A possible Cambrian stem-group gnathiferan-chaetognath from the Weeks Formation (Miaolingian) of Utah (original) (raw)
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The Weeks Formation preserves a diverse, yet largely undescribed, exceptionally-preserved fauna of late Guzhangian age. Here I describe Notchia weugi gen. et sp. nov., a new arthropod characterized by a short cephalon, a trunk with twelve tergites and weakly differentiated into two morphological regions, and a spine-bearing rectangular telson. This combination of characters is incompatible with its assignment to any known groups. The new taxon also adds to examples of convergent evolution of ramified digestive glands in arthropods, possibly as an adaptation to infrequent feeding.
First palaeoscolecid from the Cambrian (Drumian, Miaolingian) Marjum Formation of western Utah, USA
ACTA PALAEONTOLOGICA POLONICA, 2021
The middle Marjum Formation is one of five Miaolingian Burgess Shale-type deposits in Utah, USA. It preserves a diverse non-biomineralized fossil assemblage, which is dominated by panarthropods and sponges. Infaunal components are particularly rare, and are best exemplified by the poorly diverse scalidophoran fauna and the uncertain presence of palaeoscolecids amongst it. To date, only a single Marjum Formation fossil has been tentatively assigned to the palaeoscolecid taxon Scathascolex minor. This specimen and two recently collected worm fragments were analysed in this study using scanning electron microscopy and energy dispersive X-ray spectrometry. The previous occurrence of a Marjum Formation palaeoscolecid is refuted based on the absence of sclerites in the specimen, which we tentatively assign to an unidentified species of Ottoia. The two new fossils, however, are identified as a new palaeoscolecid taxon, Arrakiscolex aasei gen. et sp. nov., characterized by the presence of hundreds of size-constrained (20-30 µm), smoothrimmed, discoid plates on each annulus. This is the first indisputable evidence for the presence of palaeoscolecids in the Marjum biota, and a rare occurrence of the group in the Cambrian of Laurentia. Palaeoscolecids are now known from nine Cambrian Stage 3-Guzhangian localities in Laurentia, but they typically represent rare components of the biotas.
We describe a weakly biomineralized non-trilobite artiopodan arthropod from the Guzhangian Weeks Formation of Utah. Falcatamacaris bellua gen. et sp. nov. is typified by a thin calcitic cuticle, broad cephalon without eyes or dorsal ecdysial sutures, an elongate trunk with distinctively sickle-shaped pleural spines, and a long tailspine with a bifurcate termination. The precise affinities of Falcatamacaris gen. nov. are problematic due to the presence of unique features within Artiopoda, such as the peculiar morphology of the pleural and posterior regions of the trunk. Possible affinities with aglaspidid-like arthropods and concilitergans are discussed based on the possession of 11 trunk tergites, edge-to-edge articulations and overall body spinosity. The new taxon highlights the importance of the Weeks Formation Konservat-Lagerstätte for further understanding the diversity of extinct arthropod groups in the upper Cambrian.
Utah Geological Association Publication 45:291-336, 2016
The middle Cambrian succession of Utah’s West Desert offers an outstanding record of one of the most important periods in Earth history, and in recent decades it has provided one of the most important faunal records of this time interval in the world. A total of 18 formations comprise the middle Cambrian (Series 3) succession of the West Desert and, together, they span the entirety of the series, with the Eokochaspis through Cedaria trilobite zones represented. For more than a century the middle Cambrian strata of the area have been well-known for their abundant, diverse, and well-preserved trilobites, which are especially prominent in the Wheeler, Marjum, and Weeks formations. The paleoenvironmental conditions that promoted the preservation of articulated trilobites and other mineralized organisms also contributed to soft-bodied preservation of Burgess Shale-type biotas in those units. The particularly rich fossil record from this area includes endemic taxa that are unique to the region as well as those found elsewhere in Laurentia and on other paleocontinents. In recent years, understanding of the middle Cambrian biotas from western Utah has increased as new taxa, including many soft-bodied forms, have been discovered. In the past year alone, species diversity from the Wheeler, Marjum, and Weeks formations has been expanded considerably. Taxa new to the Wheeler Formation include the protomonaxonid Lenica cf. hindei, the vetulocystid Thylacocercus ignota, the hemichordate Sphenoecium wheelerensis, and the conulariid Cambrorhytium sp. Those from the Marjum Formation include the arthropod Dytikosicula desmatae, the cambroernid Eldonia ludwigi, and the new pterobranch hemichordate, Sphenoecium wheelerensis. The new arthropod Falcatamacaris bellua from the Weeks Formation joins two other new arthropod taxa described since 2013. The steady increase in taxonomic diversity of these units has contributed greatly to understanding the complex ecosystems that thrived in this region during the middle Cambrian. Recent work has also shed light on the living environments and circumstances surrounding exceptional preservation of the fossil assemblages. The House Range embayment, a deep water trough that first developed at the onset of Wheeler deposition, gradually filled through time, resulting in an overall shallowing upwards sequence and a general decrease in the frequency of soft-bodied preservation.
The Guzhangian Weeks Formation (House Range, Utah, USA) contains a virtually unstudied but diverse assemblage of ‘soft-bodied’ organisms. This fauna includes several enigmatic appendages of arthropods that are described in this contribution. Six appendages (two isolated and four paired appendages) are interpreted as frontal appendages of a probably new species of Anomalocaris. They are characterized by a slender morphology, 14 podomeres, ventral spines alternating in size, up to three auxiliary spines per ventral spine, and only two dorsal spines. Another isolated appendage is also tentatively assigned to Anomalocaris, but it exhibits a more robust morphology, a stronger distal tapering, and apparently simple ventral spines, suggesting that it may represent a distinct taxon. These frontal appendages represent the youngest occurrence of anomalocaridids in Laurentia and demonstrate the persistence of older, Burgess Shale-type taxa in the Weeks Formation. An assemblage of four antenniform and six robust and heavily-armed appendages is also described. These are interpreted as the serially arranged, anterior appendages of a single individual of an undetermined arthropod species. This association of three pairs of robust, spiny appendages with two pairs of antenniform structures in a Cambrian arthropod is unique.
A NEW METAZOAN FROM THE MIDDLE CAMBRIAN OF UTAH AND THE NATURE OF THE VETULICOLIA
Palaeontology, 2005
A new metazoan, Skeemella clavula gen. et sp. nov., is described from the Middle Cambrian Pierson Cove Formation of the Drum Mountains, Utah, USA. Skeemella is similar to vetulicolians, but differs from other examples of this group in the relative proportions of the anterior and posterior sections, the large number of divisions, and the elongate bifid termination. The posterior section is arthropodan in character. The similarity of this fossil to vetulicolians throws hypotheses of their deuterostome affinity into question and highlights their problematic sta- tus.
Paleontological Contributions, 2018
The Spence Shale of northern Utah is the oldest North American middle Cambrian (∼506–505 Ma) Burgess Shale-type (BST) deposit and, unlike previously thought for BST deposits, has a very diverse ichnofauna. Twenty-four ichnogenera and 35 ichnospecies were identified: Archaeonassa (A. fossulata and A. jamisoni isp. nov.), Arenicolites carbonaria, Aulichnites, Bergaueria (B. hemispherica and B. aff. perata), Conichnus conicus, Cruziana (C. barbata and C. problematica), Dimorphichnus, Diplichnites (D. cf. binatus, D. gouldi, and D. cf. govenderi), Gordia marnia, Gyrophyllites kwassizensis, Halopoa aff. imbricata, Lockeia siliquaria, Monomorphichnus (M. bilinearis, M. lineatus, and M. cf. multilineatus), Nereites cf. macleayi, Phycodes curvipalmatum, Phycosiphon incertum, Planolites (P. annularius, P. beverleyensis, and P. montanus), Protovirgularia (P. dichotoma and P. cf. pennatus), Rusophycus (R. carbonarius, R. cf. pudicus, and R. cf. cerecedensis), Sagittichnus lincki, Scolicia, Tae...