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Abstract 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.
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On the move: sloths and their epibionts as model mobile ecosystems
ABSTRACT Sloths are unusual mobile ecosystems, containing a high diversity of epibionts living and growing in their fur as they climb slowly through the canopies of tropical forests. These epibionts include poorly studied algae, arthropods, fungi, and bacteria, making sloths likely reservoirs of unexplored biodiversity. This review aims to identify gaps and eliminate misconceptions in our knowledge of sloths and their epibionts, and to identify key questions to stimulate future research into the functions and roles of sloths within a broader ecological and evolutionary context. This review also seeks to position the sloth fur ecosystem as a model for addressing fundamental questions in metacommunity and movement ecology. The conceptual and evidence‐based foundation of this review aims to serve as a guide for future hypothesis‐driven research into sloths, their microbiota, sloth health and conservation, and the coevolution of symbioses in general.
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- PAR ID:
- 10360135
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Biological Reviews
- Volume:
- 96
- Issue:
- 6
- ISSN:
- 1464-7931
- Page Range / eLocation ID:
- p. 2638-2660
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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