Cyclomylus Matthew and Granger, 1923

WANG, BANYUE, 2001, On Tsaganomyidae (Rodentia, Mammalia) of Asia, American Museum Novitates 3317, pp. 1-52 : 18

Cyclomylus Matthew and Granger, 1923

Cyclomylus Matthew and Granger, 1923:5 .

Pseudotsaganomys Vinogradov and Gambaryan, 1952:18 .

Sepulkomys Shevyreva, 1972:139 .

Tsaganomys, Bryant and McKenna, 1995 (partim): 5–16. McKenna and Bell, 1997 (partim): 191.

TYPE SPECIES: Cyclomylus lohensis Matthew and Granger, 1923 .

INCLUDED SPECIES: Cyclomylus intermedius , new species, and C. biforatus , new species.

GEOLOGICAL RANGE: Early Oligocene.

GEOGRAPHIC DISTRIBUTION: North China, Mongolia, and Kazakhstan.

EMENDED DIAGNOSIS: Small­ to medium­sized tsaganomyids; antepremolar crest absent, small oval infraorbital foramen with nearly vertical major axis, almost perpendicular to anterior margin of ventral surface of anterior zygomatic root; P4 growing from below upper incisor capsule, p4 from above lower incisor; cheek teeth unilaterally hypsodont with closed roots, short dentine part

and long pulp cavity with a flat or concave top, with core showing on worn occlusal surface; on unworn or slightly worn occlusal surface, cusps and lophs prominent, four lophs, enamel relatively thick, with cement on walls; lower cheek teeth with distinct metalophid I, hypertrophic hypoconid and posterolingually oblique external valley; p4 oval in occlusal view, with narrow trigonid, metaconid more developed than protoconid, and no metalophid I.

DISCUSSION: Matthew and Granger (1923) distinguished Cyclomylus from Tsaganomys based on its smaller size and less hypsodont cheek teeth that have closed roots. Vinogradov and Gambaryan (1952) described a new genus, Pseudotsaganomys , based on material from Kazakhstan and Mongolia. They mentioned that Pseudotsaganomys differed from Tsaganomys in having closed roots and from Cyclomylus in having a broad skull and lacking dP3. However, the holotype of Cyclomylus lohensis ( AMNH 19096) is crushed laterally and has no dP3. It is difficult to know whether dP3 is present or not based on the adult specimen. It seems there is no significant difference between Pseudotsaganomys and Cyclomylus .

Shevyreva (1972) described a new genus, Sepulkomys , from Hsanda Gol, Mongolia. She considered the presence of a P3 as a feature distinctive from the other tsaganomyids. I agree with Bryant and McKenna (1995) that the holotype of Sepulkomys eboretus ( PIN 475­50) is a young individual, in which the teeth that Shevyreva interpreted as p3 and p4 are really dP3 and dP4. Thus Sepulkomys is similar to Cyclomylus in dental formula. According to her figure (Shevyreva, 1972: fig. 4), it is identical with Cyclomylus in occlusal pattern. It appears that Pseudotsaganomys and Sepulkomys are junior synonyms of Cyclomylus .

Cyclomylus lohensis Matthew and Granger, 1923

Figures 13B , 15–19 ; table 2

Cyclomylus lohensis Matthew and Granger, 1923 (partim): 5.

Pseudotsaganomys turgaicus Vinogradov and Gambaryan, 1952: 20–22 , figs. 7–10. NEW SYN­ ONYMY.

Figures

Fig. 13. Microstructures of longitudinal sections of lower incisors of tsaganomyids. A. Tsaganomys altaicus. B. Cyclomylus lohensis. C. Coelodontomys asiaticus, new genus and species. Scale = 20 µm.

Fig. 15. Ventral view of skull of Cyclomylus lohensis (AMNH 19096, holotype) (in stereo). Scale

Fig. 16. Cyclomylus lohensis. A. Skull of AMNH 19096 (holotype). A1. Ventral view. A2. Right lateral view. A3. Anterior view. B. Anterior view of transverse section along p4 of right lower jaw (IVPP V 11458) showing the relation between p4 (alveolus) and i2.

Fig. 17. Cheek teeth of Cyclomylus lohensis. A. Right M1/2 (IVPP V 11457). A1. Posterior view. A2. Buccal view. A3. Anterior view. A4. Occlusal view. B. Occlusal view of right P4–M3 of AMNH 19096 (holotype). See figure 10 for abbreviations.

Fig. 18. Occlusal view of left lower jaw with i2, p4–m3 of Cyclomylus lohensis (IVPP V 11543)

Fig. 19. Cyclomylus lohensis A. Occlusal view of left p4–m3 (IVPP V 11543). B. Left lower jaw with i2, p4–m3 (IVPP V 11456). B1. Occlusal view. B2. Buccal view. B3. Posterior view showing the relation between i2 and m3.