Tutorial 4b: Saurischian vertebral laminae and fossae redux, by Adam Marsh
April 17, 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]
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