ORCID Profile
0000-0003-4726-0355
Current Organisation
University of Missouri
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Publisher: Informa UK Limited
Date: 23-01-2022
Publisher: Geological Society of America
Date: 22-03-2021
DOI: 10.1130/G48508.1
Abstract: Molecular phylogenetic data suggest that photosynthetic eukaryotes first evolved in freshwater environments in the early Proterozoic and ersified into marine environments by the Tonian Period, but early algal evolution is poorly reflected in the fossil record. Here, we report newly discovered, millimeter- to centimeter-scale macrofossils from outer-shelf marine facies of the ca. 950–900 Ma (Re-Os minimum age constraint = 898 ± 68 Ma) Dolores Creek Formation in the Wernecke Mountains, northwestern Canada. These fossils, variably preserved by iron oxides and clay minerals, represent two size classes. The larger forms feature unbranching thalli with uniform cells, differentiated cell walls, longitudinal striations, and probable holdfasts, whereas the smaller specimens display branching but no other diagnostic features. While the smaller population remains unresolved phylogenetically and may represent cyanobacteria, we interpret the larger fossils as multicellular eukaryotic macroalgae with a plausible green algal affinity based on their large size and presence of rib-like wall ornamentation. Considered as such, the latter are among the few green algae and some of the largest macroscopic eukaryotes yet recognized in the early Neoproterozoic. Together with other Tonian fossils, the Dolores Creek fossils indicate that eukaryotic algae, including green algae, colonized marine environments by the early Neoproterozoic Era.
Publisher: Wiley
Date: 04-11-2021
DOI: 10.1002/SPP2.1410
Abstract: Machaeridians are a unique group of Palaeozoic annelids that secreted a calcitic armour consisting of dorsally interlocking sclerites running along the entire length of the animal. Preserved remains are most commonly found as disarticulated sclerites, although rare articulated specimens have also been preserved as moulds, recrystallized calcite and even pyrite replacement. These preservational modes unfortunately have obscured direct observation of the dorsal interlocking hinge, thus impeding our understanding of the functional protection offered by this biological armour. Herein, we document and describe articulated silicified lepidocoleids ( Lepidocoleus c aliburnus sp. nov., Lepidocoleus shurikenus sp. nov. and Lepidocoleus sp.) in association with isolated sclerites of Lepidocoleus cf. kuangguoduni from the Lower Devonian (Pragian) Garra Formation of New South Wales, Australia. Articulated specimens include straight and enrolled scleritome configurations possessing opposing and alternate dorsal hinge articulation, respectively. Silicified scleritomes were analysed using x‐ray microtomography to investigate the three‐dimensional morphology, cross‐sectional geometry and dorsal hinge articulation and configuration of in idual sclerites in the armour assembly. Virtual dissection of articulated specimens alongside reconstructions of isolated sclerites reveal distinctions in sclerite morphology across opposing and alternate articulation mechanisms, including a novel system not previously observed in lepidocoleids. The combination of heterogeneous sclerite cross‐sectional geometry with sclerite overlap also serves to maintain a uniform thickness of the armour assembly and presumably improve resistance to predatory attack.
Publisher: Informa UK Limited
Date: 22-07-2019
Publisher: Wiley
Date: 19-04-2021
DOI: 10.1111/PALA.12534
Publisher: Polska Akademia Nauk Instytut Paleobiologii (Institute of Paleobiology, Polish Academy of Sciences)
Date: 2021
Publisher: Springer Science and Business Media LLC
Date: 10-01-2020
DOI: 10.1038/S41467-019-13882-Z
Abstract: The fossil record of the terminal Ediacaran Period is typified by the iconic index fossil Cloudina and its relatives. These tube-dwellers are presumed to be primitive metazoans, but resolving their phylogenetic identity has remained a point of contention. The root of the problem is a lack of diagnostic features that is, phylogenetic interpretations have largely centered on the only available source of information—their external tubes. Here, using tomographic analyses of fossils from the Wood Canyon Formation (Nevada, USA), we report evidence of recognizable soft tissues within their external tubes. Although alternative interpretations are plausible, these internal cylindrical structures may be most appropriately interpreted as digestive tracts, which would be, to date, the earliest-known occurrence of such features in the fossil record. If this interpretation is correct, their nature as one-way through-guts not only provides evidence for establishing these fossils as definitive bilaterians but also has implications for the long-debated phylogenetic position of the broader cloudinomorphs.
No related grants have been discovered for James Schiffbauer.