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

Abstract

The oldest known mesotheriids are referred to the genus Trachytherus, a taxon traditionally included in its own subfamily 'Trachytheriinae'. The ontogeny, morphological variation and systematics of the genus Trachytherus are still poorly understood and the monophyly of this taxon is questionable. For the first time, a large collection of basal mesotheriids (belonging to the genus Trachytherus) yielded by the Bolivian Salla beds (Deseadan, late Oligocene) and previously referred to T. spegazzinianus was included in a large-scale analysis. This has led to the recognition of a unique new species in the locality of Salla-Luribay, distinct from T. spegazzinianus: Trachytherus alloxus sp. nov. Skulls of this species are described and cheekteeth variation range throughout ontogeny is discussed. These new data are incorporated in a parsimony analysis of basal mesotheriids. The most probable hypothesis of a clade T. spegazzinianus-mesotheriines is discussed. The distinction of the new Salla species from the Patagonian species T. spegazzinianus confirms the faunal differences observed between these Bolivian and Patagonian Deseadan localities. Moreover, the assignment to Trachytherus spegazzinianus of mesotheriid remains from the Bolivian Lacayani deposits complicates the problem of these faunal differences. Further systematic investigations on the Lacayani fauna and on the age of the Patagonian localities are needed.

Patagonian Eocene Archaeopithecidae Ameghino, 1897 (Notoungulata): systematic revision, phylogeny and biostratigraphy

“…5.1-5.4), which led Ameghino to originally consider the presence of distinct species. The present revision and comparison of many archaeopithecid specimens permit establishing a wide intraspecific variation rather than interspecific differences, which was likewise observed in archaeohyracids (Croft et al, 2003;Billet et al, 2009;Cerdeño et al, 2010) and other notoungulate groups (Francis, 1960;Madden, 1997;Billet et al, 2008;Cerdeño et al, 2008). Indeed, Simpson (1967b) also recognized a highly variable morphology on crown pattern and dimensions in the archaeopithecid teeth samples he studied, such as the extremely variable mesial cingulum in premolars and molars.…”

“…In particular, among native ungulates from South America, ontogenetic sequences based on extreme morphological changes on dentition were described for Archaeohyracidae (Croft et al, 2003;Billet et al, 2009;Cerdeño et al, 2010), the notopithecid Transpithecus (Vera, 2012a), and other groups of notoungulates (Francis, 1960;Madden, 1997;Billet et al, 2008;Cerdeño et al, 2008).…”

Paleontology and Geochronology of the Deseadan (late Oligocene) of Moquegua, Perú

“…Until the recent naming of T. alloxus Billet et al, 2008, the mesotheriid of Salla had been referred to T. spegazzinianus. Thus, references regarding our discussion of T. alloxus (e.g., Sydow, 1988;Shockey et al, 2007) identify the trachythere of Salla as T. spegazzinianus.…”

“…In general, the animal of Cerro Mono differs from T. alloxus in its larger size and more gracile features. Due to its slightly larger size we provisionally refer it to T. spegazzinianus (see Billet et al, 2008, for the subtle differences between T. spegazzinianus and T. alloxus).…”

“…Although the taxonomic diversity recorded from Moquegua is not vast, it is significant that there are several new taxa, considering its proximity to the extensively collected Salla beds, which our study and previous geochronological studies indicate are contemporaneous. For example, hundreds of trachytheriinine specimens have been collected from Salla (see Billet et al, 2008: appendix 1 for a partial list of specimens), with numerous skulls curated in several museums (MNHNBol, MNHN-Paris, PU, UF, and UATF). None that we know of, however, are conspecific to any of the mesotheriids of Moquegua.…”