Galaxias bobmcdowalli 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 : 326-328

Galaxias bobmcdowalli Schwarzhans sp. nov.

Fig. 5A–L.

Etymology: Named in honour of the late Robert M. McDowall (1939–2011) for his many contributions to the knowledge of Recent and fossil fresh water fishes of New Zealand.

Type material: Holotype: NMNZ S.52711 ( Fig. 5A) . Paratypes: 24 specimens (19 specimens NMNZ S.52712, HH1a bed; 2 specimens NMNZ S 52713 , HH1 b bed, trench excavation; 3 specimens NMNZ S.52714, Vinegar Hill, site 2) ( Fig. 5B–I) .

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

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

Other material.— 176 specimens (133 specimens [3 altered or deformed], NMNZ S.52715, Home Hills Station , Manuherikia River near St Bathans, HH 1a bed [ Fig. 5J, L]; 19 specimens [2 altered or deformed], NMNZ S.52716, Home Hills Station , Manuherikia River near St Bathans, HH 1b bed [ Fig. 5K]; 11 specimens, Home Hills Station , Manuherikia River near St Bathans, HH 1d; 6 specimens, Vinegar Hill, site 1; 8 specimens, Vinegar Hill, site 2) .

Diagnosis.—Triangular outline with high mid−dorsal angle, sharp and long rostrum and less sharp inferior posterior angle. Ventral rim very shallow. Excisura moderate; often excisura−like incision of posterior rim at level of caudal tip. Ostium short; cauda longer than ostium, almost reaching

HH1a, inner face. I. Paratype, NMNZ S. 52712g, early Miocene, Bannockburn Formation, Manuherikia River, HH 1a, inner face. J. Teratologically deformed specimens, NMNZ S.52715a, early Miocene, Bannockburn Formation, Manuherikia River, HH 1a, anterior view (J 1), inner face (J 2). K. Teratologically deformed specimens, NMNZ S.52715b, early Miocene, Bannockburn Formation, Manuherikia River, HH 1a, inner face. L. Teratologically deformed specimens, NMNZ S.52716a, early Miocene, Bannockburn Formation, Manuherikia River, HH 1a, inner face.

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

posterior tip of otolith. Ventral field on inner face moderately wide, with distinct ventral furrow near ventral rim of otolith, often joined to it mid−ventrally.

Description.—Moderately compressed to moderately elongate, robust otoliths with triangular outline and shallow ventral rim. Size up to 4 mm. Rostrum long, sharp, massive, sometimes anteriorly thinning; excisura wide, short; antirostrum indistinct. Posterior tip massive, pointed, inferior, similarly expressed as rostrum, but not as long and sharp. Dorsal rim high, highest at about its midpoint, rarely with distinct angle. Ventral rim shallow, often with concavity below rostrum and posterior tip. Rims smooth, ventral rim sometimes delicately crenulated. OL:OH = 1.3–1.65; OH:OT = 2.4–2.9.

Inner face markedly to strongly convex, with long, narrow, deepened, nearly median sulcus. Ostium moderately narrow, anteriorly open; cauda very narrow, straight, terminating close to posterior tip of otolith, sometimes almost joined to postdorsal incision. OL:SuL = 1.1–1.25; CaL:OsL = 1.4–1.7. Dorsal field wide, with broad, fairly deep depression. Ventral field moderately wide, with ventral furrow below close to ventral rim and often joined to it along the mid−ventral portion. Its posterior stretch curving upward and inward, seemingly ‘cutting off’ posterior tip.

Outer face slightly concave, rather smooth.

Variability and ontogeny.—Otoliths of G. bobmcdowalli are remarkable for their high variability, which affects the thickness of the inner face below the sulcus, the expression of rostrum and inferior posterior tip, which range from about equally long to the rostrum being considerably longer than the posterior tip, and particularly expression of the excisura−like incision of the posterior rim, which ranges from nearly absent to about as deep as the excisura of the anterior rim. The variation of rostrum and posterior tip as well as variations of the thickness of the otolith are reflected in a large variability of measurements and their relations such as OL:OH and OH:OT.

Another remarkable aspect, not only in the case of G. bobmcdowalli , but most other otoliths (see later) is the predominance of large otoliths from truly adult specimens. It is therefore difficult to understand ontogenetic changes in this species. The few smaller specimens available ( Fig. 5G) show mostly thinner otoliths, often combined with less curvature of the inner face, and a weaker posterior tip.

A further interesting aspect with otoliths of G. bobmcdowalli , again also observed in some other common otolith−based species (see later) is the occasional occurrence of teratologically deformed specimens. The cause of these deformations is unknown, but they seem to follow a particular trend in all observed specimens ( Fig. 5J–L) in the sense that the ventral field becomes overly thickened and the sulcus, particularly the cauda, shielded by a ridge growing over it from the ventral field. Due to the thickening the sulcus becomes very deep and its opening only visible from a dorsal view. The exuberantly grown material shows some difference in structure from the “normal” otolith surface.

Remarks.— Galaxias bobmcdowalli represents the most common galaxiid otolith in the Bannockburn Formation with the widest distribution, missing only from the HH4 bed, Wharekuri Creek and the Lauder shell bed. It belongs to a species group with otoliths having a long cauda terminating close to the posterior tip of the otolith, closer in fact than observed in most Recent Galaxias species (for comparison see Fig. 4A–E). Otoliths of G. bobmcdowalli are easily recognized by their robust appearance with the triangular outline, the long, sharp rostrum, the distinct inferior posterior tip and the depression or incision of the posterior rim at the level of the cauda. They most closely resemble otoliths of G. papilionis Schwarzhans sp. nov., from which they differ in the stronger curvature of the inner face, the greater thickness (OH:OT = 2.4–2.9 versus 3.2–3.5), the long rostrum, the more regular triangular dorsal rim (versus expanded postdorsally) and the less pronounced posterior incision.

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