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

2010; Geological Society of London; Volume: 343; Issue: 1 Linguagem: Inglês

10.1144/sp343.13

2041-4927

Darren Naish,

Geological and Geochemical Analysis

Abstract Saurischian dinosaurs were pneumatic animals. The presence of invasive skeletal foramina 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 dinosaur fossils from the English Lower Cretaceous Wealden Supergroup led Richard Owen and Harry Seeley to note the pneumatic, bird-like features 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 altispinax from the Hastings Beds Group (at the time referred to Megalosaurus ), 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 Ornithopsis hulkei . Contrary to what is often stated, Seeley did not identify Ornithopsis as a pterosaur, but as an animal that might ‘bridge over’ the gap between birds and pterosaurs, 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 Wessex Formation 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 vertebrae (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.