MERYCOIDODONTIDAE THORPE, 1923

Maguire, Kaitlin Clare & Schmitz, Joshua X. Samuels and Mark D., 2022, The fauna and chronostratigraphy of the middle Miocene Mascall type area, John Day Basin, Oregon, USA, PaleoBios 35, pp. 1-51 : 32-33

MERYCOIDODONTIDAE THORPE, 1923 TICHOLEPTUS COPE, 1878

Ticholeptus zygomaticus COPE, 1878

Referred specimens —From UCMP V 67153: right i3, UCMP 35670; left p2 and p3, deciduous p4, m1 or m2, UCMP 95757; maxilla fragment with partial P4 and M1, JODA 3776; right M1 and M2, JODA 6604. From JDNM- 4*: upper dentition including right P1 through M3 and left I1 though M3, JODA 1327; lower dentition including right p2 through m3 and left i3 through m3, JODA 1328; dentary with erupting i3 through p3, dp4, m1 through m2 and erupting m3, JODA 1329. From UCMP V 4834: left P4, UCMP 39298. From UCMP V 4835: left P4, UCMP 39301; right P1 and tooth fragment, UCMP 39302. From CIT 113: p4 and m1, CIT 1730. From JDMN-71D: right c1 through p 3 in dentary fragment, JODA 295. From: JDNM-179 partial right lower canine, JODA 6509.

Occurrence — UCMP V 67153, JDNM-4*, UCMP V 4834, UCMP V 4835, CIT 113, JDNM-71D, JDNM-179.

Description and Remarks — Cope (1886) described Ticholeptus from the Cottonwood Creek beds (AMNH FM 8192) and named a new species ( T. obliquidens ) from a mandibular ramus with an entire tooth series. Lander (1998) synonymized all species in the genus to one species, T. zygomaticus , but based on the description in Cope (1886), it is unclear whether AMNH FM 8192 belongs to

T.zygomaticus . Scharf (1935) identified Ticholeptus from Mascall deposits (CIT 113, specimen CIT 1730). More recent collections confirm the occurrence of this genus, as well as identification of the species T. zygomaticus , in the Mascall Formation based on the following: P1–P3 are elongate, rectangular and the anterior intermediate crest does not form a cusp (unlike in Merychyus Leidy, 1858 ); larger in size than Merychyus (average P1–M3 length 59–152 mm); smaller in size than other contemporaneous ticholeptines; p2–p4 complexly crested ( Lander 1998). All new material assigned to this taxon is dental material. JODA 1327 and 1328 were collected by the Weatherfords as individual teeth and then plastered together into a tooth row. Therefore, toothrow measurements are inexact, but the individual tooth measurements are given in Table 7. JODA 1329 is a dentary also collected by the Weatherfords with all teeth in situ. The remaining material consists of isolated teeth referred to this species based on size. The lower premolars of UCMP 95857,JODA 295, and JODA 1328 are complexly crested, even more complex than the lower premolars of T. zygomaticus from Massacre Lake (UCMP V6160 and V6161). JODA 6509, a partial canine, and the canine of JODA 1328, are similar

Specimen C P1 P2

JODA 1327 ap 9.18 10.48 10.97

t 5.51 6.97

UCMP 39298 ap

t

UCMP 39301 ap

t

UCMP 39302 ap 9.85

t 5.36

c p1 p2

JODA 1328 ap 12.58 10.83

t 5.07

UCMP 95857 ap 9.64

t 4.56

CIT 1730 ap

t

JODA 6509 ap 12.06