Zemlyacanthus menneri, (VALIUKEVICIUS, 1992), VERGOOSSEN, 1997

Burrow, Carole Jan, Murphy, Michael & Turner, Susan, 2023, Late Silurian to earliest Devonian vertebrate biostratigraphy of the Birch Creek II section, Roberts Mountains, Nevada, U. S. A., PaleoBios 40 (4), pp. 1-32 : 9-10

ZEMLYACANTHUS MENNERI ( VALIUKEVIČIUS, 1992)

( Fig. 3H–J ; Table 1 ; Suppl. 1, figs. 18, 22)

Poracanthodes menneri Valiukevičius, 1992 , 195, pl. 1-10, text-figs. 1-12.

Zemlyacanthus menneri ; Vergoossen 1997, 45, 46.

Type material — Holotype scale LGMTI 35-360; paratypes LGMTI 35-358, 35-355, 35-354, 35-340, 35-341, 35-342, 35-350; Pod’emnaya River , outcrop 67, bed 12, October Revolution Island , Severnaya Zemlya Archipelago , Russia, Severnaya Zemlya Formation (Lower Devonian, Lochkovian).

Referred specimens —Scales at levels 513’ (156.4 m), 549’ (167.3 m), 554.5’ (169.0 m), and 556.5’ (169.6 m) in the BC II section, including three scales at 556.5’ (Suppl. 1, fig. 22), and AMF 97961, 97962 (both level 513’= 156.4 m), figured by Parkes (1995, fig. 33.9–33.12): Roberts Mountains Formation.

Description —Scales from level 556.3’ (169.6 m) strongly resemble flank scales from the type, articulated specimens of Zemlyacanthus menneri , showing overlapping apposed crown growth zones extending back from close to the anterior margin of the scale crown ( Fig.3H–J ). This anterior margin lacks well-formed ridges, with just a few short low rounded ridges occasionally present near the middle of the margin. The apposed growth zones forming the crown are denticulated, particularly in the larger more posterior zones, and sometimes comprise lines of slits/overlaps, rather than having uninterrupted overlaps. There is a sharp rim between the neck and base of the scale, with the latter protruding slightly in front of the crown. The convex base and concave neck are of similar heights.

Comparison —Some scales represented in the BC II samples closely resemble those from the type, articulated fishes ( Valiukevičius 1992, pl. 10) from the Lochkovian of October Revolution Island. Those BC II scales ( Fig. 3F, G ), tentatively assigned to Gomphonchoporus hoppei (Gross 1947) , are similar to some of the smaller scales on the type Z. menneri fish ( Valiukevičius 1992, pl. 10.8), and they are found at the same level as the scales readily assigned to Z. menneri. Overlap of scale morphotypes between different taxa is a common problem in taxonomy based on isolated scales, particularly when samples are rich in taxa but poor in numbers. Also, recognition that both scales with and without a pore canal system can belong to a poracanthodid species (e.g., Vergoossen 1999a, Burrow 2013) further complicates taxonomic assignments.

Figures

Figure 3. Poracanthodid and ischnacanthid acanthodian scales from Upper Silurian levels of the Birch Creek II section. A–E,?F,?G. Gomphonchoporus hoppei: A. UCR 949-1 (level 567.3') in crown view (from Supplement 1, fig. 24); B. UCR 944-11 (level 527.25') in laterocrown view; C, D. UCR 5439-2 (level 549') in anterocrown and laterocrown views; E. UCR 5439-3 (level 549') in basal view; F. UCR 5439-7 (level 549') in crown view; G. UCR 5439-1 (level 549') in anterocrown view. H–J. Zemlyacanthus menneri: UCR 10815-1, 2, 3 (level 556.5'), in crown views (from Supplement 1, fig. 22). M–P. Trundlelepis cervicostulata: K, L. UCR 10768-4 (level 518.3') in anterior and lateral views; M. UCR 944-17 (level 527.25') in crown view; N. UCR 944-3 (level 527.25') in crown view; O. UCR 944-23 (level 527.25'), vertical longitudinal thin section; P. UCR 944-22 (level 527.25'), horizontal thin section through crown. Q, R. Poracanthodidae gen., sp. indet. sensory line scale UCR 930-3 (level 395') in crown and posterior views. S-V. Gomphonchus sandelensis: S, T. UCR 10746-11 (level 430.5') in crown and lateral views; U,V. UCR 930-7 (level 395') in antero- and posterocrown views. W–Z. Gomphonchus mediocostatus: W. UCR 944-6 (level 527.25') in crown view; X. UCR 944-16 (level 527.25') in crown view; Y. UCR 942-1 (level 526') in crown view (from Supplement 1, fig. 20); Z. UCR 944-19 (level 527.25') in laterocrown view. Abbreviations: cgz=crown growth zones; dt=dentine tubules; h=hyphal borings; vc=vertical canals. Scale bars=0.1 mm, anterior of scale