A NEW SEMIONOTIFORM (ACTINOPTERYGII, NEOPTERYGII) FROM UPPER JURASSIC – LOWER CRETACEOUS DEPOSITS OF NORTH-EAST THAILAND, WITH COMMENTS ON THE RELATIONSHIPS OF SEMIONOTIFORMS

Abstract:  A new semionotiform fish, Isanichthys palustris gen. et sp. nov., is described from the Late Jurassic – Early Cretaceous Phu Kradung Formation, north-east Thailand. I. palustris is known from a single, nearly complete specimen found alongside abundant Lepidotes specimens at the Phu Nam Jun locality. I. palustris shows a mixture of semionotid-like characters, such as the pattern of cheek ossifications, and lepisosteid-like characters, such as the body shape and a dorsal fin opposed by an anal fin. I. palustris possesses only some of the characters currently used to define the Semionotidae. Cladistic analyses including various semionotid and gar taxa, together with Amia calva and Leptolepis coryphaenoides , suggest that the Semionotiformes (Lepisosteidae and 'Semionotidae') form a monophyletic clade, but the 'Semionotidae' taxa form an unresolved polytomy. The relationships between Semionotiformes, Halecomorphi and Teleostei are unresolved. When restricted to the best-known taxa, however, the analysis shows the monophyly of the Semionotidae sensu stricto ( Semionotus + Lepidotes ) and a sister-group relationship between halecomorphs and teleosts. These last two results are regarded as the preferred hypothesis for further studies. I. palustris is the only known example of a predaceous, probably piscivorous, 'semionotid'. It illustrates the great diversity and ecological adaptation of the semionotiforms during the Late Jurassic – Early Cretaceous. We question the phylogenetic relationships of 'ancient fishes' founded on molecular-based trees because we suspect that the use of very few Recent taxa as representatives of previously diverse lineages is an inevitable, but important, bias in the construction of such trees.     

Revision ofSemionotus bergeri Agassiz, 1833 (Upper Triassic, Germany), with comments on the taxonomic status ofSemionotus (Actinopterygii, Semionotiformes).

Semionotus bergeri Agassiz, 1833, from the Upper Triassic (Carnian) of southern Germany, the type species ofSemionotus, is here described in detail for the first time, including so far unstudied material in the Naturkunde-Museum Coburg, which allows a fairly complète reconstruction of this fish. The species is diagnosed by the présence of long frontals, about 4 times longer than wide, with antorbital lateral processes, 6–7 posterior infraorbitals, infraorbital at the posteroventral corner of the orbit notably larger than adjacent ones, infraorbitals at the posterior border of the orbit being as deep as long, and the middle élément anteroventrally expanded, dorsal fin base about two times the anal fin base.S. elegans from the Late Triassic-Early Jurassic of the Newark Supergroup in North America, is so far the best know species ofSemionotus and is the only species of this genus that has been included in phylogentic analyses. However, the comparison ofS. bergeri with other proposed speciesof Semionotus, such asS. elegans, and other semionotids casts doubt on the monophyly of this genus as currently understood, since these species exhibit a mosaic distribution of characters.      

江苏句容中生代晚期中华鳞齿鱼属(Sinolepidotus)一新种,兼论该属的系统位置

记述了在江苏句容发现的中华鳞齿鱼属(Sinolepidotus)一新种——长背鳍中华鳞齿鱼(Sinolepidotus longidorsalis sp.nov)。新种的一般形态特征如身体高纺锤形,背鳍长,臀鳍离尾鳍近,头骨外部骨片的形状及排列格局,口裂小,下颌骨有较高的冠状突,口缘牙齿高而尖,体侧中部和背区的一些鳞片高显著大于宽等,与浙江早白垩世的浙江中华鳞齿鱼(Sinolepidotus chekiangensis)很相似。但新种具有背鳍较长,背鳍鳍条数目较多,吻突尖,及鳞片后缘梳状齿不发育等特征区别于浙江中华鳞齿鱼。此外,评论了中华鳞齿鱼属的系统位置,认为它的形态特征与Paralepidotus很相似,对它原列入半椎鱼科提出疑问。根据长背鳍中华鳞齿鱼的性质并参考有关地质古生物资料,将含鱼层杨冲组的时代定为早白垩世。