Cyclomylus mashkovae Shevyreva, 1994: 112

WANG, BANYUE, 2001, On Tsaganomyidae (Rodentia, Mammalia) of Asia, American Museum Novitates 3317, pp. 1-52 : 19-32

Cyclomylus mashkovae Shevyreva, 1994: 112 , fig. the cheek teeth is near 60°. P4 is ventral to

1c, d, e, f. NEW SYNONYMY. the upper incisor. Because the skull of the Tsaganomys altaicus (partim), Bryant and Mc­ holotype is crushed laterally, it is not clear

Kenna, 1995: 5–16, fig. 10B. NEW SYNONYMY. whether the antepremolar crest is present or

HOLOTYPE: A skull, badly preserved not. The mandible is similar to that of Tsa­ ( AMNH 19096 ), from Hsanda Gol Forma­ ganomys. It is hystricognathous. The mental tion, lower red strata, Loh , Tsagan Nor Ba­ foramen is below the posterior part of the sin, Mongolia. diastema. The masseteric fossa is large and

REFERRED SPECIMENS: IVPP V 11456– reaches below m2. The lower masseteric 11467, V 11543; AMNH 84545; PIN 1401­ crest is weak and almost parallel to the lower 178, 478­3, 478­13, 1442­95, 414­m/47­1, margin of the angular process. There is a 2979/912, 2979/910 and 2979/1342. small, distinct fossa before the masseteric

GEOLOGICAL RANGE: Early Oligocene (Wu­ fossa. On the lingual side of the large angular lanbulage Formation, Hsanda Gol Formation, process the fossa for the pterygoid muscle is and Buran Formation). large and deep. The lower incisor extends be­

GEOGRAPHIC DISTRIBUTION: Qianlishan low the lower cheek teeth and ends in the District ( IVPP Locs. 79010 [V 11457], condyloid process. 79015 [ IVPP V 11458], 79016 [V 11459], The cheek teeth are relatively low, unilatother locality [V 11456]) and Saint Jacques erally hypsodont. On the upper cheek teeth ( IVPP Locs. 77045 [V 11460], 77049 [V the lingual crown is higher than the buccal 11461], 77049.2 [V 11462], 77049.5 [V one, whereas on the lower teeth the poster­ 11463], 77049.7 [V 11464], 77049.8 [V obuccal crown is higher than anterolingual 11465], 77050.b [V 11466] and 78020 [V one. In young individuals when the cheek 11467]), Nei Mongol, China; Tsagan Nor teeth are not worn the root is open. However, Basin (V 11543 and other specimens in in those teeth that are slightly worn but still AMNH), Mongolia; and Chelkar­Teniz, preserve the occlusal pattern, the roots are Chaybulak­Dzhamangora watershed and Tur­ closed ( AMNH 19096, 85545; IVPP V gai, Kazakhstan. 11456, 11457, 11460). The upper molars

EMENDED DIAGNOSIS: Single infraorbital have three closed roots: a large root lingually foramen; upper cheek teeth growing from be­ and two small roots buccally. The lower low posterior part of upper incisor and lower cheek teeth have two: a small anterior and a cheek teeth from above lower incisor; cheek large posterior root. The interval of eruption teeth relatively low unilaterally hypsodont, of the cheek teeth is rather short. While the low height difference between enamel on first and second molars still retain the occlusides of teeth, with rather thick enamel and sal pattern, both the third molar and fourth relatively well­developed cusps and lophs; premolar erupt. Thus, when the individual is upper cheek teeth with three closed roots; young ( IVPP V 11543, AMNH 19096 and lowers with two; fourth premolar larger than 84545), the occlusal pattern can be seen on molars; lower incisor having relatively thin the whole cheek tooth row from the fourth enamel, with relatively thick PE, nearly 40% premolar to third molar at the same time. of total thickness of enamel, and with nearly On the occlusal surface the enamel is rel­ 30° inclination of prisms, and PI having near­ atively thick. The cheek teeth are tetralopholy 30° inclined HSB including 3–4 prisms. dont. The relatively well­developed occlusal

DESCRIPTION: The infraorbital foramen is pattern, high crests and deep basins, can last small and oval and its vertical major axis is a long time during wear. However, the patalmost perpendicular to the anterior margin tern does not extend so deep as in other hypof the ventral surface of the anterior zygo­ sodont forms, such as Ctenodactylinae and matic root. The temporal fossae are large. Arvicolidae . When heavily worn the occlusal The sagittal crest is distinct with a prominent pattern is lost and the occlusal surface of the anterior process. The upper incisor extends cheek teeth is smooth, concave, usually with to above M1–2. The angle between the dor­ a core of secondary dentine, and bordered by sal surface of the posterior part of the upper a higher margin. The core is generally simiincisor alveolus and the occlusal surface of lar to the occlusal form of the teeth in con­

= 1 cm.

tour and slightly higher than the dentine around it. The dentine part is rather short in height. The pulp cavity is deep, with a flat or concave top and side walls parallel to the side walls of the tooth. The primary dentine seems to stop growing early. As the primary dentine is worn away, the secondary dentine is deposited, always forming a core.

On upper cheek teeth the four transverse lophs are almost equally developed. The protoloph and metaloph are nearly parallel to each other and join with the large protocone with wear. The anteroloph and posteroloph are convergent toward the protocone and form a continuous crescentic crest. Three buccal transverse valleys are deep and dammed by a slightly higher buccal edge, forming closed basins with wear. On more worn teeth the middle valley is the longest and the posterior one is the smallest (M1 of AMNH 84545). On slightly worn or unworn teeth, the posterior valley is large and separated by a longitudinal crest into two basins: the buccal one is deeper than the lingual one (M2 of AMNH 84545). On M3 of AMNH 84545 there are some accessory cusps and lophs in the posterior valley.

The p4 is quite different from that of Tsaganomys . It is oval in occlusal view and longer than wide and has a small, narrow trigonid. The metaconid and protoconid are prominent and close to each other. The metastylid is distinct. The metalophid II is short and low. The metalophid I is absent. The trigonid basin is small and open anteriorly. The talonid is much wider than the trigonid. The entoconid is prominent and separated from the metaconid by a notch. The hypertrophic hypoconid is the largest of the main cusps and extends anterobuccally. The posterolophid is well developed and reaches the entoconid. The top of the entoconid is separat­ ed from the posterolophid by a shallow broad. The hypoflexid is strongly oblique groove. The straight ectolophid joins the pro­ posterolingually and persists longer with toconid with the hypoconid or hypolophid. wear than do other valleys.

The hypolophid is slender, low, and complete The lower molars are four crested. Unlike or incomplete. The lingual middle valley is p4 the metalophid I and II are better developed and long. The prominent protoconid and metaconid are subequal and separated widely. The trigonid basin is a large, oval, closed basin. The hypolophid is slender and usually complete. No distinct entoconid is seen. The hypertrophic hypoconid is the largest cusp and extends anterobuccally. The posterolophid is well developed. In the lingual valleys the middle valley is the largest and opens lingually. The posterior valley is a closed basin. The hypoflexid is oblique posterolingually and remains later with wear than do the lingual valleys.

The Dp4 is molariform and similar to low­ er molars, except that it is longer in proportion and there is a prominent anteroconid.

As in Tsaganomys altaicus , the incisor is nearly triangular in cross section and with or without longitudinal ridges on the labial surface of the enamel. The enamel has a multiserial microstructure. However, as described by Martin (1992), and unlike Tsaganomys altaicus , the enamel is rather thin. The total enamel thickness is only about 80µm. However, the PE is relatively thick, near 40% of the total enamel thickness, and the prisms of the PE have an inclination of near 30°. The HSB, composed of 3–4 prisms, have an inclination of near 30° relative to the EDJ.

DIMENSIONS: See table 2.

DISCUSSION: Matthew and Granger (1923) briefly described Cyclomylus lohensis in their diagnosis without giving figures and measurements. This has led to great confusion in the classification of the tsaganomyids. Some paleontologists have expressed their uncertainty about their identification of the tsaganomyids (Vinogradov and Gambaryan, 1952; Kowalski, 1974). It is difficult for me to comment on the specimens of these paleontologists as no figures and plates are given or the specimens or casts are unavailable for personal observation.

Bryant and McKenna (1995) considered Cyclomylus lohensis as a junior synonym of Tsaganomys altaicus . A closer comparison of the two holotypes and other specimens reveals that Cylomylus lohensis differs from Tsaganomys altaicus in some skull and tooth morphology.

First, Matthew and Granger (1923: 3–5) mentioned that in T. altaicus the cheek teeth were very hypsodont, continuously growing, and without closed roots at any observed stage of wear; and in C. lohensis the cheek teeth were less hypsodont and the roots closed when fully grown. In the holotype of T. altaicus ( AMNH 19019) the cheek teeth have lost their occlusal pattern, but the enamel still extends to the base and the roots are still open. In contrast, in the holotype of C. lohensis ( AMNH 19096) the upper cheek teeth have three closed roots, a large lingual one and two small buccal ones, and their occlusal surfaces more or less retain lophs and valleys. Obviously, the difference in crown height of the two taxa is not age related. Correspondingly, in hypsodont Tsaganomys the upper cheek teeth extend medial to the posterior part of the upper incisor and the lower cheek teeth buccal to the lower incisor, whereas in less hypsodont Cyclomylus lohensis the uppers grow from below the upper incisor and the lowers from above the lower incisor.

Second, in T. altaicus the dentine part of the cheek teeth is much more developed, the pulp cavity is relatively short and with a pointed apex, and the ratio of the height of synonym of C. lohensis , judging by the authe dentine part of pulp cavity of the check thors’ original description. However, the auteeth is much higher than that in Cyclomylus , thors did not figure any teeth, and I am unfor which the dentine part is much shorter certain about the status of P. mongolicus . than the pulp cavity. In addition, the pulp Likewise, Cyclomylus mashkovae Shevyreva cavity in Cyclomylus has a flat or concave (1994) from Kazakhstan is likely a junior top with sides nearly parallel to the side walls synonym of C. lohensis , based on the idenof the crown (figs. 10, 17). tical cheek tooth morphology. Third, the cheek teeth of Tsaganomys have much thinner enamel on the occlusal surface, Cyclomylus intermedius , new species much weaker expression of the cusps and

Figures 20 –23; table 3 lophs, and no hypertrophied hypoconid. After being worn, the occlusal surface is con­ Cyclomylus lohensis, Young and Chow, 1956 : cave and smooth, without a core of second­ 448, 449, fig. 1. Shevyreva, 1974b: 52–56, figs. ary dentine in Tsaganomys , whereas in Cy­ 1a, b. NEW SYNONYMY. clomylus there is a core on the surface. In Tsaganomys altaicus (partim), Bryant and Mc­

Kenna, 1995: 5–16, fig. 11C. NEW SYNONYMY. addition, in Tsaganomys p4 is nearly square in occlusal view and has a low metalophid I, HOLOTYPE: A right lower jaw with i2, p4– a long metalophid II, and a wide trigonid. In m3 ( IVPP V 823), from Qingshuiying For­ Cyclomylus the p4 is oval and longer than mation, Qingshuiying, Lingwu, Ningxia, wide, lacks a metalophid I, but has a weak, China, figured by Young and Chow, 1956: short metalophid II and a very narrow tri­ fig. 1. gonid basin. REFERRED SPECIMENS: IVPP V 11453– Fourth, in Tsaganomys the major axis of 11455; AMNH 81235, 82183, 85543; PIN the oval infraorbital foramen is nearly hori­ 475­3883 and 475. zontal and almost parallel to anterior margin GEOLOGICAL RANGE: Early Oligocene (Wuof the ventral surface of the anterior zygo­ lanbulage Formation, Qingshuiying Formamatic root, whereas in Cyclomylus it is nearly tion and Hsanda Gol Formation). vertical and almost perpendicular to the an­ GEOGRAPHIC DISTRIBUTION: Qingshuiying, terior margin of the ventral surface of the Lingwu of Ningxia, Saint Jacques ( IVPP anterior zygomatic root. Loc. 77046 [ IVPP V 11453]) and Qianlishan Fifth, the microstructure of the incisor District ( IVPP Locs. 78018 [V 11454] and enamel in the two forms differs, although both 79011 [11455]) of Nei Mongol, China; and have multiserial microstructure. In Tsagano­ Tsagan Nor Basin, Mongolia. mys the PE is relatively thin, its ratio to total DIAGNOSIS: Moderately unilaterally hypenamel thickness is very low, its prisms have sodont Cyclomylus , height difference beno inclination, and its HSB include more tween shortest and highest enamel on walls prisms but with less inclination. In Cyclomylus of each cheek tooth is large, lower molars the PE is relatively thick, both the HSB and growing buccal to lower incisor, fourth preprisms of PE are inclined nearly at 30° with molar larger than molars in size, upper cheek the EDJ, and the HSB include fewer prisms. teeth with three closed roots, and lowers with The above arguments seem convincing two. enough to validate Cyclomylus lohensis as a ETYMOLOGY: Intermedius, Latin , intermeseparate taxon. diate. Pseudotsaganomys turgaicus Vinogradov DESCRIPTION: The mental foramen is an­ and Gambaryan (1952) is identical with Cy­ terior to p4. The p4 extends above lower inclomylus lohensis in cheek tooth morpholo­ cisor, but molars are slightly buccal to lower gy. Its cheek teeth are lower crowned, cov­ incisor. The lower incisor is triangular in ered by thicker enamel, with closed roots, cross section with a flat labial side. The more prominent cusps and lophs, and hyper­ enamel is thin, and the labial surface has no trophied hypoconid. Pseudotsaganomys tur­ longitudinal ridge. gaicus may be a junior synonym of C. loh­ Cheek teeth are moderately unilaterally ensis. Possibly P. mongolicus is also a junior hypsodont and more or less covered by ce­ (in stereo). Scale = 5 mm.

ment. The crown is higher than that of C. lohensis and lower than in C. biforatus . The interval of the eruption of the cheek teeth is longer than in C. lohensis . By the time of eruption of the third molar and fourth premolar, the occlusal pattern of the first and second molars have been worn away. The dentine part is very low. The pulp cavity is well developed and nearly cylindrical, with its side walls parallel to the side walls of the tooth, a nearly flat or concave top, and a slightly constricted base.

TABLE 2 Measurements (mm) of Cheek Teeth of Cyclomylus lohensis

In most of the upper cheek teeth the oc­ cernible: four lophs and three valleys (fig. clusal surface is concave, with a more or 21A). The anterior valley is almost worn less clearly expressed secondary dentine out, leaving only a small oval depression. core in the center. The core is usually oval. The middle valley is the deepest and large On one slightly worn M1/2 (= M1 or M2, and extends into the pulp cavity. The pos­ IVPP V 11454.1) the occlusal pattern is dis­ terior valley is partly preserved. The proto­

cone is large and separated from the lingual

part of the posteroloph by a small groove.

The dentine part is about 2 mm in height

(from occlusal surface to top of pulp cavity).

As in C. lohensis the upper cheek teeth have

three closed roots, one large lingual and two

small buccal ones.

The lower cheek teeth are oval in occlusal

view and have two closed roots: a small an­

terior one and a large posterior one. The p4

is larger than lower molars, with a larger an­

terior root. The occlusal surface has a distinct

core when worn, with its shape depending on

the stage of wear. It is usually oval in shape.

On worn p4 of IVPP V 823, it is crescent. Fig. 21. Cheek teeth of Cyclomylus interme­

On unworn or slightly worn cheek teeth the dius, new species. A. Right M1/2 ( IVPP V 11454.1). A1. Buccal view. A2. Occlusal view. B. occlusal pattern can be preserved. Right M1/2 ( IVPP V 11454.3). B1. Posterior The p4 is oval in occlusal view, with a view. B2. Buccal view. B3. Occlusal view. See very narrow anterior part and a broad posfigure 10 for abbreviations. terior part. As in Cyclomylus lohensis , the protoconid and metaconid are close to each other and united by a very short metalophid II. The trigonid basin is a very narrow fissure opening anteriorly. The metalophid I is absent. The hypertrophic hypoconid extends anterobuccally. The ectolophid is low and short. The short hypolophid is complete and joins the hypoconid. The strong posterolo­

H1 [= h1 ‾ h2], in mm): M1/2 (V 11454.1),

4.1 X? X? (h1 = 11.1); LM1/2 (V

11453.6), 3.14 X 3.3 X 8.8 (= 9.8 ‾ 1);

RM3 (V 11454.2), 3.95 X 4.1 X 9.85 (10.25

‾ 0.4); and LM3 (V 11454.3), 3.73 X 4.1 X

10.96 (= 11.46 ‾ 0.5). See table 3 for lower

cheek teeth.

COMPARISON: Cyclomylus intermedius is

an intermediate form between C. lohensis

and C. biforatus in tooth morphology. It dif­

fers from C. biforatus in having a single in­

fraorbital foramen, three roots on upper

teeth, and two roots on lowers. The crown is

higher than in C. lohensis . The height differ­

ence of the enamel is larger than in C. loh­

ensis, nearly twice that of the latter. For ex­ Fig. 23. Occlusal view of cheek teeth of Cy­ ample, in C. intermedius the height differclomylus intermedius , new species. A. m1–3 ence on p4 is 11.34 mm, whereas in C. loh­ ( IVPP V 11455). B. p4–m3 ( AMNH 85543). ensis it varies from 4 mm to 6.4 mm (see

tables 2 and 3). In addition, the lower molars

extend buccal to lower incisor, whereas in C. phid is separated from the large entoconid by lohensis they are above the lower incisor. a shallow notch. The middle valley opens The eruption intervals of the cheek teeth are lingually. The posterior valley is broad and longer than in C. lohensis . holds accessory crests in it. The hypoflexid is oblique posterolingually. Cyclomylus biforatus , new species In IVPP V 11455 the occlusal surface of

Figures 24–27 ; table 4 m 1 is almost totally obliterated, that of the m2 is partly preserved: four transverse lo­ HOLOTYPE: An incomplete skull ( IVPP V phids and three valleys. The anterior valley 11442), from IVPP Loc. 77046, Saint is vestigial, the middle one is long trans­ Jacques, Nei Mongol, China. versely and open lingually, and the posterior REFERRED SPECIMENS: IVPP V 11441, one is a round basin. The hypoconid is hy­ 11443–11452. pertrophic and extends anteriorly. The hy­ GEOLOGICAL RANGE: Late early Oligocene poflexid shifts anteriorly and is strongly (upper member of Wulanbulage Formation). oblique posterolingually. GEOGRAPHIC DISTRIBUTION: Saint Jacques The m3 is similar to p4, but the trigonid ( IVPP Locs. 77045 [V 11441], 77046 [V is wider and has a distinct metalophid I and 11442, 11443], 77046 [white bed II] [V longer, prominent metalophid II. The proto­ 11444], 77047 [V 11445], 77049.2 [V conid and metaconid are of nearly equal size. 11446], 77049.3 [V 11447] and other locality The trigonid basin is wide and closed. The [V 11448]) and Qianlishan District ( IVPP hypolophid may be complete or incomplete. Locs. 78018 [79] [V 11449], 78018 [upper The middle valley is open lingually until part] [V 11450], 78019 [V 11451] and 79016 worn heavily. The closed posterior valley is [V 11452]), Nei Mongol, China. about the same size as the middle valley. The DIAGNOSIS: Infraorbital foramen is sepahypoconid does not extend as anteriorly as rated into two foramina; cheek teeth high in p4. The hypoflexid is slightly oblique and crowned with great unilateral hypsodonty does not shift much anteriorly. and with only one main, closed root and The lower incisor is triangular in cross without small roots; M1–2 originate medial section and has a flat labial side. The enamel to upper incisor. is thin, and the labial surface has distinct or ETYMOLOGY: Biforatus, Latin , double indistinct longitudinal ridges. holes. The name indicates that the infraor­ DIMENSIONS: Upper cheek teeth (L X W X bital foramen into two foramina.

TABLE 3 Measurements (mm) of Lower Cheek Teeth of Cyclomylus intermedius , new species

the pulp cavity is well developed, cylindrical in form, and with a flat or concave top.

In this species only the upper incisor is known. As in other tsaganomyids, it is triangular in cross section. Its labial surface is flat with longitudinal ridges.

DIMENSIONS: See table 4.

COMPARISON: Cyclomylus biforatus differs from C. lohensis and C. intermedius in infraorbital foramen being separated into two foramina and cheek teeth being higher crowned and having only one closed root.

Figures

Fig. 20. Right lower jaw with i2, p4–m3 of Cyclomylus intermedius, new species (IVPP V 823, holotype). A. Occlusal view. B. Buccal view. C. Anterior view showing the relation between i2 and p4.

Fig. 24. Ventral view of skull of Cyclomylus biforatus, new species (IVPP V 11442, holotype) (in stereo). Scale = 1 cm.

Fig. 25. Skull of Cyclomylus biforatus, new species (IVPP V 11442, holotype). A. Anterior view. B. Left lateral view. C. Ventral view.

Fig. 26. Occlusal view of cheek teeth of Cyclomylus biforatus, new species A. Left P4–M3 (IVPP V 11442, holotype). B. Left m1–3 (IVPP V 11447).

Fig. 27. Cheek teeth of Cyclomylus biforatus, new species. A. Left upper molar (IVPP V 11443.1). A1. Occlusal view. A2. Posterior view. A3. Buccal view. B. Buccal view of logitudinal section of right upper molar (IVPP V 11443.2). See figure 10 for abbreviations.