An arctometatarsalian organism is one in which the

proximal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

part of the middle

metatarsal The metatarsal bones or metatarsus (: metatarsi) are a group of five long bones in the midfoot, located between the tarsal bones (which form the heel and the ankle) and the phalanges ( toes). Lacking individual names, the metatarsal bones are ...

is pinched between the surrounding metatarsals. The trait appears to be highly homoplastic, common in certain sorts of

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

s accustomed to running (among them the tyrannosauroids,

ornithomimosaurs Ornithomimosauria ("bird-mimic lizards") are theropod dinosaurs which bore a superficial resemblance to the modern-day ostrich. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period (geology), Period of Laurasia (now Asia ...

, and troodontids), to evenly transmit force to the metatarsals.Snively, E. (2000)
''Functional morphology of the tyrannosaurid arctometatarsus''
. University of Calgary.

References

Evolutionary biology concepts Vertebrate anatomy Skeletal system Dinosaur anatomy {{dinosaur-stub