A very inflated opinion of Tawa

Having grabbed a few minutes to go through the Tawa paper and then finding time to put pen to paper (or in these times, fingers to keyboard) there was one thing I wanted to raise about this new dinosaur. (For those who have missed out, this not-feathered theropod was named and described this week by Sterling Nesbitt and his team and is one of the earliest known theropod dinosaurs).

The thing that interested me was the evidence for pneumatisation of parts of the skeleton (hence the awful pun in the title of this post). Those who keep up with the excellent SV-POW (or even the occasional comments on here on the subject) will know that a variety of archosaurs have (or rather had in the case of the extinct ones) extensions of the lungs called air sacs that sat alongside or invaded various bones of the skeleton. Of obvious note are the birds, pterosaurs and sauropods, but actually most theropods show at least some pneumaticy (though some, like Areosteon, more than others).

The relevant point here is that although there is some evidence to suggest that all archosaurs had at least some minor pneumaticy early on in their evolution, there remains the strong possibility that the pterosaurs, sauropods and theropods all gained their pneumaticy independently. The fossil evidence is rather ambivalent. While the idea that theropods and saruopods are very closely related is hardly troubled by the possibility that they did not inherit pneumatic bones from their saurischian ancestors, it does seem a little odd and of course causes a few problems for the ‘pterosaurs-as-ornithodirans’ idea.

Happily, while not exactly solving this, Tawa does provide some new information here. In addition to being an especially basal theropod, Tawa does have pleurocoels on some of its vertebrae – they are pneumatic (and there are pneumatic invasions in parts of the skull too). The new information that Tawa brings to the table also appears to help resolve some phylogenetic questions about early theropods and other saurischians, and another early and pneumatic theropod, Chindesaurus, can now be positioned with more confidence.

Between the two this provides quite a high level of confidence that pneumaticy was around at least in the very earliest theropods and thus closes the gap between the later pneumatic theropods and the sauropods and pterosaurs. In other words while there is still no perfect continuum of pneumatic taxa between the groups, the gap has been shrunk with this new find.

Share this Post

9 Responses to “A very inflated opinion of Tawa”


  1. 1 220mya 15/12/2009 at 2:54 pm

    Thanks for the kind words! Hopefully as we work on the full description we can describe more detail about the cranial and postcranial pneumaticity in Tawa.

    • 2 David Hone 15/12/2009 at 4:54 pm

      Hi Randy, no problems, sorry it took a few days to get something out there, though with the volume of media coverage, I doubt that’s an issue. Keep up the good work!

      • 3 Roger Close 15/12/2009 at 7:19 pm

        Darren told me off for referring to lateral excavations as pleurocoels… or am I getting confused?

  2. 4 Mickey Mortimer 16/12/2009 at 4:17 pm

    “Between the two this provides quite a high level of confidence that pneumaticy was around at least in the very earliest theropods and thus closes the gap between the later pneumatic theropods and the sauropods and pterosaurs. In other words while there is still no perfect continuum of pneumatic taxa between the groups, the gap has been shrunk with this new find.”

    But before we already had the basalmost recognized theropods having pleurocoels (coelophysoids) or not (Eoraptor and herrerasaurids), depending on the preferred phylogeny. If anything, the strengthening of Eoraptor and herrerasaurids as theropods means Theropoda is less likely to have had pleurocoels ancestrally. Tawa drops out right below coelophysoids and is more derived than Eoraptor or herrerasaurids, so doesn’t tell us anything new about the distribution of pleurocoels. The recognition of pleurocoels in Chindesaurus might, if it’s a herrerasaurid. But only one step moves it sister to Tawa and more derived theropods, in which case the pleurocoels are unsurprising. Sereno (2007) already described a promaxillary fenestra in Herrerasaurus, so Tawa’s cranial pneumaticity doesn’t extend that any further either.

    • 5 David Hone 16/12/2009 at 8:33 pm

      “The recognition of pleurocoels in Chindesaurus might, if it’s a herrerasaurid.”

      But since I’m reporting on the new paper and it’s implications / interpretations then as you note, this is potentially significant. Thus, the general point I was trying to raise is (in the context of this paper) accurate. i.e. based on their phylogeny and interpretations of the specimen, then there is an increase in support for the idea of pneumaticy being a primitive character for the group. This is just a quick review of one aspect of someone else’s work and I’m largely paraphrasing and rehashing their words (well I hope so, that Randy didn’t complain so I assume it’s about right).

  3. 6 Mike Taylor 23/12/2009 at 8:17 pm

    Roger: on the use of the term “pleurocoel”, Taylor and Naish (2007:1548) wrote:

    The term ‘pleurocoel’ has been widely used to refer to the lateral excavations in the centra of sauropods and other saurischian dinosaurs. However, the blanket use of this term obscures the morphological diversity of these cavities, which varies considerably between taxa, encompassing everything from broad, shallow fossae to small, deep foramina; and some taxa have both of these. Furthermore, the term has been used inconsistently in the literature, so that characters such as ‘pleurocoels present’ in cladistic analyses are difficult to interpret. For example, in the analysis of Wilson (2002), character 78 is defined as ‘Presacral centra, pneumatopores (pleurocoels): absent (0); present (1)’ (Wilson 2002, p. 261), and Barapasaurus Jain, Kutty and Roy-Chowdhury, 1975 is scored as 0 (‘pleurocoels absent’). While Barapasaurus does indeed lack pneumatic foramina, it has shallow lateral fossae (Jain et al. 1979, pls 101­102), a feature that is not conveyed by the traditional terminology. Accordingly, we recommend that the ambiguous term ‘pleurocoel’ (and Wilson’s equivalent ‘pneumatopore’) be deprecated in favour of the more explicit alternatives ‘lateral fossa’ and ‘lateral foramen’ (Britt 1993, 1997; Wedel et al. 2000b; Wedel 2003, 2005).

    Seems like a sound policy to me.

    • 7 David Hone 24/12/2009 at 9:16 am

      Thanks for picking this up Mike, I forgot to reply to Roger’s point! And yes, I was being a bit sneaky by using a blanket term as I hadn’t gone through the Tawa paper with the detail to pick out quite what was pneumatic in what way. But yes, for the record, I agree entirely with the points raised.


  1. 1 The Archosaur Musings 2009 Awards « Dave Hone’s Archosaur Musings Trackback on 31/12/2009 at 9:04 am
  2. 2 Übergangsfossilien | kěrěng Trackback on 16/12/2012 at 4:08 pm
Comments are currently closed.



@Dave_Hone on Twitter

Enter your email address to follow this blog and receive notifications of new posts by email.

Join 453 other followers


%d bloggers like this: