Mataichthys rhinoceros Schwarzhans, 2012

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 : 344

Mataichthys rhinoceros Schwarzhans sp. nov.

Fig. 14A–F.

Etymology: Referring to the resemblance of the dorsal rim of the otolith to the dorsal head profile of a rhinoceros.

Type material: Holotype: NMNZ S.52740 ( Fig. 14A) . Paratypes: Twelve specimens, NMNZ S.52741 and 52744, same location as holotype ( Fig. 14B–F) .

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

Type horizon: HH4 bed, Bannockburn Formation, early Miocene.

Other material.— 99 specimens: 30 specimens, same location as holotype, HH4 ; 69 specimens, HH1a; 2 specimens HH1b.

Diagnosis.—OL:OH = 1.3–1.5 (OH measured at highest point of dorsal rim) in specimens longer than 4 mm. Anterior−ventral projection feeble or absent, posterior−ventral projection feeble to pronounced. Dorsal rim with broad and deep central concavity leaving only horn−like projections anterior and posterior.

Description.—Robust, moderately elongate otoliths up to nearly 5.5 mm long. OL:OH = 1.3–1.5 in specimens from 4 to 5.5 mm, 1.2–1.25 in specimens from 2.5 to 3.5 mm long; OH:OT = 2.5–2.8. No or very feeble anterior−ventral projection, indistinct to moderately developed posterior−ventral projection. Dorsal rim with deep and broad half−moon shaped depression, leaving only horn−like projections at anterior−dorsal and posterior−dorsal terminations. Ventral rim nearly straight, horizontal. Anterior rim blunt to broadly rounded, posterior rim blunt or inclined, straight. Rims irregularly undulating.

Inner face nearly flat, with somewhat rugged surface. Sulcus with median position, moderately large and deepened, typical shoe−sole shape, slightly inclined. OL:SuL 1.6–1.8. Dorsal field narrow, with dorsal depression opening to concavity of dorsal rim. Ventral field narrow, somewhat elevated, with distinct ventral furrow at moderate distance from ventral rim.

Outer face slightly convex with small central umbo, smooth.

Remarks.—Otoliths of M. rhinoceros are easily recognized by the peculiar dorsal rim with the deep, concave depression and the horn like anterior and posterior projections. In proportions they resemble M. bictenatus , but differ further in the feeble or absent anterior−ventral projection. Small specimens tend to have the dorsal depression less well developed (hence a lower index OL:OH of 1.2–1.25) and those below 2.5 mm in length can probably not be distinguished from M. bictenatus .

Mataichthys rhinoceros represents the most common species of the genus in the HH4 bed in the Bannockburn Formation at the Manuherikia River section, whereas M. bictenatus is the most common Mataichthys species at all lower levels at this location. Apart from in the HH4 level, M. rhinoceros has also been found in a lower relative frequency in the HH1a bed.

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