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Pneumaticity, the early years: Wealden Supergroup and the hypothesis of saurischian pneumaticity

Darren Naish

Geological Society, London, Special Publications 2010; v. 343; p. 229-236 doi:10.1144/SP343.13

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© 2010 Geological Society of London Pneumaticity, the early years: Wealden Supergroup dinosaurs and the hypothesis of saurischian pneumaticity

DARREN NAISH School of Earth & Environmental Sciences, Burnaby Building, Burnaby Road, University of Portsmouth, Portsmouth PO1 3QL, UK (e-mail: @gmail.com)

Abstract: Saurischian dinosaurs were pneumatic . The presence of invasive skeletal for- amina leading to large internal chambers within the skeleton strongly indicate the presence of avian-style skeletal pneumaticity of the skeleton in sauropodomorphs and non-avian theropods. While the hypothesis of skeletal pneumaticity has undergone a renaissance in recent years, it was initially promoted during the late 1800s after from the English Lower Cretac- eous Wealden Supergroup led and Harry Seeley to note the pneumatic, -like fea- tures of the vertebrae they described (Hermann von Meyer had also briefly alluded to skeletal pneumaticity in dinosaurs during the 1830s). In describing the theropod Becklespinax from the Hastings Beds (at the time referred to ), Richard Owen proposed that the laminae on the neural arch served to house ‘parts of the lungs’. He evidently imagined Becklespinax to exhibit avian-style post-cranial skeletal pneumaticity. In 1870 Harry Seeley described two sauropod vertebrae from the Wealden Supergroup, naming them hulkei. Contrary to what is often stated, Seeley did not identify Ornithopsis as a , but as an that might ‘bridge over’ the gap between and , while at the same time having some affinity with dinosaurs. The lateral foramina and internal bony cavities of one of these specimens were regarded by Seeley as allowing ‘the prolongation of the peculiarly avian respiratory system into the bones’, and he emphasized ‘the lightest and airiest plan’ of the specimen. In 1876 Owen described the sauropod Chondrosteosaurus gigas. While regarding the lateral fossae as probably having ‘lodged a saccular process of the lung’, Owen now took the opportunity to attack Seeley’s claims of pneumaticity in Ornithopsis, arguing that the internal cavities in Chondrosteosaurus ‘were occupied in the living reptile by unossified cartilage, or chondrine’. The name Chondrosteosaurus gigas (‘giant cartilage and bone lizard’) also looks like a direct assault on Seeley’s proposal of a pneumatic vertebral interior. Owen’s actions seem odd given that he was familiar with the internal morphology of avian ver- tebrae (which are often strikingly similar to those of sauropods). However, both authors have proved insighful in correctly identifying skeletal pneumaticity during this early phase of dinosaur research. A thorough historical review of early ideas on dinosaurian pneumaticity is still required.

In terms of its significance for early dinosaur discov- unnamed) tetanuran theropod of uncertain affinities eries, the Lower Wealden Supergroup of (Benson et al. 2009). southern must rank as one of the most The term ‘Wealden’ refers to a series of non- important geological units. It yielded Mantell’s marine mudstones, sandstones and other strata that original material during the 1820s, the were deposited in two sub-basins located in what armoured dinosaur armatus during is now SE England: the sub-basin of the the 1830s, the earliest sauropod discoveries during English mainland; and the Wessex sub-basin of the 1840s, and what proved to be a pivotal form in the and Dorset (Martill & Naish early ideas on the evolutionary relationship 2001; Radley 2004, 2006a, b). While the strata of between dinosaurs and birds, ,in both the Weald and Wessex sub-basins were pre- 1869. Despite the fact that Wealden exposures viously referred to as ‘the ’, they have been well explored and extensively studied are now known as the Wealden Supergroup since the early 1800s, they continue to yield new (Fig. 1). Within the Weald sub-basin, the oldest dinosaurs, with recently described taxa including unit is the – Hastings Beds the spinosauroid walkeri (Charig & Group. Younger than the Hastings Beds Group, Milner 1986), the ankylosaur Polacanthus rudg- but also occurring within the Weald sub-basin, is wickensis (Blows 1996), the allosauroid the Group: this unit is mostly Hauteri- salerii (Hutt et al. 1996), the basal tyrannosauroid vian and , but might extend into the Eotyrannus lengi (Hutt et al. 2001), the extremely as well (Allen & Wimbledon 1991). unusual neosauropod Xenoposeidon proneneukos Finally, within the Wessex sub-basin, the Wealden (Taylor & Naish 2007) and a large (as yet Group (sensu stricto) is mostly Barremian and

From:Moody, R. T. J., Buffetaut, E., Naish,D.&Martill, D. M. (eds) Dinosaurs and Other Extinct Saurians: A Historical Perspective. Geological Society, London, Special Publications, 343, 229–236. DOI: 10.1144/SP343.13 0305-8719/10/$15.00 # The Geological Society of London 2010. 230 D. NAISH

phylogeny and function of pneumaticity, there are indications that its presence may correlate not only with pulmonary structure and function but also with metabolism and growth rates (Bonde & Chris- tiansen 2003; Wedel 2003b; O’Connor 2006). A thorough review on the history of thoughts about saurischian pneumaticity has yet to appear. Here, I examine the role that Wealden Supergroup dinosaurs had in early ideas on skeletal pneumaticity.

Institutional abbreviations: HASMG, Hastings Museum and Art Gallery, Hastings, UK; NHM UK, Natural History Museum, London, UK (formerly the British Musuem (Natural History)). Fig. 1. Stratigraphic diagram showing the approximate correlations between the Weald sub-basin units of the English mainland and the Wessex sub-basin units of the Isle of Wight and Dorset. Based on Kerth and Hailwood Becklespinax, the ‘first’ pneumatic (1988), Allen and Wimbledon (1991), Martill & Naish theropod (2001) and Radley (2004, 2006a, b). Among the few theropods that are known from the Hastings Beds Group is NHMUK R1828, currently extends into the Aptian (Kerth & Hailwood 1988). It known as Becklespinax altispinax (Paul 1988). Rep- includes the Wessex and Vectis formations, both of resented only by three articulated dorsal vertebrae which crop out on the Isle of Wight. discovered by Samuel Beckles some time prior to While the Wealden Supergroup is often noted as 1855 (Owen 1855), these three vertebrae are all an important unit for discoveries that have shed new that we have of this dinosaur. However, in describ- light on dinosaur diversity, less well appreciated is ing the specimen, Owen (1856) referred to some that dinosaurs from the Wealden have also proved other material (another two vertebrae and two important in terms of shaping our views on dinosaur ribs) that apparently belonged to it but have since palaeobiology. Among the most interesting and been lost. The proximal end of the robust right vexing, and arguably most important, aspect of tibia HASM G.378 from the Hastings Beds Group, dinosaur palaeobiology is the fact that saurischians identified as indet., was suggested (and not ornithischians so far as we know) exhibited by Naish (2003) to perhaps be referable to B. altis- skeletal pneumaticity: a system of air sacs and pneu- pinax. It remains impossible to evaluate this in the matic diverticula were present in at least some of the absence of better B. altispinax remains. vertebrae, with basal forms exhibiting shallow Like many Wealden Supergroup dinosaurs, B. pneumatic fossae on their vertebral centra and altispinax has had a tumultuous nomenclatural derived forms possessing internalized pneumatic history, and I have largely avoided this area here cavities connected to foramina located within the (a full revision of B. altispinax is in preparation). fossae (Britt 1993; Wedel 2003a, b, 2004, 2007; However, Rauhut (2000) argued that Huene (1923) O’Connor 2006). Pterosaurs also exhibited skeletal proposed the generic name Altispinax for NHMUK pneumaticity, raising the possibility that it was R1828, and not for the indeterminate tooth regarded ancestral for ornithodirans and secondarily lost in as the type of Megalosaurus dunkeri by Kuhn ornithischians (Bonde & Christiansen 2003; Butler (1939) and Olshevsky (1991). Rauhut therefore con- et al. 2009). Skeletal pneumaticity has also been cluded that B. altispinax should be referred to as inferred for some basal archosauriforms (Erythrosu- Altispinax altispinax. This can be interpreted as chus africanus) and crocodile-group archosaurs, contradicting key statements in the literature. On which could suggest that it was primitive for naming Altispinax, Huene (1923) included Megalo- crown-group archosaurs or even for a more inclus- saurus dunkeri and M. oweni within the . He ive clade (Gower 2001). However, the bony ver- stated that Altispinax dunkeri ‘is distinguished tebral fossae present in these taxa do not from Megalosaurus by its enormously high neural communicate with internal chambers, and were spines in the dorsal region’ (p. 453), and thus by argued by O’Connor (2006) to resemble structures implication included NHMUK R1828 within A. that, in crocodilians and other extant reptiles, dunkeri. No specimen numbers were mentioned contain adipose tissue and are not pneumatic. nor type species allocated. Huene later referred to While it can be argued that we are still in the early NHMUK R1828 specifically when discussing stages in our understanding of the distribution, Altispinax (Huene 1926a, p. 483) and wrote ‘if it PNEUMATICITY, THE EARLY YEARS 231 were certain that [these] dorsal vertebrae belong to strength of the spines of these anterior dorsal ver- Megalosaurus dunkeri, it would be necessary to tebrae, indicate the great force with which the put it into a distinct genus, for which the name Altis- head and jaws of the Megalosaurus must have pinax, gen. nov., might be reserved’. Obviously it is been used’ (Owen 1855, Tab. XIX caption). not possible to be certain that these vertebrae belong The identification of these Lower Cretaceous to M. dunkeri. Because Huene (1923) did not indi- tall-spined vertebrae as the anterior dorsals of cate a type species for Altispinax, Kuhn (1939) Megalosaurus explains why the Crystal Palace nominated M. dunkeri for this role. Because the Megalosaurus has a shoulder hump: it incorporates type specimen for M. dunkeri is a single indetermi- Owen’s idea that the Becklespinax vertebrae were nate tooth, this therefore becomes the type for anterior dorsal vertebrae, and that they belonged to Altispinax. the same animal as did the remains from the Stones- While Huene (1923, 1926a, b) clearly intended field Slate. The idea that the dorsal vertebrae Altispinax to be attached to NHMUK R1828, his of Becklespinax were anterior dorsals persisted ambiguous wording and the inappropriate decision until relatively recently: in a 1979 painting by of Kuhn (1939) have complicated the matter. In Peter Snowball (included in Charig 1979), the the present work it is accepted that: (1) the name Becklespinax in the near distance has a low sail Altispinax shares the fate of M. dunkeri; and (2) over its shoulders, indicating that this is the NHMUK R1828 cannot be referred to this species part of the body where the tall-spined vertebrae and therefore retains Olshevsky’s (1991) name belonged. Becklespinax. However, it is also recognized that Like the vertebrae of many other saurischian Kuhn’s allocation of M. dunkeri as the type dinosaurs, the Becklespinax holotype (NHMUK species for Altispinax was counter to the spirit of R1828) exhibits deep lateral fossae (the infraprezy- the name and the content of the genus favoured by gapophyseal fossa, the infradiapophyseal fossa and Huene (1923, 1926a, b). The name Becklespinax the infrapostzygapophyseal fossa) on the sides of has been widely used in the literature in recent the neural arches (Fig. 2a). In the infradiapophyseal years and is now quite well known. Accordingly, fossa of the second vertebra, what appears to be a it would be unwise to replace it; nevertheless, it pneumatic foramen perforates the medial wall of may be appropriate for the International Commis- the fossa, invading the vertebral interior (Fig. 2b). sion on Zoological Nomenclature (ICZN to be peti- It is possible that this is a genuine foramen and tioned in future regarding this issue. The affinities of that others were present in the other fossae but are B. altispinax remain uncertain beyond : currently obscured by matrix. However, the ragged Britt’s (1993) suggestion that a close affinity with edges of the foramen raise the possibility that it is is evident are rejected, as some of the result of breakage (M. Wedel pers. comm. the characters he used to support this proposal are 2008). While it is well known today that vertebral either not present in NHMUK R1828 (e.g. small fossae and foramina demonstrate skeletal pneumati- pneumatic paraphophyses borne on pedicles) or city, this was not appreciated when Owen was are more widely distributed within (e.g. writing about Becklespinax during the 1850s. Rea- elongate neural spines). Nevertheless, B. altispinax lizing that these fossae were probably pneumatic should be regarded as a valid, diagnosable taxon, as they are in birds, Owen wrote of Megalosaurus possessing elongate neural spines (more than four that ‘Three deep depressions, probably receiving times taller than the articular surface of the centrum) parts of the lungs in the living animal, divide these in which the apices are robust and mediolaterally lamelliform butresses from each other’ (Owen thick. 1856, p. 5). His ‘lamelliform butresses’ correspond Owen (1855, 1856) assumed that the Becklespi- to what we today call laminae. Britt (1993) ident- nax vertebrae belonged to the only large theropod ified this as the very first reference to pneumaticity that had been named from Britain at the time, Mega- in any Mesozoic dinosaur, making Becklespinax losaurus, and he also misidentified the vertebrae the first non-avian dinosaur for which pneumaticity as anterior dorsals; a reasonable mistake given was ever suggested. However, O’Connor (2006) how poorly known theropods were at this time. has since noted that von Meyer (1837) alluded to Because the parapophyses are located on the skeletal pneumaticity in saurischians, and thereby neural arches and are close to the diapophyses, predated Owen. they are, in fact, posterior dorsals. Given Owen’s identification of the vertebrae as anterior dorsals, the presence of tall, robust neural spines indicated Ornithopsis and Chondrosteosaurus: the to Owen that – like a mammal with tall neural ‘first’ pneumatic sauropods spines in the shoulder region – Megalosaurus had massive muscles and ligaments supporting its The next milestone in pneumaticity came from head. Owen wrote ‘The extraordinary size and Harry Seeley (1839–1909) in his description of 232 D. NAISH

Fig. 2. NHMUK R1828, the holotype dorsal vertebrae of Becklespinax altispinax (Paul 1988) from the Hastings Beds Group of Battle, East . (a) As illustrated in left lateral view (anterior is to the left) by Owen (1855). (b) Detail of the neural arch fossae of the second vertebra showing (from left to right) infraprezygapophyseal fossa, infradiapophyseal fossa and infrapostzygapophyseal fossa. What appears to be a pneumatic foramen is present in the infradiapophyseal fossa, but this might be the result of breakage. the Wealden Group sauropod Ornithopsis hulkei that O. hulkei represented something entirely new, (Seeley 1870). O. hulkei was named for two dorsal the first member of a ‘new order of animals which vertebrae: NHMUK R2239 from East Sussex and will bridge over something of the interval between NHMUK R28632 from the Wessex Formation of birds and Pterodactyles, and probably manifest the Isle of Wight. The former was later removed some affinity with the Dinosaurs’ (Seeley 1870, from O. hulkei (then becoming the type for p. 280). Bothriospondylus elongatus Owen 1875), leaving Seeley – who has been described as ‘the most NHMUK R28632 alone associated with this name defiant’ of Victorian palaeontologists, of exhibiting and as the lectotype. The strong opisthocoely, ‘anarchic tendencies’ and of being considered large lateral foramina and camellate internal ‘strikingly individualistic’, even in his own day anatomy show that NHMUK R28632 is from a tita- (Desmond 1982) – has been criticized by modern nosauriform (Fig. 3), although it cannot be identified palaeontologists (Pereda Suberbiola & Barrett more precisely than that and whether the specimen 1999; Unwin 2001, 2006), in particular for his is diagnostic is arguable (see Naish & Martill rampant taxonomic splitting and naming of new 2007). It has sometimes been noted that Seeley dinosaur and pterosaur species, and also for his (1870) suggested that these vertebrae belonged to unusual views on how vertebrate groups were an animal ‘of the Pterodactyle kind’, and hence to related to one another. But his conclusions on life- a pterosaur (Wilson 1999; Naish & Martill 2001). styles and comments on palaeobiology were often However, he did not think that these vertebrae not unreasonable in view of current hypotheses, belonged to a giant pterosaur: rather, he thought and in fact often seem far-sighted. PNEUMATICITY, THE EARLY YEARS 233

Fig. 3. NHMUK R28632, the lectotype dorsal vertebra of Ornithopsis hulkei, a titanosauriform sauropod from the Wessex Formation of the Isle of Wight, shown in right lateral and anterior view. The large lateral cavity on the centrum and numerous internal cavities of this specimen led Seeley (1870) to propose skeletal pneumaticity in this animal. From Seeley (1870). The specimen is 223 mm long, and has a maximum height of 230 mm and maximum width of 190 mm.

Seeley (1870) was impressed with the enormous O. hulkei lectotype (NHMUK R28632), it was lateral foramina present in O. hulkei (these were the from the Wessex Formation of the Isle of Wight: main feature that led him to regard O. hulkei as it is based on two cervical vertebrae (NHMUK allied to pterosaurs and birds), and wrote: ‘Seeing R46869 and NHMUK R46870) that Naish & that in living animals these foramina exist for the Martill (2001) regarded as syntypes or as members prolongation of the peculiarly avian respiratory of a type sequence. Today, it is obvious that these system into the bones, and that no other function vertebrae are from sauropods, and their enormous is known for them, we are compelled to infer lateral foramina and camellate internal anatomy for this animal bird-like heart and lungs and (Fig. 4) show that they are from titanosauriforms brain’ (Seeley 1870, p. 280). In describing the (and not from camarasaurs as has been suggested worn anterior condyle of NHMUK R28632, in the past: see Naish & Martill 2001, 2007). Seeley noted the presence within the bone of However, Owen (1876) could not be this confident ‘enormous honeycomb-like cells of irregular and identified the material as ‘Dinosauria (?)’. polygonal form ...divided by exceedingly thin Of these vertebrae, NHMUK R46869 has and compact films of bone’ (Seeley 1870, p. 281). massive lateral fossae housing large lateral foramina Elsewhere in the paper, he referred to the internal (Fig. 4a) and, again, Owen correctly interpreted cavities as ‘air-cells’, and he also wrote of the them as pneumatic, writing: ‘The whole of the Ornithopsis vertebrae (both NHMUK R2239 and side of the centrum is occupied by a deep oblong NHMUK R28632) as ‘being constructed after the depression which, probably, lodged a saccular lightest and airiest plan’. He never explicitly process of the lung’ (Owen 1876, p. 6). Owen had stated it, but it seems reasonable to infer from the second specimen sectioned to reveal its camel- these statements that Seeley imagined the internal late interior (Fig. 4b). This is specimen NHMUK cavities of the centrum to be pneumatic: he was R46870, although its catalogue number is incor- describing what today we call the camellae (that rectly transcribed on one label in the collection as is, the numerous small pneumatic cavities that ‘46780’, a mistake repeated by Naish & Martill occupy the centrum in mamenchisaurs and (2001, p. 197). To date only one half of NHMUK titanosauriforms). In conclusion, Seeley can be con- R46870 has been published (Owen 1876, plate V; gratulated for correctly inferring vertebral pneuma- Naish & Martill 2001, text-fig. 8.4), on both ticity in O. hulkei. occasions as a mirror-image of the actual specimen. Like several of this colleagues, Seeley did not Previously unreported is that both halves of the get on particularly well with Owen. In 1876 Owen specimen were polished, and both are in the described another Wealden sauropod and, like the museum’s collection today. They are similar in 234 D. NAISH

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). Indeed, 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 producing 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 ver- tebral interior: the name Chondrosteosaurus itself Fig. 4. Cervical vertebrae of the titanosauriform almost seeming like a snub to Seeley. sauropod Chondrosteosaurus gigas from the Wessex Despite this one-upmanship, ultimately, both Formation of the Isle of Wight. (a) NHMUK R46869 in Seeley and Owen emerge from this early phase right lateral view and (b) one half of NHMUK R46870 as in research quite well, as both workers still win longitudinally sectioned, showing internal cavities. In citations for having made key early statements on total length, NHMUK R46869 is 330 mm long, and has a saurischian pneumaticity (e.g. Wedel 2003a, b; preserved height of 170 mm and a preserved width of O’Connor 2006). In the decades that followed, both 230 mm; the half of NHMUK R46870 shown here (as a Edward Cope and Othniel Marsh were to make mirror-image of the actual specimen) is 225 mm long. From Owen (1876). statements about the probable pneumaticity of sauropod vertebrae (Cope 1877; Marsh 1877), and workers such as Werner Janensch kept the idea alive during the twentieth century (e.g. Janensch 1947). Today, as CT (computerized tomography)- length (225 mm for the half figured in the literature scanning and other technological advancements and 227 mm for the other half) and similar overall, allow the interiors of bones to be better understood, bar the fact that the unfigured half has a more eroded the pneumatic nature of saurischian vertebrae is external surface and lacks its periosteum. As a unarguable and increasingly well documented. result, the thin and eroded bony boundaries of the camellae are visible on the specimen’s lateral I thank S. Chapman and P. Barrett for access to specimens surface. in the NHM collections and for arranging photography of While Seeley had implied that camellae were NHMUK R1828; J. Radley for discussion of Wealden pneumatic, Owen interpreted those of NHMUK Supergroup ; and R. Benson, M. P. Taylor, R46869 quite differently. He wrote ‘I deem it D. Unwin and M. Wedel for data and discussion on much more probable that the large cancelli pterosaurs, theropods, sauropods and pneumaticity. D. obvious at every fractured surface of this vertebra Schwarz-Wings and D. Martill made helpful comments and suggestions that improved the manuscript. Some of were occupied in the living reptile by unossified car- the text used here previously appeared on the blog site tilage, or chondrine, than by air from the lungs, and SV-POW! (available at http://svpow.wordpress.com/). 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 References recent or , had the power of flight, or belonged Allen Wimbledon to either Pterosauria or Aves’ (Owen 1876, p. 6). To ,P.& , W. A. 1991. Correlation of reflect the presence of ‘chondrine-filled’ spaces in NW European Purbeck–Wealden (nonmarine Lower Cretaceous) as seen from the English type areas. the vertebrae of this animal, Owen coined the new Cretaceous Research, 12, 511–526. name Chondrosteosaurus gigas for NHMUK Benson,R.B.J.,Brusatte, S. L., Hutt,S.&Naish,D. R46869 and R46870, meaning ‘giant cartilage and 2009. A new large basal tetanuran (Dinosauria: Thero- bone lizard’. poda) from the Wessex Formation (Barremian) of the PNEUMATICITY, THE EARLY YEARS 235

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