The Phosphatocopina (Crustacea,Arthropoda) is an important group of 'Orsten-type' preserved fossils.It is resolved as the sister-group of Eucrustacea.Here we study the labrum,the median eyes,and the inner lamella of Phosphatocopina based on the selected specimens respectively from western Hunan,South China,and Sweden.The labrum characters of different species exhibit interspecific difference.The ratio of labrum length/shield length is significant to the reconstruction of the ontogeny of phosphatocopines.The labrum characters should be introduced to the diagnosis of Phosphatocopina.In the earliest growth stage,the median eyes were inconspicuous,almost as flat as the other area of the hypstome.However,with the growth of the individuals they became conspicuous.There were two obviously concave structures on the ventral side of the hypostome in later stages,which were the positions where the median eyes should have been located.In addition,the two modes of preservation of the inner lamella,i.e.,that of shrinking and that of bulging up,are interpreted as the preservational artifact herein.
LIU Zheng 1,2 & DONG XiPing 1,2 1 School of Earth and Space Sciences,Peking University,Beijing 100871,China
The exquisitely preserved fossil embryos of Markuelia recovered from the limestones of the Middle Cambrian Haoqiao Formation and Upper Cambrian Bitiao formation in western Hunan, South China are described and illustrated in detail for the first time. A new species Markuelia elegans sp. nov. is established based mainly on embryos from the Upper Cambrian. A few of animal＇s resting eggs, which are comparable with those of the Ediacaran Doushantuo Formation, have been also found in the Upper Cambrian of western Hunan. The membrane of one egg from the uppermost Cambrian has been replaced by pyrite and the overgrowth of the pyrite crystals exhibits a unique inorganic pattern termed herein ＇Pseudoembryo＇. The taphonomic setting in deeper water with possible strong reducing conditions promoted the excellent preservation for the Markuelia specimens. The study of Markuelia provides not only constraint on the anatomy, affinity, embryonic development and phylogenetic significance of this wormlike animal and but also opens a new window onto the evolution and development of the earliest animals.
Fossils of Orsten-type preservation represented by the crustacean Skaracarida and Phosphatocopida were found in western Hunan, South China in 2005, including the important phosphatocopid species Vestrogothia spinata based on exquisitely preserved soft-bodied specimens that allow the first growth stage to be reestablished. The taxonomy of Vestrogothia spinata is revised employing the character of a two-divided limb stem of the mandible. A new foundation for the phylogeny of the Phosphatocopina using mandible characters related to crustacean appendages is postulated. Vestrogothia spinata has only previously been found from Sweden.
Although fossils of Orsten-type preservation represented by Skaracarida and Phosphatocopina were first reported from the Middle and Upper Cambrian in western Hunan, South China in 2005, diversified phosphatocopine species have never been appropriately described and elucidated in terms of their evolutionary relationships. Here, we described two new species of Phosphatocopina, Vestrogothia anterispinata sp. nov. and V. bispinata sp. nov. The evolutionary relationship among all the valid species of Phosphatocopina is discussed and the phylogeny of Phosphatocopina is reestablished using cladistic analysis. Accordingly, phosphatocopines primitively evolved along two lineages: one evolved towards the emergence of lobes; the other evolved towards the emergence of dorsal spines. Respectively, lobes originated independently three times, and dorsal spines originated only once. With regard to the dorsal rims, interdorsum originated first, whereas dorsal furrow originated independently twice on the basis of interdorsum. Probably Hesslandona may represent a polyphyletic group, whereas Vestrogothia a monophyletic group.
ZHANG HuaQiao1,2 & DONG XiPing1,2 1 School of Earth and Space Sciences,Peking University,Beijing 100871,China
Countless fossil embryo Olivooides and the hatched larvae,juveniles and adults(the latter two kinds are Punctatus) are recovered by means of acid maceration from the fine-crystalline to medium-crystalline phosphatic limestone and phosphatic micrite of Early Cambrian Kuanchuanpu Formation at the Shizhonggou section,near Kuanchuanpu Village,Ningqiang County,Shaanxi Province,China.Using the technique of Synchrotron X-ray Tomographic Microscopy,the 3D internal structure of Olivooides and Punctatus is reconstructed.The morphological and statistic analyses are also given to the stellae structure of Olivooides and Punctatus,which indicates that this structure is a result of adaptive evolution to a lifestyle of fast-attaching after hatching,probably with the function of mucilage secretion.The internal structure of Punctatus is described and discussed.The ovum-like structure,a common internal feature of Punctatus,is considered as the taphonomic structure,rather than eggs or other biological structure.This structure is thought to be formed after the burial of the animal and before or during the mineralization.The original internal structure of Punctatus is assumed to be tabulae-filled,with soft body grown on them.
CHEN Fang1,2 & DONG XiPing1,2 1 School of Earth and Space Sciences,Peking University,Beijing 100871,China
基于最近在湘西中寒武-上寒武统发现的更多的精美保存的Markuelia hunanensis标本,并且借助于同步加速器辐射X射线层析显微技术,建立了寒武纪胚胎Markuelia从卵裂(cleavage)阶段经过器官形成(organogenesis)阶段至预孵化(pre-hatching)阶段的发育序列,特别是预孵化阶段的发育序列,即从吻刺和尾刺刚刚形成的最早时期直至即将孵化(just about hatching)的最后时期的发育序列.这个发育序列提供了一个胚胎预孵化阶段的发育模式,而这一发育模式在现生的Scalidophorans(曳鳃类、兜甲类和动吻类)中尚未建立.因而,它不仅加深了对Markuelia现生后裔胚胎发育的认识,而且为这类动物的演化和发育开拓了一个新的(研究)窗口.
