Terminal Ediacaran Microfossil Biota From The Northwestern Margin Of The Yangtze Platform

Exceptionally preserved fossils in the terminal Ediacaran Period provide direct evidence for the study of early life evolution.Ediacaran successions are extensively exposed in the Ningqiang area of Shaanxi Province,located in the northwestern margin of the Yangtze Platform,South China.Clastic dolostone beds in the upper part of the Ediacaran Dengying Formation,at the Lijiagou section in the Ningqiang area,host diverse microfossils preserved in three dimension through early diagenetic phosphatization.In this study,a combined investigation of taphonomy,morphology,and paleoecology was conducted.Fossiliferous dolostone blocks were collected at the Lijiagou section.Fossil specimens were handpicked from rock matrix dissolved using acetic acid.Photos were taken by a scanning electron microscope under secondary electron images model.The main points of this thesis are summarized as following: 1.First report of a new tubular fossil Uniconotubus lijiagouensis gen.et sp.nov.The cone-shaped gross morphology and the single-layered tube wall collectively indicates that U.lijiagouensis gen.et sp.nov.has distinct morphological features with coeval tubular forms.U.lijiagouensis gen.et sp.nov.is herein reconstructed as an epibenthic animal with sessile life mode.Morphological and functional characteristics further indicate that U.lijiagouensis gen.et sp.nov.may have been a filter feeder.2.First find of diverse embryo fossils,including globular,dichotomous-dividing,trilobular,and clustered forms.These embryo fossils with different morphological features share similarities with those reported in early Ediacaran Period(e.g.,embryo fossils from the Weng'an biota).The complicated and diverse morphological characteristics of the Lijiagou embryo fossils may represent different embryonic types during development of a same animal.3.Anabaritids—the most common shelly organisms in the early Cambrian period—are reported.The Lijiagou Anabaritids shares similarities with those in the early Cambrian.However,they display distinct features in the tri-radial symmetrical patterns.This sheds pivotal insights for the study of the morphological evolution of this important fossil group.4.Report ofNamacalathus-like fossils.The fossils reminiscent of Namacalathus,found at the Lijiagou section,are likely represent the cups of Namacalathus found worldwide.5.A number of morphologically diverse problematic forms are found.Forms illustrated in this study include tubular,bifurcated,spindle-shaped,filamentous,irregular spherical,and irregular tubular.These fossil types—may have been overlooked in previous studies—could have been an important part of the marine ecosystem in the Ediacaran.