EUMYSOPINAE, Rusconi, 1935

Carvalho, Guilherme A. S. & Salles, Leandro O., 2004, Relationships among extant and fossil echimyids (Rodentia: Hystricognathi), Zoological Journal of the Linnean Society 142 (4), pp. 445-477 : 467-468

THE EUMYSOPINAE

The extant eumysopines have long been considered together (e.g. Ellerman, 1940) and comprise a formal group in all recent major classificatory works (e.g. Eumysopinae in Woods, 1993; Heteropsomyinae in McKenna & Bell, 1997). However, this implicit monophyletic condition has been recently questioned by Vucetich & Verzi (1991) and by the molecular data analyses of Lara et al. (1996) and Leite & Patton (2002). In the present study, the Eumysopinae also appear as a non-monophyletic assemblage.

Thrichomys, Clyomys , Euryzygomatomys and Carterodon emerge at the basal polytomy of the crowngroup Echimyidae , which also includes three fossil taxa ( Pampamys , Eumysops and Theridomysops ) and Clade 2, which encompasses the remaining extant echimyids plus associated fossils taxa. Nevertheless, as mentioned above, in all most parsimonious trees, Pampamys , Theridomysops, Clyomys , Euryzygomatomys and Carterodon are placed together in the same clade, to which Thrichomys , Eumysops and Protadelphomys are also occasionally associated. With the exception of Carterodon , which is considered by Vucetich & Verzi (1991) to belong elsewhere, this placement corroborates the close association of the fossil genera Theridomysops and Pampamys to the extant Clyomys and Euryzygomatomys ( Verzi et al., 1995; Vucetich, 1995). The proximity of Thrichomys to this group has also been mentioned by these authors ( Verzi et al., 1995; Vucetich, 1995), whereas Eumysops has been considered closely related to Thrichomys by Kraglievich (1965). Regarding Protadelphomys, Vucetich & Verzi (1991) consider it to group, together with Carterodon , elsewhere. Interestingly, the basal position of these taxa within Echimyidae agrees with the basal position of Euryzygomatomys in the molecular analysis of Lara et al. (1996).

Hoplomys , Proechimys and Trinomys have always been considered closely associated (e.g. Moojen, 1948; Patton & Reig, 1989). This view is corroborated by the present analysis, as these genera are grouped in a monophyletic unit (Clade 3). This clade, which does not include any fossil taxon, is supported by three unambiguous transformations: the presence of the central portion of neolophid in M 1 –M 3 (character 13: state 0), which generally shows a contact with the metalophid forming crest C (except in Trinomys denigratus and T. albispinus , which have lost the central portion of the neolophid in M 1 –M 3, and Hoplomys , which has a complete neolophid); the presence of a long and narrow rostrum relative to other echimyids (character 40: state 1); and the presence of a very welldeveloped anterior projection of the premaxillary (character 41: state 2).

Trinomys has long been considered a subgenus of Proechimys , but recently a molecular analysis ( Lara et al., 1996) suggested that both should be considered distinct valid genera. Moreover, Lara & Patton (2000) have questioned the monophyly of Trinomys , and considered it to be a composite of three different clades. In the present study, Trinomys does appear as a monophyletic group (Clade 4) supported by the presence of a deep main fold in cheek teeth (as suggested by Moojen, 1948), i.e. the presence of a deep sulcus between hypolophid and hypocone in lower cheek teeth (characters 8 and 20: state 1) and between protocone and protoloph in upper cheek teeth (character 32: state 1). Apart from these features, four other character states also seem to support the monophyly of Trinomys : the absence of the labial portion of the neolophid and the presence of a contact between the central portion of neolophid and the metalophid (forming the crest C) in little or non-worn dP 4 (character 2: state 1, character 3: state 2); and the absence of a contact between metalophid and ectolophid in lower teeth (character 5: state 2; character 17: state 1). Note, however, that some of theses are non-applicable for Trinomys denigratus (character 17) and T. albispinus (characters 3, 5 and 17); and two (characters 3 and 5) could not be determined with certainty for Trinomys mirapitanga , being then considered as unknown. The division of the genus into three distinct clades is not supported, and the only resolution within the genus is the placement of Trinomys denigratus and T. albispinus as sister-taxa.

In the consensus tree, all forms of Proechimys appear at the basal polytomy of Clade 3. However, in the most parsimonious trees Proechimys always appears as a non-monophyletic unity, because some members of the genus are more closely related to Hoplomys or Trinomys than to the other Proechimys species. This non-monophyletic condition of Proechimys had already been suggested by Moojen (1948) with regards to Trinomys , and by Patton & Reig (1989) with regards to Hoplomys . The lack of resolution does not allow testing the subdivision of Proechimys in the groups of species proposed by Patton (1987).

The other two extant eumysopines, Mesomys and Lonchothrix , form a clade (Clade 8) that appears as the sister-group of Clade 9, which includes all extant echimyines and dactylomyines plus associated fossil taxa. The association of these two genera with echimyines and dactylomyines (forming Clade 7) also appears in the results of the molecular data analyses of Lara et al. (1996) and Leite & Patton (2002). Interestingly, this result points to a single origin of the arboreal habits in Echimyidae , as discussed by Leite & Patton (2002).