内蒙古石拐群古鳕类一新属

内蒙古石拐地区石拐群召沟组中的长腹鳍大青山鳕(新属、新种) Daqingshaniscus longiventralis gen. et sp. nov. 是在我国中侏罗世地层中发现的一比较原始的古鳕类.其头骨眶后部分短,鳃盖骨大于下鳃盖骨,背鳍位于腹鳍与臀鳍之间,腹鳍基线长,鳍条都从基部分节、远端分叉,棘鳞仅见于尾上叶,全歪型尾,鳞片呈菱形.大青山鳕既与苏联南哈萨克斯坦 Karatau 地区的 Pteroniscus 很接近,又与我国新疆的维吾尔鳕 Uighuroniscus 及西德北部的 Stadthagen 地区的 Indaginilepis 相似.

A NEW PALAEONISCOID FISH FROM SHIGUAI GROUP OF NEI MONGOL

A new palaeoniscoid fish. Daqingshaniscus longiventralis gen. et sp. nov., was collected from Zhaogou Formation (belongs to Shiguai Group), Nei Mongol. Diagnosis Body fusiform, skull rounded anteriorly without well-developed rostrum, large orbits anteriorly placed. Suspensorium moderately oblique. Head with a short distance between orbit and opercular. Frontals long, parietals shorten gradually with growth. Dermosphenotic and dermopterotic present. Opercular, a dermohyal, an antorbital present. Maxilla and dentary with conical teeth. Dermal bone almostly all ornamented with striae and punctations. Dorsal fin opposite to the space between pelvic fin and anal fin, triangular. Pelvi cfin long based. All rays completely jointed and branched distally. Fringing fulcra present only on upper lobe of caudal fin, caudal fin heterocercal deep cleft, inequilobate with fine epichordal fin. Scale rhomboidal, small, hinde margin serrated. Lateral line disappearing just behind the base of upper lobe. Comparision and Discussion Daqingshaniscus is close to Pteroniscus but differs from the later in (1) fulcra only on upper lobe of caudal fin; (2) two large ridge scales in front of ventral lobe of caudal fin; (3) the hinder margin of scale serrated; (4) epichordal caudal fin-rays present; (5) the boundary between opercular and subopercular less oblique than that of Pteroniscus (the obliquities in Daqingshanis icus 15°-20°, in Pteroniscus some 30°); (6) 72-74 lateral line scales (63-66 lateral line scales on Pteroniscus). Daqingshaniscus resembles Uighuroniscus but is different from the latter in (1) all fin-rays branched distally; (2) a dermohyal (two dermohyals in Uighuroniscus); (3) about 73 scale rows (52 scale rows in Uighuroniscus); (4) epichordal fin-rays of caudal upper lobe present; (5) angle between axis of body and axis of body lobe smaller (about 145°in Daqingshaniscus while some 160°in Uighuroniscus); (6) postorbital part of maxilla with shape being rounded dorsally (but the postorbital part of maxilla with shape being triangled dorsally in Uighuroniscus). Daqingshaniscus is similar to Indaginilepis in the general characters but is distinguished from the latter by (1) all fin-rays branched distally; (2) the hinder margin of scale serrated; (3) pelvic fin long based; (4) 73 scale-rows (44 scale-rows in Indaginilepis); (5) epichordal fin-rays in upper lobe of caudal fin present; (6) subopercular with shape roughly square (but subopercular with shape nearly pentagon in Indaginilepis); (7) no well-developed hinge line at the base of the body lobe; (8) the posterior edge of the body lobe is not in distinct S-shape. Therefore, Daqingshaniscus differs from all known genera of Palaeoniscoidei and represents a new one. We divide the preserved characters of Daqingshaniscus into the two kinds, the primitive and derived. We use the latter as clue for discussing the phylogenetic position of it. It is proposed that Daqingshaniscus be classified as family Incertae sedis of Palaeonisciformes.