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

Marcelo Alfredo Reguero,David Eric Tineo,Leandro Martín Pérez,Paula Bona,Gustavo Dardo Vergani,Gloria González Ruiz,Daniel Gustavo Poiré

doi:10.1590/2317-4889202120200067

Marcelo Alfredo Reguero, David Eric Tineo + Show 5 more

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https://doi.org/10.1590/2317-4889202120200067

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Abstract

Abstract Geological studies in the northern sector of the Chaco foreland Basin, Bolivia, yielded new fossils coming from late Oligocene-late Miocene of the Petaca Formation. Few fossil mammals were known from the Subandean Region of Bolivia. We report a partially complete mandible of a hegetotheriid Hegetotheriinae (Notoungulata, Typotheria) from Abapo (Rio Grande River). The specimen (YPFB-LIT-PAL-005) is very close in size and dental morphology to the late Oligocene (Deseadan South American Land Mammal Age, SALMA) — Santacrucian (early Miocene) Prohegetotherium schiaffinoi (Kraglievich 1932) from Fray Bentos (Uruguay and Argentina), Salla (Bolivia), Divisadero Largo-Potrerillos and Quebrada Fiera (Argentina). However, mandibular characteristics, as the shape with a marked change in height along its length, increasing towards the back, a prominent masseteric crest, a deep mandibular groove, and a remarkable thickening of the ventral rim of the mandible, indicate differences between this specimen and Prohegetotherium schiaffinoi and the other Hegetotheriinae. The affinity of YPFB-LIT-PAL-005 with P. schiaffinoi suggests a late Oligocene to early Miocene for the upper bearing horizon of the Petaca Formation (in Abapo), an older age than previously assigned to the top of this unit (late Miocene), and confirms the taxon distribution between ∼ 36 ° to ∼ 17 ° south latitude.

Highlights

The South American native ungulates, which include five extinct orders (Astrapotheria, Litopterna, Notoungulata, Pyrotheria and Xenungulata), underwent a remarkable diversification during the major part of the Cenozoic Era
Geographic and stratigraphic distribution Prohegetotherium occurs in several Deseadan localities of Argentina (Patagonia, Mendoza and Corrientes) (Ameghino 1897, Bond et al 1998, Cerdeño and Reguero 2015)
Outside Argentina Prohegetotherium has been recorded in Cachapoal, Chile, Salla, Bolivia, and Fray Bentos, Uruguay

Summary

Introduction

The South American native ungulates, which include five extinct orders (Astrapotheria, Litopterna, Notoungulata, Pyrotheria and Xenungulata), underwent a remarkable diversification during the major part of the Cenozoic Era. Typotheria notoungulates include small to medium-sized forms with the following apomorphic traits: a rodent-like anterior dentition with I1 somewhat enlarged and upper molars with obliterated occlusal surface (Cifelli 1993). Within these small Typotheria, Hegetotheriidae and Archaeohyracidae are considered as forming the clade Hegetotheria (Cifelli 1993, Croft et al 2003), an entity previously regarded as a separate suborder (Simpson 1967). 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, Flynn et al 2008, Bostelmann et al 2018), and Bolivia

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