Oligosarcus itau

Mirande, Juan Marcos, Aguilera, Gastón & Azpelicueta, María De Las Mercedes, 2011, A threatened new species of Oligosarcus and its phylogenetic relationships, with comments on Astyanacinus (Teleostei: Characidae), Zootaxa 2994, pp. 1-20: 9-16

publication ID

http://doi.org/ 10.5281/zenodo.201381

persistent identifier

http://treatment.plazi.org/id/CF555B6D-FF9C-B842-D7E1-64D1FEA1F116

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Plazi

scientific name

Oligosarcus itau
status

 

Autapomorphy of Oligosarcus itau  

Oligosarcus itau   has only one autapomorphy in the present analysis:

1. The presence of a posterior branch of the posttemporal laterosensory canal (ch. 88, state 0) ( Mirande, 2010: figure 47). This character-state is present in some characids with a bony supraorbital, but it was found only in Oligosarcus itau   among the species lacking the supraorbital (node 170).

Synapomorphy of node 236 ( Bramocharax   clade)

1. The dorsoventral depression of the epioccipital bridge (ch. 5, state 1). This character state is unique to this node

and unreversed.

Oligosarcus   is the sister group of Bramocharax bransfordii   under all the analytical conditions explored, constituting the Bramocharax   clade of Mirande (2009, 2010). Relationships of the Bramocharax   clade are variable across the different analyses. In the three lowest concavities under implied weighting, these genera are included in a large clade composed of the species of the Astyanax   clade of Mirande (2010). In the remaining concavities under both implied weighting and self-weigthed optimization, the Bramocharax   clade is not included in the Astyanax   clade and it is instead related to the Rhoadsiinae   and the Pseudochalceus   clade ( Mirande, 2010). In the final hypothesis, herein proposed, the Bramocharax   clade forms a trichotomy with a clade composed of the Rhoadsiinae   and Pseudochalceus   clade and a large clade composed of most characids ( Fig. 9 View FIGURE 9 ).

Synapomorphies of node 311 ( Oligosarcus   )

1. The well developed temporal fossa (ch. 13, state 0) ( Fig. 4 View FIGURE 4 ). The temporal fossa was described by Weitzman (1962) for Brycon meeki Eigenmann & Hildebrand   , and it was observed herein occurring as parallelisms with this node in Bryconamericus emperador   , Bryconexodon juruenae Géry   , and Salminus brasiliensis (Cuvier)   . This synapomorphy is reversed in Oligosarcus pintoi   , in which the temporal fossa is absent ( Fig. 5 View FIGURE 5 ).

2. The absence of a dorsal expansion of the rhinosphenoid (ch. 48, state 0) ( Fig. 4 View FIGURE 4 ). This character-state occurs as parallelisms in node 196 and in Agoniates anchovia Eigenmann. In   Bramocharax bransfordii   , as in many other characids, the rhinosphenoid instead have a dorsal expansion projected between the olfactory nerves ( Mirande, 2010: figure 24).

3. The posteroventrally angled articulation between the second and third infraorbitals (ch. 62, state 2) ( Mirande, 2010: figure 39). This character-state is paralleled in the Characinae   (node 169), in Bryconops melanurus (Bloch)   , and Hollandichthys multifasciatus (Eigenmann)   . Usually, this character-state is associated with the elongation of the maxilla and predatory habits. However, Bramocharax bransfordii   , which shares these features, has the state 0 of this character. This character is unreversed in the analyzed species of Oligosarcus   and is shared by O. perdido   ( Ribeiro et al., 2007: figure 2 A).

4. The presence of a row of ectopterygoid teeth (ch. 159, state 1) ( Fig. 6 View FIGURE 6 ). The ectopterygoid teeth are present, among the characids lacking a supraorbital bone, only in Oligosarcus   and Xenagoniates   , among the taxa herein analyzed. This character was considered as potentially supporting the monophyly of Oligosarcus   by Ribeiro et al. (2007), fact that is corroborated in this paper.

5. The laterally displaced position of the cartilage situated dorsal to the ectopterygoid (ch. 161, state 1) ( Fig. 10 View FIGURE 10 ). Paralleled in a clade composed of the genera Acestrocephalus   , Charax   , Cynopotamus   , Galeocharax   , and Roeboides   and in Exodon paradoxus Müller & Troschel. Reversed   in Oligosarcus pintoi   in which this cartilage, as usual in the Characidae   , is parallel and close to the lateral margin of the mesopterygoid ( Fig. 11 View FIGURE 11 ).

6. The presence of paired bony lamellae bordering the laterosensory canal of the suprapreopercle (ch. 176, state 1) ( Mirande, 2010: figure 34). This character-state is only paralleled in Markiana nigripinnis (Perugia)   , among the examined taxa, and it is unreversed among the analyzed species of Oligosarcus   . However, such bony lamellae are apparently absent in O. perdido   ( Ribeiro et al., 2007: figure 2 C), not analyzed herein, and it would constitute the single known reversal of this character within Oligosarcus   .

7. The presence of two pairs of uroneurals (ch. 306, state 1). This is a relatively highly homoplastic character within the Characidae   . Paralleled in the Bryconamericus scleroparius   clade (node 244), in the node composed of Bryconexodon juruenae   and Exodon paradoxus   (node 276 of Mirande, 2010), in Galeocharax humeralis (Valenciennes)   , and in Markiana nigripinnis   . Reversed in Oligosarcus pintoi   .

Synapomorphies of node 310 ( Oligosarcus   excepting O. itau   )

1. The posterior expansion of the fourth infraorbital (ch. 68, state 1) ( Mirande, 2010: figure 34). Paralleled in the clades composed of Acestrocephalus   , Cynopotamus   , and Galeocharax   (node 210 of Mirande, 2010) and Acestrorhynchus   and Rhaphiodon   (node 174 of Mirande, 2010). This character-state is shared with Oligosarcus perdido   ( Ribeiro et al., 2007: figure 2 A), which would be included in this node.

2. The presence of seven or more pores in the laterosensory canal of the dentary (ch. 80, state 1). Paralleled in a clade including most members of the Characinae   (node 167) and in Rhaphiodon vulpinus Agassiz. This   character-state is apparently shared with O. perdido   ( Ribeiro et al., 2007: figure 2 C).

3. The presence of a pair of large conical premaxillary teeth (ch. 121, state 1) ( Mirande, 2010: figure 51). Paralleled in the clade composed of Acestrorhynchus   and Rhaphiodon   (node 174 of Mirande, 2010). Also shared with Oligosarcus perdido   ( Ribeiro et al., 2007: figure 2 B).

4. The aligned cusps in the teeth of the inner premaxillary series, when present (ch. 128, state 1) ( Mirande, 2010: figure 67). This is a highly homoplastic character. The acquisition of this state is paralleled in the clade composed of the subfamilies Aphyocharacinae   , Aphyoditeinae   , and Cheirodontinae   (node 208), in the clade composed of Attonitus   and Aulixidens   (node 245 of Mirande, 2010), in the Rhoadsiinae   (node 249), in the clade composed of Coptobrycon   , Grundulus   , and Gymnocharacinus   (node 280 of Mirande, 2010), in Hemigrammus bleheri Géry & Mahnert   , and in Odontostoechus lethostigmus Gomes. This   character is optimized in this node with the state present in Oligosarcus menezesi   and O. pintoi   because the remaining species in this clade lack teeth unambiguously attributable to those of the second row. In Oligosarcus menezesi   and O. pintoi   the premaxillary teeth of both rows are condensed in a single row, but some of them were observed to have extraosseous development and slightly posterior implantation than the remaining teeth. These teeth are, therefore, attributed to the posterior premaxillary row.

5. The presence of four or fewer teeth in the inner premaxillary series, when present (ch. 129, state 0). Paralleled in the clade composed of the Bryconamericus scleroparius   clade and the subfamilies Aphyocharacinae   , Aphyoditeinae   , Cheirodontinae   , Gymnocharacinae   , and Stevardiinae   (node 193), in the clade composed of Mimagoniates   and Pseudocorynopoma   (node 235 of Mirande, 2010), in Markiana nigripinnis   , and in Probolodus heterostomus Eigenmann. This   character is coded in the members of this clade only in Oligosarcus menezesi   , with three teeth in a presumably posterior row, and in O. pintoi   , with four. The remaining species in this clade have a single row of differently sized and shaped premaxillary teeth which are not easily attributable to neither premaxillary tooth rows, and this character was coded as inapplicable to them.

6. The abrupt decrease in size of the dentary teeth (ch. 148, state 1). Paralleled in the Bryconops   clade (node 278 of Mirande, 2010), a clade including most species in the Tetragonopterinae   (node 223 of Mirande, 2010), in Hemibrycon   (node 255 of Mirande, 2010), and in Astyanax latens   , A. paris Azpelicueta, Almirón & Casciotta   , Bryconamericus emperador   , and Hyphessobrycon herbertaxelrodi Géry.  

7. The anterodorsal portion of the quadrate equal or longer than its ventral region (ch. 150, state 1) ( Mirande, 2010: figure 73). This character-state is present in several species with predatory habits and elongated jaws, being acquired as parallelisms among the Characidae   in a clade including most members of the Characinae   (node 211 of Mirande, 2010), in the Pseudochalceus   clade (node 289), in the clade composed of Acestrorhynchus   , Agoniates   , and Rhaphiodon   (node 175 of Mirande, 2010), and in Exodon paradoxus   .

8. The absent or reduced in size bony lamellae associated with the supraneurals (ch. 282, state 0). Paralleled in the clade composed of Bario steindachneri (Eigenmann)   and Moenkhausia sanctaefilomenae (Steindachner)   (node 272 of Mirande, 2010) and independently in Acestrocephalus sardina (Fowler)   , Astyanacinus moorii   , and Nematocharax venustus Weitzman, Menezes & Britski.  

9. The notched distal tip of the sphenotic spine (ch. 366, state 1) ( Fig. 5 View FIGURE 5 ). Paralleled in Roeboexodon geryi   . This character is herein added relative to the phylogeny by Mirande (2010) and defined as: “Form of distal tip of sphenotic spine: (0) slender or somewhat expanded; (1) notched, limiting levator arcus palatini anterior and posterodorsally”. In most characids the sphenotic has a lateroventral projection, the sphenotic spine, limiting anteriorly and/or laterally the levator arcus palatini muscle. In those species the sphenotic spine is slender or somewhat expanded from lateral view, limiting the levator arcus palatini anteriorly and, in some species, also laterally (state 0; Fig. 4 View FIGURE 4 ). In most examined species of Oligosarcus   and apparently also in O. perdido   ( Ribeiro et al., 2007: figure 1), the sphenotic spine is distally notched in lateral view (state 1; Fig. 5 View FIGURE 5 ). In this state an anterior projection of the sphenotic spine limits anteriorly the levator arcus palatini, whereas the posterior section limits it posterodorsally. In Oligosarcus itau   n. sp. the sphenotic spine is expanded from lateral view, and it limits the adductor mandibulae anterior and laterally, but lacks a posterior projection limiting that muscle posterodorsally. A distally notched sphenotic spine was only observed among the characids in the remaining species of Oligosarcus   and in Roeboexodon geryi Myers   ; all the remaining species in the dataset are coded with state 0 of this character.

Character 12 refers to the relative position of the sphenotic spine relative to the orbit (see Mirande, 2010). Differing from Mirande (2010), it was herein coded as inapplicable to the species of Oligosarcus   excepting O. itau   , because in those species the anterior branch is aligned with the anterior margin of the infraorbitals but the posterior one is clearly displaced posteriorly.

Relationships of Astyanacinus moorii   . In all the performed analyses Astyanacinus moorii   is deeply nested into the Astyanax   clade ( Mirande, 2010). In the proposed hypothesis A. moorii   is the sister group of a clade composed of Astyanax abramis (Jenyns)   , A. asuncionensis Géry   , A. lineatus (Perugia)   , A. pelegrini Eigenmann   , Markiana nigripinnis   , and Psellogrammus kennedyi (Eigenmann)   (node 216). According to the present results, Astyanacinus   should be synonymized with Astyanax   . However, this issue have to be addressed in a more comprehensive phylogeny of the Astyanax   clade. The synapomorphies relating Astyanacinus moorii   with node 216 are: The relatively short frontal fontanel (ch. 23, state 0), the squared or longer than deeper fourth infraorbital (ch. 67, state 0), the presence of a posteriorly oriented branch of the laterosensory system of the fourth or fifth infraorbital (ch. 74, state 1), the presence of only three cusps in the outer premaxillary teeth (ch. 125, state 0), the presence of a single developed autogenous block of cartilage in front of the basihyal (ch. 188, state 0), and the presence of circuli extended to the posterior field of the scales (ch. 319, state 0). Most of those features are rather highly homoplastic within the Characidae   lacking a supraorbital, excepting character 319. The circuli on the posterior field of scales are absent in most species in the clade of characids lacking a supraorbital bone. The presence of those circuli occurs as parallelisms in this node and in Exodon paradoxus   , Phenagoniates macrolepis (Meek & Hildebrand)   , and Roeboides microlepis (Reinhardt)   , while it is reversed within the node including Astyanacinus moorii   only in Markiana nigripinnis   .