Tsaganomyidae Matthew and Granger, 1923

WANG, BANYUE, 2001, On Tsaganomyidae (Rodentia, Mammalia) of Asia, American Museum Novitates 3317, pp. 1-52 : 4-14

Tsaganomyidae Matthew and Granger, 1923

TYPE GENUS: Tsaganomys Matthew and Granger, 1923 .

INCLUDED GENERA: Cyclomylus Matthew and Granger, 1923 , and Coelodontomys , new genus.

RANGE: Oligocene and possible earliest Miocene of China, Mongolia, and Kazakhstan.

EMENDED DIAGNOSIS: Fossorial rodents close to Marmota in size; skull protrogomorphous, massive and low; sagittal and occipital crests prominent; orbit very small; temporal fossa very large; occiput sloping forward, very wide; braincase nearly triangular in shape, with narrow postorbital constriction; strong zygomatic arches almost forming a circle; anterior end of zygoma formed by broad vertical maxillary and jugal; small oval infraorbital foramen; jugal extending mediodorsally to meet the premaxillary; bulla flattened anteriorly, heavily septate; malleus and incus not fused; internal carotid artery system absent; mandible hystricognathous with large, flared angular process and high coronoid process; mental foramen anterior to p4; dental formula 1013/1013; incisors procumbent, with flat labial surface; upper incisor extending back into orbit, with posterior end of alveolus forming a bulge on side wall of maxillae, ending laterodorsal to M1–2; lower incisor extending back to and beneath condyle; incisor enamel multiserial; cheek teeth cylindrical, unilaterally hypsodont, four crested without hypocone; occlusal surface of cheek tooth row steplike; occlusal pattern lost very early in wear, becoming a concave surface bordered by higher margins.

DISCUSSION: The tsaganomyids were first per incisor; molars extending high into orbit, named as a subfamily, Tsaganomyinae, of passing by medially to upper incisor; lower Bathyergidae , by Matthew and Granger cheek teeth concave anterolingually and ex­ (1923) to include two genera and species, tending buccally to lower incisor; cheek teeth Tsaganomys altaicus and Cyclomylus lohen­ strongly unilaterally hypsodont, having short sis, which was followed by Teilhard de Char­ conic pulp cavity with pointed apex, ratio of din and Leroy (1942). Landry (1957) ar­ dentine part to pulp cavity high, enamel on ranged the tsaganomyids in the subfamily occlusal surface very thin, cusps and lophs Bathyerginae of the Bathyergidae . However, very low and weak, no core present after be­ Teilhard de Chardin (1926) thought they rep­ ing worn; lower cheek teeth with nearly resented a special family, a viewpoint ne­ transversely stretched external valley; nearly glected for a long time. Patterson and Wood square p4 with low metalophid I, long me­ (1982) formally raised the tsaganomyids to a talophid II, subequal metaconid and protofamily rank to include Tsaganomys , Cyclo­ conid; incisor enamel having thin PE with no mylus, and perhaps Pseudotsaganomys , Se­ inclined prisms and PI with 20–30° inclined pulkomys, and Beatomus . Other authors con­ HSB of 5–7 prisms.

sidered them cylindrodonts (Wood, 1937,

1955, 1974; Wilson, 1949; Simpson, 1945; Tsaganomys altaicus Matthew and Granger, Schaub, 1958 , Vinogradov and Gambaryan, 1923

1952; Mellett, 1968; Shevyreva, 1972,

1974a, 1974b, 1994; Kowalski, 1974; Figures 2–12 , 13A , 14 ; table 1

Huang, 1993). I agree with Teilhard de Char­ Tsaganomys altaicus Matthew and Granger, 1923 din (1926) and Patterson and Wood (1982) (partim): 2–4, figs. 1 (partim), 2 (partim). Teilthat the Tsaganomyidae warrant family rank. hard de Chardin, 1926: 29, 30, fig. 16C; pl. IV,

figs. 4–6. Bohlin, 1937: 46–48, figs. 110–123. Tsaganomys Matthew and Granger, 1923 Vinogradov and Gambaryan, 1952 (partim): 23,

24. Mellett, 1968 (partim): 6, 10. Qiu and Gu, Tsaganomys Matthew and Granger, 1923 (par­ 1988: 207, 212. Huang, 1993: 38–39, pl. II, tim): 2. Bryant and McKenna, 1995 (partim): figs. 1, 2. Bryant and McKenna, 1995 (partim): 5–16. McKenna and Bell, 1997 (partim): 191. 5–16, fig. 9.

Beatomus Shevyreva, 1972: 143 . Cyclomylus lohensis Matthew and Granger, 1923

(partim): 5. Kowalski, 1974 (partim): 158.

TYPE SPECIES: Tsaganomys altaicus Mat­ Tsaganomys sp. Teilhard de Chardin 1926: 30, thew and Granger, 1923. figs. 16A, B; p1. IV, fig. 7. Wang et al., 1981: GEOLOGICAL RANGE: Late early Oligocene 27–30. Emry et al., 1998 (partim): 308–310, to early late Oligocene, possible early Mio­ fig. 8A.

cene. Beatomus bisus Shevyreva, 1972: 143 , 144, fig. GEOGRAPHIC DISTRIBUTION: Nei Mongol, 6; 1974a: 51–53, figs. 1d, e, 2, 3.

Gansu, Ningxia provinces of China; Valley Tsaganomys minutus : Huang, 1993: 39–42, pl. II ,

figs. 3–5.

of Lakes of Mongolia; and Kazakhstan.

Beatomus gloriadei Shevyreva, 1994: 112 , figs. EMENDED DIAGNOSIS: Medium­ to large­

1a, b. NEW SYNONYMY.

sized tsaganomyids; nasal­frontal suture

more anterior in position than is premaxil­ HOLOTYPE: A skull and lower jaw ( AMNH lary­frontal suture; left and right antepre­ 19019) from the Hsanda Gol Formation , red molar crests curved and uniting before reach­ strata, Loh , Tsagan Nor basin, Mongolia. ing incisive foramen; premaxillary­maxillary Figured by Matthew and Granger, 1923: figs. suture intersecting merged antepremolar 1 (partim) and 2 (partim).

crest; infraorbital foramen oval, with major PARATYPES: AMNH 19020 and 19037 .

axis nearly horizontal, almost parallel with REFERRED SPECIMENS: IVPP V 10410.1– anterior margin of ventral surface of anterior 18, V 10411, V 10411.1–9, V 11388–V zygomatic root; angle between dorsal margin 11426, V 11539–11542, V 11825, V 11826; of posterior part of upper incisor alveolus LDV 860911.1–14; Sh 1; W 25; MNHN and occlusal surface of cheek teeth near 40°; 1924 –4; AMNH 19039, 19097, 21634, nearly straight P4 extending medially to up­ 26185, 56650, 81223A, 81249, 81261, 81269, 81356, 81357, 81360, 81364, 81390, 81392, 81464, 81465, 81474, 81480, 81483, 81486–81490, 81991, 82126, 82178, 82262, 82265, 82273, 82289, 82292, 83510, 83516, 83519, 83520, 83522, 83525–83528, 83533, 83535, 83539, 83540, 83555, 83558, 83566, 83571, 83573, 83574, 83576, 83584, 83586, 83590, 84328, 84332, 84352, 84513, 84517, 85184, 85191–85193, 85195–85204, 85234– 85238, 85240, 85250, 85251, 85253, 85257, 85258, 85261, 85264, 85265, 85271, 85273, 85275, 85276, 85282, 85283, 85285, 85286, 85291, 85302, 85309, 85541, 85784, 85786, 85787, 85789–85791, 85793–85800; PIN 475/1899, 475/1980, 475/115, 475/553, 475/ 363, 2979/909, and K 35(15)/424.

GEOLOGICAL RANGE: Late early Oligocene (upper member of Wulanbulage Formation, upper part of Ulantatal Formation, Qingshuiying Formation, Hsanda Gol Formation, yellow sandstone and lower part of red mudstone of lower member of Xianshuihe Formation, and Buran Formation), early late Oligocene and early Miocene (?) (red mudstone in Gaolanshan).

GEOGRAPHIC DISTRIBUTION: Saint Jacques ( IVPP Locs. 77045 [V 11388], 77046 [V 11389], 77046 [red bed II, V11390], 77046.2 [V 11391], 77046 [white bed II, V 11392], 77046.3 [V 11393], 77046.5 [V 11394], 77047 [V 11395], 77048.2 [V 11396], 77049.2 [V 11397], 77049.8 [V 11398], 78020 [V 11399], and other localities [V 11400–11403]) of Hanggin Qi ; Tuolimiao (V 11404) of Bulunmiao and Qianlishan District ( IVPP Locs. near 78016 [V 11405], 78018 [upper part, V 11406], 78018 [V 11407], 78018 [79] [V 11408] 78019 [V 11409], 79015 [V 11410]) of Otog Qi ; and Ulantatal (V 10410, V 10411, V 11411–11414) and Huhetaolegai ( IVPP Locs. 94003 [V 11415], 94003­2 [V 11416]) of Alxa Zuoqi in Nei Mongol; Yuanjiawowo ( IVPP Locs. 92012­ 1A [V 11421], 92013­1 [V 11422], 92013­2 [V 11423]) of Haiyuan , and Sikouzi (V 11424) of Guyuan , Ningxia; Lanzhou ( GL Locs. 9005 [V 11417], 9006 [V 11418], 9016 [V 11419], 9016B [V 11420], 9707A [V 11539], 9707C [V 11540], 9707D [V 11541], 9711 [V 11542], 9712 [V 11825], 9715 [V 11826]; the Gaolanshan [ LDV 860911 ]); Shargaltein Gol (Sh 1) and Wu­tao­ya­yu ( W 25 ) of Danhe in Gansu; and lodontomys. The complementary description other locality (V 11426) of China; Hsanda given below deals mainly with the differenc­ Gol, Loh of Tsagan Nor Basin, Mongolia (V es of Tsaganomys from the other two genera 11425, PIN 475 /1899, 475/1980, 475/115, and some additional characters, mainly based 475/553, 475/363, and other specimens in on the holotype ( AMNH 19019 ), IVPP V AMNH); and Chaybulak­Dzhamangora wa­ 10411 and V 11390, and MNHN 1924­4 . tershed ( PIN 2979 /909) and K15 , Podoro­ In general the shape of the skull is much zhinik, Zaysan Basin, Kazakhstan ( K35 [15]/ like those of fossorial rodents in having a 424). low lateral profile, narrow rostrum, broad

EMENDED DIAGNOSIS: As for the genus. cranial region, and an occiput sloping ante­

DESCRIPTION: The skull was described by riorly. The rostrum is about two­fifths of the Bryant and McKenna (1995). However, the total length of the skull. description was based on the specimens rep­ DORSAL VIEW: The skull is triangular in resenting Tsaganomys , Cyclomylus , and Coe­ shape with a narrow anterior end. The rostrum is slightly reduced anteriorly in width. The long nasals taper posteriorly in their posterior part and meet the frontal at about the level of the anterior margin of the orbit. The nasal­frontal suture is concave posteriorly. The dorsal process of the premaxillary is wide and extends more posteriorly than does the nasal. The premaxillary­frontal suture is slightly more posteriorly located than is the nasal­frontal suture and is almost parallel to the anterior part of the sagittal crest. The dorsal part of the lachrymal is large, round, with a narrow posterior process, and inserts among the jugal, premaxillary, and frontal. The very small orbit is posterior to the jugal and lateral to the lachrymal. The narrowest part of the skull is across the postorbital constriction rather than the interorbital constriction as described by Bryant and McKenna (1995). The dorsal part of the frontal is very short and wide. The parietals are long, as long as the combined length of the nasal and frontal, and roughly hexagonal in outline, with an M­shaped frontal­parietal suture. The temporal surface of the squamosal is large, with a well­developed zygomatic process uniting with the jugal. One of the particular features is that the temporal fossae are tremendous. The prominent sagittal crest starts from a pronounced anterior process on the anterolateral corner of the frontal and extends posteromedially as a curved crest. Near the frontal­parietal suture the two crests unite with each other to form a single longitudinal crest that joins with a strong occipital crest. The anterior process of the sagittal crest (the antorbital crest of Bryant and McKenna, 1995) is, in fact, located dorsomedial to the orbit, rather than anterior to it. Like the supraorbital swelling in Paramys , the anterior process of the sagittal crest appears to be homologous to the postorbital process of the Sciuridae , as suggested by Wood (1962: 16). The well­developed zygomatic arches are strongly convex outwards.

VENTRAL VIEW: The diastema between incisor and P4 is very long, nearly half the basal length of the skull. The incisive foramen is very small and narrow and located near the midpoint of the diastema. The crest, running from the alveolus of P4 to the incisive foramen, is called antepremolar crest here and may mark the lateral margin of the palate. It is concave laterally and well developed, and it sometimes forms high bony plates. Left and right antepremolar crests merge into one longitudinal crest near the midpoint between P4 and incisive foramen. The premaxillary­maxillary suture crosses the merged crest. There are distinct fossae lateral to the crests. The zygomatic process of the maxillary extends laterally anterior to P4 and forms the lower branch of the anterior root of the zygomatic arch. On the ventral surface there are wide rough areas for anchoring the masseter muscles. The two cheek tooth rows are very short in comparison with the skull and parallel to each other. The palate between them is concave transversely, with a longitudinal crest extending along the palatine suture to separate the palate into two longitudinal grooves. The posterior palatine foramina are opposite M2. The maxillarypalatine sutures are nearly M­shaped, with a V­shaped anterior part at the posterior end of the posterior palatine foramina and two lateral parts running along the lingual side of M2–3 and then turning laterally behind M3. There is a pair of distinct posterior maxillary foramina posteromedial to M3. The choana opens at the level of posterior border of M3. The very small, shallow pterygoid fossa is not perforated; it is situated far behind the anterior border of the choana. The bulla is oval in shape and slightly inflated, with ossified external auditory meatus extending laterally. The blunt mastoid process protrudes posterolaterally. The broad, short glenoid fossa consists of the zygomatic processes of squamosal and jugal. The postglenoid foramen is large.

ANTERIOR VIEW: The nostril is very small. The infraorbital foramen is small, oval, facing anteriorly and slightly ventrally, and with no evidence of passage for the masseter onto the rostrum. The major axis of the infraorbital foramen is strongly inclined and usually nearly horizontal, almost parallel to the anterior margin of the ventral surface of the maxillary. As described by Bryant and McKenna, the anterior zygomatic root is expanded to a wide, thin plate and consists of zygomatic processes of maxillary and jugal. The anterior part of the jugal expands to meet the lachrymal and premaxillary, ex­

= 1 cm.

cluding the contact between the maxillary cheek teeth is near 40°. The occlusal surface and the lachrymal. of the cheek tooth row is steplike: the pos­ LATERAL VIEW: The nostril is retracted. terior edge of the preceding tooth is slightly The anterior ends of the nasals are much lower than the anterior edge of the succeedmore posteriorly located than those of the ing one.

premaxillae. The anterior process of the tem­ As described by Bryant and McKenna poral crest is anterior to the P4. The pocket (1995), the upper molar alveoli extend into formed by jugal, lachrymal, and maxillary is the orbital area medial to the upper incisor. here interpreted as the eye socket rather than However, the alveolus of P4 reaches the methe origin of the masseter muscle (as sug­ dial side of the upper incisor only and does gested by Bryant and McKenna, 1995) be­ not extend into the orbital area.

cause there is no scar for any muscle, and, MANDIBLE: The mandible has been deto the contrary, there is a nasolachrymal fo­ scribed by Bryant and McKenna (1995) in ramen in it. As so interpreted, the orbit must detail. A few additions are given below. The be very small, and the orbital crest is formed diastema is long, and the mental foramen is by the jugal and lachrymal. In the orbit the located anterior to P4. The coronoid process orbital wing of the lachrymal extends rather is high. The condyloid process is well dewidely. Just behind the orbital crest there is veloped, with a wide, triangularly convex ar­ a crest extending posteroventally to the eth­ ticular surface, and without postcondyle exmoid foramen. It may form the anteroventral pansion. The masseteric fossa is large and margin of the temporal fossa. The very deep, with more or less distinct masseteric strong upper incisor is procumbent, extends crests. There is a small fossa situated below back into orbital area, forming a bulge on the m1–2 and anterior to the masseteric fossa. lateral side of maxillary, and ends lateral to On the lingual side of the ascending ramus M1–2. The angle between the dorsal surface no distinct mandibular foramen is visible. of the posterior part of the upper incisor al­ The medial surface of the angular process is veolus and the occlusal surface of the upper separated by a longitudinal crest into two parts: a large fossa above and a narrow flat one along the lower margin. The upper fossa may be for the insertion of the internal pterygoid muscle and the lower plate for the superficial masseter muscle, pars reflexus. The lower cheek teeth are concave anterolingually and extend buccal to the lower incisor alveolus. As in the upper cheek teeth, the occlusal surface of the lower cheek teeth row is also steplike, but the posterior edge of the preceding tooth is higher than the anterior edge of the succeeding one.

DENTITION: The cheek teeth are all cylindrical in form, strongly unilaterally hypsodont, and with an open root. The occlusal surface is covered by very thin enamel when unworn. The occlusal pattern is only very weakly expressed and is lost very early with wear. Then the occlusal surface becomes smooth, concave with higher margin, but without core on it. The enamel covers the anterior and lingual walls on the uppers and the buccal and posterior walls on the lowers. The uncovered part of the tooth may represent part of the root. The dentine between the occlusal surface and the top of the pulp cavity is called the dentine part here. It is high and probably grows continuously during the lifetime. The pulp cavity is relatively short and has a pointed apex. The ratio of the dentine part to the pulp cavity is high.

I have not yet seen any upper cheek tooth with the occlusal pattern well preserved, but seen; there is a string of tiny cusps instead. I have found some unworn lower cheek The posterolophid is complete and reaches teeth. AMNH 82289 preserves a slightly the metastylid to close the talonid basin. No worn p4. In AMNH 83510 an erupting p4 distinct entoconid and hypoconulid are visiwas found under dp4, which was removed ble. The prominent, but not hypertrophied, (figs. 11, 12). The unworn p4 is nearly hypoconid extends anterobuccally. The ecsquare in occlusal view and its trigonid is tolophid is straight. The hypoflexid (= exslightly narrower and higher than the talonid. ternal valley) is shallow and slightly oblique Very thin enamel covers the occlusal surface in posterolingual direction. On IVPP V and all side walls but extends only a short 11402 the m3 is erupting. It is oval in occludistance downward on the anterolingual wall. sal view. As in p4 the protoconid, metaconid, The occlusal pattern is very shallow, with and metalophid II are distinct, but the metavery weak cusps and lophids. The nearly lophid I is weaker. The entoconid is develequal protoconid and metaconid are separat­ oped. The hypolophid is complete and low ed by relatively long metalophid II. The me­ and joins the hypoconid. The hypoconid is talophid I is low and weak. Behind the meta­ close to the protoconid in position, and the conid there is a crest or cusp, which may be hypoflexid is shallower and more anteriorly the metastylid. No distinct hypolophid is located.

The incisors are approximately triangular tudinal ridges are usually distinct but somein cross section, with a round lingual top, an times weak or even absent. The upper incisor almost right buccomedial angle, and a flat or is slightly thinner in labiolingual direction slightly convex labial side. The enamel cov­ then is the lower one. The enamel has mulers the labial side and nearly one­fourth of tiserial microstructure. In the lower incisor, the medial and external sides. On the surface the PE is very thin, about 10% of the total of the enamel of the labial side, the longi­ thickness of the enamel (170–185µm). The

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Figures

Fig. 2. Skull of Tsaganomys altaicus (IVPP V 11390). A. Dorsal view. B. Ventral view. Scale = 3 cm.

Fig. 3. Skull of Tsaganomys altaicus (IVPP V 11390). A. Anterior view. B. Dorsal view. C. Ventral view. Abbreviations are: aal, anterior alar fissure; aasc, anterior opening of the alisphenoid canal; b, bulla; bo, basioccipital; bs, basisphenoid; eam, external auditory meatus; f, frontal; gf, glenoid fossa of squamosal; in, incisive foramen; iof, infraorbital foramen; j, jugal; l, lachrymal; m, maxillary; mstp, mastoid process; na, nasal; p, parietal; pasc, posterior opening of the alisphenoid canal; pl, palatine; pm, premaxillary; pop, postorbital process; sq, squamosal.

Fig. 4. Ventral view of skull of Tsaganomys altaicus (AMNH 19019, holotype) (in stereo). Scale

Fig. 5. Skull and lower jaw of Tsaganomys altaicus (IVPP V 11390). A. Right lateral view of skull. B. Left lower jaw. B1. Occlusal view. B2. Buccal view. Scale = 3 cm.

Fig. 6. Skull and lower jaw of Tsaganomys altaicus (IVPP V 11390). A. Left lateral view at skull. B. Left lower jaw. B1. Occlusal view. B2. Buccal view.

Fig. 7. Upper jaws of Tsaganomys altaicus showing the relation between I2 and upper cheek teeth. A. Right upper jaw with part of I2 and P4–M2 (IVPP V 11415). A1. Buccal view. A2. Anterior view. B. Right upper jaw with I2 and P4–M3 (AMNH 85273). B1. Buccal view. B2. Anterior view. B3. Occlusal view. B4. Lingual view.

Fig. 8. Left lower jaw of Tsaganomys altaicus (AMNH 19019, holotype). A. Occlusal view (in stereo). B. Lateral view. Scale = 1 cm.

Fig. 9. Lower jaws of Tsaganomys altaicus showing the relation between i2 and lower cheek teeth. A. Right lower jaw with i2 and p4–m3 (IVPP V 11417.1). A1. Occlusal view. A2. Buccal view. A3. Ventral view. A4. Anterior view. B. Anterior view of left lower jaw with p4–m2 (AMNH 82273).

Fig. 11. Occlusal view of right lower jaw with p4–m3 of Tsaganomys altaicus (AMNH 83510) (in stereo); Scale = 5 mm.

Fig. 12. Occlusal view of cheek teeth of Tsaganomys altaicus. A. Right p4–m3 of AMNH 83510. B. Right dp4–m3 of IVPP V 11402. C. Right p4 of AMNH 82289.

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. 14. Dental measurements of Tsaganomys altaicus specimens. A, B. Histograms of measurements of length of cheek tooth rows. C, D. Histograms of measurements of length of molar rows. E– L. Scatterplot of measurements of length and width of cheek teeth. Solid squares represent the holotype (AMNH 19019), and open circles represent other specimens.