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Re: Sixth "toe" for elephants
(I'm not able to download the paper)
Is the additional digit the postminimus (lateral to the sixth)?
2011/12/23 Richard W. Travsky <email@example.com>:
> For more than 300 years, the structure has puzzled researchers, but this
> study suggests that it helps to support elephants' colossal weight.
> Fossils reveal that this "pre-digit" evolved about 40 million years ago, at
> a point when early elephants became larger and more land-based.
> Lead author Professor John Hutchinson, from the UK's structure and motion
> laboratory at the Royal Veterinary College ...
> Many people, he said, thought that the structure was a huge lump of
> cartilage, and over the years its purpose or lack of purpose has been
> "Anyone who has studied elephants' feet has wondered about it. They've
> thought: 'Huh, that's weird,' and then moved on," he added.
> But Prof Hutchinson and colleagues used a combination of CT scans,
> histology, dissection and electron microscopy to solve the puzzle.
> The researchers said the structure was made of bone, although bone with a
> highly irregular and unusual arrangement.
> Science 23 December 2011:
> Vol. 334 no. 6063 pp. 1699-1703
> DOI: 10.1126/science.1211437
>> From Flat Foot to Fat Foot: Structure, Ontogeny, Function, and Evolution
> of Elephant Sixth Toes
> Several groups of tetrapods have expanded sesamoid (small, tendon-anchoring)
> bones into digit-like structures (predigits), such as pandas thumbs.
> Elephants similarly have expanded structures in the fat pads of their fore-
> and hindfeet, but for three centuries these have been overlooked as mere
> cartilaginous curiosities. We show that these are indeed massive sesamoids
> that employ a patchy mode of ossification of a massive cartilaginous
> precursor and that the predigits act functionally like digits. Further, we
> reveal clear osteological correlates of predigit joint articulation with the
> carpals/tarsals that are visible in fossils. Our survey shows that basal
> proboscideans were relatively flat-footed (plantigrade), whereas early
> elephantiforms evolved the more derived tip-toed (subunguligrade)
> morphology, including the predigits and fat pad, of extant elephants. Thus,
> elephants co-opted sesamoid bones into a role as false digits and used them
> for support as they changed their foot posture.