Abstract
The morphology and affinities of newly discovered disc-shaped, soft-bodied fossils from the early Cambrian (Series 2: Stage 4, Dyeran) Carrara Formation are discussed. These specimens show some similarity to the Ordovician Discophyllum Hall, 1847; traditionally this taxon had been treated as a fossil porpitid. However, recently it has instead been referred to as another clade, the eldonids, which includes the enigmatic Eldonia Walcott, 1911 that was originally described from the Cambrian Burgess Shale. The status of various Proterozoic and Phanerozoic taxa previously referred to porpitids and eldonids is also briefly considered. To help ascertain that the specimens were not dubio- or pseudofossils, elemental mapping using energy dispersive X-ray spectroscopy (EDS) was conducted. This, in conjunction with the morphology of the specimens, indicated that the fossils were not hematite, iron sulfide, pyrolusite, or other abiologic mineral precipitates. Instead, their status as biologic structures and thus actual fossils is supported. Enrichment in the element carbon, and also possibly to some extent the elements magnesium and iron, seems to be playing some role in the preservation process.
Highlights
Aspects of the Phanerozoic fossil record of disc-shaped fossils in general, and jellyfish fossils in particular, are somewhat cryptic, as the amount of character information generally preserved with such soft-bodied cnidarian specimens tends to be limited; any conclusions must be made with some caution (Hagadorn, Fedo & Waggoner, 2000)
The focus here is on some new material recovered from the Echo Shale Member of the Carrara Formation that seems to resemble fossil specimens at times treated as either porpitids or eldonids
We have provided two alternative taxonomic assignments, and we concur with Conway Morris, Savoy & Harris (1991, p. 149–150) that ‘‘in the absence of diagnostic soft-parts, placement of certain discoidal fossils in’’ what are today known as the capitates, can be challenging
Summary
Aspects of the Phanerozoic fossil record of disc-shaped fossils in general, and jellyfish (medusozoans) fossils in particular, are somewhat cryptic, as the amount of character information generally preserved with such soft-bodied cnidarian specimens tends to be limited (though see Ossian, 1973; Cartwright et al, 2007; Liu et al, 2014 for exceptions); any conclusions must be made with some caution (Hagadorn, Fedo & Waggoner, 2000). This is especially apposite given Caster’s As part of a discussion of the affinities of this new material, the fossil record of porpitids is briefly considered
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