

    I am reminded of a thread on 4chan where a guy showed up asking if whales were animals. We told him it was a water based colossus that laid eggs.

  22. #22 Tatarize
    July 30, 2007

    The evidence for creationism comment is wrong on another count. The evolution/creationism thing is a false dichotomy. If these were real legs then it would require that large tracts of our understanding of evolution or at the very least whale evolution is completely flawed, and massive amounts would need to be rewritten. However, that never equates to evidence for creationism.

    Creationism is stupid regardless how well founded evolution is.

  23. #23 LM
    July 30, 2007

    All I’ve got to say is “DUH.” Of course, having taught comparative anatomy for five years and dissected probably 6 dozen dogfish sharks, I *may* be a tad biased. Still. DUH.

  24. #24 Diego
    July 30, 2007

    I’m with LM here. Major Duh! I have also taught comparative vertebrate anatomy and comparative anatomy in general and that certainly means we darn well better know about claspers but as PZ pointed out there are large sections of the general public (e.g. fishermen) that ought to know about them or at least be familiar with the sight of claspers. This has GOT to have been somebody’s idea of a joke to start with.

  25. #25 Graculus
    July 30, 2007

    I’m actually most surprised that a worker at the Malaysian Fisheries Development Board, who found this animal, didn’t recognize that these were just ordinary claspers. Anyone who has worked with sharks for even a little while would know about these structures. I suspect someone at the board is pulling the media’s, and the public’s, leg.

    I think what happened is that a perfectly ordinary picture got picked up by someone in the media out of context. Then they phoned some expert (but not the source of the photo), and only asked them about “sharks with legs”, implying that it was a confirmed find, not a misunderstood picture on the internet.

    This will make the rounds for as long as the rotting basking shark… for-frikkin-ever.

  26. #26 Stanton
    July 30, 2007

    This will make the rounds for as long as the rotting basking shark… for-frikkin-ever.

    But, hopefully, this won’t stink as badly.

  27. #27 Kseniya
    July 30, 2007

    The rotting basking shark…? I don’t know that one.

    [googles]

    Ah. I see! This was like the badly decomposed beluga carcass, found on a beach in Siberia about a year ago, which sparked some wild speculation about ichthyosaurs and such.

  28. #28 Bob
    July 30, 2007

    And just in time for Shark Week.

  29. #29 Lago
    July 30, 2007

    Yep, another sign that creationists need basic anatomy training. Are there really people so unworldly that they do not know what a clasper is?

    Like the above mentioned Basking shark. Everyone tried to claim it was a Plesiosaur even though, to anyone who has dissected a shark, it was obviously the rotting skeleton of large shark…

    I also saw the decomposing beluga mentioned above on one website, and yes, they were claiming it to be some type of ichthyosaur, or other type of ancient sea creature. I posted a detailed response as to why it was a whale, and everyone just stopped posting after that.

  30. #30 Lago
    July 30, 2007

    Oh my God, I just read some of the posts on the linked site!

    There really are people that freakin’ stoopid…

  31. #31 Silmarillion
    July 30, 2007

    Sharks with legs? What next – fish with hands? 😉

  32. #32 daudi
    July 30, 2007

    I think Dr. Yasin had been misinformed. He was referring to the recently caught coelecanth fish caught in Sulawesi having legs, and certainly would have known about shark claspers.

  33. #33 Chang Yang
    July 30, 2007

    Just to point out the original source of the news:

    Link

    Anyway the digg thread about this issue has quite a lot of people who got carried away with evolution vs. creationism bickering.

    Link

  34. #34 Matt
    May 17, 2009

    “yeah but the first feet probably were not “feet” either. the process of evolution involves mutations, and this is an example of a mutation could have lead to feet. it would be unintelligent to assume that the first feet were actually intended to be used in the way land animals use them. It would be even more unintelligent to think that something hand designed everything on earth..”

    so legs really used to be sex organs? all this time, i had no idea that i was using my penis to walk.
    dude, seriously. feet evolved on fish that lived either at the bottom of the ocean or in shallow water first. in either of those, feet would help it move around. eventually they started finding land and walking up on to it. the fish that couldn’t survive very long on land died off and the ones that could lived. this is called natural selection. only the strong survive. of the fish that survived, some of them probably were able to breath air somewhat, but of course they wouldn’t be able to get enough to survive. the ones that could get enough air to last the longest on land would live, the others would die off. eventually, gills would develop into lungs after several million years of species dying off and being replaced by new and better species. the mud skipper has both gills and lungs and is believed to be a transitional species. if you’re gonna start telling people how things work, make sure you know what you’re walking about.

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