We shall call it ‘Mini-hallux’

And it didn’t even cost me one million dollars either. This post is little more than an excuse to show of Tyrannosaurus feet again but it does give me the chance to talk about the hallux a little more. This has had a bit of a mention in the past with the issue of it’s reversed (or otherwise) condition in basal birds. For those who are lost, I should really mention that the hallux is slightly unnecessarily jargon-y word for the first toe of the foot (the equivalent of the human big toe). While this has a key role in perching in birds, in the non-avian theropods it was rarely up to much. Even the earliest forms had ditched the fifth toe, and basically walked on their middle three toes, with the hallux rather reduced and lying off to the side as you can see here. In fact this is even lost entirely in a few, including the derived ornithomimosaurs.

The first metatarsal is also positioned at the midpoint of the 2nd as well. You might expect it to have shrunk such that it remained up at the top of the foot, with all the metatarsals in a line, but that’s clearly not the case. In fact, there is even a bit of an articulation on the 2nd metatarsal which is useful as in many specimens the hallux is lot but it’s original position can still be clearly marked by this.

6 Responses to “We shall call it ‘Mini-hallux’”

  1. 1 Heinrich Mallison 02/05/2011 at 9:13 am

    An interesting thing, the mini-hallux! What was it “for”? Especially in a semi-reverted condition? To me, it always looks like a preening tool.

    • 2 David Hone 02/05/2011 at 9:22 am

      In a few it could be, but I can’t see rexy doing much with that. It might help a bit with grip in soft substrates too – you do sort of see that effect with say the reduced lateral toes in various ungulates. I’ve seen at least a couple of theropod tracks that preserve this too when they have sunk deep enough into the substrate. It could just be more or less just under neutral selection too if it’s not doing very much at all, and jsut hasn’t been lost.

    • 3 Schenck 02/05/2011 at 1:48 pm

      Adaptation is not supposed to be the Null Theory, no?

  2. 5 kattato garu 03/05/2011 at 5:17 pm

    Would that be the lovely Oxford NHM again? So many good fossils in that small space…

  1. 1 Dromaeosaur feet « Dave Hone's Archosaur Musings Trackback on 03/05/2011 at 8:56 am
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