Quadrapyrgites from the lower Cambrian of South China:growth pattern,post-embryonic development,and affinity

Quadrapyrgites is a microfossil reported with embryonic and post-embryonic stages from the lower Cambrian small shelly fauna of South China,and is closely related to Olivooides.Their development mode and systematic positions are hot topics in palaeoembryology and evolutionary biology in recent years,but are still under debate.Here,we present a description on the growth pattern and post-embryonic development of Quadrapyrgites quadratacris recovered from the lower Cambrian of South China.The growth zone of Q.quadratacris is situated at the oral end,and new terminal lobes are generated within the oral aperture.The terminal lobes are first in control of the opening and closure of the tubes,and later transferred to be crests,thus elongating the tubes.The post-embryonic development is characterized by a one-by-one addition of crests on the post-embryonic tissue,and an ontogenetic sequence with crest number from 1 to 17 is reconstructed.During the ontogeny,the embryonic tissue remains stable in size and morphology.The oral aperture is the only opening of the tubes,while a possible anus on the apical end does not occur.Quadrapyrgites was proposed to be the sister group of Olivooides,and now this is strengthened by the identical growth pattern and post-embryonic development.The comprehensive data from anatomy,growth pattern and post-embryonic development reject the stemlineage cycloneuralian affinity for Quadrapyrgites and Olivooides,and instead support a coronate scyphozoan hypothesis.

Phosphatized rare star-like mouth disc of Punctatus and its functional morphology from the earliest Cambrian of the South Shaanxi China

The Meishucun stage is the prelude in decipher-ing the Cambrian Explosion.In this prominent stage,rapid radioactive evolution and body-plan innovation have taken place and different associations of organism have been shaped.In this paper we report several 3D-preserved rare star-like fossils with finely preserved soft tissues which were recovered from the Kuanchuanpu Member of the Dengying Formation in South Shaanxi,China in 2003.By studying on functional morphology and analogy with mouthpart of Punctatus,there are evidences that this star-like organism approaches the coelenterates in systematic classification and the centre of star-like organism is its mouth.The appearance of coelenterates marks the real beginning of metazoan evolution.Therefore,it has the prominent position in the origin and evolutionary history of organisms.Perhaps the star-like organism represents the early types of coelenterate with original tentacles.These new materials provide new evidence for the origin,evolution and the functional evolution of the metazoan during the early stage of the Cambrian Explosion.