Euroxenomys, SAMSON AND RADULESCO, 1973

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 : 22-23

EUROXENOMYS SAMSON AND RADULESCO, 1973

Euroxenomys sp. FIG.12A , �

Referred specimen —Left P4, JODA 4682.

Occurrence —JDNM-4.

Description —The P4 is rooted and mesodont, and measures ap= 3.6 mm and t= 3.7 mm. The tooth is dominated by a deep hypoflexus and mesoflexus, though a paraflexus and two metafossettes are present. The hypoflexus is long, extending anteriorly and buccally beyond the paraflexus. The paraflexus extends about 1/3 across the occlusal surface of the tooth and due to wear it is almost closed to create a parafossette. The mesoflexus is long and the lingual portion curves posteriorly. Posterior to the mesoflexus there are two small fossettes compris- ing the metafossette. The tooth is well worn, but the hypostria is long, extending to the base of the enamel, and the parastria is persistent.

Remarks —Both Euroxenomys and Monosaulax Stirton, 1935 are fairly similar in dental morphology, and are known from early and middle Miocene sites in North America ( Sutton and Korth 1995, Flynn et al. 2008). JODA 4682 belongs to Euroxenomys based on the rooted, mesodont P4 with a long hypostria and persistent parastria. While Monosaualax also displays rooted, mesodont premolars with a generally similar loph pattern, the stria of that taxon are distinctly shorter ( Sutton and Korth 1995, Flynn et al. 2008).

Euroxenomys is well known from Europe and is considered to be closely related to the giant beaver Trogontherium Fischer von Waldheim, 1809 ( Hugueney 1999). Euroxenomys has not previously been described from the Pacific Northwest, but it is known from several Hemingfordian and Barstovian sites in North America ( Sutton and Korth 1995, Korth 2001, Flynn et al. 2008). Euroxenomys wilsoni Korth, 2001 is known from the Hemingfordian Martin Canyon Quarry A fauna of Colorado and Runningwater fauna of Nebraska ( Wilson 1960, Korth 2001), while E. inconnexus Sutton and Korth, 2005 is known from the early Barstovian Anceney Local fauna of Montana ( Sutton and Korth 1995). JODA 4682 is larger than described specimens of the similar age E. inconnexus ( Sutton and Korth 1995) , and more comparable in size to specimens of E. wilsoni from the Hemingfordian Martin Canyon Quarry A fauna of Colorado ( Wilson 1960, Korth 2001).

This is not the only beaver known from the Mascall Formation or other middle Miocene sites in Oregon. McLaughlin et al. (2016) recently described the late Hemingfordian Hawk Rim fauna, which is also a part of the Mascall Formation, and among the taxa described was an incisor fragment from the large beaver Anchitheriomys sp. Roger, 1885. Shotwell (1968) described two species of Monosaulax from early Barstovian Quartz Basin localities ( M. typicus and M. progressus ) of southeast Oregon. While Anchitheriomys is interpreted as terrestrial, both Euroxenomys and Monosaulax are reconstructed as having had semi-aquatic habits based upon phylogenetic inferences and postcranial morphology ( Rybczynski 2007, Samuels and Van Valkenburgh 2008). The presence of multiple semi-aquatic beavers in the Pacific Northwest in the middle Miocene likely reflects changes in climate at the time and resulting resurgence of woodlands in the region ( Retallack 2007, Samuels and Hopkins 2017).

Figures

Figure 12. Euroxenomys sp. left P4, JODA 4682. A. Occlusal view. B. Medial view. Scale bar=1mm.