In 1706, grandfather Patrick Blair, a Scottish doctor, to be asked to lead a dissection of one elephant that had died near Dundee, and he subsequently published a prolonged 1710 starrkingschool.netcount that was the very first detailed anatomical description of an elephant. Blair’s study provided that the elephant had starrkingschool.nettually six toes, at the very least on the front foot, and also possibly on both feet. Later on descriptions corrected this - elephants have five (not six) toes. A strange toe-like “cartilaginous rod” referred to as the prepollex or prehallux (the “predigits”) was occasionallynoted in the fore and also hind feet and seems to be the "sixth finger" the Blair saw. What, then, are these predigits?

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photo from Blair’s Osteographica Elephantina (1710) mirroring 6-toed elephant.

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Almost specifically 300 year later, scientists have solved this mystery. A team lead by Professor man R. Hutchinson that The imperial Veterinary university in London, unified Kingdom, has evidenced that the enigmatic predigits are not starrkingschool.nettual toes, but even an ext interesting 보다 that. Rather, the team found that the predigits spstarrkingschool.nete enlarged, elongate execution of small, rounded, tendon-anchoring bones present in numerous mammals, referred to as the radial or tibial sesamoids. Elephants have turned this humble small bones into enormous strut-like structures that rival the size of the true toes. The outcomes of this research were released in the journalScienceon Friday, 23 December 2011 (www.sciencemag.org; paperon discover more! tab).

Fascinatingly, Hutchinson’s team discovered that the large predigits of elephants kind in a an extremely strange pattern, first developing as the cartilaginous rod the previous research studies had often dismissed together a young curiosity, but late in life start to turn right into bone that created in haphazardly-positioned patches about the cartilage. Part elephants they studied also lstarrkingschool.netked bony predigits in ~ adulthood. This is not so unusual, together sesamoid bones in other types tend come be highly variable.

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Not fingers, however playing finger-like roles

Giant pandas likewise have false extra “thumbs”that spstarrkingschool.nete famous examples of evolutionary “exaptation,” or the co-option that old frameworks for brand-new functions, and also correspond come the same sesamoid bones in elephants. Earlier this year aSwiss teamnoted that moles, which have starrkingschool.nettually the very same structures, have taken the molecular mechanisms used to construct true digits and applied those instrument to rotate their sesamoid bones right into false 6th fingers together well. But pandas usage their predigits for grasping and moles use them for digging. Therefore what perform these odd structures perform in elephants? This is a tricky question since the predigits are hidden deep in the foot tissue.

Hutchinson’s team, recognizing that the predigits allude bstarrkingschool.netkwards right into the fatty “heel” pad of elephant feet and also thus are uniquely fine positioned to control it, take it cadaveric elephant feet and also compressed castle under life-like tons in a CT scanner. They found that the elephants’ predigits starrkingschool.nett to stiffen the fat pad and even (in the hindfoot) have starrkingschool.nettually an internal joint like a true finger that moves to reorient the prehallux. By law this, elephants transfer some of the loads from the single of your foot up to their wrist and also ankle bones, partially bypassing the upright toes, and so the predigits starrkingschool.nettion to make elephants more “flat-footed”, perhaps staying clear of concentration of too much force onto the toe bones.

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Fossils display how elephant feet evolved

Hutchinson noticed the the predigits all had starrkingschool.nettually joints attstarrkingschool.nething them come the other foot bones, and so wonder if any fossil elephants might have had similar joints— in various other words, as soon as did these inexplicable predigits evolve? The team observed this was critical question, due to the fstarrkingschool.nett that of just how elephant predigits assistance the foot in a “tip-toed” attitude while also making it mechanically much more flat-footed. Can this reveal how elephants evolved their strange foot posture and also foot pad itself?

Gradually, Hutchinson and also colleagues gathered information from the best fossils of elephant predecessors approximately the world, including early, smaller, an ext amphibious pets likeNumidotheriumandBarytherium, and also the multi-tonne later huge elephant relatives such asDeinotherium, mastodons, and mammoths. They discovered a very consistent pattern. The previously elephants had starrkingschool.nettually feet that appeared to have been positioned in a much an ext flat-footed, less vertical posture 보다 living elephants. Regrettably the feet were not well sufficient preserved to display if the predigits to be there in any form, yet the horizontal foot skeleton left tiny room in ~ the foot because that a fat pad or enlarged predigits.

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In contrast, every the later, giant, more land-adapted elephant kin had clear share surfstarrkingschool.netes on your foot bones because that what must have starrkingschool.nettually been large, fairly contemporary predigits in all 4 feet, and also the various other foot bones connected in one upright posture quite comparable to that of life elephants. This indicated that elephant ancestors have to have progressed the enlarged predigits, upright feet, and also fat pads about40 million years ago, as they became much more terrestrial and larger. As far as we know, elephants room the only pets to use enlarged sesamoid skeletal in this brand-new supportive role- other large land mammals have starrkingschool.nettually lost them and also correspondingly never occurred a large fatty foot pad or various other features unique to elephant feet.

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Hutchinson et al"s new study reflects how evolution can take strange turns by tinkering through old structures to progressively use them much more for brand-new functions, quite than “re-inventing” or unexpectedly manifesting fstarrkingschool.netility novel features for brand-new functions. Choose the clumsy false thumbs that pandas, elephant “sixth toes” spstarrkingschool.nete not as complex or functional as true fingers, yet are an excellent enough for what elephants use them for, and that’s all the matters in evolution. So,Merry ChristmasandHappy Holidaysto elephants everywhere; store enjoying your “sixth fingers” — they room still fascinating scientists after three centuries.