Pleurocoelus: the birth of excellence
April 24, 2008
Othniel Charles Marsh, who was always careful to base all of his hundreds of new taxa on the best, most diagnostic material available (Alert: Sarcasm detected!), named Pleurocoelus nanus based on a handful of junenile sauropod vertebrae centra from the Arundel clays of Maryland (Marsh 1888). Here’s the dorsal. As you can see, it is loaded with unique features like big pneumatic fossae, which at the time were only known in all other sauropods (we have since found some with less pneumaticity in the dorsals, or none at all), and the absence of a neural arch, which is shared with any sufficiently immature vertebrate.
Here’s a cervical, which was not figured by Marsh (1888). These views are after Lull (1911:pl. 15), as modified by Wedel (2003:fig. 10); pfs stands for pneumatic fossa.
And a sacral, again from Marsh (1888).
To be fair, the criteria for “diagnosably distinct” in the 1880s were different than they are now. Wilson and Upchurch (2003) addressed this in their revision of Titanosaurus: as we find and describe more fossil taxa, characters that originally diagnosed small taxonomic groups (like species and genera) are often found to be more broadly distributed. For example, the original diagnosis of Titanosaurus ended up applying to almost everybody in the clade Titanosauria. It is conceivable that in the future we will discover an entire clade of xenoposeidonids with identical weird dorsals and all of their diagnostic characters elsewhere in the skeleton, and the longish list of weird characters that diagnose Xenoposeidon will turn out to be present in all xenoposeidonids. There’s not much we can do about this, other than to keep working, revisit old diagnoses from time to time and see if they need updating, and generally be nice about it.
I am cool with not being nice about Pleurocoelus, though, because of what happened later. But that’s a story for another post.
Note: In 2005 Carpenter and Tidwell sunk Pleurocoelus into Astrodon, which is totally cool by me, and which makes Astrodon the correct name for the poorly-known Arundel titanosauriform, just like Apatosaurus is the correct name for the Morrison diplodocine that is built like a brick outhouse. But in this series I am Telling a Tale about the Days of Yore, past tense, pre-2005, so I’m using Pleurocoelus.
References
- Carpenter, K., and Tidwell, V. 2005. Reassessment of the Early Cretaceous sauropod Astrodon johnsoni Leidy 1865 (Titanosauriformes). Pp. 78-114 in. Tidwell, V., and Carpenter, K. (ed.) Thunder-lizards: The Sauropodomorph Dinosaurs. Indiana University Press, Bloomington.
- Lull, R.S. 1911. Systematic paleontology of the Lower Cretaceous deposits of Maryland: Vertebrata. Lower Cretaceous Volume, Maryland Geological Survey, 183–211.
- Marsh, O.C. 1888. Notice of a new genus of Sauropoda and other new dinosaurs from the Potomac Formation. American Journal of Science, 3rd Series 35:89-94.
- Wedel, M.J. 2003. The evolution of vertebral pneumaticity in sauropod dinosaurs. Journal of Vertebrate Paleontology 23(2):344-357.
- Wilson, J.A., and Upchurch, P. 2003. A revision of Titanosaurus (Dinosauria – Sauropoda), the first ‘Gondwanan’ dinosaur genus. Journal of Systematic Palaeontology 1:125–160.
Sauropod Vertebra Picture of the Week 
April 24, 2008 at 10:11 pm
> I am cool with not being nice about Pleurocoelus…
I am, too, because, you know, he’s dead, right?
April 24, 2008 at 11:53 pm
Dead and synonymized, baby. It couldn’t have happened to a more deserving taxon.
April 25, 2008 at 12:33 pm
Hey, don’t forget: Astrodon johnsoni is Maryland’s official State Dinosaur!
April 25, 2008 at 10:35 pm
I meant Marsh. I suppose we could synonymize him, too, but with what?
April 27, 2008 at 3:33 am
I meant Marsh. I suppose we could synonymize him, too, but with what?
Let’s see. Prolific 19th-century American palaeontologist; described hundreds of species, including many important dinosaurs; spent inherited wealth on bitter fossil-hunting rivalry… He’s not diagnosably different from Cope!
But he was nine years older, so he gets to keep his name. Still, I’m pretty sure synonymizing those two falls under .
April 27, 2008 at 1:27 pm
>I meant Marsh.
LOL!
>He’s not diagnosably different from Cope!
I saw that coming!
>Still, I’m pretty sure synonymizing those two falls under not being nice.
I have wondered before, did the Cope/Marsh rivalry actually benefit palaeontology, by getting a lot more material (competitively) out where it could be given attention? Or was their feud destructive (sometimes literally, I have heard)? Were they each individually more productive through rivalry, or did the quality of their respective work suffer thereby?
Such personal agendas and individual ambition (and the results thereof) live on as a hot topic in the field of cold old bones, it seems… mentioning no aetosaurs by name, but…
May 24, 2008 at 4:13 am
I am eager to remark that there is ever so not slight of a problem with referring a poorly based taxon to another poorly based taxon, Pleurocoelus nanus to Astrodon pusillus. The later is based on teeth, and only by a stretch of imagination and constriction of likelihood of species diversity in a quarry can one then project that another taxon belongs to that taxon, instead. This sounds like lumping for lumping’s sake. I think the best thing to have done was list both as nomina dubia and just shelve the taxa for the future.
May 24, 2008 at 4:09 pm
(I assume you mean Astrodon johnstoni.)
Actually, I agree that this was a poor synonymisation. Since Pleurocoelus was based on at least somewhat diagnostic bones, that would have been a better name to retain. Synonymising it with Astrodon is rather like synonymising Cetiosaurus with Cardiodon.