Apatosaurines on the brain right now.
I’ve been thinking about the question raised by Jerry Alpern, a volunteer tour guide at the AMNH, regarding the recent Tschopp et al. (2015) diplodocid phylogeny. Namely, if AMNH 460 is now an indeterminate apatosaurine, pending further study, what should the museum and its docents tell the public about it?
Geez, Apatosaurus, it’s not like we’re married!
I think it’s a genuinely hard problem because scientific and lay perspectives on facts and hypotheses often differ. If I say, “This animal is Apatosaurus“, that’s a fact if I’m talking about YPM 1860, the genoholotype of Apatosaurus ajax; it would continue to be a fact even if Apatosaurus was sunk into another genus (as Brontosaurus was for so long). We might call that specimen something else, but there would always be a footnote pointing out that it was still the holotype of A. ajax, even if the A. part was at least temporarily defunct – the scientific equivalent of a maiden name.* For every other specimen in the world, the statement, “This animal is Apatosaurus” is a hypothesis about relatedness, subject to further revision.
* This is going to sound kinda horrible, but when one partner in a marriage takes the other’s surname, that’s a nomenclatural hypothesis about the future of the relationship.
Things that look fairly solid and unchanging from a distance – specifically, from the perspective of the public – often (always?) turn out to be fairly fuzzy or even arbitrary upon closer inspection. Like what is Apatosaurus (beyond the holotype, I mean) – or indeed, what is a planet.** There is no absolute truth to quest for here, only categories and hypotheses that scientists have made up so that we can have constructive conversations about the crazy spectrum of possibilities that nature presents us. We try to ground those categories and hypotheses in evidence, but there will always be edge cases, and words will always break down if you push them too hard. Those of us who work on the ragged frontier of science tend to be fairly comfortable with these inescapable uncertainties, but I can understand why people might get frustrated when they just want to know what the damned dinosaur is called.
** Triton, the largest body orbiting Neptune, is almost certainly a captured Kuiper Belt object, and it’s bigger than Pluto. Moon or planet? Probably best to say a former dwarf planet currently operating as a satellite of Neptune – but that’s a mouthful (and a mindful, if you stop to think about it), not a short, convenient, easily-digestible label. Any short label is going to omit important information. This is related to the problem of paper title length – below some threshold, making something shorter means making it incomplete.
What I would say
I suppose the short version that is most faithful to the Tschopp et al. results is:
This skeleton (AMNH 460) might be Apatosaurus or Brontosaurus or a third, new thing – scientists aren’t sure yet.
A reasonable follow-up sentence – and an answer to the inevitable “Why not?” – would be:
They have to look at 477 anatomical details for lots of skeletons and weigh all the evidence, and that takes time.
Personally, if I was talking to museum visitors I would lean in conspiratorially and say:
If you want to call it Apatosaurus or Brontosaurus, go ahead – those are both ‘live’ hypotheses, and even the world’s experts on this problem can’t tell you that you’re guessing the wrong way – at least not yet.
And if there was a kid in the group, I’d add:
Maybe you’ll be the one to figure it out!
What would you say?
P.S. I wouldn’t change the signage. It could still turn out to be Apatosaurus, and the Tschopp et al. results do not lend themselves to easy label-ification.
P.P.S. With some modification for taxonomy, all of this applies to the Field Museum diplodocid FMNH P25112 as well.
[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]
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
- Wilson, J. A. 1999. A nomenclature for vertebral laminae in sauropods and other saurischian dinosaurs. Journal of Vertebrate Paleontology 19(4): 639-653. DOI: 10.1080/02724634.1999.10011178
- Wilson, J. A., Michael, D. D., T. Ikejiri, E. M. Moacdieh, and J. A. Whitlock. 2011. A nomenclature for vertebral fossae in sauropods and other saurischian dinosaurs. PLoS One 6(2): e17114. DOI: 10.1371/journal.pone.0017114
- Wilson, J. A. 2012. New vertebral laminae and patterns of serial variation in vertebral laminae of sauropod dinosaurs. Contributions From The Museum of Paleontology, University of Michigan 32(7): 91-110. ISSN 0097-3556
February 13, 2015
According to Rare Historical Photos from the 1860s to the 1960s, this is the iceberg that sank the Titanic:
Clearly this was no iceberg, but a gigantic Apatosaurus vertebra, most of it hidden under water. Here is an artist’s impression:
They get everywhere, don’t they?
February 8, 2015
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:
No ambiguity here: the epipophysis is even labelled.
But we can find epipophyses even outside Archosauriformes. Here, for example, is the the rhynchosaur Mesosuchus:
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:
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):
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:
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) …
… and some much more convincing epipophyses in the better known and more spectacular protorosaur Tanystropheus:
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:
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:
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!
- 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.
February 6, 2015
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.
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?
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.
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?
February 5, 2015
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.
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:
(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:
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:
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:
184.108.40.206. 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?
- Brusatte, Stephen L., Sterling J. Nesbitt, Randall B. Irmis, Richard J. Butler, Michael J. Benton, and Mark A. Norell. 2010. The origin and early radiation of dinosaurs. Earth-Science Reviews 101(1):68-100.
- 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, no. 17. 135 pages.
- Wellnhofer, Peter. 1985. Neue pterosaurier aus der Santana-Formation (Apt) der Chapada Do Araripe, Brasilien. Paläontographica A 187:105-182. [in German]