Scelidotherium leptocephalum Owen, 1839a

Scelidotherium leptocephalum Owen, 1839a

Referred material: Skull, atlas, five vertebrae, scapula, radius, ulna, femur, two tibias, two fibulae, two foot bones, humerus, one complete hand, two isolated hand bones, patella, and ribs: PIMUZ A/ V 508 ( Figs. 5 View Fig , 6 View Fig , 7 View Fig ); skull, right humerus, one radius, two femurs, two fibulae, one rib, and six caudal vertebrae: PIMUZ A/ V 509

( Fig. 11 View Fig ); cranium and one phalanx bearing claw: PIMUZ A/ V 510; skull (including ear ossicles), isolated teeth, vertebrae, ribs, two clavicles, left scapula, and right humerus: PIMUZ A/ V 513 ( Fig. 10 View Fig ); upper jaw fragment bearing four broken teeth: PIMUZ A/ V 515; anterior part of the mandible: PIMUZ A/ V 517; jaw fragment: PIMUZ A/ V 521; two caniniforms and one mf1 or mf2: PIMUZ A/ V 522; one tibia and one finger: PIMUZ A/ V 531; seven postcranial bones: PIMUZ A/ V 532; mandible and many postcranial bones: PIMUZ A/ V 4128; maxillary bearing left Mf1 and Mf2: PIMUZ A/ V 4130; right posterior half of the cranium and right mandible: PIMUZ A/ V 4149.

Comment: Te species S. leptocephalum was originally the assignment proposed by Roth (1889) and Schulthess (1920) for most of the scelidothere specimens at PIMUZ collection. Te present study confirms the greater abundance of this species relative to other scelidotheres, although several specimens were reassigned to other species (see below). Te completeness of the specimens ranges from almost complete skeletons to isolated tooth fragments, but several specimens are particularly well-preserved. PIMUZ A/V 508, PIMUZ A/V 509, PIMUZ A/V 510, and PIMUZ A/V 513 include well-preserved craniodental remains and all the specimens preserve the dentition. Te attribution to the genus Scelidotherium is confirmed by the presence of a relatively narrow nasal cavity, an almost straight cranial roof in lateral view, an elongated premaxilla, and teeth of relatively small size compared to the size of the cranium ( Miño-Boilini et al., 2014). For the two specimens with at least one femur preserved, PIMUZ A/V 508 and PIMUZ A/V 509, assignment to the genus Scelidotherium is also supported by short femora possessing a medial inclination of the proximal end relative to the distal end and a concave medial surface of the femoral stem ( Miño-Boilini et al., 2014). Te distinction between the two species of Scelidotherium found in the Pampean Region, i.e., S. leptocephalum and S. bravardi , is more complex. S. leptocephalum is recognized as a large species present mainly in the late Ensenadan, Bonaerian and Lujanian while S. bravardi is significantly smaller in size and is mainly recovered in the Ensanadan ( Miño-Boilini & Quiñones, 2020; Miño-Boilini et al., 2014). For PIMUZ A/V 508, PIMUZ A/V 509, and PIMUZ A/V 513, assignment to S. leptocephalum is supported by their large size, narrow anterior predental region of the mandibular ramus more ventral than in S. bravardi , elliptical Cf1 with a slight lingual lobe, and upper teeth without apicobasal sulci ( Miño-Boilini et al., 2014). Also, the humeri show a double entepicondylar foramen, a feature that was included in the diagnosis of S. bravardi ( Miño-Boilini et al., 2014) , and also of Ca. tarijensis , but not in Ca. cuvieri ( Miño-Boilini, 2016) . Te presence of the double foramen on the humerus seems to represent a variable trait, but not a diagnostic character. I therefore prefer to retain the original attribution for these three specimens to S. leptocephalum . For PIMUZ A/V 510, the teeth are heavily altered but the cranium of the specimen is large and, in all respects, similar to the S. leptocephalum illustrated in the study by Miño-Boilini and Quiñones (2020; Fig. 3B View Fig —FMNH P 14,294) and consequently referred to this species. For six specimens, only the dentition features provide specific information. PIMUZ A/V 515 exhibits the upper dentition from Mf1 to Mf4, in particular the shape of Mf2 and Mf4 correspond to elongated triangles without grooves and without distinctive lobes in occlusal view. Tis tooth morphology together with the relatively large size supports the assignment to Scelidotherium (Corona et al., 2013; Miño-Boilini et al., 2014). Comparison with the tooth pattern presented by Corona et al. (2013) supports the same conclusion for the upper and lower dentition of PIMUZ A/V 517, PIMUZ 521, PIMUZ A/V 522, PIMUZ A/V 4149, and PIMUZ A/V 4130. For specimens with mf3, such as PIMUZ A/V 521, I note that the tooth does not show a straight posterior lobe but a C-shaped curve in occlusal view, as recognized in S. leptocephalum and unlike S. bravardi ( Miño-Boilini et al., 2014) . Tree specimens are distinguishable only on the basis of postcranial elements. PIMUZ A/V 531 show a metacarpus, probably the II, and a tibia very similar to those of PIMUZ A/V 508. Te same conclusion emerges from the comparison of the autopodial bones and the tibia of PIMUZ A/V 532 with PIMUZ A/V 508. On the other hand, PIMUZ A/V 4128 exhibits several isolated elements of the autopodium, including bones of the hand, but considering its small size and the stage of the tooth eruption from the mandible, the specimen is young or at least subadult, limiting comparisons with the broad description of adult specimens in the study of Nieto et al. (2021). As there are no different features compared to the previously mentioned specimens except for a smaller size, I prefer to retain the original attribution to S. leptocephalum . Te presence of several ontogenetic stages, with PIMUZ A/V 4128 and PIMUZ A/V 4130 being particularly young specimens, and the abundance of S. leptocephalum highlights the significance of the Roth collection at PIMUZ.