Systematic revision of Hegetotherium and Pachyrukhos (Hegetotheriidae, Notoungulata) and a new phylogenetic analysis of Hegetotheriidae

More than 40 remains of Tremacyllus Ameghino 1891 (Notoungulata, Hegetotheriidae, Pachyrukhinae) from La Pampa Province (Argentina) are analyzed. They were recovered from different outcrops of the late Miocene Cerro Azul Formation at Laguna Chillhué, Quehué, Telén, Salinas Grandes de Hidalgo, Estancia Ré, Bajo Giuliani, Barrancas Coloradas and Caleufú. During the late Miocene, pachyrukhines are represented by two genera, Tremacyllus and Paedotherium. The present sample of Tremacyllus allows dental morphological variation to be evaluated, especially in lower and upper premolars. This study shows high variability in the diagnostic characters of two purported species, T. impressus (Pliocene-Pleistocene of the Pampean Region) and T. incipiens (late Miocene of Catamarca). We interpret these differences to actually correspond to intraspecific variation and, consequently, propose their synonymy. T. impressus has priority over T. incipiens, and an emended diagnosis is provided. This nomenclatural action implies, in turn, the extension of the biochron of Tremacyllus impressus from the late Miocene to the Pleistocene. T. impressus differs from Paedotherium in its smaller size, the presence of post-incisive impressions that extend beyond the level of P2 (reaching the anterior margin of P3), M3 shorter or equal to M2, relatively shorter mandibular symphysis, and lower premolars not molariform and more imbricated. Within the studied sample, we identify several juvenile specimens that confirm the dental eruption pattern previously proposed for Tremacyllus based on fewer remains.

(2018) Renata Sostillo et al.   AMEGHINIANA

Dental shape variation of Neogene Pachyrukhinae (Mammalia, Notoungulata, Hegetotheriidae): systematics and evolutionary implications for the late Miocene Paedotherium species

(2017) M. D. Ercoli et al.   JOURNAL OF SYSTEMATIC PALAEONTOLOGY

Phylogeny and paleobiogeography of Hegetotheriidae (Mammalia, Notoungulata)

(2017) Federico D. Seoane et al.   JOURNAL OF VERTEBRATE PALEONTOLOGY

Systematics and stratigraphical range of the hegetotheriids Hegetotheriopsis sulcatus and Prohegetotherium sculptum (Mammalia: Notoungulata)

(2016) Alejandro Gustavo Kramarz et al.   JOURNAL OF SYSTEMATIC PALAEONTOLOGY

New mammal faunal data from Cerdas, Bolivia, a middle-latitude Neotropical site that chronicles the end of the Middle Miocene Climatic Optimum in South America

(2016) Darin A. Croft et al.   JOURNAL OF VERTEBRATE PALEONTOLOGY

Deciduous dentition and eruption pattern in late Miocene Pachyrukhinae (Hegetotheriidae, Notoungulata) from La Pampa Province, Argentina

(2016) Esperanza Cerdeño et al.   HISTORICAL BIOLOGY

Un nuevo Notungulado Hipsodonte (Hegetotheriidae, Pachyrukhinae) del Mioceno tardío de la Cordillera Oriental, provincia de Salta, Noroeste de Argentina.

(2015) Marcelo Alfredo Reguero et al.   Andean Geology

The Hegetotheriidae (Mammalia, Notoungulata) assemblage from the late Oligocene of Mendoza, central-western Argentina

(2015) Esperanza Cerdeño et al.   JOURNAL OF VERTEBRATE PALEONTOLOGY

Un nuevo Notungulado Hipsodonte (Hegetotheriidae, Pachyrukhinae) del Mioceno tardío de la Cordillera Oriental, provincia de Salta, Noroeste de Argentina.

(2015) Marcelo Alfredo Reguero et al.   Andean Geology

The Serrialis Bone, Interparietals, “X” Elements, Entotympanics, and the Composition of the Notoungulate Caudal Cranium

(2014) R.D.E. MacPhee   BULLETIN OF THE AMERICAN MUSEUM OF NATURAL HISTORY

The Inter-Relationship between Dietary and Environmental Properties and Tooth Wear: Comparisons of Mesowear, Molar Wear Rate, and Hypsodonty Index of Extant Sika Deer Populations

(2014) Mugino Ozaki Kubo et al.   PLoS One

Milk molars or extra premolars in Mesotheriinae (Mesotheriidae, Notoungulata): New insights into an old controversy

(2013) Esperanza Cerdeño et al.   GEOBIOS

The Cranial Anatomy of the Miocene NotoungulateHegetotherium mirabile(Notoungulata, Hegetotheriidae) with Preliminary Observations on Diet and Method of Feeding

(2012) Dakota E. McCoy et al.   Bulletin of the Peabody Museum of Natural History

Late Oligocene mesotheriids (Mammalia, Notoungulata) from Salla and Lacayani (Bolivia): implications for basal mesotheriid phylogeny and distribution

(2010) GUILLAUME BILLET et al.   ZOOLOGICAL JOURNAL OF THE LINNEAN SOCIETY

New Observations on the Skull of Pyrotherium (Pyrotheria, Mammalia) and New Phylogenetic Hypotheses on South American Ungulates

(2009) Guillaume Billet   JOURNAL OF MAMMALIAN EVOLUTION

Craniodental anatomy of late Oligocene archaeohyracids (Notoungulata, Mammalia) from Bolivia and Argentina and new phylogenetic hypotheses

(2009) GUILLAUME BILLET et al.   ZOOLOGICAL JOURNAL OF THE LINNEAN SOCIETY

TNT, a free program for phylogenetic analysis

(2008) Pablo A. Goloboff et al.   CLADISTICS