Trundlelepis cervicostulata, BURROW, 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 (1975), pp. 1-32 : 10

TRUNDLELEPIS CERVICOSTULATA BURROW, 1997

( Fig. 3K–3P ; Table 1 ; Suppl. 1, figs. 18–21)

Trundlelepis cervicostulata Burrow 1997 , 57, fig. 4A-E, pl. 3 figs. 7-11.

Diagnosis —see Burrow (2002).

Type material — Holotype scale MMMC02239 ; paratypes scales MMMC02236 , 02234 ; GSNSW locality C607, near Trundle , central New South Wales, Australia, Connemarra Formation (Lower Devonian, Lochkovian).

Referred specimens —Scales were recovered from most levels from 513’–532’ (156.4-162.2 m), including UCR 944-3, -12, -17 (level 527.25’= 160.7 m), UCR 10768- 4 (level 518.3’= 158 m), and thin sections UCR 944-22, -23 (level 527.25’= 160.7 m): Roberts Mountains Formation.

Description —Scales have a flat crown, longer than wide, with 6–8 strong ridges leading back from the anterior margin and tapering out before the central area of the crown ( Fig. 3K, M, N ). The median ridges are often slightly asymmetrical in cross section, being steeper on the outer face, but the area between these ridges is at the same level as the rest of the crown, without a median sulcus. Some scales have one or two round pores opening out through the outer growth zone in the posterior half of the scale. The neck is deep all round, with ‘buttressing’ posteriorly. The large, convex base usually protrudes in front of the anterior margin of the crown, sometimes to the extent that the bulk of the base is forward of the crown ( Fig. 3O ). As with other scales from the section, hyphal borings penetrate densely, but the tissues forming the crown ( Fig. 3O, P ) are recognisable as syncitial mesodentine (sensu Valiukevičius and Burrow 2005) and orthodentine. Unlike poracanthodids with extensive pore canal systems, growth zones are discernible in the whole crown. Wide-calibre pore canals form a simple system comprising a few vertical canals from the undersurface to the upper surface of the crown, near the lateral edges ( Fig. 3P ).

Comparison —The scales show a range of profiles and crown ornament, comparable with that in the type material from the Lochkovian of southeastern Australia ( Burrow 1997, 2002, figs. 21A–21F, 23A–23D, 32A–32G). This taxon represents perhaps the last stage in the loss of a pore canal system in the scale crown for poracanthodids – a progression noted by Vergoossen (e.g., 1999a) – with only some scales having vertical, unconnected canals penetrating the outermost crown growth zones. Several other latest Silurian or earliest Devonian scales with comparable morphology from other regions could also be from Trundlelepis cervicostulata , including ones from the Přidolí of the Klonk Beds, Czechia ( Märss 1997, pl. 7.3–7.10: captioned Gomphonchus sp. 3 , Gomphonchus sp. ) and Sweden ( Vergoossen 2002b, fig. 45: captioned Acanthodii gen. et sp. indet.). The lack of distinctive crown features can make identification of scales from this species difficult when based only on morphology, as several latest Silurian–earliest Devonian taxa also have scales with a deep neck, convex anteriorly protruding base, and a flat crown with subparallel or radial ridges along the anterior margin. For example, Arenaceacanthus arcuatacanalis Valiukevičius (2004a) and Bracteatacanthus assiduus Valiukevičius (2004a) from the Přidolí of Lithuania, Nostovicina paravolborthi ( Valiukevičius 2003b) from the Přidolí of Timan–Pechora, and Nostolepis tcherkesovae Valiukevičius (1994) from the Lochkovian of Taimyr and Timan–Pechora have a similar morphology, but none of these taxa have morphotypes with the simple vertical canals penetrating the posterior crown growth zones exhibited in some scales of Trundlelepis from the type locality as well as the BC II section.

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