Parazhelestes mynbulakensis (Nesov, 1985) Archibald & Averianov, 2012

Archibald, J. David & Averianov, Alexander, 2012, Phylogenetic analysis, taxonomic revision, and dental ontogeny of the Cretaceous Zhelestidae (Mammalia: Eutheria), Zoological Journal of the Linnean Society 164 (2), pp. 361-426 : 379-384

PARAZHELESTES MYNBULAKENSIS

(NESOV, 1985B) COMB. NOV.

FIGURES 11–17

(See Appendix 4 for synonymies, referred illustrations, and referred specimens.)

Holotype: CCMGE 36 /12000, left dentary with m2 and alveoli for m3.

Type locality and horizon: CBI-4b, Dzharakuduk, Kyzylkum Desert, Uzbekistan. Bissekty Formation, Upper Cretaceous (middle- upper Turonian). Found in 1980.

Diagnosis: Differs from P. robustus in lower teeth averaging 13% smaller (range equals 4 to 21%) and upper teeth averaging 10% smaller (range equals 7 to 13%) and width of M3 subequal to M2 [37(0)].

Description: Maxilla. The known portions of the maxilla for P. mynbulakensis are similar to that bone in Aspanlestes , but some structural differences do exist. In P. mynbulakensis the jugal facet is closer to the alveolar margin above all molars (above the distal root of M1 to M 2-3 in Aspanlestes ). The infraorbital foramen is placed above the distal root of P4 or between the roots in P. mynbulakensis (URBAC 00–24, 02–59, 04–162) (but above the mesial root of P 4 in Aspanlestes ). In the most complete maxillary fragment (URBAC 04–162) there is not a wedge-like palatine facet anterior to the medial opening of the infraorbital foramen, and no detectable facets for maxilloturbinals.

Palatine. In ZIN 88468 there is a partial horizontal (palatal) process of the palatine attached to the maxillary fragment ( Fig. 11 ). The anterior portion of the process overlaps the maxilla ventrally and the maxilla- palatine suture is located close to the lingual border of the upper molars. There may be a postpalatine torus. Medial and posterior to M3 there is a longitudinally elongated complex depression bordered by elevated bone walls. This depression may correspond to the postpalatine foramen or minor palatine foramen in Zalambdalestes ( Wible et al., 2004) .

Upper dentition. The upper incisors, canine, and anterior premolars are not known for P. mynbulakensis . Judging from alveoli in URBAC 04–162 ( Fig. 12 ), P2 and probably P1 were double-rooted and relatively unreduced. P3 was also double-rooted, but much smaller than P2 (CCMGE 11/12176, URBAC 04–162). In URBAC 02–59 the P3 was lost and its alveoli were filled by bone, leaving a diastema between P2 and P4. As in Aspanlestes , the distal root of P4 is labiolingually wider than the mesial root (CCMGE 11/12176, URBAC 02–59), suggesting that P4 had a welldeveloped protocone swelling.

The P5 is known from several maxillary fragments and isolated specimens. The structure of P5 is essentially the same as in A. aptap . The development of the metacone is highly variable. In CCMGE 11/12176 ( Fig. 13 ) and URBAC 02–83, 04–109 the metacone swelling is almost indistinguishable. It is slightly more pronounced in URBAC 00–42, 02–1, and 02–59. In an unworn (unerupted) P5, URBAC 98–20, the metacone is a distinct trenchant cusp separated by a deep notch from the paracone; but with wear this cusp is easily eliminated leaving only a swelling distal to the paracone. A relatively worn CCMGE 21/12953 is unique in having the metacone as a distinct cusp widely separated from the paracone ( Nesov et al., 1998: fig. 12F–H). Some specimens (URBAC 98–20, 02–59) show a well-developed metastyle distolabial to the metacone. The paraconule is present in all specimens and the metaconule is absent. The precingulum is usually shorter than the postcingulum. URBAC 02–59 is unique in having the precingulum but not the postcingulum.

The DP 5 is known from five isolated specimens. It is somewhat larger than DP5 of A. aptap , but similar in structure. The specimens vary in development of the preparastyle, which can be smaller than the parastyle or almost the same size. The biggest discrepancy between the size of the preparastyle and parastyle is in URBAC 04–168 . In URBAC 04–151 , 04–168 , 04–206 , and 04–397 there is a distinct cingular cusp C connected by a transverse ridge to the centrocrista. In URBAC 04–213 the cusp C is much less developed, not more than a crenulation on the ectocingulum. In URBAC 04–151 and 04–397 there is a smaller additional cingular cusp immediately mesial to the cusp C. A small cingular cusp E is present in four specimens (in URBAC 04–213 this area of ectocingulum is missing). The lingual cingula vary in development. The precingulum is shortest in URBAC 04–151 and longest in URBAC 04–168 .

The upper molars M1-2 are known from several maxillary fragments and numerous isolated specimens. The structure of these teeth is basically the same as in A. aptap . The most variable part of the crown is the ectocingulum. A majority of M1s have no stylar cusps. In some M1s there is a small, but distinct stylocone (URBAC 98–18, 98–108, 02–8), crenulations in C and E cusp positions (CCMGE 11/12176, URBAC 98–19), or in C position (URBAC 02–8), or distinct cusp in E position (URBAC 98–18, 02–8, 04–99). The M1s of CCMGE 11/12953 and URBAC 02–27 have a distinct cusp C connected by a transverse ridge with the centrocrista, as in DP5s. The M2 appears to be less variable. No M2 has a stylocone or cusp C and only two M2s have a distinct stylar cusp E (URBAC 04–121 and 04–192). Two quite worn M2s (URBAC 02–28 and 06–93) still have a strong preparacrista extending mesially between the parastyle and preparastyle.

The M3 is known from a single isolated and quite worn specimen (URBAC 03–179; Fig. 14 ). Compared to M2, it has a larger and more labially projecting parastylar lobe, very reduced metastylar lobe, and a more mesiolabially positioned protocone. The metacone and the metaconule are relatively unreduced. In contrast to the M1-2, the postcingulum is much shorter than the precingulum. The M3 lingual root preserved in a maxillary fragment ZIN 88468 ( Fig. 11 ) shows that the lingual side of this tooth is aligned with other molars.

Dentary. The structure of the dentary in preserved fragments is the same as in Aspanlestes (the coronoid processes are not known for P. mynbulakensis ). The posterior end of the mandibular symphysis is between the roots of p2 (ZIN 88470), the distal root of p2 (six specimens), between p2 and p3 (URBAC 98–24), the mesial root of p3 (URBAC 00–11, 06–92), or between the roots of p4 (URBAC 02–104). The posterior shift of the mandibular symphysis is probably ontogenetically correlated. In URBAC 06–113 there are two small anterior mental foramina under i2 and one larger under the mesial root of canine. Two other specimens also preserve an anterior mental foramen under i3 (URBAC 04–193) or under the distal root of the canine (ZIN 88481). In other specimens the distal-most of the anterior mental foramina is under the mesial root of p1 (eight specimens), distal root of p1 (five specimens), or mesial root of p3 (URBAC 03–40). In ZIN 88482 and URBAC 98–24 this foramen is very large and extends for the whole length of p1. In URBAC 02–104 there is a lateral groove from below p1 to the mesial root of p3, which houses two large mental foramina at its ends. The posterior mental foramen is under the mesial root of p5 (seven specimens), between the roots of p5 (two specimens), or under the distal root of p5 (five specimens). The labial mandibular foramen is usually represented by three to six relatively large irregular openings.

The condylar and angular processes are preserved only in IZANUz P2155-M-1 ( Nesov et al., 1998: fig. 17). The shape and configuration of these processes and the mandibular foramen are essentially the same as in URBAC 02–77 of Aspanlestes . The medial end of the condylar process is completely preserved (abraded in URBAC 02–77) and pointed, giving a tear-like shape of the condyle in posterior view.

Lower dentition. In URBAC 06–113 ( Fig. 15 ), i2-3 are incompletely preserved, with most of the crowns eliminated by wear or breakage. Numerous edentulous anterior dentary fragments provide information about the lower incisors and canine. Most specimens had three lower incisors, with large i1-3 (i1 is somewhat smaller than i2-3) and a minute i4 wedged on the labial side between the alveoli for i3 and the canine. The root of i4 can be seen in URBAC 99–109 ( Fig. 16 ). The i4 position can be absent in some specimens, such as URBAC 98–13 ( Fig. 17 ).

The lower canine was a large, double-rooted tooth; its mesial root was shorter (URBAC 98–13, 06–113; Figs 15 , 17 ) or as large as the distal root (URBAC 99–109; Fig. 16 ). In ZIN 88470 the tip of the erupting lower canine crown is preserved with the remainder of crown in its crypt. It has a flattened lingual side with the apex deflected somewhat distally. In the deciduous canine the distal root was relatively smaller than in the permanent canine.

The p1, judging from its alveoli, was a small, double-rooted tooth set obliquely (the smaller mesial root was more labial than the distal root) in the dentary between the larger canine and p2.

The p2 is known from dentary fragments URBAC 97–3 and 02–13 ( Fig. 15 ). It is a relatively large, double-rooted tooth with a high main cusp and a small distal accessory cusp (there is no mesial accessory cusp). The mesial side of the main cusp is almost vertical; its apex is deflected somewhat distally. There is a very faint lingual cingulid above the mesial root. An unerupted p2 is also preserved in URBAC 00–68 and 06–111.

The p3, judging from the alveoli, was smaller than p2 and p4, but slightly larger than p1. It is aligned with other premolars in most specimens, but in URBAC 02–13 it is set obliquely to the longitudinal axis of the dentary, with the mesial root placed more labially than the distal root ( Fig. 15 ). The latter specimen is also unique in having the mesial root distinctly larger than the distal root, whereas in other specimens the distal root is somewhat larger than the mesial root. In some specimens p3 is absent and may have been lost during ontogeny (e.g. ZIN 88482, URBAC 99–109). In URBAC 99–109 there is a short diastema between the p2 and p4 with a little hole attached to the mesial alveolus of p4, possibly representing the distal alveolus for p3 ( Fig. 16 ). In ZIN 88482 there are no traces of p 3 in the diastema between p2 and p4.

The p4 is known from three dentary fragments (ZIN 88477, 88485, URBAC 99–109; Fig. 15 ). The p4 is a simple double-rooted tooth like p2, with a high main cusp having an almost vertical mesial side. The posterior accessory cusp is larger than in p2. There is a very small anterior accessory cusp (URBAC 99–109), or a short, faint mesial cingulid in its place (ZIN 88477).

The p5 is known from three dentary fragments and three isolated specimens ( Figs 16 , 17 ). This tooth is close in structure to p 5 in Aspanlestes and is as variable as in the latter taxon. The paraconid is absent in CCMGE 1/12953 (there is a very short mesial cingulid in its place), a minute cingular cusp in ZIN 82580 (the mesial cingulid on this specimen is much longer than in CCMGE 1/12953), a distinct, but still very small cusp at the base of the protoconid, closer to the lingual side of the latter (URBAC 98–16, 99–109, 04–226), or a larger and more elevated cusp, approximating the position of the paraconid in m1 (URBAC 98–13). In URBAC 98–13 and 99–109 there is a prominent mesial cingulid extending from the paraconid to around the labial base of the protoconid. The metaconid is represented by a metaconid swelling on the lingual side of the protoconid in most specimens, but in URBAC 98–13 it is a distinct cusp separated from the protoconid by a wide protocristid groove ( Fig. 17 ).

The dp5 is known from one dentary fragment and two isolated specimens. This tooth is almost identical in morphology and only slightly larger than dp 5 in Aspanlestes . One structural difference does exist: the precingulid in the dp5 of P. mynbulakensis is much reduced and ridge-like compared with the prominent cusp-like precingulid in this tooth in Aspanlestes .

The lower molars are known from several dentary fragments [amongst which URBAC 98–13 and 99–109 are most complete ( Figs 16 , 17 )] and a number of isolated specimens. The structure of the molars is identical to that in Aspanlestes . In m1 the variation concerns the postcingulid, which can be faint (URBAC 00–80, 04–399) or strong (other specimens). One m1 is unique in having an almost complete labial cingulid (URBAC 04–398). In another m1 there is a labial cingulid around the talonid and hypoflexid (URBAC 04–227). Other m1s totally lack the labial cingulid. In m2, as in m1, the most variable structure is the postcingulid. The postcingulid is absent in URBAC 06–65, faint in URBAC 03–170, 04–6, 04–123, and stronger in other specimens. In one m2 (URBAC 98–112) there is an almost complete labial cingulid connected with the postcingulid. The known sample of m3s shows no variation.

Measurements: See Appendices 2 and 3.

Figures

Figure 11. Parazhelestes mynbulakensis, ZIN 88468, stereophotographs and line drawings left palatine and maxilla with worn M1-2 and M3 fragment. A, anterior; B, occlusal; C, lingual views.

Figure 12. Parazhelestes mynbulakensis, URBAC 04–162, right maxillary fragment with M2 and alveoli for P1-P5, and M1. Stereophotographs of M2, A, occlusal; B, labial; C, distal views. D, photograph and line drawing of occlusal view of maxillary fragment.

Figure 13. Parazhelestes mynbulakensis, CCMGE 11/12176, stereophotographs and line drawings of right maxillary fragment with P3 alveoli, P4 roots, P5, M1-2. A, labial; B, occlusal; C, lingual views.

Figure 14. Parazhelestes mynbulakensis, stereophotographs of URBAC 04–168, right DP5, A, occlusal, labial, and distal views, and URBAC 03–179, left M3, B, occlusal, labial, and distal views.

Figure 15. Parazhelestes mynbulakensis, dentary fragments, stereophotographs of URBAC 06–113, left dentary fragment with i1 alveolus, i2-4 fragments, i4 alveolus, and canine roots, A, anterior and labial views; stereophotographs of URBAC 02–13, left dentary fragment with p2, p3 roots, and p4 anterior root and talonid; B, labial, occlusal, and lingual views; stereophotographs of URBAC 97–03, right dentary fragment with p1 alveoli, p2, p3 alveoli, p4 lacking anterior, p5 roots, and m1 alveoli, C, lingual, occlusal, and labial views; photographs of URBAC 97–03 showing ventral margin of dentary, D, labial and E, lingual (dashed line shows missing anteroventral margin); stereophotographs of ZIN 88477, left dentary fragment with p4, anterior root of p5, and alveoli for p3, F, lingual, occlusal, and labial views.

Figure 16. Parazhelestes mynbulakensis, stereophotographs URBAC 99–109, left dentary with i1-4, c, p1-3(?) roots or alveoli, and p4-5, m1-3. A, stereophotograph and line drawing of anterior end. Light grey indicates roots teeth and dark grey indicates alveoli. B, stereophotograph of teeth in labial, occlusal, and lingual views. Photographs showing entire dentary, C, lingual view and D, labial view.

Figure 17. Parazhelestes mynbulakensis, stereophotographs URBAC 98–13, left dentary with i1-3, c, p1-4 alveoli, and p5, m1-3. A, stereophotograph and line drawing of anterior end. Light grey indicates teeth and dark grey indicates alveoli. B, stereophotograph of teeth in labial, occlusal, and lingual views. Photographs showing entire dentary, C, lingual view and D, labial view.