摘要
Bengtson和Yue首次确定Olivooides和Markuelia为化石胚胎,建立了Olivooides的胚胎和胚后发育序列,并且提出Olivooides的亲缘关系是刺细胞类(Bengtson and Yue,1997;Yue and Bengtson,1999)。在过去的10年中,许多论述寒武纪化石胚胎的文章问世,极大地提高了人们的认识。其中,Steiner等识别出Pseudooides为化石胚胎,并且推想了Pseudooides的发育序列(Steiner et al.,2004a,b)。基于在中国湖南西部中、上寒武统发现的许多精美保存的标本,对Markuelia进行了解剖学、亲缘关系和支序分析研究,限定Markuelia的亲缘关系为Scalidophora(动吻动物门、兜甲动物门和曳鳃动物门的统称)的干群。尝试性地建立了Markuelia的发育序列,特别是预孵化阶段的发育序列,即从吻刺形成的最早时期直至即将孵化的最后时期的发育序列。因为最近发现了保存完美的Olivooides预孵化阶段、孵化阶段以及未成年个体阶段(Olivooides和Punctatus之间的过渡类型)的标本,重新建立了Olivooides的胚胎和胚后发育序列。尽管Olivooides的亲缘关系仍然有争议,但多数作者支持其亲缘关系为刺细胞类。然而,迄今所描述的大多数寒武纪化石胚胎的亲缘关系,特别是谜一般的化石胚胎——Pseudooides的亲缘关系仍然不得而知。由于Markuelia孵化后的幼虫、未成年个体或成年个体的标本还未发现,其胚后发育序列则无从谈起,令人信服的原肠胚阶段的化石胚胎也未见报道。今后,可靠的原肠胚阶段的化石的发现很可能要借助于同步加速器辐射X射线层析显微技术。总之,寒武纪化石胚胎的研究还有很多悬而未决的问题。
Bengtson and Yue first identified Olivooides and Markuelia as fossil embryos,established the embryonic and post-embryonic developmental sequences of Olivooides,and hypothesized its cnidarian affinity（Bengtson and Yue,1997;Yue and Bengtson,1999）.In the last decade,many papers on Cambrian fossil embryos have been published,which has dramatically increased our knowledge on them.Among others,Steiner et al.identified Pseudooides as fossil embryo and proposed its developmental sequences（Steiner et al.,2004 a,b）.The anatomy,affinity,and cladistic analysis of Markuelia were studied based on much more exquisitely preserved specimens recovered from Middle and Upper Cambrian in western Hunan,China.Markuelia was constrained as a stem Scalidophora（phyla Kinorhyncha,Loricifera,and Priapulida）.The developmental sequences were tentatively established,from cleavage through organogenesis to the pre-hatching of Cambrian embryo Markuelia,especially the developmental sequences during the pre-hatching stage,i.e.,from the earliest period when the scalids and tail spines only took shape to the latest period（just about hatching）.Because the well-preserved specimens of Olivooides that respectively represent the pre-hatching stage,the hatching stage,and the stage of the earliest juvenile（the intermediate form between Olivooides and Punctatus） have been recovered recently,the embryonic and post-embryonic developmental sequences of Olivooides are reestablished with more confidence.Although the phylogenetic affinities of Olivooides remain controversial,many authors support the cnidarian affinity.Nevertheless,the affinities of the majority of Cambrian fossil embryos described to date remain unknown,especially the enigmatic fossil embryo Pseudooides.Since the specimens of the hatched larva,juvenile or adult of Markuelia have never been found,the post-embryonic developmental sequences of Markuelia could not be discussed.The convincing fossil embryos of the gastrula stage have not been reported.The feasible avenue to discover the fossil embryos of unequivocal gastrula stage is most probably in the light of synchrotron-radiation X-ray tomographic microscopy.In short,there are many open questions in the study of Cambrian fossil embryos.
出处
《古生物学报》
CAS
CSCD
北大核心
2009年第3期390-401,共12页
Acta Palaeontologica Sinica
基金
国家自然科学基金(40772008
40572003)
高等学校博士学科点专项科研基金(20060001059)
现代古生物学和地层学国家重点实验室基金(083101)联合资助
