The Irish paleontologist and Yale professor Derek Briggs—no relationship to the other famous Irish paleontologist Sir Arthur “Artie” O’Dactyl—is famous for his work on the Burgess Shale fauna. He’s actually speaking today on that fauna at Chicago’s Field Museum, but I’ll be unable to attend. But we can all still marvel at some new work on younger specimens just published by Briggs and his colleages, reported in the early online edition of the Proceedings of the National Academy of Sciences (reference below, not sure if there’s free download for non-subscribers). There’s also a description of the work for nonscientists at the BBC’s site.
Briggs et al. describe a Silurian fossil (about 430 million years old) from a formation in the UK, a fossil that appears to have a unique method of brood care. It was a tiny fossil, only 1 cm long, and finding out what it really was took careful preparation: grinding it away bit by bit (and of course destroying the specimen), and imaging it at each stage to produce a three-dimensional reconstruction. The animal proved (see below) to be an early arthropod.
What Briggs et al. found in the reconstruction was remarkable. Tethered to the “tergites” of the specimen (the post-cranial segments of the beast) were ten capsules, each attached by a long filament. And each of those roughly triangular, kite-shaped capsules (ranging 0.5 to 2.0 mm in size) consists of an outer shell containing a mass of tissue, some with limbs visible. The capsules are tethered to the parent specimen with long filamentous threads. Here’s what it looks like in reconstruction:
What were these weird attachments? The most likely explanation is that they’re offspring of the specimen, being carried around—perhaps for protection of the developing embryos.
Although weird, this is not completely unknown in animals. As the authors point out, the developing embryos of the freshwater crayfish Astacida are atttached to the mother by smaller stalks, and I’ve managed to find a photo of that in a paper from 2004:
However, these aren’t the long filaments (or tough embryo-containing capsules) described in the Briggs et al. paper. In that respect, what they found in this specimen, named Aquilonifer spinosus, is unique among animals. By the way, the source of the name is described by the authors:
The name of the new taxon refers to the fancied resemblance between the tethered individuals and kites, and echoes the title of the 2003 novel The Kite Runner by Khaled Hosseini (aquila, eagle or kite; –fer, suffix meaning carry; thus aquilonifer, kite bearer; spinosus, spiny, referring to the long lateral spines on the tergites).
I can’t think of any other animal named after a novel, but I’m sure there must be at least one.
The authors suggest, and reject, two other possibilities for these tethered kite-like structures: they could be parasites, or they could be epizoans (nonparasitic organisms that colonize others). They rule out parasites because there doesn’t appear to be any advantage for a parasite to absorb nutrients from a host through such long threads, and because the places where the threads attach to the “host”—on its spines—aren’t a great place to suck nutrients from.
They also argue that epizoans are unlikely because none are known that attach in this way, because ten epizoans probably would have killed the specimen (which was apparently alive and healthy when preserved), and because A. spinosus could have cleaned off such epizoans with its long head appendages. I agree with the authors that these capsules, particularly because some contain tissue with legs, are likely to represent a heretofore unknown form of brood care.
Finally, where does this new species fit? As I noted above, it’s an arthropod, at least based on the cladistic analysis conducted by the authors. The cladogram based on many morphological characters puts it with the arthropods (node 1), but in particular with the Mandibulata (node 4), the subgroup that includes centipedes, millipedes, crustaceans, and “hexapods” (insects and three other and much smaller groups):
The upshot: the paper doesn’t really produce new generalizations about life, but rather the discovery of a particular way of life that was completely surprising. There’s nothing wrong with such an anecdotal observations, for that’s the kind of thing—the multifarious and unexpected variety of life—that keeps our wonder alive.
Addendum, by Greg Mayer: Jerry did not get a chance to go to hear Derek Briggs at the Field Museum yesterday but I did, and Jerry asked for a report.
Briggs talked mostly about his work on the “kite runner” (which, he noted, he named after Khaled Hosseini’s 2003 novel), so I won’t restate what Jerry covers admirably above. Briggs mentioned that the reviewers were less certain than he was that the ‘kites’ were juveniles, rather than parasites or something else, and that he did see the reviewers’ point, but still thinks they are juveniles. He showed a number of neat 3-dimensional rotating videos of their fossil reconstructions. For a museum audience, it was a bit wince-inducing, but understandable, to know that the method of preparation destroyed the specimen. Briggs is a also a museum guy, and is working to develop non-destructive forms of imaging, and was consulting on this trip with physicists at Argonne National Laboratory. Such imaging would also be enormously time saving, as the specimens come in nodules, and they don’t know what fossil is in a nodule till it’s ground through a considerable ways. He also quipped that PNAS (where his paper was published) stands for “Probably Not Acceptable in Science“, which is a “nerdy science joke“. (BTW, I think Jerry’s Artie O’Dactyl also eminently qualifies as a “nerdy science joke“!)
He made two other interesting points. First, the apparent extinction of many of the unusual soft-bodied forms at the end of the Cambrian seems to be a preservational artifact. There is a period from the late Cambrian into the Ordovician from which no lagerstatten are known. (Lagerstatten are deposits with unusual preservation in which soft parts are fossilized, such as the Burgess Shale of British Columbia.) Cambrian “weirdos” are now turning up in these later lagerstatten. For example, anomalocarids (well known in the Burgess Shale), are also now known from the Fezouata, Morocco, lagerstatte, which is Ordovician. There are a lot of taxa represented in the Ordovician, which is the peak of diversity origination, referred to as “GOBE” (the Great Ordovician Biodiversification Event).
Second, he talked a fair amount about limb evolution in arthropods, and noted that an early horseshoe crab, Dibasterium, had an extra row of legs compared to modern Limulus. In Limulus, it turns out that important “leg genes” are also activated in the embryo in a row of small spots parallel and lateral to the actual legs– in just the places where Dibasterium‘s extra legs are! (The developmental work was done by someone else.) This reminded me of the phenomenon in vertebrates with reduced numbers of toes in which toe primordia develop a bit, and then regress.
Briggs, D. E. G., D. J. Siveter, D. J. Siveter (one is Derek, the other David!), M. D. Sutton, and D. Legg. 2016. Tiny individuals attached to a new Silurian arthropod suggest a unique mode of brood care. Proc. Nat. Acad. Sci. USA: Published online before print, April 4, 2016, doi:10.1073/pnas.1600489113