Fig 1.
Premaxilla of Ossubtus xinguense, GEA 1999, female, 181.7 mm SL, (a) external view, (b) internal view; asp Ascending Process of Premaxilla, lpr Lateral Process of Premaxilla, rte Replacement Teeth, 1–5 Labial premaxillary teeth, 1’-2’ Lingual premaxillary teeth.
Fig 2.
Premaxilla of herbivorous Serrasalmidae in external view, respectively: (a) Mylesinus paraschomburgkii, GEA 1185, 62 mm HL; (b) Tometes sp. Tocantins, GEA 1945, 280 mm SL; (c) Myleus setiger, GEA 1972, 45 mm HL; (d) Myloplus rubripinnis, GEA 2238, 58 mm HL. 1–5 Labial premaxillary teeth; Scale bars = 5 mm.
Fig 3.
Ossubtus xinguense, holotype, INPA 6535, female, 170.2 mm SL, Brazil, Rio Xingu at rapids downstream Altamira.
Fig 4.
Adults of Ossubtus xinguense: GEA 1973, (a) male, 202.7 mm SL; (b) female, 168.5 mm SL. Brazil, Rio Xingu, Volta Grande.
Fig 5.
Juveniles of Ossubtus xinguense: (a) MPEG 30686, 66.4 mm SL (photographed alive), (b) 45.6 mm SL (preserved).
Table 1.
Morphometric characteristics of Ossubtus xinguense (n = 216).
Range includes the type specimens. Hol = Holotype, SD = Standard Deviation. Measurements 1–23 are expressed as percentages of standard length, and 24–33 as percentages of head length.
Fig 6.
Left lateral view of neurocranium in Ossubtus xinguense, GEA 1999, female, 181.7 mm SL, oriented in natural position; c1-4 Compound centra 1–4, bas Basioccipital, epi Epiotic, eth Lateral Ethmoid, exo Exoccipital, fro Frontal, mth Mesethmoid, nas Nasal, neu Neural Complex, oph Obitosphenoid, par Parietal, pro Prootic, psh Parasphenoid, ptr Pterotic, pts Pterosphenoid, rhi Rhinosphenoid, sph Sphenotic, so Supraorbital, sup Supraoccipital, tri Tripus, vom Vomer.
OLF Olfactory fossae (white outline), PTF Posttemporal fossae.
Fig 7.
Head in Ossubtus xinguense, GEA 1999, male, 183.7 mm SL; ang Anguloarticular, ant Antorbital, bra Branchiostegal Rays, ce Ceratohyal, den Dentary, epi Epiotic, eth Lateral Ethmoid, fro Frontal, int Interopercle, io Infraorbital Series, max Maxilla, mth Mesethmoid, nas Nasal, ope Opercle, oph Obitosphenoid, par Parietal, pmx Premaxilla, pre Preopercle, ptr Pterotic, qu Quadrate, sub Subopercle, so Supraorbital, sup Supraoccipital, vom Vomer.
Fig 8.
Dentary of Ossubtus xinguense, GEA 1999, female, 181.7 mm SL, (a) lateral view, (b) lingual view; aar Anguloarticular, cor Coronomeckelian, den Dentary, lsy Lamellae at Symphysis, ret Retroarticular, 1–4 Dentary teeth.
Fig 9.
Hyopalatine arch of Ossubtus xinguense, GEA 1999, female, 181.7 mm SL in lateral view (anterior is right); ect Ectopterygoid, hyo Hyomandibular, int Interopercle, mes Mesopterygoid, met Metapterygoid, ope Opercle, plt Autopalatine, pre Preopercle, qu Quadrate, sub Subopercle, sym Symplectic.
Fig 10.
Pectoral girdle of Ossubtus xinguense, GEA 1999, female, 181.7 mm SL, (a) external view, (b) internal view; ext Extrascapular, cle Cleithrum, cor Coracoid, mso Mesocoracoid, scl Supracleithrum, scp Scapula, pcl1-3 Postcleithrum 1–3.
Fig 11.
Pelvic girdle and abdominal serrature of Ossubtus xinguense, GEA 1999, female, 181.7 mm SL, (a) vetral view, (b) internal view; btr Basipterygium, isc Ischiatic, mdr Medial Radial, ssi Simple Postpelvic Spines, pps Pairs of Postpelvic Spines.
Fig 12.
Ossubtus xinguense, GEA 1999, male, 183.7 mm SL.
Ventrolateral view of the second anal-fin lobe in mature males, distal tip of each lepidotrichia with a pair of stiff hooks laterally curved.
Fig 13.
Caudal-fin skeleton of Ossubtus xinguense, GEA 1999, male, 183.7 mm SL; e1-2 Epural 1 and 2, h1-6 Hypurals 1 to 6, hs Haemal Spine, ns Neural Spine, ph Parhypural, PU2-3 Preural Centrum 2 and 3, U Compound Ural Centrum, un1-2 Uroneural 1 and 2.
Fig 14.
Geographic distribution of Ossubtus xinguense in Xingu River basin; (star) probable type locality in Volta Grande do Rio Xingu, (opened diamond) newly recorded sites on Iriri and Xingu rivers based on museum specimens, and (closed square) additional sites reported by local fishermen.
Fig 15.
Rapids with rock outcrops covered by aquatic macrophytes of the family Podostemaceae.
Cachoeira Grande of the Rio Iriri, main left bank tributary of Xingu River.
Fig 16.
Scatter plot of scores on first (PC1, x-axis) and second (PC2, y-axis) principal components from morphometric analysis of Ossubtus xinguense.
Juveniles (gray triangle) n = 68, Females (closed diamond) n = 65 including the holotype (gray diamond), Males (opened square) n = 83. Ellipses represent 95% confidence intervals, and crosses represent the centroid for each group.
Table 2.
Principal component scores calculated from 33 linear measurements (sexually dimorphic features excluded) taken on 216 specimens of Ossubtus xinguense.
Loadings with absolute magnitude equal to or greater than 0.2 appear in bold.