Gladiobranchus probaton Bernacsek & Dineley 1977

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.