Proadinotherium sp.
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publication ID |
https://doi.org/ 10.4202/app.00301.2016 |
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persistent identifier |
https://treatment.plazi.org/id/03ADD838-FF88-FF86-8B15-FC00FA7887FB |
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treatment provided by |
Felipe |
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scientific name |
Proadinotherium sp. |
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Fig. 2A–D, G View Fig .
Material.—MCNAM-PV 4238, right M2; MCNAM-PV 4960, left m2; MCNAM-PV 3843, left m3; MCNAM-PV
4085, right calcaneum; MCNAM-PV 4215, right astragalus. All from Quebrada Fiera, Mendoza, Argentina, Deseadan SALMA, late Oligocene.
Description.— Dentition: MCNAM-PV 4238 ( Fig. 2A View Fig ), an incomplete, worn right M2, is the only upper tooth from Quebrada Fiera so far assigned to Toxodontidae . It is similar in outline and appearance to the molars of Adinotherium (early Miocene, Santacrucian SALMA). Lingual and posterior borders as well as the roots are missing. The oclusal surface presents the typical Y-shaped central fossette, as well as two fossettes at the distal half; the most labially placed is circular and tiny whereas the other is larger and ovoid (length twice width), anterolabially–distolingually oriented; the ectoloph bears a wide, smooth paracone fold.
The m2 (MCNAM-PV 4960; Fig. 2B View Fig 1 View Fig , B 2 View Fig ) and m3 (MCNAM-PV 3843; Fig. 2C View Fig 1 –C View Fig 3 View Fig ) are narrow and high teeth. The trigonid is broken in m2, but appears to be almost quadrangular. In m3 the trigonid is crescent-shaped with the protoconid pointing anterolabially (as in m2). The m2 presents a fossettid formed by the closing of meta-entoconid fold and the accessory fossettid is not observable; instead, the m3 has the lingual folds open and a well-developed accessory fossettid. The morphology (quadrangular trigonid, closed lingual folds and developed roots), size and degree of wear of the m2 correspond to an adult specimen whereas the very little worn m3 resembles the recently erupted molars of young specimens of Adinotherium (e.g., AMNH 9517; see also Scott 1912: pl. 18).
Calcaneum: MCNAM-PV 4085 ( Fig. 2D View Fig ; Table 1) is a relatively small and gracile bone, more elongated and with more slender body than the calcanei of Nesodon and Adinotherium . Its size is slightly greater than that of Proadinotherium muensteri (e.g., MACN Pv-17576; Fig. 2E View Fig , Table 1), Proadinotherium sp. (e.g., YPM VP-25075) and Adinotherium (e.g., MACN 2100, MACN 8515; Table 1), but they share the general outline and disposition of the articular facets. The tuber is relatively short (APD) and wide, with its posteromedial area projecting both medially and proximally. There is a well-marked posteromedial depression on the tuber corresponding to the tendinous sulcus ( Fig. 2D View Fig 1 View Fig ), which does not extend on the proximal face. The sustentaculum is short and the sustentacular facet is subelliptic and flat, placed at a rather vertical plane ( Fig. 2D View Fig 3 View Fig ). The ectal facet is high and narrow, subdivided into two main flattened areas that make a smooth angle in between, which results in a slight convexity of the whole articulation, medially oriented. The fibular facet is very convex, barely projected proximally and distally; although it projects anteriorly from the corpus of the bone, difference with the anterior point of the tuber is not great, which render a roughly rectangular outline to the calcaneum in lateral view. The contact between the fibular and ectal facets is at the distal part of the latter ( Fig. 2D 2 View Fig , D 3 View Fig ). In anterior view, the distal area of the bone is wide, hiding the navicular facet on the medial face. The latter is seen in medial view; it is elliptical and placed at the distal border; it reaches the sustentacular facet and forms an angle of ~60°. The distal facet for the cuboid is concave and kidney-shaped and differs from P. muensteri , whose facet is less concave and more squared.
Astragalus: The morphology and size of MCNAM-PV 4215( Fig.2G View Fig , Table2) are similar to those of Proadinotherium muensteri (MACN A 12048; Fig. 2H View Fig ) and Adinotherium Scott 1912 ). The bone is relatively higher and narrower than specimens assigned to or labeled as Pronesodon and Nesodon ( Ameghino 1894; Scott 1912; SHP personal observation). The trochlea is asymmetrical and deeper than in these two genera; the lateral condyle is much more developed than the medial one ( Fig. 2G View Fig 1 View Fig ). On the posterior face, there are two articular facets for the calcaneum, higher than wide height double width), separated by a deep, wide groove Fig. 2G 2 View Fig ). The lateral facet is proximodistally concave and a long depression separates it from the lateral side of the trochlea. The medial facet is flattened, wider distally than proximally; it reaches the posterior part of the navicular facet. At the proximal end of the groove between facets, there is a tiny astragalar foramen that does not go through the bone. The astragalar neck is short, but more developed than in Pronesodon and Nesodon . The navicular articulation ( Fig. 2G View Fig 3 View Fig ) is very convex anteroposteriorly, but wide and extended medially with respect to the trochlea; its APD is greater laterally than medially. On the medial face, the trochlea presents two projected articular areas; the proximal one is small and subtriangular whereas the other extends mediodistally forming like a shelf supported by a tuberosity placed over the lateral end of the navicular facet. Both areas take part in the articulation with the tibia and are barely united to each other by the trochlear border. On the lateral face ( Fig. 2G View Fig 4 View Fig ), the depression posterior to the trochlear border is elongate, with its proximal end reaching the narrow separation between the lateral side of the condyle and the calcaneum facet, such as occurs in the mentioned MACN A 12048.
As commented above, these two tarsals have a roughly similar size to the mesotheriid Trachytherus . For instance, the astragalus ( Table 2) is relatively close to the smaller specimens of T.alloxus represented in the bivariate plot in Shockey et al. (2016: fig. 5A), but its morphology differs; the mesotheriid shows developed neck, semispherical distal facet, and a distolateral projection (see also Shockey et al. 2007). The calcaneum ( Table 1) is clearly longer than that of T. alloxus ( Shockey and Anaya 2008: 153 and appendix), which differs in the tuber, without proximomedial projection, and the relative position of astragalar facets, the sustentacular one, more distally placed ( Shockey and Anaya 2008: fig. 7.8).
With respect to notohippids, the tendinous sulcus of the calcaneum is deeper in this group; AMNH 29579 (listed as Rhynchippus pumilus by Shockey et al. 2012: appendix 2) and YPM VP-52313 (labeled as R. equinus ) are much smaller and with the tuber less projected posteromedially ( Fig. 2F View Fig ). The astragalus MACN A 12100, labeled as “ Morphippus imbricatus ” Ameghino, 1897 ( Fig. 2I View Fig ), is relatively narrower than MCNAM-PV 4215, its medial condyle is higher, which render the trochlea deeper, and the neck is relatively longer; besides, the lateral condyle is less acute, the sustentacular facet is narrow distally (contrary to that of MCNAM-PV 4215), and the proximomedial corner is less projected.
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