Details

Autor(en) / Beteiligte

• Gavazzi, Lia M.
• Kjosness, Kelsey M.
• Reno, Philip L.

Titel

Ossification pattern of the unusual pisiform in two‐toed (Choloepus) and three‐toed sloths (Bradypus)

Ist Teil von

• Anatomical record (Hoboken, N.J. : 2007), 2022-07, Vol.305 (7), p.1804-1819

Ort / Verlag

Hoboken, USA: John Wiley & Sons, Inc

Erscheinungsjahr

2022

Quelle

Wiley Online Library Journals Frontfile Complete

Beschreibungen/Notizen

• Two‐toed (Choloepus sp.) and three‐toed (Bradypus sp.) sloths possess short, rounded pisiforms that are rare among mammals and differ from other members of Xenarthra like the giant anteater (Myrmecophaga tridactyla) which retain elongated, rod‐like pisiforms in common with most mammals. Using photographs, radiographs, and μCT, we assessed ossification patterns in the pisiform and the paralogous tarsal, the calcaneus, for two‐toed sloths, three‐toed sloths, and giant anteaters to determine the process by which pisiform reduction occurs in sloths and compare it to other previously studied examples of pisiform reduction in humans and orangutans. Both extant sloth genera achieve pisiform reduction through the loss of a secondary ossification center and the likely disruption of the associated growth plate based on an unusually porous subchondral surface. This represents a third unique mechanism of pisiform reduction among mammals, along with primary ossification center loss in humans and retention of two ossification centers with likely reduced growth periods in orangutans. Given the remarkable similarities between two‐toed and three‐toed sloth pisiform ossification patterns and the presence of pisiform reduction in fossil sloths, extant sloth pisiform morphology does not appear to represent a recent convergent adaptation to suspensory locomotion, but instead is likely to be an ancestral trait of Folivora that emerged early in the radiation of extant and fossil sloths.