Tarsometatarsus

Since time immemorial, Tarsometatarsus has been the subject of fascination, study and debate. Its impact has transcended all cultural, geographical and temporal barriers, leaving an indelible mark on the history of humanity. From the remotest reaches of the past to the most immediate present, Tarsometatarsus has been an object of adoration, analysis, and contemplation. In this article, we will explore in depth the many facets of Tarsometatarsus, unraveling its meaning, its influence and its relevance in today's world. Throughout the pages that follow, we will embark on a fascinating journey through history, science, culture and society, in search of a more complete and enriching understanding of Tarsometatarsus.

Pigeon skeleton. Number 8 indicates both left and right tarsometatarsus

The tarsometatarsus is a bone that is only found in the lower leg of birds and some non-avian dinosaurs. It is formed from the fusion of several bones found in other types of animals, and homologous to the mammalian tarsus (ankle bones) and metatarsal bones (foot). Despite this, the tarsometatarsus of birds is often referred to as just the shank, tarsus or metatarsus.

Tarsometatarsal fusion occurred in several ways and extents throughout bird evolution. Specifically, in Neornithes (modern birds), although the bones are joined along their entire length, the fusion is most thorough at the distal (metatarsal) end. In the Enantiornithes, a group of Mesozoic avialans, the fusion was complete at the proximal (tarsal) end, but the distal metatarsi were still partially distinct.

Cast of the type specimen of Heterodontosaurus tucki. Left tarsometatarsus is clearly visible.

While these fused bones are best known from birds and their relatives, avians are neither the only group nor the first to possess tarsometatarsi. In a remarkable case of parallel evolution, they were also present in the Heterodontosauridae, a group of tiny ornithischian dinosaurs quite distantly related to birds. The oldest remains of this taxon date from the Late Triassic more than 200 million years ago, and predate the first birds with tarsometatarsi by nearly 100 million years.

References

  • Proctor NS, Peterson RJ and Lynch PJ (1993) Manual of Ornithology: Avian Structure and Function. New Haven, CT: Yale University Press.