Gladiobranchus probaton Bernacsek & Dineley, 1977

Hanke, Gavin F. & Davis, Samuel P., 2008, Redescription of the acanthodian Gladiobranchus probaton Bernacsek & Dineley, 1977, and comments on diplacanthid relationships, Geodiversitas 30 (2), pp. 303-330 : 306

Gladiobranchus probaton Bernacsek & Dineley, 1977 ( Figs 1-13 )

HOLOTYPE. — NMC 22700A.

MATERIAL EXAMINED. — UALVP 19259, 32448, 32469, 38679, 41669, 41857, 41858, 41862, 42095, 44046, scales: 45366-45396.

HORIZON AND AGE. — All known Gladiobranchus specimens are from the single UALVP locality 129 in Early Devonian (Lochkovian) dark grey argillaceous limestone of the Delorme Group, Delorme Formation, District of Mackenzie.

TYPE LOCALITY. — In talus below the UALVP locality 129 (62°32”N, 127°45”W), also known as the MOTH fish layer, MOTH section, section 43 ( Gabrielse et al. 1973), Central Mackenzie Mountains, Northwest Territories, Canada. The descriptive geology of the locality was summarized by Hanke et al. (2001), Hanke (2002), Hanke & Wilson (2004), and Zorn et al. (2005).

REVISED DIAGNOSIS. — Diplacanthoid acanthodians with rostral plates having enlarged tubercles along posterolateral edges; an enlarged anterior circumorbital plate with radiating rows of tubercles situated posterolateral to the rostrum; single ovate, enlarged postorbital plate ornamented with spiky tubercles associated with the circumorbital plate series; perichondrally ossified Meckel’s cartilage with strong symphyseal connection; dorsally-directed process positioned mid-way along Meckel’s cartilage; dermal mandibular splint absent; heavily-ornamented, spathiform opercular plates cover the entire gill chamber laterally; pectoral dermal plate armour absent; two pairs of prepectoral spines inserted between scales on the isthmus; axial ridge of scapular blade of scapulocoracoid separating postbranchial and posterior laminae of coracoid region; medial surface of scapulocoracoid flat; paired fin-spines possessing simple reclined nodular ornament on anterior-most ribs; anterior dorsal fin-spine approximately twice the length of posterior dorsal fin-spine; enlarged body scales with fine surface ridges surround base of fin-spines; body scales behind branchial chamber, on fins, and along dorsal and ventral midline posterior as far as caudal peduncle ornamented with fine parallel ridges whereas body scales at mid-flank possess unornamented crowns; body scale histology consisting of few, thick growth zones in crown and flat to slightly tumid mass of basal tissue; body scale neck and basal tissue expanded perpendicular to long-axis of scale crown.

Figures

FIG. 1. — Gladiobranchus probaton Bernacsek & Dineley, 1977, composite reconstruction based on the holotype (NMC 22700A) and UALVP 41862, 41858, 38679, and 41857.

FIG. 2. — Photograph of the holotype of Gladiobranchus probaton Bernacsek & Dineley, 1977 (NMC 22700A). Scale bar: 1 cm.

FIG. 3. — Articulated specimen of Gladiobranchus probaton Bernacsek & Dineley, 1977 (UALVP 41862): A, photograph; B, camera lucida drawing (1st.prp. pair is between lt. and rt.pfs). Scale bars: 1 cm.

FIG. 4. — Articulated specimen of Gladiobranchus probaton Bernacsek & Dineley, 1977 (UALVP 41858): A, photograph; B, camera lucida drawing. Scale bars: 1 cm.