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.
Sue, the iconic Tyrannosaurus rex that has inhabited the Field Museum of Natural History‘s Stanley Field Hall since 2000, is coming down. But, shortly after she comes down, she’ll be going up– upstairs that is. The Museum announced plans last year to replace Sue in Stanley Field Hall with a model of Patagotitan mayorum, a much larger dinosaur than Tyrannosaurus rex. At the same time, they’ll be adding plants and pterosaurs to the Hall. Bill Simpson (who for some reason appears to be being assisted by Ricky Gervais) explains what’s going to happen to her in this video. (And continue watching the next video, also featuring Bill, that comes up after the first finishes.)
A similar model of Patagotitan has been on display at the American Museum of Natural History in New York for a couple of years now. It doesn’t even fit in the dinosaur hall there, and its head and neck poke out into the hall way to greet visitors arriving by elevator! Sue will be moving upstairs to the Field’s second floor, whose balconies overlook the Hall, where she’ll join the rest of the dinosaurs in the Evolving Planet exhibit. Sue is a theropod, and though in the same order of dinosaurs as Patagotitan, which was a sauropod, Sue and her kin ate creatures like Patagotitan and its kin.
I had gotten to see Sue up close during the study and preparation phases prior to her being placed on exhibit, and wanted to say farewell (for a little while), so I went down to see her before the deconstruction. These are pictures from a visit in late December.
Sue towers over her human prey admirers in Stanley Field Hall.Getting closer to Sue’s business end.The better to eat you with.The somewhat old-fashioned painted reconstruction on the second floor, overlooking Sue down below. Sue’s skull, which is too heavy to be supported on the body of the mounted skeleton in Stanley Field Hall, has always resided in a separate display case on the second floor balcony, just below this painting.One of the pterosaurs is already in position.
I went down again last month, and took a few more pictures, mostly closer shots of interesting parts of her anatomy.
A closer view of her teeth.Her reduced, two-fingered, forelimbs. The functional significance of this feature is much speculated on, but unknown.Her strong, 4-toed (3 forward, 1 back) hind foot. These provided a powerful mode of locomotion.Au revoir, Sue!
The tale of how Sue got from South Dakota to the Field Museum is a long and tortuous one, and not very edifying; but that’s a story for another post.
The Earth is about 4.54 billion years old, and the oldest undisputed life on our planet appears as bacterial “microfossils” 3.5 billion years ago. But because bacteria are already quite complicated organisms, it’s a good bet that life (however you define it), began well before that. But how long? The seas weren’t around much before about 4 billion years (the Earth was too hot), and there was no oxygen. Life, if it existed about then, was probably adapted to extreme temperatures and was anaerobic (not requiring oxygen).
A new paper in Nature by Matthew Dodd et al. (free access, reference below) has reported what may be traces of life (iron-containing filaments and tiny tubes) that resemble the kind of life found in modern hydrothermal vents, as well as in undisputed microfossils. The age of the sediments, which are from Hudson Bay in Quebec, Canada, spans a range between 3.77 and 4.28 billion years. They can’t narrow it down much more than this large range, and of course the press is concentrating on the 4.28-billion-year date, because that’s about the earliest life could have formed given the state of the Earth then.
I won’t go into detail about the paper: it’s a hard slog even for an evolutionary biologist, for it’s largely geology and paleobiology. But one expert I asked said that the results are very interesting but not conclusive, and that the age range of course is quite large. Here are a few photographs of what may be the remnants of ancient bacteria. First are the filaments (click to enlarge pictures):
(From paper): a, Filaments from the NSB attached to a terminal knob (arrow) coated with nanoscopic haematite. b, Filaments from the Løkken jaspers coated with nanoscopic haematite and attached to terminal knobs (red arrows) and branching (orange arrows). Inset, multiple filaments attached to a terminal knob. c, Filaments from the NSB in quartz band with haematite rosettes (green arrow). Inset, branching filament (orange arrow). Green box defines d. d, Filament from the NSB enveloped in haematite (inset, same image in cross polars).
And the tubes:
(From the paper): a–f, Tubes from the NSB. a, Tubes associated with iron oxide band. b, Depth reconstruction of tubes with haematite filament (arrow). Inset, image of tubes at the surface. c, Tube showing a twisted filament (red arrow) and walls (black arrow). d, Strongly deformed tubes. e, Depth reconstruction of tubes. f, Two tubes attached to terminal knob (arrows); lower image taken in false colour. g, h, Tubes from the Løkken jaspers. g, Tube showing filament (red arrow) and walls (black arrow). h, Aligned tubes (green arrows).
These of course are not microfossils themselves, which are the fossilized remains of ancient bacteria, but simply traces of what may be ancient bacteria.
But many experts in the field were skeptical of the new study — or downright unconvinced.
Martin J. Van Kranendonk, a geologist at the University of New South Wales, called the patterns in the rocks “dubiofossils” — fossil-like structures, perhaps, but without clear proof that they started out as something alive.
. . . And if these are fossils 4.2 billion years old, then scientists will have evidence that life began quickly on Earth, not long after the oceans formed.
Yet Frances Westall, the director of research at the CNRS-Centre de Biophysique Moléculaire in Orléans, France, isn’t convinced these are fossils at all. “I am frankly dubious,” she said.
For one thing, she has argued, the filaments in the Nuvvuagittuq rocks are too big. She and her colleagues have found filaments formed by bacteria in rock dating back 3.3 billion years, and these are far smaller.
On the early Earth, bacteria were forced to stay small, Dr. Westall said, because the atmosphere did not yet have enough oxygen to fuel their growth.
From someone more enthusiastic:
“I think the authors have done a good job,” said David Wacey, who researches the origins and evolution of life at the University of Western Australia. With the new evidence, he said, “One comes up with a pretty convincing biological scenario” for the origins of the mysterious rock features.
Dr. Wacey was not surprised that the new work had drawn criticism. “It may be many years before a consensus is reached,” he said. “But this is how science progresses.”
I think the last sentence is the operative one. This is by no means evidence for early life, or even for its age, but it was certainly worth publishing and will doubtlessly lead to more work. If life really did exist 4.3 billion years ago, then it means that it didn’t take long after Earth’s conditions were “right” for carbon-based and water-requiring life to begin proliferating.
In a market in Myanmar, the Chinese scientist Xing Lida, shown in the picture below, found a piece of amber about the size of a dried apricot, and it had an inclusion. The seller, thinking the inclusion was a piece of plant, raised the price, for biological items in amber dramatically increase its value. Still, Xing bought the piece at a relatively low price, for the seller didn’t realize that the inclusion was not a plant, but part of a theropod dinosaur! And so it was: part of the theropod’s tail, which was sprinkled with feathers. The specimen turned out to be from the mid-Cretaceous, about 99 million years old. It’s a remarkable piece:
The specimen: a bit of theropod dinosaur tail with very clear feathersRyan McKellar and Xing Lida (discoverer of the specimen) with some amber from the site. Photo from CNN.
That specimen tells us something about the nature and evolution of dinosaur feathers, which evolved long before the feathers were used for flight in the birds that evolved from theropods. The function of these feather rudiments still isn’t known, but they were likely to be for thermoregulation and could also have served as ornamentation. (Sexual selection is probably ruled out since there doesn’t seem to have been sexual dimorphism in the feathers.)
The paper, by Lida Xing et al. (reference below, along with link that may or may not allow you to get the full pdf), is the first to describe not only feathers in amber, but also mummified skin and skeleton. It apparently belonged to a non-avian coelurosaur, the group of feathered dinosaurs from which birds are descended (not all paleontologists and ornithologists agree about that scenario, though most do). Based on the tail, the animal was very small: a CNN report on the finding says the specimen could fit in the palm of your hand, and was about the size of a sparrow. Can you imagine a dinosaur that small?
The remarkably preserved feathers were examined with phase-contrast X-ray scanning (right below), which showed a paired series of feathers along the midline of the dorsal (top) part of the tail (the bottom is sparsely feathered). Some color can be discerned, suggesting the dinosaur was white and chestnut brown, also like a sparrow. In B, below, you can see some of the vertebrae; there are eight full ones and part of a ninth—a remarkably large section of tail, and showing that the bird was indeed small. (All photo captions are from the original paper.)
Photomicrographs and SR X-Ray μCT Reconstructions of DIP-V-15103 (A) Dorsolateral overview. (B) Ventrolateral overview with decay products (bubbles in foreground, staining to lower right). (C) Caudal exposure of tail showing darker dorsal plumage (top), milky amber, and exposed carbon film around vertebrae (center). (D–H) Reconstructions focusing on dorsolateral, detailed dorsal, ventrolateral, detailed ventral, and detailed lateral aspects of tail, respectively. Arrowheads in (A) and (D) mark rachis of feather featured in Figure 4A. Asterisks in (A) and (C) indicate carbonized film (soft tissue) exposure. Arrows in (B) and (E)–(G) indicate shared landmark, plus bubbles exaggerating rachis dimensions; brackets in (G) and (H) delineate two vertebrae with clear transverse expansion and curvature of tail at articulation. Abbreviations for feather rachises: d, dorsal; dl, dorsalmost lateral; vl, ventralmost lateral; v, ventral. Scale bars, 5 mm in (A), (B), (D), and (F) and 2 mm in (C), (E), (G), and (H).
For reference: here are the parts of a modern bird feather; the important parts are the rachis, or main shaft, the barbs, branches off the shaft, and barbules, the smaller branches off the barbs bearing hooks that hold the barbules together—like Velcro—into a single apparatus.
Parts of a feather: 1. Vane, 2. Rachis, 3. Barb, 4. Afterfeather, Hollow shaft, calamus
This picture shows a series of rachis-like structures that splay out from a single place, and each of those is covered with branches, which the authors interpret as barbules:
Photomicrographs of DIP-V-15103 Plumage (A) Pale ventral feather in transmitted light (arrow indicates rachis apex). (B) Dark-field image of (A), highlighting structure and visible color. (C) Dark dorsal feather in transmitted light, apex toward bottom of image. (D) Base of ventral feather (arrow) with weakly developed rachis. (E) Pigment distribution and microstructure of barbules in (C), with white lines pointing to pigmented regions of barbules. (F–H) Barbule structure variation and pigmentation, among barbs, and ‘rachis’ with rachidial barbules (near arrows); images from apical, mid-feather, and basal positions respectively. Scale bars, 1 mm in (A), 0.5 mm in (B)–(E), and 0.25 mm in (F)–(H). See also Figure S4.
Below is a close-up of the feather, which shows a “weakly-developed” rachis off of which ramify alternately-placed barbs, themselves bearing barbules. According to the authors, this supports one of two alternative forms of feather development proposed by evolutionists, with both shown in the bottom part of the figure below. In one scenario (top), the barbs ramify from a developmental focus, then coming to branch directly opposite each other off a rachis, withe the barbules evolving later, becoming asymmetrical to form a flying surface.
The second scenario, which the authors say this specimen supports, is the development of barbules on the barbs before one of them (I think) evolves into a rachis with alternatingly-oriented barbs (that’s this specimen, circled in the figure as an intermediate). Then the barbs evolutionarily move to positions opposite each other on the rachis. Thus, this intermediate supports the bottom evolutionary scenario.
I have to admit that I’m not familiar with the controversy about feather development, and if there are facts to add here I’ll leave them to more knowledgable readers.
DIP-V-15103 Structural Overview and Feather Evolutionary-Developmental Model Fit (A and B) Overview of largest and most planar feather on tail (dorsal series, anterior end), with matching interpretive diagram of barbs and barbules. Barbules are omitted on upper side and on one barb section (near black arrow) to show rachidial barbules and structure; white arrow indicates follicle. (C) Evolutionary-developmental model and placement of new amber specimen. Brown denotes calamus, blue denotes barb ramus, red denotes barbule, and purple denotes rachis [as in 5, 12]. Scale bars, 1 mm in (A) and (B).Finally, you might say, “Well, this may not be the developmental pathway for modern bird feathers, but only for the lineage that contained this species.” But that’s unlikely since paleontologists and developmental biologists tell us that feathers evolved only once, so this specimen does have a bearing on feather evolution. (By the way, the supposedly unique evolution of human intelligence is often used by theologians to claim that that our intelligence, with the ability to apprehend the divine, must have itself been promoted by God. But feathers and elephant trunks are evolutionary one-offs, too! Could it be that God is a bird?)
There’s a new paper in Nature that has everyone excited, for it reports what is said to be the earliest evidence for microbial life—”microbial structures” dated 3.7 billion years ago. The paper, by Allen P. Nutman et al. (reference and free link at bottom), describes what are said to be ancient traces of stromatolites—layered colonies of cyanobacteria that trap sediments and are thus fossilized—from a part of southwest Greenland that harbors old rocks.
The earliest previous evidence for microbial life are microfossils dated at 3.4-3.5 billion years old, coming from the Strelley Pool formation of West Australia. (Wacey et al., Nature Geoscience 4:698-702). The Nutman et al. finding, if true, pushes back the known existence of cells by 200-300 million years, no small chunk of time. (There is some evidence, though not very convincing, for carbon of biological origin dating back 4.1 billion years.)
What is the new evidence for 3.7 billion-year-old life? It’s largely structures in dated rocks that Nutman et al. interpret as stromatolites, structures like those shown below (“strom” means “stromatolite”). The pointy structures are identified as the remains of ancient stromatolites, though I wonder why the middle one isn’t labeled “strom”:
Image is inverted because layering is overturned in a fold. b, Interpretation of a, with isolated stromatolite (strom) and aggregate of stromatolites (stroms). Locally, lamination is preserved in the stromatolites (blue lines). Layering in the overlying sediment (red lines) onlaps onto the stromatolite sides. A weak tectonic foliation is indicated (green lines). c, Asymmetrical stromatolite and d, linked domical stromatolites from the Palaeoproterozoic28 Wooly Dolomite, Western Australia. The lens cap is 4 cm in diameter. Image c is left-right-reversed for comparison with panels a, b.
Nutman et al. give other evidence too, including isotopic data, the presence of minerals that said to be biogenic, and the presence of layers (“lamellae”) in the stromatolite-looking bits. But the most touted (and convincing to others) evidence are pictures like those above.
I checked with some well known paleontologists and sedimentologists, however, and they don’t find even the “fossil” data very convincing. (I’ll withhold their names for the time being.) The pointy bits above, they say, could be “flame structures“: simple deformation of clay or mud that occurs when it’s pushed up by heavier overlying layers of sand. This could produce (and has produced) the kind of structures seen in the photo above, but without any presence of life. Further, the layers in the structures might not represent layers of ancient microbes, but simply layers in the underlying mud that, after all, could be produced by successive sedimentation events.
The rest of the evidence, I’m told, may be suggestive of life but hardly convincing. The paper is tough going, which you’ll see if you read it, so all I want to do is note that the evidence for life given in this paper is questioned by some experts.
Nevertheless, we still have pretty good evidence for bacterial cells existing 3.4-3.5 billion years ago, and such cells are pretty complex. That means that life got started pretty soon after the Earth cooled down, roughly 4.3 billion years ago. These cells, after all, had to have undergone a very long period of evolution from the initial replicating molecule (or whatever it was) that constituted the first “life”.
So take this 3.7 billion year date with a grain of NaCl. That doesn’t mean it’s wrong, just that there are formidable problems with finding solid evidence for life in ancient rocks. Not many of those rocks exist on Earth any more, and those that do could have been changed or deformed in a way that would make life hard to detect. Further, the best evidence for life are microfossils like those shown below, but even these are somewhat controversial. Proving that such structures are fossil bacteria rather than inclusions or artifacts is often hard to do.
Nevertheless, the photos below, and other data from the Wacey et al. paper, have convinced most paleontologists that there were microbial cells around 3.4-3.5 billion years ago.
Why do paleontologists fight bitterly about the “first” cells if it’s only a mere matter of 300 million years (!)? Well, there’s cachet to be gained by finding the earliest good evidence for life, but, beyond that, finding complex cells soon after Earth cooled down gives us a good time scale for how long it takes to go from simple chemicals to “life” (I see the origin of “life” as a somewhat subjective point, as it varies depending on your definition). Pushing dates of cells further back tells us that that transition could be even faster than we once envisioned.
a,b,e, Clusters of cells, some showing cell wall rupturing (arrows in a,b), folding or invagination (arrow in e). c,d,h, Chains of cells with cellular divisions (arrows). f,i–j, Cells attached to detrital quartz grains, exhibiting cell wall rupturing and putative escape of cell contents (arrow in f), preferred alignment of cells parallel to the surface of the quartz grain (arrows in i), and constriction or folding between two compartments (arrow in j). g, Large cellular compartment with folded walls (arrows).
Regular readers may recall that a few weeks back we had a guest post from Ross Piper about the spectacular ‘kite runner’ fossil Aquilonifer spinosus, which Jerry posted about. Ross argued that the tiny organisms attached to the main fossil may not have been offspring, as Derek Briggs and colleagues, but instead Deutonymph mites that attach to organisms in order to disperse (this is called ‘phoresis’ so they are ‘phoretic mites’), and which we have previously described here.
Ross submitted a letter to the Proceedings of the National Academy of Sciences, where the fossil originally appeared, and this has now appeared, along with a brief reply from Briggs et al. Both the letter and the reply are behind a paywall, so I’ll give some quotes here:
Ross writes:
The relatively large number of small individuals associated with the Silurian fossil is one reason why Briggs et al. (1) reject them as epizoans. The authors state that “[Aquilonifer] is unlikely to have tolerated the presence of so many drag-inducing epizoans” (1). Deutonymphs are known to travel in groups and they are often found in profusion on a suitably vagile host. Frequently, one deutonymph is attached next to the other, even if other beetle body parts are free of mites (3). Indeed it has even been shown that phoretic deutonymphs prefer places already infested by deutonymphs (4). The impact of these passengers on the flying ability of a beetle is unknown, but it must be at least as significant as the impact of tethered phoronts on the swimming ability of an aquatic host.
One other feature of the Aquilonifer fossil that points to a phoretic interpretation 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. Instead, the tethered individuals are scattered across the body of Aquilonifer, which is very similar to mite deutonymphs.
Briggs et al reply:
Clearly these two examples are profoundly separated by time (∼430 Mya) and ecology (the one fully marine, the other terrestrial), but it is worth considering the possibility that the adherence of tiny arthropods to Aquilonifer represents the behavior of some sort of marine mite ancestor. (…)
We considered the possibility that the arthropods attached to Aquilonifer represent epizoans or parasites and concluded that this is less likely than their being juveniles (2). We focused on behavioral comparisons with crustaceans because they represent almost the entire diversity of modern aquatic arthropods; marine chelicerates, in contrast, are very rare (e.g., horseshoe crabs). Aquatic mites (Hydrachnidia) invaded water secondarily from land, probably in the Mesozoic, and most are freshwater (7, 9). Aquatic mites include examples that apparently attach their eggs to their limbs (10). Some aquatic mites (members of the Halacarida) are marine and occupy habitats from subtidal to abyssal (9). At least some freshwater mites are dispersed from one water body to another by a parasitic association with flying insects (9). Phoresy is practiced by mites that live on the strandline but is an unlikely strategy for fully marine (subaquatic) mites and we can find no reports that it occurs.
The evidence indicates that any similarity between the attachment of mites to hosts today, and that of the tiny individuals to Aquilonifer, is convergent. The individuals attached to Aquilonifer had at least six pairs of appendages confined to one portion of the body (2), whereas mites have fewer extended limbs that are usually more uniformly distributed. Furthermore, Aquilonifer does not appear to have been primarily a swimmer, and therefore was not an ideal dispersal agent, and whereas it could have adjusted its molting cycle to avoid casting off juveniles, it is unlikely to have done so to favor epizoans.
And that’s more or less it. We aren’t much further on, and I personally didn’t find Briggs et al’s response particularly convincing – certainly not enough to justify the rather peremptory title to their reply: ‘Aquilonifer’s kites are not mites’. However, because the fossil was destroyed in the scanning process, unless we find something similar, it isn’t likely this will be resolved one way or the other…
As I mentioned when in Portland, I encountered reader Bruce Thiel at my free will talk; Bruce’s avocation is preparing fantastic fossils that he finds locally. I’ve featured some of his preparations before; have a look, as I’ve never seen anything like them. Using a dental drill and working slowly and meticulously, he produces fossils like the ones below, whose photos just arrived in my email. (Go here to see how a preparation proceeds.) He doesn’t sell them, though preparations like this fetch high prices; instead, Bruce gives them to museums and scientists to study. So let’s have a paleontological “readers’ wildlife” today. Bruce’s notes are indented:
Here are some other interesting crabs I’ve prepared. Background information about the fossils and the discovery and preparation procedure can be found here [JAC: the second link above].
All the crabs shown are about 30 million years old and are Pulalius vulgaris, except for the last picture. This crab in the next two pictures was mashed and not particularly well-preserved—until I got to the eyestalks and claws, so I went as close as I could between the claws. The eyestalks are 1.5cm apart–slightly over 1/2 inch—so there was not a lot of working area.
The next crab was one of three given to the Smithsonian. What looks like googly-eyes are two attached barnacles.
The next two crabs host tube worms, and are at Kent State being studied for epibionts. The chip in the middle of the carapace is what fossils preparers call “the mark of discovery.” Most of the round or oval-shaped concretions are blank or contain bits of wood, shell or decomposed organic material. In working down into the middle of the rock with the pneumatic jackhammer to see what they contain, if one is too aggressive or not paying close attention, one can “nick” the shell with the pneumatic tool as I did in this case. Both crabs have interesting snake-shaped worms lurking on their shell. One of the questions experts would like to answr is if the worms attach while the crab was alive or after death and during decomposition.
This is one of the smaller crabs I’ve worked on. I held my breath when uncovering the tiny claw. My thumbnail is shown for comparison.
These are two Macroacaena schencki crabs from the Keasey Formation, Oregon (33 – 35 MYO). We think the larger and wider of the two is female but determination awaits further research.
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.
