Mataichthys bictenatus Schwarzhans, Scofield, Tennyson, and T. Worthy, 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 : 339-342

Mataichthys bictenatus Schwarzhans, Scofield, Tennyson, and T. Worthy sp. nov.

Figs. 8–10 , 13A–O.

?2006 Gobiomorphus sp. ; McDowall et al. 2006b: fig. 3.

Etymology: For the bictenate nature of the scales, meaning alternating primary and secondary peripheral cteni—a feature a unlike any modern Gobiomorphus species ( Roberts 1993; McDowall et al. 2006b).

Type material: Holotype: NMNZ S.52752, skeleton with otolith in situ ( Figs. 8A, B , 9E , 10A, B, E ) . Paratypes: 55 otolith specimens, NMNZ S.52733–34, Home Hills Station, Manuherikia River near St Bathans, Otago, early Miocene , Bannockburn Formation, HH 1a bed ( Fig. 13A–O) .

Type locality: Location 4 at Mata Creek near St Bathans , Otago .

Type horizon: Bannockburn Formation, early Miocene.

Other material.—One fragmentarily preserved skull with otoliths (sagitta, lapillus) in situ (NMNZ S.52753, Fig. 8C ), same location as holotype. 6454 otolith specimens: 5599 specimens same location as paratypes; 519 specimens Manuherikia River, HH 1b bed, trench excavation; 17 specimens Manuherikia River, HH 4; 78 mostly juvenile specimens Manuherikia River, HH 1d; 59 specimens, Vinegar Hill, site 1; 182 specimens, Vinegar Hill, site 2.

Comment.— Mataichthys bictenatus is by far the most common fish species in the Bannockburn Formation as evidenced by the abundance of its otoliths. It is also the only species known from skeletal remains with otoliths in situ. The Mata Creek number 4 location has yielded a complete fish skeleton and a somewhat disintegrated and distorted isolated skull from M. bictenatus , both with otoliths in situ. The specimens were found at the base of a small low−relief channel less than 1 m wide and 20 cm thick ( Fig. 8D ), probably representing a scour fill in a nearshore lake environment. The complete fish skeleton was excavated in three pieces plus a number of smaller counterslab pieces and has a total length of about 18 cm. The specimen represents a rare opportunity in fish palaeontology to identify and describe a new species based on a skeleton with otoliths in situ. The embedding rock is soft and the fish bones often thin and fragile. It was therefore decided to take a CT−scan of the skeleton prior to preparation, which was then prepared to uncover fin rays for meristic counts and the otolith. The description of the skeleton was substantially aided by the use of the CT−scans. Due to relatively poor exposure of a large part of the head, the description of the skeleton is based mainly on meristic counts, the description of the caudal skeleton and morphometric measurements wherever possible. The presence of the otolith face (G 1), ventral view (G 2). H. Mogurnda furva Allen and Hoese, 1986 , Recent, 06 ° 25’S – 143 ° 19’E, WAM 31685−001, inner face (H 1), ventral view (H 2). I. Hypseleotris compressus (Krefft, 1864) , Recent, Cape York, Australia, BMNH 67.5.6.52−60, inner face (I 1), ventral view (I 2). J. Culius fuscus (Forster, 1801) , Recent, Viti Levu, collection W. Schwarzhans, donated by ZMH, inner face (J 1), ventral view (J 2). K. Oxyeleotris lineolatus (Steindachner, 1867) , Recent, northern Australia, collection W. Schwarzhans, donated by WAM, inner face. L. Oxyeleotris caeca Allen, 1996 , Recent, 06 ° 35’S – 143 ° 30’E, WAM 31208−001, inner face. M. Oxyeleotris aruensis (Weber, 1911) , Recent, Aru Island, SMF 6746−52, inner face. N. Oxyeleotris marmorata (Bleeker, 1852) , Recent, Borneo, Kapuas, BMNH 1982.3.29.219, inner face (N 1), ventral view (N 2). O. Eleotris acanthopoma Bleeker, 1853 , Recent, 21 ° 34’S – 165 ° 31’E, WAM 31370−001, inner face. P. Milyeringa veritas Whitley, 1945 , Recent, northern Western Australia, collection W. Schwarzhans, donated by WAM, inner face (P 1), dorsal view (P 2).

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in situ allowed us to link the skeleton with the most numerous taxon represented by otoliths.

Diagnosis.—Skeleton: Vertebrae 12+16 = 28, second dorsal I+10, ventral I+7, anal I+6 (or 7, assuming one missing), origin of anal under the 4 th ray of the second dorsal, caudal skeleton with hypurals 1+2 fused and hypurals 3+4+urostylar fused, 3 epurals broad narrowly separated, hemal spine on last vertebra short. Otolith: OL:OH = 1.3–1.5 in specimens larger than 3.5 mm long. Anterior−ventral and posterior−ventral projections distinct, often pointed. Dorsal rim moderately high, regularly rounded.

Description of skeleton.—Standard length (SL) of the only complete specimen about 17.5 cm, which is larger than most extant species of the genus Gobiomorphus , except for G. gobioides . Body slender; body depth at ventral fin base about 16% SL. Head length about 27% SL. Vertebrae 28, 12 precaudal and 16 caudal. First dorsal fin (D1) with 6 spines. Second dorsal fin (D2) with 1 spine and 10 rays, the rays being incompletely preserved. Anal fin with 1 spine and 6 rays (plus 1 probably missing). Pelvic fin poorly preserved. Ventral fins presumably separate, not fused as in gobiids, judging from the regular shape of the fin, with 1 spine and 7 rays. Caudal fin rays 15, thereof 1 only as imprint (not visible on CT). Anal fin origin under 13 th vertebra and under 4 th ray of D2. Predorsal length about 40 % SL; preanal length about 65% SL; distance origin D1 to origin D2 about 16% SL. Upper jaw length about 13% SL. From base of ventral fin to anal fin origin about 35% SL. Scales ctenoid, with single row of cteni, having alternating primary and secondary short and stout peripheral cteni of equal length, about 4–6 mm in size depending on location on body, 9–10 vertical scale rows at anal fin origin ( Fig. 10 ).

Vertebrae with long neural and haemal spines. Neural spine on last caudal vertebra short, haemal spine on last caudal vertebra long, uniformly broad. Caudal skeleton ( Fig. 9 ) with hypurals 1+2 fused and hypurals 2+4 and urostylar fused (typical gobioid caudal skeleton). Hypural 5 small, parhypural long, 3 epurals broad, narrowly placed, but not fused (third epural as imprint). Vertebrae 3 to 12 with long ribs, longest on vertebrae 5 and 6, vertebrae 4 to 12 with epipleural spines. Head bones mostly covered in matrix or poorly visible on CT−scan except for parts of supraoccipital, opercle, parasphenoid, pterygoid, maxilla, premaxilla, dentale and frontal. Premaxilla and dentale with small conical multiserial teeth, however only partly preserved. Mouth open and gill cover probably also open indicating suffocation of fish prior to sediment embedment. Branchiostegal rays 5+. A partly disintegrated skull (NMNZ S.52753) has revealed a well preserved quadratum and articular.

Description of otolith.—Robust, moderately elongate otoliths up to nearly 6.5 mm long ( Fig. 13A–O). OL:OH = 1.3–1.5 in otoliths from 3.5 to 6.5 mm, 1.1–1.3 in otoliths from 1 to 3 mm long; OH:OT = 3.0–3.3. Anterior−ventral and posterior−ventral projections distinct, often pointed, the posterior one often more strongly developed. Dorsal rim moderately high, regularly rounded. Ventral rim nearly straight, horizontal. Anterior and posterior rims inclined, anterior rim straight or slightly convex, rarely concave, posterior rim usually concave. Rims irregularly undulating, crenulated in juveniles.

Inner face nearly flat, with somewhat rugged surface. Sulcus with median position, moderately large and deepened, typical shoe−sole shape, slightly inclined. OL:SuL 1.6–2.0. Dorsal field high, with well marked dorsal depression. Ventral field narrower, somewhat elevated, with distinct ventral furrow. Ventral furrow close to ventral rim anteriorly, curving upward and away from ventral rim posteriorly.

Outer face slightly convex with small central umbo, irregularly ornamented or smooth.

Variability and ontogeny of otoliths.—Otoliths of M. bictenatus exhibit a rather wide range of morphological variation, mostly associated with details of the outline, particularly of the anterior part of the otolith. The anteriorim is usually straight to slightly concave with a more or less well developed anterior−ventral rostrum−like projection. In some instances the anterior rim is slightly convex and the anterior−ventral corner nearly without projection. The strength of the posterior−ventral projection is also variable to some extent, but never lost. The variability of the ratios OL:OH and OL:SuL is larger than would typically be expected from Recent comparative eleotrid otoliths.

Ontogenetic effects are mostly associated with more ornamentation in smaller otoliths. Also the index OL:OH increases significantly with increasing size.

Otolith deformations.—Etched or deformed specimens, which are altered to such an extent that they could easily be regarded as representing different species, are fairly common. The deformations are usually expressed by over−thickening of the otolith, particularly by a convex inner face and a deep sulcus. Similar effects have been observed in a few otoliths of Galaxias bobmcdowalli (see above). Some typically deformed specimens are figured on Fig. 14, of which two ( Fig. 14Q, S) are considered to represent M. bictenatus . The cause of all these observed deformations is not known.

Etched specimens are even more common and are mostly

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characterized by smoothed and thick otolith rims. Specifically the dorsal rim, which is usually thinner than the ventral rim, becomes eroded and reduced first. Also as a result, the sulcus appears to be much larger than usual, mostly because of the erosion of the otolith rim, but also as a result of etching of the sulcus margins. A typical example is shown ( Fig. 14O) and another rather extremely etched specimen ( Fig. 14P). Both specimens are thought to represent M. bictenatus .

It is unclear what has caused the etching as well as the deformation of these otoliths, whose numbers are well above those expected from better known marine otolith assemblages. Judging from the good preservation of the otoliths, the deformation probably originated in the living fish, so may be the expression of some sort of illness. The etching is almost certainly of secondary origin, and has occurred either as a result of transport and physical erosion of the otolith prior to embedding or, possibly more likely judging from appearance and also in comparison to observations from marine environments, a result of chemical/marginal solution etching. In the case of the latter, a possible explanation could, for instance, be that the fish had been a prey item and etching occurred during the passage through the intestinal tract.

Comparisons.—Only one species of Gobiomorphus attains a similar size; G. gobioides from New Zealand reaches up to 25 cm SL. The following comparison therefore focuses primarily on these two species. Mataichthys bictenatus differs in the lower number of anal fin rays (I+6 or 7 versus I+9–10), the higher number of ventral fin rays (I+7 versus I+5–6), the separation of the epurals (versus all three joined), the slightly more slender shape (body depth at ventral fin base about 16% SL versus 25% SL), the longer predorsal length (45% SL versus 38% SL), the distance origin D1 to origin D2 about 16% SL (versus 19% SL) and the presence of marked posterior−ventral and often also anterior−ventral projections in the otolith (versus rounded anterior− and posterior−ventral joints).

McDowall et al. (2006b) figured and described a fish skeleton imprint preserved in somewhat distorted dorsal view from the Bannockburn Formation near Fiddlers Flat, which is the Manuherikia River section (see fossil record number H41/f 66 in Fig. 2 ). It is about 16 cm long and they reported that it had 26 to 28 vertebrae (some uncertainty due to preservation). Its fins and caudal skeleton are poorly preserved. One fin, interpreted as pectoral, seems to contain at least 13 rays, but this is clearly incomplete due to preservation. Another fin−imprint, probably representing a dorsal fin (D2), has almost disintegrated. Given the proximity of location and stratigraphy, the little information retrievable from the McDowall et al. (2006b) specimen does not contradict a tentative association with M. bictenatus .

Remarks.— Mataichthys bictenatus is by far the most common fish species in the Bannockburn Formation. Its otoliths are abundant in all levels of the Manuherikia River section and at Vinegar Hill. Exceptions are the poorly sampled Wharekuri Creek site and the Lauder shell bed, where the latter is probably younger stratigraphically and where M. bictenatus seems to be replaced by another species tentatively placed in the genus (gen. aff. Mataichthys sp. , see below). The majority of otoliths were found at Manuherikia River , bed HH1a. Interestingly, this location is dominated by large, adult otoliths usually longer than 3 mm, many of which are poorly preserved, deformed or etched. In contrast, the HH1d bed about 3.5 m deeper in the section has yielded almost exclusively juvenile specimens of the same species below 2.5 mm in length and mostly of excellent preservation. This difference is probably the result of different facies and taphonomic environments, which are not yet understood.

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

Figures

Fig. 8. Skeleton finds of eleotrid fishes and field location. A. Skeleton of Mataichthys bictenatus Schwarzhans, Scofield, Tennyson, and T. Worthy gen. et sp. nov., holotype, photograph of slabs with information about counterslabs (red) and splinter with otic capsule (red) and otolith in situ (red) spliced in digitally, NMNZ S.52752, location 4, Mata Creek, Bannockburn Formation, early Miocene. Photographs of slab and counterslabs mounted. B. Skeleton of M. bictenatus, CT−scans of slabs with information about counterslabs (green) spliced in digitally, same specimen as top row. Note that CT−scan images can be distorted and are not used for morphometrics. CT of slabs and counterslabs mounted. C. Head slab of M. bictenatus, found associated with specimen above, with otolith in situ, NMNZ S.52753. D. Photograph of Mata Creek location depicting sedimentary lense from which the fish slabs originated.

Fig. 9. Comparison of the caudal skeleton of Miocene Mataichthys bictenatus and Recent eleotrids based on x−rays (scaled to same size). A. Gobiomorphus gobioides (Valenciennes, 1837), NMNZ P.32815. B. Gobiomorphus australis (Krefft, 1864), ZMUC Jrn.374. C. Gobiomorphus cotidianus McDowall, 1975, NMNZ P.12719−B. D. Philypnodon grandiceps (Krefft, 1864), ZMUC Jrn.115. E. Mataichthys bictenatus Schwarzhans, Scofield, Tennyson, and T. Worthy gen. et sp. nov. (holotype, NMNZ S.52752, location 4, Mata Creek, Bannockburn Formation, early Miocene). F. Butis humeralis (Valenciennes, 1837), ZMUC Jrn.93. G. Ophiocara porocephala (Valenciennes, 1837), ZMUC Jrn.101. H. Ophieleotris aporos (Bleeker, 1854), ZMUC P.781801. I. Culius fuscus (Bloch and Schneider, 1801), ZMUC P.781283. Abbreviations: EP, epurals; H 1+2, fused hypurals 1 and 2; H 3+4+ U, fused urostylar complex and hypurals 3 and 4; H 5, hypural 5; PH, parhypural; PU 2, preural centre 2.

Fig. 10. Comparison of the body scale morphology of Miocene Mataichthys bictenatus with Recent eleotrids. A. Mataichthys bictenatus Schwarzhans, Scofield, Tennyson, and T. Worthy gen. et sp. nov. (holotype, NMNZ S.52752, location 4, Mata Creek, Bannockburn Formation, early Miocene). B. Close−up of Mataichthys bictenatus depicting few preserved alternating primary and secondary cteni. C–E. Schematic drawings of the insertion of cteni on body scales in Gobiomorphus gobioides (Valenciennes, 1837) (from McDowall et al. 2006b) (C), Eleotris sp. (from Roberts 1993) (D), and Mataichthys bictenatus (E).

Fig. 2. Stratigraphic section showing the basal part of the Bannockburn Formation at the Manuherikia River location, New Zealand. FRN, Fossil Record Number in the archival Fossil Record File of the Geological Society of New Zealand.