by Greg Mayer
In my post on the genitalia of ratfish (which are shark relatives), I noted that although no extant sharks had similar structures, some fossil ones did, so here are what two species of these sharks looked like. Both are members of the family Stethacanthidae, known for its sexual dimorphism.
Fig. 1. Female (above) and male Falcatus falcatus (Carboniferous of North America). Note the pelvic claspers on the male, and the roughened denticles atop the head, as well as on the head clasper
How exactly the male ratfish uses his head clasper during mating is obscure (at least to me), and the use of the head clasper (the spine of the first dorsal fin) in the shark Falcatus would also be obscure, except that a pair has been found fossilized in flagrante delicto, the female grasping the head clasper in her mouth, her body parallel to and above the male’s. There would have to be more to their mating than this to bring the male’s pelvic claspers in to position, but it does provide at least a partial picture of mating and courtship in this fossil species. A nice photo of the fossil pair is at the fine website on Fossil Fishes of Bear Gulch maintained by Richard Lund and Eileen Grogan. They also have a photo of the rather similar Damocles serratus (presumably so named because its own sword [clasper] was always hanging over its head).
Equally bizarre is Stethacanthus, with a brush-like set of denticles atop the first dorsal fin, a large first dorsal fin spine, and roughened denticles atop the head. It’s not clear exactly how, or for what, this structure was used, but the fact that it occurs only in males, and that the related Falcatus (and almost certainly Damocles as well) used a similar structure in mating, suggests some sort of sexual behavior function.
Fig. 2. Male (to left) and female Stethacanthus altonensis (Carboniferous of North America).
Lund and Grogan provide further discussion and illustration at their website, and one of Lund’s papers is in the American Museum of Natural History’s digital library of its scientific publications. Matt Celeskey at the Hairy Museum of Natural History has reconstructions of both Falcatus and Stethacanthus.
Filling a demand that I didn’t know existed, in the mid 1990’s two excellent and well-illustrated popular accounts of the history of fishes were published, both emphasizing the fossil record. WEIT readers should enjoy both; Long has more on these odd sharks and ratfish.
Long, J.A. 1995. The Rise of Fishes: 500 Million Years of Evolution. Johns Hopkins University Press, Baltimore.
Maisey, J.G. 1996. Discovering Fossil Fishes. Henry Holt, New York.
Damocles serratus – what a brilliant name!
Figure 2 looks more like an AWACS radar than a head clasper.
Yay for fish!
Ah, sexual adaptations. So that’s why fishes have all the fin?!
OT, but it should be noted that Jerry Coyne asked a legitimate question about evil and the existence of god, the only problem is that he has no standing to ask such a question. Only theists get to ask it:
http://www.evolutionnews.org/2009/09/theodicy_without_god.html#more
Likewise, the Egnorant one has no standing to discuss any problems of evolution, for he doesn’t belong to the church of Darwinism (as IDiots call it).
There you are, all problems are solved. We can’t ask about god and evil, and they can’t criticize evolution. No hypothetical discourse is legitimate.
They are, though, the ones who wish to promote knowledge and debate.
Glen Davidson
Just a bit more. Egnor simply hasn’t captured any sense of complexity of thought, rather ironic for people who claim to understand complexity:
Actually, what we readily understand is that we evolved a sense of “good and evil” as social beings, we just recognize that it’s a fallible and derived sense.
Above all, we actually explain why “evil” exists to a considerable extent, and Egnor has no explanation whatsoever, just a vain attempt to make those who do think to shut up.
Glen Davidson
http://tinyurl.com/mxaa3p
“There you are, all problems are solved. We can’t ask about god and evil, and they can’t criticize evolution.”
I can live with that. I’m plenty willing to leave god and evil alone if they’ll STFU about evolution…
Did Falcatus falcatus really have such big eyes, it looks like a cartoon fish.
They do look rather joyful, but since they are probably about to mate I can understand that.
I wondered the same thing. The pic’s sorta reminiscent of sad-eyed moppets airbrushed on black velvet & sold on the streets of Tijuana.
Yes, they had big eyes. See the photo of the fossils at Fossil Fishes of Bear Gulch above (or just go here: http://www.sju.edu/research/bear_gulch/pages_fish_species/Falcatus_falcatus.php )
GCM
Thanx, Greg,
In their commentary there they say the the large size indicates a highly visual predator, but so are (for instance) hawks, and their eyes are nowhere near that size. I wonder if it could indicate that they inhabited murky water, or that the degree of innervation to light receptors was low relative to modern fishes. In either event, a greater signal-to-noise, or at least greater overall signal could be achieved by a larger eye.
Oooookayyyyy …
Those falcati look like some sorta spooky, happy, manga fish.
Could it be that these head ornaments evolved via sexual selection?
Yes.
GCM
“a pair has been found fossilized in flagrante delicto, the female grasping the head clasper in her mouth, her body parallel to and above the male’s.”
Oral sex! Fish invented it first!! Did Inner Fish pick up on that?
I think Dr Shubin missed that one.
Who did the artwork? I love those pieces!
Mouse over the pictures; the artists’ names come up. Both are from Wikipedia. Do look at the artwork by Lund, Grogan, and Celeskey, linked to in the pieces, as well.
GCM
Off-topic: Ardipithecus ramidus