I have been (still) working on the titanosaur phylogeny you have seen in my last few posts. This time, because inspiration struck, I have decided to go beyond the recent minimal-word, main picture posts of late, and instead I am going to list off and describe basically every discrete (non-obvious) anatomical feature you need to know on, who else, sauropods. Also, thanks to SV-POW for convincing me sauropods are far better than theropods, and thanks to all those long-dead palaeontologists who described such scanty remains as to give me lots of abandoned material to work on without needing to worry about others.
First up, of course (thanks SV-POW) are the vertebrae. Vertebrae are by far the most distinctive feature of sauropods, with their large size, unusual shape, and unique accumulation of laminae (detailed soon). However, as I found out fairly recently, these vertebrae are not as unique as you may think. Many an old sauropod (thanks Owen *sigh*) was described based on a chimaera of both true sauropod and “Iguanodon” caudals, just review the history of Pelorosaurus conybeari/brevis if you don’t believe me. Apparently these vertebrae are only truly different in the internal and discrete features (you can thank me later for posting this, making lives easier). Also, as I seem to be alone in thinking, since days of yore (thanks again Owen *sigh*), mosasaurs also have surprisingly similar caudal vertebrae, likely behind Owen’s interpretation of the relationships of Cetiosaurus. Based on personal observations of the vertebrae, mosasaurs, particularly Plioplatecarpus (seen below), differ mainly in the transverse process not being reduced.
Plioplatecarpus sp. procoelous caudal vertebrae. Image from (and copyright) Northtexasfossils.com
Now, enough with the similarities and such of vertebrae, it is time to go through the most commonly used terms and features in sauropod vertebrae, beginning with the anatomy.
The vertebrae itself is little more than a single link in a chain, like one loop on a string of chain mail, although the ways they connect are different. The most important terms, without any doubt, are the general terms of location, Anterior, Posterior, Dorsal and Ventral. They mean front, back, top and bottom respectively. In caudal vertebrae, the terms Anterior and Posterior are sometimes swapped with Proximal and Distal, respectively, but mean the same thing, so don’t get confused. Without any distinct features present (such as in heavily eroded vertebrae), it can be very hard to tell the difference between anterior and posterior, but in vertebrae, the dorsal side always hold the Neural arch, a small tunnel through which “flows” the spinal chord, the nerve “highway” of our bodies. The main part of the vertebrae is the Centrum, which is a ball-and-socket joint that allows the main flexibility in the spine, while keeping it strong. The anterior face is called the Condyle, and the posterior face is called the Cotyle. In the side of the centrum most often is a depressed, or straight up hole, which is called the Pleurocoel. On the top of the neural arch is the Neural spine, a generally tall, often flattened peak. Anterior to this spine if the Prezygapophysis (pre for anterior), and posterior is the Postzygapophysis (post for posterior). These Zygapophyses are the dorsal links of the vertebrae that help them to keep their shape and strength, and form interlocking connections that, while being flexible, can also be incredibly rigid. On the side of the Neural arch in all but the posterior caudal vertebrae is the Diapophysis, also called the Transverse process. This is the dorsal articulation for ribs, which are pretty important to keep an animal from, you know, having the skin unable to keep the internal organs internal. Ventral to the diapophysis in cervical vertebrae, but anteroventral in dorsal vertebrae, are another rib articulation, called the Parapophysis. On the centrum, there are a few different terms to describe the type of ball-and-socket joint present. When both the Condyle and Cotyle are flat, it is called Amphiplatayan. When both Condyle and Cotyle are concave, this is called Amphicoelous. With a ball in front, the vertebrae it Opisthocoelous. Only found in caudal vertebrae, the Cotyle can have the ball, which is called Procoelous, and in very derived taxa both ends can have a ball, called Biconvex. There is also the state of one face being concave, and the other being flat, alternately called Procoelous/Distoplatyan or Procoelous-Opisthoplatyan (See the first comment here for a discussion of the differences).
Giraffatitan cervical from (and copyright) Janensch (1950), but modified by the great guys at SVPOW. The neural arch (not labelled) spans from the top of the centrum to the base of the neural spine.
Laminae are, in there meaning, small upraised areas present in vertebrae, often, but not always, as ridges. As what I would have once called an extreme layman with regards to laminae, one single realization made me into a master of laminar terms (still dwarfed by true sauropod experts though). This realization was, in a case like the Posterior Centrodiapophyseal laminae (PCDL), the main thing to do is break up the name. In this case, the words strung together are Posterior, Centrum and Diapophysis. From this, we can now tell that the lamina spans from the Centrum to Diapophysis, and it is the posterior one of these lamina (often branching itself from the Posterior centrum; in all cases, with only one lamina to the diapophysis from the centrum, there is no PCDL). This method can be used for all lamina, the key is to know the names for the anatomical features detailed, which is why I go over them above. There are a very large number of laminae in derived taxa, such as Dongyangosaurus, and often these laminae can be used to distinguish taxa.
Dongyangosaurus dorsal vertebrae, from and copyright Lu et al 2008.
There really is a huge number of laminae, which are named based off of
Whitlock (2011) Wilson (1999) Janensch (1950), unless you are looking at Harris (2006), which instead uses bird laminae. Here are the lamina from the above image (the L at the end of each always means laminae, apart from the Pleurocoel [PL]):
- SPDL – Spinodiapophyseal lamina
- SPRL – Spinoprezygapophyseal lamina
- PODL – Postzygodiapophyseal lamina
- SSPDL – Subsidiary spinodiapophyseal lamina
- CPOL – Centropostzygapophyseal lamina
- CPOL1 – Centropostzygapophyseal lamina 1
- CPOL2 – Centropostzygapophyseal lamina 2
- PRDL – Prezygapodiapophyseal lamina
- PPDL – Parapodiapophyseal lamina
- CPRL – Centroprezygapophyseal lamina
- ACPL – Anterior centroparapophyseal lamina
- PCPL- Posterior centroparapophyseal lamina
- SCPL – Subsidiary centroparapophyseal lamina
- PCDL – Posterior centrodiapophyseal lamina
- TPRL – Intraprezygapophyseal lamina
A few of these laminae (CPOL 1 & 2, SSPDL) are relatively rare among taxa, but most of these are found across nearly every sauropod.
The final section of the discrete anatomical features in vertebrae is pneumaticity. Pneumaticity in vertebrae comes in the form of air pockets scattered throughout the inside of the vertebrae. When these pockets are large and cavernous, they are called Camerate, but when they are small and numerous they are called Camellate. Camerate taxa usually have very large, deep, and expansive pleurocoels, with the coel feeding this air pocket from the outside. Camellate vertebrae most often still have this pleurocoel, but in nearly every case it is small and restricted, with the rest of the vertebrae having the “spongy” texture. Often there are small external entrances to these camellae, which are called Fossae, and sometimes even the Pleurocoel can be found within a fossa.
Internal pneumaticity. Tornieria shows camerae, Malawisaurus has camellae in the neural arch only, and Saltasaurus has a camellate centrum. From Wedel & Taylor (2013).
This brings me to (what I think it) the end of this post, which AFAIK covers the main discrete anatomical terms and features you need to know, about Sauropod vertebrae.
- Wedel MJ, Taylor MP (2013) Caudal Pneumaticity and Pneumatic Hiatuses in the Sauropod Dinosaurs Giraffatitan and Apatosaurus. PLoS ONE 8(10): e78213. doi:10.1371/journal.pone.0078213
- Janensch, W. (1950). “The Skeleton Reconstruction of Brachiosaurus brancai.”: 97–103.
- Lu Junchang; Yoichi Azuma; Chen Rongjun; Zheng Wenjie; Jin Xingsheng (2008). “A new titanosauriform sauropod from the early Late Cretaceous of Dongyang, Zhejiang Province”. Acta Geologica Sinica (English Edition) 82 (2): 225–235. doi:10.1111/j.1755-6724.2008.tb00572.x.