October 28, 2007
Here is another beautiful but (so far) unidentifiable isolated dorsal vertebra from the Wealden Supergroup. Rather than the usual orthogonal views (anterior, posterior, lateral) this is in an oblique view: right anterolateral.
This vertebra is one of two that, together, make up the specimen BMNH R90. For my own convenience I have assigned them lower-case latters so each can be referred to individually. I call this one R90a. R90b is pretty similar, and it seems a reasonable assumption that they are from the same individual.
As with the wonder that is BMNH R2523, I don’t know what R90a is yet. A preliminary cladistic analysis indicates that it is a neosauropod, probably macronarian and most likely somphospondylian, but that is based on very weak resolution and will quite likely change once I’ve added my suite of new dorsal-vertebra characters to the matrix.
October 22, 2007
Welcome to another SV-POW! world first: the first ever outing (to my knowledge) of a photo of BMNH R5333, an articulated set of two-and-a-bit titanosaur caudal vertebrae. These vertebrae come from the famous Wessex Formation of the Isle of Wight: they are from the Lower Cretaceous, and specifically from the Barremian. The specimen is shown here in left lateral view: contrary to what you might expect, the bulbous, convex condyle on these vertebrae is located on the posterior articular surface, while the concave cotyle is located on the anterior articular surface (see Tutorial 2 if you need help with these terms). Vertebrae that have their concave articular faces positioned anteriorly are termed procoelous, and many (but not all) titanosaurs are characterised by procoelous caudal vertebrae. Why titanosaurs had procoelous caudal vertebrae is a good question. Some dinosaur workers have suggested that the ball-in-socket articulations present here might have given their owners a particularly strong or flexible tail that they might have used as a prehensile organ, or as mobile ‘fifth limb’ used when the animals were rearing up to eat from trees.
For those of you that care, BMNH R5333 was figured (but not discussed or mentioned) by Blows (1998): other than that I don’t think it’s ever been covered in the literature. For shame!
October 18, 2007
October 15, 2007
We promised non-presacrals and non-brachiosaurids, so here’s a diplodocid caudal vertebra in right lateral view. Most of the neural spine is blown off. The huge hole in the side of the vert is legit, though. That’s a pneumatic foramen (literally, air hole), through which air-filled tubes connected to the respiratory system entered the bone–just like in birds. More on that later. Mike and I are off to the Society of Vertebrate Paleontology meeting in Austin. Will you get the not-promised but so far always delivered extra post this week? Time alone will tell.
By the way, I see that I stupidly did not include any form of scale bar here. This bone is about the size of a really big toaster. If you dropped it on your foot, you’d never dance again. Not bad, considering it comes from about halfway down the tail…
October 11, 2007
In the last post, Matt promised you non-brachiosaurs, sacrals and caudals. And so I bring you the gift of … brachiosaur dorsals! Feast your eyes, gloat your soul, on the last four presacral vertebrapresacral vertebrae 4-7 of the Brachiosaurus altithorax holotype FMNH P25107. [My mistake -- for some reason, I called these the last four when I originally wrote this post. Now fixed -- Mike, 11 September 2009.]
These bones form part of the first brachiosaurid sauropod ever described. It was initially reported by Elmer S. Riggs in 1901, described and named by him in 1903, and described in more detail, again by Riggs, in 1904.
It’s still one of the best brachiosaurid specimens, consisting of the last seven dorsal vertebrae, sacrum, first two caudals, left coracoid (NOT right as stated by Riggs), right humerus, ilium and femur, and ribs. Sadly no skull elements or cervicals, though.
Here we see the bones in an oblique left anterodorsolateral aspect, with your humble chronicler in the background, measuring something so quickly that motion blur hides his craggy, manly features. That I am in the photo means that Matt must have taken it. It’s one of 122 photos that we took of these dorsals, in a single long, crazy day that, apart from brachiosaur dorsals, was also filled with brachiosaur humeri, giraffe cervicals and Godzilla rolls (sushi). Ah, happy days!
October 8, 2007
This one’s not about the morphology of the vertebrae, but rather their cumulative effect. The subject is the mounted Brachiosaurus outside the Field Museum in Chicago. The picture was taken in July 2005 by me or by Mike; we had two Nikon Coolpix cameras going and just pooled the photos.
We’ll get you some sacrals, caudals, and non-brachiosaurids one of these days. We swear.
October 4, 2007
At the risk of turning this blog into Brachiosaurus brancai 8th Cervical Picture of the Day, here’s a quick tutorial on your basic sauropod vertebral anatomy, using everyone’s favourite cervical vertebra.
This picture shows the same vertebra as was photographed in the very first SV-POW! entry. I’ve composited the figures of this element from Janensch (1950), an exhaustive and lavishly illustrated monograph on the vertebrae and ribs of B. brancai. Parts of this vertebra’s right-hand side are missing, as is apparent in the anterior and posterior views, but most of it is excellently preserved.
First things first: directions. In standard anatomical descriptions of dinosaurs, the direction towards the front is called anterior, and towards the back is posterior — so an anterior view (such as the top left part of this picture) is looking at the front of the vertebra. Upwards is dorsal, downwards is ventral. Sticking out sideways is lateral, and towards the midline is medial. These directions can be combined into single words that describe oblique directions such as anteroventral, posterolateral and anteroventromedial. (Some poor misguided souls use “cranial” and “caudal” in place of “anterior” and “posterior”, but we’ll have none of that here.)
The main body of the vertebra, the roughly cylindrical part, is called the centrum. At the front of the centrum in sauropod cervicals and most dorsals is a ball which fits into a corresponding socket at the back of the preceding one. The ball is called a condyle, the socket is called a cotyle.
Dorsal to the centrum is the neural arch, which is surmounted by the neural spine. A hollow passageway runs through the neural arch from front to back: this houses the spinal cord, and is called the neural canal. (You can’t really see it in the pictures above; you can make it out much more clearly in the BMNH R2523 photos, anterior and posterior.)
Two processes (which just means pointy bits) project laterally from each side of the vertebra: in cervicals they mostly hang downwards a bit, i.e. they project ventrolaterally. (It is a bit of a mystery to me why we say “project ventrolaterally” in scientific writing instead of “hang down”, but there it is.) The dorsal pair of processes are the diapophyses (singular diapophysis, pronounced dye-a-POFF-a-siss). The ventral pair are the parapophyses. They are the articulation points for the ribs. In cervical vertebrae, the ribs are often fused to the processes that support them; in dorsal vertebrae they are free, attached only by soft tissue. (In the pictured specimen, the ribs are broken off very close to their point of origin. In life, they would have projected backwards as thin cylinders a couple of meters long.)
As you see, the diapophysis, parapophysis and fused cervical rib form a loop lateral to the centrum. This loop doesn’t really have a name — it’s called the ansa costro-transversaria in birds, but very few palaeontologists use avian anatomical nomenclature for sauropods. So we three just call it the “cervical rib loop”.
Finally (for now), we have the zygapophyses. There are two pairs of these: prezygapophyses at the front, and postzygapophyses at a location that I will not insult your intelligence by stating. When vertebrae are strung together in a line, their zygs articulate, but they can slide past each other to a limited degree, allowing some flexibility. How much flexibility is a matter of some debate which we may revisit in another post. The facets of the prezygs always face anteromedially (that’s upwards and inwards, remember?) and the postzygs ventrolaterally, although their precise orientation varies along the spinal column.
That it for now. Coming soon in subsequent tutorials: fossae and foramina; laminae; variation along the column; and much, much more. Remember to tell all your friends that this is where the party is.