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Reassessment of the Silurian Problematicum Rutgersella As Another Post-Ediacaran Vendobiont

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Reassessment of the Silurian Problematicum Rutgersella As Another Post-Ediacaran Vendobiont Alcheringa: An Australasian Journal of Palaeontology ISSN: 0311-5518 (Print) 1752-0754 (Online) Journal homepage: http://www.tandfonline.com/loi/talc20 Reassessment of the Silurian problematicum Rutgersella as another post-Ediacaran vendobiont Gregory J. Retallack To cite this article: Gregory J. Retallack (2015): Reassessment of the Silurian problematicum Rutgersella as another post-Ediacaran vendobiont, Alcheringa: An Australasian Journal of Palaeontology, DOI: 10.1080/03115518.2015.1069483 To link to this article: http://dx.doi.org/10.1080/03115518.2015.1069483 Published online: 16 Sep 2015. Submit your article to this journal Article views: 12 View related articles View Crossmark data Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=talc20 Download by: [University of Oregon] Date: 20 September 2015, At: 12:33 Reassessment of the Silurian problematicum Rutgersella as another post-Ediacaran vendobiont GREGORY J. RETALLACK RETALLACK, G.J., XX.XXX.2015. Reassessment of the Silurian problematicum Rutgersella as another post-Ediacaran vendobiont. Alcheringa 39, xxx–xxx. ISSN 0311-5518 Rutgersella is a problematic fossil from the early Silurian (Llandovery) Shawangunk Formation of New Jersey, at first interpreted as a jellyfish comparable with Ediacaran fossils, such as Dickinsonia. Three proposed species of Rutgersella from the same locality are here regarded as growth or reproductive variants of a single species, R. truexi. Sedimentary structures, associated trace fossils and petrographic examination now show that they were sessile organisms of intertidal mudflats. These fossils have been dismissed as pyrite suns, but thin-sections show that they were weakly pyritized, organic structures, with a quilted hollow internal structure, similar to Seilacher’s constructional and taxonomic concept of Vendobionta. As for Cambrian Swartpuntia, and Devonian Protonympha, Rutgersella may be a post-Ediacaran vendobiont. The biological affinities of Rutgersella are problematic, but are compared with coenocytic green algae, cellular slime moulds, puffball-like fungal fruiting bodies and foliose lichens. Gregory J. Retallack [[email protected]], Department of Geological Sciences, University of Oregon, Eugene, OR 97403-1272, USA. Received 23.2.2015; revised 16.6.2015; accepted 1.7.2015. Key words: Rutgersella, Silurian, Pennsylvania, Problematicum, Vendobiont. DISCOVERY of Rutgersella in black shales of New (Gehling et al. 2000). This paper, thus, addresses the Jersey was initially considered significant, because they following questions concerning the enigma of were regarded as a Silurian holdover of ‘Dipleurozoa’ vendobionts. Can Rutgersella be included within the (Johnson & Fox 1968). ‘Dipleurozoa’ is a now- Vendobionta? Do vendobionts form a coherent clade abandoned taxon of bilaterally symmetrical jellyfish with an Ediacaran to Devonian range? What kinds of erected by Harrington & Moore (1956) for Dickinsonia organisms were Vendobionta? and similar Ediacaran fossils (Fedonkin 1985). Such Pyritization, as found in Rutgersella, is a form of Ediacaran fossils are now regarded as Vendobionta permineralization of histology, which has proven reveal- (Seilacher 1992), but this paper revisits the Ediacaran ing for plant fossils (Matten 1973). This paper thus holdover conclusion of Johnson & Fox (1968). Plausi- includes a petrographic study of Rutgersella, for com- ble post-Ediacaran Vendobionta are rare but well docu- parison with other pyritized problematica (El Albani Downloaded by [University of Oregon] at 12:33 20 September 2015 mented: Cambrian Swartpuntia (Jensen et al. 1998) and et al. 2010). However, pyritization also led Cloud Tirasiana (Crimes & McIlroy 1999, Hagadorn et al. (1973) to dismiss Rutgersella as a pyrite sun, and thus 2000, Yang 2010), Ordovician Rutgersella (Retallack a pseudofossil. Cloud’s pseudofossil interpretation also 2009) and Devonian Protonympha (Conway Morris & is addressed here by comparative taphonomic and Grazhdankin 2005, 2006). More controversial are Cam- petrographic studies. brian Ediacaria (Crimes et al. 1995), Emmonsaspis, Thaumaptilon (Conway Morris 1993) and Stromatoveris (Shu et al. 2006), which are preserved in a different Materials and methods way than Ediacaran vendobionts (MacGabhann et al. Type material of Rutgersella was examined in the old 2007,Laflamme et al. 2013). Rutgersella, however, is Geological Museum of Rutgers University in New preserved both in sandstone, like Ediacaran Dickinsonia Brunswick, New Jersey. Additional material was from South Australia (Retallack 2009) and also, as collected for thin-sectioning and measurement from the demonstrated here, in pyritic shales, like Ediacaran locality in Delaware Water Gap and curated in the Con- Dickinsonia from Russia (Dzik & Ivantsov 2002, don Collection of the Museum of Natural and Cultural Dzik 2003) and Aspidella from Newfoundland History of the University of Oregon. New collections also allowed precise location of the fossils within a newly measured geological section. Also prepared were © 2015 Association of Australasian Palaeontologists petrographic thin-sections and a polished thick-section http://dx.doi.org/10.1080/03115518.2015.1069483 2 GREGORY J. RETALLACK ALCHERINGA of the fossil and associated sediments. A cross-section lower greenschist facies (Epstein & Epstein 1972). of Rutgersella was also examined with a Helios scan- Alteration of conodonts (CAI 4−4.5) and coalified debris ning electron microscope with EDAX chemical (vitrinite reflectance 3.5%) in Silurian rocks of eastern analytical capability in the Center for Advanced Pennsylvania are evidence of burial temperatures of Materials Characterization (CAMCOR) at the University 190−300°C and burial depths of 6.7−7.9 km (Epstein of Oregon. et al. 1977). Pyritic black shale with Rutgersella is at the top of 6 m of grey siltstone and sandstone exposed in wood- Geological setting land below massive cliff-forming sandstones and con- Delaware Water Gap is a village named for the valley glomerates of the upper Lizard Creek Member, where the Delaware River flows through a prominent 108−113 m above the base of the Shawangunk Forma- strike ridge of quartzites of the Shawangunk Formation, tion (Fig. 2). The Lizard Creek Member with its flaser along the state border between Pennsylvania and New and linsen bedding (Fig. 3D), claystone breccias Jersey (Fig. 1). Grey conglomerates and sandstones of (Fig. 3C) and mudcracks (Fig. 2) has been considered the Shawangunk Formation unconformably overlie dark an intertidal to lagoonal facies of synorogenic, braided grey shales of the Martinsburg Formation, and are in turn stream conglomerates and sandstones (Clarke & conformably overlain by red beds of the Bloomsburg Ruedemann 1912, Willard 1928, Swartz & Swartz Formation. Rutgersella fossils were found in the Lizard 1930, Smith 1970, Smith & Saunders 1970). Creek Member of the Shawangunk Formation (Berg & An intertidal–estuarine palaeoenvironment for Dodge 1981) at a locality north of the parking lot at Rutgersella is also compatible with evidence from other ‘Point of the Gap Overlook’ wayside kiosk (N40.96812° fossils from the same site (Table 1). The eurypyterid W75.12255°), 1.6 miles southwest of Delaware Water fauna of this site includes the same mix of walking and Gap village (Johnson & Fox 1968). This locality is near swimming taxa as found at Otisville, New York the base of a thick clastic wedge, and metamorphosed to (Plotnick 1999, Tetlie 2007). These have been consid- ered stratigraphically equivalent (Clarke & Ruedemann 1912), but the Otisville beds are stratigraphically higher and equivalent to fish-bearing siltstones within the lower Bloomsburg Formation nearer Delaware Water Gap village (Beerbower & Hait 1959). Fish fragments from the Rutgersella site are similar to freshwater forms (Vernonaspis sp. indet. Smith 1970) better known from the non-marine Bloomsburg Formation (Beerbower & Hait 1959). Hints of marine influence come from inar- ticulate brachiopods (Lingula sp.), indeterminate cepha- lopod fragments (Albright 1987) and a bivalve: the latter found during this study (Fig. 4H), and identified here as Modiolopsis subcarinata Hall (1852). Trace fossils from this locality are evidence of lim- ited marine influence (Metz 1998), especially the Downloaded by [University of Oregon] at 12:33 20 September 2015 widespread ichnotaxon Arthrophycus alleghaniensis (Fig. 4I), now regarded as feeding burrows (Seilacher 2007) of a marine isopod (McCoy et al. 2012). U-shaped burrows of Arenicolites sp. (Metz 1998) are characteristic of marine lugworms (Seilacher 2007). Nevertheless, eight ichnogenera (Table 1) represents low behavioural diversity, comparable with non-marine Cambrian−Ordovician ichnofossil assemblages (Retallack 2009). In contrast, Late Ordovician (Katian) marine ichnofossils from Cincinnati, Ohio, have been assigned to 24 ichnogenera, including a diverse range of trilobite and echinoderm traces (Osgood 1970) not found at Delaware Water Gap. Diversity of up to 21 ichnogenera is found in Silurian marine rocks of Canada (Pickerill et al. 1977, 1988, Narbonne 1984). One of these trace fossils (‘Chondrites sp. cf. C. arbuscula’ of Metz 1998) is very abundant in some Fig. 1. Locality for Rutgersella truexi near Delaware Water Gap, New beds, but is probably not a fossil burrow system, like Jersey. Geological formations are from Berg & Dodge (1981). genuine feeding burrows of Chondrites (Seilacher ALCHERINGA THE SILURIAN PROBLEMATICUM
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