Saurischian laminae and fossae v2 - Adam Marsh 2015

[Hi folks, Matt here. I’m just popping in to introduce this guest post by Adam Marsh (UT Austin page, LinkedIn, ResearchGate). Adam is a PhD student at UT Austin’s Jackson School of Geosciences, currently working for a semester as a Visiting Student Researcher at my old stomping ground, Berkeley’s UCMP.  Adam’s been working at Petrified Forest National Park in the summers and most of his research is on the Navajo Nation in Arizona. His major interest is in how we perceive extinctions in the fossil record. Specifically, he’s exploring the geochronology of the Glen Canyon Group to look at the biotic response to the end-Triassic mass extinction. He’s also working on an overhaul of the early saurischian dinosaurs of western North America – hence this post. It’s timely because I was just talking in the last post about putting together infographics to spread your ideas; here Adam’s very nice diagram serves as a quick guide and pointer to several papers by Jeff Wilson and colleagues. Many thanks to Sarah Werning for suggesting that Adam and I get acquainted over vertebrae. Update the next day: both the diagram above and the PDF linked below have been updated to fix a couple of typos. Also, there are now black and white versions – see below.]

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If you’re like me, you don’t count sheep when you fall asleep, you count laminae. These struts of bone and their affiliated fossae connect and span between major structural features on vertebral neural arches such as prezygapophyses, postzygapophyses, parapophyses, diapophyses, hyposphenes, hypantra, and the neural spine. Presumably, laminae bracket and fossae house outgrowths of pneumatic diverticula from the respiratory system, which has been covered extensively on this blog in sauropodomorph dinosaurs.

Talking about these complicated structures is cumbersome; they’ve been called buttresses, ridges, struts, etc. throughout descriptive skeletal literature. But what we call things is important, especially when we introduce laminae and other vertebral structures to the rigors of phylogenetic systematics, where homologous apomorphies reign supreme. In order to avoid arguing about whether one structure is called the potato or the tomato, Jeff Wilson and others introduced a strategy of naming vertebral laminae (Wilson, 1999) and the fossae (Wilson et al., 2011) that they surround using the same vertebral landmarks that most tetrapod anatomists agree upon (see the parade of –apophyses above). The process is very simple. Vertebral laminae are named for the two structures that they connect; the prezygodiapophyseal lamina (prdl) connects the prezygapophysis and the diapophysis, so each neural arch will have two prdls. Vertebral fossae are named for the two major laminae that constrain them; the prezygocentrodiapophyseal fossa (prcdf) opens anterolaterally and is delineated dorsally by the prezygodiapophyseal lamina and ventrally by the anterior centrodiapophyseal lamina. Again, each neural arch will have two prcdfs. Those of you who are black belt vertebral anatomists, to borrow a favorite phrase from my advisor, might be interested in serial variation and how these structures change up and down the vertebral column. Until I get my act together and publish some cool new saurischian data, I will refer you to Wilson (2012). [We’ve also touched on serial variation in laminae in this post and this one. – MJW]

Saurischian laminae and fossae v2 bw - Adam Marsh 2015

Same thing in black and white, with labels

 

You might have noticed that the names are a mouthful and take up their fair share of typed characters. In my research of early saurischian dinosaurs, I’ve run across quite a few of these laminae everywhere from herrerasaurids to sauropodomorphs to coelophysoids to Dilophosaurus. Even though I’ve drawn, photographed, and written about various laminae and fossae, I still need to remind myself of what goes where and what it’s called. Believe me, vertebral lamina nomenclature does not lend itself well to Dem Bones covers. As a result, I’ve put together a reference figure that might be useful for those of you who are dealing with this or even teaching it to students. At the very least, you can put it on the ceiling above your bed so that it’s the first thing you see when you open your eyes in the morning.

Four main vertebral laminae are present plesiomorphically in archosaurs: the anterior and posterior centrodiapophyseal laminae, the prezygodiapophyseal lamina, and the postzygodiapophyseal lamina. This means that the prezygocentrodiapophyseal, postzygocentrodiapophyseal, and centrodiapophyseal fossae are present, and sometimes the top of the transverse process is concave between the neural spine and the zygapophyses to form the spinodiapophyseal fossa. I know that a certain sister group of Sauropodomorpha can get disparaged around these parts, but the truth is that theropods build long necks, too, and sometimes in very different ways than sauropodomorphs. When you are writing about the various vertebral buttresses and chonoses, don’t get frustrated with the names, because Wilson and his colleagues have actually made it much easier for us to talk to one another about presumably homologous structures without needing an additional degree in civil engineering.

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Here’s the figure again in PDF form: Marsh, Adam 2015 saurischian laminae and fossae diagram v2

And in black and white for those who prefer it that way: Marsh, Adam 2015 saurischian laminae and fossae diagram v2 bw

References

According to Rare Historical Photos from the 1860s to the 1960s, this is the iceberg that sank the Titanic:

 photo of the iceberg that sunk the Titanic, taken the morning of April 15, 1912 from board of the ship “Prinz Adalbert”, before knowing the Titanic had sunk. The smear of red paint along the base of the berg (bottom right) prompted the chief steward to take the picture.

photo of the iceberg that sunk the Titanic, taken the morning of April 15, 1912 from board of the ship “Prinz Adalbert”, before knowing the Titanic had sunk. The smear of red paint along the base of the berg (bottom right) prompted the chief steward to take the picture.

Clearly this was no iceberg, but a gigantic Apatosaurus vertebra, most of it hidden under water. Here is an artist’s impression:

iceberg

They get everywhere, don’t they?

Having given pterosaurs all the glory in two earlier posts, it’s time to move yet further away from the sauropods we know and love, and look at epipophyses outside of Ornithodira.

Here, for example, is the basal archosauriform Vancleavea. (Thanks to Mickey Mortimer, whose a comment on an earlier post put us onto this, and various other candidate epipohysis-bearers which we’ll see below.)

Here is a pair of Vancleavea cervical vertebrae:

Nesbitt et al. (2009: fig. 11A). Vertebrae of Vancleavea campi. Two articulated cervical vertebrae (PEFO 33978) in left lateral view.

Nesbitt et al. (2009: fig. 11A). Vertebrae of Vancleavea campi. Two articulated cervical vertebrae (PEFO 33978) in left lateral view.

No ambiguity here: the epipophysis is even labelled.

But we can find epipophyses even outside Archosauriformes. Here, for example, is the the rhynchosaur Mesosuchus:

Dilkes (1998: fig. 7A). Mesosuchus browni. Holotype SAM 5882. Partial skull and jaws and cervical vertebrae in left lateral view.

Dilkes (1998: fig. 7A). Mesosuchus browni. Holotype SAM 5882. Partial skull and jaws and cervical vertebrae in left lateral view.

Check out the rightmost vertebra (C7), clicking through for the full resolution if necessary. There is a definite eminence above the postzyg, separated from it by a distinct groove. Unless the drawing is wildly misleading, that is a definite epipophysis, right there.

But even more basal archosauromorphs have epipophyses. Check out Teraterpeton, described by Hans-Dieter Sues in 2003:

Sues (2003: figure 7). Teraterpeton hrynewichorum, NSM 999GF041 (holotype), cervical and anterior dorsal vertebrae and ribs, associated with right scapula (sc), ?clavicles (cl?), ?interclavicale (ic?), and incomplete right humerus (h), in right lateral view. Scale bar = 1 cm. a.p., accessory process above postzygapophysis; ax, axis; c3, c4, cervical vertebra 3 and 4, respectively; t, displaced tooth.

Sues (2003: figure 7). Teraterpeton hrynewichorum, NSM 999GF041 (holotype), cervical and anterior dorsal vertebrae and ribs, associated with right scapula (sc), ?clavicles (cl?), ?interclavicale (ic?), and incomplete right humerus (h), in right lateral view. Scale bar = 1 cm. a.p., accessory process above postzygapophysis; ax, axis; c3, c4, cervical vertebra 3 and 4, respectively; t, displaced tooth.

This is another one where the epipophysis is labelled (though not recognised as such — it’s just designated an “accessory process”).

Can we go yet more basal? Yes we can! Here are cervicals 2 and 3 of the trilophosaur Trilophosaurus (in an image that I rearranged and rescaled from the published original for clarity):

Spielmann et al. (2008: figure 30, rearranged). Cervical vertebrae 2-3 (i.e. axis and C3) of Trilophosaurus buettneri TMM 31025-140. Top row: right lateral. Second row: dorsal, with anterior to the left. Third row, left to right: anterior, left lateral, posterior. Bottom row: ventral, with anterior to the left.

Spielmann et al. (2008: figure 30, rearranged). Cervical vertebrae 2-3 (i.e. axis and C3) of Trilophosaurus buettneri TMM 31025-140. Top row: right lateral. Second row: dorsal, with anterior to the left. Third row, left to right: anterior, left lateral, posterior. Bottom row: ventral, with anterior to the left.

The parts of this image to focus on (and you can click through for a much better resolution) are the postzyg at top right of the left-lateral view, which has a distinct groove separating the zygapophyseal facet below from the epipohysis above; and the posterior view, which also shows clear separation on both sides between these two structures.

While we’re playing with trilophosaurs here’s here’s another one (probably), Spinosuchus:

Spielmann et al. (2009: figure 3N). Spinosuchus caseanus holotype UMMP 7507, 5th cervical vertebra in left lateral view.

Spielmann et al. (2009: figure 3N). Spinosuchus caseanus holotype UMMP 7507, 5th cervical vertebra in left lateral view.

Again, the groove separating postzygapophyseal facet from epipophysis (at top right in the image) is clear.

But there’s more! Even the protorosaurs, pretty much the most basal of all archosauromorphs, have convincing epipophyses. Here are two that I found in Dave Peters’ post from two years ago, which I only discovered recently. [Here I must insert the obligatory disclaimer: while Dave Peters is a fine artist and has put together a really useful website, his ideas about pterosaur origins are, to put it mildly, extremely heterodox, and nothing that he says about phylogeny on that site should be taken as gospel. See Darren’s write-up on Tet Zoo for more details.]

Dave shows some probable, but not super-convincing epipophyses in the protorosaur Macrocnemus (shaded purple here) …

Cervicals 1-6 of the protorosaur Macrocnemus, modified from an uncredited image on Dave Peters' site. Postzygapophyses in yellow, epipophyses in purple.

Cervicals 1-6 of the protorosaur Macrocnemus, modified from an uncredited image on Dave Peters’ site. Postzygapophyses in yellow, epipophyses in purple.

… and some much more convincing epipophyses in the better known and more spectacular protorosaur Tanystropheus:

Unspecified single cervical of Tanystropheus, from Dave Peters' site. Postzygapophysis in yellow, epipohysis in purple.

Unspecified single cervical of Tanystropheus, from Dave Peters’ site. Postzygapophysis in yellow, epipohysis in purple.

Frustratingly, Dave doesn’t attribute these images, so I don’t know where they’re originally from (unless they’re his own artwork). Can anyone enlighten me? There’s a nice illustration in figure 57 of Nosotti’s (2007) epic Tanystropheus monograph that is at least highly suggestive of epipophyses:

Nosotti (2007:figure 57). Reconstruction of an anterior cervical vertebra (A) and of a mid-cervical vertebra (B) in small-sized specimens of Tanystropheus longobardicus. Left lateral view. Not to scale. Watercolor: Massimo Demma. Abbreviation pzp = postzygapophyseal process.

Nosotti (2007:figure 57). Reconstruction of an anterior cervical vertebra (A) and of a mid-cervical vertebra (B) in small-sized specimens of Tanystropheus longobardicus. Left lateral view. Not to scale. Watercolor: Massimo Demma. Abbreviation pzp = postzygapophyseal process.

But it’s not as good as the one Peters used, as that one shows a distinct notch between postzyg and epipophysis, so I’d like to track that down if I can.

With this, I believe I am done on cataloguing and illustrating epipophyses, unless something dramatic turns up. (For example, this commenter thinks that nothosaurs have epipophyses, but I’ve not been able to verify that.) Here’s what we’ve found — noting that we’ve illustrated epipophyses on every taxon on this tree except Crocodylia:

tree

So it seems that epipophyses may well be primitive at least for Archosauromorpha — which implies that they were secondarily lost somewhere on the line to modern crocs.

With this lengthy multi-part digression complete, hopefully, we’ll get back to sauropods next time!

References

  • Dilkes, David W. 1998. The Early Triassic rhynchosaur Mesosuchus browni and the interrelationships of basal archosauromorph reptiles. Philosophical Transactions of the Royal Society of London B 353:501-541.
  • Kellner, Alexander W. A., and Yukimitsu Tomida. 2000. Description of a new species of Anhangueridae (Pterodactyloidea) with comments on the pterosaur fauna from the Santana Formation (Aptian-Albian), Northeastern Brazil. National Science Museum monographs, Tokyo, 17. 135 pages.
  • Nesbitt, Sterling J., Michelle R. Stocker, Bryan J. Small and Alex Downs. 2009. The osteology and relationships of Vancleavea campi (Reptilia: Archosauriformes). Zoological Journal of the Linnean Society 157:814-­864.
  • Nosotti, Stefania. 2007. Tanystropheus longobardicus (Reptilia, Protorosauria): re-interpretations of the anatomy based on new specimens from the Middle Triassic of Besano (Lombardy, Northern Italy). Memorie della Societa Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di Milano 35(III). 88pp.
  • Spielmann, Justin A., Spencer G. Lucas, Larry F. Rinehart and Andrew B. Heckert. 2008. The Late Triassic Archosauromorph Trilophosaurus. New Mexico Museum of Natural History and Science Bulletin 43.
  • Justin A. Spielmann, Spencer G. Lucas, Andrew B. Heckert, Larry F. Rinehart and H. Robin Richards III. 2009. Redescription of Spinosuchus caseanus (Archosauromorpha: Trilophosauridae) from the Upper Triassic of North America. Palaeodiversity 2:283-313.
  • Sues, Hans-Dieter. 2003. An unusual new archosauromorph reptile from the Upper Triassic Wolfville Formation of Nova Scotia. Canadian Journal of Earth Science 40:635-649.

This just in, from Zurriaguz and Powell’s (2015) hot-off-the-press paper describing the morphology and pneumatic features of the presacral column of the derived titanosaur Saltasaurus. (Thanks to Darren for bringing this paper to my attention.)

Now, as everyone knows, titanosaurs don’t have epipophyses. In fact, they’re the one major sauropod group where Matt has not observed them.

Until today.

Zurriaguz and Powell (2015:figure 3B). Anterior cervical vertebra PVL 4017-3 of Saltasaurus loricatus, in dorsal view (rotated 90° from the paper)

Zurriaguz and Powell (2015:figure 3B). Anterior cervical vertebra PVL 4017-3 of Saltasaurus loricatus, in dorsal view (rotated 90° from the paper)

Look at the left postzygapophysis, at top left of this image. Doesn’t that look like there’s a distinct rounded eminence sticking out towards the camera?

No? Not convinced? All right, then, how about this?

Zurriaguz and Powell (2015:figure 4B). Mid-anterior cervical PVL 4017-138 of Saltasaurus loricatus in right lateral view.

Zurriaguz and Powell (2015:figure 4B). Mid-anterior cervical PVL 4017-138 of Saltasaurus loricatus in right lateral view.

This time, look at the right postzyg (again at top left in the image). Doesn’t that look like there are two separate bony structures up there separated by a notch? A postzygapophyseal facet below, and an epipophysis above? Right?

Huh? What’s that? Just damage, you say?

All right. Let’s bring out the smoking gun.

Zurriaguz and Powell (2015:figure 5). Last anterior cervical vertebra (PVL 4017-5) of Saltasaurus loricatus in right lateral view. (Ignore the inset square for our purposes: it's in the original.)

Zurriaguz and Powell (2015:figure 5). Last anterior cervical vertebra (PVL 4017-5) of Saltasaurus loricatus in right lateral view. (Ignore the inset square for our purposes: it’s in the original.)

Again up at top left, we seem to have a clear case of a ventrally directed postzygapophyseal facet surmounted by a separate eminence which can only be an epipophysis. It even seems to be roughened for tendon attachment.

What does this mean? Only the same thing we said last time: The more we look for epipophyses, the more we find them. Amazing how often that turns out to be true of various things.

We seem to be headed towards the conclusion that epipophyses, while never ubiquitous, pop up in all sorts of places scattered all across the ornithodiran tree, encompassing birds, other theropods, sauropods, prosauropods, several groups of ornithischians, and both pterodactyloid and “rhamphorhynchoid” pterosaurs.

But what about outside Ornithodira?

Can we find epipophyses even out there, in the wilderness?

Stay tuned!

References

It’s well known that there is good fossil material of the giant azhdarchid pterosaur Quetzalcoatlus out there, but that for various complicated reasons it’s yet to be published. But as part of our ongoing quest for pterosaur epipophyses, I have obtained these photos of a pretty well preserved single cervical, probably C3, which is either Quetzalcoatlus or something pretty darned close.

TMP 1992.83.7, Quetzalcoatlus sp., cervical 3. Top, dorsal view; bottom, ventral view. Scale bar = 10 cm.

TMP 1992.83.7, Cf. Quetzalcoatlus, cervical 3. Top, dorsal view; bottom, ventral view. Anterior is to the left. Scale bar = 10 cm. Click through for high resolution.

My thanks go, in chronological order, to Rob Knell of QMC for taking the photos; to Don Brinkman for permission to share them publicly; and to Mike Habib (the USC one, not the Elsevier one) for passing them on to me. (The composition is my own work, which anyone is free to reuse so far as I’m concerned.)

Here’s what Mike Habib says about the specimen:

… well preserved TMP azhdarchid cervical vertebra. It is likely a CIII vert, and appears to be from an animal very similar to the small morph of Quetzalcoatlus in overall morphology. The associated humerus is just about an exact match. This cervical, however, does not quite match the proportions of any of the Q. sp. cervical verts, though that’s not a surprise given that the animals come from different horizons. There is a much larger, but poorly preserved cervical vert at the TMP as well (a Q. northropi sized animal, give or take).

Here are Mike’s measurements:

  • maximum length: 142.2 mm
  • minimum mediolateral breadth: 39.3 mm
  • minimum dorsoventral breadth: 27.4 mm
  • midshaft mediolateral breadth 40.0 mm
  • midshaft dorsoventral breadth 27.0 mm
  • mediolateral breadth across prezygapophyses: 65.6 mm
  • mediolateral breadth across postzygapophyses: 68.5 mm
  • dorsoventral breadth at postzygapophyses: 35.8 mm

(I mean those are the measurements that Mike provided for the vertebra, not the measurements of Mike himself. He’s much bigger than that.)

So does this specimen have epipophyses? Frustratingly, there don’t seem to be lateral or posterior-view photos, so it’s very hard to tell from these dorsal and ventral ones. Happily, the same specimen was illustrated and briefly described by Godfrey and Currie (2005:294-299), along with several other less well-preserved cervicals — so we do have drawings of these other views:

Godfrey and Currie (2005:figure 16.1). Azhdarchid cervical vertebra (TMP 92.83.7) in (A) dorsal, (B) left lateral, (C) ventral, (D) anterior, (E) posterior, and (F) posterodorsal views. Abbreviations: hyp, hypapophysis; nc, neural canal; pn, pneumatopore; prz, prezygapophysis.

Godfrey and Currie (2005:figure 16.1). Azhdarchid cervical vertebra (TMP 92.83.7) in (A) dorsal, (B) left lateral, (C) ventral, (D) anterior, (E) posterior, and (F) posterodorsal views. Abbreviations: hyp, hypapophysis; nc, neural canal; pn, pneumatopore; prz, prezygapophysis.

(The specimen number given here is slightly different from that given for the photos, but matches the label in the ventral-view photo. I assume that the leading “93” part of the specimen number is a year, and that it’s sometimes but not always given in four digits.)

The text of the description does not mention epipophyses, and skips very lightly over the whole postzygapophyseal area. But figures 16.1B (lateral) and 16.1E (posterior) both seem to show distinct bulbous eminences well above the postzygapophyseal facets. I think these have to be epipophyses. So Mark Witton’s caution not to write off azhdarchid epipophyses on the strength of their apparent absence in Phosphatodraco proves well-founded.

What is the moral here?

The more we look for epipophyses, the more we find them.

Which will be strangely familiar to anyone who remembers our experience with caudal pneumaticity in sauropods, which was: the more we looked for it, the more we found it.

If we have an SV-POW! motto (other than “sauropods are awesome”, of course), it’s “Measure your damned dinosaur!“. But if we had a third motto, it would be like unto it: look at your damned dinosaur. Or pterosaur, as the case may be. The odds are, you’ll see things you weren’t expecting.

Many thanks for the various people who chipped in, both in comments on the last post and in this thread on twitter, where I asked a bunch of pterosaur experts for their thoughts on epipophyses in pterosaurs. I now know more than I previously knew about epipophyses outside of Sauropoda — and especially outside Dinosauria. I’ll try to credit everyone who contributed.

Occasional SV-POW!sketeer Darren Naish claims that according to the literature, ornithischians lack epipophyses — something that we’ve seen is untrue. I never got references out of him, though. Can anyone point me to the guilty literature?

Darren also gave me the rather cryptic instruction “Look at Anhanguera monographs. Sorry, can’t check myself.” Like something from a spy novel. Checking out Kellner and Tomida (2000), I found their illustration of the Anhanguera atlas/axis complex, in figure 14B, suggestive:

KellnerTomida2000-fig14

It took me a while to figure this out, but I think this is showing the first three cervicals, not two: the atlas is tiny, and is smushed onto the front of the axis; C3 is shown, but only in outline, and is ignored in the caption.

As labelled, the postzygapophyseal facet of the axis is tiny — and there’s a definite protuberance above it, which can only be an epipophysis. But we’d need photos to be confident. The good news is that there is a photo in the paper — part A of the same figure. But the bad news is that here’s how it looks in my scan:

KellnerTomida2000-fig14a

Not so helpful. If anyone has a good scan — or better still an original photo — I’d like to see it.

Darren also commented “Most big pterosaurs lack epipophyses. Ornithocheirids may be the exception”, but there his hints dried up. Mark Witton cautioned me: “Not sure for azhdarchids. Well preserved verts have reduced features, but not entirely absent as badly preserved verts suggest.” So perhaps the Phosphatodrado vertebrae in the last post are not so compelling as they seem.

Liz Martin suggested “off the top of my head you could check Wellnhofer papers. 1991 and 1985 I think show verts.” But I couldn’t find any vertebrae in the only Wellnhofer (1985) that I have; and there are at least three Wellnhofer publications from 1991, which I’ve not checked yet. Any more guidance, anyone?

So how widespread are epipohyses? Brusatte et al. (2010:73) gave “Epipophyses on the cervical vertebrae” as a synapomorphy diagnosing Dinosauria:

2.4.1.4. Epipophyses on the cervical vertebrae. Epipophyses are projections of bone, likely for muscle and ligament attachment, which protrude from the dorsal surfaces of the postzygapophyses of the cervical vertebrae. All basal dinosaurs possess epipophyses (Langer and Benton, 2006), although the size, shape, length, and projection angle of these processes vary considerably (e.g., compare Coelophysis (Colbert, 1989) with the more derived theropod Majungasaurus (O’Connor, 2007)). Basal ornithischians (e.g., Heterodontosaurus) only have epipophyses on the anterior cervical vertebrae, whereas saurischians have epipophyses in nearly all cervical vertebrae (Langer and Benton, 2006). Epipophyses are not present in the closest relatives of dinosaurs (e.g., Marasuchus, Silesaurus), but are present in some crurotarsans (e.g., Lotosaurus and Revueltosaurus).

It’s surprising that they’d mention dinosaurs and croc-line archosaurs, but overlook pterosaurs, which are phylogenetically bracketed by that group. But there’s lots of useful detail to follow up in the citations, which I’ll be doing soon.

So: moving down the tree from Sauropoda, we see epipophyses:

  • often but not always in sauropods
  • rarely in basal sauropodomorphs
  • often, maybe always, in theropods
  • intermittently but not infrequently in ornithischians
  • in at least some basal dinosauriforms
  • in some groups of pterosaurs but not others
  • in at least some croc-line archosaurs — but not, for example, in alligators.

Does anyone know of epipophyses outside Archosauria?

We seem now to be stumbling towards a conclusion of sorts, which is that epipophyses seem to be rather phylogenetically labile, coming and going within numerous lineages. As with so many vertebral features, they also vary with serial position, which complicates matters; and, I dare guess, with ontogeny.

I’ve not been able to locate any publications that are specifically about epipophyses (just lots that mention them in passing). Does anyone know of such a thing?

References

Matt’s last post contained a nice overview of the occurrence of epipophyses in sauropodomorphs: that is, bony insertion points for epaxial ligaments and muscles above the postzygapophyseal facets. What we’ve not mentioned so far is that these structures are not limited to sauropods. Back when we were preparing one of the earlier drafts of the paper that eventually became Why sauropods had long necks; and why giraffes have short necks (Taylor and Wedel 2013a), I explored their occurrence in related groups. But that section never got written up for the manuscript, and now seems as good a time as any to fix that.

Theropods (including birds)

Most obviously, epipophyses occur in theropods, the sister group of sauropodomorphs.

Taylor and Wedel (2013a: figure 11). Archosaur cervical vertebrae in posterior view, Showing muscle attachment points in phylogenetic context. Blue arrows indicate epaxial muscles attaching to neural spines, red arrows indicate epaxial muscles attaching to epipophyses, and green arrows indicate hypaxial muscles attaching to cervical ribs. While hypaxial musculature anchors consistently on the cervical ribs, the principle epaxial muscle migrate from the neural spine in crocodilians to the epipophyses in non-avial theropods and modern birds, with either or both sets of muscles being significant in sauropods. 1, fifth cervical vertebra of Alligator mississippiensis, MCZ 81457, traced from 3D scans by Leon Claessens, courtesy of MCZ. Epipophyses are absent. 2, eighth cervical vertebra of Giraffatitan brancai paralectotype HMN SII, traced from Janensch (1950, figures 43 and 46). 3, eleventh cervical vertebra of Camarasaurus supremus, reconstruction within AMNH 5761/X, “cervical series I”, modified from Osborn and Mook (1921, plate LXVII). 4, fifth cervical vertebra of the abelisaurid theropod Majungasaurus crenatissimus,UA 8678, traced from O’Connor (2007, figures 8 and 20). 5, seventh cervical vertebra of a turkey, Meleagris gallopavo, traced from photographs by MPT.

Taylor and Wedel (2013a: figure 11). Archosaur cervical vertebrae in posterior view, Showing muscle attachment points in phylogenetic context. Blue arrows indicate epaxial muscles attaching to neural spines, red arrows indicate epaxial muscles attaching to epipophyses, and green arrows indicate hypaxial muscles attaching to cervical ribs. While hypaxial musculature anchors consistently on the cervical ribs, the principle epaxial muscle migrate from the neural spine in crocodilians to the epipophyses in non-avial theropods and modern birds, with either or both sets of muscles being significant in sauropods. 1, fifth cervical vertebra of Alligator mississippiensis, MCZ 81457, traced from 3D scans by Leon Claessens, courtesy of MCZ. Epipophyses are absent. 2, eighth cervical vertebra of Giraffatitan brancai paralectotype HMN SII, traced from Janensch (1950, figures 43 and 46). 3, eleventh cervical vertebra of Camarasaurus supremus, reconstruction within AMNH 5761/X, “cervical series I”, modified from Osborn and Mook (1921, plate LXVII). 4, fifth cervical vertebra of the abelisaurid theropod Majungasaurus crenatissimus,UA 8678, traced from O’Connor (2007, figures 8 and 20). 5, seventh cervical vertebra of a turkey, Meleagris gallopavo, traced from photographs by MPT.

In this figure from the 2013 paper, the rightmost images show cervical vertebrae of Majungasaurus (an abelisaurid theropod) and a turkey, both in posterior view. The red arrows indicate epaxial musculature pulling on the epipophyses. They are particularly prominent in Majungasaurus, rising almost a full centrum’s height above the postzygapophyseal facets.

The epipophyses are very prominent in the anterior cervicals of Tyrannosaurus, but much less so in its posterior cervicals — presumably because its flesh-tearing moves involved pulling upwards more strongly on the anterior part of the neck. Here’s a photo of the AMNH mount, from our post T. rex‘s neck is pathetic:

amnh-tyrannosaurus-is-pathetic

You can see something similar in the neck of Allosaurus, and the trend generally seems to be widespread among theropods.

Ornithischians

Note the very prominent epipophyses protruding above the postzygs in the anterior cervicals of this Heterodontosaurus in the AMNH public gallery:

Cast of AMNH 28471, Heterodontosaurus tucki, collected from the Early Jurassic Voisana, Herschel district, South Africa. Anterior to the left.

Cast of AMNH 28471, Heterodontosaurus tucki, collected from the Early Jurassic Voisana, Herschel district, South Africa. Neck in left lateral view.

Here’s the hadrosaur Corythosaurus:

AMNH 5338, Corythosaurus casuarius, from the Campanian of the Red Deer River, Alberta, Canada. Collected by Barnum Brown and P. C. Kaisen, 1914. Cervicals 1-4 in right lateral view.

AMNH 5338, Corythosaurus casuarius, from the Campanian of the Red Deer River, Alberta, Canada. Collected by Barnum Brown and P. C. Kaisen, 1914. Cervicals 1-4 in right lateral view.

The prominent vertebra is C2: note that is has both a modest blade-like neural spine and prominent epipophyses — but that already by C3 the epipophyses are gone. Here is that C2 postzyg/epipophyses complex is close-up, clearly showing anteroposteriorly directed striations on the epipophysis, presumably representing the orientation of the attaching ligaments and muscles:

As previous image: close-up of posterior part of C2.

As previous image: close-up of posterior part of C2.

Here’s a close-up of the neck of the boring ornithopod Tenontosaurus, also in the AMNH gallery. (I’m not sure of the specimen number — if anyone can clarify, please leave a comment).

AMNH ?3554, Tenontosaurus tilletti, cervcials 2-4 in right lateral view.

AMNH ?3554, Tenontosaurus tilletti, cervicals 2-4 in right lateral view.

The interesting thing here is that it its axis (C2) seems to lack epipophyses (unlike C3), and to have a tall blade-like neural spine, as seen in mammals. We don’t really see C2 spines this big in other dinosaurs — compare with the much more modest spine in Corythosaurus, above. The texture of this part of the Tenontosaurus specimen looks suspicious, and I wonder whether that neural spine is a fabrication, created back in the day by AMNH staff who were so used to mammals that they “knew” what a C2 should look like? Anyway, the epipophysis above the postzyg of C3 is very distinct and definitely real bone.

Pterosaurs

Things get much more difficult with pterosaurs, because their cervicals are so fragile and easily crushed (like the rest of their skeleton, to be fair). While it’s easy to find nice, well-preserved ornithischian necks on display, you don’t ever really see anything similar for pterosaurs.

As a result, we have to rely on specimen photographs from collections, or more often on interpretive drawings. Even high-resolution photos, such as the one in Frey and Tischlinger (2012: fig 2) tend not to show the kind of detail we need. Usually, the only usable information comes from drawings made by people who have worked on the specimens.

Here, for example, is Rhamphorhynchus, well known as the most difficult pterosaur to spell, in figure 7 from Bonde and Christiansen’s (2003) paper on its axial pneumaticity:

BondeChristiansen2003-axial-pneumaticity-of-rhamphorhynchus-fig7It’s not the main point of the illustration, but you can make out clear epipophyses extending posteriorly past the postzygapophyseal facets in at least C3 and C5 — in C4, the relevant area is obscured by a rib. (Note that the vertebrae are upside down in this illustration, so you need to be looking towards the bottom of the picture.)

I’m pretty sure I’ve seen a better illustration of Rhamphorhynchus epipophyses, but as I get older my memory for Rhamphorhynchus epipophyses is no longer what it used to be and I can’t remember where. Can anyone help?

But also of interest is the azhdarchid pterosaur Phosphatodraco, here illustrated by Pereda Suberbiola et al. (2003):

Pereda Suberbiola et al. (2003: fig. 3). Phosphatodraco mauritanicus gen. et sp. nov, OCP DEK/GE 111, Late Cretaceous (Maastrichtian), Morocco: (a) cervical five in two fragments, ventral and left lateral views; (b) cervical six in ventrolateral view; (c) cervical seven in ventral view; (d) cervical eight in left lateral view; (e) cervical nine in posterior view; (f) cervical six in anterior view. c, centrum; co, condyle; ct, cotyle; hyp, hypapophysis; nc, neural canal; ns, neural spine; poe, postexapophysis; poz, postzygapophysis; prz, prezygapophysis; su, sulcus; tp, transverse process.

Pereda Suberbiola et al. (2003: fig. 3). Phosphatodraco mauritanicus gen. et sp. nov, OCP DEK/GE 111, Late Cretaceous (Maastrichtian), Morocco: (a) cervical five in two fragments, ventral and left lateral views; (b) cervical six in ventrolateral view; (c) cervical seven in ventral view; (d) cervical eight in left lateral view; (e) cervical nine in posterior view; (f) cervical six in anterior view. c, centrum; co, condyle; ct, cotyle; hyp, hypapophysis; nc, neural canal; ns, neural spine; poe, postexapophysis; poz, postzygapophysis; prz, prezygapophysis; su, sulcus; tp, transverse process.

The cervicals of Phosphatodraco seem to have no epipophyses. So they were not ubiquitous in pterosaurs.

What does it all mean? This post has become a bit of a monster already so I’ll save the conclusion for another time. Stay tuned for more hot epipophyseal action!

References

  • Bonde, Niels and Per Christiansen. 2003. The detailed anatomy of Rhamphorhynchus: axial pneumaticity and its implications. pp 217-232 in: E. Buffetaut and J-M Mazin (eds), Evolution and Palaeobiology of Pterosaurs. Geological Society, London, Special Publications 217. doi:10.1144/GSL.SP.2003.217.01.13
  • Frey Eberhard and Helmut Tischlinger. 2012. The Late Jurassic Pterosaur Rhamphorhynchus, a Frequent Victim of the Ganoid Fish Aspidorhynchus? PLoS ONE 7(3):e31945. doi:10.1371/journal.pone.0031945
  • Janensch, Werner. 1950. Die Wirbelsaule von Brachiosaurus brancai. Palaeontographica, Supplement 7 3:27-93.
  • O’Connor Patrick M. 2007. The postcranial axial skeleton of Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. pp 127-162 in: S. D. Sampson., D. W. Krause (eds), Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. Society of Vertebrate Paleontology Memoir 8.
  • Osborn, Henry F., and Charles C. Mook. 1921. Camarasaurus, Amphicoelias and other sauropods of Cope. Memoirs of the American Museum of Natural History, New Series 3:247-387.
  • Pereda Suberbiola, Xabier, Nathalie Bardet, Stéphane Jouve, Mohamed Iarochène, Baadi Bouya and Mbarek Amaghzaz. 2003. A new azhdarchid pterosaur from the Late Cretaceous phosphates of Morocco. pp 79-90 in: E. Buffetaut and J-M Mazin (eds), Evolution and Palaeobiology of Pterosaurs. Geological Society, London, Special Publications 217. doi:10.1144/GSL.SP.2003.217.01.08
  • Taylor, Michael P., and Mathew J. Wedel. 2013. Why sauropods had long necks; and why giraffes have short necks. PeerJ 1:e36 doi:10.7717/peerj.36
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