Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
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!
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).
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).
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:
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.
References
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.
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):
Fig. 2. Cladogram showing the phylogenetic position of A. spinosus gen. et sp. nov. Shown is a strict consensus of the 12 most parsimonious trees of 142.16612 steps (consistency index = 0.513; retention index = 0.870), produced using New Technology search options in TNT (tree analysis using new technology) and using implied character weighting with a concavity constant of three. Numbers above nodes are GC support values. 1, Euarthropoda (crown- group); 2, total-group Chelicerata; 3, Artiopoda; 4, total-group Mandibulata; 5, Mandibulata (crown-group).
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.
h/t: Barrie
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.
While in Ottawa, I spent a couple of engrossing hours at The Canadian Museum of Nature. I don’t have a picture of the entire building (built around 1905), but here’s one from Wikipedia. The incongruous glass addition was put on between 2004 and 2010 to replace the original stone tower, whose weight was causing the building to settle into the local clay:
The building is festooned with Canadian-themed animals and decorations. Here’s a carved beaver, one of Canada’s two National Animals (the other is not a moose or a polar bear).
A wolf carved on the staircase inside:
And a moose-themed stained glass window:
Our first stop was the ongoing insect exhibit, with both live and pinned insects. I of course favored the live ones, especially the series of giant beetles. I have no records of what these three are (they’re all huge), but I’m sure readers can identify them. They were all nomming too—and their food looked like banana.
Another huge beetle with horns:
And a big golden one. I have no scale for these, as they were in glass cases, but they were at least two inches long.
The large creature below is a Malaysian jungle nymph (Heteropteryx dilatata). It’s famous for laying the largest eggs of any insect (up to half an inch long, or 1.3 cm), and Wikipedia adds this information:
Females reach a length of 25 centimetres (9.8 in), one of the world’s heaviest bugs, and the males a length of 10 centimetres (3.9 in). The females of this species are very aggressive and much larger, wider, and brighter-colored than the male. The female is lime green and has short, rounded wings, however their short length doesn’t allow them to fly. The males are much smaller and a mottled brown colour. Both sexes have small spikes on their upper bodies, more numerous in the female, who also has very large spines on her hind legs that can snap together as a scissor-like weapon.
This one is clearly a male.
Here’s a female (from Wikipedia); note the spikes:
And both sexes; the sexual dimorphism is clear:
Back to my photos: this one is of Mesohippus, one of the “transitional forms” in the evolution of horses. It lived 30-40 million years ago in what is now North America, and had three toes, having lost one from its ancestor. (Modern horses, of course, retain only the single toe, as the two side toes were lost.)
Its relative size from the link above:
And a shot I took of the toes. You can see that they’re already reduced, and wind up as the “splint bones” on the side of the leg of modern horses.
As I said, the toes became the split bones, a vestigial feature (prone to fracture and injury) attesting to modern horses’ descent from multi-toed ancestors:
On to whale evolution and the transitional forms. The Museum had a nice series showing whale evolution, and here’s one putative ancestor, Pakicetus, discovered and analyzed by Phil Gingerich and colleagues. It’s considered a “basal” cetacean because it has certain features of the ear found only in later and modern whales.
Once thought to be semi-squatic, Pakicetus is now thought to have been largely terrestrial, perhaps spending a bit of time in the water. Here’s a reconstruction:
A bit later in whale evolution we get Ambulocetus, which could clearly walk and swim. It’s thought to have been mostly aquatic, lurking like crocodiles in the shallows to strike animals on land. The rear limbs show modifications for movement in water:
Here’s a reconstruction of Ambulocetus:
The most recent fossil whale in the museum (beside the modern one shown below) is that of Dorudon, which was fully aquatic and lived about 40 million years ago. I didn’t take a photo of the entire fossil, but here are the rear legs, clearly vestigial (unconnected to the rest of the skeleton), but just as clearly the remnants of rear limbs:
Here’s a skeleton from the Senckenberg Museum in Frankfurt am Main:
And a reconstruction (from Wikipedia), showing the tiny rear limbs sticking out from the side. Modern whales have even smaller remnants of those limbs (see below):
Here are all three stages of leg evolution in one shot, in chronological order starting from the bottom:
Here’s a cool dinosaur fossil with head armor and spikes that point both backwards and forwards. I’m sure either Matthew (a dino aficionado) or a reader can identify it, as I’ve forgotten:
Reconstruction of a feathered dinosaur, probably a theropod:
And here’s a species that wasn’t a felid but shows convergent evolution with the “true” cats. I took a photo of the sign below so I could remember it:
And here it is: Hoplophoneus, a member of the extinct family Nimravidae in the Carnivora. It was the size of a leopard and lived in North America about 35 million years ago.
I was amused to find that the French word for “raccoon” (which of course is a New World mammal) is “washing rat”. It is not a rodent, but a procyonid.
Finally, the Museum had an entire skeleton of a blue whale (Balaenoptera musculus), the heaviest animal known to have existed in all the history of life. It weighs about 180,000 kilograms (multiply by 2.2 to get pounds), or about 200 US tons. I photographed its vestigial limbs, which are unconnected to the rest of the skeleton:
This coming Monday, February 1, at 7 PM in the Student Union Cinema, the University of Wisconsin-Parkisde will present Luis Chiappe, Director of the Dinosaur Institute of the Natural History Museum of Los Angeles County, will speak on “Birds of Stone: Avian Fossils from the Age of Dinosaurs”.
Dr. Luis Chiappe of the LACM
Many of the features commonly associated with birds (feather, wings, hollow bones, wishbones) were inherited from their dinosaurian ancestors, and these features arose at various times during the birds’ long Mesozoic history. New fossils have laid out this evolutionary saga in great detail, allowing us to trace the changes from the earliest birds, such as Archaeopteryx, to the dawn of modern birds. The talk, part of UW-Parkside’s Science Night series, is intended for the general public.
At noon on Monday, in Molinaro Hall D 139, Dr. Chiappe will present a more technical talk at the Biological Sciences Colloquium entitled “Birding in the Mesozoic: Recent Insights on the Early Evolution of Birds”. There’s also a small exhibit in the UWP Library, “Dinosaurs and Birds: The Art of Science”, that you can stop in and see.
Both talks are free and open to the public. For the evening talk, parking in the Student Union lot is free after 6:30 PM. For the noon talk, there are metered spots, but if any WEIT readers are planning to come, email and I’ll see what we can do. The talks are presented in conjunction with the exhibit “Dinosaurs Take Flight: The Art of Archaeopteryx”, by Silver Plume Exhibitions in conjunction with the Yale Peabody Museum, at the Kenosha Public Museum, on display now through March 27th.
This is a very well done exhibit, combining fine reproductions of almost all of the eleven known Archaeopteryx specimens (the real ones almost never travel!), with an exploration of how several distinguished paleo-artists create their works, including Julius Cstonyi, whose work we’ve highlighted here at WEIT before.
Anyone from Chicago to Milwaukee is within range, and you can make a day of it– the exhibit at the KPM, two talks, and a stop in UWP’s Library. Even if you can’t make it Monday, the exhibit at KPM is well worth a trip on some other day. Here’s a tidbit– a realistic sculpture– from Dinosaurs Take Flight; I hope to post a fuller report later.
Just in: a cool fossil courtesy of reader James Blilie:
This photo isn’t of a living thing; but rather its traces: A tetrapod trackway in Permian or Carboniferous sedimentary rocks, Cedar Mesa, southern Utah. 2001, Kodachrome 64, probably a Pentax A 20mm f/2.8 lens. Probably f/11 at 1/125 sec. Pure speculation, but it could be from Eryops, or a similar animal. Scale: Those marks are probably 3-4 inches in diameter (7.5 – 10 cm). This first (and only) trackway I’ve found “in the wild” on my own. I might not have noticed it if it hadn’t been for the angle of the sun.
Here’s a reconstruction of the large Eryops (up to 3 meters), a semi-aquatic carnivore that lived about 300 million years ago:
Reader Kevin Voges, a retired university professor in New Zealand, sent a photo of a bird I didn’t know existed (or, if I did—and I probably posted about it years ago!—I’ve forgotten). It’s the tui (Prosthemadera novaeseelandiae), once called the “parson bird” because of its striking white collar, and it’s endemic to NZ. Kevin’s notes:
Just the one photo from me. We’ve been planting natives on our property in the Wakatipu (New Zealand), as well as trying to keep the predator population down, and I put in some bird feeders. This Tui has just moved in this year, apparently they tend to stay once they’ve arrived. The early Europeans called it the parson bird! The yellow on its head is pollen from a flax plant (you can see them at the back).
Tui is the Maori name, not sure of its origin. The Maori have a range of other names, depending on location and age, but Tui is the most common name. The tufts are called poi. We put sugar water in the feeders (one cup per litre), which helps them through the winter when there are less blossoms about. There are a few food sources on our place, flax and fuchsia, with more on the way as the trees mature, but he obviously likes the sugar as well.
Kevin adds, “They are good mimics as they have two voice boxes. Apparently the Maori taught them quite complex speeches“. Here’s a video of a permanently injured (and therefore captive) tui named “WoofWoof,” who speaks prolificially in a Kiwi accent, makes kissing noises, and even whistles “Pop goes the weasel”:
And while we’re on birds from down under, reader Ben Batt (who sent us “spot the stone curlew”), provides more photos:
Bush Stone-curlew (Burhinus grallarius). These birds were quite tame, and would usually just walk away or crouch down and freeze as we approached. They skulk about in an amusingly shifty way, freezing whenever you look at them:
It has long been known that some snakes are two-legged, because many modern species have two legs– externally visible hind limbs– a fact we’ve noticed here at WEIT before.
Hindlimbs (‘spurs’) of a ball python (Python regius). The spurs are next to the anal scale, which covers the vent of the cloaca. (Front of snake is toward top of photo.)
These small external legs, capped by keratinous claws, are supported internally by vestigial femurs and a vestigial pelvis. They are larger in males, and are used during courtship. In the fossil record, snakes with much larger hind limbs have been known since Georg Haas described Pachyrachis in 1979 and Ophiomorphus in 1980 from the early Late Cretaceous (about 95 mya). In these the legs were less rudimentary than in modern snakes, having, in addition to the femur and pelvis, a distinct tibia and fibula, and tarsal bones. That legless tetrapods would have legged ancestors is of course expected, and for the caecilians, a modern group of legless amphibians, a four-legged progenitor was described by Farish Jenkins and colleagues several years ago.
In a new paper paper in Science, David Martill, Helmut Tischlinger, and Nicholas Longrich describe a four-legged snake from the late Early Cretaceous (about 120 mya), of Brazil, giving it the rather aptly descriptive name Tetrapodophis, “four-legged snake”. The fore and hind legs are small, but well developed, with five digits on each. The limbs are suggested to have been used during prey capture. They also interpret it as being fossorial. This is significant, as the two major theories of snake origin are that they came from fossorial (burrowing) ancestors, or that they came from marine ancestors (some of the closest known relatives of snakes are extinct aquatic lizards, and Haas’s specimens come from marine sediments).
T. amplectus appendicular morphology. Fig. 4 from Martill et al. (2015). (A) Forelimb. (B) Manus. (C) Hindlimbs and pelvis. (D) Pes. (E) Pelvis. Abbreviations: fem, femur; fib, fibula; hu, humerus; il, ilium; lym, lymphapophysis; man, manus; mc, metacarpal; mt, metatarsals; ph, phalanges; ra, radius; sr, sacral rib; tib, tibia; ul, ulna; un, ungual.
A long, flexible body, recurved teeth, and intramandibular joint (for opening the mouth wide) all suggest to Martill and colleagues that Tetrapodophis was a constrictor, preying on other vertebrates. This also has significance for what it says about the origin of snakes. Under the fossorial theory, the earliest snakes should have been insectivorous or eating other small prey (as are many supposedly primitive burrowing snakes today). Under the marine theory, the earliest snakes should have been predators of prey “bigger than their heads“, having large, extensible mouths, and associated adaptations of the skeleton and musculature– such snakes are called macrostomatan (literally, ‘large mouthed’). Haas’s two-legged marine snakes are macrostomatan. Martill and colleagues have found what they consider to be a very early macrostomatan, yet fossorial, snake– a cross between the two theories.
Tetrapodophis constricting and eating a small mammal, reconstruction by Julius Cstonyi.
Almost immediately upon its publication, the paper became enmeshed in a series of overlapping controversies, which, while nothing compared to the brouhaha over the insults traded between Nicki Minaj and Taylor Swift, has created quite a stir in the small world of science social media. There are at least three areas in which questions have been raised, so let’s take them one at a time.
Where (and thus when) is the type specimen of Tetrapodophis from? It turns out that the authors of the paper don’t actually know the provenance of the specimen. They have made an inference about it (and they may very well be right), but the fact that they do not even mention the assumed nature of the specimen’s provenance in the paper is shocking. A specimen’s provenance is absolutely crucial information in systematic biology; it is especially so for fossil specimens, because in most instances it is only by examining the geological context of the discovery (the associated fossils within the bed, and the nature of the over- and underlying beds) that we can date the fossil. In this case, we are not really sure where the specimen came from, and thus we cannot be certain of when the specimen died and was entombed in sediment.
I read the paper, and did not realize the provenance was uncertain. The uncertainty, and the argument for why the authors felt they could identify the provenance, are buried in an online supplement. To some it may seem like I’ve been a bit “hey you damned kids, get off of my lawn” about it”, but I’ve long complained of the growing practice of journals, especially Science, of burying key details of papers in ephemeral online sources, and in this case such warnings have come home to roost. Where (and thus when) it’s from is just about the most basic thing you can say about a fossil, and to hide the fact that in this case it’s unknown in an online supplement is unconscionable.
In the online material, Martill and colleagues state that “no notes as to its [the specimen’s] acquisition or provenance are available.” However, in an interview with the BBC, Martill says that he first saw the specimen at the Museum Solnhofen in an “exhibition of Brazilian fossils”, so some notes on provenance seem to have been available to the Museum. Another source states that the exhibit was of fossils specifically from the “Crato Formation”.
Is the fossil, as the authors claim, from the Nova Olinda member of the Crato Formation of Ceara, Brazil? It might well be. Martill is an expert on the formation. Certain fossil localities do have a distinctive lithology and preservation– I can (usually) recognize Green River Formation fossils myself. But to not mention this up front, and provide the justification for the assignment to provenance in the paper, is beyond the pale.
Is Tetrapodophis even a snake? In a news posting on Science‘s website, Michael Caldwell alleges that the specimen is not a snake; in fact, he says, it’s not even a reptile. Rather, the article says, Caldwell thinks it might be a surviving member of a “group of extinct amphibians that died out during mass extinctions about 251 million years ago, long before Tetrapodophis appeared on the scene.” (I’m not sure what amphibians he’s thinking of– perhaps microsaurs or lysorophids?) This would be astonishing– that a group survives 150 million years without a fossil record and then reappears (which does, though, have a partial precedent in the coelacanth), and that the authors and reviewers of a paper in Science could be so wildly off in the identification of the subject of the paper. This of course is not impossible, but it would be surprising. I have only seen the published figures, but Martill and colleagues do discuss and defend the characters by which they assign the specimen to the snakes. Caldwell has published on early snakes and should know their morphology, but he has not seen the specimen either, so it’s hard to give full credence to his views. We’ll have to wait till others get to look at the specimen more closely, or perhaps for a monographic treatment by Martill and colleagues. This is the scientifically most important controversy (although the first controversy is right up there, because much of its significance as a four-legged snake depends on its supposed time of occurrence).
Should fossil collecting and/or exporting require a permit or license? Since the specimen has no collecting data accompanying it, it is unclear if the specimen was collected legally. Fossil collecting in Brazil has required a license since 1942 (or perhaps 1988– recent sources diverge on the date). This is of course not a scientific question, but a question of public policy that has implications for science. To a great extent, the controversy is an old one in paleontology– does amateur and commercial collecting enhance or retard the growth of scientific knowledge? There are strong opinions on both sides. In the United States, this argument flared up over Tyrannosaurus Sue, which was discovered and collected by commercial collectors, but eventually seized from them without recompense (one even went to jail). The downside of such regulation is that many specimens will never come to light, or, if found, will be tossed aside and left to degrade, as their possession would be illegal. A commercial black market may develop, in which the best fossils may be found, but then disappear, unstudied, into private collections. The upside is that specimens will have known provenance, and be of maximal scientific value. Martill has long argued (also here) that in Brazil the permitting system has become so corrupt that scientists are driven out of the field, and that, through bribery, commercial trade flourishes, while many fossils are left to erode and break, as no one may legally save them. He also says it was not always so– for years he worked successfully under Brazil’s regulations. His view:
‘Protecting fossils’ criminalises palaeontologists. Laws banning fossil collecting and private fossil collections deter amateur palaeontologists, drive them underground and stifle curiosity. Fossils left in the ground weather away and are lost. Banning commercial collecting loses tax revenue.
A group of Brazilian paleontologists led by Max Langer, in a strong riposte to one of Martill’s pieces, wrote
Instead, the Brazilian perspective is that taking fossils out of the country is depleting its scientific resources. Brazil has a growing, but still minor scientific community. For palaeontology, keeping the fossils in the country is a way of promoting scientific opportunities. International partnerships are most welcome, but simply allowing fossils to leave Brazil to be studied by foreign scientists mostly helps science in the other countries.
On the issue of regulation, my own view is an in-between one. An analogy can be made (one which Martill disputes) with wildlife conservation. Many species and natural areas require protection. It is often scientists who are at the forefront of advocating for such protections, even though it will add to the difficulty of doing scientific work on the protected species and habitats. It is true that sometimes such regulations can be over-zealously enforced against scientists (in part because they are so visible and have no economic clout), while ignoring the truly endangering factors. But when scientifically informed and sensibly applied, these protections are welcomed by scientists. And, indeed, Martill describes a formerly good relationship with the Brazilian authorities. I do not know enough about the situation in Brazil to have an informed opinion on whether Brazilian policy and practice on this matter has achieved the right balance to encourage discovery and scientific research, while maintaining proper stewardship of their resources.
Another analogy with wildlife conservation issues is what to do with illegally collected specimens. It is standard for wildlife enforcement agencies to donate such materials to museums or educational institutions (although their value as scientific specimens is lowered by the frequent lack of provenance). More controversial is what to do with seized specimens of commercial, but no scientific, value. For example, some advocate the destruction of seized elephant ivory, while others argue that that only drives up prices, leading to more poaching. In the case of fossils, what scientific value there is in them can be extracted by describing them (again subject to the constraints of knowledge of provenance) and placing them in museums (not, by any means, destroying them!).
Regarding the issue of whether fossils should be exported, I am sympathetic to the need to develop scientific institutions throughout the world, and thus to build local collections and relationships between foreign and local institutions and researchers. This must be tempered by recognition that not all places are in a position to care for important collections or engage in collaboration. In this regard, I would note that Brazil has at least one distinguished student of early snake evolution, Hussam Zaher, and at least some excellent museums, although I do not know enough about the situation with the Crato fossils to have an informed opinion on that specific case. I would point to the recent return of Tiktaalik to the Canadian Museum of Nature after 11 years of study in the U.S., and Costa Rica’s policy of a division of collected specimens among foreign and Costa Rican institutions as policies that seem to be working.
The Brazilian journalist Herton Escobar has conducted an email interview with Martill. In it, Martill’s frustration with being denied further access to his field sites in Brazil is evident. He asserts (correctly, in my opinion) that the scientific value of the fossil is not affected by the legality of its collection (to which, I should add, there is no suggestion that Martill or his colleagues were involved in its collection– he first saw it in Museum Solnhofen during a class field trip); its value is affected by the lack of certain provenance. In response to a question as to whether he had sought a Brazilian collaborator, Martill said he did not. Not seeking a Brazilian collaborator is fair enough– he worked with colleagues in England and Solnhofen, close to him and the fossil, and he had at best difficult personal relationships with Brazilian workers at the time. But Martill also goes off on an odd rant about ethnic and sexual diversity in research groups– not at all what Escobar was asking about.
Haas, G. 1979. On a new snakelike reptile from the Lower Cenomanian of Ein Jabrud, near Jerusalem. Bulletin du Museum national d’Histoire naturelle 4: 51–64.
Haas, G. 1980. Remarks on a new ophiomorph reptile from the lower Cenomanian of Ein Jabrud, Israel. pp. 177–192. In Jacobs, L.L.,
ed., Aspects of Vertebrate History. Museum of Northern Arizona Press, Flagstaff, Arizona.
Martill, D.M., H. Tischlinger, and N.R. Longrich. 2015. A four-legged snake form the Early Cretaceous of Gondwana. Science 349:416-419.
Many readers sent me a note about this paper, but, given my schedule, I simply hadn’t gotten around to reading it. Fortunately, Greg did, and gives us a nice summary of what it means.
by Greg Mayer
In the latest issue of Nature, Simon Conway Morris and Jean-Bernard Caron provide a detailed description of Metaspriggina walcotti, a poorly known and enigmatic fossil from the famous Burgess Shale of British Columbia. Originally described by Alberto Simonetta and Emilio Insom in 1993 from a single specimen that had been collected by Charles Walcott around 1910, in 2008 Conway Morris referred a second Walcott specimen to the species, and redescribed the species based on these two specimens. It was Conway Morris who first referred Metaspriggina to the chordates (the group that includes vertebrates, lancelets and tunicates). He and Caron have now redescribed Metaspriggina again, this time on the basis of 100 new specimens from British Columbia, and also referred specimens from a few other North American localities to the genus. The new material is very well preserved, and allows a much more detailed reconstruction.
Metaspriggina reconstruction by M. Collins.
The results of their studies are very interesting. Metaspriggina has the basic chordate features of a notochord, postanal tail, and gills. In addition it has segmented muscles, and the “vertebratey” features of eyes, nasal sacs, and perhaps cranial cartilages and arcualia. (The latter are arrayed along the notochord, and would be ancestral vertebrae.) Most interesting to me is that there are seven sets of paired branchial bars (gill arches), all but the most anterior supporting laterally directed gill filaments. The direction of the latter is significant. In jawed fishes and their descendants, the gills extend laterally from the skeletal arches, while in lampreys and hagfish (the cyclostomes) the gills extend medially from the arches. The lateral gills in Metaspriggina suggest that this is the primitive condition, retained by jawed fishes, and that the medial placement in cyclostomes is derived. The seven pairs of arches also suggest that the many arches of cyclostomes is another derived feature, and that therefore Metaspriggina more closely resembles the jawed fish ancestor. The anteriormost arch, perhaps the homologue of the jaw, differs from the other arches in being more robust.
An, anus; Brv, branchial bars (ventral element); Brd, branchial bars (dorsal element); Brp, branchial bar processes; Es, oesophagus; Ey, eyes; Gu, gut; He?, possible heart; Li, liver; Mo?, possible position of mouth; My, myomere; Na, nasal sacs; No, notochord; Ph, pharyngeal area . (From Fig. 2)
In their phylogenetic analysis, Metaspriggina is close to Haikouichthys and Myllokunmingia, two other very early Cambrian vertebrates from the Chengjiang of China. Metaspriggina (ca. 500-515 mya) is slightly younger than the Chinese forms (ca. 520 mya). An interesting side result of their phylogenetic analysis is that Pikaia, formerly the only known Burgess Shale chordate, and usually considered a cephalochordate (i.e. a relative of lancelets, which is what they look like to me) comes out crownward of the cephalochordates, in fact as the sister-group (i.e. closest relative) of the vertebrates.
This paper is a real advance in our knowledge of vertebrate evolution. It is becoming clear that there is an at least modestly diverse Cambrian fauna of jawless fishes, and that these fossils will help us understand the origin of vertebrates and jawed vertebrates in a way that the extant jawless fishes (the cyclostomes) cannot, due to the latter being collateral relatives with their own long separate evolutionary history and corresponding suite of derived characters. These Cambrian fossils seem to provide a better model for the ancestral vertebrates than do the modern lampreys and hagfishes.
I would also add that these early Cambrian vertebrates look very much like what ancestral vertebrates were hypothesized to look like prior to their discovery.
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Conway Morris, S. 2008. A redescription of a rare chordate, Metaspriggina walcotti Simonetta and Insom, from the Burgess Shale (Middle Cambrian), British Columbia, Canada. Journal of Paleontology 82:424–430.
Conway Morris, S. And J.-B. Caron. 2014. A primitive fish from the Cambrian of North America. Nature 512:419-422. abstract only
Simonetta, A. M. and E. Insom. 1993. New animals from the Burgess Shale (Middle Cambrian) and their possible significance for the understanding of the Bilateria. Bolletino di Zoologia 60:97–107. pdf
A note for taxonomy geeks: In his 2008 paper, and again in this latest one, Conway Morris refers to the second specimen collected by Walcott as the “lectotype”. This is completely wrong. The specimen upon which a new species is based is the holotype; additional specimens upon which the original description is based are called paratypes. In the old days, before the current rules were codified, authors would frequently base a new species description on several specimens, without specifying a particular specimen to be the name-bearer or holotype. When no holotype was designated, all the specimens had equal status, and were called syntypes. This is bad in case it should turn out that the original set of specimens actually comprised more than one species (this happened a lot). A later author, in order to insure nomenclatural stability, is permitted to choose from among the syntypes a single specimen to be the primary type of the species. This selected syntype then becomes the lectotype, the other syntypes becoming paralectotypes. A lectotype has the same status as a holotype, in that it fixes application of the name should the type series prove to be composite.
So what’s wrong with the second specimen being a lectotype? Well first off, the second specimen was not part of the original type series, and so cannot possibly be a lectotype. (Simonetta and Insom mentioned this specimen, but thought it taxonomically distinct from Metaspriggina, so it was not part of the basis of the description of Metaspriggina— only the first specimen was.) If a holotype is lost or destroyed, or for some other very good (and rare) nomenclatural reason, it is possible to designate a new primary type, which would be called a neotype. But the holotype of Metaspriggina (the single original specimen) is still in existence and readily observable, so there is absolutely no need to try to designate a new primary type. This is inside baseball and perhaps small beer, but it’s really puzzling how Conway Morris seems not to understand the rules of nomenclature, and how this has not been caught by reviewers or editors.
