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Journal of Paleontology 92(1):71–79
and stratigraphical occurrence of D. micans in Northeast Greenland, see Skovsted (2003, 2006). In southern Labrador (eastern Canada), Discinella micans
occurs in the lower part of the Forteau Formation (Labrador Group). The species is relatively common in the basal Devils Cove member and in the overlying Middle Shale member (see Knight 2013; Knight and Boyce, 2015; Skovsted et al., in press for detailed characterization of the Forteau Formation). In our material, D. micans occurs in interreef limestones mainly com- posed of echinoderm shell debris adjacent to the archaeocyathid patch reefs, which formed in an inboard shelf setting during a transgression (Spencer, 1980; Skovsted et al., in press). Discinella micans also occurs in the Devils Cove member of the Forteau Formation in western Newfoundland (CBS, personal observation, 2016), but these specimens have not been closely studied in the present work. A total of over 900 specimens were recovered from a suit of samples derived mainly from beach cliffs along the Straights of Belle Isle, east of Forteau, collected by A.R. Palmer and student in 1978 and 1979 (material now at the Institute for Cambrian Studies [ICS] at the University of Chicago) and by CBS in 2007. The majority of specimens were recovered from the section at Fox Cove (for details, see Skovsted et al., in press). Selected specimens from acid-resistant residues (dissolved
Figure 1. Map of North America showing known distribution of Discinella micans (Billings, 1871). Small stars indicate approximate locations in North Greenland (1), western Newfoundland (4), southern Quebec (5), and New York State (6 and 7). Large stars indicate locations in Northeast Greenland (2) and southern Labrador (3) sampled for the present investigation.
important aspects of the morphology and variability of these problematic shells have never been described before, and we will focus our work on new morphological details that may increase our understanding of the ontogeny and functional morphology of mobergellans. New observations described for the first time herein are the morphology of the larval shell, the variability of the anteriormost muscle scars, and a range of different unusual shell morphologies and deformations that may constrain the functional morphology of mobergellans.
Materials and methods
The material for the present contribution was derived from two areas of eastern Laurentia: the fjord area of Northeast Greenland and the coastal region of southern Labrador. The Greenland material was derived from the lower Cambrian Bastion and Ella Island formations where Discinella was first reported by Poul- sen (1932) and subsequently in greater detail by Skovsted (2003).Atotal of about 800 specimens ofD. micans were found in acid resistant residues of limestone samples collected by J.S. Peel under the auspices of the Geological Survey of Greenland (GGU) from the upper Bastion Formation and the overlying Ella Island Formation of Albert Heim Bjerge and C.H. Ostenfeld Nunatak. Rare specimens of a second mobergellan, Aktugaia? sp., were reported from the Bastion Formation by Skovsted (2006), but this material is too poorly preserved to be analyzed in detail herein. For detailed information on the geology, age,
in 10% acetic acid) were gold-coated and investigated using SEM facilities at Uppsala University and Swedish Museum of Natural History in Stockholm.
Repositories and institutional abbreviations.—All illustrated specimens from Greenland are housed in the Swedish Museum of Natural History (SMNH) in Stockholm, Sweden, while spe- cimens from Labrador are housed at the Provincial Museum of Newfoundland and Labrador (NFM), St. John’s, Newfound- land, Canada.
Taxonomic remark
The taxonomic status of the name Discinella micans (Billings, 1871) is somewhat uncertain following more than 100 years of unusual taxonomic practices in studies of mobergellans (e.g., Billings, 1871; Hall, 1872; Moberg, 1892; Hedström, 1923, 1930; Fisher, 1962; see also discussions in Bengtson, 1968; Skovsted, 2003). However, a full taxonomic revision of the genus should, in our view, be carried out in connection with a larger revision of the family Mobergellidae and is thus outside the scope of the present contribution. We therefore adhere to the established use of the name Discinella micans in the present contribution awaiting future resolution of mobergellan taxonomy.
Discinella micans from Northeast Greenland and southern Labrador
The shells of Discinella micans from Greenland and Labrador are circular to subcircular discs with flat or weakly convex or concave lateral profile (Skovsted, 2003). The external surface is ornamented by fine concentric growth lines at regular intervals, presumably reflecting growth of the shell through addition of
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