Guest post: Kite runner fossil – babies or phoretic mites?

JAC:  Both Matthew and I had forgotten about Matthew’s 2013 post here on mites, describing a phenomenon that might explain the  the “Kite Runner fossil that received a lot of attention.  At that time the Kite Runner wasn’t known, but biologist/author Ross Piper submitted a post (he’s a friend of Matthew) arguing that the objects tethered to the Kite Runner arthropod might not be progeny, but phoretic symbionts (“phoretic” animals are ones that used members of other species to transport them). Pity that Derek Briggs and his colleagues didn’t read WEIT before they published their paper!

By Ross Piper

Last week Jerry posted a discussion of the ‘Kite Runner’ fossil, an intriguing 1 cm-long fossil arthropod that was found in 430 myr old volcanic ash. Aquilonifer spinosus is intriguing because of the small objects that are tethered to the animal, which Derek Briggs and his colleagues interpret as the animal’s offspring. They conclude that the fossil represents a unique form of brood care unknown in the animal world, something that Jerry agreed with. Here it is again in all its glory:


I am a little sceptical, as there is another possibility that the authors did not fully consider. I think that the smaller organisms may be using A. spinosus to hitch a ride, rather than being babies. This kind of behaviour is known as phoresis.

Briggs et al. discussed the possibility that the attached structures are phoronts/epizoans/parasites, and dismissed this idea (again, Jerry found their arguments convincing). However, in looking for potential phoretic candidates they only looked at crustaceans. But if we look at mites, specifically a stage in the life-cycle of Uropodina mites known as the deutonymph, we can find a very good match. Furthermore, these mites and their weird life-style have been discussed here about three years ago!

These mites are fond of habitats that are very patchily distributed in space and time, such as mounds of dung, carcasses, dead wood and other similarly attractive places. Mites are small and wingless, so to reach new habitats they enlist the help of animals they share these habitats with, in particular various beetles (Aphodiidae, Geotrupidae, Scarabaeidae).[1]

To attach themselves to the shiny exoskeleton of a beetle that can fly very swiftly Uropodina mites have evolved the ability to tethering themselves to a beetle using a long anal pedicel (Figure 1 and 2).

Figure 1

Uropodina mite deutonymph (Urobovella nova) detached from its beetle vehicle. Arrow indicates point of attachment to beetle. Scale bar: 200 µm. Taken from reference 3.

Like the silk of a spider, the pedicel is secreted by glands in the rear part of the mite’s body and extruded from its anus.[2] The mite rubs its anus against the beetle before extending its hind legs or walking away from the anchor point to extend the tether.3

Both the glands from which the pedicel is produced, and the way it hardens, suggest it the pedicel is made of some form of silk. As an entomologist I have seen these deutonymphs atop their pedicels on numerous occasions, often a profusion of them on a single beetle (Figure 2).

Figure 2

Uropoda orbicularis deutonymphs on the dung beetle Aphodius prodromus. Note the lengths of the pedicels in C and D and the scattered distribution of the deutonymphs. It is thought that pedicel length is related to risk of detachment (longer pedicels when risk of detachment is greater). Taken from reference 2.

In the post from 2013, WEIT published these photos from Daniel Llaveneras from a beetle he found in the Andes, which he posted here:

Beetle is roughly 3 cm long

Definitely not a mold!

I think something like these mites is a better interpretation of the Aquilonifer fossil ‘babies’.

Briggs et al argued that the relatively large number of small individuals associated with the fossil was evidence against these being hitchhikers: “[Aquilonifer] is unlikely to have tolerated the presence of so many drag-inducing epizoans”.

But the Deutonymphs shown in the photos travel in groups and are often found in profusion on their host. Frequently, one deutonymph is attached next to the other, even if other beetle body parts are free of mites.2 In fact, these phoretic deutonymphs atually prefer places already infested by deutonymphs.3 [iii] The impact of these passengers on the flying ability of a beetle is unknown, but it must be at least as significant as the potential impact on an aquatic host.

Something else that points to a phoretic interpretation for the A. spinosus fossil is the location of the tethered individuals. If they were genuinely offspring you would expect them to be clustered in one area to limit their impact on the parent’s swimming/foraging abilities (this is what we can see in the modern crayfish with attached embryos, which Jerry included in his post). Instead the tethered individuals are scattered across the body of Aquilonifer, which is very similar to mite deutonymphs (Figure 2).

I was also struck by this the description of the attached individuals in the Briggs et al. paper:

‘The very small size and consequent lack of detail revealed by the grinding technique make the individuals attached to Aquilonifer difficult to interpret….The outer covering of the capsules resembles a carapace that encloses the body and opens at one extremity.’

The deutonymphs of some other mites with their extended carapace are good fit for this description, as per this image from the excellent macromite blog:

Although there are no known mites of the same age as this Aquilonifer fossil, mites are known from the early Devonian4 and there are marine mites today. Having hitch-hikers rather than babies would still be pretty exciting, and a consideration of modern mites would have enriched the paper. That having been said, it is hard to see how we could test between the baby and the hitchhiker hypotheses.

Cutting edge technology and the ability to visualise small specimens in three dimensions has revolutionised palaeontology, but in the clamour to interpret how these long dead animals lived we sometimes run the risk of overlooking the insights offered by the remarkable adaptations of living organisms.



1. Bajerlein D, Witaliński W (2014). Localization and density of phoretic deutonymphs of the mite Uropoda orbicularis (Parasitiformes: Mesostigmata) on Aphodius beetles (Aphodiidae) affect pedicel length. Naturwissenschaften 101:265–272.

2. Bajerlein D, Witaliński W, Adamski Z (2013). Morphological diversity of pedicels in phoretic deutonymphs of Uropodina mites (Acari: Mesostigmata). Arthropod Struct Dev 42(3):185-96.

3. Faasch H (1967). Beitrag zur Biologie der einheimischen Uropodiden Uroobovella marginata (C. L. Koch 1839) und Uropoda orbicularis (O. F. Müller 1776) und experimentelle Analyse ihres Phoresieverhaltens. Zool Jahrb Abt Syst 94: 521–608.

4. Hirst S (1923). On some arachnid remains from the Old Red Sandstone (Rhynie chert Bed, Aberdeenshire). Annals and Magazine of Natural History (Series 9), 12: 455-474.



  1. Joseph McClain
    Posted April 14, 2016 at 10:22 am | Permalink

    Very interesting. Would remoras be considered phoretic symbionts? They attach and reattach, does that make a difference? And barnacles?

    • John Harshman
      Posted April 14, 2016 at 11:15 am | Permalink

      Phoresis generally refers to hitching a ride purely in order to get somewhere, at which point you deplane. Remoras want to be near sharks in order to get food, and barnacles are permanently attached. So I think neither one would count.

      • Joseph McClain
        Posted April 14, 2016 at 12:49 pm | Permalink

        Very good. Thanks.

  2. eric
    Posted April 14, 2016 at 10:27 am | Permalink

    Interesting counterpoint. Keep the science posts coming! 🙂

  3. GBJames
    Posted April 14, 2016 at 10:30 am | Permalink

    Most interesting.

  4. Posted April 14, 2016 at 10:31 am | Permalink

    Very very cool! Amazing little critters those mites!

  5. Loic
    Posted April 14, 2016 at 10:31 am | Permalink

    Very interesting post. Ross convinced me. Looks more likely than babies. (Im a layman)

    Not a useful comment, but I guess we have to make such comment or JAC might threaten to stop scientific posts. 😉

    • GBJames
      Posted April 14, 2016 at 10:32 am | Permalink

      😉 !

    • Steve Pollard
      Posted April 14, 2016 at 11:02 am | Permalink

      I would not even dare to make a comment, other than that I am lost in wonder at these remarkable images and the insight that has gone into interpreting them.

      • Posted April 14, 2016 at 11:05 am | Permalink

        Your comments help support these science threads. Keep them coming.

    • gravelinspector-Aidan
      Posted April 21, 2016 at 3:48 am | Permalink

      A simple “sub” would probably suffice. The point was (probably) that the WP system couldn’t tell if someone read the post when read on the main page of the blog, so Jerry only got informed of a “view” of the post from people who clicked-through to the post body (loading a new page, which WP did count) to read and/ or comment.
      Therefore, a “sub” should help WP keep PCC(E) accurately informed of the readership of the science posts. And any others.
      Personally, my browsing habit is to go to the most-recent post, then work back on the “previous” button until I see a post I’ve read already. Then I look at my comment notifications. That way, everything I read gets noticed by WP as at least one view ; multiple views are registered if I need to read someone else’s comments and reply.

  6. Posted April 14, 2016 at 10:34 am | Permalink

    I lean to the phoretic interpretation because it is known in nature. Tethered brood-care would be, as Briggs et al admit, unique. How likely is it that this extinct species used this brood-care method given that it is unknown in other species?

    • darrelle
      Posted April 14, 2016 at 11:45 am | Permalink

      I agree. Tethered brood-care is possible, but this interpretation, with the photos of extant critters that look so similar to the ‘Kite Runner’ fossil supporting it, seems significantly more plausible. At the moment.

      • loren russell
        Posted April 14, 2016 at 5:58 pm | Permalink

        I’d give about equal odds for phoresis and brood-care/brood-transport. The superficial resemblance to uropodid deutonymphs is not persuasive to me — phoresy in the latter presumably dates from sometime in the late Mesozoic in terrestrial habitats. [Incidentally, the modern exemplars may be mutualistic, not merely hucking rides — these mites, as well as adults of other mites that catch rides on dung and carrion beetles — probably help clean the beetles’ substrates of competing fly larvae and eggs.]

        Ideally, you would want to resolve the kites’ appendages to determine if they are likely larvae of the bearer [eg, basal-mandibulate clade], or arachnid-ish. Unfortunately, the fossil was destructively sampled — what we see is what we get.

  7. Charlie Jones
    Posted April 14, 2016 at 10:48 am | Permalink

    The mites reminds me of an opposite situation, in which Darwin working on modern barnacles carefully removed all marine mites that he found are certain barnacle specimens. Eventually he realized that they were not mites, but were in fact male barnacles. The males had reduced themselves to nothing more than tiny penis parasites permanently attached to the females.

    Other barnacles, as many WEIT readers will know, are famous for having the longest penises relative to body size in the animal kingdom. And this raises another possibility: The mysterious creatures attached to Aquilonifer spinous may be the males, dragged along by their elongate Members! 😉

    • Mark Sturtevant
      Posted April 14, 2016 at 11:26 am | Permalink

      Given this point, which is a damn good one, and the fact that the arthropod is possibly a crustacean, I agree that this opens the possibility that the hitchhikers here could be males.

    • darrelle
      Posted April 14, 2016 at 11:47 am | Permalink

      Very interesting!

    • rickflick
      Posted April 14, 2016 at 8:16 pm | Permalink


      • neil
        Posted April 15, 2016 at 3:00 am | Permalink

        i think that almost anything sounds more plausible than it being a brood of young; sadly, i feel that this was released as one of those “we haven’t been in the news for ages, put out a press release!” incidents where they’ve sought attention before thinking it through.
        Another option: could the things on stalks be hatching parasites, caught in the act of leaving the dead host in the way that ichneumon (speling alert! 🙂 ) wasps hatch from parasitized caterpillars?

  8. Chris G
    Posted April 14, 2016 at 10:48 am | Permalink

    Fascinating, amazing photographs, genuinely interesting to dip into new areas of knowledge and scientific investigation I wouldn’t otherwise access.
    But I don’t have any view or comment to make on the content/arguments/reasoning, don’t understand all the terminology/concepts, and I can’t say I follow Jerry’s site specifically for this kind of posting.
    However, my reading is broadened despite being more attracted by the religious/political/human-society stuff.
    So thanks for the wide mix Jerry, it is appreciated.

  9. Posted April 14, 2016 at 10:54 am | Permalink

    Just another example how terribly difficult it is to interpret fossils! If I remember correctly, there was a similar story about Oviraptor – it was named so because the eggs below a fossil were presumed stolen for breakfast from another species, then scientists moved to the opinion that the fossil was a mother guarding her own eggs.

  10. Michael Scullin
    Posted April 14, 2016 at 10:58 am | Permalink

    Years ago I snagged a dragonfly which had a “large” red mite attached at the base of a wing. Since then I pay more attention and have seen all manner of tiny mites on all manner of insects. What is amazing to me is that all the organs and paraphernalia it takes to sustain a life smaller than a period can be crammed into a creature so small. I’ve never seen anything like this (I’m in Iowa), but somehow it doesn’t surprise me. My entomological education takes the form of one class in college, but I have served as host for chiggers and ticks so I have some familiarity with the eight legged critters.Most spiders are welcome at our house where we have a fondness for the jumping spiders which are already out and about.No Drosophila yet, but after Jerry retired a swarm showed up at out compost bucket. I once did a squash of fruitfly salivary glands for the giant chromosomes. Got an “A.”

    • peter
      Posted April 14, 2016 at 2:49 pm | Permalink

      “where we have a fondness for the jumping spiders which are already out and about”

      I love those too..and Tarantulas. Where I live now we have a lot of funnelweb weavers, living in the holes and cracks in stonewall houses and the walls dividing properties.

      and we have a lot of those, up two inches long.

      they look somewhat like the fossilized arthropod.

      • Michael Scullin
        Posted April 14, 2016 at 9:26 pm | Permalink

        When I lived in southern Minnesota in an ancient house (1862 newspapers used for insulation) we had a lot of those centipedes. If one dropped on your neck from the ceiling you would be anything but fossilized. I guess they found a lot to eat in our field-stone basement.

  11. Torbjörn Larsson
    Posted April 14, 2016 at 11:22 am | Permalink

    I can’t believe I forgot that post!

    I am also floored yet again by mites and their behavior.

  12. BobTerrace
    Posted April 14, 2016 at 11:23 am | Permalink

    Side note to PCCE:

    I read many of the science posts without commenting. I most often read them in email or in my RSS reader Feedly. In either case, there would not be a click reference to the articles.

    Also, I read the daily Reader’s Wildlife photographs the same way but hardly ever comment.

    • HaggisForBrains
      Posted April 15, 2016 at 4:08 am | Permalink


  13. Mark Sturtevant
    Posted April 14, 2016 at 11:30 am | Permalink

    The phoretic mite idea seems pretty good, as is the possibility mentioned by C. Jones above that the hitchhikers are parasitic males.
    Other possibilities? Are there algae like these things? Big stalked protists? Of course with the latter two possibilities one would expect to see them on other animals as well.

  14. nickswearsky
    Posted April 14, 2016 at 11:59 am | Permalink

    Now this story becomes more interesting! Thanks for keeping up on it.

  15. blasphemyisavictimlesscrime
    Posted April 14, 2016 at 12:15 pm | Permalink

    I love this science in action business. Please continue with the posts.

  16. Bob Bottemiller
    Posted April 14, 2016 at 12:17 pm | Permalink

    As Swift wrote:
    Big fleas have little fleas,
    Upon their backs to bite ’em,
    And little fleas have lesser fleas,
    and so, ad infinitum.

  17. Jiten
    Posted April 14, 2016 at 12:35 pm | Permalink

    Truly fascinating!

  18. Posted April 14, 2016 at 12:36 pm | Permalink

    Now that you mention it, I’ve seen photos of these kinds of tethered mites recently on a microphotography blog. I did not connect them to this.

  19. Pliny the in Between
    Posted April 14, 2016 at 12:39 pm | Permalink

    How can anyone accuse science of unraveling the rainbow when you see how amazing is the reality and variety of living creatures

  20. Posted April 14, 2016 at 1:46 pm | Permalink

    This is great! Write this up and submit it to an appropriate venue.

    • Posted April 14, 2016 at 3:29 pm | Permalink

      I think Ross is doing exactly that.

  21. Merilee
    Posted April 14, 2016 at 2:47 pm | Permalink


  22. Petra Sierwald
    Posted April 14, 2016 at 3:22 pm | Permalink

    Somebody had to bring up mites. I usually try to avoid thinking about them: there are so many of them…
    Tethered mites are rather common in certain millipedes (all terrestrial). I am working on a morphological atlas of millipedes, and we use UV light (cool images) and SEM for it. Especially millipedes of the polydesmid family Platyrhacidae live in some form of symbiosis with numerous other organisms, also with tethered mites. I found several specimens with tethered mites on the antennae, on the legs, and on the underside of their ‘side wings’ (called paranota). These mites have short stalks. When I saw them, I closed my eyes. I do not want to get into mites, there are so many mites, they are hard to work with, and there are not many mites specialists.
    The day in a life among the millipedes..
    See the beautiful Platyrhacidae, go to Wikipedia and check the link to external images)

  23. Beau Quilter
    Posted April 14, 2016 at 3:24 pm | Permalink


  24. Posted April 14, 2016 at 4:23 pm | Permalink

    Great post! I find your argument quite convincing.

    Posted April 14, 2016 at 4:56 pm | Permalink

    Reminds me of a ee cummings poem

    fleas have fleas
    have fleas
    that bite’em
    ad infinitum

    • gravelinspector-Aidan
      Posted April 21, 2016 at 4:07 am | Permalink

      Hmmm, Cummings or Swift? I’ve seen the poem attributed to Swift many times before.

  26. keith cook±
    Posted April 14, 2016 at 6:20 pm | Permalink

    The story of life goes on at the same time making me feel like I need a haircut. It has to be a very successful way of making a living TRex would be envious.

  27. W.Benson
    Posted April 14, 2016 at 7:08 pm | Permalink

    Seems that this 430 myr old mystery is going to take a little longer to solve. Phoretic hitchhiking seems to be a reasonable explanation. I find it hard to believe that a female would lay eggs/embryos rather randomly on its body (or that of the male). There must be a best place to carry eggs that would have been favored by natural selection. Parasites must take what they can get.
    Thank you for the interesting essay.

  28. jaxkayaker
    Posted April 14, 2016 at 11:23 pm | Permalink

    Thanks to Ross, Greg & PCCE. Also to Charlie Jones. Since phoretic mites & parasitic males are known to exist, I think these are more likely than the original explanation, which still might be true. However, extraordinary claims, yada yada.

  29. Dale Franzwa
    Posted April 15, 2016 at 12:28 am | Permalink

    I did read this post and the other one too. Interesting.

  30. Diane G.
    Posted April 15, 2016 at 1:25 am | Permalink

    Great hypotheses (the author’s & some of the commentators’), super pictures! Thanks so much for this, Ross!

  31. scrubmuncher
    Posted April 16, 2016 at 4:41 am | Permalink

    Thanks for all the comments. I should have made it clear in the post I am using mite deutonymphs as examples of how phoronts/epizoans can adhere to their carrier/host as an alternative explanation of the ‘kite runner’ fossil. This is not to say that the ‘smaller individuals’ are definitely mites. Arthropods certainly, but there are many other things they could be. To my mind what really makes a strong case for the alternative explanation is the wide distribution of the ‘smaller individuals’ over the body of Aquilonifer.

  32. John Scanlon FCD
    Posted April 17, 2016 at 10:19 am | Permalink

    I was surprised that anyone is still using the grinding technique for 3D fossils; there’s nothing wrong with (G.G. Simpson described clever apparatus for the method in 1933) except that it’s been superseded by micro-CT. Very high resolution can be obtained using synchrotron radiation, and it’s non-destructive (as long as you don’t stand in front of the beamline).

    • gravelinspector-Aidan
      Posted April 21, 2016 at 4:13 am | Permalink

      Briggs et al have no doubt tried micro CT. IIRC, Brigg is based in Oxford, near the DIAMOND synchroton source, which is suitable for the technique. Briggs alone has the authority to get time on top-of-the-line equipment, even without this magnificent Lagerstatten in his collecting bag.
      If there is insufficient mineralogical or compositional contrast between matrix and fossil, then micro CT wouldn’t have anything to “get hold of.”

%d bloggers like this: