Muscular Reconstruction and Functional Morphology of the Forelimb of Early Miocene Sloths (<i>Xenarthra, Folivora</i>) of Patagonia

Earth and Environmental Science Transactions of the Royal Socie

Bargo²,

Vizcaı́no

et al. 2015

Pilosa include anteaters (Vermilingua) and sloths (Folivora). Modern tree sloths are represented by two genera, Bradypus and Choloepus (both around 4-6 kg), whereas the fossil record is very diverse, with approximately 90 genera ranging in age from the Oligocene to the early Holocene. Fossil sloths include four main clades, Megalonychidae, Megatheriidae, Nothrotheriidae, and Mylodontidae, ranging in size from tens of kilograms to several tons. Modern Vermilingua are represented by three genera, Cyclopes, Tamandua and Myrmecophaga, with a size range from 0.25 kg to about 30 kg, and their fossil record is scarce and fragmentary. The dependence of the body size on phylogenetic pattern of Pilosa is analysed here, according to current cladistic hypotheses. Orthonormal decomposition analysis and Abouheif C-mean were performed. Statistics were significantly different from the null-hypothesis, supporting the hypothesis that body size variation correlates with the phylogenetic pattern. Most of the correlation is concentrated within Vermilingua, and less within Mylodontidae, Megatheriidae, Nothrotheriidae and Megalonychidae. Influence of basal metabolic rate (BMR), dietary habits and substrate preference is discussed. In anteaters, specialised insectivory is proposed as the primary constraint on body size evolution. In the case of sloths, mylodontids, megatheriids and nothrotheriids show increasing body size through time; whereas megalonychids retain a wider diversity of sizes. Interplay between BMR and dietary habits appears to be the main factor in shaping evolution of sloth body size.

Section: Slothssupporting

confidence: 58%

“…2016). Following Pujos et al (2012), digging abilities might be a basal feature for mylodontids, and possibly of even more basal mylodontoids such as the Miocene Nematherium (see Bargo et al 2012;Toledo et al 2013).…”

Section: Slothsmentioning

confidence: 99%

Evolution of body size in anteaters and sloths (Xenarthra, Pilosa): phylogeny, metabolism, diet and substrate preferences

Earth and Environmental Science Transactions of the Royal Socie

Bargo²,

Vizcaı́no

et al. 2015

“…The actions of these muscles are important in both digging, as in N. nasua and N. olivacea , and food manipulation. The development and location of the medial distal crest of the ulnar diaphysis, site of attachment of m. pronator quadratus , is related with autopodium movements (Argot, ; Taylor, ; Toledo et al, ). This muscle is involved in the maintenance of structural integrity between radius and ulna near the carpus, as the forces imposed on this mobile part of the forearm would tend to dislocate it (Argot, ).…”

Section: Discussionmentioning

confidence: 99%

“…We present an exhaustive description of the pectoral girdle and forelimb elements of Cyonasua in the context of the correlation between form and function, proposed by Radinsky () and applied in numerous paleobiological studies of the postcranial skeleton (e.g., Andersson, ; Argot, , , ; Argot & Babot, ; Candela & Picasso, ; Ercoli, Prevosti, & Álvarez, ; Hildebrand, ; Taylor, , , , ; Toledo, Bargo, & Vizcaíno, , ; Vizcaíno, Bargo, & Fariña, ). We also discuss and elaborate palaeocological hypotheses about the role of Cyonasua in the late Cenozoic communities of South America.…”

Section: Introductionmentioning

confidence: 99%

Comparative osteology and functional morphology of the forelimb ofCyonasua(Mammalia, Procyonidae), the first South American carnivoran

Tarquini

Morgan

et al. 2019

Journal of Morphology

Self Cite

Extant procyonids only inhabit the Americas and are represented by six genera (Procyon, Nasua, Nasuella, Bassaricyon, Potos, and Bassariscus); all of them, except Bassariscus, are present in South America. The first records correspond to the early Miocene in North America (NA) and the late Miocene in South America (SA). Cyonasua was the first carnivoran to enter SA from NA, before the Great American Biotic Interchange, and went extinct in the early middle Pleistocene. This extinct procyonid is recorded in several localities of Argentina, and also in Venezuela. Paleobiological studies of procyonids are interesting from evolutionary and biogeographical viewpoints. In this study, the pectoral girdle and forelimb of 10 specimens of Cyonasua are described and compared with extant South American procyonids using a qualitative approach. Additionally, four functional morphology indexes were calculated for them and compared with an ecologically diverse sample of living carnivorans. Results indicate that Cyonasua most resembles Nasua nasua and Procyon cancrivorus, even though the extinct procyonid possessed peculiar features. Cyonasua had robust and relatively short forelimb bones, with strong stabilized joints, and movements associated with the sagittal plane, which suggest a tendency toward terrestrial habits, related to their ability to resist relatively high bending and shearing stresses. However, some features indicate a freedom in their range of movements, with moderate supination ability, compatible with climbing. When combined with previous analyses of dietary habits and estimated body mass, the morphology of Cyonasua would be well suited for digging and prey manipulation, allowing them to prey on small and relatively large‐sized vertebrates, as well as to avoid some of the predators that were dominant in the Cenozoic of South America.

“…Lycalopex). In addition, Nasua, considered as both scansorial and a ground-dweller (McClearn 1992;Glaston 1994;Beisiegel 2001), presents certain features similar to those of tree-dwellers (e.g., Potos), including a wide antero-posterior ulnar shaft, required for insertion of several flexor muscles that function in both climbing and digging (Stalheim-Smith 1984;Vizcaíno & Milne 2002;Toledo et al 2013). The intermediate position of †Cyonasua sp.…”

Section: Locomotory and Substrate Preferencementioning

confidence: 99%

The forelimb of †Cyonasua sp. (Procyonidae, Carnivora): ecomorphological interpretation in the context of carnivorans

Tarquini

Earth and Environmental Science Transactions of the Royal Socie

Morgan

et al. 2015

The procyonid †Cyonasua is endemic to South America and recorded from the Late Miocene to the Early Pleistocene. This paper studies the forelimb of †Cyonasua sp. (late Pliocene of Miramar, Argentina), using an ecomorphological approach to infer morphological adaptations linked to substrate preference and locomotory mode, as well as to grasping and digging ability. Twenty linear measurements of forelimb and pectoral girdle were taken from †Cyonasua sp. and a sample of 87 specimens of extant carnivoran families (Procyonidae, Mustelidae, Ursidae, Viverridae, Canidae and Felidae). Raw values were transformed to minimise the effect of size. Morphological variation was explored by principal component analysis (PCA); substrate preference and locomotory mode were further analysed by multivariate analysis of variance (MAV) and discriminant analysis (DA); grasping and digging ability were analysed by DA. In the PCA morphospace, †Cyonasua sp. occupied a unique position, close to extant procyonids. DA classified it as non-specialised digger with poor grasping ability. The results lead to the interpretation of †Cyonasua sp. as having a moderately stabilised elbow joint with poor pronation-supination, although some climbing skills cannot be ruled out. Thus, †Cyonasua sp. could have had generalised habits, in agreement with reconstructed palaeoenvironmental conditions.