Kryptobaatar dashzevegi Kielan−Jaworowska, 1970

Kielan-Jaworowska, Zofia, Hurum, Jørn H. & Badamgarav, Demchig, 2003, An extended range of the multituberculate Kryptobaatar and distribution of mammals in the Upper Cretaceous of the Gobi Desert, Acta Palaeontologica Polonica 48 (2), pp. 273-278 : 274-275

Kryptobaatar dashzevegi Kielan−Jaworowska, 1970

Figs. 1, 2 .

Synonyms: Gobibaatar parvus Kielan−Jaworowska, 1970 ; Tugrigbaatar saichanensis Kielan−Jaworowska and Dashzeveg, 1978 .

Comment.— Kryptobaatar dashzevegi is one of the best known multituberculate species, described in detail in numerous publications by Kielan−Jaworowska (1970, 1980, 1998), Kielan−Jaworowska and Dashzeveg (1978, referred to as Tugrigbaatar saichanensis ), Kielan−Jaworowska and Gambaryan (1994), Gambaryan and Kielan−Jaworowska (1995), Rougier et al. (1996), Kielan−Jaworowska and Hurum (1997), Wible and Rougier (2000); see also Smith et al. (2001) for description of K. mandahuensis . We confine our description to the new specimen (PM 120/108) found at Hermiin Tsav I in the Gobi Desert ( Mongolia), during the 2000 Nomadic Expedition “Dinosaurs of the Gobi” (see Kielan−Jaworowska et al. 2002) by the third author, and to a comparison with previously described materials. For description of Hremiin Tsav beds see Gradziński and Jerzykiewicz (1972).

Description.—PM 120/108 is an incomplete skull, slightly compressed laterally, with the right zygomatic arch and left postorbital process (with broken tip) preserved, and damaged basicranial and occipital regions. The dentaries are missing. The state of preservation of the bone and teeth is poor and the sutures are hardly discernible. The bones of the cranial roof are strongly broken, preserved in the middle part of the roof and missing anteriorly and posteriorly.

Both I2s, covered with a honey−colored enamel band (limited to the anterior part of the teeth), are arranged obliquely and meet one another at the tips. The I3s are missing. On the right side only P1–P3 have been preserved; on the left side P2, P3, M1, and M2 are present. P1 and P2 are three−cusped; P3 is four−cusped and smaller than P1 and P2. The cusp formulae of the molars are: M1,?4:4:ridge; M2, 1:2:3. On M1 the cusps in the middle of the outer row are broken and the outermost part of the tooth is missing, and therefore we are not sure if there were 4 or 5 cusps in the outer row ( Fig. 2A 4). The cuspules on the medial ridge in M1 are not discernible.

Measurements of the teeth are given in Table 1.

sandstone 10 mm

Comparisons.—As may be seen in Table 1 and Fig. 2 , the length and width of the upper premolars and molars, and cusp formula of M 1 in PM 120/108 from Hermiin Tsav I, fall within the range of variability of specimens of K. dashzevegi from the Djadokhta Formation at Bayan Zag and Tögrög, and from the Ukhaa Tolgod beds at Ukhaa Tolgod. Kielan−Jaworowska and Hurum (1997) argued that the teeth in K. dashzevegi , in particular M1, show a high degree of variability (see also fig. 4 of their paper showing M1 with five cusps in the outer row and five cuspules on the inner ridge, and plate 3: fig. 7 in Kielan−Jaworowska and Hurum 2001, showing M1 with five cusps in the outer row and three cuspules on the inner ridge).

Kielan−Jaworowska and Hurum (1997) recognized within the specimens of K. dashzevegi two types of skull structure, referred to as “wide snout” and “narrow snout”. They admitted that the differences between the two types might be in part due to the state of preservation (dorso−ventral versus lateral compression), and also to the individual age, the older individuals having a wider skull. PM 120/108 resembles more the “narrow snout” ( Kielan−Jaworowska and Hurum 1997: fig. 3) than the “wide snout” (fig. 2 in the same paper).

Figures

Fig. 2. Comparison of teeth in Kryptobaatar dashzevegi. A. PM 120/108, Hermiin Tsav I, Gobi Desert, Mongolia; upper incisors (A1), right P1−P3 (A2), left P2, P3 (A3), left M1, M2 (A4). B. Right M2, ZPALMgM−I/52, Djadokhta Formation, Bayan Zag. C. Right M1 and M2, ZPALMgM−I/8, Djadokhta Formation, Bayan Zag. All SEM micrographs in occlusal view. M1 in A4 appears narrower than it originally was because of break of the middle cusps in outer row and outer margin.