Blastomeryx, COPE, 1877

Maguire, Kaitlin Clare & Schmitz, Joshua X. Samuels and Mark D., 2018, The fauna and chronostratigraphy of the middle Miocene Mascall type area, John Day Basin, Oregon, USA, PaleoBios 35, pp. 1-51 : 36

BLASTOMERYX COPE, 1877

Blastomeryx gemmifer COPE, 1874

FIG. 21

Referred specimens —From UCMP -3043: right dentary fragment with m2 and m3, UCMP 39309. From JDNM-4*: lower left premolar, JODA 2256; m2, JODA 2257; left dentary with p3 through m3, JODA 2359; right M3, 2376; right M1, JODA 2377; left dentary fragment with m2 and m3, LACM 5934. From UCMP V 4823: left p2, JODA 6623. From UCMP V 4835: right maxilla fragment with P4 and M1, UCMP 39310.

Occurrence —JDNM-4*, UCMP -3043, UCMP V 4823, UCMP V 4835.

Description —Specimens are attributed to this taxon based on slightly reduced premolars, brachydont molars, and size (Prothero 2008). Referred specimens with m2 have anteroposterior length of 8.5–9.4 mm. JODA 2359 has an m1–m3 length of 30.32 mm. Specimens from the Mascall Formation are on the larger spectrum of specimens assigned to this species; however, they are smaller than Parablastomeryx Frick, 1937 specimens from Virgin Valley, as well as those reported here from the Mascall fauna.

Remarks —Prothero (2008) placed all species of Blastomeryx into a single species, B. gemmifer , based on size comparisons. The size of postcranial material such as astragali and podials (i.e., UCMP 496, 1730, 1746) indicates they are referable to Blastomeryx (Prothero 2008) . One fragmentary tooth specimen, JODA 6503, collected at JDNM- 71 in the lower unit of the Mascall Formation is most likely Blastomeryx , but because of its fragmentary nature, it is only assigned to Blastomerycinae here. Its presence, along with Parablastomeryx , suggests the clade was present and diverse in the lower unit of the Mascall Formation. Downs (1956) mentions YPM 14314, a partial maxilla with P4–M2 attributed to Blastomerycini and as possibly belonging to the Mascall; however, the original locality description says “down river from the cove”, meaning down river from Turtle Cove in the John Day Formation, yet there are no Mascall deposits down river from Turtle Cove. Downs (1956) also mentions USNM 7720, a lower molar, which is now attributed to the Arikareean of the John Day Formation. Moschids have been found from the upper John Day Formation strata south of Kimberly, OR ( Hunt and Stepleton 2004); thus, the specimens mentioned by Downs (1956) may have come from those strata.

Figures

Figure 21. Blastomeryx gemmifer left dentary fragment with p3-m3 in occlusal view, JODA 2359. Scale bar=1cm.