Kielantherium gobiense Dashzeveg, 1975

Lopatin, Alexey & Averianov, Alexander, 2007, Kielantherium, a basal tribosphenic mammal from the Early Cretaceous of Mongolia, with new data on the aegialodontian dentition, Acta Palaeontologica Polonica 52 (3), pp. 441-446 : 442-444

Kielantherium gobiense Dashzeveg, 1975

Figs. 1–3 .

1975 [cf.] Aegialodon [sp.]; Kielan−Jaworowska 1975: 105, 106.

1975 Kielantherium gobiensis Dashzeveg, 1975: 402 , figs. 1, 2.

1976 Aegialodon gobiensis ; Fox 1976: 1117.

1978 Kielantherium gobiensis ; Crompton and Kielan−Jaworowska 1978: 257, figs. 2, 3.

1979 Kielantherium gobiensis ; Kielan−Jaworowska et al. 1979: 183, fig. 10−1.

1984 Prodelttheridium [lapsus calami for Prodeltatheridium] kalandadzei [nomen nudum]; Reshetov and Trofimov 1984: 12.

1984 Kielantherium gobiensis Dashzeveg, 1975 ; Dashzeveg and Kielan−Jaworowska 1984: 219, figs. 1, 2.

1990 Kielantherium gobiensis ; Butler 1990: fig. 3.

1992 Kielantherium ; Butler 1992: fig. 1.

1995 Kielantherium ; Sigogneau−Russell 1995: fig. 7C.

2000 Kielantherium gobiensis Dashzeveg, 1975 ; Kielan−Jaworowska et al. 2000: 599, fig. 29.17.

2001 Kielantherium gobiensis ; Kielan−Jaworowska and Cifelli 2001: fig. 5A.

2001 Kielantherium ; Luo et al. 2001: fig. 2.

2004 Kielantherium gobiensis Dashzeveg, 1975 ; Kielan−Jaworowska et al. 2004: 419, fig. 11.4A.

2006 Kielantherium gobiense Dashzeveg, 1975 ; Lopatin and Averianov 2006b: 1092, fig. 1 [correction of the species name according to the neuter gender of the generic name].

Holotype: PSS 10−14 , right lower molar, possibly m2.

Type locality: Höövör (variously spelled Khoboor, Khobur, Khoobur, and Khovboor), northern Gobi Desert, Mongolia.

Type horizon: Züünbayan [= Dzun Bayan, = Dzunbain] Svita (alternatively referred to as Khulsangol [= Khulsyngol] or Döshuul [= Dushuul,

= Dushi Ula] Svita), Aptian–Albian, Early Cretaceous.

Material.— PIN 3101/110, right upper molar, possibly M2; PSS 10−16, right dentary fragment with m1–4 and alveoli or roots of four double−rooted premolars, and broken alveolus for another premolar or the canine; PIN 3101/32, right dentary fragment with m1.

Diagnosis.—As for genus.

Description.—The outline of the upper molar, probably an M2 ( PIN 3101/110; Fig. 1 ), forms a near isosceles triangle dominated by the paracone and metacone, with an extensive stylar shelf and a very small protocone. The paracone and metacone closely approximate each other and are connate, with a very short and shallow centrocrista; the paracone is distinctly higher than the metacone. The lingual slopes of the paracone and metacone are slightly convex while their labial slopes are slightly concave. The preparacrista is mesiolabially directed and connects with the parastyle rather than with a minute stylocone; in the centre of the preparacrista there are two small cusp−like eminences. The parastylar wing ( Kielan−Jaworowska et al. 2004) is well developed. A distinct preparastyle is present lingual to the parastyle. The parastylar groove is well developed. The ectoflexus is distinct and of moderate depth. There are three small stylar cusps distal to the stylocone on the ectocingulum. The postmetacrista is more transverse than the preparacrista and bears a well developed postmetacrista cusp (cusp “ c ” in Crompton 1971, emended as “ C ” in Kielan−Jaworowska et al. 2004). There is a very small, ridge like metastyle. The protocone is a small, distinct but very low cusp; it is about one−fourth the height of the paracone. The protocone is narrow labiolingually and slightly elongate mesiodistally. The preprotocrista is rather long, extending mesiolabially towards the preparastyle. This labially extended preprotocrista and the preparacrista provide for double−rank prevallum/postvallid shearing, a distinctive synapomorphic feature of Tribosphenida ( Fox 1975; Luo et al. 2002; Kielan−Jaworowska et al. 2004). The postprotocrista is much shorter, terminating at the lingual base of the metacone. There are no conules. The crown is slightly worn, with prominent wear facet 1 along the preparacrista, on the mesial slope of the paracone apex, and along the parastylar groove and wear facet 2 along the postmetacrista and on the metacone apex. On the centrocrista the small wear facets 3 and 4 are confined to the paracone and metacone, respectively. There is also a distinct wear facet 5 along the preprotocrista. There are three roots; the preserved labial roots are rather long. The not preserved lingual root, supporting the protocone, apparently was distinctly smaller than the labial roots.

The lower molar ( PIN 3101/32; Figs. 2 , 3 ) is identified as m1 because the protocristid is almost transverse to the long axis of the dentary, as in m1 of PSS 10−16 ( Dashzeveg and Kielan−Jaworowska 1984: fig. 2B), whereas in the holotype (m2; Crompton and Kielan−Jaworowska 1978: fig. 3B) and in m2–4 of PSS 10−16, it is more oblique, with the metaconid placed somewhat posterior to the protoconid. The crown is dominated by a large trigonid, whereas the talonid is much smaller, some 24% of the trigonid length. The crown is higher labially than lingually because the crown basal margin is distinctly lowered labially. The apices of the protoconid and metaconid are broken off. In the trigonid the protoconid is the most massive and was almost certainly the tallest cusp, with its base (which is somewhat triangular in cross section) occupying most of the trigonid area. The trigonid basin is small and widely open lingually, with the bases of the paraconid and the metaconid well separated. The paraconid is a distinct, ridge like cusp, almost vertically directed. The paraconid is mesiodistally compressed, with a sharp paracristid, while the metaconid is more rounded at the base. On the anterior side at the base of the paraconid there are two prominent cingulid cusps, the mesiolingual cuspule e and the mesiolabial cuspule f. These cusps are well separated and apparently abutted against the distal margin of the ultimate premolar. The mesiolingual cuspule e is a continuation of a sharp vertical crest along the mesiolingual edge of the paraconid, but separated from the latter crest by a distinct notch. The distal metacristid ( Fox 1975) is a distinct, sharp crest, extending from the lingual side of the metaconid (possibly from its apex) towards the base of the hypoconid. The hypocristid is also high and sharp, separated from the distal metacristid by a distinct notch. The talonid is two−cusped, with the hypoconid about twice as large as the hypoconulid and placed midway along the width of the talonid, relatively close to the level of the protocristid notch. The talonid cusps are positioned close to one another. The lingual side of the hypoconid is almost vertical, sloping into the relatively small talonid basin. The hypoconulid is lower than the hypoconid and forms a short posterior wall of the talonid basin; it bears a sharp postcristid on its labial slope. The talonid basin is widely open lingually, without even an incipient entoconid; although bordered lingually by a distinct ridge (entocristid). The entocristid bears at least one crenulation, similar to that described for the K. gobiense holotype ( Dashzeveg 1975). The crown is at a very early stage of wear, showing only an incipient wear facet 3 in the hypoflexid produced by the paracone, the highest upper crown cusp. The two roots are almost equal in length.

Measurements.—See Table 1.

Remarks.—When found, PIN 3101/32 was a dentary fragment with two molars (m1–2) and alveoli for the ultimate premolar and m3 ( Fig. 3 ). Kielan−Jaworowska (1975) noted a similarity of this specimen to Aegialodon and subsequently it was included in the material of K. gobiense in the original description of this species, established upon a single lower molar from the Ulaanbaatar collection ( Dashzeveg 1975). Subsequently, this specimen suffered serious damage, and now only m1 adherent to a small piece of the dentary is preserved ( Fig. 2 ). Apparently it was broken along the crack seen on this specimen in a drawing from the PIN archive ( Fig. 3B ) and the posterior part of the specimen is now missing. This specimen was attributed to “ Prodeltatheridium kalandadzei ” [nomen nudum] by Boris A. Trofimov (Paleontological Institute, Moscow), according to the label accompanying this drawing.

The lower molar (m1) in PIN 3101/32 appears to be somewhat larger than previously known lower molars of Kielantherium ( Table 1). However, the actual measurements of the teeth in the previously known specimens of Kielantherium ( PSS 10−14 and 10−16) were never published. Our values for these specimens as given in Table 1 were taken from the published figures of them, so whether the differences in dimensions between PIN 3101/32 and these teeth are real is not entirely certain.

Figures

Fig. 1. Tribosphenic mammal Kielantherium gobiense Dashzeveg, 1975. PIN 3101/110, right upper molar, possibly M2. Höövör, Mongolia; Early Cretaceous. SEM micrographs. In occlusal view (A, stereopair); explanatory drawing of occlusal view (B), posterior (C), labial (D), and lingual (E) views.

Fig. 2. Tribosphenic mammal Kielantherium gobiense Dashzeveg, 1975. PIN 3101/32, right dentary fragment with m1 as now preserved. Höövör, Mongolia; Early Cretaceous. SEM micrographs. In occlusal (A, stereopair), lingual (B), anterior (C), posterior (D), and labial (E) views.

Fig. 3. Kielantherium gobiense Dashzeveg, 1975. PIN 3101/32, right dentary fragment with m1–2 and alveoli for the ultimate premolar, and m3. Original unpublished drawing by Konstantin P. Meshkov of the specimen from the PIN archive before damage. Höövör, Mongolia; Early Cretaceous. This drawing should be considered with caution as the tooth proportions are not always exact, particularly wrong is depicting of the m1 talonid in lingual view (C), showed as a part of the m2 crown. In occlusal (A), labial (B), and lingual (C) views.