TY - JOUR
T1 - From flat foot to fat foot
T2 - Structure, ontogeny, function, and evolution of elephant "sixth toes"
AU - Hutchinson, John R.
AU - Delmer, Cyrille
AU - Miller, Charlotte E.
AU - Hildebrandt, Thomas
AU - Pitsillides, Andrew A.
AU - Boyde, Alan
PY - 2011/12/23
Y1 - 2011/12/23
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=84455194213&partnerID=8YFLogxK
U2 - 10.1126/science.1211437
DO - 10.1126/science.1211437
M3 - Article (Academic Journal)
C2 - 22194576
AN - SCOPUS:84455194213
SN - 0036-8075
VL - 334
SP - 1699
EP - 1703
JO - Science
JF - Science
IS - 6063
ER -