A unique fossil insect with scissors on its head and thorax

It’s Darwin Day, and so we shall have a new paper on the mysteries of evolution. In this case we have a report of an insect whose head and thorax have structures that constitute a pair of scissors—the only insect known to have anything like that. It’s a fossil in Burmese amber, 100 million years old, and the mystery is what the scissors are for.

The report is a new paper in Current Biology by Ming Bai et al. (reference below; free access and pdf using legal Unpaywall app for Chrome). In that paper the authors describe a remarkably well preserved insect that they call Caputoraptor elegans, which has been placed, along with just one other species, in the appropriately named order Alienoptera. We don’t know its precise evolutionary placement, but it appears from morphology to be most closely related to mantids (Mantodea) and a bit less related to cockroaches (Blattodea).

Here’s a dorsal (top) view of C. elegans; the scale bar is 1 mm. Note the big compound eyes, the trapezoidal head, the extended “neck” of the thorax, and the wings.  There are nine specimens, all determined from genitals to be female). You can se the scissors, with the blades comprising a sharp, pointed extension of each side of the rear of the head, and serrated “blades” on on the front of the thorax. It’s pretty clear from this and the following photos that these edges would articulate:

Here’s a top view of the head and anterior thorax showing the knife edge of the head (“ge”) and the serrated edge of the first thoracic segment (“pe”):

Finally, a side view of the head showing the opposing holding/cutting surfaces. Note that there are small hairs (setae: “ps”) protruding from the serrations; the authors think these are sensory hairs that would trigger the scissors to close when they detect an object. Closing would occur as the head bends towards the neck. The compound eyes (“ce”) are huge—like a mantid’s.

As I said, this feature is absolutely unique to this species, and is missing the other member of its extinct order. But what was it used for? The authors broach three possibilities given in this diagram:

In “A” we see the authors’ preferred hypothesis: the scissors were used by females to hold the male’s wings during mating. They presume that, like grasshoppers, roaches, and mayflies, mating occurs with the female atop the male.  This could be tested if they could find male specimens, for under the mating hypothesis, males should be lacking the scissors. That is, the trait would be sexually dimorphic, with males not having it because it has no function for them.

“B” shows a “defensive” hypothesis: the scissors could be use to grab attackers like the ant shown. The authors don’t find this hypothesis particularly good because “with its limited opening angle, [the scissors] would not seriously affect larger or strongly sclerotized attackers”, and “would not work in the case of strikes from above or behind, which apparently excludes most predators.”

“C” shows a predatory function for the scissors. The authors don’t think this is likely because “this mechanism has a limited opening angle and no range extension, as is the case with the raptorial forelegs of mantises. Moreover, closing was very likely triggered by the sensory hairs on the prothoracic ridge. This would imply that Caputoraptor had to move over potential prey before jamming it between the scissors. It is apparently that only small, weakly sclerotized, and slow-moving insects would have been suitable.” But those kind of prey could be taken by the mandibles, with the scissors being unnecessary.

Of course, it could have been used in multiple ways. Unless we find a specimen in the process of attacking or defending (not likely), we won’t know, but we could rule out “A” more easily because, as a trait used by females to hold males, it should be sexually dimorphic—not found in male specimens. One male specimen could settle that issue.

One more note: the authors conclude from the shape of the feet and the short forewings, that this was an arboreal (tree dwelling) creature. The feet have pan-shaped devices on the tips that characterize modern insects that walk on smooth surfaces like leaves, and modern leaf-dwelling insects don’t need a long forewing to protect the hindwings.  Further, the triangular shape of the head and the large eyes suggest that this was a predator, perhaps eating things like aphids or scale insects (both occur in Burmese amber).  So what we have is a mantid-like insect that also lived like a mantid. The authors include a reconstruction:

 

Happy Darwin Day! Old Charlie would be pleased to contemplate such a weird creature.

h/t: Matthew

__________

Bai, M., R. G. Beutel, W. Zhang, S. Wang, M. Hörnig, C. Gröhn, E. Yan, X. Yang, and B. Wipfler. A new Cretaceous insect with a unique cephalo-thoracic scissor device. Current Biology 28:438-443.e431. DOI: https://doi.org/10.1016/j.cub.2017.12.031

48 Comments

  1. ThyroidPlanet
    Posted February 12, 2018 at 10:58 am | Permalink

    I like this

    But

    I think using the word “scissor” is mostly marketing. Later, the authors call it a “scissor-like” device. There are lots of different tools that are like scissors, some doing shearing, some anvil-type cutting…

    But that’s all insinuating theres cutting going on.

    What this looks like, and they argue strongly, is better termed (I think off-the-top-of-my-head) a clamp, or grip. That would eliminate C from their diagram I think.

    But I quibble…

    https://en.m.wikipedia.org/wiki/Scissors

    • Posted February 12, 2018 at 12:29 pm | Permalink

      I wondered about “scissor” too – it suggests to me that one would thereby have a hypothesis that the item in question was used for *cutting*, not merely grasping or holding in place.

    • Mark Sturtevant
      Posted February 12, 2018 at 1:32 pm | Permalink

      Yes. At best it can only be a clamping tool, not a cutting tool.

    • glen1davidson
      Posted February 12, 2018 at 1:38 pm | Permalink

      “Pliers” would be a better term than “scissors.”

      Scissors are typically understood to mean shears, and there’s nothing like shearing going on there. Hinge-clamp, or pliers.

      Glen Davidson

    • Posted February 12, 2018 at 2:15 pm | Permalink

      Lordy, the nit-pickers are out today. Okay, I’ll change it to “pliers”. Are you all happy now? 🙂

      • glen1davidson
        Posted February 12, 2018 at 2:16 pm | Permalink

        Ecstatic!

      • ThyroidPlanet
        Posted February 12, 2018 at 2:43 pm | Permalink

        The authors started it.

        But this is a thing, right – scientists use common terms in off-hand ways for things in nature – that’s good. But here, I’d argue the object – a machine, in fact – has a specific function and the animal has a formation with a specific …. am I going off the rails here?… anyway, I like “pliers” better, but “clamp” maybe better… perhaps because I have little else to contribute….

        … actually, I was wondering if you deliberately omitted the title, so as to direct readers over to the paper… so I didn’t reproduce it here.

        • Posted February 13, 2018 at 11:34 am | Permalink

          Actually, there *are* people who deny that organs have functions (because they weren’t deliberately built for anything in particular). I think the view is a bit odd, but there you go.

  2. Michael Fisher
    Posted February 12, 2018 at 11:01 am | Permalink

    Please note Unpaywall is also available at the same source for Firefox [& Waterfox & Pale Moon & others that use Firefox code]

  3. jorgensen28ryan
    Posted February 12, 2018 at 11:17 am | Permalink

    Perhaps this was ruled out due to the presence of the sensory hairs, but maybe they functioned as a sound generating structure.

    • Mark Sturtevant
      Posted February 12, 2018 at 1:33 pm | Permalink

      Stridulation! Worth considering. But normally it would be the males that do that.

  4. glen1davidson
    Posted February 12, 2018 at 11:20 am | Permalink

    Edwina Scissorhead.

    It’ll be a B movie, at best.

    Glen Davidson

  5. Liz
    Posted February 12, 2018 at 11:27 am | Permalink

    I love the honey cream and clayish greens in the images. If they do find a male without the scissors or grips, I wonder if there would also be differences in wing sensitivity. Before this, I was familiar only with a different C. elegans, Caenorhabditis elegans. https://en.wikipedia.org/wiki/Caenorhabditis_elegans

    • Michael Fisher
      Posted February 12, 2018 at 11:41 am | Permalink

      i don’t know if wing sensitivity can be ascertained from a fossil of an extinct beastie. I also admired the artist reconstruction. HERE’S A MODEL of it, Caputoraptor elegans which I think can be translated as “Elegant Thief Head”

  6. busterggi
    Posted February 12, 2018 at 11:32 am | Permalink

    Note the jagged edges? That makes them pinking shears, not scissors. Be accurate – be scientific!

  7. Nobody Special
    Posted February 12, 2018 at 11:49 am | Permalink

    Could it be a type of leaf-cutting or crimping device? A crimped leaf would be easier to fold and would make a safe place to lay eggs out of sight of predators.

  8. Posted February 12, 2018 at 12:59 pm | Permalink

    Has anyone considered the possibility it was used to hold a fiddle?

  9. rickflick
    Posted February 12, 2018 at 1:24 pm | Permalink

    Totally bizarre! What’s next? An insect with block and tackle?

  10. Mark Sturtevant
    Posted February 12, 2018 at 1:31 pm | Permalink

    I don’t get their description of female on top mating for grasshoppers and roaches. I have always seen males on top in the case of ‘hoppers, and in roaches they are always butt to butt, facing away from each other. Although that must be in a later step of mating for them.
    Mayflies? No idea.

    • loren russell
      Posted February 12, 2018 at 2:14 pm | Permalink

      Female superior is pretty much plain-vanilla across many order within the insect world.

      My Special Bug is built that way, with the male’s front wings turned into a snap-trap to secure his lady’s antennae whilst doing it. It only seems complicated if you lack an exoskeleton, I guess..

  11. Posted February 12, 2018 at 1:43 pm | Permalink

    Even if it has the mating function of option (A), it would not necessarily be sexually dimorphic, it seems to me. Human males have nipples even though they don’t breastfeed, etc. Traits with a sex-specific function often become dimorphic if there is a selective pressure for them to be lost in the sex where they are not useful; bright plumage in birds to attract a mate is often present only in males, for example, because being conspicuous as a female has the negative side effect of increased visibility to predators. It’s not clear that there would be any negative effect entailed in possessing these “scissors”, so there might be no selection towards dimorphism. Dimorphism might evolve anyway, due to drift, but it would probably be much slower to evolve, and might not happen at all. So I am not convinced that it is true that “one male specimen could settle that issue”. Am I missing something?

    • Posted February 12, 2018 at 2:18 pm | Permalink

      Males have nipples but they don’t have breasts. In general, traits useful in only one sex tend to disappear in the other. And yes, if one male specimen appears with the “pliers”, then that pretty much says the character didn’t evolve for the female to hold the male. Of course they could have mated in other ways in which the trait is useful in both sexes, but most people would go to another possible function. There’s usually a selective pressure to lose a character that isn’t used because of the metabolic energy it takes, or the fact that the character might make it easier to get injured or impede function (peacocks).

    • loren russell
      Posted February 12, 2018 at 2:24 pm | Permalink

      I really can’t think of any similar case where a de novo sexual clasper also occurs in the “non-clasping” sex. Of course, it’s possibly, perhaps likely, that a pre-existing spiny or rugose prothorax existing in both sexes, ready to be co-opted in this mating position..

    • Adam M.
      Posted February 12, 2018 at 2:38 pm | Permalink

      One male specimen could settle the issue if it didn’t have the ‘scissors’. If it did, then it’d still be an open question…

      • Posted February 12, 2018 at 2:55 pm | Permalink

        Yes, it’s a one-way test, as I indicated (or thought I did).

        • Posted February 12, 2018 at 3:55 pm | Permalink

          Ah, Jerry, if your claim is only of a one-way test (absence in males indicates a female-specific function) then my comment above is superfluous. But you wrote: “we could rule out “A” more easily because, as a trait used by females to hold males, it should be sexually dimorphic—not found in male specimens”. Saying that we could “rule out “A”” seems to suggest that it is a two-way test: not only would absence in males indicate a sex-specific function (“ruling in” A), but *presence* in males would indicate a *non-sex-specific* function (“ruling out” A). And that also seemed to be what you were arguing in your reply to me above (“And yes, if one male specimen appears with the “pliers”, then that pretty much says the character didn’t evolve for the female to hold the male.”). So now I am not clear whether you are claiming that a male specimen would be a one-way test only, or a two-way test. Or am I confused somehow?

          • Posted February 12, 2018 at 5:49 pm | Permalink

            If a male doesn’t have the pliers, then that suggests it’s used by females to hold males. If males have them, it SUGGESTS that that explanation is incorrect, but is not quite as dispositive. The absence is stronger evidence for A than their presence is against A.

            • Posted February 12, 2018 at 5:56 pm | Permalink

              Aha, makes sense, thanks for clarifying. :->

            • Nobody Special
              Posted February 12, 2018 at 8:51 pm | Permalink

              If, as I suggested earlier today, the scissors/pliers were a leaf-cutting or creasing tool to facilitate the hiding of eggs, wouldn’t that be an adaptation that would most likely only be manifest in the sex doing the actual work of laying and hiding eggs?

      • gravelinspector-Aidan
        Posted February 15, 2018 at 6:24 pm | Permalink

        One male specimen could settle the issue

        That’s the annoying thing about amber fossils. Since the sampling of the environment is essentially random, and then the droplets of set sap are transported, and hydrodynamically sorted further mixing things up before the final deposition … and then the whole process repeated in the mining process, the chances of actually finding another specimen are purely down to the number in the deposit. It’s not like you can go back to where this particular amber grain came from and search for neighbouring grains with an increased chance of hosting another of this species.

  12. Mark R.
    Posted February 12, 2018 at 4:22 pm | Permalink

    How does one land a job creating artistic representations of extinct creatures. What a cool job.

  13. kelskye
    Posted February 12, 2018 at 6:44 pm | Permalink

    It surprises me that creationists don’t use insects more for their attacking evolution. The evolution of the things creationists care about generally is well-attested by biologists, and the sheer weirdness seem in insects has some genuine puzzles and baffling features. Though I suppose it’s not really the evolution they care to disprove…

    Will questions like this ever in principle be able to be solved by genomic analysis among related species and reconstruction through computer modeling?

    • loren russell
      Posted February 12, 2018 at 8:22 pm | Permalink

      NOt really –Alienoptera are extinct, with no closely related insects for genomic analysis. We can just about grasp their way of life by looking for unrelated analogues among living insects.

  14. eric
    Posted February 12, 2018 at 6:45 pm | Permalink

    Very nice article on a cool insect!

    My hypothesis is that they used the scissors to shred unworthy submissions to their journals. 🙂

  15. Posted February 12, 2018 at 6:53 pm | Permalink

    It’s amazing how we find so many weird structures in nature.

    Must be god! /s

    • Nobody Special
      Posted February 12, 2018 at 8:57 pm | Permalink

      The ‘unicorn horn’ tusk of the narwhal is one of my favourite weird structures. We still don’t know the purpose of the tusk, but do know that it isn’t for fighting or defence, appears to play no part in sexual selection or ranking within a pod, and only the males have them.

      • Mark R.
        Posted February 12, 2018 at 10:42 pm | Permalink

        This on Wiki…don’t know the veracity.

        The tusk is an innervated sensory organ with millions of nerve endings connecting seawater stimuli in the external ocean environment with the brain.[22][23][24][25] The rubbing of tusks together by male narwhals is thought to be a method of communicating information about characteristics of the water each has traveled through, rather than the previously assumed posturing display of aggressive “male-to-male rivalry“.[24] In August 2016, drone videos of narwhals surface-feeding in Tremblay Sound, Nunavut showed that the tusk was used to tap and stun small Arctic cod, making them easier to catch for feeding.[26][27]

        Females also have tusks…small percentage.

        • Nobody Special
          Posted February 13, 2018 at 4:32 am | Permalink

          Interesting, but a bit spurious since none of the suggested uses of the tusk help explain why they’re typically male-only. The stunning of fish could easily be learned behaviour, and I fail to see how information on the environments passed through can be communicated by the rubbing together of what are really just weird teeth.

  16. Matis Attila
    Posted February 13, 2018 at 3:50 pm | Permalink

    If Alienoptera is indeed closely related to Mantodea, then maybe these lateral scissors where used in a similar gruesome manner during copulation: to decapitate males, in order to stimulate sperm deposition and use the male’s body as a post-copulation food source. Mantises mate in male-on-top position, but the scissors could be used either way to efficiently decapitate the male from either sides. This would also explain why no males have been found so far 🙂


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