División Paleontología Vertebrados, Museo de La Plata, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata (UNLP), Av. 60 and 122, La Plata, Buenos Aires, B1900FWA, Argentina.
Consejo Nacional de Investigaciones Científicas y Técnicas - CONICET, Ciudad Autónoma de Buenos Aires, Argentina.
J Morphol. 2021 Apr;282(4):612-627. doi: 10.1002/jmor.21333. Epub 2021 Feb 22.
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.
皮肤骨化（骨质鳞、真皮骨、骨板）独立出现在各种四足动物谱系中。然而，在哺乳动物中，皮肤骨化仅存在于一些有蹄类动物中。这个分支包括贫齿目（犰狳及其亲属）和披毛目，包括食蚁兽和树懒。在现存的有蹄类动物中，真皮骨化总是存在于贫齿目中，而在披毛目中则不存在。然而，在已灭绝的树懒中，有少数分类群具有皮肤骨化。在莫利顿洞穴（智利南部）发现的带有真皮骨化的已灭绝地懒木乃伊皮肤的记录，其年代为晚更新世，这使我们能够分析它们的微观和宏观形态。本研究的主要目的是使用射线照相术仔细检查一部分犰狳皮。分析了骨板的排列、形态和内部结构，并将结果与以前的研究进行了讨论。我们得到的结果表明，骨板的形状和大小各不相同，表皮有四种不同的骨板排列模式：即无骨板区、骨板排列紊乱区、骨板列区和镶嵌区。后者有两种变体，骨板形成玫瑰花或星形的簇。骨板的薄片允许我们识别和描述骨的解剖特征及其生长方式。最后，讨论了皮肤盔甲的古生物学和功能考虑因素，以及它的系统发育和时间意义。
