If you’ve been keeping an eye on the newswires you’ll have seen that a very exciting new theropod dinosaur was described about a week ago now: Aerosteon riocoloradensis Sereno et al., 2008, an allosaurid allosauroid from the Santonian Anacleto Formation of Mendoza Province, Argentina. Hooray again for open-access publishing: Sereno et al. (2008) is published in PLoS ONE, and as such is 100%, no-holds-barred, open-access for the whole world (Fig. 16 from Sereno et al. (2008) shown here]. There is no question that Aerosteon is a neat animal and a very significant discovery. We have here a non-avian theropod – one positioned right down at the base of the tetanuran radiation to boot – that doesn’t just have the vertebral pneumaticity that is widespread and normal for saurischian dinosaurs, it also has a pneumatic furcula and ilium and even – shock horror – pneumatic gastralia…
I can understand that, to those not involved in primary research on dinosaurs (and not about to go and suddenly read up on several decades of primary literature), this research might look as innovative, ground-breaking and novel as implied. Indeed, some articles in the blogosphere make it look as if this is the first thing that anyone has ever written on skeletal pneumaticity in dinosaurs. However, those of us involved in research on post-cranial pneumaticity in dinosaurs are not entirely happy with the paper, for two reasons.
Firstly, whereas other people who have recently published on post-cranial pneumaticity have argued that pneumatisation of the posterior part of the vertebral column indicates the presence of abdominal air sacs like those seen in birds (e.g., Britt 1997, Wedel 2003a, b, 2005, 2007, O’Connor & Claessens 2005, O’Connor 2007), Sereno et al. (2008) cite work on ostriches to promote the idea that cervical air sacs were responsible for pneumatising the entire vertebral column, arguing that ‘paraxial cervical air sacs extended posteriorly along the [vertebral] column’ (p. 3). This is really odd, because comprehensive and compelling research on extant birds by O’Connor & Claessens (2005) showed that this is, so far as we can tell, never the case: at most, cervical air sacs extend (in the skeleton) only as far back as the mid-dorsals, and never further. Furthermore, the work on ostriches that Sereno et al. (2008) cite emphatically does not support the model they promote. Could non-avian saurischians have been different from birds? That’s not impossible, but it would require a special solution when one is not needed. For a very comprehensive review and further discussion please see Matt Wedel’s article at SV-POW! In total contrast to what Sereno et al. (2008) state, we can be very confident that bird-like abdominal air sacs were present in non-avian saurischians [the non-tetanuran Majungasaurus, reconstructed with abdominal air sacs by O'Connor & Claessens (2005), shown in adjacent image].
Secondly, what also makes this paper odd is that the authors don’t credit other workers where it would be appropriate. Given the very careful and extensive work done on extant birds by O’Connor and Claessens (2005), for example, they are under-cited and even discussed by Sereno et al. (2008) as having presented an alternative, erroneous model. And where Sereno et al. (2008) mention an idea that is not novel to their study, they fail to give credit where it’s due. For example, they note that a ‘new basal theropod close to Eoraptor‘ possesses pneumatic cavities of some sort (they consistently use the problematic, ambiguous term ‘pleurocoel’) in its mid-cervical vertebrae: an observation which suggests that the air sac system evolved right down at the base of Saurischia. The presence of a new basal saurischian (as you may know, Eoraptor may not really be a theropod, but might instead be outside of a theropod + sauropodomorph clade within Saurischia) with pneumatic cavities would indeed be neat, but the observation made by Sereno et al. (2008) is exactly the same as that made previously by Britt (1997), O’Connor (2006) and Wedel (2006, 2007). Wedel (2006, 2007) did not of course have a ‘new basal theropod close to Eoraptor‘ – instead, he used boring old Coelophysis and Theco- – Pantydraco – but I would submit that it was unjust and unfair of Sereno et al. (2008) not to cite him [diagram below, from Wedel (2006), shows position of vertebral pneumatic cavities in juvenile Gallus, Coelophysis and Theco- - Pantydraco].
Aerosteon is neat and significant, and there’s no doubt in my opinion that its description should have appeared in a high-profile, quality publication. But the support of an erroneous model that flatly contradicts everything we know (viz, the idea that cervical air sacs can pneumatise posterior dorsals, sacrals and caudals and that this is more likely than the presence of bird-like abdominal air sacs), and the unfair criticism and non-citation of the work of others have meant that it will be less well-received than it should have been. Please see the SV-POW! articles here and here for a more in-depth look. On the plus side, it provides quite the incentive to push some other in-prep papers up the list in terms of priority.
Refs – -
Britt, B. B. 1997. Postcranial pneumaticity. In Currie, P. J. & Padian, K. (eds). The Encyclopedia of Dinosaurs. Academic Press (San Diego), pp. 590-593.
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.
Sereno, P. C., Martinez, R. N., Wilson, J. A., Varricchio, D. J., Alcober, O. A. & Larsson, H. C. E. 2008. Evidence for avian intrathoracic air sacs in a new predatory dinosaur from Argentina. PLoS ONE 3(9): e3303. doi:10.1371/journal.pone.0003303
- . 2005. Postcranial skeletal pneumaticity in sauropods and its implications for mass estimates. In Wilson, J. A. & Curry-Rogers, K. (eds). The Sauropods: Evolution and Paleobiology. University of California Press (Berkeley), pp. 201-228.