Thylophorops chapalmalensis, Ameghino, 1908

Beck, Robin M. D., Voss, Robert S. & Jansa, Sharon A., 2022, Craniodental Morphology And Phylogeny Of Marsupials, Bulletin of the American Museum of Natural History 2022 (457), pp. 1-353 : 319

† Thylophorops

SPECIES SCORED: † Thylophorops chapalmalensis (type species).

GEOLOGICAL PROVENANCE OF SCORED SPECIMENS: “Barranca Parodi,” Chapadmalal Formation; but several specimens that we examined to score this taxon lack locality data.

AGE OF SCORED SPECIMENS: As noted above (in the account for † Sparassocynus ), the Chapadmalal Formation is thought to fall within the interval from 3.3 ± 0.2 Mya to about 5 Mya.

ASSIGNED AGE RANGE: 5.000 –3.100 Mya.

REMARKS: † Thylophorops chapalmalensis was originally described as Didelphys † chapalmalense by Ameghino (1908), but it was referred to the newly erected genus † Thylophorops by Reig (1952). Goin and Pardiñas (1996) subsequently referred a second species—originally described by Ameghino (1904) as D. † perplana —to † Thylophorops . Goin et al. (2009b) described a third species, † T. lorenzinii , which is the largest known didelphid described to date, with an estimated body mass of 4.8–7.4 kg. † Thylophorops chapalmalensis , the only species we examined to score character data, had an estimated body mass of 3.1–3.4 kg (Goin et al., 2009b), which overlaps the known range of body mass for the largest living didelphid, Didelphis virginiana (see Jones et al., 2009).

Most authors (Simpson, 1972; Reig et al., 1987; Goin, 1991; Goin et al., 2009b; Voss and Jansa, 2009) have considered † Thylophorops to belong to the extant didelphid tribe Didelphini sensu Voss and Jansa (2009) , which also includes Chironectes , Didelphis , Lutreolina , and Philander . Reig et al. (1987: 73) suggested a close relationship between † Thylophorops and Lutreolina , a possibility also acknowledged by Simpson (1972: 15), who wrote that “classification of chapalmalensis as a fairly robust species of Lutreolina is not ruled out by the available information.” By contrast, Goin (1991) and Goin et al. (2009b) argued for closer affinities with Didelphis and Philander .