Possible ctenophoran affinities of the precambrian “sea‐pen”Rangea

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Abstract
The Namibian Kuibis Quartzite fossils ofRangeaare preserved three‐dimensionally owing to incomplete collapse of the soft tissues under the load of instantaneously deposited sand. The process of fossilization did not reproduce the original external morphology of the organism but rather the inner surface of collapsed organs, presumably a system of sacs connected by a medial canal. The body ofRangeahad tetraradial symmetry, a body plan shared also by the White Sea Russian fossilBomakelliaand possibly some other Precambrian frond‐like fossils. They all had a complex internal anatomy, smooth surface of the body, and radial membranes, making their alleged colonial nature unlikely. Despite a different style of preservation, the Middle Cambrian Burgess Shale frond‐likeThaumaptilonshows several anatomical similarities toRangea. The body plan of the Burgess Shale ctenophoreFasciculus, with its numerous, pinnately arranged comb organs, is in many respects transitional betweenThaumaptilonand the Early Cambrian ctenophoreMaotianoascusfrom the Chengjiang fauna of South China. It is proposed that the irregularly distributed dark spots on the fusiform units of the petaloid ofThaumaptilonrepresent a kind of macrocilia and that the units are homologous with the ctenophoran comb organs. These superficial structures were underlain by the complex serial organs, well represented in the fossils ofRangea. The Precambrian “sea‐pens” were thus probably sedentary ancestors of the ctenophores. J. Morphol. 252:315–334, 2002.