MYLAGAULIDAE

Calede, Jonathan J. M. & Hopkins, Samantha S. B., 2012, Intraspecific versus interspecific variation in Miocene Great Basin mylagaulids: implications for systematics and evolutionary history, Zoological Journal of the Linnean Society 164 (2), pp. 427-450 : 444-446

MYLAGAULIDAE SPECIES A

FIGURE 13

Synonymy: Epigaulus minor (in part) Shotwell, 1958; Mylagaulus sp. (in part) Shotwell, 1963; Mylagaulus sp. (in part) Shotwell, 1958.

Referred material: From the Beatys Butte Fauna: UCMP 188927 (V-85105), P4, UOMNH F-17681 (UO 2417, Cox Butte), partial skull with left and right P4. From Juntura Formation (Black Butte Fauna): UOMNH F-6165 (UO 2343), UOMNH F-6166 (UO 2343), P4s.

Distribution: Early Barstovian Beatys Butte Fauna of Oregon; Late Clarendonian Juntura Formation, Oregon.

Discussion: Specimens UOMNH F-6165 and UOMNH F-6166 from Black Butte are curated with two different specimen numbers but they are premolars of opposite sides and Shotwell (1958) reported that they were collected on float a few inches apart from each other. They appear to represent the left and right P4 of a single individual because the unusual fossette morphologies and wear stages are identical. The outline of the tooth is simple, similar to other mylagaulids but the shape of the lakes shown in Figure 13 is complex. In particular, the branching pattern of the anterofossette is not a simple ‘Y’ but rather consists of two parallel anteroposteriorly elongated lakes joined by a labiolingually orientated lake perpendicular to the first two. The anterolabial fossette of UOMNH F-6165 exhibits a high degree of complexity as well. It extends to the posterolingual side of the tooth and branches anteroposteriorly. The posterolabial fossette in both specimens is horseshoe-shaped and consists of the metafossette of Shotwell (1958) joined to another, parallel labial fossette, which is an additional lake of different homology. The peculiar fossette morphology of these specimens and the large size of the teeth suggest that this single individual represents a new species, possibly even a new genus. Certainly the size and morphology preclude attribution to Hesperogaulus ; the morphology of the fossettes is somewhat like Ceratogaulus and Mylagaulus from the Great Plains, although the occlusal morphology is distinct enough that the specimens cannot be clearly attributed to any known species. No formal description of this possible new species, sympatric with H. shotwelli , will be undertaken here and awaits discovery of a more complete specimens that will allow comparison with existing mylagaulid genera.

Specimen UCMP 188927, from the Barstovian Beatys Butte fauna, is also a very large mylagaulid. The tooth is wide labiolingually as well. This single upper left P4 shows no branching of the lakes. It is at a late stage of wear (stage 3) and younger specimens of the same species would be expected to show some branching of the anterofossette. The fossettes are orientated and elongated anteroposteriorly. There are seven fossettes on the occlusal surface of this tooth. As mentioned earlier for other taxa, there is an additional posterolabial fossette not homologous to the lakes described by Shotwell (1958: fig. 7) or Hopkins (2008: fig. 1). As a result of its large size and its peculiar occlusal morphology, this individual may represent a rare, large species similar to the Black Butte specimen.

UOMNH F-17681 from Cox Butte in the Beatys Butte fauna is a partial skull of a large mylagaulid. The P4s exhibit an occlusal morphology similar to that of Al. vetus , but with more elongated fossettes. The size of the teeth is within the range of Al. vetus but the P4 of specimen UOMNH F-17681 is more elongated labiolingually, appearing rounder than that of an Al. vetus . The outline of the teeth of the Cox Butte specimen is different from that of the teeth of Al. vetus . The tooth is still separated in an anterior and a posterior lobe but the posterolabial indentation found in UCMP 121693 (a mature individual of Al. vetus ) is not as pronounced in the Cox Butte specimen. The additional fossette of the posterolabial corner of the tooth described in all Formation or fauna Taxa present

Massacre Lake Alphagaulus vetus

Virgin Valley Alphagaulus vetus , Mylagaulidae indet.

Beatys Butte Hesperogaulus gazini , Mylagaulidae ‘species A’.

Sucker Creek Hesperogaulus gazini

Mascall Hesperogaulus gazini , Alphagaulus vetus , Mylagaulidae indet.

Simtustus Hesperogaulus gazini

Drewsey Hesperogaulus wilsoni , Hesperogaulus shotwelli

McKay Hesperogaulus wilsoni

Esmeralda Hesperogaulus shotwelli

Truckee Hesperogaulus shotwelli

Thousand Creek Hesperogaulus shotwelli

Juntura Hesperogaulus shotwelli , Mylagaulidae ‘species A’, Mylagaulidae indet.

other taxa discussed in this paper is present in this specimen as well. This specimen possibly represents another specimen of a new, rare, large new taxon.

The occurrence of mylagaulids in the formations and faunas of Oregon and Nevada is summarized in Table 4. The specimens of large, rare mylagaulids from the Barstovian and Clarendonian of Oregon suggests that at least one additional lineage of large mylagaulids was present and lived sympatrically with the smaller H. shotwelli and H. gazini . Further field work in the Miocene deposits of south-eastern Oregon will hopefully recover additional material of this poorly known taxon.

Figures

Figure 13. Occlusal morphology of the fourth premolars of Mylagaulidae species A. Numbers refer to wear stages described in the text. Anterior is to the left of the figure. A, UOMNH F-6166, right P4; B, UOMNH F-17681, right P4; C, UCMP 188927, left P4 (mirrored). Scale bar = 1 cm.