摘要
盘县新民乡羊圈村及其邻区关岭组上段产出两种混鱼龙:Mixosaurus panxianensis Jiang et al.,2006和Phalarodon cf.P.fraasi Merriam,1910,含混鱼龙类化石层时代应为中三叠世安尼期Pelsonian亚期。"Mixosaurus yangjuanensis Liu and Yin,2008"命名所依据的正模标本无关键的头骨特征,选取的头后骨骼做鉴定特征对混鱼龙类种一级分类无意义,鉴定特征所依据的基本骨块存在鉴定错误;"Mixosaurus maotaiensis"的厘定应无效;盘县动物群中无Mixosaurus cornalianus出现。
Family Mixosauridae is a monophyletic group strongly supported by the phylogenetic analysis and contains two sister genera, Mixosaurus and Phalarodon. The first mixosaurid record from Asia and Chi na, a single fragmentary specimen from Maotai （north ern Guizhou, southwestern China）, was reported by Young （1960, 1965）, and the name Mixosaurusrnao taiensis Young, 1965 was erected. In subsequent studies, this taxon was rarely considered valid because its holotype is very fragmentary and has no taxonomic value at the species level, and is not diagnostic. Hence, ＂Mixosaurus maotaiensis Young, 1965＂ is a nomen dubium. To preserve this historical species name with the specimens from Panxian of Guizhou may be understandable, but it does not comply with the International Code of Zoological Nomenclature. Abundant and completely articulated skeletons of Middle Triassic marine reptiles, including ichthyosaurs, placodonts, nothosaurs, archoosaur and protorosaur, were recently excavated from the upper Mem ber of Guanling Formation in near Yangjuan Village of Xinmin District in Panxian County （western Guizhou）. The marine reptile fossil horizon can be ascribed to the conodont Nicoraella kockeli Zone, which indicates that the age of the horizon is middle Pelsonian of Middle Anisian in the Middie Triassic. Two mixosaurid taxa from this horizon were reported. One is Mixosaurus panccianensis Jiang et al. , 2006, which is separated from other mixosaur species by both cranial and postcranial characters such as the jugal with a small posteroventral flange. The other is Phalarodon el. P. fraasi Merriam, 1910, which is identified by its characteristic dentition and its narial shelf. Many mixosaurid specimens from Panxian were purchased, not collected scientifically and not prepared in detail by trained technicians. Liu and Yin （2008） erected a name Mizosaurus .yangjuanensis on a small individual in ventral view. The species lacks uniquely derived diagnostic characters, partly because the skull of the only specimen is unexposed, whereas cranial characters are important in distinguishing among mixosaurid species. Its postcranial features obviously indicate its Mixosaurid affinity, and its broad and short humerus can ascribe it into the genus Mixosaurus. However, the lack of information caused by unfinished preparation prevents a phylogenetic analysis and hence a clear diagnosis of the species. Furthermore, they clearly misidentified important bones that they used for their diagnosis of ＂Mixosaurus yangjuanensis＂. 1） the ＂coracoid＂ is actually the right scapula in ventral view, and its dotted-lined ＂long＂ anterior extension is not ,true. Correspondingly, the ＂scapula＂ is the true right coracoid in ventral view; 2） the ＂radius＂ is actually the ulna, and the ＂ulna＂ is the true radius; 3） the ＂nlnare＂ should be the true radiale, the ＂radiale＂ should be the true pisiform 1, and the ＂supposed fourth centralia＂ should be the true ulnare; 4） the ＂extra rudimentary sixth and seventh fingers＂ are very unusual, and should be scrutinized further given that their specimen exhibits signs of modification during preparation. Besides above problems, Liu and Yin （2008） reported another two species of Mixosaurus from same locality and same horizon： ＂Mixosaurus cornalianus＂ and ＂ Mixosaurus maotaiensis ＂. Their specimen of ＂Mixosaurus cornalianus＂ has no diagnostic features of true Mixosaurus cornalianus, is definitely not Mixosaurus cornalianus but shows a diagnostic feature of Mixosaurus panxianensis. Their emended diagnosis of ＂Mia＇osaurus maotaiensis ＂ does not contain any autoapomorphy, and instead lists synapomorphies of Family Mixosauridae and even Order Ichthyosauria as if they are unique to this species. Such an emendation is invalid.
出处
《古生物学报》
CAS
CSCD
北大核心
2008年第3期377-384,共8页
Acta Palaeontologica Sinica
基金
国家自然科学基金(Nos.40672002,40302009)
教育部新世纪人才支持计划(NCET-07-0015)联合资助
关键词
混鱼龙
关岭组上段
安尼期
中三叠世
盘县
贵州
Mixosaurid. upper Member of Guanling Formation, Anisian, Middle Triassic, Panxian, Guizhou
