Hesperocynus dolgopolae (Reig, 1952)

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 : 317-318

† Hesperocynus

SPECIES SCORED: † Hesperocynus dolgopolae (type and only described species).

GEOLOGICAL PROVENANCE OF SCORED SPECIMENS: Level 20 (sensu Stahlecker; see Riggs and Patterson, 1939) of the Andalhuala Formation, Catamarca Province, Argentina; Arroyo Seco de la Frazada, La Huertita Formation (previously middle section of the Aisol Formation; Forasiepi et al., 2009, 2011; Garrido et al., 2014), Mendoza Province, Argentina.

AGE OF SCORED SPECIMENS: Esteban et al. (2014: fig. 2) summarized the stratigraphy of the Andalhuala Formation and published radiometric dates for the various Levels sensu Stahlecker (see Riggs and Patterson, 1939). Of these, Butler et al. (1984) gave a radiometric date of 6.70 ± 0.05 Mya for Level 15, while Latorre et al. (1997) presented a radiometric date of 5.64 ± 0.16 Mya for Level 23, which collectively bracket Level 20, from which the Andalhuala Hesperocynus specimen was collected. This falls within the late Miocene Huayquerian SALMA (9–5.28 Mya; Prevosti and Forasiepi, 2018: table 1.1 ). Garrido et al. (2014) renamed the “middle section of the Aisol Formation” as the La Huertita Formation and identified it as Montehermosan-Chapadmalalan based on biostratigraphy. The ages of the Montehermosan and Chapadmalalan SALMAs are discussed above (see † Sparassocynus ).

ASSIGNED AGE RANGE: 6.750 –3.100 Mya.

REMARKS: Based largely on information provided by a partial skull from the La Huertita Formation (MHNSR-PV 1046), Forasiepi et al. (2009) erected the genus † Hesperocynus to include specimens originally referred to † Thylatheridium dolgopolae (Reig, 1958a; Goin and Montalvo, 1988; Goin et al., 2000). Forasiepi et al. (2009) noted that † H. dolgopolae shares derived craniodental similarities with † Sparassocynus (a partial posterior braincase of † H. dolgopolae, FMNH P-15225, had previously been identified as † Sparassocynus sp. by previous authors; Reig, 1958b; Reig and Simpson, 1972; Simpson, 1974), but is somewhat more plesiomorphic, and they classified both genera within Sparassocynidae . As already discussed (see † Sparassocynus , above), the total-evidence analyses of Beck and Taglioretti (2020) recovered † Hesperocynus and † Sparassocynus as a triballevel clade within Didelphidae (Sparassocynini) . Our analyses provide an additional test of the relationship between † Hesperocynus and † Sparassocynus and Recent didelphids.

We were able to examine FMNH P-15225, a partial posterior braincase of † H. dolgopolae from the Andalhuala Formation (see Simpson, 1974: figs. 7–10), but not the well-preserved skull from the Aisol Formation (MHNSR–PV 1046) described by Forasiepi et al. (2009). A number of character scores (particularly those relating to the dentition) have therefore been taken directly from Forasiepi et al.’s (2009) description and figures. As well as the Andalhuala and Aisol formations, † H. dolgopolae specimens have been collected from the Cerro Azul Formation (La Pampa Province, Argentina; Goin et al., 2000; Abello et al., 2002; Forasiepi et al., 2009), but this last material has not been used for scoring purposes here and was not used to inform the assigned age range of our † Hesperocynus terminal (see Püschel et al., 2020).