This is a Galeamopus, roughly two feet long, sculpted by James Herrmann (who also made the life-size Aquilops sculpture and bust) for the Cincinnati Museum Center.

Here’s what it looks like on the other side.

From behind.

And from the front.

I dig this. I’m sure someone else must have done this half-skeletal reconstruction, half-fleshed life restoration style of sculpture before, but I can’t think of any museum-quality examples. The bronze is a nice touch.

Here’s a convincingly chunky Allosaurus.

About the sculpting process, James wrote (in an email with permission to cite):

I worked on all of the museum pieces with Glenn Storrs, Ph.D., vertebrate paleontologist with the Cincinnati Museum Center. He would tell me what he envisioned and provide me with reference material, I would sculpt it, take the clay to Glenn for his critique, take it back and make revisions. We went through several cycles of this for each piece and when I received the final approval I took each piece to the foundry.

Tyrannosaurs are to museums what roller-coasters are to amusement parks. Here’s Daspletosaurus.

My favorite thing about these sculptures is why they’re done in bronze. It’s not just for posterity. James again:

The idea was to provide a small sculpture of each skeletal reconstruction on display for people to touch and feel. It was felt that this element of touch would be particularly important to accommodate the needs of the visually impaired museum visitor. I will feel like I have achieved success when the patina is rubbed off parts of the bronze.

One more, a life-size bust of Galeamopus.

In addition to having these on display at the Cincinnati Museum Center, James will be producing these sculptures as limited editions. If you’re interested, please visit http://www.herrmannstudio.com/.

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We have summer-house in the garden, divided into two rooms. One of the rooms functions as a shed:

Among the many things in that shed, there’s some light scaffolding which we’ve used to paint the back of the house. The wide ladder-like object is part of this:

But we can’t use that scaffolding now — even though I need to to take the top off a tree — because birds have built a nest on the top rung, and hatched some eggs there:

Here’s the next in close-up. There are four babies in here: three that are easy to spot because of their open beaks, and one more with a closed beak to the right. (The parent has, for the moment, flown away.)

They were sitting absolutely still with open mouths, perhaps as a way to cool down on what was quite a hot day.

Can anyone tell me what kind of birds these are? And, more importantly, how close they are to maturity, so that they fly away and I can get my scaffolding back?

Having spent much of the last few days playing with the cervical vertebrae of a subadult apatosaur, and trying to make sense of those of the mounted adult, neck ontogeny is much on our minds. Here’s an example from the less charismatic half of Saurischia.

I was forcibly struck, when seeing a cast of Jane the juvenile Tyrannosaurus in the museum gift-shop, by how weedy its neck is:

This being the Carnegie Museum, it was with us the work of a moment to scoot across to the Cretaceous gallery and compare with the neck of an adult, CM 9380:

As you can see, the transformation of the neck is every bit as dramatic as that of the skull, as a slender animal optimised for pursuit grows into a total freakin’ monster.

Someone ought to quantify this. I’m talking to you, theropod workers! (We’ll be busy over here with sauropods.)


Here are the full, uncropped and uncorrected, versions of the photos that I extracted the above from:

This is truly a magnificent museum.

(Matt’s photo, taken in the public gallery of the Carnegie Museum.)

 

Birds have little blobs of tissue sticking out on either side of the spinal cord in the lumbosacral region (solid black arrow in the image above). These are the accessory lobes of Lachi, and they are made up of mechanosensory neurons and glycogen-rich glial cells (but they are not part of the glycogen body, that’s a different thing that lies elsewhere — see this post).

These accessory lobes have been known since at least 1889, when they were first described by Lachi. But the function was mysterious until recently.

Starting in the late 1990s, German anatomist and physiologist Reinhold Necker investigated the development, morphology, and function of the lumbosacral canals of birds. These are not pneumatic spaces, they’re fluid-filled tubes that arch above (dorsal to) the spinal cord in the lumbosacral regions of birds. In a sacral neural canal endocast they look like sets of ears, or perhaps caterpillar legs (below image in the above slide).

Here’s the same slide with the top image labeled, by me.

In our own bodies, the meningeal sac that surrounds the spinal cord is topologically simple, basically a single long bag like a sock with the spinal cord running through the middle. In the lumbosacral regions of birds, the meningeal sac is more like a basket in cross-section, with dorsally-arching loops — the lumbosacral canals — forming the basket handles (lower image in the above slide). Evidently cerebrospinal fluid can slosh through these meningeal loops and push on the accessory lobes of Lachi, whose mechanosensory neurons pick up the displacement. This is essentially the same system that we (and all other vertebrates) have in the semicircular canals in our inner ears, which give us our sense of equilibrium.

Evidence that the lumbosacral canals function as organs of equilibrium comes not only from anatomy but also from the behavior of experimentally-modified birds. If the lumbosacral canals are surgically severed, creating the ‘lesion’ mentioned in the above figure, the affected birds have a much harder time controlling themselves. They can do okay if they are allowed to see, as shown on the left side of the above figure, but if they are blindfolded, they don’t know how to orient themselves and flop around clumsily. Meanwhile, blindfolded birds with their lumbosacral canals intact can balance just fine.

All of this is documented in a series of papers by Necker and colleagues — particularly useful are Necker (1999, 2002, 2005, 2006) and Necker et al. (2000). Necker (2006) seems to be the summation of all of this research. It’s very well-documented, well-reasoned, compelling stuff, and it’s been in the literature for over a decade.

So why is no-one talking about this? When I discovered Necker’s work last spring, I was stunned. This is HUGE. In general, the central nervous systems of vertebrates are pretty conserved, and animals don’t just go around evolving new basic sensory systems willy-nilly. Minimally I would expect congressional hearings about this, broadcast live on C-SPAN, but ideally there would be a talk show and a movie franchise.

I was equally blown away by the fact that I’d never heard about this from inside the world of science and sci-comm. Necker’s discovery seemed to have been almost entirely overlooked in the broader comparative anatomy community. I searched for weaknesses in the evidence or reasoning, and I also searched for people debunking the idea that birds have balance organs in their butts, and in both cases I came up empty-handed (if you know of counter-evidence, please let me know!). It’s relevant to paleontology, too: because the lumbosacral canals occupy transverse recesses in the roof of the sacral neural canal, they should be discoverable in fossil taxa. I’ve never heard of them being identified in a non-avian dinosaur, but then, I’ve never heard of anyone looking. You can also see the lumbosacral canals for yourself, or at least the spaces they occupy, for about three bucks, as I will show in an upcoming post.

Incidentally, I’m pretty sure this system underlies the axiomatic ability of birds to run around with their heads cut off. I grew up on a farm and raised and slaughtered chickens, so I’ve observed this firsthand. A decapitated chicken can get up on its hind legs and run around. It won’t go very far or in a straight line, hence the jokey expression, but it can actually run on flat ground. It hadn’t occurred to me until recently how weird that is. All vertebrates have central pattern generators in their spinal cords that can produce the basic locomotor movements of the trunk and limbs, but if you decapitate most vertebrates the body will just lie there and twitch. The limbs may even make rudimentary running motions, but the decapitated body can’t stand up and successfully walk or run. Central pattern generators aren’t enough, to run you need an organ of balance. A decapitated bird can successfully stand and run around because it still has a balance organ, in its lumbosacral spinal cord.

You may recognize some of the slides that illustrate this post from the Wedel et al. (2018) slide deck on the Snowmass Haplocanthosaurus for the 1st Palaeontological Virtual Congress. Those were stolen in turn from a much longer talk I’ve given on weird nervous system anatomy in dinosaurs, which I am using piecemeal as blog fuel. Stay tuned!

So, birds have balance organs in their butts. We should be talking about this. The comment thread is open.

References

  • Lachi, P. 1889. Alcune particolarita anatomiche del rigonfiamento sacrale nel midollo degli uccelli. Lobi accessori. Att Soc Tosc Sci Nat 10:268–295.
  • Necker, R. 1999. Specializations in the lumbosacral spinal cord of birds: morphological and behavioural evidence for a sense of equilibrium. European Journal of Morphology 37:211–214.
  • Necker, R. 2002. Mechanosensitivity of spinal accessory lobe neurons in the pigeon. Neuroscience Letters 320:53–56.
  • Necker, R. 2005. The structure and development of avian lumbosacral specializations of the vertebral canal and the spinal cord with special reference to a possible function as a sense organ of equilibrium. Anatomy and Embryology 210:59–74.
  • Necker, R. 2006. Specializations in the lumbosacral vertebral canal and spinal cord of birds: evidence of a function as a sense organ which is involved in the control of walking. Journal of Comparative Physiology A, 192(5):439-448.
  • Necker, R, Janßen A, Beissenhirtz, T. 2000. Behavioral evidence of the role of lumbosacral anatomical specializations in pigeons in maintaining balance during terrestrial locomotion. Journal of Comparative Physiology A 186:409–412.
  • Wedel, M.J., Atterholt, J., Macalino, J., Nalley, T., Wisser, G., and Yasmer, J. 2018. Reconstructing an unusual specimen of Haplocanthosaurus using a blend of physical and digital techniques. Abstract book, 1st Palaeontological Virtual Congress, http://palaeovc.uv.es/, p. 158 /  PeerJ Preprints 6:e27431v1

In short, no. I discussed this a bit in the first post of the Clash of the Dinosaurs saga, but it deserves a more thorough unpacking, so we can put this dumb idea to bed once and for all.

As Marco brought up in the comments on the previous post, glycogen bodies are probably to blame for the idea that some dinosaurs had a second brain to run their back ends. The glycogen body is broadly speaking an expansion of the spinal cord, even though it is made up of glial cells rather than neurons — simply put, help-and-support cells, not sensory, motor, or integration cells. When the spinal cord is expanded, the neural canal is expanded to accommodate it; as usual, the nervous system comes first and the skeleton forms around it. This creates a cavity in the sacrum that is detectable in fossils.

avian lumbosacral specializations - glycogen body

Giffin (1991) reviewed all of the evidence surrounding endosacral enlargements in dinosaurs (primarily sauropods and stegosaurs) and concluded that the explanation that best fit the observations was a glycogen body like that of birds. I agree 100%. The endosacral cavities of sauropods and stegosaurs (1) expand dorsally, instead of in some other direction, and (2) expand and contract over just a handful of vertebrae, instead of being more spread out. Of the many weird specializations of the spinal cord in birds, the glycogen body is the only one that produces that specific signal.

If any part of the nervous system of birds and other dinosaurs might be described as a ‘second brain’, it wouldn’t be the glycogen body, it would be the lumbosacral expansion of the spinal cord, which really is made up of neurons that help run the hindlimbs and tail (more on that in this previous post). But there’s nothing special about that, it’s present in all four-limbed vertebrates, including ourselves. Interestingly, that bulk of extra neural tissue in the sacral region of birds was referred to as a sort of ‘second brain’ by Streeter way back in 1904, in reference to the ostrich, but it’s clear that he meant that as an analogy, not that’s it’s literally a second brain.

So to sum up, a gradual expansion of the spinal cord to help run the hindlimbs and tail IS present in dinosaurs — and birds, and cows, and frogs, and us. But if that qualifies as a ‘second brain’, then we also have a ‘third brain’ farther up the spinal cord to run our forelimbs: the cervical enlargement, as shown in the above figure. These spinal expansions aren’t actual brains by any stretch and referring to them as such is confusing and counterproductive.

The sharp expansion of the neural canal over just a few vertebrae in birds does not house a ‘second brain’ or even an expansion of the neural tissue of the spinal cord. It contains the glycogen body, which is not made of neurons and has no brain-like activity. The sacral cavities of non-avian dinosaurs replicate precisely the qualities associated with the glycogen bodies of birds, and there’s no reason to expect that they contained anything else. That we don’t know yet what glycogen bodies do, even in commercially important species like chickens, may make that an unsatisfying answer, but it’s what we have for now.

The next installment will be way weirder. Stay tuned!

References

  • Giffin, E.B.,1991. Endosacral enlargements in dinosaurs. Modern Geology 16: 101-112.
  • Streeter, G.L. 1904. The structure of the spinal cord of the ostrich. American J. Anatomy 3(1): 1-27.

I planned to post this last spring but I never got around to it. I think I have a mental block about discussing the glycogen body. Partly because I’ve been burned by it before, partly because no-one knows what it does and that’s unsatsifying, partly because I didn’t want to plow through all the new literature on it (despite which, the function remains unknown).

Then I decided, screw it, I’ll let the slides speak for themselves, and the actual text of the post can just be navel-gazing and whingeing. Which you are “enjoying” right now.

So, there’s the glycogen body. It balloons out between the dorsal halves of the spinal cord, it’s made of glial cells (neuron support cells) that are packed with glycogen, and nobody knows why it’s there. On the graph of easy-to-find and frustrating-to-study it is really pushing the envelope.

Update: the role of the glycogen body in the ‘second brain’ myth is covered in the next post.

Previous entries in the “Bird neural canals are weird” series:

Here are some stubbornly-not-updated references for the images I used in the slides:

  • Huber, J.F. 1936. Nerve roots and nuclear groups in the spinal cord of the pigeon. Journal of Comparative Neurology 65(1): 43-91.
  • Streeter, G.L. 1904. The structure of the spinal cord of the ostrich. American Journal of Anatomy 3(1):1-27.
  • Watterson, R.L. 1949. Development of the glycogen body of the chick spinal cord. I. Normal morphogenesis, vasculogenesis and anatomical relationships. Journal of Morphology 85(2): 337-389.