February 9, 2012
I only became aware of the term Academic Spring the other day but I instantly loved it. The OA wars have heated up significantly in the past few weeks, and Academic Spring crystallizes a lot of what is going on.
Although we always welcome new readers, and no-one who cares about science can afford to be ignorant about access to scholarly publications, we do sometimes feel that at SV-POW! we are mostly preaching to the converted. But access is not just a problem for scientists and academics, it’s a problem for everyone, including physicians, patient groups, engineers, small business owners, students, and, frankly, anydamnbody who wants to inspect the fruits of the research their taxes paid for. So it’s important to get the message out, broadly, to the most people possible, in as many venues as possible, until Joe and Jane Citizen get mad enough about the situation to demand better behavior by their elected representatives and better service from the corporations that allegedly have their interests at heart.
To that end, Mike has a new piece up at The Independent today. Because he couldn’t assume that his readers would be familiar with the OA wars or Academic Spring, he had to lay out the whole case in a limited number of words. I think he did a bang-up job. Because the piece is so self-contained (although it has some choice links that are worth following up), it serves as a front-line report for those of us familiar with the OA wars, and a solid overview for everyone else. Go check it out.
Finally, since you haven’t gotten a lot of sauropod action lately, here are some small Giraffatitan humeri in the basement of the Museum für Naturkunde with Vanessa Graff for scale. You can tell these are small ones because they’re Vanessa-sized or smaller; the big ones are taller than I am…and they’re still from subadults. Must blog sometime about the awesomeness of the basement full o’ sauropods at the MfN, but not today. Excelsior!
December 13, 2011
December 9, 2011
As previously reported, the lot of us are in Bonn for the sauropod biology workshop. Last night we met up at the welcome reception at the Goldfuss Museum. It was the first time for Mike and Darren to meet Vanessa Graff and Paco Gasco in person, and of course we all got to meet people we didn’t know previously who are here for the workshop. There is an outstanding series of talks lined up. Three days with some of the world’s best workers talking about sauropods all the time? Yeah, I reckon we can handle that.
No sauropods in the Goldfuss Museum, so we naturally hung out the biggest saurischian around (even if it is a vulgar, overstudied theropod).
This and any future posts for the next few days will necessarily be brief; gotta go learn about sauropods!
November 18, 2011
- Part 1: introduction
- Part 2: the head
- Part 4: body, tail, limbs, base, and skull
- Part 5: posture
- Part 6: texture and color
- Part 7: verdict
It is probably no surprise, given my proclivities, that I have more to say about the neck than about anything else. So unless I develop an abnormal curiosity about and mastery of, say, sauropod foot anatomy in the next few days, this will be the longest post in the series.
As with the head, the neck of the Apatosaurus maquette illustrates a lot of interesting anatomy. Some of this is unique to Apatosaurus and some of it is characteristic of sauropods in general. I’ll start with the general and move toward the specific.
As we’ve discussed before, the necks of most sauropods were not round in cross section (see here and here). The cervical ribs stuck out far enough ventrolaterally that even with a lot of muscle, the neck would have been fairly flat across the ventral surface, and in many taxa it would have been wider ventrally than dorsally.
The non-circular cross section would have been exaggerated in Apatosaurus, which had simply ridiculous cervical ribs (photo above is from this post). The widely bifurcated neural spines would also have created a broad and probably flattish surface on the dorsal aspect of the neck. The extreme width of the vertebrae and the cervical ribs created a very broad neck base. As in Camarasaurus, the base of the neck was a substantial fraction of the width of the thorax (discussed here). Consequently, the cervico-thoracic junction probably appeared more abrupt in narrow-necked taxa like Diplodocus and Giraffatitan, and more smoothly blended in Apatosaurus and Camarasaurus.
All of these features–the non-circular cross-section, the flattish dorsal and ventral surfaces, the wide neck base blending smoothly into the thorax–are captured in the Apatosaurus maquette.
The ventrolateral ‘corners’ of the neck have a ribbed appearance created by, well, ribs. Cervical ribs, that is, and big ones. In contrast to most other sauropods, which had long, overlapping cervical ribs, diplodocoids had short cervical ribs that did not overlap. But in Apatosaurus they were immense, proportionally larger than in any other sauropod and probably larger than in any other tetrapod. What Apatosaurus was doing with those immense ribs is beyond me. Some people have suggested combat, akin to the necking behavior of giraffes, and although I haven’t seen any evidence to support that hypothesis over others, neither does it strike me as far-fetched (an important nuance: giraffes use their heads as clubs, clearly not an option for the small-headed and fragile-skulled sauropods). Whatever the reason, the cervical ribs of Apatosaurus were amazingly large, and may well have been visible from the outside.
Mounted skeleton of Apatosaurus louisae in the Carnegie Museum, from Wikipedia.
Now this brings me to a something that, although not universal, has at least become fairly common in paleoart. This is the tendency by some artists to render (in 2D, 3D, or virtually) sauropods with dished-in areas along the neck, between the bony loops where the cervical ribs fuse to the centra. I am going to be as diplomatic as I can, since some of the people who have used this style of restoration are good friends of mine. But it’s a fine example of shrink-wrapped dinosaur syndrome, and it simply cannot be correct.
Adjacent cervical ribs loops in sauropods would have been spanned by intertransversarii muscles, as they are in all extant tetrapods. And outside of those single-segment muscles were long belts of flexor colli lateralis and cervicalis ascendens, which are also anchored by the cervical rib loops. All of these muscles are present in birds, and only vary in their degree of development in different parts of the neck and in different taxa. The spaces between adjacent cervical rib loops are not only not dished-in, they actually bulge outward, as in the turkey neck above.
And we’re still not done; running up through the cervical rib loops, underneath all of those muscles, were pneumatic diverticula. Not just any diverticula, but the big lateral diverticula that carried the air up the neck from the cervical air sacs at the base of the neck to the vertebrae near the head end (diverticula are reconstructed here in a cervical vertebra of Brachiosaurus, from Wedel 2005: fig. 7.2). Now, it’s unlikely that the diverticula exerted any outward pressure on the lateral neck muscles, but they were still there, occupying space (except when the muscles bulged inward and impinged on them during contraction), and with the muscles they would have prevented the neck from having visible indentations between the cervical rib loops of adjacent vertebrae.
Okay, so sauropod necks shouldn’t be dished in. But might the cervical ribs have stuck out? It might seem like the same question, only seen from the other side, but it’s not. We’ve established that adjacent cervical rib loops supported bands of single-segment muscles that spanned from one vertebra to the next, and longer, multi-segment muscles that crossed many vertebrae. But could the bony eminences of the cervical ribs have projected outward, through the muscle, and made bumps visible through the skin? The idea has some precedent in the literature; in his 1988 paper on Giraffatitan, Greg Paul (p. 9) argued that,
The intensely pneumatic and very bird-like neck vertebrae of sauropods were much lighter in life than they look as mineralized fossils, and the skulls they supported were small. This suggests that the cervical musculature was also light and rather bird-like, just sufficient to properly operate the head-neck system. The bulge of each neck vertebra was probably visible in life, as is the case in large ground birds, camels, and giraffes.
Paul has illustrated this in various iterations of his Tendaguru Giraffatitan scene; the one below is from The Princeton Field Guide to Dinosaurs (Paul 2010) and is borrowed from the Princeton University Press blog.
There is much to discuss here. First, I have no qualms about being able to see individual vertebrae in the necks of camels and giraffes, and it’s not hard to find photos that show these. It makes sense: these are stinkin’ mammals with the usual seven cervical vertebrae, so the verts have to be longer, proportionally, and bend farther at each joint than in other long-necked animals. I’m more skeptical about the claim that individual vertebrae can be seen in the necks of large ground birds. I’ve dissected the necks of an ostrich, an emu, and a rhea, and it seems to me that the neck muscles are just too thick to allow the individual vertebrae to be picked out. In a flamingo, certainly–see the sharp bends in the cranial half of the neck in the photo below–but flamingos have freakishly skinny necks even for birds, and their cervicals are proportionally much longer, relative to their width, than those of even ostriches.
What about sauropods? As discussed in this post, sauropod cervicals were almost certainly proportionally closer to the surface of the neck than in birds, which would tend to make them more likely to be visible as bulges. However, the long bony rods of the cervical ribs in most sauropods would have kept the ventral profile of the neck fairly smooth. The ossified cervical ribs of sauropods ran in bundles, just like the unossified hypaxial tendons in birds (that’s Vanessa Graff dissecting the neck of Rhea americana below), and whereas the latter are free to bend sharply around the ventral prominences of each vertebra, the former were probably not.
All of which applies to sauropods with long, overlapping cervical ribs, which is most of them. But as mentioned above, diplodocoids had short cervical ribs. Presumably they had long hypaxial tendons that looked very much like the cervical ribs of sauropods but just weren’t ossified. Whether the vertebrae could have bent enough at each segment to create bulges, and whether the overlying muscles were thin enough to allow those bends to be seen, are difficult questions. No-one actually knows how much muscle there was on sauropod necks, not even within a factor of two. There has been no realistic attempt, even, to publish on this. Published works on sauropod neck muscles (Wedel and Sanders 2002, Schwarz et al. 2007) have focused on their topology, not their cross-sectional area or bulk.
But then there’s Apatosaurus (AMNH mount shown here). If any sauropod had a chance of having its cervical vertebrae visible from the outside, surely it was Apatosaurus. And in fact I am not opposed to the idea. The cervical ribs of Apatosaurus are unusual not only in being large and robust, but also in curving dorsally toward their tips. If one accepts that the cervical ribs of sauropods are ossified hypaxial tendons–which seems almost unarguable, given that the cervical ribs in both crocs and birds anchor converging V-shaped wedges of muscle–then the ossified portion of each cervical rib must point back along the direction taken by the unossified portion of the tendon. In which case, the upwardly-curving cervical ribs in Apatosaurus suggest that the muscles inserting on them were doing so at least partially from above. So maybe the most ventrolateral portion of each rib did stick out enough to make an externally visible bulge.
Maybe. Many Apatosaurus cervical ribs also have bony bumps at their ventrolateral margins–the ‘ventrolateral processes’ or VLPs illustrated by Wedel and Sander (2002: fig. 3). If these processes anchored neck muscles, as seems likely, then even the immense cervical ribs of Apatosaurus might have been jacketed in enough muscle to prevent them from showing through on the outside.
Still. It’s Apatosaurus. It’s simply a ridiculous animal–a sauropod among sauropods. If this were a model of Mamenchisaurus and it had visible bulges for the cervical rib loops, I’d be deeply skeptical. For Apatosaurus, it’s at least plausible.
Because the cervical ribs are visible in the maquette as distinct bulges, it’s possible to count the cervical vertebrae. Apatosaurus has 15 cervicals, and that seems about right for the maquette. The neck bumps reveal 11 cervicals, but they don’t run up all the way to the head. This is realistic: the most anterior cervicals anchored muscles that supported and moved the head, and these overlie the segmental muscles and cervical ribs in extant tetrapods. The most anterior part of the neck in the maquette, with no cervical rib bumps, looks about the right length to contain C1-C3. Plus the 11 vertebrae visible from their bumps, that makes 14 cervicals, and the 15th was probably buried in the anterior body wall.
One last thing: because the cervical ribs are huge, the neck of Apatosaurus was fat. To the point that the head looks almost comically tiny, even though it’s about the right size for a sauropod head. I first got a visceral appreciation for this when I was making my own skeletal reconstruction of Apatosaurus, for a project that eventually evaporated into limbo. Once you draw an outline of flesh around the vertebrae, the weirdness of the massive neck of Apatosaurus is thrown into stark relief. Apatosaurus is robust all over, but even on such a massive animal the neck seems anomalous. I don’t know what Apatosaurus was doing with its neck, but it’s hard not to think that it must have been doing something. Anyway, I bring this up because the maquette captures the neck-fatness very well. So much so that when I sit back from the computer and my eyes roam around the office and fall on the maquette, I can’t help thinking, for the thousandth time, “Damn, that’s weird.”
In sum, the neck of the Sideshow Apatosaurus maquette gets the non-circular cross-section right, appears to have the correct number of cervical vertebrae, and looks weirdly fat, which turns out to be just right for Apatosaurus. The bumps for the individual vertebrae are plausible, and the maquette correctly avoids the dished-in, emaciated appearance–cocaine chic for sauropods–that has become popular in recent years. It manages to be eye-catching and even mildly disturbing, even for a jaded sauropodologist like yours truly, in that it confronts me with the essential weirdness of sauropods in general, and of Apatosaurus in particular. These are all very good things.
Next time: as much of the rest of the body as I can fit into one post (all of it, it turned out).
- Paul, G.S. 1988. The brachiosaur giants of the Morrison and Tendaguru with a description of a new subgenus, Giraffatitan, and a comparison of the world’s largest dinosaurs. Hunteria 2(3):1-14.
- Paul, G.S. 2010. The Princeton Field Guide to Dinosaurs. Princeton University Press, 320 pp.
- Schwarz, D., Frey, E., and Meyer, C.A. 2007. Pneumaticity and soft−tissue reconstructions in the neck of diplodocid anddicraeosaurid sauropods. Acta Palaeontologica Polonica 52(1):167–188.
- Wedel, M.J. 2005. Postcranial skeletal pneumaticity in sauropods and its implications for mass estimates; pp. 201-228 in Wilson, J.A., and Curry-Rogers, K. (eds.), The Sauropods: Evolution and Paleobiology. University of California Press, Berkeley.
- Wedel, M.J., and Sanders, R.K. 2002. Osteological correlates of cervical musculature in Aves and Sauropoda (Dinosauria: Saurischia), with comments on the cervical ribs of Apatosaurus. PaleoBios 22(3):1-6.
November 7, 2011
This is the second post on the Wedel lab’s recently acquired skull of Ursus americanus, the American black bear. The first installment covered ended with the disinterred-but-still-filthy skull bits sitting on my dining room table. This post covers putting the teeth back in, and just enough anatomy to justify putting up more cool pictures.
About five minutes after I took the last picture from the last post, I put the cranium and mandible to soak in warm, soapy water and spent the rest of the day doing other things. Last night I got a couple of old toothbrushes and scrubbed off most of the dirt from the external surfaces of the skull. I alternated toothbrush work with running water from the bathtub faucet over and through the skull bits. I also used one of the rubber nasal aspirator bulbs (or “snot suckers”, as new parents in the real world invariably call them)–which make tremendous water guns–to sluice out some of the grimier cavities. It was fun to force water into the mandibular foramen and see it come shooting out the mental foramen, along the canal traveled by the inferior alveolar nerve and vessels.
All of the teeth were loose in their sockets, and the incisors and upper canines were either falling out or could be pulled out without too much trouble. I yanked all of the teeth that I could, figuring that it was better to yank-and-glue rather than leaving them loose. I set the loose teeth on separate plates, one upper, one lower, arranged in the same order they were in the alveoli, and let everything air dry overnight.
Shown above is my setup for replacing the teeth:
- a trash bag for protecting the table
- a dish towel to provide a soft surface
- the bear skull pieces
- loose teeth on their respective plates
- five minute epoxy
- toothpicks for mixing and spreading the epoxy
I had been going to use something less hardcore for the gluing, but fortunately Vicki got home and I was able to draw on her experience from reconstructing loads of human skulls from archaeological and forensic sites. She said just go with epoxy, and so I went.
Here we are about halfway through the process. A few tips, some obvious, some maybe less so:
- Even if you’ve done a perfect job of keeping the teeth in order, test-fit them anyway. If nothing else, this will give you a visceral sense of what the tooth feels like sliding into the socket, and it will help you figure out how much glue to apply. Also, test fit adjacent teeth together so you’ll know if they have to go back in in a particular order; sometimes one tooth is at a subtle angle and blocks the next tooth from coming out or going back in.
- Better to put the glue in the socket than on the tooth. The roots are not much smaller in diameter than the alveoli and the crowns stand out a bit from the bone (although the ‘exposed’ roots would have been covered with gums in life). If you put the glue on the tooth you’re liable to either have it bulldozed off by the alveolar rim as you slide the tooth into the socket, or you’ll put too much on and have a bunch of worthless glue on the exposed portion of the root.
- If the teeth are worn, like the incisors are here, it’s nice to do a bunch at once so you can get all of the wear surfaces lined up as they were in life. Better than having one tooth set up completely and then realizing it was all the way forward/back/in/out and the other teeth can’t match its orientation.
Everything back in. There are a couple of incisors still AWOL, and a few premolars, but the dentition is still reasonably complete (remember that I am used to working on Early Cretaceous North American sauropods, so a little completeness goes a long way). I ran a thin bead of epoxy around the bases of all of the teeth that had not come out of the alveoli, to hopefully rein in any future wanderlust on their parts.
Sweet action. I wish I had something more intellectual to say here, but I really don’t.
Nasal turbinates. Holy crap, were these a pain to get clean. I didn’t get them completely clean, there’s probably enough dirt up in there to germinate something. But I asymptotically approached the point where removing more dirt would have meant damaging the turbinates, which are at least manilla-envelope-thin if not laser-printer-paper-thin.
A closeup of the infraorbital foramen on the right, which transmitted the infraorbital artery and vessels in life. The neurovascular tracks on the external surface of the bone are pretty sweet; you can see them on the left side, in context, two photos up.
In addition to closing our jaws in a hinge-like motion, we can slide them fore and aft and also from side to side. Those kinds of motions are fine when you’ve got comparatively weak jaws like ours, and we still occasionally get into trouble–jawbreakers are so named for a reason. But those non-hinge-like motions would be disastrous for something that can close its jaws with several hundred pounds of force. So most big carnivores have wide, almost cylindrical jaw joints that constrain the motion to being almost purely hinge-like. In mustelids (weasels and kin), which have the strongest bites for their sizes of any mammals, the condyle is so cylindrical and the fossa so deeply enclosing (imagine a Q sitting inside a very slightly larger C–that’s the jaw joint seen from the side) that sometimes you simply can’t get the jaws to disarticulate after death. This ain’t quite that extreme, but it’s closer to the mustelid condition than the human. Not surprising, since weasels are united with bears and seals in the clade Arctoidea.
And here’s why bears need those cylindrical jaw joints: check out the muscle attachment scars on the back of the mandible. These are for the temporalis and masseter muscles, the same muscles you can feel bulging out on the side of your head and the corners of your jaw when you bite down forcefully or grit your teeth. IIRC, the maximum bite force a human can exert is around 180 pounds, and lions can do something like 900 pounds. Not sure where Ursus americanus falls, but definitely on the please-don’t-bite-me end of the scale.
And here’s why those muscle attachment scars are so big. The zygomatic arches are only partly complete here, but you can see how wide is the space between the left arch and the braincase. All of that space–two full inches, mediolaterally–was filled with temporalis muscle that provided most of the power for jaw-closing. This is why pit bulls have such wide, flat-looking heads: they have normal-sized dog brains and huge, thick jaw muscles. See also: my hyena dissection photos.
Looking very dog-like here in anterior view. There are some butchery marks on the skull, most noticeably across the external nares here, and along the mandibles. Not sure what that’s all about, since I can’t reconcile the stated backstory–cop shoots dangerous bear, buries head in backyard–with a need to make repeated cuts across the snout and jaws. And no, they’re not shovel marks. I knew that already, and Vicki confirmed that the marks are peri-mortem (around the time of death, but impossible to confirm as pre- or post-mortem). Anyway, I’m not complaining. Despite the damage, the skull is still an awesome thing, and the cut marks add a touch of mystery. I’ll post more pictures when I get the left temporal region glued back on.
November 6, 2011
After three months as a paleontology grad student, this morning Vanessa I. Graff got to sink a shovel in the service of science. Now, it was a bear skull, deliberately buried in someone’s back yard, so technically today’s exploits fall under the heading of contemporary zooarcheology rather than paleontology, but we’ll take what we can get.
This story has a backstory. The guy on the right here is Hossein Aziz, one of my advisees among the DO students at Western. His landlady’s ex-husband is in law enforcement, and about a year and a half ago he had to shoot a bear that had become a threat to humans. He buried the head in the backyard and separated from his then wife. She found out from Hossein that one of his professors was a paleontologist and offered to donate the skull to science, if only we’d come dig it up. So we did. Involved in the excavation (right to left in the above photo) were Hossein, his girlfriend Lia, my son London, Vanessa, and yours truly.
Additional note: Hossein’s landlady is a British expatriate, and she served us proper English tea. It was the most civilized dig I have been on, which, admittedly, is sort of like being the least worthless Kardashian. Anyway, the tea was great, and we all had a good time.
My wife, Dr. Vicki Wedel, was out of town, but she lent us her archaeological toolkit, so we had nice trowels and kneepads and such. Here Hossein is pretending to advise Vanessa and London on what they should be doing, which is funny because that’s usually my job (pretending, that is).
After about half an hour of digging, we found intact vertebrate remains! And there was much rejoicing.
First out of the ground was the mandible, which is in essentially perfect shape.
Ursus americanus mandible and lower dentition, Homo goofballensis for comparison and scale.
Lia and London clearing dirt from around the cranium, which looks disturbingly hominoid from this angle.
There really aren’t any words for what’s going on here. Just bask a moment in the glory and move on.
We were going for American Gothic here, but Vanessa blew it by smiling. Standard.
Lia and Hossein marveling at what is, after all, a pretty badass critter. Even a small bear has seriously impressive teeth, which you hope to never find embedded in your flesh.
Still, it can be fun to pretend otherwise.
Here’s what we have. The occipital region is just gone. The left temporal region is more intact and has a long crack leading away across the frontals. On the right, everything from the zygomatic process of the maxilla to the occiput is just gone. So I reckon the rifle bullet went in on the left and blew out an exit wound the size of an orange on the right side of the bear’s head.
After a good rinse in the tub, all the bits are now soaking in soapy water. I’ll post more pictures when I get it all cleaned up and presentable. In the meantime, many thanks to Hossein’s landlady for the skull, the tea, and her amused tolerance at having a bunch of dirty people digging in her yard, and to Hossein, Lia, Vanessa, and London for their work. It was a pretty darned good way to start the weekend.
October 31, 2011
October 6, 2011
Vanessa Graff and I spent yesterday working in the herpetology and ornithology collections at the Natural History Museum of Los Angeles County (LACM). The herpetology collections manager, Neftali Comacho, pointed us to this skull of Alligator mississippiensis. It’s not world’s biggest gator–about which more in a second–but it’s the biggest I’ve seen in person. Normally it lives in a big rubbermaid tub in the collections area, but this Sunday it will be out on display for Reptile and Amphibian Appreciation Day (RAAD) at the LACM. RAAD will include guest talks, tours of the collections, and live animal demonstrations. If you’re in SoCal and you’re into herps–or have kids, grandkids, nephews or nieces that are into herps–it will be well worth checking out. While you’re there, don’t neglect the newly renovated Age of Dinosaurs and Age of Mammals halls, which are frankly phenomenal: spacious, well-lit, loads of actual material on display, skeletons you can walk all the way around, informative but unobtrusive signage, tasteful integration with existing architecture…I could go on. Better if you just go and see for yourself.
About that gator. First the bad news. It came to the LACM from another collection, and has no data–no locality, no date collected, nothing. The skull is also missing all of its teeth, the left retroarticular process, the back end of the braincase and the occipital condyle. I think the latter losses were probably caused by a foramen of Winchester.*
Now, the awesome news. The length from the snout tip to the end of the articulars was 680mm and from the snout to the end of the quadrates was 590mm. Irritatingly I did not get a dorsal head length, which is the gold standard for comparative croc skull measurements, because I only reread Darren’s giant croc skull post after I got home last night. Going from the photos, I think the dorsal head length was right around 50 cm (beware, the yardstick in the photos is marked off in inches).
Darren’s post led me to this one, which has some very useful measurements (yay!) of giant croc skulls. The table at the end of that post lists alligator skulls with dorsal head lengths of 58, 60, and 64 cm, so the big LACM gator is nowhere near being the world’s largest. In fact, the 64 cm skull would be a quarter again as large, which is a truly horrifying thought. Still, it’s a big damn skull from a big damn gator.
You might get the impression that here in the Wedel lab we are shamelessly obsessed with giant saurians. And that is in fact true. But we also look at tiny ones, too. Here I’m playing with the skull of a little Tomistoma, the false gharial. Tomistoma is notable because another individual of the genus produced the longest skull of any known extant crocodilian–a whopping 84 cm dorsal head length (photos of this monster are in both of the giant croc skull posts linked above).
The moral of the story? If the sign says don’t go swimming, don’t go swimming. Go to RAAD instead, and see the giant alligator skull, and a ton of other cool stuff besides. And if you’re into gator skulls or just like geeking out on awesome anatomy, check out the 3D Alligator Skull site, a joint project of the Holliday lab and Witmer lab. Have fun!
* bullet hole
August 27, 2011
August 23, 2011
freezer full of interesting dead animals + great anatomy student who actually wants to get up on Saturday morning and dissect = happiness
The rhea has been the gift that keeps on giving. Saturday was my fourth session with some part of this bird, going back to 2006 (previous posts are here, here, and here). The first two sessions were just about reducing the bird to its component parts, and the last session was all about midline structures.
The goal for the neck is to dissect down to the vertebrae and document everything along the way–muscles, tendons, fascia, blood vessels, and especially diverticula. In the past I have been pessimistic about the chances of seeing diverticula without having them injected with latex or resin or something. But this bird is changing my mind, as we saw in a previous post and as you can see below.
The goal for Vanessa is to grok all of this anatomy, and hopefully make some publishable observations along the way. She has a chance to do something that I think is rather rare for a sauropod paleobiologist, which is to get a firm, dissection-based grounding in bird and croc anatomy before she first sets foot in a museum collection to play with sauropod bones.
That sounds awesome, and probably will be awesome, but before there can be any awesomeness, the fascia has to be picked off the neck. And by ‘picked’ I mean ‘actually cut away, millimeter by arduous millimeter’. It wasn’t that bad everywhere–the fascia over the long dorsal muscles came off very easily. But the lateral neck muscles were actually originating, in part, from the inner surface of the fascia. That’s not unheard of, it happens in the human forearm and leg all the time, but I’ve never seen it as consistently as in this rhea. So picking fascia took a loooong time–that’s what Vanessa is doing in the photo at top.
Once the fascia was off, Vanessa started parting out the long tendons of the hypaxial muscles in the left half of the neck. Meanwhile, I started stripping fascia from the right half. I had forgotten that the right half of the neck still had the trachea and esophagus adhered to the side. That probably sounds weird, given that our trachea and esophagus–and those of most mammals–run right down the middle of our necks and aren’t free to move around much. In birds, they’re more free-floating and can drift around between the skin and the vertebral muscles, sometimes even ending up dorsal to the vertebral column–there’s a great x-ray of a duck in a 2001 paper that shows this, which I’ll have to blog sometime.
Anyway, when I cut the fascia to pull back the trachea and esophagus, I found that they were separated from the underlying tissues by a dense network of pneumatic diverticula winding through the fascia.
I had heard, anecdotally, of networks of diverticula described as looking like bubble wrap. I can now confirm that is true, for at least some networks. What was especially cool about these is that they were occupying space that would be filled with adipose or other loose connective tissue in a mammal, which illustrates the point that pneumatic epithelium seems to replace many kinds of connective tissue, not just bone–something Pat O’Connor has talked about, and which I also briefly discussed in this post.
I should mention that there was no connection between these diverticula and the trachea, as there is between the subcutaneous throat sac and the trachea in the emu (story and pictures here).
While I was geeking out on diverticula, Vanessa was methodically separating the long hypaxial muscles, which looked pretty cool all fanned out.
And that’s all we had time for on Saturday. But we’re cutting again soon, so more pictures should be along shortly.