Tracing the Paleobiology of Paedotherium and Tremacyllus (Pachyrukhinae, Notoungulata), the Latest Sciuromorph South American Native Ungulates – Part I: Snout and Masticatory Apparatus

Snout shape and masticatory apparatus of the rodent‐like mesotheriid ungulates (Notoungulata, Typotheria): exploring evolutionary trends in dietary strategies through ancestral reconstructions

“…2018; Ercoli et al . 2019, 2020) it can be inferred that the masticatory apparatus of the analysed mesotheriids and hegetotheriids would enable them to perform stronger masticatory efforts than other notoungulates and extant ungulates. These functional inferences are unexpected for species whose diets are composed exclusively of soft leaves, but do not preclude their consumption (Zelditch et al .…”

“…Patterson (1934) recognized that trachytheriines ( Trachytherus Morphotype) possess an incipient development of the zygomatic plate, whereas this structure is well developed in mesotheriines (‘Intermediate’ and Mesotherium morphotypes), reaching a proto‐sciuromorph masseteric condition convergent with some rodents and other typotherians (Patterson 1934; Ercoli et al . 2019, 2020). Our analyses also reveal differences in the development of the zygomatic plate even within mesotheriines.…”

“…Considering that the posterior margin of the incisive foramina is related to the transit of the major palatine artery, Ercoli et al . (2020) stated that the posterior extension or location of this structure in gnawing mammals could be related to the relocation of sensitive tissues behind the infoldings of the lips, and also inferred the presence these infoldings in pachyrukhines (Notoungulata, Hegetotheriidae). Interestingly, the infolding of the lips, analogous to the condition in rodents, is also present in other gnawing groups of mammals such as wombats (see Ade 1999), in which we also observed a posterior location of the incisive foramina (see Tyndale‐Biscoe 2005; Sharp & Trusler 2015).…”

“…2017; see also Ercoli et al . 2020). Both low cusp relief (or even flattened occlusal surfaces) and the alignment of numerous enamel layers are considered to be typical features of extant grazers (Hiiemae & Crompton 1985; Reguero et al .…”

“…2019; but see Ercoli et al . 2020 for variants among pachyrukhines). Regarding mesotheriids, we infer more important grinding and coarse cutting actions than crushing ones and a better tooth design to process fibrous (tough) food items rather than turgid or brittle ones, although crushing would be relatively more important in small mesotheriine taxa.…”