| Cotyledion tylodes is a benthic goblet-shape animal with round-to-oval plates only occurred in the Chengjiang biota of Cambrian Epoch 2,Age 3.As a benthic organism,Cotyledion has been reported with various sessile modes,which are great significance for the study of ecological evolution during Cambrian,such as niche differentiation and substrate revolution.However,many controversies exist in morphology and autecology of Cotyledion.This thesis aims to investigate the morphology,autecology and development of Cotyledion with traditional description methods plus SEM-EDX and statistics analysis.After comparative studies on the morphology of 145 specimens from 5sections in 3area in Eastern Yunnan,it is confirmed that the tentacles of Cotyledion lack sub-structures for feeding,such as cilia.It is also revealed that the movement of the tentacles is driven by the contraction and expansion of the Cotyledion calyx,not by the contraction of the tentacles themselves.It is confirmed that the plates are located below the integument,rather on the body surface.The previously interpreted ‘U-shape gut’ is indeed being a taphonomic arefacts rather real biological structure;And the holdfast is a bi-parted structure,composed of an enlarged structure and a distal end disc.Analysis on the body height,calyx size,stem length and the size of plates of 51 wellpreserved specimen of Cotyledion reveals that both the calyx and stem mainly grow along top-bottom axis,with the calyx having a period of ‘rapid enlargement’.The plates grown together with the body with a constant rate.The new plates emerge among the elder plates and maintain nearly the same growth rate.These statistic data allow to identify three developmental stages of the ontogeny of Cotyledion,i.e.a larval stage(<15mm),a juvenile stage(15-35mm),and an adult stage(>35mm).Based on the analysis of the morphology of the holdfast and the attached shells,the autecology of Cotyledion is inferred.Analysis on the morphological function of tentacles and calyx suggest Cotyledion might be a predation rather than suspension feeder.Cotyledion attached on the bioclast by holdfast-disc + mucus.Currently,there is insufficient evidence about Cotyledion attached on living organism as well as the silty mudstone substrate.Furthermore there are indeed specimen showing multiple individuals liveing together,attached on a single point(to each other?).This thesis reveals the detailed morphological features,ontogenetic process and autecological habit of Cotyledion,which provides key information for the phylogenetic position of Cotyledion,deepens the undertanding of benthic sessile animals in the Cambrian marine ecosystem. |
