Pyritonema cupra, Tapanila, 2008

Wisshak, Max, 2017, Taming an ichnotaxonomical Pandora’s box: revision of dendritic and rosetted microborings (ichnofamily: Dendrinidae), European Journal of Taxonomy 390, pp. 1-99 : 62-63

Pyrodendrina cupra Tapanila, 2008

Fig. 23

Pyrodendrina cupra Tapanila, 2008: 129 , figs 3–7.

Rosette A – Tapanila 2005: 172, fig. 7.3–7.4.

Without name – (?) Bromley et al. 2007: 526, fig 32.5.

Pyrodendrina cupra – Buatois et al. 2017: 161, fig. 75F (holotype).

Original diagnosis

Rosette-shaped boring with shallow canals that bifurcate radially from a central node located below shell surface. Deep vertical canals extend radially below the central node. Canals taller than wide, with tapered terminals.

Original description

The dendrinid microborings are subdivided into three parts, which occupy successive depths within the shell. Nearest the outer shell surface, the proximal part of the microboring consists of dominantly horizontal radial canals, the middle part is a central node, and the distal part (most deeply penetrating portion) consists of dominantly vertical radial canals. The overall profile of the boring has an hourglass shape and in plan view the boring is oval in extent. The maximum diameter of the rosette is on average 445 μm, with a central node diameter of 105 μm. The maximum depth of penetration (distal-most extent) observed is 312 μm. The proximal part of the microboring has the greatest lateral extent. It consists of roughly a dozen primary radial canals that may bifurcate at an angle of 33–98° to form secondary canals. All proximal canals are 33–50% taller than they are wide (mean width is 16 μm). The canals radiate from multiple points on the central node, roughly 50 μm below the shell surface. The length of individual canals averages 140 μm, and these bifurcate at an average distance of 44 μm away from the central node. Surface apertures of the proximal canals are most abundant away from the center of the microboring, i.e., toward the periphery of the rosette. The vertical dimension of the canals enlarges toward their connection with the central node, giving them the appearance of buttresses. The central node is polyhedral, typically having a greater horizontal (radial) dimension (80–100 μm) than vertical (50–60 μm). The node typically initiates roughly 50 μm below the shell surface and extends to a depth of 100–150 μm before branching into the distal part. […] The distal part of the microboring consists of canals that radiate distally from the apices of the polyhedral central node. Up to 9 distal canals are observed in one rosette. The canals extend in a dominantly vertical path, but may form broad curves toward their distal part. As with proximal canals, distal canals are thickest nearest the central node and they have greatest dimension in the vertical plane. Branching in the distal canals is less frequent than in the proximal canals. The width of the distal canals averages 41 μm at their contact with the central node and they extend distally for an average length of 187 μm to give the microboring a penetrative depth of up to 312 μm. The maximum horizontal span of the distal canals (~300 μm) generally does not exceed the diameter of the proximal rosette. […] Different specimens exhibit different ontogenetic stages in the development of the microborings. The rosetted microboring appears to initiate as a single vertical canal. Unbranched solitary canals are observed at a maximum depth of ~100 μm. The solitary canal continues to penetrate to a depth of ~200 μm and branches once to form a hooked appearance, although no proximal branches are evident at this point of the microboring’s development. A third branch in the development of the boring produces a trident shape with a maximum penetration of ~300 μm. At the trident phase of branching, all distal canals are dominantly vertical, roughly equidistant, and connected at their branching point by a widening of adjacent canals, akin to the webbing between fingers. Proximal canals appear to originate during the trident phase, and the widened branch point of the distal canals appears to serve as the initiation of the central node. An increased number of distal and proximal canals along with a widening of the confluent central node characterize the mature phase […].

Type material, locality and horizon

Holotype ( Fig. 23 A–B) and paratype are cast in epoxy from a shell of the brachiopod Pentamerus palaformis Jin & Copper, 2000 from locality A1187 (UTM: 12E/1 544400/ 5454300), southern Anticosti Island , Québec, Canada. Goéland Member , Jupiter Formation , Early Silurian. They are deposited at the Geological Survey of Canada, Ottawa, Ontario, Canada ( GSC 10854 ).

Stratigraphical range

Late Ordovician to Early Silurian (Tapanila 2008).

Remarks

Even though Pyrodendrina cupra was found to be very common in the Late Ordovician to Early Silurian of Anticosti Island, with nearly 1 out of 10 brachiopods (5 different species) containing specimens filled with pyrite, iron oxide or micrite, it has not been reported from elsewhere. However, dendrinids preserved as internal moulds in cystoid plates from the Upper Ordovician of Sardinia, as described by Bromley et al. (2007), could represent incompletely preserved P. cupra . The phenomenon of incomplete casts was also addressed by Tapanila (2008), who based his original description on a combination of stereomicroscopy and scanning electron microscopy of epoxy resin casts, as well as micro-CT of pyritefilled specimens.

Figures

Fig. 23. Pyrodendrina cupra Tapanila, 2008. A–B. SEM of the holotype, cast in epoxy from a shell of the brachiopod Pentamerus palaformis Jin & Copper, 2000 from the Early Silurian of Anticosti Island, Canada.