Pyritized tube feet in a protasterid ophiuroid from the Upper Ordovician of Kentucky, U.S.A
نویسنده
چکیده
A single specimen of the protasterid ophiuroid Protasterina flexuosa from the Kope Formation (Cincinnatian, Upper Or− dovician) of Kentucky exhibits three−dimensionally pyritized tube feet. This represents the first report of soft−tissue pres− ervation in an echinoderm from the type−Cincinnatian series. The tube feet are solid and lack all internal structure. They consist of aggregated masses of small euhedral to subhedral pyrite crystals suggesting that pyritization, although de− cay−induced and mediated, did not necessarily replicate soft−tissues but might instead have formed inside the void−spaces left behind during the decay process. The discovery of pyritized soft−tissue as delicate as ophiuroid tube feet suggests that similar forms of soft−tissue preservation might be found in other taxa in the Kope Formation. Perhaps much more impor− tantly, this unexpected occurrence demonstrates the incompleteness of our knowledge of permissible conditions for the preservation of soft−tissues and it thereby indicates promise for discovery of other such occurrences in diverse organisms in unexpected settings. Systematics of Paleozoic ophiuroids remains problematic in spite of many years of study by capa− ble paleontologists. The incomplete but well−preserved specimens treated here include the types of Protasterina flexuosa and Protasterina fimbriata as well as previously undescribed specimens. Together they permit a revised diagnosis and de− tailed description of the genus Protasterina. Protasterina fimbriata is the type species of the genus but is a subjective ju− nior synonym of Protaster flexuosus (= Protasterina flexuosa). The genus is clearly differentiated from the only other known protasterid ophiuroid from the Cincinnatian series, Taeniaster spinosus, and from all other protasterid genera.
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Water vascular system architecture in an Ordovician ophiuroid.
Understanding the water vascular system (WVS) in early fossil echinoderms is critical to elucidating the evolution of this system in extant forms. Here we present the first report of the internal morphology of the water vascular system of a stem ophiuroid. The radial canals are internal to the arm, but protected dorsally by a plate separate to the ambulacrals. The canals zig-zag with no evidenc...
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