Abstract
The non-biomineralized artiopod Emeraldella brutoni Stein, Church & Robison, from the middle Cambrian (Drumian) Wheeler Formation in Utah represents the only confirmed occurrence of the genus Emeraldella outside of the stratigraphically older (Wuliuan) Burgess Shale Konservat-Lagerstätte in British Columbia. The hitherto known sole specimen of this species is preserved in dorsal view and lacks critical information on the ventral appendages. Here, we redescribe E. brutoni based on a new completely articulated specimen that illustrates the appendage organization in exceptional detail. The main body consists of a cephalic region covered by a semicircular head shield, a trunk including 10 tergites with expanded pleurae plus a cylindrical terminal segment, and a long articulated tailspine. The head carries a pair of elongate and flexible antennae, a pair of lateral eyes, and three pairs of post-antennal appendages. We report the presence of eyes in Emeraldella for the first time. The first post-antennal limb solely consists of an endopod with well-developed paired spiniform endites. The remaining cephalic appendages and those associated with all but the last trunk segments possess exopods terminating in paddle-shaped, distal lobes fringed with robust setae. The cylindrical terminal segment bears a pair of posteriorly oriented caudal flaps reminiscent of trunk exopods, and a styliform, possibly uniarticulate tailspine longer than the main body. The new data on E. brutoni suggests an exopodal origin for the paired caudal structures in Vicissicaudata, and improve our understanding of the fundamental organization of this major clade within Artiopoda.
Highlights
The House Range and the Drum Mountains of western Utah are internationally renowned for their richly fossiliferous Miaolingian (“middle Cambrian”) strata, and the beautifully preserved trilobites they contain
The exploitation of the local federal lands by fossil dealers and amateur collectors searching for trilobites led to the realization that these three Miaolingian units contain the remains of non-biomineralizing organisms (Robison, 1991; Lerosey-Aubril et al, 2018)
Each new soft-bodied fossil recovered from these beds can significantly improve our understanding of the anatomy or palaeocology of these taxa, and refine our depiction of these ancient biotas
Summary
The House Range and the Drum Mountains of western Utah are internationally renowned for their richly fossiliferous Miaolingian (“middle Cambrian”) strata, and the beautifully preserved trilobites they contain. A total of 40 years after the beginning of their scientific explorations, the Cambrian Konservat-Lagerstätten of western Utah are not “minor” anymore, as once described by Conway Morris (1985) These deposits have yielded between 20 and 45 soft-bodied species each (Robison, Babcock & Gunther, 2015; Lerosey-Aubril et al, 2018) and qualify as Tier 2 Burgess Shale-type deposits (Gaines, 2014). Our current restudy of the Wheeler biota from the House Range reveals that 20 of the 45 soft-bodied species it contains (44.4%) are described in the scientific literature based on a single fossil, and an additional nine species (another 20%) are known from only two or three specimens In this context, any new soft-bodied fossils from these Konservat-Lagerstätten hold the promise for significantly improving our understanding of these exceptional Cambrian biotas. The new specimen is preserved in a different orientation from that of the type material, providing valuable insights into the as-yet unknown appendicular anatomy of this taxon
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