Toxodontidae, Owen, 1845

Pino, Santiago Hernández Del, Seoane, Federico D. & Cerdeño, Esperanza, 2017, New postcranial remains of large toxodontian notoungulates from the late Oligocene of Mendoza, Argentina and their systematic implications, Acta Palaeontologica Polonica 62 (1), pp. 195-210 : 200

Toxodontidae gen. et sp. indet.

Fig. 3 .

Material.—MCNAM-PV 3907, left calcaneum fragment from Quebrada Fiera, Mendoza, Argentina, Deseadan SALMA, late Oligocene.

Description.—The specimen MCNAM-PV 3907 ( Fig. 3 , Table 1) consists of the tuber and a fragment of the ectal facet ofacalcaneumthatislargerandmorerobustthanthatassigned to Proadinotherium ( Fig. 2D ). The tuber is short in APD and wider, more rectangular outlined than in MCNAM-PV 4085. The medial half of the tuber is elevated, but less pointed. The tendinous sulcus is relatively longer and more centered on the posterior face ( Fig. 3A ). The remaining facet indicates that the “neck” of the bone ( Fig. 3B ) is shorter than in MCNAM-PV 4085. Compared with the calcanei of the leontiniid Gualta cuyana ( Cerdeño and Vera 2015) , MCNAM-PV 3907 is a little smaller, the tuber is relatively wider and presents a well-developed tendinous sulcus that is hardly marked in the specimens of Gualta ; besides, though the area is incomplete, it seems that the medial and the sustentacular facets for the astragalus would be closer than in the leontiniid. Therefore, we assign tentatively the calcaneum fragment MCNAM-PV 3907 to a toxodontid; based on its size and differences with Proadinotherium , it could correspond to a taxon more similar to the lower Miocene genus Nesodon , which could be the genus Pronesodon if the deep revision of this taxon eventually confirms its taxonomic validity. With respect to Nesodon (e.g., MACN A 9070–9073), MCNAM-PV 3907 has a better marked tendinous sulcus, the tuber is not anteriorly pointed (lower APD) and the neck is relatively shorter. These features might imply not only taxonomic but functional differences, but this evaluation is beyond the aim of this paper.

Figures

Fig. 3. Toxodontidae gen. et sp. indet. from Quebrada Fiera, Mendoza, Argentina; Deseadan SALMA (late Oligocene), MCNAM-PV 3907, left calcaneum fragment, posterior (A) and anterior (B) views.

Fig. 2. Toxodontian notoungulates from South America. A–D. Proadinotherium sp. from Quebrada Fiera, Mendoza, Argentina; Deseadan SALMA (late Oligocene). A. MCNAM-PV 4238, right M2, occlusal view. B. MCNAM-PV 4960, left m2, labial (B1) and occlusal (B2) views. C. MCNAM-PV 3843, left m3, lingual (C1), labial (C2), and occlusal (C3) views. D. MCNAM-PV 4085, right calcaneum, posterior (D1), medial (D2), and anterior (D3) views. E. Proadinotherium muensteri Ameghino, 1902 from Colhue Huapi lake, Chubut, Argentina; Colhuehuapian SALMA (early Miocene), MACN Pv-17576 (cast), left calcaneum, medial view. F. Rynchippus equinus Ameghino, 1897 (Notohippidae) from Salla, Bolivia; Deseadan SALMA (late Oligocene),YPM VP-52313, left calcaneum, anterior (F1) and posterior (F2) views. G. Proadinotherium sp. from Quebrada Fiera, Mendoza, Argentina; Deseadan SALMA (late Oligocene), MCNAM-PV 4215, right astragalus, anterior (G1), posterior (G2), distal (G3), and lateral (G4) views. H. Proadinotherium leptognathum Ameghino, 1894 from Santa Cruz, Argentina; Deseadan SALMA (late Oligocene), MACN A 12319, left astragalus, anterior view. I. “Morphippus imbricatus” Ameghino, 1897 (Notohippidae) from Sarmiento Formation, Chubut, Argentina; Deseadan SALMA (late Oligocene), MACN A 12100, left astragalus, anterior view.