The earliest well-documented occurrence of sexual dimorphism in extinct sloths: evolutionary and palaeoecological insights

Boscaini, Alberto; Gaudin, Timothy J.; Toledo, Néstor; Quispe, Bernardino Mamaní; Antoine, Pierre‐Olivier; Pujos, François

doi:10.1093/zoolinnean/zlz011

Cited by 16 publications

(19 citation statements)

References 43 publications

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“…size, shape, and inclination of the caniniforms) of adult individuals, possibly reflecting the presence of two morphs. These differences were observed in other extinct species of ground sloths and suggested as indicators of sexual dimorphism [30][31][32] (and references therein). Its record in the sample studied here could be an evidence of sexual dimorphism also in L. armatus.…”

Section: Resultsmentioning

confidence: 62%

Gregariousness in the giant sloth Lestodon (Xenarthra): multi-proxy approach of a bonebed from the Last Maximum Glacial of Argentine Pampas

Tomassini

Montalvo

Garrone

et al. 2020

Sci Rep

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Megamammals constituted an important component in the pleistocene faunal communities of South America. Paleobiological and paleoecological studies involving different megamammal taxa have increased significantly in the last years, but there are still several poorly-known issues of its life history. In this work, we analyze an assemblage composed of 13 individuals of different ontogenetic stages, and possibly different sex, belonging to the giant ground sloth Lestodon armatus (Xenarthra, folivora), recovered from playa del Barco site (pampean Region, Argentina). A dating of 19,849 years Cal BP allows assigning this assemblage to a period of the MIS (Marine Isotope Stage) 2 related to the end of the Last Glacial Maximum. Based on multiple lines of research (e.g. taphonomy, paleopathology, osteohistology, isotopy), we interpret the origin of the assemblage and diverse paleobiological and paleoecological aspects (e.g. social behavior, ontogenetic changes, sexual dimorphism, diseases, resource and habitat use, trophic relationships) of L. armatus. evidence suggests that the assemblage was formed by a local single event of catastrophic mortality, which affected different members of a social group. This record represents the first accurate evidence of gregariousness for this ground sloth, providing new data on a poorly-known behavior among extinct folivora. In the last years there have been multiple studies on the Quaternary South American megamammals (estimated body mass ≥ 1,000 kg), including ground sloths 1-8 (and references therein). Even so, there are several aspects of their life history that have not been addressed in detail, such as growth patterns, diseases, social behavior, habitat preference, feeding strategies, and trophic relationships with other mammals, both endemic to South America and immigrants from North America. Sloths (Xenarthra, Folivora), one of the most conspicuous groups of mammals, include representatives of, at least, five monophyletic families, Bradypodidae, Megalonychidae, Megatheriidae † , Mylodontidae † , and Nothrotheriidae †9,10. Representatives of this clade were very abundant and diverse in the Quaternary terrestrial

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Section: Resultsmentioning

confidence: 62%

Gregariousness in the giant sloth Lestodon (Xenarthra): multi-proxy approach of a bonebed from the Last Maximum Glacial of Argentine Pampas

Tomassini

Montalvo

Garrone

et al. 2020

Sci Rep

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“…This widespread dispersal of the clade may be related to the peculiar feeding adaptations of mylodontines, the only folivorans which displayed morphological traits that are indicative of grazing habits (Bargo, Toledo, & Vizcaíno, ; Bargo & Vizcaíno, ; Pujos, Gaudin, De Iuliis, & Cartelle, ). Also, trophically related sexual dimorphism has been proposed for several mylodontines, and its adaptive value can be regarded as an additional possible driver for the wide distribution of the clade (Boscaini, Gaudin, Toledo, et al, ). Better understanding of the anatomy and phylogeny of these taxa may yet provide further paleobiological insights into this important and unusual group of herbivorous, late Cenozoic clade of American mammals.…”

Section: Discussionmentioning

confidence: 99%

A reappraisal of the phylogeny of Mylodontidae (Mammalia, Xenarthra) and the divergence of mylodontine and lestodontine sloths

2019

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The phylogeny of mylodontid sloths has recently been the subject of multiple studies. Contrasting hypotheses have been proposed, especially for the relationships among late Miocene–Pleistocene mylodontines and lestodontines. In this paper, a new and detailed phylogenetic analysis is conducted, after adding new characters and taxa previously unexplored from a phylogenetic point of view. New features derived from postcranial skeletal anatomy are added to previous studies based on craniodental evidence. In this way, the current reappraisal represents the first exhaustive phylogenetic study on the Mylodontidae that incorporates features coded for the entire skeleton. When available, multiple specimens of each bony element are observed for each operational taxonomic unit, in order to take into account intraspecific variation. The taxonomic sample of this study considers Mylodontinae at the specific level. However, many other Mylodontidae are considered, and their phylogenetic relationships tested. The taxonomic sample of this study is enriched with new taxa from central and northern South America, with the aim of compensating for the knowledge bias in favour of austral mylodontids, which have historically been more extensively studied than those from tropical latitudes. Special emphasis is given to the phylogenetic relationships of Mylodontinae, and particularly to the mylodontine and lestodontine sloths, that are recovered in the present study as monophyletic clades, and together form a larger monophyletic group. According to the present results, the Mylodontini–Lestodontini split occurred at the middle–late Miocene transition, giving rise to independent adaptive radiations across South and North America.

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“…Agonistic blows performed with claws of the forelimbs could produce remarkable injuries, and a dermal armor could play a protective role. Lydekker (1894), McDonald (2006) and Boscaini et al (2019) proposed sexual dimorphism for Mylodontini. McDonald (2006) hypothesized polygamous herd behavior in mylodontids sloths, whereas Boscaini, Gaudin, Toledo, et al (2019) proposed ecological segregation in addition to morphological dimorphism.…”

Section: Discussionmentioning

confidence: 99%

“…Lydekker (1894), McDonald (2006) and Boscaini et al (2019) proposed sexual dimorphism for Mylodontini. McDonald (2006) hypothesized polygamous herd behavior in mylodontids sloths, whereas Boscaini, Gaudin, Toledo, et al (2019) proposed ecological segregation in addition to morphological dimorphism. If the presence of dermal ossification in mylodontine sloths was a sex‐related character, its expression could have been greater in one sex than in the other, or even exclusive of males.…”

Section: Discussionmentioning

confidence: 99%

The dermal armor of mylodontid sloths (Mammalia, Xenarthra) from Cueva del Milodón (Última Esperanza, Chile)

Toledo

Boscaini

Pérez

2021

Journal of Morphology

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Dermal ossifications (osteoderms, dermal ossicles, osteoscutes) appear independently in various tetrapod lineages. In mammals, however, dermal ossifications are only present in some members of Xenarthra. This clade includes Cingulata (armadillos and their relatives), and Pilosa, including Vermilingua (anteaters) and Folivora (sloths). In extant xenarthrans, osteoderms are invariably present in cingulates whereas they are absent in pilosans. Among extinct sloths, however, a limited number of taxa possessed dermal ossifications. Records of mummified skins of ground sloths bearing osteoderms found in Cueva del Milodón (Southern Chile), with a late Pleistocene age, allowed us to analyze their micro‐ and macroscopic morphology. The main goal of this study is to closely examine a portion of a mylodontid skin portion using radiography. The arrangement, morphology and internal structure of the ossicles are analyzed and the results are discussed in the context of previous research. The results we obtained indicate that ossicles vary in shape and size, and the integument has four different patterns of arrangement of the ossicles: that is, areas without ossicles, disorganized ossicles, rows, and mosaic areas. The latter has two variants, with clusters of ossicles forming rosettes or stars. Thin sections of the ossicles allowed us to recognize and describe anatomical features of the bone and its mode of growth. Finally, paleobiological and functional considerations of the dermal armor are discussed along with its phylogenetic and chronological implications.

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The earliest well-documented occurrence of sexual dimorphism in extinct sloths: evolutionary and palaeoecological insights

Cited by 16 publications

References 43 publications

Gregariousness in the giant sloth Lestodon (Xenarthra): multi-proxy approach of a bonebed from the Last Maximum Glacial of Argentine Pampas

Gregariousness in the giant sloth Lestodon (Xenarthra): multi-proxy approach of a bonebed from the Last Maximum Glacial of Argentine Pampas

A reappraisal of the phylogeny of Mylodontidae (Mammalia, Xenarthra) and the divergence of mylodontine and lestodontine sloths

The dermal armor of mylodontid sloths (Mammalia, Xenarthra) from Cueva del Milodón (Última Esperanza, Chile)

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