Sauropod Vertebra Picture of the Week

For the first time in SV-POW! history, a full week has passed between successive posts — well, at least we didn’t actually fail with the “of the week” part, even if it was a close thing. It’s been a busy week, for reasons that will soon be apparent; and for the same reasons, the posting frequency will ramp right up in another week or so.

We usually don’t like to follow one tutorial directly with another, preferring to sweeten the deal by putting out a sheer-beauty-of-sauropod-vertebrae post in between tutorials. But this time, we need to push the tutorial out straight away, because it’s about laminae; and we’re going to be talking a lot about laminae in the next fortnight.

So with that disclaimer, please brace yourself for what even I have to admit is by no means a particularly beautiful picture:

You’ll recognise this picture from Tutorial 2: Basic vertebral anatomy; but this time I’ve highlighted and labelled the laminae in red.

Now let me admit right off the bat that this looks horrible and complicated. When you see the names of the laminae written out in full — the PRDL, for example, is the prezygadipophyseal lamina — it doesn’t help much, either. But this complexity is an illusion: in truth, laminae are not complex structures — they’re just sheets of bone — and the nomenclature that we use for them is not so much complicated as explicit.

One of the nice things about laminae is that they are just about the only anatomical feature that has a single key paper that you can read to learn pretty much everything you need to know. That paper is Jeff Wilson’s 1999 offering A nomenclature for vertebral laminae in sauropods and other saurischian dinosaurs (JVP 19:639-653). Like all Jeff’s publications, it can be freely downloaded from his publications page, [NOTE in 2013: not any more!] so a hat-tip there for open-access publication. (One of these days, an SV-POW! post is going to be an extended rant about the absurd current publication/copyright/access situations … but not today.) Anyway, if you want more details on laminae after reading this post, Wilson 1999 is definitely the place to go — use of his nomenclature is near-universal these days.

So here’s how it works. In tutorial 2, we learned about the “landmarks” on a sauropod vertebra — most of which are shared by the vertebrae of other tetrapods: the centrum, neural arch and neural spine, pre- and postzygapophyses, diapophyses and parapophyses. Laminae are sheets of bone connecting one landmark to another. And each lamina is simply named after the two landmarks that it connects. So suppose you have a lamina connecting the spine to the postzygapophysis: that would be a spinopostzygapophyseal lamina. A lamina connecting the anterior aspect of the parapophysis with the centrum is an anterior centroparaphophyseal lamina.

Wilson’s paper did three important things: it enumerated nineteen of the most common laminae; it standardised what order the landmarks are named in (so it’s a spinopostzygapophyseal lamina, not a postzygapospinal lamina or similar); and it specified standard four-letter abbreviations for each lamina, as in SPOL for the spinopostzygapophyseal lamina and ACPL for anterior centroparapophyseal lamina. You can look these up in Wilson 1999; but if you know what the landmarks are, it’s usually obvious what the four letters stand for. (Actually, Wilson’s abbreviations are composed of lower-case letters, like “spol”; but Matt, Darren and I find it more convenient to use capitals so that it’s easy to form plurals like “SPOLs”.)

As I said, Wilson listed 19 laminae.  There are a few others that occur less often and didn’t get a mention in that paper, such as a ?unique spinoparapophyseal laminae on the 7th dorsal vertebra of the ubiquitous B. brancai type specimen HMN SII. But the picture above only shows nine. That’s because of serial variation. Wilson’s paper figures eight different vertebrae (four cervicals and four dorsals) and it’s apparent as you look at them that different lamina come in and drop out at different points along the sequence. For example, some dorsal vertebrae have a paradiapophyseal lamina that connects the parapophysis with the diapophyis, but you don’t get that in cervicals.

One of the ways we can determine which taxon a sauropod vertebra belongs to is by looking at its laminae.

That’s all for now, I have to go and watch a Harry Potter film with the boys.

UPDATE, September 25, 2011

Wilson (1999) is no longer freely available, and this tutorial is quite a bit less useful without it as a universally available reference, so here are all 19 of the commonly named laminae and their abbreviations.

ACDL – anterior centrodiapophyseal lamina

PCDL – posterior centrodiapophyseal lamina

PRDL – prezygodiapophyseal lamina

SPDL – spinodiapophyseal lamina

PODL – postzygodiapophyseal lamina

PPDL – paradiapophyseal lamina

CPRL – centroprezygapophyseal lamina

SPRL – spinoprezygapophyseal lamina

TPRL – intraprezygapophyseal lamina

CPOL – centropostzygapophyseal lamina

SPOL – spinopostzygapophyseal lamina

Med. SPOL – medial spinopostzygapophyseal lamina

Lat. SPOL – lateral spinopotzygapophyseal lamina

TPOL – interpostzygapophyseal lamina

ACPL – anterior centroparapophyseal lamina

PCPL – posterior centroparapophyseal lamina

PRPL – prezgyoparapophyseal lamina

PRSL – prespinal lamina

POSL – postspinal lamina