Gomphonchoporus hoppei, (GROSS, 1947)

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 : 8-9

GOMPHONCHOPORUS HOPPEI ( GROSS, 1947)

( FIG. 3A–3E ,?3F,?3G; TABLE 1 ; SUPPL. 1, FIGS. 12?, 18–25)

Gomphonchus hoppei Gross 1971 , 56–58, figs. 21C, 21D, 22E, 23, 24A–D, pl. 1.28–1.30, 2.1–2.3, 3.36, 9.4–9.9.

Gomphonchoporus hoppei Vergoossen 1999a , 242– 244, figs. 40–57.

Diagnosis —see Vergoossen (1999a).

Type material — Holotype: scale MB.f.449 ( Gross 1947, pl. 24 fig. 7); from the Beyrichienkalk, northern Germany; exact collection locality unknown (Late Silurian, Přidolí?).

Referred specimens —Scales at most levels from 513′–591.5’ (156.4-180.3 m), and possibly level 468’ (142.6 m) in the BC II section, including UCR 944-11 (527.25’= 160.7 m), UCR 5439-2, 3, UCR 5439-1, 7? (level 549’= 167.3 m); and AMF 97959, 97960 (level 513’= 156.4 m), figured by Parkes (1995, fig. 33.5–33.8, captioned as Acanthodian 1 and Poracanthodes sp. ): Roberts Mountains Formation.

Remarks —As discussed by Vergoossen (1999a), the type scales described and figured by Gross (1947, 1971) were abraded, with delicate structures missing, in particular, the lateral areas of the posterior crown. For this reason, Vergoossen (1999a) nominated well-preserved scales from a northern Netherlands erratic as neotype and paratypes. However, the type specimen is still reposited in the MB.f collection so those allocations are not valid. Being better preserved than the type scales, those from the Netherlands erratic are more useful for comparative purposes.

Description —Scales from BC II are comparable with the scale nominated by Vergoossen as a neotype (1999a, pl. 4.42–4.44) and have numerous ridges leading back from the anterior margin ( Fig. 3A ), whereas others have a shallow median sulcus running back from the anterior edge of the crown to the level of the lateral corners, and only a few short low ridges running back from the anterior margin ( Figs. 3A–3D ,?3F,?3G). The straight anterior edges of the crown meet at an acute angle. The posterior crown is formed of appositional growth zones, expressed on the surface as long slits paralleling the straight posterolateral edges of the crown, or with more anterior growth zones appearing to overlap the growth zone behind ( Fig. 3A ). Few of the BC II scales have the posterolateral edges preserved, but at least one scale ( Parkes 1995, fig. 33.5, 33.6) has the close-set denticulations that are visible on the well-preserved scales figured by Vergoossen (1999a). The scale neck is concave all round, and of comparable height to the base, with a marked rim separating neck and base. A strong median ridge rises from the posterior base towards the lower surface of the crown ( Fig. 3A, B ), and the undersurface of the posterior crown ( Fig. 3E ) shows the wide canal openings that typify poracanthodid scales. Some scales with relatively long aligned slits on the posterior crown surface ( Fig. 3F, G ) are tentatively assigned to the species.

Comparison —Some scales approach the morphology of small (fin?) scales from Zemlyacanthus menneri ( Valiukevičius 1992, pl. 10.6–10.8), but only have straight slits and pore openings in the posterior area of the crown, rather than zigzag slits extending close to the anterior margin that characterize Z. menneri , and so are assigned on this basis to G. hoppei .

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