山东昌乐早始新世五图组鼩形类(Soricomorpha,Insectivora, Mammalia)

山东早始新世五图组曾发现原始獏类,Homogalax wutunensis,最近又采到一批化石。这里仅记述其中的一种食虫类,可归入鼩形亚目的昌乐鼩(Changlelestes dissetiformis gen. et sp.nov.)。昌乐鼩与亚洲早第三纪食虫类(Ernosorex.Ictopidium和Tupaiodon)可能有较为密切的亲缘关系,本文将它们归入新科——Changlelestidae fam.nov.。昌乐鼩科与Plesiosoricidae和Soricidae有一些相同的进步特征,这些科与Nyctitheriidae有共同的差别。

A NEW SORICOMORPH (MAMMALIA, INSECTIVORA) FROM THE EARLY EOCENE OF WUTU BASIN, SHANDONG CHINA

Wutu Basin is a small Paleogene sedimentary basin, situated about 170km east of Jinan, the capital of Shandong Province. An index fossil of Early Eocene, Homogalax wurunensis, has been reported from the Wutu Formation by Chow and Li(1963, 1965). Recent collecting not only has produced extensive statistically-significant samples, but also has yielded uncommon specimens of micromammals. In this paper a soricomorph insectivoran is described.Soricomorpha Gregory, 1910 (Saban, 1954) Changlelestidae fam. nov.Type genus Changlelestes gen. nov.lncluding genera Ernosorex Wang, 1990Tupaiodon Matthew et Granger, 1924Ictopidium Zdansky, 1930Diagnosis Dental formula: ?, 1, 4, 3/3,, 4, 3. Upper canine tall, laterally compressed; P1-2/ small, P3/ right-angled triangle in outline, with an anterior edge vertical to buccal edge; P4/no metacone and conule, with a strong bladelike metastylar crest; M1/ distinctly larger than M2/ in size, M1-2/ paracone and metacone sharp with clear centrocrista, conules developed and hypocone incipient in early forms; bladelike metastylar crest strong on M1/, less developed on M2/. Lower incisois inclining anteriorly, with cuspate lateral margin, lower canine small, premolariform or incisiform; P/1—2 simple and single-rooted; P/3—4 doublerooted and main cusp tall and sharp, P/3 with small paraconid, P/4 paraconid distinct but low, metaconid variable, talonid short and unbasined, usually with a small lingual cuspute; lower molars displaying progressive reduction size from M/1 to M/3, trigonid compressed anteroposteriorly, talonid as wide as, or wider than, trigonid, talonid basin deep, entoconid tall and hypoconid low generally.Remarks Usually Tupaiodon and Ictopidium are considered as erinaceomorphs and are allocated to the family Erinaceidae or Dormaaliidae, but recently Ictodipium was questioned whether it is an erinaceomorph(Novacek et al., 1985). Some new material referable to Ictopidium lechei have been found from the type locality, "the River Section" of the Yuanqu Basin(Tong, MS). milarities of Tupaiodon and Ictopidium with the new genus in dental anorphology suggest that the Asiatic genera are certainly related. Changlelestes dissetiformis gen. et sp. nov.Type A right maxillary with P4/—M3 (IVPP V10306-1), right and left mandibles with P/1-M/3(V10306-2) and P/4-M/3(V10306-3) respectively, I/3-C/1(V10306-4), and right I/1—2(V10306-5).Referred specimens Right mandible with C/1-P/1 and P/3-M/3(V10306.1); left upper maxillary with P2/-M2/(V10306.2); right maxillary with P2/-M2/(V10306.3-1), left P4/M1/(V10306.3-2), left C/1-P/1(V10306.3-3); right maxillary with C1/-M2/(V10307.1-1), left mandible with I/3-P/2 and P/4-M/3(V10307.1—2), left I/2(V10307.1-3) and left I/1(V10307.1-4); left mandible with C/1-M/3(V10307.2-1) and right mandible with C/1-P/2 and M/2 (V10307.2-2).Locality and Horizon IVPP V10306.1—3 from East mine, and V10307.1—2 from Northwest mine, north of Village Xishangtuan of Changle County, Shandong.Etymology Changle in reference to fossil locality; and lestes Gr. "robber". common suffix denoting an insectivoran.Diagnosis Three lower incisors small and near equal in size; lower canine premolariform and slightly larger than the adjacent teeth; P/1 present; P/4 paraconid rather developed but less elevated, metaconid small relative to its protoconid and located on the lingual edge of protoconid about half way up the crown; M/1—2 talonid as wide as trigonid, hypoconulid distinct and separating from entoconid by a distinguishable notch; cristid obliqua of M/1 strong, usually extending to apex of metaconid; upper canine single-rooted, crown as tall as P4/; P1-2/ small, P1/ single-rooted, P2/ double-rooted; P3-4/ no hypocone; M1-2/ paracone and metacone sharp, centrocrista clear, paraconule and metaconule unreduced with anterior and posterior crests; hypocone incipient on M1-2/, preprotocrista and postmetacrista extending to parastyle and metastyle respectively.Remarks In dental morphology the naterial from the Wutu Formation is close to the known nyctitheres, especially to Leptacodon. The American genus also has cuspate lower incisors(Krishtalka, 1976). The Wutu specimen are clearly distinct from those of nyctitheres in having molars reduced in size from M1/1 to M3/3, and by P3/-M2/ with strong bladelike metastylar crest, P4/ without metacone, lower molars with hypoconulid more separated from entoconid, P/4 less molariform with short unbasined talonid, and P/2 single-rooted. By these characters the Wutu species is also distinguishable from those of the family Ceutholestidae, created by Rose and Gingerich(1983).Ernosorex jilinensis from the Huadian For nation of Jilin Province is a certain soricomorph, as pointed out by Wang(1990), and has a close affinity to Changlelestes. The great similarities between the Jilin and Shandong specimens lie in the construction of lower incisors. Three lower incisors in the two species are equal in size and procumbent with cuspate lateral margin, two cuspules on I/1 and three on I/2. The two soricomorphs are distinct. The lower incisors of E. filinensi enlarged, distinctly larger than C/1, P/1 is absent, P/4 with reduced paraconid and metaconid, and talonid of M/1 widened and hypoconulid faint.Tupaiodon and lctopidium are usually considered erinaceomorphs and allocated to Erinaceidae or Dormaaliidae. Their cheek teeth, in fact, are close to those of Changlelestes in morphology. The three Asiatic genera have un educed P3/3(reduced in dormaaliids), right triangle P3/ with protocone positioned anteriorly (isosceles triangle in outline and protocone central in position in early members of erinaceomorphs), metastylar crest strong on P3/-M2/ (weak in most of erinaceomorphs), progressive molar size reduction of first through third (first two molars basically equal in size in dormaaliids), and main cusp of P/3—4 sharp (stout in erinaceomorphs). These common characters which are different from erinaceomorphs, also show that close affinities among the Asiatic genera is probably. However, the reference of the two genera, Tupaiodon and Ictopidum, to the family Changllestidae is not certain, it is only a tentative hypothesis at present.Changlelestes shares some common derived characters with plesiosoricids and soricids: P/1—2 reduced, P/2 single-rooted, P/4 with unbasined talonid and lower molars progressively reduced in size from M1/1 to M3/3. These traits are also their common differences from nyctitheres. Nyctitheres which first appeared in the Paleocene of North America are generally believed to be broadly ancestral to the later soricomorphs. The above-menioned common derived traits suggest that Changlelestes has a closer affinity to plesiosoricids and soricids than to Nycititheriidae, although the Asiatic genus certainly is not their direct ancestor. Nyctitheres are thought to be an offshoot in the early diversification of soricomorphs. Another hypothesis on the relationships of these soricomorphs under deliberation is, that Tupaiodon and Plesiosorex differ from the others by their double-rooted upper canine and P/4 with relatively developed paraconid and metaconid. herefore, a close relationship between them is suggested. Up to now, the knowledge on the interrelationships and evolution of early insectivorans is so limited that only through a great deal of discoveries of new key specimens shall we be able to understand the precise relationships of early insectivorans.