A new species and the record of Hemihegetotherium (Notoungulata, Hegetotheriidae) in the Middle to Late Miocene of Patagonia, Argentina

A singular Hegetotheriinae (Notoungulata, Typotheria) from the late Oligocene-Early Miocene of the Subandean Region of Bolivia

“…Comparing directly with the latter sample, YPFB-LIT-PAL-005 shows a similar imbrication of the p4, with elongated trigonid and a posterolingual inflexion of m3, but a different elongation of p3 and a distinctive inflexion/groove in m3. These features can be present in some Miocene hegetotheriids (Cerdeño and Reguero 2015, Seoane and Cerdeño 2019, Vera 2019). However, several morphological features seen on the mandibular ramus of YPFB-LIT-PAL-005, i.e., dentary exhibiting a marked change in height along its length, a prominent masseteric crest and a remarkably thick ventral margin of the dentary, make differences between this specimen and Prohegetotheium schiaffinoi.…”

“…Hegetotheriids have been traditionally divided into two subfamilies: Hegetotheriinae and Pachyrukhinae (Simpson 1945). The paraphyletic Hegetotheriinae (Croft and Anaya 2006, Reguero and Prevosti 2010, Cerdeño and Reguero 2015, Seoane et al 2017 includes the following genera: Prohegetotherium Ameghino 1897, from the Deseadan (late Oligocene) and Santacrucian (early Miocene, middle Member of the Mariño Formation) South American Land Mammal Ages (SALMAs) of Mendoza, Argentina, and the Deseadan (late Oligocene) of Bolivia and Uruguay; Sallatherium Reguero and Cerdeño 2005, from the Deseadan of Bolivia; Hegetotheriopsis Kramarz and Paz (2013) from the Deseadan and Colhuehuapian SALMAs (late Oligocene-early Miocene) of Argentina; Hegetotherium Ameghino 1887 from the Colhuehuapian, Santacrucian and Colloncuran SALMAs (early Miocene-early middle Miocene) of Argentina, as well as Chile (Croft et al 2004, Flynn et al 2005, Bostelmann et al 2018, and Bolivia A singular Hegetotheriinae (Notoungulata, Typotheria) from the late Oligocene-Early Miocene of the Subandean Region of Bolivia (Cerdas and Nazareno localities; Croft et al 2009, Croft et al 2016; and Hemihegetotherium Rovereto (1914) (including Pseudohegetotherium) from the Collon Curá Formation (middle-late Miocene), the Chasicoan (late Miocene) and Huayquerian (late Miocene) of Argentina (Croft and Anaya 2006, Kramarz and Bond 2017, Vera 2019, and Quebrada Honda (Croft and Anaya 2006) and Muyu Huasi (Villarroel and Marshall 1989), Bolivia.…”

Propachyrucos Robustus Roth, 1899 (Notoungulata, Hegetotheriidae) Wrongly Synonymized With Hemihegetotherium Cf. H. Tantillum Vera, 2019

“…without any systematic discussion, likely based on the stratigraphic provenance of Pachyrukhos (see Vera, 2019). Mones (1986) listed these species as belonging to Propachyrucos, but posterior authors followed Pascual et al's proposal (Kramarz et al, 2011;López et al, 2018).…”

“…However, they considered both species as nomina dubia, because their p2 is not known and this tooth would allow assigning them to one of the two valid species: Pachyrukhos moyani Ameghino, 1885, and Pa. politus (Ameghino, 1902); Pa. robustus was not discussed by . Vera (2019) revised Propachyrucos robustus (wrongly spelled Propachyrukhos in that paper) and, simultaneously, defined the species Hemihegetotherium tantillum Vera, 2019, based on specimens from the Collón Curá Formation. She revised the holotype of P. robustus, MLP 12-3161, and proposed the synonymy of this species name with Hemihegetotherium cf.…”

“…H. tantillum sp. nov. Vera (2019) explained that MLP 12-3161 is close to Hemihegetotherium, but the incompleteness of its m3 prevented its identification at species level. Based on its similar size to H. tantillum, Vera proposed the mentioned synonymy, which we consider a confusing and erroneous nomenclatural act.…”