The dromaeosaur pubis – ornithischian saurischians

It would of course be silly to say that bird have anything but a bird-like pelvis, but of course birds descended from the saurischian dinosaurs (the lizard hips) and not the ornithischian (bird hipped) dinosaurs. Birds then and their closest relatives are therefore saurischians with an ornithischian condition. The differences between the pelves of the two groups we have covered before but as with much in evolution, it’s not like birds just popped into place with their pubic bones pointing backwards.

Here then are the pubes of (somewhat inevitably) Sinornithosaurus. While the pelvis of this animal are disarticulated, you should be able to see that the ‘arms’ of the bone while mostly straight, then curve posteriorly such that the spoon shaped ends finish under the ischia (the bones that sits behind the pubes). A more typical saurischian pubis would point forwards to a degree, so we can see that this droamaeosaur pubis (or rather pubes, both are there and fused together at the end) is somewhat transitional between a more normal anteriorly facing pubis of other saurischians and the very posteriorly facing one of birds.

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