Prototroctes, Gunther, 1864

Schwarzhans, Werner, Scofield, R. Paul, Tennyson, Alan J. D., Worthy, Jennifer P. & Worthy, Trevor H., 2012, Fish remains, mostly otoliths, from the non-marine early Miocene of Otago, New Zealand, Acta Palaeontologica Polonica 57 (2), pp. 319-350 : 332-334

Prototroctes vertex Schwarzhans sp. nov.

Fig. 7I–O.

Etymology: From Latin vertex, twist, referring to the inclined, twisted axis of the otolith.

Type material: Holotype: NMNZ S.52729 ( Fig. 7I) . Paratypes: 25 specimens (21 specimens NMNZ S.52731, same location as holotype; 4 specimens NMNZ S.52730, same location as holotype, HH1b bed, trench excavation) ( Fig. 7J–N) .

Type locality: Home Hills Station, Manuherikia River near St Bathans , Otago .

Type horizon: HH1a bed, Bannockburn Formation, early Miocene.

Other material.—1265 specimens: 1131 specimens (2 deformed, NMNZ S.52732, Fig. 7O), Home Hills, Manuherikia River near St Bathans, HH1a bed; 20 specimens, Home Hills Station , Manuherikia River near St Bathans, HH 1b ; 33 specimens, Vinegar Hill , site 1 , 81 specimens, Vinegar Hill , site 2 .

Diagnosis.—Compact, very compressed otoliths with inclined, twisted vertical otolith axis. OL:OH = 0.7–0.9. Ventral rim deep, posteriorly pronounced. Dorsal rim high, anteriorly pronounced, usually with marked postdorsal indentation.

Description.—Compact, very high−bodied otoliths with deep, regularly rounded, posteriorly pronounced ventral rim. Size up to nearly 3 mm. Rostrum short, stout; excisura moderately deep, broad; antirostrum short, blunt. Posterior rim inclined, ventrally pronounced, gently curving. Dorsal rim high, highest anteriorly, with marked indentation postdorsally. Rims smooth or slightly undulating. OH:OT = 3.5–3.8.

Inner face strongly convex, somewhat twisted due to inclined vertical axis of otolith. Sulcus long, narrow, deepened, slightly supramedian. Ostium as narrow as cauda, very short, anteriorly open; cauda slightly swinging, terminating close to posterior rim of otolith, with ventrally pointed tip. OL:SuL about 1.1; CaL:OsL = 1.8–2.3. Dorsal field anteriorly expanded, high. Dorsal depression ventrally well marked, opening posteriorly to the indentation of the posterior−dorsal rim. Ventral field wide, smooth, with faint ventral furrow moderately close to ventral rim.

Outer face flat to slightly concave, smooth.

Variability and ontogeny.—The variability of the otoliths of this species is moderate, mainly confined to variations of the expression of the dorsal rim and slight variations in the ratio

http://dx.doi.org/10.4202/app.2010.0127

OL:OH, the most compressed and probably deformed shape being depicted in Fig. 7O. Ontogenetic changes are more prominent with the typical expression of the dorsal rim usually not apparent in otoliths smaller about 1.8 mm long. Also there is a clear trend of decreasing index OL:OH with size.

Remarks.—The compressed form with the inclined vertical otolith axis and the twisted inner face as well as the peculiar shape of the dorsal rim all distinguish P. vertex from P. modestus . Smaller, diagnostically less mature and less compressed specimens of P. vertex, however, are not always easy to distinguish from those of the more rare P. modestus .

Stratigraphic and geographic range.—Bannockburn Formation, Manuherikia River and Vinegar Hill.