Dryosaurus skull

In addition to the mounted skeleton shown yesterday, as usual the Carnegie provided a little extra something. In this case it’s a nearly complete skull of a young Dryosaurus (the label lies in the orbit and it’s facing to the left).

I must confess to knowing little about this ornithischian (also true of many ornithischians I admit) though it helps illustrate one small point. Not that long ago, it was thought that sometime in the Middle to Late Jurassic there was a landbridge from Africa to North America. This was invoked to explain the apparent incredible similarity between the Tendaguru and Morrison faunas. Both had Dryosaurus, and Allosaurus and Brachiosaurus, and both had stegosaurs and diplodocids.

However, better examination of the available material makes the Tendaguru brachiosaur not Brachiosaurus, the allosaur not Allosaurus and the small ornithopod is Dysolotosaurus and not Dryosaurus. In short, there’s no need to invoke a special land-bridge since the two faunas are not identical. Similar sure, with each having representatives of the same families, but that’s hardly surprising – look to the modern world and the two continents feature felids, canids, mustelids, bovids and others and such comparable faunas are quite normal.

12 Responses to “Dryosaurus skull”

  1. 1 220mya 11/01/2012 at 6:33 pm

    I think its important to stress that what’s relevant is not whether these are the same genera, but are they sister taxa phylogenetically, or at least are the placed together in restricted clades? The brachiosaurids and small ornithopods are still thought to be very closely related, and we do have good congeners shared between the Morrison Fm and Portugal.

    • 2 David Hone 11/01/2012 at 6:52 pm

      I do think the original hypothesis had at times been framed as ‘they’re the same so must have been a single continuous fauna’. Even sister taxa could still be part of a continuous fauna (like lions and tigers say), but it’s rather extreme to suggest that a whole continuous populations of numerous genera / species extend from east Africa through to central U.S.A. If most of them aren’t conspecific / congeneric then dramatic (or very unlikely) hypotheses are required to explain this.

    • 3 Mike Taylor 18/01/2012 at 1:13 am

      I don’t expect to see Brachiosaurus and Giraffatitan coming out as sisters when we get an analysis with multiple brachiosaurids. (In my 2009 paper, they were the only brachiosaurs in the analysis.)

  2. 5 Andrew McDonald 11/01/2012 at 8:22 pm

    The phylogenetic analysis of Barrett et al. (2011, Special Papers in Palaeontology) found Dysalotosaurus to be sister taxon to a clade composed of Valdosaurus from the Early Cretaceous of England and Elrhazosaurus from the Early Cretaceous of Niger. Dryosaurus was more basal in Dryosauridae.

  3. 6 ReBecca 13/01/2012 at 6:08 am

    Did that specimen have any note of where it is from?

  4. 8 ReBecca 13/01/2012 at 7:45 am

    No worries. I tried to look it up on their online catalog, but it is not listed. My husband will be out there next week to do some work in collections, so I can have him check it out then. Thanks 🙂

  5. 9 Mike Taylor 18/01/2012 at 2:01 pm

    Why won’t WordPress let me reply to your reply? Oh well …

    “Out of interest Mike, what would you expect to intervene? The archbishop is the obvious candidate for me, anything else?”

    Could be anything. I don’t have any fixed ideas, but Cedarosaurus, Venenosaurus, Sonorasaurus if anyone ever coded it, Sauroposeidon, Paluxysaurus, “true Eucamerotus” … any or all of the above.

    • 10 David Hone 18/01/2012 at 2:08 pm

      It has a fixed number of indents (3 I think) hence the lack of reply-reply options. Just reply to the last thing in the thread and it will pop out indented below the others.

      Sure any of these *could* come bout b/w B. and G., but do you have any specific reasons why? Obviously untested but in your opinion can you see some traits that look like they’d drag say Brachio and Sauroposeidon together at the expense of G.?

      • 11 Mike Taylor 18/01/2012 at 2:17 pm

        No, no specific reasons for favouring any one topology over any other. Just that when you have nine brachiosaurids in the mix, and a huge number of potential sister-group relationships, there is nothing about Brachiosaurus and Giraffatitan that makes me think they are particularly close to each other.

        But this is just speculation. Let’s wait till someone publishes such a study. (I know of two in the works, neither of them by me.)

      • 12 David Hone 18/01/2012 at 2:33 pm

        Fair enough, just curious really. Glad there’s stuff coming though, that is good news.

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