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

 

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Please welcome Mirarce eatoni

November 13, 2018

Skeletal reconstruction of Mirarce by Scott Hartman (Atterholt et al. 2018: fig. 19). Recovered bones in white, missing bones in gray. The humerus is 95.9mm long.

Today sees the publication of the monster enantiornithine Mirarce eatoni (“Eaton’s wonderful winged messenger”) from the Kaiparowits Formation of Utah, by Jessie Atterholt, Howard Hutchinson, and Jingmai O’Connor. Not my critter, not my story, but it is SV-POW!-adjacent. (Just here for the paper? Here’s the link.)

Xiphoid process of sternum of Mirarce (Atterholt et al. 2018: fig. 5). Scale bar = 1cm.

As of this past summer, I knew that Jessie had a prehistoric monster coming out soon, and I knew that Brian Engh liked bringing prehistoric monsters to life, and I suspected that if the two reagents were combined, the rest of us might get something cool out of it.

Jessie and Brian talking about Mirarce, Utah for scale. July 13, 2018.

I did some heavy eavesdropping while the three of us were stomping around southern Utah looking for dinosaurs, so I got to hear Jessie and Brian batting ideas back and forth. By the end of our Utah trip Brian had sketches, and not long after, finished art (his post on Mirarce, including process sketches, is here). If you’ve seen one of my talks in the last month or so, you’ve gotten a teaser (with Jessie’s and Brian’s permission), and I know the piece got shown around a bit at SVP, too. You’ve waited long enough, here you go:

Not that the art is the whole story! Mirarce is a legitimately awesome find and Jessie and her coauthors poured a ton of work into the description. I’d tell you all about it, but much more capable and bird-fluent folks are on that already, and I have spinal cord and brainstem lectures to polish. So I’m gonna leave you with some links, which I’ll try to keep updated as different outlets get the story out:

Reference

Atterholt, J., Hutchinson, J.H.., and O’Connor, J.K. 2018. The most complete enantiornithine from North America and a phylogenetic analysis of the Avisauridae. PeerJ 6:e5910 https://doi.org/10.7717/peerj.5910

The Sunday after SVP, Brian Engh and I visited the museum in Albuquerque. I was quite taken with the mounted T. rex. It’s waaaay more interesting and dynamic than any other T. rex mount I’ve seen. It even beats the “Rockette rex” in Denver (which I really like and need to blog about), by virtue of putting the body and head down at eye level where you can study them up close.

The only thing I don’t like about this mount is that it has the dumb teeth-hanging-out-too-far thing going on. Why the heck people don’t fix that, I have no idea. Like, even if that’s the way the jaws are molded, cut off the excess and glue the crowns back up where they belong. Or fix the friggin’ mold. It’s not like the problem hasn’t been obvious for decades.

On the upside, pretty much everything else about this mount is awesome. Brian and I spent a fair amount of time working through the muscle attachments and thinking about how bulky the animal would have been in life. The answer is “very”.

Pretty cool to think that a fleshier, more aggro version of this was the last thing that many animals ever saw. And by ‘cool’ I mean ‘terrifying’.

Diverticulum, diverticula

November 4, 2018

This is not ‘Nam. This is Latin. There are rules.

The term for a small growth off an organ or body is diverticulum, singular, or diverticula, plural. There are no diverticulae or God forbid diverticuli, no matter what you might read in some papers. Diverticuli is a word – it’s the genitive form of diverticulum. But I’ve never seen it used that way in an anatomy or paleo paper. Diverticuli and diverticulae as alt-plurals for diverticulum are abominations that must be stomped out with extreme prejudice. If you want to get cute with alternative spellings, Wiktionary says you can use deverticulum. Wiktionary does not warn you that you will be mocked for doing so, but it is true nonetheless.

Stop jacking up straightforward anatomical terms, authors who should know better.

Here’s a swan. Unlike diverticuli and diverticulae, this unlikely morphology is real.

 

In a comment on the last post, Mike wrote, “perhaps the pneumaticity was intially a size-related feature that merely failed to get unevolved when rebbachisaurs became smaller”.

Caudal pneumaticity in saltasaurines. Cerda et al. (2012: fig. 1).

Or maybe pneumaticity got even more extreme as rebbachisaurids got smaller, which apparently happened with saltasaurines  (see Cerda et al. 2012 and this post).

I think there is probably no scale at which pneumaticity isn’t useful. Like, we see a saltasaurine the size of a big horse and think, “Why does it need to be so pneumatic?”, as if it isn’t still one or two orders of magnitude more massive than an ostrich or an eagle, both of which are hyperpneumatic even though only one of them flies. Even parakeets and hummingbirds have postcranial pneumaticity.

Micro CT of a female Anna’s hummingbird. The black tube in the middle of the neck is the supramedullary airway. Little black dots in the tiny cervical centra are air spaces.

We’re coming around to the idea that the proper way to state the dinosaur size question is, “Why are mammals so lousy at being big on land?” Similarly, the proper way to state the pneumaticity question is probably not “Why is small sauropod X so pneumatic?”, but rather “Why aren’t some of the bigger sauropods even more pneumatic?”

Another thought: we tend to think of saltsaurines as being crazy pneumatic because they pneumatized their limb girdles and caudal chevrons (see Zurriaguz et al. 2017). Those pneumatic foramina are pretty subtle – maybe their apparent absence in other sauropod clades is just because we haven’t looked hard enough. Lots of things have turned out to be pneumatic that weren’t at first glance – see Yates et al. (2012) on basal sauropodomorphs and Wedel and Taylor (2013b) on sauropod tails, for example.

Back of the skull of a bighorn sheep, showing the air spaces inside one of the broken horncores.

Or, even more excitingly, if the absence is genuine, maybe that tells us something about sauropod biomechanics after all. Maybe if you’re an apatosaurine or a giant brachiosaurid, you actually can’t afford to pneumatize your coracoid, for example. One of my blind spots is a naive faith that any element can be pneumatized without penalty, which I believe mostly on the strength of the pneumatic horncores of bison and bighorn sheep. But AFAIK sauropod girdle elements don’t have big marrow cavities for pneumaticity to expand into. Pneumatization of sauropod limb girdles might have come at a real biomechanical cost, and therefore might have only been available to fairly small animals. (And yeah, Sander et al. 2014 found a pneumatic cavity in an Alamosaurus pubis, but it’s not a very big cavity.)

As I flagged in the title, this is noodling, not a finding, certainly not certainty. Just an airhead thinking about air. The comment thread is open, come join me.

References

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

Ripple rock. Not from the Morrison, but from the overlying Dakota – Lower Cretaceous.

Now this is from the Morrison. My son, London, spotted this tiny tooth of a Jurassic croc while working in the quarry. That’s my thumb and London’s index finger for scale.

London’s index finger again, pointing at a different Morrison tooth. This one’s from a theropod, still exposed in a sandstone block in one of Stovall’s old quarries from the 1930s.

On a completely different hillside, I spotted this skull, of a modern rodent. Vole, maybe? Not my bailiwick, but if you know who this belongs to, let me know in the comments.

Moonrise – and the end of this post. Catch you in the future.