The study of bone microstructure of fossil vertebrates (i.e., paleohistology) has demonstrated to be a very important source of paleobiological information. Paleohistological studies are based on the standardized analysis of petrographic thin sections. Although the development of new technologies (e.g., microtomography) have provided non-destructive procedures for the study the fossil tissues, thin sections are still the main source of information in paleohistology. In this contribution, we provide a detailed protocol for sampling and thin-sectioning preparation of bone tissue from both fossil and extant vertebrates. We describe the most common procedures for sampling and also some particularities related to variations in equipment and sampling techniques. The main goal of this contribution is to offer an alternative protocol for research teams of recent formation and/or with limited funding.

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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