August 21, 2014
I have often argued that given their long hindlimbs, massive tail-bases, and posteriorly-located centers of mass, diplodocids were basically bipeds whose forelimbs happened to reach the ground. I decided to see what that might look like.
Okay, now obviously I know that there are no trackways showing sauropods actually getting around like this. It’s just a thought experiment. But given how close the center of mass of Diplodocus is to the acetabulum, I’ll bet that this pose was achievable in life. If diplodocids had just pushed the CM a few cm farther back, they might have dispensed with forelimbs entirely, or done something different with them, like re-evolved grasping hands.
Image modified from Gilmore (1932: plate 6). Here’s a horizontal-necked bipedal Diplodocus and the original pose:
UPDATE the next day: I had forgotten that Niroot had already done a bipedal Apatosaurus, and a much more convincing one than mine. Go see it.
- Gilmore, C. W. 1932. On a newly mounted skeleton of Diplodocus in the United States National Museum. Proceedings of the United States National Museum 81, 1-21.
April 22, 2014
5. Brian Kraatz, 2004
In the spring of 2004, I was killing time over in Tony Barnosky’s lab at Berekeley, talking to Brian Kraatz about something–mammals, probably. Brian told me that I should consider going to the International Congress of Zoology that was happening in Beijing that fall. He’d actually told me about it several times, but I kept forgetting about it. It seemed remote from my concerns. Finally, though, the day before the abstracts were due, I thought, “Why not?” I could get travel money from the department and it would get me over there to see a lot of Asian dinosaurs in person.
I was also intrigued because presenters could submit either abstracts or short papers, and I had an idea for a short paper. I had been thinking a lot about how pneumaticity got started in dinosaurs and how much we could infer about that, so that evening I stayed up until about 3 AM banging out what would become Wedel (2006), pretty much as it was published, except for the figure, which was added later.
That got me to Beijing, where I spent a lot of time talking with Paul Barrett, who saw my talk and later invited me to contribute a talk to an SVP symposium on prosauropods, which grew into Wedel (2007) and became a chapter of my dissertation. And that got me an invite from Adam Yates and Matt Bonnan to join them in writing up the first really solid evidence of pneumaticity in prosauropods (Yates et al. 2012).
When I wandered over to the Barnosky lab to kill time that day, Brian wasn’t in. Instead I got to talking with Alan Shabel about food webs in East African riparian ecosystems. The habitats and faunas he was talking about put me in mind of the Morrison Formation of the American West. I wondered if the quantitative ecological analysis that Alan was working on would yield any insights into how Late Jurassic ecosystems worked. And that fired a few neutrons at the Van Valen papers I’d been reading for Kevin Padian’s paleobiology seminar, and precipitated a chain reaction. The paper that came out of that, “Sauropod dinosaurs as Van Valen’s energy maximizers”, was published in Paleobiology in 2007. That’s how I got into quantifying energy flow through dinosaur-dominated ecosystems.
I was presenting some of that work at an ecology conference in 2008 when I got invited to join a team of biologists going to the Galapagos. I was particularly interested in the role of extant dinosaurs (i.e., birds) in ecosystems dominated by bradymetabolic reptiles. Some of the data from that trip and one subsequent expedition went into my 2013 paper on the rise of dinosaurs during the Triassic. But most importantly, it got me working in the Galapagos, which I had wanted to do ever since I was a kid.
4. Mike Taylor, 2000
My first paper came out in the first issue of the Journal of Vertebrate Paleontology in 2000. It was the one in which Rich Cifelli and Kent Sanders and I designated OMNH 53062, a string of four sauropod vertebrae from southeast Oklahoma, as the type specimen of a new dinosaur, Sauroposeidon proteles. I had been collecting business cards and mailing addresses from people at SVP since 1997, and I had a list of about 100 people that I thought would appreciate a reprint of the paper. So when the reprints arrived from the publisher, I printed out a bunch of form letters, made an assembly line of reprints, letters, and envelopes on the big table in the OMNH vert paleo library, and killed an afternoon getting everything assembled and ready to ship out.
Also about this time I received a polite email from some English guy named Mike Taylor, asking for a reprint. I wrote back and said that I’d be happy to send him one. I don’t know what he wrote back next, but it was sufficiently interesting that it kicked off a conversation that has now been going on for 14 years. When Vicki and I went to England on spring break in 2004, we stayed with Mike and Fiona in London. I went back over for SVPCA in London in 2005, and after 2009, I started going to SVPCA every year instead of SVP. That’s how I got to know Dave Hone. I got acquainted with Darren separately–we were sending each other reprints in 2001, I think, and talking sporadically about brachiosaurs. I think that Mike and Darren also met separately, and possibly if I hadn’t been around, they still would have ended up working together. But my papers with Mike–which account for seven of the nine I’ve published since my dissertation–wouldn’t have happened, or would have come out very differently. And you wouldn’t be reading this blog.
I first met Mike Taylor at the SVP meeting in Bristol in 2009. He had done that paper on that weird vertebra with Darren a couple of years before. We got together over a few pints and discovered that we had a lot of interests in common–Star Wars, Tolkien, C.S. Lewis–but c’mon, who can’t you say that about in this geek-infested business? He’s a nice guy, and we’re friends, but we’re not what you’d call close.
I spent most of my time at that meeting catching up with Matt Bonnan. We’d been friends since the late 90s, and we’d written the paper on the probable brachiosaurid metacarpal in 2004, but we hadn’t collaborated much. Well, we were both out of grad school and into stable jobs, and we really put our heads together that meeting. Two streams of papers came out of that: first, the sauropod biomechanics papers, which merged his limb development stuff with my pneumaticity stuff, and secondly, all of our work on quantifying serial variation using geometric morphometrics.
Although the first set of papers has attracted more attention–certainly more media attention–it’s the second set that give me more satisfaction. I’ve always been interested in serial homology, I just didn’t have a novel approach. But with Matt’s help I was able to combine morphometrics and phylogenetics to produce developmental phylogenies of serially repeated structures. That by itself is pretty cool, but when you bring it into the extant realm you can put the gene expression patterns right into the analysis. The stuff we’re doing with axial development in chickens right now–man, I don’t know if I’ll ever find the time to write another paper about extinct dinosaurs, when there’s so much fun to be had with the living ones.
3. Brooks Britt, 1997
In the summer of 1997, I was on a multi-thousand-mile quest to determine whether OMNH 53062 was a new dinosaur, or just a big example of something already known. Vicki and I had been to D.C. that spring, partly as our first vacation as a married couple, and partly so that I could see the Astrodon/Pleurocoelus material at the Smithsonian. That summer, I mapped out an epic tour of museums in the West. With our friend Tyson Davis, Vicki and I went to Dinosaur National Monument, the Utah Museum of Natural History in Salt Lake, the BYU Earth Sciences Museum in Provo, and the Museum of Western Colorado in Grand Junction.
The main reason we went to Grand Junction was because at the time, the MWC had some of the BYU Brachiosaurus material from Dry Mesa Quarry on exhibit. Rich Cifelli and I weren’t sure what OMNH 53062 was yet, but we thought it looked an awful lot like Brachiosaurus. Brooks Britt was the curator there at the time, and he took us down to the basement and showed us some of the sauropod material from the Lower Cretaceous Dalton Wells Quarry. Brooks was particularly excited to show us the pneumatic features in the vertebrae. I told him about the big vertebrae from Oklahoma that I was working on, and he said, “You should get those vertebrae CT scanned, to get a look at the pneumatic spaces inside.” I smiled and nodded and thought to myself, “Dude, you are completely crazy. I am an undergrad on an independent study. No way do I have the juice to get giant dinosaur bones CT scanned.” But I didn’t forget about what he’d said. When we got back to Oklahoma, I mentioned it to Rich–and then I forgot about it.
Happily for me, Rich did not forget about it. A few months later, he was at a university function with the director of OU’s University Hospital, and he mentioned the idea of CT scanning the dinosaur bones. The hospital director was all for it–the CT machines frequently had down time on Saturdays, and the hospital would trade time on the machines for publicity when we published our results. That December, I was in Rich’s office for one of our weekly meetings when he said, “Hey, are you still interested in CT scanning the vertebrae? Because if you want to, we can make it happen.” I don’t remember what I said, but I assume it was some variant of “Hell yeah!”
We took the first jacket up to the hospital in January, 1998. We got decent results. The vertebrae were so big and dense that the scans were plagued by beam-hardening artifacts, but we could see that internal structure was honeycombed by dozens or hundreds of thin-walled cavities. The problem was, we had no idea what that meant–a few physical cross-sections of sauropod vertebrae had been published over the years, most notably by Heber Longman in 1933 and Werner Janensch in 1947–but to my knowledge no CT scans of sauropod vertebrae had ever been published, and you could probably count on your fingers the number of published CT scans of fossils of any kind. Brooks had a bunch in his 1993 dissertation, but that was unpublished, and I wouldn’t get a copy for several more months. So we had no baseline.
But we did have Kent Sanders, a radiologist at the hospital who was hot on this stuff and helped us read the films. And we had a museum full of dinosaur bones and access to a CT scanner on the weekends. So that’s how I spent most of the Saturdays in 1998–drive to the museum, fill the trunk of the car with dinosaur bones, drive up to Oklahoma City and spend the day scanning with Kent. I wasn’t supposed to do my MS thesis on pneumaticity, but when the primary project I had been working on didn’t look like it was going to pan out, I realized that I had enough CT scans of sauropod vertebrae that with a little selective hole-filling I could describe the evolution of vertebral pneumaticity in sauropods. So that became my Master’s thesis.
That conversation with Brooks Britt in the summer of 1997 was a turning point for me. Until then I’d been interested in OMNH 53062 for what it could tell us about the animal that it had once been part of. But when Brooks started telling me about the taphonomy of the Dalton Wells Quarry, I realized that the Oklahoma vertebrae were telling another story, too: the story of what had happened to that animal. So that’s the angle we played up in the paper–how did these vertebrae get separated from the rest of the critter? Mesozoic murder mystery!
Then the next summer I was out with Rich’s crew in Montana, working in the Cloverly Formation. I actually spent most of my time with Des Maxwell and his group at the Wolf Creek quarry, which was a sauropod bonebed. I did a poster on that quarry for SVP in 2000, and I wrote my MS thesis on the taphonomy of the quarry.
While all of this was going on, I was spending more and more time talking with Brooks Britt. He had done his dissertation on pneumaticity in fossil archosaurs, but he had all kinds of interesting things going on related to taphonomy, including modification of dinosaur bones by termities, and evidence of fungal hyphae in dinosaur bones. Brooks had done his Bachelor’s and Master’s work at BYU before going to Calgary for his dissertation. He encouraged me to think about going to BYU for my PhD work. The more I thought about it, the more sense it made–I freaking love Utah, and the chance to go live and work there was too good to pass up. I started out as one of Ken Stadtman’s grad students, but when Brooks got the job at BYU in 2002, he agreed to come on as my co-advisor. I’m mainly interested in what you can infer about terrestrial ecosystems from tracks left on bones, so that’s what I did my dissertation on. Most of the chapters were on sauropods, naturally, but I did have that one project looking at invertebrates, fungi, and microbes–or their traces–in faunal bone I collected from Capitol Reef National Forest in the summer of 2005. Now that was a fun project.
While I was working at BYU, Vicki got her PhD in anthropology from the University of Utah. Both of us had field sites in southern Utah, and we really fell in love with that part of the state. After we finished our degrees we moved to St. George, which is just gorgeous. Vicki coordinates the excavation and repatriation of Native American remains and artifacts from Utah federal lands, and I teach geology at Dixie State University. When I’m not digging, teaching, or hiking, I blog about sauropod taphonomy. My friends tease me because it’s such a geeky niche thing, but it makes me happy.
2. Rich Cifelli, 1996
You know how sometimes you end up working on something just because it’s there? That’s how I started working on sauropods.
Immediately after I left Trish Schwagmeyer’s office, I marched down to the museum, barged into Rich’s office, threw myself in a chair, and asked him if he’d sponsor me on an independent study. He said that he’d be delighted to–what did I want to work on? Dinosaurs, I said, dinosaurs! “Well, we have these big sauropod vertebrae from southeastern Oklahoma that need to be identified.” We went and had a look. It wasn’t my dream project–I was more interested in big theropods and ceratopsians–but I said I’d take the job. There was a little paperwork to fill out. We conceived a one-semester project, to be completed in the fall of 1996, to identify the specimen, OMNH 53062, to the family level. Rich loaned me some of his sauropod papers to photocopy so that I could get up to speed on the anatomy. I spent the fall of 1996 grokking sauropod vertebral morphology and trying to figure out what this thing was.
Immediately after I left Trish Schwagmeyer’s office, I marched down to the museum, barged into Rich’s office, threw myself in a chair, and asked him if he’d sponsor me on an independent study. He said that he’d be delighted to–what did I want to work on? Dinosaurs, I said, dinosaurs–especially big theropods or ceratopsians! “Well, we have these ceratopsian odds and ends that Stovall collected back in the 30s and 40s. They’ve been catalogued all this time as Pentaceratops and Triceratops, but someone should probably check on those IDs.” Wow, my dream project–of course I pounced on it! There was a little paperwork to fill out. We conceived a one-semester project, to be completed in the fall of 1996, to identify the specimens to the genus level. Rich loaned me some of his ceratopsian papers to photocopy so that I could get up to speed on the anatomy. I spent the fall of 1996 grokking ceratopsian cranial morphology and trying to figure out what those things were.
Well, it turns out that they were Pentaceratops and Triceratops after all. So no big news, but I did learn a lot on that project: how to photograph and measure fossils, how to read scientific papers. Mostly it just got me back in the museum.
You know how sometimes you end up working on something just because it’s there? That’s how I started working on Tenontosaurus. I’ll confess, at first I didn’t have any deep, abiding love for “Tonto”. I scorned it as the world’s most boring dinosaur–no horns, spikes, frills, claws, or sails, basically just a scaly cow with a longer tail. But, man, these things were pouring out of the Antlers Formation like water out of a tap. We had adults, subadults, big juveniles, little juveniles, even a few bones from individuals so small they must have been yearlings. I started working on them in my spare time, and got a little project going on the post-hatching ontogeny of Tenontosaurus. When I graduated with my BS in the fall of 1997, it just made sense to stick around and keep working on Tenontosaurus for my MS.
Naturally I was presenting this stuff at SVP every fall, and that’s where I met Jack Horner. He thought my ontogenetic work on Tenontosaurus would be good preparation for tackling hadrosaur ontogeny and diversity. So I went to MSU for my PhD work. After I finished I got the job I have now, teaching geology in Missouri. Even when I was living in Montana, I’d still get into the OMNH collections for a day or two of research whenever I was back in Oklahoma. Now that I’m just five hours away, I’m back at OMNH all the time. There’s just so much to work on–Eolambia, the small ornithopod material from the Cloverly Formation, and especially the teeth. The OMNH has hundreds of these little ornithopod teeth from the microsites in the Cedar Mountain Formation, the Cloverly Formation, and the Antlers Formation. Nobody wants to work on them, except me. While I was working on Tenontosaurus I had to come up with some size-independent characters that I could use to determine the ontogenetic age of ornithopods based on their teeth. Once I had those, all of those teeth catalogued as “Ornithopoda indet.” became a goldmine.
I certainly never saw myself becoming “the ornithopod tooth guy”–what an oddly specific thing to be an expert on! But to me they are beautiful, intricate, and endlessly fascinating. Who knows, maybe one of these days I’ll take all of my best photographs and start a Tumblr.
1. Trish Schwagmeyer, 1996
Trish: “You’re blowing it. You want to do research, but no-one is going to trust you with a project if you can’t take care of the basic stuff like keeping your grades up.”
Me: [face-burning, fully convicted silence]
Trish: “You are capable of much more than this. I know that these grades are not reflective of your best work. This is your chance to prepare yourself for the career you want. You owe it to yourself to do better than this.”
Me: [sucking it up] “I understand. And I’ll do better. Other than getting my grades up, what else can I do to make myself attractive to graduate programs?”
Trish: “Find a professor that you like and do an independent study. Get some research experience.”
Yow. I will remember that for as long as I live. “You’re blowing it.” Thank God that alone out of everyone in my life, Trish Schwagmeyer had the guts to look me in the eye and call me out.
Trish: “Your grades last semester were a little rough.”
Me: “Yeah. O-chem II was murder.”
Trish: “And biochem.”
Me: “Yeah. Biochem.”
Trish: “Have you noticed that you get As and Bs in your language and history classes, and Cs in your math and science classes?”
Me: “Yeah, of course. Math and science are hard. Language and history are…”
Trish: “Are what?”
Me: “I dunno. Fun. More like play.”
Trish: “Maybe you’re in the wrong major.”
Yow. I will remember that for as long as I live. “Maybe you’re in the wrong major.” Thank God that alone out of everyone in my life, Trish Schwagmeyer had the guts to look me in the eye and diagnose the problem.
Immediately after I left her office, I marched over to the registrar and changed my major from Zoology to Letters. And breathed a huge sigh of relief. After that, I just cruised. I got my degree, stayed at OU for a Master’s in classical languages, and now I teach Latin at a private high school in Oklahoma City. I should have known that a career in science wasn’t in the cards. The evidence was written all over my transcript. Paleontology is still interesting to me–I doubt if I will ever stop being fascinated by dinosaurs–but it just wasn’t a realistic career option. I’m so glad I found my true calling.
September 11, 2013
We’ve blogged a lot of Bob Nicholls‘ art (here, here, and here) and we’ll probably continue to do so for the foreseeable future. We don’t have much choice: he keeps drawing awesome things and giving us permission to post them. Like this defiantly shaggy Apatosaurus, which was probably the star of the Morrison version of Duck Dynasty. Writes Bob:
On my way home at the airport I did a sketch of your giant Apatosaurus* — see attachment. My thought was that massive thick necks were probably pretty sexy things to apatosaurs, so maybe sexually mature individuals used simple feathers (stage 1, 2 or 3?) to accentuate the neck profile. The biggest males would of course have the most impressive growths so in the attached sketch your giant has one of the biggest beards in Earth’s history! What do you think of this idea?
Well, I think it’s awesome. And entirely plausible, for reasons already explained in this post.
“Now, wait,” you may be thinking, “I thought you guys said that sauropod necks weren’t sexually selected.” Actually we made a slightly different point: that the available evidence does not suggest that sexual selection was the primary driver of sauropod neck elongation. But we also acknowledged that biological structures are almost never single-purpose, and although the long necks of sauropods probably evolved to help them gather more food, there is no reason that long necks couldn’t have been co-opted as social billboards. This seems especially likely in Apatosaurus, where the neck length is unremarkable** but the neck fatness is frankly bizarre (and even inspired a Star Wars starfighter!).
I also love the “mobile ecosystem” of birds, other small dinosaurs, and insects riding on this Apatosaurus or following in its train. It’s a useful reminder that we have no real idea what effect millions of sauropods would have on the landscape. But it’s not hard to imagine that most Mesozoic terrestrial ecosystems were sauropod-driven in a thousand cascading and ramifying chains of cause and effect. I’d love to know how that worked. At heart, I’m still a wannabe chrononaut, and all my noodlings on pneumaticity and sauropod nerves and neural spines and so on are just baby steps toward trying to understand sauropod lives. Safari by way of pedantry: tally-ho!
For other speculative apatosaurs, see:
** Assuming we can be blasé about a neck that is more than twice as long (5 m) as a world-record giraffe neck (2.4 m), for garden variety Apatosaurus, or three times that length for the giant Oklahoma Apatosaurus (maybe 7 m).
July 26, 2013
Now, for me to try to draw dinosaurs next to Brian is more than a little intimidating. I really felt the need to bring my A-game. So this is what I came up with. I’m posting it not because I think it is particularly likely* but because the blog has been a little sauropod-lite this summer, and heck, it’s Friday.
* Although frigatebirds and anoles and such might have some things to say about that.
This post is just an excuse for me to show off Brian Engh’s entry for the All Yesterdays contest (book here, contest–now closed–here). The title is a reference to this post, by virtue of which I fancy myself at least a spear-carrier in what I will grandly refer to as the All Yesterdays Movement.
Oddly enough, I don’t have a ton to say about this; I think Brian has already explained the thinking behind the piece sufficiently on his own blog. In the brave new world of integumentarily enhanced ornithodirans, these diamantinasaurs are certainly interesting but not particularly outlandish (Brian’s already done outlandish). And it’s pretty darned hard to argue that sauropods never went into caves, although I can’t off the top of my head think of any previous spelunking sauropods (I’m not counting Baylene in Disney’s Dinosaur; feel free to refresh my memory of others in the comments). The glowworms are not proven, but biogeographically and stratigraphically plausible, which is probably as good as we’re going to get given the fossilization potential of bioluminescence.
I’m much more excited about this as a piece of art. I got to see a lot of the in-progress sketches and they were wonderful, with some very tight, detailed pencil-work. The danger in investing that kind of effort is that then you’re tempted to show it off, and if I had any worry about the finished piece, it was that it would be over-lit to show off all the details. But it isn’t. I can tell you from seeing the pencil sketches that the detail went all the way down, but Brian was brave enough to let some of that go, especially on the animals’ legs, to get the lighting effect right. My favorite touches are the reflections in the water, and the fallen pillar in the foreground–toppled by a previous visitor, perhaps–with new mineral deposits already forming on it.
All in all, it takes me back to the best paleoart from my childhood, which made me think, “Wow, these were not monsters or aliens, they were real animals, as real, and as mundane in their own worlds, as deer and coyotes and jackrabbits.” * **
And that’s pretty cool. What do you think?
* Okay, maybe not in those exact words. I am translating a feeling I had when I was nine through 28 years of subsequent experience and vocabulary expansion.
** My major discovery in the last two decades is that deer and coyotes and jackrabbits are just as exotic as dinosaurs, if only you learn to really see them. And before Mike jumps me for saying that, I said ‘just as exotic’, not ‘just as awesome‘.
UPDATE the next day
That’s game, set, and match on the glowworm issue.
February 27, 2013
Well, this is rad. And adorable. Brian Switek, whom we adore, commissioned a fuzzy juvenile sauropod from Niroot, whom we adore, for his (Brian’s) upcoming book, My Beloved Brontosaurus, which I am gearing up to adore. And here is the result, which I adore, borrowed with permission from Love in the Time of Chasmosaurs.
There is much to like here. Here’s my rundown:
- Small forefeet that are the correct shape: good. Maybe too small, given that young animals often have big feet. But better too small than too big, given how often people screw this up.
- Pronounced forelimb-hindlimb disparity: win.
- Fat neck: pretty good.
In fact, let me interrupt the flow of praise here to put in Brant Bassam’s dorsal view of his mounted Phil Platt model Apatosaurus skeleton. I’ve been meaning to post about this for a while now and haven’t gotten to it, so now’s a good time: just look at how friggin’ FAT that neck is, and how it blends in with the body, and how the tail gets a lot skinnier a lot quicker (and, yeah, caudofemoralis, but not that much). Now, go look at a bunch of life restorations of Apatosaurus–drawings, paintings, sculptures, toys, whatever–and see how many people get this wrong, by giving Apatosaurus a too-skinny neck. The answer is, damn near everyone.
Okay, back to Niroot’s baby:
- Proportionally shorter neck and tail because it’s a juvenile: win.
- Neck wrinkles possibly corresponding to vertebrae: okay, just this once.
- Greenish fuzz possibly functioning as camouflage: We-ell…
Yes, it’s true that all of the known sauropod skin impressions show scales, not fuzz. But. We don’t have anything like full-body coverage. And I suspect that there is a collection bias against fuzzy skin impressions. Scaly skin impressions are probably easier to recognize than 3D feathery skin impressions (as opposed to feathers preserved flat as at Liaoning and Solnhofen) because the latter probably just look like wavy patterns on rock, and who is looking for feather impressions when swinging a pickaxe at a sauropod’s back end? And how many sauropods get buried in circumstances delicate enough to preserve dinofuzz anyway? Also, some kind of fuzz is probably primitive for Ornithodira, and scales do not necessarily indicate that feathers were absent because owl legs. So is this speculative? Yes. Is it out of the question? I think not. In the spirit of Mythbusters, I’m calling it ‘plausible’.
Oh, one more thing: Niroot posted this in honor of Brian Switek’s birthday. Happy birthday, Brian! (You owe me a book!)
November 29, 2012
It’s been a while since I posted here. I haven’t gone off SV-POW! or anything, just going through one of my periodic doldrums (read: super-busy with Other Stuff). I’m writing now to draw your attention to two books that I’m pretty darned excited about.
The first is All Yesterdays: Unique and Speculative Views of Dinosaurs and Other Prehistoric Animals, by John Conway, Memo Kosemen, and Darren Naish, with skeletal diagrams by Scott Hartman (lulu, Amazon). This is sort of an SV-POW! love-fest, in that Darren is One Of Us, John and Scott let us use their art a lot–even the goofy stuff–and get a shout-out now and then, and I’ve been awed by the work of Memo–a.k.a. Nemo Ramjet–for longer than SV-POW! has existed (he also created Brontosapiens!). But wait–there’s more! One of the first people to review the book is Emily Willoughby, who was also as far as we know the first person after Paco Gasco to illustrate Brontomerus–that image is still Bronto‘s flagship portrait on Wikipedia.
But enough navel-gazing. The book is based around the mind-blowing presentations “All Yesterdays” and “All Todays” at SVPCA 2011 and 2012, both delivered by John Conway. True story: “All Yesterdays” was the intro to the icebreaker/mixer thing at Lyme Regis, so right after the talk people jumped up to grab pints and socialize. Sometime in the next few minutes, John was separately approached by three different paleontologists who thought that “All Yesterdays” should be a book, and wanted to help write it. Those three hopefuls were Darren, Mike, and me. I’m extremely happy that Darren is the one on the book. Mike and I can wrangle sauropods and we’re both “All [Some]days” fanboys, but the book really needed someone approaching tetrapod omniscience, and that’s obviously Darren.
Whoops, that was actually just another paragraph of navel-gazing. Anywho, I knew after this year’s SVPCA that there would be a book, but I had no idea it would be out so soon. I can’t tell you much about the book itself, for two reasons. First, my dead-tree copy is still en route from lulu.com. Second, I wouldn’t tell you much about the book if I could, because you should see it for yourself. It’s firmly in the tradition of speculative zoology but also has a serious point to make about the memes that drive a lot of paleoart. That’s all you need to know–get the book and prepare to be surprised, amused, amazed, and moved to wonder.
The other new book I’m all het up about is Zombie Tits, Astronaut Fish, and Other Weird Animals, by Becky Crew (Amazon, New South Books). My mutual admiration pact with Bec goes back to 2009. She blogged about one of my posts, I blogged about how indescribably wonderful her blog was, she published something I wrote–my first paying gig as a writer, I think. Now she’s blogging at SciAm, which is great, because although she’s smart, irreverent, and freakin’ hilarious, she’s also mortal, and we need to get as much of that good stuff out of her head and into general circulation as possible while she’s still around. (She’s not sick or anything, she’s just going to die sometime in the next century, and if you read her blog I think you’ll agree that that’s too damn soon.) Zombie Tits does not seem to be available stateside yet, but I will keep a weather eye on things and post an update when that changes.
I’ll probably review both books here in due time, if by “review” one means “alternately drool over and hyperbolically gush about with no attempt at objectivity whatsoever”. And I do mean precisely that.
It’s been a while since we’ve served you up a sauropod, so, finally and fittingly, here’s John Conway’s playful Camarasaurus taking a mud bath. Or maybe just trying to hide its hideousness; as the authors of All Yesterdays note, “Camarasaurus [...] is considered by some experts to be among the ugliest of all sauropods”.
September 18, 2012
Friday evening I was in a pub with Mike, Darren, John Conway, and Emma Lawlor. We were killing time waiting for the Pink Giraffe Chinese restaurant down the street to open. I was chatting with John about “All Todays”, his speculative presentation with Cevdet Kosemen (a.k.a. Nemo Ramjet) on how future sentients might reconstruct Holocene animals if they were known only from fossils. Like his “All Yesterdays” presentation last year, John’s flights of scientific fancy had fired my imagination and gotten me thinking about how paleontology forms sort of a skin or membrane between the bubble of what we know and the surrounding ocean of what we don’t. I decided that we should pass a pad around and each sketch a speculative sauropod.
My own entry is based on the holotype of Mamenchisaurus hochuanensis, which was found almost complete except for the skull (naturally) and forelimbs. I have often joked that diplodocids were basically bipeds whose forelimbs happened to reach the ground. Mamenchisaurs were probably not that back-heavy, but their presacral vertebrae were extremely pneumatic and if our hypothetical future paleontologists had no other sauropod material to work with, I think it’s possible that they would reconstruct the M. hochuanensis holotype as a biped.
I’m not sure there’s much to say about Mike’s brachiosaur, beyond the Ebert-like observation that if a brachiosaur dressed up in a coat and top hat and went cruising for dames, this, I am forced to conclude, is more or less how it would look.
John Conway also drew a mamenchisaur, this time Mamenchisaurus youngi with its bizarrely bent-back sacrum. John’s explanation for the weird sacrum brings to mind ground sloths and–for those who saw “All Yesterdays” at SVPCA 2011–a certain black-feathered therizinosaur. I’d also like to note that he knocked this out in about 5 minutes, thus demonstrating the difference between a professional artist and a mere doodler like myself.
Darren’s hindlimb-less sauropod complements my bipedal Mamenchisaurus. Here the animal, evidently known from only the front half of the skeleton, has been restored as a giant bird. Dig the giant thumb claws and spreading metapodials. Surely, you say, future paleontologists of any species or machine culture would know a pectoral girdle when they saw one. But I’ll bet a sauropod scapulocoracoid could pass for an ilium, if said future paleontologists were still in the early stages of understanding the morphology and diversity of vertebrates. Remember that Seeley described the sauropod Ornithopsis as “a gigantic animal of the pterodactyle kind” based on its pneumatic vertebrae. There is also a long and honorable (?) tradition of mistaking sauropods for hadrosaurs (Sonorasaurus), theropods (Bruhathkayosaurus), and tree trunks (Sauroposeidon), so don’t be too quick to rule this out.
What I want to see next is a skeletal reconstruction of Darren’s sauro-bird, using only elements from the front half of a sauropod skeleton. Anyone want to give it a shot?
Our penultimate entry is Emma’s rendering of an evil bastard snake devouring an innocent baby sauropod. Tragically this one is not speculative–we have very good fossil evidence that the scene shown here really happened, probably a lot. She tried to make it up to us with a smiley face on the next page, but it was too late. We were so depressed after this that we could barely choke down four courses of excellent Chinese food.
One more for the road: a totally new depiction of the enigmatic sauropod Xenoposeidon by yours truly. I expect to see this incorporated into future talks and papers dealing with European sauropod diversity in the Early Cretaceous. Just credit me as you normally would.
That’s all, folks. I hope that speculative sauropod sketches get to be a Thing, and that we see lots more of them from future conferences.
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.
I have a new paper out:
Update June 6, 2012: the final version was formally published yesterday, so the rest of this paragraph is of historical interest only. Like Yates et al. on prosauropod pneumaticity, it is “out” in the sense that the manuscript has been through peer review, has been accepted for publication, and is freely available online at Acta Palaeontologica Polonica. Technically it is “in press” and not published yet, but all that formal publication will change is to make a prettier version of the paper available. All of the content is available now, and the paper doesn’t include any of those pesky nomenclatural acts, and so, as with the prosauropod pneumaticity paper, I don’t see any reason to pretend it doesn’t exist. Think of the accepted manuscript as the caterpillar to the published version’s butterfly: different look, but same genome.
This one came about because last summer I read a review of Richard Dawkins’s book, The Greatest Show on Earth: The Evidence for Evolution. The review mentioned that the book includes a lengthy discussion of the recurrent laryngeal nerve (RLN) in the giraffe, which is a spectacularly dumb piece of engineering and therefore great evidence against intelligent design creationism. It wasn’t the first time I’d heard of the RLN, of course. It’s one of the touchstones of both human anatomy and evolutionary biology; anatomy because of its clinical importance in thyroid surgery, known for more than two millennia, and evolutionary biology because it is such a great example of a developmental constraint. (Dawkins’s coverage of all of this is great, BTW, and you should read the book.)
No, the reason the book review inspired me to write the paper was not because the RLN was new to me, but because it was overly familiar. It is a cool piece of anatomy, and its fame is justly deserved–but I am sick and tired of seeing the stinkin’ giraffe trotted out as the ultimate example of dumb design. My beloved sauropods were way dumber, and it’s time they got some credit.
But first, let’s talk about that nerve, and how it got to be there.
No necks for sex? How about no necks for anybody!
Embryos are weird. When you were just a month old (counting from fertilization), you had a set of pharyngeal arches that didn’t look radically different from those of a primitive fish. These started out quite small, tucked up underneath your comparatively immense brain, and each pharyngeal arch was served by a loop of artery called an aortic arch. What we call the arch of the aorta in an adult human is a remnant of just one of these embryonic aortic arches, and as you’ve no doubt noticed, it’s down in your chest, not tucked up next to your brain. When you were in the embryonic stages I’m talking about, you didn’t yet have a neck, so your brain, pharyngeal arches, aortic arches, and the upper parts of your digestive system were all smooshed together at your front end.
One thing you did have at that stage was a reasonably complete peripheral nervous system. The nerve cell bodies in and near your central nervous system sent out axons into the rest of your body, including your extremities. Many of these axons did not persist; they failed to find innervation targets and their parent neurons died. Imagine your embryonic central nervous system sending out a starburst of axons in all directions, and some of those axons finding targets and persisting, and others failing and dying back. So the architecture of your nervous system is the result of a process of selection in which only some cells were successful.
Crucially, this radiation and die-off of axons happened very early in development, when a lot of what would become your guts was still hanging under your proportionally immense brain like the gondola on a blimp. This brings us to the recurrent laryngeal nerve.
Going back the way we came
The fates of your embryonic pharyngeal arches are complex and I’m not going to do a comprehensive review here (go here for more information). Suffice it to say that the first three arches give rise to your jaws and hyoid apparatus, the fourth and sixth form your larynx (voicebox), and fifth is entirely resorbed during development. Update: I made a pharyngeal arch cheat sheet.
There are two major nerves to the larynx, each of which is bilaterally paired. The nerve of the fourth pharyngeal arch becomes the superior laryngeal nerve, and it passes cranial to the fourth aortic arch. The nerve of the sixth pharyngeal arch becomes the inferior or recurrent laryngeal nerve, and it passes caudal to the sixth aortic arch. At the time that they form, both of these nerves take essentially straight courses from the brainstem to their targets, because you’re still in the blimp-gondola stage.
If you were a shark, the story would be over. The more posterior pharyngeal arches would persist as arches instead of forming a larynx, each arch would hold on to its artery, and the nerves would all maintain their direct courses to their targets.
But you’re not a shark, you’re a tetrapod. Which means that you have, among other things, a neck separating your head and your body. And the formation of your neck shoved your heart and its associated great vessels down into your chest, away from the pharyngeal arches. This was no problem for the superior laryngeal nerve, which passed in front of the fourth aortic arch and could therefore stay put. But the inferior laryngeal nerve passed behind the sixth aortic arch, so when the heart and the fourth and sixth aortic arches descended into the chest, the inferior laryngeal nerve went with them. Because it was still hooked up to the brainstem and the larynx, it had to grow in length to compensate.
As you sit reading this, your inferior laryngeal nerves run down your neck into your chest, loop around the vessels derived from the fourth and sixth aortic arches (the subclavian artery on the right, and the arch of the aorta and ductus arteriosus on the left) and run back up your neck to your larynx. Because they do this U-turn in your chest and go back the way they came, the inferior laryngeal nerves are said to ‘recur’ to the larynx and are therefore more commonly referred to as the recurrent laryngeal nerves (RLNs).
An enlightening diversion
The RLN is the poster child for “unintelligent design” because it is pretty dumb. Your RLNs travel a heck of a lot farther to reach your larynx than they ought to, if they’d been designed. Surely an intelligent designer would have them take the same direct course as the superior laryngeal nerve. But evolution didn’t have that option. Tetrapod embryos could not be built from the ground up but had to be modified from the existing “sharkitecture” of ancestral vertebrates. The rules of development could not be rewritten to accommodate a shorter RLN. Hence Dawkins’s love affair with the RLN, which gets 7 pages in The Greatest Show on Earth. He also appeared on the giraffe episode of Inside Nature’s Giants, in which the RLN was dug out of the neck and the continuity of its ridiculous path was demonstrated–probably the most smack-you-in-the-face evidence for evolution that has ever been shown on television (said the rabid fan of large-tetrapod dissections).
Incidentally, the existence and importance of the RLN has been known since classical times. The RLN innervates the muscles responsible for speech, and on either side it passes right behind the thyroid gland, which is subject to goiters and tumors and other grotesque maladies. So a careless thyroidectomy can damage one or both of the RLNs; if one gets snipped, the subject will be hoarse for the rest of his or her life; if both are cut, the subject will be rendered mute. The Roman physician Galen memorably demonstrated this by dissecting the neck of an immobilized but unanesthetized pig and isolating the RLNs (Kaplan et al. 2009). One moment the poor pig was squealing its head off–as any of us would be if someone dug out our RLNs without anesthesia–and the next moment Galen severed the RLNs and the animal abruptly fell silent, still in unbelievable pain but now without a mechanism to vocally express its discomfort.
The name of the nerve also goes back to Galen, who wrote:
I call these two nerves the recurrent nerves (or reversivi) and those that come upward and backward on account of a special characteristic of theirs which is not shared by any of the other nerves that descend from the brain.
Like at least some modern surgeons, Galen does not seem to have been overly burdened by humility:
All these wonderful things, which have now become common property, I was the first of all to discover, no anatomist before me ever saw one of these nerves, and so all of them before me missed the mark in their anatomical description of the larynx.
Both of those quotes are from Kaplan et al. (2009), which is a fascinating paper that traces the knowledge of the recurrent laryngeal nerve from classical times to the early 20th century. If you’d like a copy and can’t get hold of one any other way, let me know and I’ll hook you up.
Share and share alike
By now you can see where this is going: all tetrapods have larynges, all tetrapods have necks, and all tetrapods have recurrent laryngeal nerves. Including giraffes, much to the delight of Richard Dawkins. And also including sauropods, much to the delight of yours truly.
Now, I cannot show you the RLN in a living sauropod, nor can I imagine a scenario in which such a delicate structure would be recognizably preserved as a fossil. But as tetrapods, sauropods were bound to the same unbreakable rules of development as everything else. The inference that sauropods had really long, really dumb RLNs is as secure as the inference that they had brainstems, hearts, and larynges.
Giraffes have necks up to 2.4 meters long (Toon and Toon 2003), so the neurons that make up their RLNs approach 5 meters in the largest indiividuals. But the longest-necked sauropods had necks 14 meters long, or maybe even longer, so they must have had individual neurons at least 28 meters long. The larynx of even the largest sauropod was probably less than 1 meter away from the brainstem, so the “extra” length imposed on the RLN by its recurrent course was something like 27 meters in a large individual of Supersaurus. Take that, Giraffa.
One way or another
It is possible to have a nonrecurrent laryngeal nerve–on one side, anyway. If you haven’t had the opportunity to dissect many cadavers, it may come as a surprise to learn that muscles, nerves, and blood vessels are fairly variable. Every fall in Gross Anatomy at WesternU, we have about 40 cadavers, and out of those 40 people we usually have two or three with variant muscles, a handful with unusual branching patterns of nerves, and usually half a dozen or so with some wackiness in their major blood vessels. Variations of this sort are common enough that the better anatomy atlases illustrate not just one layout for, say, the branching of the femoral artery, but 6-10 of the most common patterns. Also, these variations are almost always asymptomatic, meaning that they never cause any problems and the people who have them usually never know (ask Mike about his lonely kidney sometime). You–yes, you, gentle reader!–could be a serious weirdo and have no idea.
Variations in the blood vessels seem to be particularly common, possibly because the vessels develop in situ with apparently very little in the way of genetic control. Most parts of the body are served by more than one artery and vein, so if the usual vessel isn’t there or takes an unusual course, it’s often no big deal, as long as the blood gets there somehow. To wit: occasionally a person does not have a right subclavian artery. This does not mean that their right shoulder and arm receive no blood and wither away; usually it means that one of the segmental arteries branching off the descending aorta–which normally serve the ribs and their associated muscles and other soft tissues–is expanded and elongated to compensate, and looks for all the world like a normal subclavian artery with an abnormal connection to the aorta. But if the major artery that serves the forelimb comes from the descending aorta, and the 4th aortic arch on the right is completely resorbed during development, then there is nothing left on the right side to drag the inferior laryngeal nerve down into the torso. A person with this setup will have an inferior laryngeal nerve on the right that looks intelligently designed, and the usual dumb RLN on the left.
Can people have a nonrecurrent laryngeal nerve on the left? Sure, if they’ve got situs inversus, in which the normal bilateral asymmetry of the internal organs is swapped left to right. Situs inversus is pretty darned rare in the general population, occurring in fewer than 1 in 10,000 people. It is much more prevalent in television shows and movies, where the hero or villain may survive a seemingly mortal wound and then explain that he was born with his heart on the right side. (Pro tip: the heart crosses the midline in folks of both persuasions, so just shoot through the sternum and you’ll be fine. Or, if you’re worried about penetration, remember Rule #2 and put one on either side.) Anyway, take everything I wrote in the preceding paragraph, mirror-image it left to right, and you’ve got a nonrecurrent laryngeal nerve on the left. But just like the normally-sided person who still has an RLN on the left, a person with situs inversus and no remnant 4th aortic arch on the left (double variation alert!) still has an RLN looping around the aorta and ductus arteriosus on the right.
Bottom line: replumb the vessels to your arms, swap your organs around willy-nilly, you just can’t beat the aorta. If you have an aorta, you’ve got at least one RLN; if you don’t have an aorta, you’re dead, and no longer relevant to this discussion.
Nonrecurrent laryngeal nerves–a developmental Hail Mary?
But wait–how do we know that the inferior laryngeal nerve in embryonic sauropods didn’t get rerouted to travel in front of the fourth and sixth aortic arches, so it could be spared the indignity of being dragged into the chest later on?
First of all, such a course would require that the inferior laryngeal nerve take an equally dumb recurrent course in the embryo. Or maybe it should be called a procurrent course. Instead of simply radiating out from the central nervous system to its targets in the sixth pharyngeal arch, the axons that make up the RLN would have to run well forward of their normal course, loop around the fourth and sixth aortic arches from the front, and then run back down to the sixth pharyngeal arch. There is simply no known developmental mechanism that could make this happen.
Even if we postulated some hypothetical incentive that would draw those axons into the forward U-turn, other axons that took a more direct course from the central nervous system would get to the sixth pharyngeal arch first. By the time the forwardly-recurring axons finished their intelligently-routed course and finally arrived at the sixth pharyngeal arch, all of the innervation targets would be taken, and those axons would die off.
Also, at what point in the evolution of long necks would this forwardly-looping course supposedly be called into existence? Ostriches and giraffes have RLNs that take the same recurrent course as those of humans, pigs, and all other tetrapods. The retention of the recurrent course in extant long-necked animals is further evidence that the developmental constraint cannot be broken.
Finally, the idea that a non-recurrent laryngeal nerve would need to evolve in a long-necked animal is based on the perception that long nerve pathways are somehow physiologically taxing or otherwise bad for the animals in which they occur. But almost every tetrapod that has ever lived has had much longer neurons than those in the RLN, and we all get on just fine with them.
In dire extremity
Probably you seen enough pictures of neurons to know what one looks like: round or star-shaped cell body with lots of short branches (dendrites) and one very long one (the axon), like some cross between an uprooted tree–or better yet, a crinoid–and the Crystalline Entity. When I was growing up, I always imagined these things lined up nose to tail (or, rather, axon to dendrite) all down my spinal cord, arms, and legs, like boxcars in a train. But it ain’t the case. Textbook cartoons of neurons are massively simplified, with stumpy little axons and only a few to a few dozen terminals. In reality, each neuron in your brain is wired up to 7000 other neurons, on average, and you have about a hundred billion neurons in your brain. (Ironically, 100 billion neurons is too many for your 100 billion neurons to visualize, so as a literal proposition, the ancient admonition to “know thyself” is a non-starter.)
Back to the axons. Forget the stumpy little twigs you’ve seen in books and online. Except for the ganglia of your autonomic nervous system (a semi-autonomous neural network that runs your guts), all of the cell bodies of your neurons are located in your central nervous system or in the dorsal root ganglia immediately adjacent to your spinal cord. The nerves that branch out into your arms and legs, across your face and scalp, and into your larynx are not made of daisy chains of neurons. Rather, they are bundles of axons, very long axons that connect muscles, glands, and all kinds of sensory receptors back to the nerve cell bodies in and around your brain and spinal cord.
Indulge me for a second and wiggle your toes. The cell bodies of the motor neurons that caused the toe-wiggling muscles to fire are located in your spinal cord, at the top of your lower back. Those motor neurons got orders transmitted down your spinal cord from your brain, and the signals were carried to the muscles of your feet on axons that are more than half as long as you are tall.
Some of your sensory neurons are even longer. Lift your big toe and then set it down gently, just hard enough to be sure that it’s touching down on the floor or the sole of your shoe, but not hard enough to exert any pressure. When you first felt the pad of your toe touch down, that sensation was carried to your brain by a single neuron (or, rather, by several neurons in parallel) with receptor terminals in the skin of your toe, axon terminals in your brainstem, and a nerve cell body somewhere in the middle (adjacent to your sacrum and just a bit to one side of your butt crack, if you want the gory details). That’s right: you have individual sensory neurons that span the distance from your brainstem to your most distal extremity. And so does every other vertebrate, from hagfish to herons to hippos. Including, presumably, sauropods.
I had you set your toe down gently instead of pushing down hard because the neurons responsible for sensing pressure do not travel all the way from toe-tip to brainstem; they synapse with other neurons in the spinal cord and those signals have been through a two-neuron relay by the time they reach your brainstem. Ditto for sensing temperature. But the neurons responsible for sensing vibration and fine touch go all the way.
If you want to experience everything I’ve discussed in this post in a single action, put your fingertips on your voicebox and hum. You are controlling the hum with signals sent from your brain to your larynx through your recurrent laryngeal nerves, and sensing the vibration through individual neurons that run from your fingertips to your brainstem. Not bad, eh?
Getting back to big animals: the largest giraffes may have 5-meter neurons in their RLNs, but some of the sensory neurons to their hindfeet must be more like 8 meters long. I don’t think anyone’s ever dissected one out, but blue whales must have sensory neurons to the tips of their flukes that are almost 30 meters (98 feet) long (subtract the length of the skull, but add the lateral distance from body midline to fluke-tip). And Supersaurus, Amphicoelias, and the like must have had neurons that were approximately as long as they were, minus only the distance from the snout-tip to the back of the skull. I could be wrong, and if I am I’d love to be set straight, but I think these must have been the longest cells in the history of life.
Oh, one more thing: up above I said that almost every tetrapod that has ever lived has had much longer neurons than those in the RLN. The exceptions would be animals for which the distance from brainstem to base of neck was longer than the distance from base of neck to tip of limb or tail, so that twice the length of the neck would be longer than the distance from base of skull to most distal extremity. In that case, the neurons that contribute to the RLN would be longer than those running from brainstem to tail-tip or toe-tip. Tanystropheus and some of the elasmosaurs probably qualified; who else?
In this post I’ve tried to explain the courses that these amazingly long cells take in humans and other vertebrates. I haven’t dealt at all with the functional implications of long nerves, for which please see the paper. The upshot is that big extant animals get along just fine with their crazy-long nerves, and there’s no reason to assume that sauropods were any more troubled. So why write the paper, then? Well, it was fun, I learned a lot (dude: axoplasmic streaming!), and most importantly I got to steal a little thunder from those silly poseurs, the giraffes.
Department of Frivolous Nonsense: yes, I titled the paper after those TV ads for Chili’s hamburgers from a few years back. If you never saw them, the ads compared mass-produced, machine-stamped fast-food burgers with restaurant burgers painstakingly built by hand, and concluded with, “Chili’s Big-Mouth Burgers: monuments of inefficiency!”
Update: All of this is out of date now that the paper has been formally published. Department of Good Karma: since the paper is at the “accepted manuscript” stage, I still have the chance to make (hopefully minor) changes when I get the proofs. As is always, always, always the case, I caught a few dumb errors only after the manuscript had been accepted. Here’s what I’ve got so far, please feel free to add to the list:
- Page 1, abstract, line 3: pharyngeal, not pharyngial
- Page 1, abstract, line 8: substitute ‘made up’ for ‘comprised’
- Page 6, line 12: substitute ‘make up’ for ‘comprise’
- Page 9, line 5: citation should be of Carpenter (2006:fig. 3), not fig. 2
- Page 10, line 7: “giant axons of squid are”, not ‘ares’
- Page 12, entry for Butler and Hodos should have year (1996)
- Page 12, entry for Carpenter has ‘re-evaluation misspelled
- Page 16, entry for Woodburne has ‘mammalian’ misspelled
(Notes to self: stop trying to use ‘comprise’, lay off the ‘s’ key when typing bibliography.)
- Butler, A.B., and Hodos, W. 1996. Comparative Vertebrate Neuroanatomy: Evolution and Adaptation. 514 pp. Wiley–Liss, New York.
- Kaplan, E.L, Salti, G.I., Roncella, M., Fulton, N., and Kadowaki, M. 2009. History of the recurrent laryngeal nerve: from Galen to Lahey. World Journal of Surgery 33:386-393. DOI 10.1007/s00268-008-9798-z
- Toon, A., and Toon, S.B. 2003. Okapis and giraffes. In: M. Hutchins, D. Kleiman, V. Geist, and M. McDade (eds.), Grzimek’s Animal Life Encyclopedia, 2nd ed. Vol 15: Mammals IV, 399–409. Gale Group, Farmington Hills.
- Wedel, M.J. 2012. A monument of inefficiency: the presumed course of the recurrent laryngeal nerve in sauropod dinosaurs. Acta Palaeontologica Polonica 57(2):251-256.