Paedotherium

MacPhee, R. D. E., 2014, The Serrialis Bone, Interparietals, “ X ” Elements, Entotympanics, And The Composition Of The Notoungulate Caudal Cranium, Bulletin of the American Museum of Natural History 2014 (384), pp. 1-69 : 1-69

Paedotherium (Hegetotherioidea, Hegetotheriidae , Pachyrukhinae) and Relatives

The target genera Paedotherium and Pachyrukhos (nec Pachyruc [h] us, Pachyrucos [ McKenna and Bell, 1997: 466]), which are morphologically extremely similar, contain many named species. As Cerdeño and Bond (1998) have shown, sorting out which nominal species belongs to which genus is not a straightforward matter, and in the past generic assignment often seems to have been based on age rather than morphology. In any case, apart from the teeth, discernible differences in the crania of these taxa are few and possibly largely size related, with definite Pachyrukhos being somewhat more robust than definite Paedotherium . For the purposes of this study, little of value is lost by frequently ganging them together as “pachyrukhines.”

Pachyrukhinae is an indisputably monophyletic clade of hegetotheres whose known range extends from Deseadan or even Tinguirirican to?Ensenadan time ( Cerdeño and Bond, 1998; Reguero et al., 2007; Reguero and Prevosti, 2010; Billet, 2011). Pachyrukhinae is invariably paired with Hegetotheriinae to form Hegetotheriidae , the sister group of which is the grouping of “late” nominal archaeohyracids identified by Billet et al. (2009; Billet, 2011). No cranial material of earlier members of Pachyrukhinae (Deseadan Prosotherium and allies; see Reguero and Prevosti, 2010) has been described.

SPECIMENS STUDIED. Available specimens of Paedotherium (figs. 8–12) were in much better condition than those of Pachyrukhos . The sample examined in this paper includes AMNH-VP 45914, an excellent skull of Paedotherium chapadmalense (probably a synonym of P. typicum ) and some good material of P. bonaerense (as relimited by Cerdeño and Bond [1998], here including MLP unnumbered1 and P. insigne MLP 99-X-2-1). A number of other Paedotherium specimens in table 1 (e.g., MLP unnumbered2), mostly lacking dentitions, cannot be validly referred to species and are thus listed as “sp.” Other specimens: Pachyrukhos typicus MACN 1251 -52; Pachyrukhos sp. MACN 5886. A representative of the related taxon Hegetotherium andinum ( MLP 12-2914a) was examined but not scanned. (This genus needs revision, and this species name may not be valid; G. Billet, personal commun.)

Mesotherium pachygnathum AMNH-VP 14509, representing a second family, Mesotheriidae , was only cursorily examined and was judged a poor candidate for scanning. However, the late survival of this genus suggests that good material should exist and should be sought for future work.