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

Abstract

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

The paleoecology of Pleistocene giant megatheriid sloths: stable isotopes (δ13C, δ18O) of co-occurring Megatherium and Eremotherium from southern Brazil

“…The teeth of xenarthrans are formed mostly of dentine, regarded as more prone to diagenetic modification compared to enamel because of its higher organic content, lower hardness, and smaller crystallites (MacFadden et al, 2010), thus making enamel the preferred material for isotope analysis. Nevertheless, isotopic studies on teeth of extinct sloths have been performed, showing that such analysis is feasible on dentin as well (Kohn et al, 2005;Ruez, 2005;Domingo et al, 2012;França et al, 2014;Silva, 2015;Dantas et al, 2017;Larmon et al, 2019;Pansani et al, 2019;Oliveira et al, 2020;Tomassini et al, 2020). The teeth of megatheriid sloths are prismatic, hypsodont, with subrectangular to subtriangular transverse outline and bilobate occlusal surfaces formed by transversal sharp crests separated by a deep valley (Owen, 1861;Spillmann, 1948;Sicher, 1953;Cartelle & De Iuliis, 1995;Vizcaíno, 2009).…”

“…The Megatherium from Chuí Creek fed on C3 and C4 plants with a smaller proportion (<40%) of the latter (Table 2), a diet similar to that of modern African elephants from Kenya (Bocherens et al, 1996), fossil camelids (Hemiauchenia) from Florida (Feranec & MacFadden, 2000) and Megatherium from Argentina (Praderio et al, 2012;Bocherens et al, 2017;Domingo et al, 2020;Tomassini et al, 2020). Compared to the other mammals from Chuí Creek, the proportion of C4 plants in the diet of this individual was intermediate between Toxodon and Notiomastodon (Figure 3).…”

“…Despite some anatomical differences in skull and jaw bones, both species share morphological features of browsers (narrow muzzle) and grazers (hypsodont teeth, Figure 6. A, distribution of fossils of Megatherium americanum and Eremotherium laurillardi with associated isotopic data found across South America; records of Eremotherium without isotopic data are also shown (from Paula Couto, 1979;Cartelle & De Iuliis, 1995;Rossetti et al, 2004;Praderio et al, 2005;Martinelli et al, 2012;Bocherens et al, 2017;Lopes & Pereira, 2019;Pansani et al, 2019;Domingo et al, 2020;Oliveira et al, 2020;Tomassini et al, 2020;Asevedo et al, 2021). B, Comparative δ 13 C data of both megatheriids across the continent.…”

Una Fauna Local Lujanense (Pleistoceno Superior–Holoceno Inferior) del sur de Uruguay: Santa Regina, Departamento de Colonia

“…El material figurado se asigna al género Morenelaphus en base a las siguientes características: astas dicotómicas bifurcadas, base del asta con roseta fuertemente marcada y formada por excrecencias óseas circulares soldadas, pedúnculo desarrollado, superficie con tubérculos. Recientes estudios sugieren su asociación a ambientes de pasturas semiarboladas (Tomassini et al, 2020;Rotti et al, 2021 et al (2019). Debido a que la epífisis distal se encuentra fusionada a la diáfisis se infiere que se trata de un individuo adulto.…”

Spinal fracture reveals an accident episode in Eremotherium laurillardi shedding light on the formation of a fossil assemblage

“…Despite its paleobiological significance, bone fractures in past animals remain underexplored when compared with other types of paleopathological conditions (e.g., arthritis 9 , and infections 10 ), especially concerning the Pleistocene megafauna from South America. Recently, few cases of fractures have been described to this fauna, including a case in the ground sloth Nothrotherium maquinense 11 and two independent cases in the giant ground sloth Eremotherium laurillardi 12 , 13 .…”