Asionyctia guoi, Missiaen & Smith, 2005

Missiaen, Pieter & Smith, Thierry, 2005, A new Paleocene nyctitheriid insectivore from Inner Mongolia (China) and the origin of Asian nyctitheriids, Acta Palaeontologica Polonica 50 (3), pp. 513-522 : 514-517

Asionyctia guoi sp. nov.

Holotype: IMM 2004 −SB−1, left dentary fragment with p4–m1 and alveoli of p2–3.

Paratypes: IMM 2001 −SB−9,left dentary fragment with p4 and alveoli of i1–p3 ; IMM 2004 −SB−2, right dentary fragment with p3–4 and alveoli of c–p2 ; IMM 2001 −SB−10, right dentary fragment with m1–2 and alveoli of m3 ; IMM 2001 −SB−11, left m3 ; IMM 2004 −SB−3, right P4 ; IMM 2001 −SB−12, left M1 ; IMM 2001 −SB−13, left M2 ; IMM 2001 −SB−14, fragmentary right M3 ; IMM 2001 −SB−15, fragmentary left M3 .

Referred material: At present the collection of Asionyctia guoi from Subeng contains 8 more dentulous dentary fragments, 55 isolated teeth and 21 identifiable fragmentary cheek teeth.

Type locality and age: Subeng (N 43 ° 31´50´´ E 111 ° 44´04´´ 955 m above sea level), Erlian Basin , Inner Mongolia, China. Upper part of the Nomogen Formation , late Paleocene, Gashatan ALMA .

Etymology: In honor of the Chinese paleontologist Dian−Yong Guo ( IMM) for his contribution to the knowledge of the fossil vertebrates of Inner Mongolia.

Diagnosis.—Asionyctiine nyctitheriid differing from all other Asionyctiinae by the paraconid positioned high on p4. Differing from Oedolius , Voltaia , and Bayanulanius by the lower molars with an oblique crest that joins the trigonid low on the trigonid wall and the smaller hypoflexid. Further differing from Oedolius by its less reduced paraconid and the presence of an entocristid on the lower molars. Differing from Bumbanius by the absence of a metaconid on p4, from Voltaia by its single talonid cusp on p4 and the smaller and more reduced lower premolars, and from both by its smaller size.

Measurements.—See Table 1.

Description

The mandible has two mental foramina, a large one positioned below the posterior root of p2 and the anterior root of p3 and a small one positioned below the roots of p4. It contains the alveoli for three anteriorly projecting incisors. The alveolus for i3 is followed by a large alveolus for the canine and by two small alveoli. No small uniradicular teeth fitting these alveoli were found and the position and size of these alveoli seems to indicate that p1 is absent and p2 is double−rooted and moderately smaller than p3. The absence of p1 would be unique among nyctitheriids; lacking further confirmation, we prefer to handle this feature with a certain care but at least it is clear that Asionyctia guoi has undergone a reduction of the anterior lower premolars but not of the other lower antemolar teeth.

The p3 is double−rooted with a moderately high protoconid that is situated above the anterior root. The small paraconid is positioned high on the anterior side of the protoconid, and from the posterolingual side of the protoconid a ridge descends to a single median talonid cusp.

The p4 is premolariform and larger than p3, subequal to m 1 in length. p4 has a well−developed paraconid and paracristid, both positioned high on the protoconid, and a small anterolabial cingulum, but the metaconid is completely undeveloped. A strong crest descends posterolingually from the protoconid to a single, median talonid cusp. A talonid basin is not developed, but a small lingual notch is consistently present.

The m1 has an anteriorly projecting paraconid that is crestiform and fused with the paracristid. The protoconid is slightly larger and higher than the metaconid. The anterolabial cingulum is well−developed and can continue along the base of the protoconid. The hypoconulid is slightly closer to the entoconid than to the hypoconid and is the smallest talonid cusp, while the hypoconid and entoconid are subequal in height. The ridge between hypoconid and hypoconulid often exhibits considerable wear and in worn specimens the hypoconid may be the lowest of the talonid cusps. The oblique crest joins the trigonid low on the trigonid wall.

The m2 differs from m 1 in having a slightly less anteriorly projecting paraconid, and a shorter and wider trigonid that is slightly larger than the talonid.

The m3 resembles m2 but is somewhat smaller with a narrower talonid and a distinct hypoconulid.

P4 is premolariform and lacks a metacone, the crown consisting of a small parastyle, a large paracone and a large crest descending posterolabially from the paracone. Additional observations show the development of a small protocone and postcingulum, but neither conules nor hypocone are developed.

M1 is rectodont with a low, straight centrocrista. The paracone and protocone are subequal in height, and both are only slightly higher than the metacone. The ectocingulum bears a small parastyle; the metastylar crest and ectoflexus are moderately developed, but stylar cusps are absent. The trigon is transversely elongated, with two subequal conules, well−developed conule crests, and pre− and postprotocrista. The precingulum is small but always present; the postcingulum is relatively small with a hypocone and a remarkably straight posterior border.

M2 differs from M1 by its more labially orientated parastylar lobe, deeper ectoflexus and by its more transversely elongated trigon.

M3 is transversely shorter than M1 and M2. The labial side has a moderate parastyle; the lingual side presents a minute precingulum and a small postcingulum.