Sauropod pneumaticity, the early years
May 19, 2008
In this article I’d like look at something that I’ve just spoken about at a conference: the ‘Dinosaurs – A Historical Perspective’ meeting held in London on May 6th and 7th (my thoughts on the conference can be found here and here). Mike attended too (and, like me, gave a talk), but Matt couldn’t make it. Anyway…
Today, the idea that sauropods (and non-avian theropods) were pneumatic animals is well established and universally accepted (a minority view – promoted by those who insist that birds cannot be dinosaurs – maintains that non-avian dinosaurs were not pneumatic, but I see no indication that the workers concerned know what they’re talking about). Indeed, sauropod pneumaticity has been discussed a lot here at SV-POW! But have people always regarded sauropods as pneumatic? As someone particularly interested both in pneumaticity and in the dinosaurs of the Lower Cretaceous Wealden Supergroup of southern England, the whole ‘Pneumaticity: the Early Years’ story is of special interest to me. I hope you get something out of it too…
Actually, the very first dinosaur (not just sauropod, but dinosaur) identified as exhibiting skeletal pneumaticity is from the Wealden, and it’s a theropod: it’s the large tetanuran Becklespinax altispinax, discovered prior to 1855 in the Hastings Beds Group of East Sussex (the Hastings Beds Group is the oldest unit in the Wealden Supergroup: for more see the Tet Zoo article here). Consisting only of three articulated posterior dorsal vertebrae, Becklespinax exhibits deep fossae on the sides of the neural arches (by now you’ll all be familiar with the names for the different vertebral laminae present in saurischians, but the fossae have names too: in Becklespinax, we’re talking about the infraprezygapophyseal fossa, the infradiapophyseal fossa, and the infrapostzygapophyseal fossa). The key thing is that, in describing these vertebrae, Richard Own (1804-1892) realised that these fossae were probably pneumatic as they are in birds, and in his 1856 article on Megalosaurus (he assumed that the Becklespinax vertebrae belonged to Megalosaurus), he wrote that ‘Three deep depressions, probably receiving parts of the lungs in the living animal, divide these lamelliform butresses from each other’ (Owen 1856, p. 5). His ‘lamelliform butresses’ are what we call laminae. This is the very first reference to pneumaticity in any Mesozoic dinosaur (Britt 1993), so Becklespinax is the first non-avian dinosaur for which pneumaticity was ever suggested.
The next milestone in pneumaticity came from Harry Seeley (1839-1909) in his description of the Wealden sauropod Ornithopsis hulkei (Seeley 1870). O. hulkei was named for two dorsal vertebrae: BMNH R2239 from East Sussex and BMNH R28632 from the Isle of Wight, but the former was later removed from O. hulkei (then becoming the type for Bothriospondylus elongatus), leaving BMNH R28632 alone associated with this name and as the lectotype* [the specimen is shown below, from Seeley 1870]. The strong opisthocoely, large lateral foramina and camellate internal anatomy show that BMNH R28632 is from a titanosauriform (it can’t really be identified more precisely than that and whether it’s diagnostic is arguable: see Naish & Martill 2007. For previous SV-POW! comments on the specimen go here). It’s often noted that Seeley suggested that these vertebrae belonged to an animal ‘of the Pterodactyle kind’. However, he did not think that these vertebrae belonged to a giant pterosaur (as, oops, Naish & Martill (2001) said): rather, he thought that O. hulkei represented something entirely new, the first member of a ‘new order of animals which will bridge over something of the interval between birds and Pterodactyles, and probably manifest some affinity with the Dinosaurs’ (Seeley 1870, p. 280).
* When a species is erected for more than one specimen, the specimens are all called syntypes. When one syntype from a series is later elected to serve as the type specimen for the species, it is called the lectotype.
Seeley – who has been described as ‘the most defiant’ of Victorian palaeontologists, of exhibiting ‘anarchic tendencies’, and of being considered ‘strikingly individualistic’, even in his own day (Desmond 1982) – gets a lot of flack these days, in particular for his rampant taxonomic splitting and naming of new dinosaur and pterosaur species, and also for his unusual views on how vertebrate groups were related to one another. But I often think that his conclusions on lifestyles and comments on palaeobiology are really not unreasonable in view of what we think today, and in fact often seem quite far-sighted.
Here’s where we come back to pneumaticity: Seeley (1870) was very impressed with the enormous lateral foramina present in O. hulkei (these were the main feature which led him to regard O. hulkei as allied to pterosaurs and birds), and he wrote: ‘Seeing that in living animals these foramina exist for the prolongation of the peculiarly avian respiratory system into the bones, and that no other function is known for them, we are compelled to infer for this animal bird-like heart and lungs and brain’ (Seeley 1870, p. 280). In describing the worn condyle of BMNH R28632, Seeley noted the presence within the bone of ‘enormous honeycomb-like cells of irregular polygonal form … divided by exceedingly thin and compact films of bone’ (Seeley 1890, p. 281). Elsewhere in the paper, he referred to the internal cavities as ‘air-cells’, and he also wrote of the Ornithopsis vertebrae (both BMNH R2239 and BMNH R28632) as ‘being constructed after the lightest and airiest plan’. He never explicitly stated it, but I infer from these statements that Seeley imagined the internal cavities of the centrum to be pneumatic: he was describing what today we call the camellae (that is, the numerous small pneumatic cavities that occupy the centrum in mamenchisaurs and titanosauriforms). So, all in all, I say well done Seeley for correcting inferring vertebral pneumaticity in O. hulkei.
Like most Victorian palaeontologists, Seeley did not get on particularly well with the most prolific, most respected and most politically powerful Victorian palaeontologist, Richard Owen [although it’s not really accurate to regard Owen just as a palaeontologist: sure, he did palaeontology, but his contribution to mainstream zoology and anatomy was massive and equally significant, if not more so]. In 1876, Owen described another Wealden sauropod and, like the O. hulkei lectotype (BMNH R28632), it was from the Isle of Wight’s Wessex Formation: it’s based on two cervical vertebrae (BMNH R46869 and BMNH R46870: one is shown below). Today, it is obvious that these vertebrae are from sauropods, and their enormous lateral foramina and camellate internal anatomy show that they’re from titanosauriforms (and not from camarasaurs as has been suggested in the past: see Naish & Martill 2001, 2007). However, Owen couldn’t be this confident that identified the material as ‘Dinosauria (?)’.
The big deal for our story is that these vertebrae have massive lateral fossae housing large lateral foramina, and again Owen correctly interpreted them as pneumatic, writing: ‘The whole of the side of the centrum is occupied by a deep oblong depression which, probably, lodged a saccular process of the lung’ (Owen 1876, p. 6). So far so good. But Owen had one of these two Wessex Formation specimens (BMNH R46870) sectioned, revealing its incredible (and beautiful) interior [it’s the image shown at the very top]. The internal anatomy of this specimen illustrates camellate texture so well that it’s almost becoming a poster-child in talks and articles on sauropod vertebrae. But while, as we just saw, Seeley had implied that camellae were pneumatic, Owen interpreted them quite differently. He wrote ‘I deem it much more probable that the large cancelli obvious at every fractured surface of this vertebra were occupied in the living reptile by unossified cartilage, or chondrine, than by air from the lungs, and consequently have no grounds for inferring that the whale-like Saurian, of which the present vertebrae equals in length the largest one of any Cetacean recent or fossil, had the power of flight, or belonged to either Pterosauria or Aves’ (Owen 1876, p. 6). To reflect the presence of ‘chondrine-filled’ spaces in the vertebrae of this animal, Owen coined for it the new name Chondrosteosaurus gigas, meaning ‘giant cartilage and bone lizard’.
Quite why Owen was happy with pneumatic lateral fossae, but not with pneumaticity within the body of the centrum itself, seems odd, especially when Owen was very familiar with avian anatomy (he specifically referred to the internal anatomy of avian vertebrae in, for example, his 1859 article on pterosaur vertebrae [Owen 1859]). As you can see in Tutorial 3, the internal anatomy of bird and sauropod centra are so similar that it is difficult not to conclude that what applies for one applies for the other. However, it is clear from Owen’s quote given above that, when interpreting C. gigas, he was not just doing an objective description, but also had an axe to grind: he was specifically refuting Seeley’s statements on O. hulkei, hence the rejection of the idea that C. gigas might have been capable of flight, or that it might be allied to pterosaurs or birds. For whatever reason, Owen was also making note of the fact that he disagreed with Seeley’s idea of a pneumatic vertebral interior: the name Chondrosteosaurus itself almost seems like a snub to Seeley.
Despite this one-upmanship, ultimately, both Seeley and Owen come out of this early phase in research pretty well, as both workers still win citations for having made key early statements on saurischian pneumaticity (e.g., Wedel 2003, O’Connor 2006). Edward Cope (1840-1897), who liked Seeley and said nice things about him, was to note during the 1870s that sauropod vertebrae were probably pneumatic, and Othniel Marsh (1831-1899) did likewise. What happened in the field of dinosaur pneumaticity after this? Well, that’s a story for another time: for the time being I will direct you to Wedel (2003).
Britt, B. 1993. Pneumatic Postcranial Bones in Dinosaurs and Other Archosaurs. Unpublished PhD thesis, University of Calgary (Alberta).
Desmond, A. J. 1984. Archetypes and Ancestors: Palaeontology in Victorian London 1850-1875. The University of Chicago Press, Chicago.
Naish, D. & Martill, D. M. 2001. Saurischian dinosaurs 1: Sauropods. In Martill, D. M. & Naish, D. (eds) Dinosaurs of the Isle of Wight. The Palaeontological Association (London), pp. 185-241.
Naish, D. & Martill, D. M. 2007. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia. Journal of the Geological Society, London 164, 493-510.
O’Connor, P. M. 2006. Postcranial pneumaticity: an evaluation of soft-tissue influences on the postcranial skeleton and the reconstruction of pulmonary anatomy in archosaurs. Journal of Morphology 267, 1199-1226.
Owen, R. 1856. Monograph on the fossil Reptilia of the Wealden and Purbeck Formations. Part III. Dinosauria (Megalosaurus). Palaeontographical Society Monographs 9, 1-26.
Owen, R. 1859. On the vertebral characters of the Order Pterosauria, as exexmplified in the genera Pterodactylus (Cuvier) and Dimorphodon (Owen). Philosophical Transactions of the Royal Society of London 149, 161-169.
Owen, R. 1876. Monograph on the fossil Reptilia of the Wealden and Purbeck Formations. Supplement 7. Crocodilia (Poikilopleuron). Dinosauria (Chondrosteosaurus). Palaeontographical Society Monographs 30, 1-7.
Seeley, H. G. 1870. On Ornithopsis, a gigantic animal of the pterodactyle kind from the Wealden. Annals and Magazine of Natural History, Series 4, 5 279-283.