If you followed along with the last post in this series, you now have some bird vertebrae to play with. Here are some things to do with them.

1. Learn the parts of the vertebrae, and compare them with those of other animals

Why are we so excited about bird vertebrae around here? Mostly because birds are reasonably long-necked living dinosaurs, and although their vertebrae differ from those of sauropods in relative proportions, all of the same bits are present in roughly the same places. If you know the parts of a bird vertebra and what each one does, you have a solid foundation for inferring the functions of sauropod vertebrae. Here’s a diagram I made for my SVP poster with Kent Sanders way back in 1999. I used an ostrich vertebra here but you should be able to find the same features in a cervical vertebra of just about any bird.

These are both middle cervical vertebrae in right lateral view. A middle cervical vertebra of a big ostrich will be between 3 and 4 inches long (7.5-10 cm), and one from a big brachiosaur like Giraffatitan will be about ten times longer.

I should do a whole post on neck muscles, but for now see this post and this paper.

2. Put the vertebrae in order, and rearticulate them

It is often useful to know where you are in the neck, and the only way to figure that out is to determine the serial position of the vertebrae. Here’s an articulated cervical series of a turkey in left lateral view, from Harvey et al. (1968: pl. 65):

Harvey’s “dorsal spine” is the neural spine or spinous process, and his “ventral spine” is the carotid process. The “alar process” is a sort of bridge of bone connecting the pre- and postzygapophyses; you can see a complete version in C3 in the photo below, and a partial version in C4.

Speaking of that photo, here’s my best attempt at rearticulating the vertebrae from the smoked turkey neck I showed in the previous post, with all of the vertebrae in left dorsolateral view.

These things don’t come with labels and it can take a bit of trial and error to get them all correctly in line. C2 is easy, with its odd articular surface for the atlas and narrow centrum with a ventral keel. Past that, C3 and C4 are usually pretty blocky, the mid-cervicals are long and lean, and then the posterior cervicals really bulk out. Because this neck section had been cut before I got it, some of the vertebrae look a little weird. Somehow I’m missing the front half of C6. The back half of C14 is also gone, presumably still stuck to the bird it went with, and C7 and C12 are both sectioned (this will come in handy later). I’m not 100% certain that I have C9 and C10 in the right order. One handy rule: although the length and neural spine height change in different ways along the column, the vertebrae almost always get wider monotonically from front to back.

And here’s the duck cervical series, in right lateral view. You can see that although the specific form of each vertebra is different from the equivalent vert in a turkey, the same general rules apply regarding change along the column.

Pro tip: I said above that these things don’t come with labels, but you can fix that. Once you have the vertebrae in a satisfactory order, paint a little dot of white-out or gesso on each one, and use a fine-point Sharpie or art pen to write the serial position (bone is porous and the white foundation will keep the ink from possibly making a mess). You may also want to put the vertebrae on a string or a wire to keep them in the correct order, but even so, it’s useful to have the serial position written on each vertebra in case you need to unstring them later.

3. Look at the air spaces

One nice thing about birds is that all of the species that are readily commercially available have pneumatic traces on and in their vertebrae, which are broadly comparable to the pneumatic vertebrae of sauropods.

The dorsal vertebrae of birds are even more obviously similar to those of sauropods than are the cervicals. These dorsal vertebrae of a duck (in left lateral view) show a nice variety of pneumatic features: lateral fossae on the centrum (what in sauropods used to be called “pleurocoels”), both with and without foramina, and complexes of fossae and foramina on the neural arches. Several of the vertebrae have small foramina on the centra that I assume are neurovascular. One of the challenges in working with the skeletal material of small birds is that it becomes very difficult to distinguish small pneumatic foramina and spaces from vascular traces. Although these duck vertebrae have small foramina inside some of the lateral fossae, the centra are mostly filled with trabecular, marrow-filled bone. In this, they are pretty similar to the dorsal vertebrae of Haplocanthosaurus, which have fossae on the neural arches and the upper parts of the centra, but for which the ventral half of each centrum is a brick of non-pneumatic bone. For more on distinguishing pneumatic and vascular traces in vertebrae, see O’Connor (2006) and Wedel (2007).

This turkey cervical, in left posterolateral view, shows some pneumatic features to nice advantage. The lateral pneumatic foramina in bird cervicals are often tucked up inside the cervical rib loops where they can be hard to see and even harder to photograph, but this one is out in the open. Also, the cervicals of this particular turkey have a lot of foramina inside the neural canal. In life these foramina are associated with the supramedullary diverticula, a set of air-filled tubes that occupy part of the neural canal in many birds — see Atterholt and Wedel (2018) for more on this unusual anatomical system. The development of foramina inside the neural canal seems to be pretty variable among individuals. In ostriches I’ve seen individuals in which almost every cervical has foramina inside the canal, and many others with no foramina. For turkeys it’s even more lopsided in my experience; this is the first turkey in which I’ve found really clear pneumatic foramina inside the neural canals. This illustrates one of the most important aspects of pneumaticity: pneumatic foramina and cavities in bones show that air-filled diverticula were present, but the absence of those holes and spaces does not mean that diverticula were absent. Mike and I coined the term “cryptic diverticula” for those that leave no diagnostic traces on the skeleton — for more on that, see the discussion section in Wedel and Taylor (2013b).

Finally, it’s worth taking a look at the air spaces inside the vertebrae. Here’s a view into C12 of the turkey cervical series shown above. The saw cut that sectioned this neck happened to go through the front end of this vertebra, and with a little clean-up the honeycomb of internal spaces is beautifully displayed. If you are working with an intact vertebra, the easiest way to see this for yourself is to get some sandpaper and sand off the front end of the vertebra. It only takes a few minutes and you’ll be less likely to damage the vertebrae or your fingers than if you cut the vertebra with a saw. Similar complexes of small pneumatic cavities are present in the vertebrae of some derived diplodocoids, like Barosaurus (see the lateral view in the middle of this figure), and in most titanosauriforms (for example).

I have one more thing for you to look for in your bird vertebrae, and that will be the subject of the next installment in this series. Stay tuned!

References

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When I started working on sauropods, I thought their vertebrae were cool but they were loaded with weird structures that I didn’t understand. Then I dissected my first ostrich neck and suddenly everything made sense: this was a muscle attachment, that was a pneumatic feature, this other thing was a ligament scar. Everyone who is interested enough to read this blog should give themselves the same “Aha!” moment. You don’t even have to eat the birds yourselves, lots of people don’t like bird necks and will give them away if you ask.

If you get a whole bird, the neck is usually included with the giblets. Around Thanksgiving and Christmas you can often find bundles of spare turkey necks at your grocer or butcher.

This spring I picked up some smoked turkey necks at the grocery store. I wanted to make turkey stew and I figured I might as well get some toys in the bargain. Here are some neck segments in the crock pot.

And here they are after a few hours of cooking. Time to separate the meat from the bones. That neck segment in the middle of the above photo is a pretty good match for the ostrich neck cross-section in this post.

Here are parts of three vertebrae with the long, multi-segment muscles removed, but with the shorter single-segment muscles still connecting them. Anterior is to the right; that’s a cervical ribs sticking out at the lower right “corner”.

Here’s a single intact cervical in left lateral view with most of the meat off, but ready for a long simmer to loosen the remaining crud. This is roughly the same orientation as the lateral view of Mike’s famous turkey cervical.

Meat goes back in the pot.

Bones go on to the next stage: simmering. One of the nice things about the stepwise process of cleaning bones is that you can stop at any point, put the bones in the freezer, and come back days or months later. This bowl of bones went into the freezer in exactly the state you see here, and I didn’t pull them out and finish cleaning them until last week.

If you have a pot-sized strainer, it makes things easier, especially for rinsing. These aren’t turkey vertebrae, these are the verts from my Thanksgiving ducks. But the principle and the process are the same.

After simmering for an hour or two, it’s time to pick off the loosened muscles, ligaments, cartilage, and so on. Here are two similar turkey cervicals after simmering, in dorsal view with anterior to the right. The one on the left has not been cleaned and has all kinds of crud stuck to it, including a big chunk of intervertebral ligament sticking out between the rami of the postzygapophyses. The one on the right has been through a first-pass cleaning.

What tools should you use? Whatever you have to hand. I like old toothbrushes for scrubbing off little bits of muscle and tendon, toothpicks for shoving spinal cord bits through the neural canal and for picking bits of meat out of hard-to-reach places, and the Mark 1 thumbnail for planing off articular cartilage, as shown here with the back end of a duck cervical.

Here’s the outcome of a cleaning session: on the left, the bowl I used for cleaning the vertebrae. In the top middle, the pile of gloop I pulled off. And on the right, a bowl of cleaned turkey and duck vertebrae, ready for degreasing.

Here are the vertebrae of a couple of ducks after soaking overnight in 3% hydrogen peroxide, the ordinary stuff you get at the drugstore or dollar store.

Here’s another bowl with turkey vertebrae. They were all at the bottom of the bowl when I went to bed, floating when I got up the next morning. This is pretty common with lightweight pneumatic vertebrae: the oxygen bubbling out of the hydrogen peroxide has gotten trapped in the internal air spaces and made the vertebrae buoyant.

After a night in the hydrogen peroxide, it’s time to rinse and dry the vertebrae. I put this mixed lot of turkey and duck verts on a plate with a paper towel and left them out on the kitchen counter. In the summertime, when it’s hot and dry, I might put them outside for a bit and they’d be dry in a couple of hours. Indoors in the winter it can take a couple of days for the vertebrae to get completely dry.

Here’s the same batch of vertebrae a couple of days later, clean and dry and ready for whatever comes next.

Which bird should you use? Bigger birds have vertebrae that are easier to clean, harder to damage, and more fun to look at, but use whatever you can get your hands on. This photo shows the axis, a middle cervical, and a posterior cervical from the turkey (top) and duck (bottom). Note that the duck was so young that the cervical ribs hadn’t fused and they fell off during the cleaning process.

If you’ve been following along, you have some nice clean bird vertebrae to play with. So what now — what should you do with them? That will the subject of an upcoming post. Stay tuned!

The 1st Palaeontological Virtual Congress is underway now, and will run through December 15. Mike and I have two presentations up:

“What do we mean by the directions ‘cranial’ and ‘caudal’ on a vertebra?” by Mike and me, which consists of a video Mike made presenting a slide show that he put together. The presentation sums up our thinking following the series of vertebral orientation posts here earlier this summer and fall, which are all available here.

“Reconstructing an unusual specimen of Haplocanthosaurus using a blend of physical and digital techniques” by me and a gang of WesternU-based collaborators, including Jessie Atterholt and Thierra Nalley, both of whom you saw in our recent pig-hemisecting adventures. Almost everything I’ve written on this blog about Haplocanthosaurus in 2018 was part of the run-up to this presentation (except, somewhat ironically, the post about pneumaticity), which also includes quite a bit that I haven’t put on the blog yet. So even if you follow SV-POW!, the 1PVC slideshow should have plenty of stuff you haven’t seen yet.

IF you can see it–you have to be a registered 1PVC ‘attendee’ to log in to the site and see the presentations. So probably you are either already registered and this post is old news, or not registered and this post seems useless. Why would I bother telling you about stuff you can’t see?

The answer is that neither Mike or I intend for our work to disappear when 1PVC comes to an end on December 15. Both of us are planning to put our abstracts and slide decks up as PeerJ Preprints, which is our default move for conference presentations these days (e.g., this, this, and this). I believe Mike is also going to post his video to YouTube. So the work will not only live on after the congress is over, it will jump to a much broader audience. We’re looking forward to letting everyone see what we’ve been up to, and I’m sure we’ll have some more things to say here when that happens.

So, er, go see our stuff if you’re a 1PVC attendee, and if you’re not, hang in there, we’ll have that stuff out to you in a few days. UPDATE: The Haplo presentation is up now (link).

We’ve posted a lot here about how crazy the cervical vertebrae of apatosaurines are (for example: 1, 2, 3), and especially the redonkulosity of their cervical ribs. But I think you will agree with me that this is still an arresting sight:

That’s MWC 1946, a mid-cervical from the Mygatt-Moore Quarry that was figured by Foster et al. (2018: fig. 18 A-B) and referred with the rest of the Mygatt-Moore apatosaur material to Apatosaurus cf. louisae (entirely correctly, in my view). This is a ventral view, with the condyle down by the scale bar.

Here’s the same thing cropped from the background to emphasize its unbelievableness:

and mirrored and restored a bit in GIMP to give a taste of its probable appearance in life (if you had an apatosaur, an x-ray machine, and a lot of confidence about not getting stepped on):

For obvious reasons, my nickname for this specimen is the Brontosmasher.

Keep in mind that the centrum was full of air in life, whereas the cervical ribs and the bony struts that support them are just huge slabs of bone. I strongly suspect that the volume of bone in the cervical ribs and their supporting struts is vastly more than in the centrum and neural arch. I will soon have the ability to test that hypothesis–I have this specimen on loan from Dinosaur Journey for CT scanning and 3D modeling. Watch this space.

Many thanks to Julia McHugh at Dinosaur Journey for access to the specimen and assistance during my frequent visits.

Reference

  • Foster, J.R., Hunt-Foster, R.K., Gorman, M.A., II, Trujillo, K.C., Suarez, C.A., McHugh, J.B., Peterson, J.E., Warnock, J.P., and Schoenstein, H.E. 2018. Paleontology, taphonomy, and sedimentology of the Mygatt-Moore Quarry, a large dinosaur bonebed in the Morrison Formation, western Colorado—implications for Upper Jurassic dinosaur preservation modes: Geology of the Intermountain West 5: 23–93.

What it says on the tin. This is a specimen from the UCMP comparative collection.

I was just going to post this photo with zero commentary, but I can’t help myself. Note that on the two vertebrae in the middle, the crista transverso-obliqua (what in non-avian dinos would be the spinopostzygapophyseal lamina or SPOL) rises higher than either the neural spine apex or the epipophyses. That’s crazy. And it demonstrates something we also see in sauropods, which is that laminae are not merely the plates of bone left behind after pneumatization has scooped all of the unnecessary material out of a normal vertebra–sometimes they are additive structures, too.

If all of that sounded like gibberish, I can sympathize. I spent my first few months as a sauropodologist just learning the lingo (another thing I should blog about sometimes). Here’s a labeled version:

As long as I’m yapping, note the light shining through the honeycombed internal structure of these highly pneumatic vertebrae. For more on the ridiculous pneumaticity of pelican bones, see this post and this one. For more on the homology of bird and sauropod vertebrae, see Wedel and Sanders (2002), and for more on laminae as additive versus reductive structures, see the discussion on pages 210-212 of Wedel (2007).

References

 

The more I look at the problem of how flexible sauropod necks were, the more I think we’re going to struggle to ever know their range of motion It’s just too dependent on soft tissue that doesn’t fossilise. Consider for example the difference between horse necks (above) and camel necks (below).

The skeletons of both consist of vertebrae that are pronouncedly opisthocoelous (convex in front and concave behind), so you might think their necks would be similarly flexible.

But the balls of horse cevicals are deeply embedded in their corresponding sockets, while those of camels have so much cartilage around and between them that the tip of the ball doesn’t even reach the rim of the socket. As a result of this (and maybe other factors), camel necks are far more flexible than those of horses.

Which do sauropod necks resemble? We don’t currently know, and we may never know. It will help if someone gets a good handle on osteological correlates of intervertebral cartilage.

 


[This post is recycled and expanded from a comment that I left on a Tetrapod Zoology post, but since Tet Zoo ate that comment it’s just as well I kept a copy.]

Here’s the story of my fascination with supramedullary airways over the last 20 years, and how Jessie Atterholt and I ended up working on them together, culminating with her talk at SVPCA last week. (Just here for the preprint link? Here you go.)

Müller (1908: fig. 12). Upper respiratory tract, trachea, and lungs in pink, air sacs and diverticula in blue. DSPM = diverticulum supramedullare.

Way back when I was working on my Master’s thesis at the University of Oklahoma and getting into pneumaticity for the first time, Kent Sanders found Müller (1908) and gave me a photocopy. This would have been the spring or summer of 1998, because we used some of Müller’s illustrations in our poster for SVP that year (Wedel and Sanders 1998). Müller’s description of pneumatic diverticula in the pigeon formed part of my intellectual bedrock, and I’ve referenced it a lot in my pneumaticity papers (complete list here).

One of the systems that Müller described is the diverticulum supramedullare, a.k.a. supramedullary diverticula, or, informally, supramedullary airways (SMAs). Traditionally these are defined as pneumatic diverticula that enter the neural canal and lie dorsal (supra) to the spinal cord (medulla), although O’Connor (2006) noted that in some cases the diverticula could completely envelop the spinal cord in a tube of air. I yapped about SMAs a bit in this post, and they’re flagged in almost every ostrich CT or dissection photo I’ve ever published, here on the blog or in a paper.

CT sections of a Giraffatitan cervical, with connections between the neural canal and pneumatic chambers in the spine highlighted in blue. Modified from Schwarz & Fritsch (2004: fig. 4).

Fast forward to 2006, when Daniela Schwarz and Guido Fritsch documented pneumatic foramina in the roof of the neural canal in cervical vertebrae of Giraffatitan. As far as I know, this was the first published demonstration of SMAs in a non-bird, or in any extinct animal. Lemme repeat that: Daniela Schwarz found these first!

OMNH 60718: too ugly for radio. This is an unfused neural arch in ventral view. Anterior is to the left. Neurocentral joint surfaces are drawn over with ladders; pneumatic foramina lie between them.

Shortly thereafter I independently found evidence of SMAs in a sauropod, in the form of multiple pneumatic foramina in the roof of the neural canal in an unfused neural arch of a basal titanosauriform (probably a brachiosaurid) from the Cloverly Formation of Montana. It’s a pretty roadkilled specimen and I was busy with other things so I didn’t get around to writing it up, but I didn’t forget about it, either (I rarely forget about stuff like this).

Then in 2013 I went to the Perot Museum in Dallas to see the giant Alamosaurus cervical series, and I also visited the off-site research facility where juvenile Alamosaurus from Big Bend is housed. When Ron Tykoski let me into the collections room, I was literally walking through the door for the first time when I exclaimed, “Holy crap!” I had spotted an unfused neural arch of a juvenile Alamosaurus on a shelf across the room, with complex pneumatic sculpting all over the roof of the neural canal.

Title slide for the 2014 SVPCA presentation.

The Big Bend and Cloverly specimens were the basis for my talk on SMAs at SVPCA in 2014, coauthored with Anthony Fiorillo, Des Maxwell, and Ron Tykoski. As prep for that talk, I visited the ornithology collections at the Natural History Museum of Los Angeles County, photographed a lot of bird vertebrae with foramina inside their neural canals, and shot this pelican video. That was four years ago – why no paper yet? It’s because I wanted one more piece of smoking-gun evidence: a CT scan of a bird that would show a direct communication between the SMAs and the air spaces inside a vertebra, through one or more foramina in the roof, wall, or floor of the neural canal.

A spectrum of pneumatic traces in the neural canals of birds, including complexes of large or small foramina, isolated foramina, and sculpting without foramina.

In 2017, Jessie Atterholt taught in our summer anatomy course at WesternU as an adjunct (her full-time employment was at the Webb Schools in Claremont, home of the Alf Museum). Jessie and I had been acquainted for a few years, but we’d never had the opportunity to really talk science. As we chatted between dissections, I learned that she had a huge warchest of CT scans of whole birds from her dissertation work at Berkeley (we’d missed each other by a few years). My antennae twitched: one nice thing about SMAs is that, being bounded by bone, they can’t collapse after death, unlike more peripheral diverticula. And air is jet black on CT scans, so SMAs are easy to spot even on comparatively low-res scans. All you need is one or two black pixels. I proposed a collaboration: we could use her CT scans to survey the presence and distribution of SMAs in as many birds as possible.

Vertebral diverticula in two sagittally-exploded cervical vertebrae of a turkey. Anterior is to the left, #5 is the SMA. Cover (1953: fig. 2). Yes, I know this is gross – if anyone has a cleaner scan, I’m interested.

You might think that such a survey would have been done ages ago, but it’s not the case. A few authors have mentioned supramedullary airways, and O’Connor (2006) gave a good description of some of the variation in SMAs in extant birds as a whole. But the only detailed accounts to illustrate the morphology and extent of the SMAs in a single species are Müller (1908) on the common pigeon and Cover (1953) on the domestic turkey. I’d seen what I suspected were traces of SMAs in the vertebrae of many, mostly large-bodied birds, and I’d seen them in CTs of ostriches and hummingbirds, and in ostriches and turkeys in dissection. But Jessie was offering the chance to see both the SMAs and their osteological traces in dozens of species from across the avian tree.

SMAs in a micro-CT of a female Anna’s hummingbird, Calypte anna. Scale bars are in mm.

Real life intervened: we were both so busy teaching last fall that we didn’t get rolling until just before the holidays. But the project gradually built up steam over the course of 2018. One story that will require more unpacking later: everything I’ve written on this blog about neural canals, Haplocanthosaurus, or CT scanning in 2018 is something serendipitously spun out of the SMA survey with Jessie. Expect a lot more Atterholt and Wedel joints in the near future – and one Atterholt et al. (minus Wedel) even sooner, that is going to be big news. Watch this space.

It didn’t hurt that in the meantime Jessie got a tenure-track job teaching human anatomy at WesternU, to run the same course she’d taught in as an adjunct last year, and started here at the beginning of June. By that time we had an abstract on our findings ready to go for this year’s SVP meeting. Alas, it was not to be: we were out in the field this summer when we learned that our abstract had been rejected. (I have no idea why; we’ve increased the taxonomic sampling of SMAs in extant birds by a factor of six or so, most of our important findings are in the abstract, and we mentioned the relevance to fossils. But whatever.)

We were bummed for a day, and then Jessie decided that she’d submit the abstract to SVPCA, only slightly chopped for length, and go to Manchester to present if it was accepted – which it was. Unfortunately I’d already made other plans for the fall, so I missed the fun. Fortunately the SVPCA talks were livestreamed, so last Friday at 1:30 in the morning I got to watch Jessie give the talk. I wish the talks had been recorded, because she knocked it out of the park.

Title slide for the 2018 SVPCA presentation.

And now everything we’re in a position to share is freely available at PeerJ. The SVPCA abstract is up as a PeerJ preprint (Atterholt and Wedel 2018), the longer, rejected SVP abstract is up as a supplementary file (because it has a crucial paragraph of results we had to cut to make the length requirement for SVPCA, and because why not), and our slideshow is up now, too. I say ‘our’ slideshow but it’s really Jessie’s – she built it and delivered it with minimal input from me, while I held down the sauropod side of our expanding empire of neural canal projects. She has the paper mostly written, too.

Oh, and we did get the smoking-gun images I wanted, of SMAs communicating with pneumatic spaces in the vertebrae via foramina in the neural canal. Often these foramina go up into the neural arch and spine, but in some cases – notably in pelicans and the occasional ratite – they go down into the centrum. So I now have no excuse for not getting back to the sauropod SMA paper (among many other things).

We’re making this all available because not only are we not afraid of getting scooped, we’re trying to get the word out. SMAs are phylogenetically widespread in birds and we know they were present in sauropods as well, so we should see some evidence of them in theropods and pterosaurs (because reasons). I made such a nuisance of myself at the recent Flugsaurier meeting, talking to everyone who would listen about SMAs, that Dave Hone went and found some pneumatic foramina in the neural canals of Pteranodon vertebrae during the conference – I suspect just to shut me up. That’ll be some kind of Hone-Atterholt-Wedel-and-some-others joint before long, too.

Anyway, point is, SMAs are cool, and you now have everything you need to go find them in more critters. Jessie and I are happy to collaborate if you’re interested – if nothing else, we have the background, lit review, and phylogenetic sampling down tight – but we don’t own SMAs, and we’ll be nothing but thrilled when your own reports start rolling in. Unexplored anatomical territory beckons, people. Let’s do this.

References