April 18, 2013
I guess pretty much all researchers must suffer from Imposter Syndrome every now and then — the sense of not really belonging, not knowing enough, not getting enough done to justify our position. I particularly remember feeling this after being awarded my Ph.D: the sense that I couldn’t possibly know enough about enough to be worthy of it. Even now, several years down the line, I sometimes look at my papers and think, pfft, there’s nothing to them, anyone could have done that.
I thought of this tonight because of a a tweet I just saw from M. J. Suhonos, Digital Technologies Development Librarian at Ryerson University:
What do you do on those days when you realize you're no good at anything and wonder why you ever bothered?—
MJ Suhonos (@mjsuhonos) April 18, 2013
And the advice I gave in response:
The reason I say this is because a few days ago I did a phone interview for a news piece, and was sort of surprised to find myself talking confidently and fluently, just like someone who knows what he’s talking about. Until I realised that’s what always happens when I do an interview. And that’s because, well, heck, I do know my subject (otherwise why would they even be talking to me?)
And I bet you know your subject, too. You just need to see your own knowledge against the backdrop of what a normal person knows.
Meanwhile, as a contribution to John Conway’s superb “grumpy Hypsilophodon” meme, I give you: this.
April 8, 2013
Last night London and I spent the night in the Natural History Museum of Los Angeles County (LACM), as part of the Camp Dino overnight adventure. So we got lots of time to roam the exhibit halls when they were–very atypically–almost empty. Above are the museum’s mounted Triceratops–or one of them, anyway–and mounted cast of the Mamenchisaurus hochuanensis holotype, presented in glorious not-stygian-darkness (if you went through the old dino hall, pre-renovation, you know what I mean).
We got there early and had time to roam around the museum grounds in Exposition Park. The darned-near-life-size bronze dinos out front are a minor LA landmark.
The rose garden was already closed, but we walked by anyway, and caught this rainbow in the big fountain.
After we checked in we had a little time to roam the museum on our own. I’ve been meaning to blog about how much I love the renovated dinosaur halls. The bases are cleverly designed to prohibit people touching the skeletons without putting railings or more than minimal glass in the way, and you can walk all the way around the mounted skeletons and look down on them from the mezzanine–none of that People’s Gloriously Efficient Cattle Chute of Compulsory Dinosaur Appreciation business. Signage is discreet and informative, and so are the handful of interactive gizmos. London and I spent a few minutes using a big touch-screen with a slider that controlled continental drift from the Triassic to the present–a nice example of using technology to add value to an exhibit without taking away from the real stuff that’s on display. There are even a few places to sit and just take it all in. That’s pretty much everything I want in a dinosaur hall.
Also, check out the jumbotron on the left in the above photo. It was running a (blessedly) narration-free video on how fossils are found, collected, prepared, mounted, and studied, on about a five-minute loop. Lots of pretty pictures. Including this next one.
There are a couple of levels of perspective distortion going on here, both in the original photo and in my photo of that photo projected on the jumbotron.
Still, I feel confident positing that that is one goldurned big ilium. I’m not going to claim it’s the biggest bone I’ve ever seen–that rarely ends well–but sheesh, it’s gotta be pretty freakin’ big. And apparently a brachiosaurid, or close to it. Never mind, it’s almost certainly an upside-down Triceratops skull. Thanks to Adam Yates for the catch. I will now diminish, and go into the West.
Triceratops, Styracosaurus, and Einiosaurus–collect the whole set!
Of course, the centerpiece of the second dinosaur hall–and how great is it that there are two!?–is the T. rex trio: baby, juvenile (out of frame to the right), and subadult. Yes, subadult: the “big” one is not as big as the really big rexes, and from the second floor you can see unfused neural arches in some of the caudal vertebrae (many thanks to Ashley Fragomeni for pointing those out to me on a previous visit).
Awwwww! C’mere, little fella!
Still, this ain’t Vulgar Overstudied Theropod Picture of the Week. Here are some sweet pneumatic diplodocid caudals in the big wall o’ fossils (visible behind Mamenchisaurus in the overhead photo above). The greenish color is legit–in the Dino Lab on the second floor, they’re prepping a bunch of sauropod elements that look like they were carved out of jade.
Sudden violent topic shift, the reason for which will be become clear shortly: London and I have been sculpting weapons of mass predation in our spare time. In some of the photos you may be able to see his necklace, which has a shark tooth he sculpted himself. Here are a couple of allosaur claws I made–more on those another time.
The point is, enthusiasm for DIY fossils is running very high at Casa Wedel, so London’s favorite activity of the evening was molding and casting. Everyone got to make a press mold using a small theropod tooth, a trilobite, or a Velociraptor claw. Most of the kids I overheard opted for the tooth, but London went straight for the claw.
Ready for plaster! Everyone got to pick up their cast at breakfast this morning, with instructions to let them cure until this evening. All went well, so I’ll spare you a photo of this same shape in reverse.
We were split into three tribes of maybe 30-40 people each, and each tribe bedded down in a different hall. The T. rex and Raptor tribes got the North American wildlife halls, but our Triceratops tribe got the African wildlife hall, which as a place to sleep is about 900 times cooler. Someone had already claimed the lions when we got there, so London picked hyenas as our totem animals.
Lights out was at 10:30 PM, and the lights came back on at 7:00 this morning. Breakfast was out from 7:15 to 8:00, and then we had the museum to ourselves until the public came in at 9:30. So I got a lot of uncluttered photos of stuff I don’t usually get to photograph, like this ammonite. Everyone should have one of these.
London’s favorite dino in the museum is Carnotaurus. It’s sufficiently weird that I can respect that choice.
Not that there’s anything wrong with the old standards, especially when they’re presented as cleanly and innovatively as they are here.
Finally, the LACM has a no tripod policy, and if they see you trying to carry one in they will make you take it back to your car. At least during normal business hours. But no one searched my backpack when we went in last night, and I put that sucker to some good use. Including getting my first non-bigfoot picture of the cast Argentinosaurus dorsal. It was a little deja-vu-ey after just spending so much time with the giant Oklahoma Apatosaurus–elements of the two animals really are very comparable in size.
If you’re in the LA area and interested in spending a night at the museum–or at the tar pits!–check out the “Overnight Adventures” page on the museum’s website. Cost is $50 per person for members or $55 for non-members, and worth every penny IMHO. It’s one of those things I wish we’d done years ago.
January 19, 2013
A Brontomerus on the edge of a jumbled forest of partially knocked over trees. While I won’t be finishing this particular drawing I decided I want to develop this idea a bit further – I think it would be cool to show a group of brontomeri rearing and grazing on the edge of a forest where a lot of the trees are leaning and show signs of heavy grazing, particularly by giants who rear up, bear hug them and rip down their branches. I’m talking tore-up bark around hand-claw height, trees that are growing bent, but then straighten up above max-bronto height, and maybe a constellation of camptosaurs and pterosaurs living around the brontos for food and protection… anyway, just an idea. Any thoughts?
Yeah. I judge it rad. And plausible. I love the heavy texturing on Bronto and the way the background is simple and evocative at the same time. I like the idea of a forest modified by sauropods for their use. I would like to see more plants damaged by sauropods (but still surviving)–and vice versa. For the proposed full version, the camptosaurs will have to be replaced by tenontosaurs, this being the Early Cretaceous. But they’re both ornithopods, so probably no one will know or care.
Anyway, I’m pretty sure Brian wants genuine feedback, and not just predictable gushing from yours truly. The comment field is open.
Bonus Engh sketch: a rearing Miragaia.
January 14, 2013
My friend, colleague, and sometime coauthor Dave Hone sent the above cartoon, knowing about my more-than-passing interest in sauropod neurology. It was drawn by Ed McLachlan in the early 1980s for Punch! magazine in the UK (you can buy prints starting at £18.99 here).
I know that this isn’t the only image in the “oblivious sauropods getting eaten” genre. There’s a satirical drawing in Bakker’s The Dinosaur Heresies showing a sleeping brontosaur getting its tail gnawed on by some pesky mammals. I’ll scan that and post it when I get time. I’m sure there must be others in a similar vein–point me to them in the comments or email me and I’ll post as many as I can get my hands on.
I wouldn’t post stuff like this if I didn’t think it was funny. But if you want the real scoop on whether sauropods could have responded quickly to injuries to their distant extremities, here’s the deal:
First of all, sauropods really did have individual sensory nerve cells that ran from their extremities (tip of tail, soles of feet)–and from the rest of their skin–to their brainstems. In the longest sauropods, these cells were probably something like 150 feet long, and may have been the longest cells in the history of life. We haven’t found any fossils of these nerves and almost certainly never will, but we can be sure that sauropods had them because all vertebrates do, from hagfish on up. That’s just how we’re built. (This is all rehash for regular readers–see this post and the linked paper.)
So how long does it take to send a nerve impulse 150 feet? The fastest nerve conduction velocities are in the neighborhood of 120 meters per second, so a signal from the very tip of the tail in a 150-foot sauropod would take about half a second to reach the brain.
Is it possible that sauropods had accelerated nerve conduction velocities, to bring in those distant signals faster? To the brain, probably not. The only ways to speed up a nerve impulse are to increase the diameter of the axon itself, which some invertebrates do, and to increase the thickness of the myelin sheath around the axon, which is what vertebrates tend to do (some invertebrates have myelin-like tissues that apparently help accelerate their nerve impulses, too). Fatter axons mean fatter nerves, and for at least half the trip to the brain, the axons in question are part of the spinal cord. And we know that sauropod spinal cords were pretty small, relative to their body size, because the neural canals of their vertebrae, through which their spinal cords passed, are themselves small–Hatcher wrote about this more than a century ago. So there’s a tradeoff–sauropods could have had very fast, very fat axons, but not very many of them, and therefore poor “coverage” at their extremities, with nerve endings widely spaced, or better coverage with more axons, but those axons would be skinnier and therefore slower. We don’t know which way they went.
Incidentally, you can experiment with the density of sensory nerve endings in your own body. Close your eyes or blindfold yourself, and have a friend poke you in various places with chopsticks. Seriously–start with the two chopsticks right together, and gradually spread them out until you can feel two distinct points (or, if you want to get really tricky, have your friend mix up the close and widely spread touches so there’s no direction for you to anticipate). The least sensitive part of your body is your back–over your back and shoulders, you’ll probably have a hard time distinguishing points of touch that are less than an inch apart. On your hands and face, you’ll probably be able to distinguish points only a few millimeters apart; in fact, for fingertips you’ll probably need finer instruments than chopsticks–maybe toothpicks or pins, but I take no responsibility for any accidental acupuncture!
Back to sauropods. Could predators have taken advantage of the comparatively long nerve conduction velocities in sauropods? I seriously doubt it, for several reasons:
- Simple reflex arcs are governed by interneurons in the spinal cord. The tail-tip-to-spinal-cord distance was a lot shorter than the tail-tip-to-brain route. Even over the round trip of “sensory impulse in, motor impulse out”, it would have been at worst equal, and that’s assuming the nerve impulse had to go all the way to the base of the tail.* Call it half a second, max.
- It gets worse: the peripheral nerves outside the spinal cord are not limited by the size of the neural canal, so they can be more heavily myelinated, with faster conduction times. For example, each of the sciatic nerves running down the backs of your thighs is much larger in cross-section than your entire spinal cord. If sauropod peripheral nerves were selected for fast conduction, they might have been bigger and faster than anything around today.
- Half a second is not much time for a theropod to formulate a plan, especially if Step 1 of the plan is “grab 150-foot sauropod by the tail”.
- This assumes that said theropod was able to sneak right up to the sauropod without being detected. You go try that with a big wild herbivore and let me know how it works out. (Also, a big animal tolerating your presence, because you are pathetically small and weak, is not the same as it being unaware of your presence.)
- All of this assumes the theropod only went for the bony whip-lash at the tip of the tail–the fastest-moving extremity, and the least-nourishing single bite anywhere on the target. If the theropod went for a meatier bite closer to the base of the tail, it would have to sneak closer to the sauropod’s head (better chance of being spotted), and the nerve conduction delay would be shortened.
- A 150-foot sauropod would probably mass somewhere between 50 and 100 tons, and would be capable of dealing incredible damage to even the largest theropods, which maxed out around 15 tons. There’s a good reason predators go after the young, sick, and weak. Smaller sauropods would be less dangerous, but they’d also have faster tail-to-central-nervous-system-and-back reaction times.
- A theropod big enough to go after a 150-foot sauropod would also be subject to fairly long nerve-conduction delays, which would limit whatever trifling advantage it might have gotten from such delays in the sauropod.
So, although I have no doubt that in their long history together, giant theropods did occasionally tackle full-grown giant sauropods–because real animals do all kinds of weird things if you watch them long enough, and lions will take on elephants when they get desperate–I am extremely skeptical that the theropods enjoyed any advantage based on the “slow” nervous systems of those sauropods.
* Some relevant hard-core anatomy for the curious: sauropods have neural canals in their tail vertebrae, and usually far down their tails, too. But that doesn’t mean much–you have neural canals to the bottom half of your sacrum, but your spinal cord stops around your first or second lumbar vertebra. From there on down, you just have nerve roots. So the shortest reflex arc from your big toe has to go up to your lower back and return. Why is your spinal cord so short? Basically because your central nervous system stops growing when you’re still a child–it will add new connections after that, and a few new cells in your olfactory bulbs and hippocampus, but it won’t get appreciably bigger or longer. After mid-childhood, your body keeps growing but your spinal cord stays the same length, so you end up with this freaky little-kid spinal cord tucked up inside your grown-up vertebral column. Weird, huh?
So did sauropod spinal cords stop at mid-back or go all the way into the tail? We have several conflicting lines of evidence. In extant reptiles, the spinal cord does extend into the tail in at least some taxa (I haven’t done anything like a complete survey, just read a couple of papers). Birds are no help because their tails are extremely short, but their spinal cords do extend into the synsacrum (and expand there, thanks to the glycogen body, which was probably also present in sauropods and responsible for the inaccurate “second brain” meme). But then birds grow up very fast, with even the largest reaching full size in a year or two, so they don’t share our problem of the body outgrowing the nervous system. We know that sauropods grew pretty quickly, but they also took a while to mature–somewhere between one and three decades, probably. Did that protracted growth period give their vertebral columns the time to outgrow their spinal cords? I have no idea, because the division of the spinal cord into roots happens inside the dura mater and doesn’t leave any skeletal traces that I know of. Someone should go figure it out–or at least figure out if it can be figured out!
September 28, 2012
Over on Facebook, where Darren posted a note about our new paper, most of the discussion has not been about its content but about where it was published. We’re not too surprised by that, even though we’d love to be talking about the science. We did choose arXiv with our eyes open, knowing that there’s no tradition of palaeontology being published there, and wanting to start a new tradition of palaeontology being routinely published there. Having now made the step for the first time, I see no reason ever to not post a paper on arXiv, as soon as it’s ready, before — or maybe even instead of — submitting it to a journal.
(Instead of? Maybe. We’ll discuss that below.)
The key issue is this: science isn’t really science until it’s out there where it can be used. We wrote the bulk of the neck-anatomy paper back in 2008 — the year that we first submitted it to a journal. In the four years since then, all the observations and deductions that it contains have been unavailable to the world. And that is stupid. The work might just as well never have been done. Now that it’s on arXiv, that’s over. I was delighted to get an email less than 24 hours after the paper was published, from an author working on a related issue, thanking us for posting the paper, saying that he will now revise his own in-prep manucript in light of its findings, and cite our paper. Which of course is the whole point: to get our science out there where it can do some damage.
Because the alternative is horrible, really. Horribly wasteful, horribly dispiriting, horribly retarding for science. For example, a couple of weeks ago in his SVPCA talk, David Norman was lamenting again that he never got around to publishing the iguanodont systematic work that was in his dissertation, I-don’t-know-how-many-years-ago. The result of that interminable delay is that others have done other, conflicting iguanodont systematic work, and Norman is now trying belatedly to undo that and bring his own perspective. A terrible an unnecessary slowing of ornithopod science, and a waste of duplicated effort. (Thankfully it’s only ornithopods.)
And of course David Norman is very far from being alone. Pretty much any palaeontologist you talk to will tell you of a handful of papers — many more in some cases — that were finished many years previously but have never seen the light of day. (I still have a couple myself, but there is no point in resurrecting them now because progress has overtaken them.) I wonder what proportion of all Ph.D work ever sees the light of day? Half? Less? It’s crazy.
Publish now, publish later
So, please folks: we all need to be posting our work on preprint servers as soon as we consider it finished. It doesn’t mean that the posted versions can’t subsequently be obsoleted by improved versions that have gone through peer-review and been published in conventional journals. But it does mean that the world can know about the work, and build on it, and get the benefit of it, as soon as it’s done.
You see, we have a very fundamental problem in academia: publishing fulfils two completely separate roles. Its primary role (or at least the role that should be primary) is to make work available to the community; the secondary role is to provide a means of keeping score — something that can be used when making decisions about who to appoint to jobs, when to promote, who gets grants, who gets tenure and so on. I am not going to argue that the latter shouldn’t happen at all — clearly a functioning community needs some way to infer the standing of its participants. But I do think it’s ridiculous when the bean-counting function of publication trumps the actual publication role of publication. Yet we’ve all been in a position where we have essentially complete work that could easily go on a blog, or in the PalAss newsletter, or in a minor journal, or somewhere — but we hang onto it because we want to get it into a Big Journal.
Let me say again that I do realise how unusual and privileged my own position is: that a lot of my colleagues do need to play the Publication Prestige game for career reasons (though it terrifies my how much time some colleagues waste squeezing their papers into two-and-a-half-page format in the futile hope of rolling three sixes on the Science ‘n’ Nature 3D6). Let’s admit right now that most palaeontologists do need to try to get their work into Proc B, or Paleobiology, or what have you. Fair enough. They should feel free. But the crucial point is this: that is no reason not to post pre-prints so we can all get on with actually benefitting from your work in the mean time.
Actually, I feel pretty stupid that it’s taken me this long to realise that all my work should go up on arXiv.
So are there any special cases? Any kinds of papers that we should keep dry until they make it into actual journals? I can think of two classes that you could argue for — one of them convincingly, the other not.
First, the unconvincing one. When I discussed this with Matt (and half the fun of doing that is that usually neither of us really knows what we think about this stuff until we’re done arguing it through), he suggested to me that we couldn’t have put the Brontomerus paper on arXiv, because that would have leaked the name, creating a nomen nudum. My initial reaction was to agree with him that this is an exception. But when I thought about it a bit more, I realised there’s actually no compelling reason not to post such a paper on arXiv. So you create a nomen nudum? So what? Really: what is the negative consequence of that? I can’t think of one. OK, the name will appear on Wikipedia and mailing lists before the ICZN recognises it — but who does that hurt? No-one that I can think of. The only real argument against posting is that it could invite scooping. But is that a real threat? I doubt it. I can’t think of anyone who would be barefaced enough to scoop a taxon that had already been published on arXiv — and if they did, the whole world would know unambiguously exactly what had happened.
So what is the one real reason not to post a preprint? I think that might be a legitimate choice when publicity needs to be co-ordinated. So while nomenclatural issues should not have stopped us from arXiving the Brontomerus paper, publicity should. In preparation for that paper’s publication day, we did a lot of careful work with the UCL publicity team: writing non-specialist summaries, press-releases and FAQs, soliciting and preparing illustrations and videos, circulating materials under embargo, and so on. In general, mainsteam media are only interested in a story if it’s news, and that means you need to make sure it’s new when they first hear about it. Posting the article in advance on a publicly accessible archive would mess that up, and probably damage the work’s coverage in the press, TV and radio.
Publication venues are a continuum
It’s become apparent to us only gradually that there’s really no clear cut-off where a paper becomes “properly published”. There’s a continuum that runs from least to most formal and exclusive:
SV-POW! — arXiv — PLOS ONE — JVP — Nature
1. On SV-POW!, we write what we want and publish it when we want. We can promise you that it won’t go away, but you only have our word for it. But some of what we write here is still science, and has been cited in papers published in more formal venues — though, as far as I know, only by Matt and me so far.
2. On arXiv, there is a bit more of a barrier to clear: you have to get an existing arXiv user to endorse your membership application, and each article you submit is given a cursory check by staff to ensure that it really is a piece of scientific research rather than a diary entry, movie review or spam. Once it’s posted, the paper is guaranteed to remain at the same URL, unchanged, so long as arXiv endures (and it’s supported by Cornell). Crucially, the maths, physics and computer science communities that use arXiv uncontroversially consider this degree of filtering and permanence sufficient to constitute a published, citeable source.
3. At PLOS ONE, your paper only gets published if it’s been through peer-review — but the reviewing criteria pertain only to scientific soundness and do not attempt to evaluate likely impact or importance.
4. At JVP and other conventional journals, your paper has to make it through a two-pronged peer-review process: it has to be judged both sound scientifically (as at PLOS ONE) and also sufficiently on-topic and important to merit appearing in the journal.
5. Finally, at Nature and Science, your paper has to be sound and be judged sexy — someone has to guess that it’s going to prove important and popular.
Where along this continuum does the formal scientific record begin? We could make a case that all of it counts, provided that measures are taken to make the SV-POW! posts permanent and immutable. (This can be done submitting them to WebCite or to a service such as Nature Precedings used to provide.) But whether or not you accept that, it seems clear that arXiv and upwards is permanent, scientific and citeable.
This raises an interesting question: do we actually need to go ahead and publish our neck-anatomy paper in a more conventional venue? I’m honestly not sure at the moment, and I’d be interested to hear arguments in either direction. In terms of the progress of science, probably not: our actual work is out there, now, for the world to use as it sees fit. But from a career perspective, it’s probably still worth our while to get it into a journal, just so it can sit more neatly on our publication lists and help Matt’s tenure case more. And yet I don’t honestly expect any eventual journal-published version to be better in any meaningful way than the one on arXiv. After all, it’s already benefitted from two rounds of peer-review, three if you count the comments of my dissertation examiners. More likely, a journal will be less useful, as we have to cut length, eliminate illustrations, and so on.
So it seems to me that we have a hard choice ahead of us now. Call that paper done and more onto making more science? Or spend more time and effort on re-publishing it in exchange for prestige? I really don’t know.
For what it’s worth, it seems that standard practice in maths, physics and computer science is to republish arXiv articles in journals. But there are some scientists who routinely do not do this, instead allowing the arXiv version to stand as the only version of record. Perhaps that is a route best left to tenured greybeards rather than bright young things like Matt.
Citing papers in arXiv
Finally, a practicality: since it’ll likely be a year or more before any journal-published version of our neck-anatomy paper comes out, people wanting to use it in their own work will need to know how to cite a paper in arXiv. Standard procedure seems to be just to use authors, year, title and arXiv ID. But in a conventional-journal citation, I like the way that the page-range gives you a sense of how long the paper is. So I think it’s worth appending page-count to the citations. And while you’re at it, you may as well throw in the figure and table counts, too, yielding the version that we’ve been using:
- Taylor, Michael P., and Mathew J. Wedel. 2012. Why sauropods had long necks; and why giraffes have short necks. arXiv:1209.5439. 39 pages, 11 figures, 3 tables.
May 3, 2012
I’m in Chicago, visiting the Field Museum, which means two things: Brachiosaurus (see below), and Mold-A-Rama. Downstairs from the great hall, on the ground floor, they have Mold-A-Rama machines, and I cannot resist their siren song.
The Mold-A-Rama is the king of novelty souvenirs. You can keep your stamped pennies, little pewter spoons, hand-painted bells, and refrigerator magnets. None of them is worthy to sully the presence of the awesome Mold-A-Rama. You put in two dollars, and then you get to watch as this hissing, clanking 1950s machine with tubes and wires and lights actually makes your item right in front of your eyes. A few minutes later, BAM, you’re holding a hot, smelly hunk of probably carcinogenic plastic that is so fresh from the mold that it is still a bit soft. You can’t buy that kind of authenticity–except from a Mold-A-Rama.
This is my first Mold-A-Rama Triceratops. I already have a T. rex from my last visit, way back in 2005, which I can now pass on to my son. I also have a Stegosaurus, a Brontosaurus (shown but not commented on here), and a Trachodon. Yeah, yeah, I know the real animals are known as Apatosaurus and Edmontosaurus these days, but I’m not talking about the real animals. I’m talking about Mold-A-Rama, and trust me, the Mold-A-Rama critters are Brontosaurus and Trachodon. They drag their tails, they live in swamps, they’re cold-blooded and they died out from racial senescence (in about 1975, I think).
Finally, because Mike will straight-up murder me if I post from Chicago without it, here’s your friendly local not-quite-fully-mature mounted holotype specimen of Brachiosaurus:
March 29, 2012
By one of those happy coincidences that you sometimes get, today saw the publication of not one but two dinosaur ontogeny papers: this morning I was sent a copy of Woodruff and Fowler (2012) on ontogenetic changes in the bifid spines of diplodocoids, and tonight I was alerted to Werning (2012) on Tenontosaurus growth trajectories based on osteohistology.
It’s interesting to compare them. The obvious conclusion is that, while sauropod vertebrae are intrinsically better than ornithopod long-bones, the latter make much, much better subjects for ontogeny studies.
The problem that Woodruff and Fowler have is that they’re working from a small selection of mostly isolated elements, nearly all of them damaged by breakage and/or crushing, and uncontrolled for serial position beyond some basic binning. As a result, the taxonomic identifications are really rather arbitrary and unsupported — as they say (p. 2), “for the purposes of this study, original taxonomic designations were not reexamined” — and indeed re-examination would not necessarily help much.
As a result, they are left with rather a circular argument, as follows:
- Small specimen X is Suuwassea.
- Small specimen Y is assigned to Apatosaurus, because someone once said so.
- But Y has a less bifid neural spine than adult Apatosaurus.
- So spine bifurcation increases through ontogeny in Apatosaurus.
- So small specimen X belongs to Apatosaurus, too.
- => Suuwassea is Apatosaurus [Note: I stupidly wrote "Diplodocus" here in the first posted version. Now corrected to Apatosaurus.]
I don’t find this at all convincing. (Neither does Matt: we discussed this briefly today, and at more length at the Bonn workshop where Cary presented this work.) Leaving aside the observation that the conclusion fits in neatly with the Horner Lab’s ongoing everything-is-just-a-Triceratops-growth-stage project, there isn’t really much that Cary could have done differently here: the necessary specimens (i.e. multiple near-complete associated individuals of unambiguous taxonomic identity) just don’t exist.
(Mind you, figure 7A is about the least convincing evidence of bifurcation I’ve ever seen.)
Ornithopod long bones
By contrast, Sarah Werning has a much better story to tell, largely just because she’s working with much better material. Tenontosaurus is known from many complete and near-complete individuals, there is no real uncertainty about the material all belonging to the same taxon, and the elements (long bones) are much less subject to crushing and breakage than vertebrae.
Of course it also helps that Sarah has done astonishingly careful, detailed work. I don’t think I’m giving much away when I say that this paper has been many years in the making — as the Acknowledgements say “This work was completed in partial fulfillment of the requirements for the Master of Science degree, Department of Zoology, University of Oklahoma.” And it’s been a looong time since Sarah was at Oklahoma. But I get the sense that this reflects taking the time and putting in the effort to Get It Right, rather than standard-issue procrastination.
Perhaps the most impressive part of this paper, though, is methodological:
High-resolution histological images of the cross-sections are digitally reposited online for scholarly use at MorphoBank (http://MorphoBank.org), project p494; see Table 2 for a list of slides and accession numbers. Digital images larger than 25,000 pixels in either dimension were digitally scaled (reduced to 17,000–20,000 pixels in the larger dimension) to allow processing on MorphoBank and because most image editing software does not support editing of gigapixel jpg files. These edits were made after scale bars had been added. Images in full resolution can be obtained from the author.
As you can see, these are ridiculously high-resolution images. By making them freely available, Sarah is doing everything she can to enable others to replicate or correct her work — or to use the data for other purposes that she’s not yet thought of. This is a big win for the progress of science, and I want to publicly congratulate Sarah for doing it. I would love to see this become standard behaviour.
(It’s a bit strange that the paper links onto the the MorphoBank home page rather than directly to the Tenontosaurus project. Here you go.)
PLoS ONE vs. Journal of Morphology
A final thought, before I finally go to bed. When I saw Cary’s paper in the Journal of Morphology I thought to myself, “good for him, he’s got that into a really good journal” — which is true. But then when Sarah’s came in, I found myself comparing PLoS ONE. Here’s what I came up with:
Access. A no-brainer: PLoS ONE wins hands down, being open-access while J. Morph. is paywalled.
Charges. The flip side of the first category: J. Morph. wins because (as far as I can tell from the Author Guidelines) there is no publication charge. PLoS ONE charges $1350.
Length. Another PLoS ONE win, because it imposes no limits whatsoever on length, figure count, etc. Cary’s paper is no lightweight at 11 pages, but PLoS’s liberality with page-space means that Sarah’s is well over twice as long at 25 pages. Now of course not all papers need to be long; but for those that do, cutting to a journal’s length limit is a painful and stupid process.
Image Colour. Again, PLoS ONE wins — it’s very rare these days to see a greyscale specimen image in a PLoS journal. But to be fair to J. Morph., the author guidelines do say: “All color figures will be reproduced in full color in the online edition of the journal at no cost to authors. For the printed version free color figures are at the editors discretion.” So it looks like Cary and Denver dropped the ball on this.
Image Resolution. No question. PLoS ONE wins by a mile. Click through the two representative images above: the PLoS one has 3.5 times as many pixels, and that’s after I added a 10% wide margin around the J. Morph. image. And if you want to use these illustrations as basis for new images, remember PLoS also lets you download the original full-resolution submitted image in a lossless format.
DOI Resolution. When I added the references below, I noticed that the DOI for the J. Morph. article doesn’t resolve yet, which is careless. PLoS ONE wins in this category, resolving just fine.
Impact Factor. Yes, it’s a stupid number and we all hate it. But some people still seem to take it seriously, so we may as well look. And PLoS ONE wins with 4.411 to J. Morph.’s 2.087 — more than double.
Putting it all together, based on the seven categories that I evaluated here (and no doubt I missed some), it looks like the only reason to go with J. Morph. ahead of PLoS ONE is to avoid the publication fee. By this point, PLoS ONE has made itself an absolutely mainstream journal for palaeo, and the obvious first choice for most projects.
- Werning, Sarah. 2012. The ontogenetic osteohistology of Tenontosaurus tilletti. PLoS ONE 7(3):e33539. doi:10.1371/journal.pone.0033539
- Woodruff, D. Cary, and Denver W. Fowler. 2012. Ontogenetic influence on neural spine bifurcation in Diplodocoidea (Dinosauria: Sauropoda): a critical phylogenetic character. Journal of Morphology, online ahead of print. doi:10.1002/jmor.20021 [Direct Link, since the DOI doesn't seem to work.]
December 13, 2011
November 30, 2011
- Part 1: intro
- Part 2: the head
- Part 3: the neck
- Part 4: body, tail, limbs, base, and skull
- Part 6: texture and color
- Part 7: verdict
There are really only a couple of interesting points to discuss for posture: the neck and the feet.
The neck posture is fine. Easy to say, but since I’m one of the “sauropods held their necks erect” guys, it might need some unpacking.
On one hand, animals really do use stereotyped postures, especially for the neck and head (Vidal et al. 1986, Graf et al. 1995, van der Leeuw et al. 2001). The leading hypothesis about why animals do this is that the number of joints and muscle slips involved in the craniocervical system permits an almost limitless array of possible postures, and that having a handful of stereotyped postures cuts down on the amount of neural processing required to keep everything going. That doesn’t mean that animals only use stereotyped postures, just that they do so most of the time, when there’s no need to deviate.
This might work something like the central pattern generators in your nervous system. When you’re walking down the sidewalk thinking about other things or talking with a friend, a lot of the control of your walk cycle is handled by your spinal cord, not your brain. Your brain is providing a direction and a speed, but the individual muscles are being controlled from the spinal cord. Key quote from the Wikipedia article: “As early as 1911, it was recognized, by the experiments of T. Graham Brown, that the basic pattern of stepping can be produced by the spinal cord without the need of descending commands from the cortex.”
But then you see a puddle or some dog doo and have to place your foot just so, and your brain takes over for a bit to coordinate that complex, ad hoc action. After the special circumstance is past, you go back to thinking about whatever and your spinal cord is back in charge of putting one foot in front of the other. This is the biological basis of the proverbial chicken running around with its head cut off: thanks to the spinal cord, the chicken can still run, but without a brain it doesn’t have anywhere to go (I have witnessed this, by the way–one of the numerous benefits to the future biologist of growing up on a farm).
Similarly, if the craniocervical system has a handful of regular postures–alert, feeding, drinking, locomoting, and so on–it lightens the load on the brain, which doesn’t have to figure out how to fire every muscle slip inserting on every cervical vertebra and on the skull to orient the head just so in three-dimensional space. That doesn’t mean that the brain doesn’t occasionally step in and do that, just like it takes over for the spinal cord when you place your feet carefully. But it doesn’t have to do it all the time.
van der Leeuw et al. (2001) took this a step further and showed that birds not only hold their heads and necks in stereotyped postures, they move between stereotyped postures in very predictable ways, and those movement patterns differ among clades (fig. 7 from that paper is above). There is a lot of stuff worth thinking about in that paper, and I highly recommend it, along with Vidal et al. (1986) and Graf et al. (1995), to anyone who is interested in how animals hold their heads and necks, and why.
So, on one hand, its wrong to argue that stereotyped postures are meaningless. But it’s also wrong to infer that animals only use stereotyped postures–a point we were careful to make in Taylor et al. (2009). And it’s especially wrong to infer that paleoartists only show animals doing familiar, usual things–I wrote the last post partly so I could make that point in this one.
For example, I think it would be a mistake to look at Brian Engh’s inflatable Sauroposeidon duo and infer that he accepts a raised alert neck posture for sauropods. He might or might not–the point is that the sauropods in the picture aren’t doing alert, they’re doing “I’m going to make myself maximally impressive so I can save myself the wear and tear of kicking this guy’s arse”. The only way the posture part of that painting can be inaccurate is if you think Sauroposeidon was physically incapable of raising its neck that high, even briefly (the inflatable throat sacs and vibrant colors obviously involve another level of speculation).
Similarly, the Sideshow Apatosaurus has its neck in the near-horizontal pose that is more or less standard for depictions of diplodocids (at least prior to 2009, and not without periodic dissenters). But it doesn’t come with a certificate that says that it is in an alert posture or that it couldn’t raise its neck higher–and even if it did, we would be free to ignore it. Would it have been cool to see a more erect-necked apatosaur? Sure, but that’s not a new idea, either, and there are other restorations out there that do that, and in putting this apatosaur in any one particular pose the artists were forced to exclude an almost limitless array of alternatives, and they had to do something. (Also, more practically, a more erect neck would have meant a larger box and heftier shipping charges.)
So the neck posture is fine. Cool, even, in that the slight ribbing along the neck created by the big cervical ribs (previously discussed here) gives you a sense of how the posture is achieved. Visible anatomy is fun to look at, which I suspect is one of the drivers behind shrink-wrapped dinosaur syndrome–even though it’s usually incorrect, and this maquette doesn’t suffer from it anyway.
Next item: the famous–or perhaps infamous–flipped-back forefoot. I have no idea who first introduced this in skeletal reconstructions and life restorations of sauropods, but it was certainly popularized by Greg Paul. It’s a pretty straightforward idea: elephants do this, why not sauropods?
Turns out there are good reasons to suspect that sauropods couldn’t do this–and also good reasons to think that they could. This already got some air-time in the comments thread on the previous review post, and I’m going to start here by just copying and pasting the relevant bits from that discussion, so you can see four sauropod paleobiologists politely disagreeing about it. I interspersed the images where they’re appropriate, not because there were any in the original thread.
Mike Taylor: the GSP-compliant strong flexion of the wrist always look wrong to me. Yes, I know elephants do this — see Muybridge’s sequence [above] — but as John H. keeps reminding us all, sauropods were not elephants, and one might think that in a clade optimsied for size above all else, wrist flexibility would not be retained without a very good reason.
Adam Yates: Yes I agree with Mike here, the Paulian, elephant-mimicking hyperflexion of the wrist is something that bugs me. Sauropod wrist elements are rather simple flat structures that show no special adaptation to achieve this degree of flexion. [Lourina sauropod right manus below, borrowed from here.]
Heinrich Mallison: Hm, I am not too sure what I think of wrist flexion. Sure it looks odd, but if you think it through the very reasons elephant have it is likely true in sauropods. And given the huge amount of cartilage mossing on the bones AND the missing (thus shape unknown) carpals I can well imagine that sauropods were capable of large excursions in the wrist.
Mike: What are those reasons?
Heinrich: Mike, long humeri, very straight posture – try getting up from resting with weak flexion at the wrist. Or clearing an obstacle when walking. I can’t say too much, since this afternoon this has become a paper-to-be.
Mike: OK, Heinrich, but the Muybridge photos (and many others, including one on John H.’s homepage) show that elephants habitually flex the wrist in normal locomotion, not just when gwetting up from resting or when avoiding obstacles. Why?
The interesting thing here is that this is evidence of how flawed our (or maybe just my) intuition is: looking at an elephant skeleton, I don’t think I would ever have guessed that it would walk that way. (That said, the sauropod wrist skeleton does look much less flexible than that of the elephant.)
Matt: (why elephants flex their wrists) Possibly for simple energetics. If the limb is not to hit the ground during the swing phase, it has to be shortened relative to the stance limb. So it has to be bent. Bending the limb at the more proximal joints means lifting more weight against gravity. Flexing the wrist more might be a way to flex the elbow less.
(sauropod wrists look less flexible) Right, but from the texture of the ends of the bones we already suspect that sauropods had thicker articular cartilage caps than do mammals. And remember the Dread Olecranon of Kentrosaurus (i.e., Mallison 2010:fig. 3).
Mike: No doubt, but that doesn’t change the fact that elephant wrists have about half a dozen more discrete segments.
Matt: Most of which are very tightly bound together. The major flexion happens between the radius and ulna, on one hand, and the carpal block on the other, just as in humans. Elephants may have more mobile wrists than sauropods did–although that is far from demonstrated–but if so, it’s nothing to do with the number of bony elements. [Loxodonta skeleton below from Wikipedia, discovered here, arrow added by me.]
(Aside: check out the hump-backed profile of the Asian Elephas skeleton shown previously with the sway-backed profile of the African Loxodonta just above–even though the thoracic vertebrae have similar, gentle dorsal arches in both mounts. I remember learning about this from the wonderful How to Draw Animals, by Jack Hamm, when I was about 10. That book has loads of great mammal anatomy, and is happily still in print.)
And that’s as far as the discussion has gotten. The Dread Olecranon of Kentrosaurus is something Heinrich pointed out in the second of his excellent Plateosaurus papers (Mallison 2010: fig. 3).
Heinrich’s thoughts on articular cartilage in dinosaurs are well worth reading, so once again I’m going to quote extensively (Mallison 2010: p. 439):
Cartilaginous tissues are rarely preserved on fossils, so the thickness of cartilage caps in dinosaurs is unclear. Often, it is claimed that even large dinosaurs had only thin layers of articular cartilage, as seen in extant large mammals, because layers proportional to extant birds would have been too thick to be effectively supplied with nutrients from the synovial fluid. This argument is fallacious, because it assumes that a thick cartilage cap on a dinosaur long bone would have the same internal composition as the thin cap on a mammalian long bone. Mammals have a thin layer of hyaline cartilage only, but in birds the structure is more complex, with the hyaline cartilage underlain by thicker fibrous cartilage pervaded by numerous blood vessels (Graf et al. 1993: 114, fig. 2), so that nutrient transport is effected through blood vessels, not diffusion. This tissue can be scaled up to a thickness of several centimeters without problems.
An impressive example for the size of cartilaginous structures in dinosaurs is the olecranon process in the stegosaur Kentrosaurus aethiopicus Hennig, 1915. In the original description a left ulna (MB.R.4800.33, field number St 461) is figured (Hennig 1915: fig. 5) that shows a large proximal process. However, other ulnae of the same species lack this process, and are thus far less distinct from other dinosaurian ulnae (Fig. 3B, C). The process on MB.R.4800.33 and other parts of its surface have a surface texture that can also be found on other bones of the same individual, and may indicate some form of hyperostosis or another condition that leads to ossification of cartilaginous tissues. Fig. 3B–D compares MB.R.4800.33 and two other ulnae of K. aethiopicus from the IFGT skeletal mount. It is immediately obvious that the normally not fossilized cartilaginous process has a significant influence on the ability to hyperextend the elbow, because it forms a stop to extension. Similarly large cartilaginous structures may have been present on a plethora of bones in any number of dinosaur taxa, so that range of motion analyses like the one presented here are at best cautious approximations.
One of the crucial points to take away from all of this is that thick cartilage caps did not only expand or only limit the ranges of motions of different joints. The mistake is to think that soft tissues always do one or the other. The big olecranon in Kentrosaurus probably limited the ROM of the elbow, by banging into the humerus in extension. In contrast, thick articular cartilage at the wrist probably expanded the ROM and may have allowed the strong wrist flexion that some artists have restored for sauropods. I’m not arguing that it must have done so, just that I don’t think we can rule out the possibility that it may have. And so the flipped-back wrist in the Sideshow Apatosaurus does not bother me–but not everyone is convinced. Welcome to science!
Ever since I saw Jensen’s (1987) paper about how mammals are so much better than dinosaurs because their limb-bones articulate properly, I’ve been fuming on and off about this — the notion that the clearly unfinished ends we see are what was operating in life. No.
Finally, interest in articular cartilage is booming right now, as Mike blogged about here. In addition to the Dread Olecranon of Kentrosaurus, see the Dread Elbow Condyle-Thingy of Alligator from Casey Holliday’s 2001 SVP talk, and of course the culmination of that project in Holliday et al. (2010), and, for a more optimistic take on inferring the shapes of articular surfaces from bare bones, read Bonnan et al. (2010).
Next time: texture and color.
- Bonnan, M.F., Sandrik, J.L., Nishiwaki, T., Wilhite, D.R., Elsey, R.M., and Vittore, C. 2010. Calcified cartilage shape in archosaur long bones reflects overlying joint shape in stress-bearing elements: Implications for nonavian dinosaur locomotion. The Anatomical Record 293: 2044-2055.
- Graf, W., Waele, C. de, and Vidal, P.P. 1995. Functional anatomy of the head−neck movement system of quadrupedal and bipedal mammals. Journal of Anatomy 186: 55–74.
- Holliday, C.M., R.C. Ridgely, J.C. Sedlmayr and L.M. Witmer. 2010. Cartilaginous epiphyses in extant archosaurs and their implications for reconstructing limb function in dinosaurs. PLoS ONE 5(9): e13120. doi:10.1371/journal.pone.0013120
- Mallison, H. 2010. The digital Plateosaurus II: An assessment of the range of motion of the limbs and vertebral column and of previous reconstructions using a digital skeletal mount. Acta Palaeontologica Polonica 55 (3): 433–458.
- Taylor, M.P., Wedel, M.J. and Naish, D. 2009. Head and neck posture in sauropod dinosaurs inferred from extant animals. Acta Palaeontologica Polonica 54(2): 213-220.
- van der Leeuw, A.H.J., Bout, R.G., and Zweers, G.A. 2001. Evolutionary morphology of the neck system in ratites, fowl, and waterfowl. Netherlands Journal of Zoology 51(2):243-262.
- Vidal, P.P., Graf, W., and Berthoz, A. 1986. The orientation of the cervical vertebral column in unrestrained awake animals. Experimental Brain Research 61: 549-559.
November 28, 2011
Photo copyright Derek Bromhall, borrowed from ARKive.
Let’s say you want to paint an elephant. Where will you locate your elephant, and what will it be doing?
If you depict an elephant standing on a glacier at 14,000 feet, your depiction is accurate, because elephants have been caught doing that. Elephant, standing in a dunescape with no water or vegation in sight: accurate, for the same reason. Elephant, swimming in the ocean out of sight of land: accurate. Elephant, scraping salt out of the wall of a cave: accurate. Elephant, rearing to pull down otherwise unreachable vegetation: accurate. Elephant beating the hell out of a monitor lizard for no apparent reason: accurate. Depictions of elephants doing these things might not be familiar–at least to those of us who don’t live around elephants and therefore don’t get to see them doing all the wacky stuff that real animals do–but they are all accurate, in that elephants actually do these things. A lot, apparently, given that all of the above behaviors were documented in the space of just a few decades. Who knows what you might see if you could watch all the elephants, all the time, for a million years or so.
Is there any reason to think that extinct animals were any less versatile?
On the other hand, just because elephants occasionally go for strolls on glaciers or voluntarily rear up on their hind legs to reach higher does not mean that glaciers are their usual habitat or that rearing is a big part of their behavioral repertoire. So these things are accurate, in that they do happen, unfamiliar, in that they are not widely known by most laypeople*, and unusual, in that they are in the long tail of elephant behavior.
* Before you flood the comment section with, “I knew that about elephants!”, consider the implicit possibility that you are not most laypeople. Does your grandmother know that elephants do all this weird stuff?
So we’ve got three potentially orthogonal axes: accuracy, familiarity, usualness. If this was xkcd, at this point I’d draw a Venn diagram. But it’s not and I’m lazy, so I’m just going to pick three possibilities that illustrate an ascending scale of weirdness. First, the most vanilla (by behavioral weirdness, not artistic achievement) wildlife art depicts animals doing things that they actually do (accurate), frequently (usual), that are known to most people (familiar): giraffes eating out of trees, lions with bloody faces crowded around a dead zebra. Second, art that depicts animals doing things that they actually do (accurate), frequently (usual), that are not known to most people (unfamiliar): hummingbirds eating dirt, mud turtles (kinosternids) climbing trees. Third, art that depicts animals doing things that they actually do (accurate), infrequently (unusual), that are not known to most people (unfamiliar): mammals raising the adopted offspring of other species that are their typical predators or prey, grey whales in the Mediterranean Sea.
The question is, what expectations do we have for paleoart or wildlife art in general? Do paleoartists have a responsibility to only depict extinct animals doing things that are accurate, usual, and familiar? Maybe, if an art director for a book or documentary requested a vanilla dinosaur doing vanilla stuff, but outside of that situation?
As will probably come as no surprise, I skew pretty hard in the other direction. Paleoartists are vastly more important to paleontology than wildlife artists are to zoology, because they have to do everything that artists of extant wildlife do–and one more crucial thing. If, say, a mammalogist needs to be reminded of the complexity and sheer otherness of her study animals, she can usually go out and observe them for a while, and see herbivores eating meat and carnivores eating plants and interspecies sex and all kinds of crazy stuff that real animals do. Paleontologists do not have the same luxury. It is all too easy to slip into the trap of thinking that we know what our animals were like in life. Consider, for example, the difference in temperament between black and white rhinos, or African and Asian elephants, and then consider Morrison sauropods or Two Medicine ceratopsians, and tell me you know anything about the behavioral differences between Apatosaurus and Diplodocus and their ecological ramifications. We need to be periodically shaken out of our comfortable assumptions and creeping anthropomorphizing (sensu Witton–not just attributing human traits to animals, but casting them in standard roles). We need to be confronted with the essential weirdness–and indeed unknowability–of our study animals. And we need paleoartists to do at least some of this shaking and confronting.
I’m not saying that paleoartists have a responsibility to deliver the unfamiliar or unusual in their art, any more than they have a responsibility to only draw vanilla stuff. I don’t think that paleoartists have a responsibility to anything but accuracy, and I mean accuracy in the inclusive, “not directly contradicted by the fossil record” sense* instead of the exclusive, “only what the evidence will support” sense. I’m saying that we–paleontologists, dino enthusiasts, science writers, museum docents, interested citizens–need the unfamiliar and unusual in paleoart as much or more than we need the comfortable and familiar, and we can only ask for it and be grateful when it appears.
* Hat tip to John Conway for this very useful turn of phrase.
Now, on the flip side, just because there is a huge amount that we will never know about extinct animals does not mean that we should give up trying, or that we should play down the reasonable inferences that we can make. Triceratops probably fought each other more than Centrosaurus, for example, or at least inflicted more damage on the squamosals of their conspecifics (evidence, discussion, link to paper). Would a painting showing two Centrosaurus beating the hell out of each other with their horns and doing all kinds of gnarly damage to each others’ heads therefore be inaccurate? Of course not–I am certain that at some point in the multi-million-year history of centrosaurs, two of them did in fact beat the hell out of each other in just that way. But neither would that painting show their usual mode of settling differences, so far as we can tell from our current interpretation of the available fossils (count the caveats there). That’s what the usualness axis is all about–getting comfortable with the distinction between what animals occasionally do and what they commonly do.
Scavenging Styracosaurus by Mark Witton–go here for the full-size version and Mark’s thoughts on ceratopsian carnivory.
There is a lot that we simply won’t ever know. Which is why I advise caution in assessing accuracy. As long as whatever the animal is doing doesn’t violate the laws of physics, I think it’s hard to rule out that it could have happened, somewhere, at least once. So the interesting discussions will probably center not around accuracy but around usualness. It’s hard to argue that a styracosaur never scavenged a carcass, but do we think that scavenging and even predation were common behaviors for ceratopsians? Given that squirrels are notorious for killing and eating chipmunks, and that deer apparently eat the eggs and nestlings of ground-nesting birds as often as they can get them, the possibility that carnivory was a usual feature of ceratopsian behavior is worthy of serious consideration. At least, we can say that (1) it is consistent with the behavior of many extant herbivores, and (2) it is something that ceratopsians were well-equipped to carry out. And given those antecedents, it is a difficult hypothesis to falsify. Then again, “difficult to falsify” does not mean “true”–so there is room for interesting discussions.
And that’s really what this post is all about: fostering productive conversations. I have seen and been part of many paleobiology conversations that went nowhere because accuracy, familiarity, and usualness were all scrambled up–often in my own mind. I’m not saying that this particular parsing of the issues is the best possible–indeed, I hope that it inspires someone else to come up with something better. But I also think that it is better than nothing, and that couching things in these terms might help us zero in on our points of genuine disagreement, and thereby make some progress, whether we’re talking about paleobiology, paleoart, or both.
What do you think?
UPDATE: Dave Hone has blogged on this sort of “what if” stuff, at least thrice: here, here, and here. That last post includes more of John Conway’s art from his “All Yesterdays” slideshow at the SVPCA 2011 icebreaker, which was awesome.