Complete craniomandibular and dental remains of Microtypotherium choquecotense (Notoungulata, Typotheria, Mesotheriidae) from the middle Miocene of the Bolivian Altiplano

FERNÁNDEZ-MONESCILLO, M.; ANTOINE, P.-O.; MAMANI QUISPE, B.; MÜNCH, P.; BOSCAINI, A.; ANDRADE FLORES, R.; MARIVAUX, L.; PUJOS, F.

Buenos Aires

Congreso; XII Congreso de la Asociación Paleontológica Argentina; 2021

We report new complete craniomandibular and dental remains of the mesotheriine notoungulate Microtypotherium choquecotense, from the Choquecota-Hakallinca type locality, Totora Formation (middle Miocene, Bolivia). Microtypotherium choquecotense is the most abundant taxon in this locality, with ca. 57% of the mammalian fossil recovered (15 out of 26). We estimate for an adult individual (Museo Nacional de Historia Natural, La Paz, Bolivia, MNHN-Bol-V 13223), a body mass of 21.69±3.79 or 21.26±4.88 kg, based on cranial or mandibular measurements, respectively. The studied fossils widely improve our knowledge of the morphology of the so-far elusive M. choquecotense, as well as other early-diverging mesotheriines with which it shares some characteristics (e.g., Altitypotherium spp.), such as I1 oval in occlusal view and with smooth enamel, median lobe of M1-2 aligned lingually with the protoloph and metaloph, well-differentiated septum at the incisive foramen, and parallel upper diastemata. Autapomorphic features include an oval i1 (which differentiates it from the trapezoidal shape as seen in Altitypotherium/Rusconitherium) and P4 with a marked enamel fold on the lingual edge. The presence of the latter trait is particularly striking as it has been either considered for differentiating late-diverging mesotheriines (Pseudotypotherium spp. and Mesotherium; also present in Caraguatypotherium) from earlier-diverging genera or for distinguishing species within Eutypotherium. In short, this character seems to occur much earlier in the evolutionary history of mesotheriines than previously thought and it might document intraspecific variation as well, as a polymorphic feature, within Microtypotherium and Eutypotherium.