The best-preserved presacral vertebra of Vouivria damparisensis (Mannion et al. 2017: fig. 10).

New goodies out today in PeerJ: Tschopp and Mateus (2017) on the new diplodocid Galeamopus pabsti, and Mannion et al. (2017) redescribe and name the French ‘Bothriospondylus’ as Vouivria damparisensis.

C7 of Galeamopus pabsti (Tschopp and Mateus 2017: fig. 24).

Both papers are packed with interesting stuff that I simply don’t have time to discuss right now. Possibly Mike and I will come back with subsequent posts that discuss these critters in more detail. We both have a connection here besides our normal obsession with well-illustrated sauropods – Mike reviewed the Galeamopus paper, and I reviewed Vouivria. Happily, both sets of authors chose to publish the peer-review histories, so if you’re curious, you can go see what we said.

For now, I’ll just note that C7 of Galeamopus pabsti, shown above, is intriguingly similar in form to Vertebra ‘R’ of YPM 429, the ‘starship’ Barosaurus cervical (illustrated here). Mike and I spent a lot of time puzzling over the morphology of that vert before we convinced ourselves that much of its weirdness was due to taphonomic distortion and a restoration and paint job that obscured the fact that the metapophyses were missing. Given our ongoing project to unravel the wacky morphology of Barosaurus, I’m looking forward to digging into the morphology of G. pabsti in more detail.

I’ll surely irritate Mike by saying this, but my favorite figure in either paper is this one, Figure 4 from Tschopp and Mateus (2017). I can’t remember ever seeing an exploded skull diagram like this for a sauropod before, but it’s extremely helpful and I love it.

And that’s all for now. Go read these papers – they’re both substantial contributions with intriguing implications for the evolution of their respective clades. Congratulations to both sets of authors for producing such good work.

References

  • Mannion PD, Allain R, Moine O. (2017) The earliest known titanosauriform sauropod dinosaur and the evolution of Brachiosauridae. PeerJ 5:e3217 https://doi.org/10.7717/peerj.3217
  • Tschopp E, Mateus O. (2017) Osteology of Galeamopus pabsti sp. nov. (Sauropoda: Diplodocidae), with implications for neurocentral closure timing, and the cervico-dorsal transition in diplodocids. PeerJ 5:e3179 https://doi.org/10.7717/peerj.3179

Here’s my face.

I went to the dentists’ office recently for a regular checkup and cleaning, and when my dentist learned that I taught human anatomy, he volunteered to send me a high-res copy of my panoramic x-ray. I couldn’t think of any plausible scenario wherein someone could use it for evil, and it has lots of cool stuff in it besides teeth, so decided to post it so I could yakk about it.

First things first: my teeth are in pretty good shape. I had to have my wisdom teeth (3rd molars) pulled back in 2009, and my upper 1st molar on the left has a root canal and a porcelain crown, which stands out bright white on the radiograph. Everyone else is present and looking good. If it’s been a while since you’ve covered this, the full human dentition consists of 2 incisors, 1 canine, 2 premolars, and 3 molars on each side, top and bottom, for a total of 32 teeth. Because I’ve had all four 3rd molars removed, I’m down to 28.

I could go on and on about the cool stuff in this image. Here are 12 things that stand out:

  1. The mandibular condyle, which is the articular end of the mandible that fits into the mandibular fossa, a shallow socket on the inferior surface of the temporal bone, to form the temporomandibular joint (TMJ). There’s an articular disk made of fibrocartilage inside the joint, which separates it into two fluid-filled spaces, one against the condyle and one against the fossa. This allows us to do all kinds of wacky stuff with our lower jaws besides simply opening and closing them, such as slide the jaw fore and aft or side to side. This is a strong contrast to most carnivores, which bite down hard and therefore need a jaw joint that works as a pure hinge. See this post for pictures and discussion of the jaw joint in a bear skull.
  2. The coronoid process of the mandible, which is a muscle attachment site. A few fibers of the masseter and buccinator muscles can encroach onto the coronoid process, but mostly it is buried in the temporalis, one of the primary jaw-closing muscles. Put your fingers on the side of your head a little above and in front of your ear and bite down. That muscle you feel bulging outward is the temporalis. Back in the 1960s, Melvin Moss (1968) discovered that if he removed the temporalis muscles from newborn rats, the coronoid processes would fail to develop. Moss’s ambition was to discover the quanta of anatomy, which in his view were “functional matrices” – finite sets of soft tissues related by development and function, which might contain “skeletal units” that grew because of the morphogenetic demands of the functional matrices. His tagline was, “Functional matrices evolve, skeletal units respond”. Not all of Moss’s ideas have aged well in light of what we now know about the genetic underpinnings of skeletal development, but he wasn’t completely wrong, either, and functional matrix theory is still an interesting and frequently productive way to think about the interrelationships of bones and soft tissues. For more horrifying/enlightening Moss experiments on baby rats, see this post.
  3. The mandibular angle, which is another muscle attachment. The medial pterygoid muscle attaches to the medial surface, and the masseter attaches laterally. You can feel this, too, by putting your fingers over your mandibular angle and biting down – that’s the masseter you feel bulging outward. Note that the angle flares downward and outward on either side of my jaw. This flaring of the angle tends to be more pronounced in males than in females, and it is one of many features that forensic anthropologists (like the one I belong to) take into account when attempting to determine biological sex from human skeletal remains. Like most sexually dimorphic features of the skeleton, this is a tendency along a spectrum of variation rather than a binary yes/no thing. There are women with flared jaw angles (Courtney Thorne-Smith, probably) and men with slender mandibles, so you wouldn’t want to sex a skeleton by that feature alone.
  4. The mandibular canal, a tubular channel through the mandible that houses the inferior alveolar artery, vein, and nerve. This neurovascular bundle provides innervation and blood supply to the tooth-bearing part of the mandible and to the teeth themselves, and emerges through the mental foramen to provide sensory innervation and blood supply to the chin.
  5. The upper surface of the hard palate, formed by the palatine process of the maxilla anteriorly and by the palatine bones posteriorly. The palate is the roof of the mouth and the floor of the nasal airways.
  6. The median septum of the nasal cavity, formed by cartilage anteriorly, the perpendicular plate of the ethmoid bone superiorly, and the vomer posteriorly and inferiorly.
  7. The blue lines are the inferior margins of my maxillary sinuses – air-filled spaces created when pneumatic diverticula of the nasal cavity hollow out the maxillae. You have these, too, as well as air spaces in your frontal, ethmoid, sphenoid, and temporal bones. It looks like many of the roots of my upper molars stick up into my maxillary sinuses. This is not an illusion, as shown below.
  8. When I had the root canal on my left upper 2nd molar, the endodontist filled the pulp cavities of the tooth roots with gutta-percha, a rigid natural latex made from the sap of the tree Palaquium gutta. Gutta-percha is bioinert, so it makes a good filling material (it was also used to insulate transoceanic telegraph cables), and it’s radiopaque, which allows endodontists to confirm that the cavities have been filled completely. The other teeth show the typical structure of a dense enamel crown, less dense dentine forming the bulk of the tooth, and radiolucent pulp cavities containing blood vessels and nerves.
  9. This is the rubber bit I gripped with my incisors to keep my teeth apart and my head motionless while the CT machine rotated around me to make the scan. Not that cool in a science sense, but I figured it deserved a label.
  10. Note that the roots of the canines go farther into the jaws than those of the other teeth. This is true for all four canines, it’s just easiest to see with this one. This is a pretty standard mammalian thing, for taxa that still have canines – they tend to be big and mechanically important, so they have deep roots. Even though our canines are absolutely and proportionally much smaller than those in the other great apes, we can still see traces of their earlier importance, like these deep roots.
  11. In places you can see the trabecular internal structure of my mandible clearly. As someone who geeks out pretty much anytime I get a look inside a bone, this tickled me.
  12. The remains of an alveolus or tooth socket. I had my 3rd molars out almost a decade ago, and by now the sockets will have mostly filled in with new trabecular bone. But you can still see the ghostly outline of at least this one – a sort of morphogenetic trace fossil buried inside my mandible. I assume that in another decade or two this will have disappeared through regular bone remodeling.

Here’s a closeup of my left upper 2nd premolar and first two (and only remaining) molars. The gutta-percha filling the pulp cavities of the three roots of the 1st molar is obvious. The disparity in root length is mostly illusory – this was an oblique shot and the two ‘short’ roots are foreshortened.

Here’s the same image with the roots of the 2nd molar traced in pink, and the inferior margin of the maxillary sinus traced in blue. It’s not that uncommon for upper molar roots to stick up into the maxillary sinuses. That was true of my 3rd molars as well, and when I had them taken out, the endodontist had to put stitches into my gums to close the holes. Otherwise I would have had open connections between my oral cavity and maxillary sinuses, which would have sucked and been dangerous. Nasal mucus in the maxillary sinuses could have drained into my mouth, and food I was chewing could have been forced up into the sinuses, where it would have decomposed and caused a truly vile sinus infection.

In a developmental sense, it’s not that the roots of the teeth grow upward into the sinuses, it’s that the sinuses grow downward, eroding the bone around the roots of the teeth. This happens well after the teeth are done forming – the sinuses continue to expand as long as the skull is growing, and they retain the potential to remodel the surrounding bone for as long as we live. Even in cases like mine where the roots of the molars stick up into the sinuses, the tooth roots are still covered by soft tissue, including branches of the superior alveolar artery, vein, and nerve that enter the pulp cavities of the tooth roots through foramina at their tips.

If you ask your dentist for copies of your own dental x-rays, you’ll probably get them. If you do, have fun exploring the weird territory inside your head.

Reference

  • Moss, M. L. (1968). A theoretical analysis of the functional matrix. Acta Biotheoretica, 18(1), 195-202.

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I’m back in Oklahoma for the holidays, and anytime I’m near Norman I pop in to the OMNH to see old friends, both living and fossil. Here’s the Aquilops display in the hall of ancient life, which has been up for a while now. I got some pictures of it when I was here back in March, just never got around to posting them.

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Aquilops close up. You can’t see it well in this pic, but on the upper right is a cast of the Aquilops cranium with a prosthesis that shows what the missing bits would have looked like. That prosthesis was sculpted by – who else? – Kyle Davies, the OMNH head preparator and general sculpting/molding/casting sorceror. You’ve seen his work on the baby apatosaur in this post. I have casts of everything shown here – original fossil, fossil-plus-prosthesis, and reconstructed 3D skull – and I should post on them. Something to do in the new year.

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The Aquilops display is set just opposite the Antlers Formation exhibit, which has a family of Tenontosaurus being menaced by two Deinonychus, and at the transition between Early and Late Cretaceous. The one mount in the Late Cretaceous area is the big Pentaceratops, which is one of the best things in this or any museum.

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Evidence in support of that assertion. Standing directly in front of this monster is a breathtaking experience, which I highly recommend to everyone.

It’s just perfect that you can see the smallest and earliest (at least for now) North American ceratopsian adjacent to one of the largest and latest. Evolution, baby!

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I didn’t only look at dinosaurs – the life-size bronze mammoth in the south rotunda is always worth a visit, especially in holiday regalia.

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No holiday post about the OMNH would be complete without a shot of “Santaposeidon” (previously seen here). I will never get tired of this!

The chances that I’ll get anything else posted in 2016 hover near zero, so I hope you all have a safe and happy holiday season and a wonderful New Year.

rabbit-facial-tilt-and-locomotion-kraatz-sherratt-2016-fig5

Facial tilt in extant leporids is strongly correlated with locomotor mode – fast movers have more strongly tilted faces. There’s a lot of homoplasy, which is to be expected with characters that are strongly driven by current function. Kraatz and Sherratt (2016: fig. 5).

Judgmental readers will recall that I have dabbled in mammal skulls, thanks to the corrupting influence of my friend and colleague, Brian Kraatz. At the end of my last post on this sordid topic, I mentioned that Brian and Emma Sherratt were working on a version 2.0 based in 3D morphometrics. The first volley from that project was published today in PeerJ.

Happily for all of us, Brian and Em confirmed the relationship between facial tilt and locomotor mode that we first documented last year, using more taxa, more landmarks, and two more dimensions (Kraatz and Sherratt 2016: 12):

…in accordance with previous findings by Kraatz et al. (2015), facial tilt angle is correlated with locomotor mode (D-PGLS, F(2,17) = 11.13, P = 0.003), where lower facial tilt angle, meaning more pronounced cranial flexion, is found in cursorial species, and high angles are found in generalist species.

That’s just the most personally relevant tip of a very large, multifaceted iceberg, including a monster supplementary info package on FigShare with, among other things, 3D models of bunny skulls. It’s all free and awesome, so go have fun.

lagomorph-facial-tilt-evolution-kraatz-sherratt-2016-fig7

That homoplastic pattern shown in figure 5, above? It’s been going on for a while. I’m gonna go out on a limb and guess that Hypolagus was a rocket. Kraatz and Sherratt (2016: fig. 7).

References

Today, we were at the BYU Museum of Paleontology, which is in a ridiculously scenic setting with snow-capped mountains on the horizon in almost every direction.

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We got through a lot of good work in collections, and we’ll show you some photos from there in due course. But for today, here are a couple of pictures from the public galleries.

First, here in a single photo is definitive proof that the “Toroceratops hypothesis” is wrong:

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Say what you want about ontegenetic trajectories, that huge and well ossified Triceratops is not a juvenile of anything.

Good, glad we go that sorted out.

Meanwhile, at the even better end of the gallery, here is a very nice — and very well lit — cast of the famous articulated juvenile Camarasaurus specimen CM 11338 described by Gilmore (1925):

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Further bulletins as events warrant.

References

Gilmore, Charles W. 1925. A nearly complete articulated skeleton of
Camarasaurus, a saurischian dinosaur from the Dinosaur National
Monument, Utah. Memoirs of the Carnegie Museum 10:347-384.

 

Enter Sarmientosaurus

April 28, 2016

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Fig 6. Cranium of Sarmientosaurus musacchioi gen. et sp. nov. (MDT-PV 2). Computed tomography-based digital visualization in right lateral (A), left lateral (B), rostral (C), caudal (D), dorsal (E), and ventral (F) views. Scale bar = 10 cm. http://dx.doi.org/10.1371/journal.pone.0151661.g006

Yesterday we got a treat: the description of a new titanosaur, Sarmientosaurus musacchioi, based on some decent cervical vertebrae and an almost absurdly nice skull from the Upper Cretaceous of Argentina (Martinez et al., 2016). It was published in PLOS ONE so it’s free to the world, including a 3D PDF of the skull and some awesome visualizations. Get all that good stuff here.

I had one day’s warning about this – Brian Switek contacted me on Monday to ask if I’d be willing to lend my thoughts on the new critter for his news article for National Geographic, which you can read here. As always, I sent more stuff than he could use, so I’m recycling the long form for the rest of this post.

Brian’s first question was about how Sarmientosaurus stands out. I wrote:

Sarmientosaurus has probably the most complete and best-preserved skull of any sauropod from South America to date. It’s kind of funny – for so long we had so few good skulls from brachiosaurs and titanosaurs, and now we’re getting them, but without much of the rest of the skeleton. In North America, unquestionably the nicest Cretaceous sauropod skull is that of the brachiosaurid Abydosaurus, but all we have with the skull is a bit of the neck. Same situation now with this new titanosaur, Sarmientosaurus. I’m not complaining – great skulls without bodies are still great skulls! – but it will be nice to someday connect heads and bodies.

Also, the authors are to be commended – I don’t think anyone has ever done such a thorough job describing the skull of a sauropod dinosaur. This paper will become the standard to which all others are compared going forward.

I stand by all of that. This new paper is just ridiculous in quantity and quality of descriptive detail. Do you like technicolor sauropod palates? Here, have a technicolor sauropod palate:

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Fig 8. Palate of Sarmientosaurus musacchioi gen. et sp. nov. (MDT-PV 2). Computed tomography-based digital visualization in ventral view indicating palatal bones (ectopterygoids, palatines, pterygoids, and vomers) and the right suborbital fenestra. Abbreviations see text. Scale bar = 10 cm. http://dx.doi.org/10.1371/journal.pone.0151661.g008

The next question from Brian was about the head posture and the inference drawn by Martinez et al. (2016) that Sarmientosaurus fed at ground level. My take:

It doesn’t seem unlikely to me that Sarmientosaurus had a downward-facing snout. As for being a low grazer, I am skeptical. The inner ear usually tells us something about the alert posture of an animal, not its feeding posture. Take rhinos – some of them graze from the ground, and some of them browse up higher, but they all carry their heads the same way. Most grazers have wide snouts, whereas that of Sarmientosaurus is pointed and even a little narrower than that of Giraffatitan. That’s a curious shape for a supposed grazer.

So there are three points to unpack here. First, I chose my words deliberately in saying that the inner ear tells us “something” about the alert posture, because in fact the horizontal semicircular canals (HSCCs) aren’t great even at that. As I wrote in this post seven years ago:

Where SCCs have really attracted attention in paleontology is the “more or less” horizontal orientation of the HSCCs in living animals. Some authors have argued that if you set the HSCCs level or close to level, you can figure out how the head was oriented in life.

Well, maybe. The problem is that there is a LOT of variation around level. In birds surveyed by Duijm (1951), HSCC orientation varied by 50 degrees among taxa, from 20 degrees below horizontal to 30 degrees above. Furthermore, in humans HSCC orientation varies by up to 20 degrees among individuals. Possibly humans are weirdly variable, but it seems at least equally likely that most critters are and we’ve only discovered that variation in humans because of the huge sample size.

However you slice it, those are darn big error bars around any given head posture. That doesn’t mean that HSCC orientations in dinosaurs and other extinct vertebrates are worthless for determining posture (they may also be a source of taxonomic information). Strictly speaking, it means that preserved HSCCs can get us in the 50-degree ballpark but can’t narrow things down any further. This is one of those areas in paleontology where we’re just going to have to live with a certain amount of uncertainty, at least for now.

As far as I know, that’s all still true. But I’d love to be wrong.

Second, there’s the difference between alert posture and feeding posture. Go watch horses graze – the skull is practically vertical while they’re feeding, but that’s not the orientation you get from the HSCCs. So if I’m skeptical about ignoring the error bars around HSCC orientation to determine alert posture, I’m even more skeptical about trying to infer feeding posture from them. Also, the rhino point – we have an extant group with closely related taxa where one is a grazer (white rhino, Ceratotherium) and one is a browser (black rhino, Diceros). They hold their heads about the same. So feeding preference will not necessarily be reflected in normal, non-feeding head posture.

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Fig 34. Comparison of titanosauriform sauropod dinosaur skulls in dorsal view. (A) Giraffatitan brancai (redrawn from Wilson and Sereno [103]). (B) Sarmientosaurus musacchioi gen. et sp. nov. (C) Nemegtosaurus mongoliensis (redrawn from Wilson [11]). (D) Rapetosaurus krausei (redrawn from Curry Rogers and Forster [13]). (E) Tapuiasaurus macedoi (redrawn from Zaher et al. [14]). Not to scale. http://dx.doi.org/10.1371/journal.pone.0151661.g034

Third, muzzle shape. Most grazers have wide mouths, but as I said in the email to Brian – and as this figure shows – the snout of Sarmientosaurus is narrower than that of Giraffatitan, and I don’t think anyone is seriously proposing that Giraffatitan was a grazer. So if Sarmientosaurus was more committed to low-level feeding than more basal titanosauriforms, its face was evolving in the wrong direction. Just sayin’.

(Incidentally, I am hugely in favor of figures like 33 and 34 in Martinez et al., 2016, which make it easy to compare the new critter to a selection of reference taxa. I wish everyone would do this all the time.)

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Fig 33. Comparison of titanosauriform sauropod dinosaur skulls in right lateral view. (A) Giraffatitan brancai (redrawn and modified from Wilson and Sereno [103]). (B) Abydosaurus mcintoshi (redrawn and modified from Chure et al. [98]). (C) Sarmientosaurus musacchioi gen. et sp. nov. (D) Nemegtosaurus mongoliensis (redrawn and modified from Wilson [11]). (E) Rapetosaurus krausei (redrawn from Curry Rogers and Forster [13]). (F) Tapuiasaurus macedoi (redrawn from Zaher et al. [14]). Not to scale. http://dx.doi.org/10.1371/journal.pone.0151661.g033

Finally (final for the purposes of the interview), Brian noted that in the media sauropods are often depicted as all being pretty much the same, and he asked what made Sarmientosaurus stand out. My response:

Until now, the skulls we’ve found of basal titanosauriforms – brachiosaurs and relatives – and more derived titanosaurs haven’t looked much alike. To me Sarmientosaurus is cool because it bridges that gap. From the top and the front the skull looks a lot like those of Brachiosaurus and Giraffatitan – really wide, pretty big teeth, long toothrow. But from the side, the smaller nostrils and long snout have obvious similarities to more derived titanosaurs like Nemegtosaurus. And they phylogenetic analysis confirms that, which is nice. But you can take one look at this thing and say, “Yeah, cool, we’ve been waiting for someone like you.”

The lateral views of titanosauriform skulls in the above figure nicely illustrate my point. If you took the Giraffatitan skull in A and the Tapuiasaurus skull in F and did a 50% morph between them, you’d get something pretty darned close to Sarmientosaurus. And about halfway between Giraffatitan and the really derived saltasaurids is where the phylogenetic analysis puts Sarmientosaurus. The gestalt of the skull nicely reflects the animal’s relationships, which does not always happen.

Oh, there are cervical vertebrae, too, and a seriously weird ossified tendon that is apparently not a cervical rib, but those will keep for another post.

The take-home here is that although I disagree with the authors on a few points of paleobiological interpretation, the Sarmientosaurus fossils are spectacular and Martinez et al. (2016) have done a tremendous job of describing and illustrating them. And the paper is free to anyone who wants it, as it should be. One of the great delights of the last few years has been watching PLOS ONE and PeerJ become the preferred outlets for high-quality descriptive work on dinosaurs.

Now if we can just find more of this thing!

Reference

Martínez RDF, Lamanna MC, Novas FE, Ridgely RC, Casal GA, Martínez JE, et al. (2016) A Basal Lithostrotian Titanosaur (Dinosauria: Sauropoda) with a Complete Skull: Implications for the Evolution and Paleobiology of Titanosauria. PLoS ONE 11(4): e0151661. doi:10.1371/journal.pone.0151661

 

 

Several drinks later, they all die and somehow become skeletonised, and that’s how they all land up on a table in my office:

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Top left: pieces of monitor lizard Varanus exanthematicus. Cervical vertebrae 1-7 on the piece of paper, femora visible above them, bits of feet below them. Awaiting reassembly. The whole skeleton is there.

Top right, on a plate on top of some lizard bits: skull, cervicals and feet of common pheasant Phasianus colchicus. The skull has come apart, and I can’t figure out how to reattach the quadrates. One of the feet is cleanly prepped out and waiting to be reassembled, while the other retains some skin for now.

Bottom left: skull and anterior cervicals of red fox Vulpes vulpes. Lots of teeth came out during the defleshing process, and will need to be carefully relocated and glued after the skull has finished drying out.

Bottom right: skull and anterior cervicals of European badger Meles meles. The skull is flat-out awesome, and by far my favourite among my mammal skulls. If tyrannosaurs were medium-sized fossorial mammals, they’d have badgers’ skulls for sure. A few teeth that came out have been glued into place; once the glue is dry, this skull is done.