The Gothic Cathedral of the Triceratops family: Kosmoceratops. Creative Commons Sampson SD, Loewen MA, Farke AA, Roberts EM, Forster CA, et al. "New Horned Dinosaurs from Utah Provide Evidence for Intracontinental Dinosaur Endemism". PLoS ONE 5 (9): e12292. DOI:10.1371/journal.pone.0012292.
Note: Clarifications/corrections added below. See comments section.
Ya know, some headlines write themselves. This past month an article in PLoS One announced the discovery of this new, vaguely-late-’80s-esque addition to the ceratopsian oeuvre (let’s face it: dude’s got bangs). What a startling and beautiful structure atop this dinosaur’s head! — like a shark-tooth necklace, or a very ambitious sea star. But the real news here seems to be that dinosaurs were no different than modern animals: they were subject to the whims of sexual selection as well as natural selection. And oh, what a harsh mistress sexual selection can be to the poor males of the species.
You see, what females really desire is an honest indicator of fitness. Males will try to fake their way to reproductive success (aka gettin’ some) in any way they can. It’s in their genes’ best interest, since they can generally impregnate as many females as they like with little cost. Females, on the other hand generally incur great cost in reproducing. Eggs and pPregnancies and raising offspring (*see Ben’s astutue comment below) are expensive energetically, while sperm and a father’s contribution to child-rearing are usually cheap. If you’re a female member of a few unlucky species, you could be stuck looking after your young for days, even months(!) before they leave the nest. Bummer.
So if you’re female, you want to be choosy. Not just any old male will do. You want a male who has demonstrated his fitness in a way that can’t be faked or cheated. This selection pressure, incurred by females, has led to the evolution of energetically expensive (and often ridiculous but strikingly beautiful) or cerebrally-demanding male traits. Witness peacock tails, bower bird bowers, sage grouse struts, mockingbird songs, and Shakespearean sonnets. Intelligence or fluorescent feathers can’t be faked; one must genuinely be bright to sing snippets of 30 songs or construct an elaborate love nest. One must genuinely be healthy and strong to grow the avian equivalent of a day-glo Persian Rug and nonetheless escape the clutches of hungry predators. Thus females can make informed decisions about whom to let sire their offspring*.
Well, no matter how long ago they lived, dinosaurs were still subject to the same cruel female whims, it seems. Enter Kosmoceratops, the elaborately frilled dinosaur. For once, biologists gave the bony crown atop ceratopsian dinosaurs (the frill) a beautiful, apt name. But what’s the deal with all those horns? Well, scientists suspect (according to the article in Time) that the horns were probably useless in taking on predators and may have even made it harder for the animals to move around. They suggest they were either used to intimidate other males of the species, or attract females. To me, they have sexual selection (i.e. useless, borderline dangerous, but unspeakably sexy to females**) written all over them.
Strangely, it seems these ornately-horned dinosaurs evolved *before* the simpler (and perhaps more elegant) frills of Triceratops, Nedoceratops, and a few other species, so Kosmoceratops or one of its close relatives was thus in fact the *ancestor* of Triceratops, not the other way around. Here is an example of evolution operating in the direction of complex to simple, or baroque –> neoclassical, if you will. So take note: evolution doesn’t always mean simple –> complex. All that matters is that the trait is changing in a way that leads to more offspring. Perhaps the gnarly frills proved too unwieldy, difficult to clean and maintain, or less tasteful to females than they at first seemed. Maybe the ladies decided that scarlet chest crests were the new sexy of the early 70’s million B.C.
To explore how the ceratopsian dinosaurs fit into the rest of their thundering kin, see here, and click on “Ornithischia”.
And just a quick note — I did hear about the discovery of the possible culprits in Honeybee Colony Collapse Disorder, and you will be hearing my thoughts on that (and description of the perpetrators) here soon. : )
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*Oddly, and for reasons I don’t entirely understand (except that the predator-free islands of the tropical birds of paradise (from which many of my examples are drawn) has allowed sexual selection to run amok), much research into the world of sexual selection has been done in birds. In one experiment involving birds whose females evidently found extremely long tail feathers erotic beyond belief, sadistic biologists clipped or gave tail feather extensions to variously naturally-endowed males. They found the birds’ reproductive success depended only on the length of those tail feathers, whether honestly come by or not: artificially-lengthened males suddenly found themselves getting much luckier than their better naturally-endowed but snipped brethren. Presumably, in nature, the birds can’t cheat the system by ordering a Swedish Tail Feather Enlarger.
** there are any number of human analogs that suggest themselves here
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I enjoy your blog very much and thought you might find this interesting. You may already have seen it!
http://meanjin.com.au/spike-the-meanjin-blog/post/the-kraken-wakes/
Cool — very interesting! Thanks!
Hey Jen,
I have a couple of quibbles with this post, as someone who studies sexual selection in living dinosaurs. I think your post is a little too complicit with the distorted “Mad Men” idea of sexual selection that is so popular in the. . . popular literature. It’s kind of a pet peeve of mine.
First, as can be seen in the paper in PLOS 1 (thanks for the link!), the authors only found the skulls. So, no one actually knows which sex these crazy skulls belonged to. They could have been female. There are, in fact, many species of birds in which the female is larger, more ornate, and more promiscuous. There are even more cases of “reverse” sexual dimorphism in fish, insects, and reptiles. So many, in fact, that if we weren’t mammals (in which all females pay an extraordinarily high gestation cost), we probably wouldn’t call it “reverse” dimorphism at all.
Second, the idea that sperm is cheap and eggs are expensive is not really accurate. It’s not fair to compare one sperm to one egg. Really, one should compare the two sexes’ investments over the reproductive bout. It is true that many females invest more in reproduction than males, but that is probably because they control the site of fertilization, and thus are more certain that the offspring they are caring for are their own. In species where one sex is promiscuous, it is inevitably the one that has less certainty about paternity, regardless of whether or not their gametes have flagella. George Williams has a section on this in his classic book “Adaptation and Natural Selection”. It would be tiresome to cite too many examples, so I’ll just mention two factoids: in some Drosophila species, the male ejaculate contains a single, meter-or-more-long sperm; and in Syngnathid fish (seahorses et al.), fertilization occurs in the male’s pouch, and females are larger, showier, more aggressive, and more promiscuous.
Quibbles or rant? You decide.
crap! I forgot to put a “” after Drosophila.
I thought about the fact these could be females too, but the experts seemed think it was evidence for sexual selection so I went with it. But on the other hand, if these are females, what if the males’ skulls are *twice* as horny? : ) And yes, at a massively multicellular level like our own, eggs aren’t significantly more expensive than sperm, and reproductive investment is really the material thing. Good point. I will be more cautious in the future. Thanks!
Jen