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

Title

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

Creator

Lia M Gavazzi
Kelsey M Kjosness
Philip L Reno

Date

2022

Description

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.

Source

Anat Rec (Hoboken)
. 2022 Jul;305(7):1804-1819. doi: 10.1002/ar.24832. Epub 2021 Nov 25.

Language

English

Citation

Lia M Gavazzi, Kelsey M Kjosness , and Philip L Reno, “Ossification pattern of the unusual pisiform in two-toed (Choloepus) and three-toed sloths (Bradypus),” NEOMED Bibliography Database, accessed April 13, 2024, https://neomed.omeka.net/items/show/12116.