Paleobiological inferences on middle Eocene native ungulates from South America: Functional morphological analysis of Notostylops and Notopithecus

Abstract

Eocene early-diverging representatives of South American extinct notungulates are traditionally considered to have been "generalists" and "non-specialized" in terms of the appendicular skeleton and locomotor behavior, as is the case with the notostylopid Notostylops, a middle Eocene iconic taxon from Patagonia (Argentina). However, they are mainly known from dental remains, and associated cranial and postcranial elements are scarce. The discovery of a nearly complete specimen attributed to N. murinus allows us to: (1) increase the knowledge of the anatomy of its appendicular skeleton; (2) identify isolated bones from several collections and suggest different taxonomic interpretations for published specimens; (3) perform a biomechanical and functional study using functional morphological analysis to infer its paleoecological attributes (e.g. posture, locomotor habit, estimated speed, and body mass); and (4) establish morphofunctional comparisons, based on possible functional ranges, with other extinct earlydiverging notoungulates from the middle Eocene, such as the Notopithecid Notopithecus. Our evidence suggests that Notostylops was a medium-sized mammal (8.5−20 kg), which could achieve a dynamic digitigrade posture that allowed a scansorial secondary locomotor habit and a speed of up to 50 km/h. However, Notopithecus was a small-sized mammal (0.6−1.4 kg) with a plantigrade posture both in a static and dynamic context, terrestrial habits, and a speed of up to 35 km/h. Therefore, we conclude that these Eocene notoungulates show different locomotor capabilities, which can be associated with early niche diversifications, clearly contrasting with the "all-generalists" paradigmatic view.

Paleohistology of Caraguatypotherium munozi (Mammalia, Notoungulata, Mesotheriidae) from the early late Miocene of northern Chile: A preliminary ontogenetic approach

“…Future studies in this direction will reveal higher complexity in the Notoungulate fauna, which recent research (e.g. [11,100]) such as the present one, are just starting to unveil.…”

“…During the Cenozoic, the South American native ungulates (SANUs) represented a particular and diverse group of phylogenetically related clades, presently grouped in the orders Xenungulata, Pyrotheria, Astrapotheria, Notoungulata and Litopterna, plus few endemic, early Paleogene "condylarthra" [1][2][3]. These extinct mammals exhibited one of the most divergent variety of body sizes and morphological adaptations, including fully cursorial locomotion in the medium sized Proterotheriidae [4], mass graviportal standing in gigantic toxodontids, astrapotheres, and pyrotheres [5][6][7][8], and scansorial, cursorial and semi-fossorial habits in diverse lineages within the small to medium-sized typotheres [9][10][11]. Studies based on collagen protein chains (proteomics) extracted from Pleistocene fossils (i.e., Toxodontia and Litopterna), have placed SANUs within Laurasiatheria, specifically as a sister group to extant Perissodactyla (e.g.…”