A NEW CARBONIFEROUS PLATYSOMOID FISH FROM NINGXIA,NORTHWEST CHINA
【Abstract in Chinese】 本文记述的标本采自宁夏中卫晚石炭世土坡组下部,属于个体较小的扁体鱼类,身长与身高近相等,约3cm。眼眶大,眶下感觉管明显。鳃盖骨大致呈长条形,下鳃盖骨大小与鳃盖骨相近,前鳃盖骨呈椭圆状,匙骨强壮。锁骨保存于匙骨前上部。背、腹棘鳞发育。胸鳍小,腹鳍没有保存。背鳍中等长,臀鳍与背鳍等长,均起点位于身体最高点后。尾鳍呈外形对称的歪型尾。全身覆盖长条形鳞,胸鳍下方具有一枚异常大型的鳞片。经过与北美、澳洲以及中国浙江的扁体鱼类标本对比,发现其间有明显差异,应为一新属新种——小型宁夏扁体鱼(Ningxiaplatysomus parvus gen.et sp.nov.),归于扁体鱼亚目,科不定。
【Abstract】 A new genus and species of platysomoid fish is described here. The specimens were excavated form the Namurian(Upper Carboniferous),at Daliushu Village, Zhongwei, Ningxia Hui Autonomous Region, Northwest China.In the same bed, there were palaeonisciformes fish Huanghelepis and many other invertebrate fossils including insects(Lu,2002;Lu et al.,2002)Class Osteichthyes Huxley,1880 Subclass Actinopterygii Cope,1887(sensu Rosen et al.,1981)Suborder Platysomoidei Berg,1937 Genus Ningxiaplatysomus gen.nov.Ningxiaplatysomus parvus gen.et sp.nov.Holotype GMC V2445 a,b,nearly complete fish specimen with its counterpart.Paratype GMC V2446,half complete fish specimen,only the latter half body and few pectoral bones preserved.Etymology Ningxia,Chinese pinyin for the locality name where the fossil was found;parvus,Latin means small sized.Horizon and Locality Upper part of Tupo Fm.(about Namurian C in age),Upper Carboniferous,Zhongwei of Ningxia,China.Diagnosis Small-sized platysomoid fish with a total length about 3cm,nearly the same as its height.Orbital large and its first suborbital long.Opercular long, nearly the same size as the subopercular.Preopercular oval in shape.Strong cleithrum with a clavicle at its front point;17column scales,with an unusual big scale beneath the front part of the cleithrum.Dorsal and ventral fulcra developed. Pectoral fin small,and the normal long dorsal fin beginning at middle of the body.Tail heterocercal.Description This holotype specimen is a small platysomoid fish,and its length is almost like its height,which both are nearly 3cm.The frontal is long and with wide top and narrow bottom.The parietal is smaller and nearly round.The extrascapular and the posttemporal are not well preserved.The orbital is relatively large,and the sensory nerve tube is clear.The "Y"-shaped parasphenoid can be roughly seen partly,with the upper branch 30°upperwards.A sensory nerve tube can be seen under the orbital,and it divides into two tubes behind the orbital.The opercular is nearly wedge-shaped, narrowing upperwards.The subopercular is low and wide,nearly the same size as the opercular. The preopercular is almost oval in shape,connecting the opecular and subopercular. There are ornaments of diagonal ridges in the surface of the opercular and the preopercular,but not in the subopercular.The bigonial arch is not preserved.The branchiostegal ray is not seen,even without any remnant evidences,and it was very probable that the Ningxiaplatysomus has no branchiostegal ray or just not more than one.The cleithrum is quite strong with the clavicle before it.There is an unusual big scale beneath the front part of the cleithrum.The pectoral fin-rays are not very clear.The pelvic fin is not seen in the specimen,probably absent. The dorsal fin is normally long,and the anal fin is as long as the dorsal fin,which are all beginning after the tallest part of the body.The caudal fin is heterocercal,which are almost symmetrical,but this specimen only retains the upper half.The dorsal fulcra are developed in the dorsal edge in front of the dorsal fin and the ventral fulcra can be seen in front of the not well-preserved anal fin.The body scales are rhombic at dorsal part,and rectangular at the ventral part.There are nearly 17 column scales.The highest scale,which is in the 7th column,is 7mm long.The paratype specimen is a half platysomoid fish.Its head and dorsal part of the body are missing.However,its size,shape and the position of the fins are all as same as the holotype.Moreover,the unusual big scale under the pectoral fin is clearer than that of the holotype,and the pectoral fin-rays are covered by a series of small round scales,which have a concentrically ringed pattern not like other scales on the body.Another good preservation of the paratype is its nearly complete caudal fin,but unfortunately it has been deformed and the fin-rays are bent.Comparisons and Remarks The first established platysomoid fish in China were discovered in the Permian strata at Changxing,Zhejiang,which was described by Wei(1977).Then in 1986,another specimen of the same locality was described by Wang(1986).The newmaterials are the first discovery of platysomoid fish fossil in the Carboniferous of China.The new fish described above has a great lateral flat body shape,body covering by rhombic scales dorsally and long rectangular scales ventrally.The body scale size is much larger below the lateral line than that of above the lateral line.The opercular system has a certain connecting way without the interopercular.The cleithrum connects with the clavicle tightly. The dorsal fin is symmetric to the anal fin.The caudal fin is strong biforked"V"-shaped.All these show that the new materials should belong to Platysomoidei.However, compared to the other Platysomoidei in North America,Australia and Zhejiang of China,there are still some characters of the new two specimens,which can’t be found in other platysomoid fish,as follows:firstly,the new material has only one suborbital,but the other platysomoid fish have 5 at least;Secondly,the new material has no branchiostegal ray or only one,but other platysomoid fish have more,such as Platysomus superbus,which has 6;Finally,there is an unusual big scale under the front part of the cleithrum in the new material,but in other platysomoid fish the scales just become a little bigger from the front to the back.We conclude here that the new materials belong to a new genus and species,Ningxiaplatysomus parvus gen.et sp.nov.,within the Suborder Platysomoidei, but leave its Family position open,because of the new material’s insufficient preservation, particularly on the headskull part.
- 【Source】 古生物学报 ,Acta Palaeontologica Sinica , Editorial E-mail ,2015(02)
- 【CLC code】Q915