Amazonspinther dalmata
Creators: name: Bührnheim, Cristina M.
name: Carvalho, Tiago P.
name: Malabarba, Luiz R.
name: Weitzman, Stanley H.
Publisher: name: Zenodo
Year: 2008
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Actinopterygii
Characiformes
Characidae
Amazonspinther
Amazonspinther dalmata

description: Monophyly of <i>Amazonspinther dalmata</i> + <i>Spintherobolus</i> A close relationship between <i>Amazonspinther dalmata</i> and <i>Spintherobolus</i> is strongly supported by fifteen unam- biguous synapomorphies, described below. The first ten characters herein analyzed were more extensively discussed by Malabarba (1998) and Weitzman &amp; Malabarba (1999) as synapomorphies for <i>Spintherobolus</i>, and are herein expanded as synapomorphies of <i>A. dalmata</i> + <i>Spintherobolus</i>. A complex, patterned series of exposed neuromasts is distributed on the head and body (ch. 69 in Malabarba, 1998: 216, see discussion under ch. 15 in Weitzman &amp; Malabarba, 1999: 12-13, figs. 4, 10 and 11). This is a character shared by <i>A. dalmata</i> and <i>Spintherobolus</i> species. Patterns of exposed neuromasts found in <i>A. dalmata</i> are similar and homologous to those of <i>Spintherobolus</i> (compare Fig. 4 here with Weitzman &amp; Malabarba, 1999: 124, 10). The dentary has a large anterior fenestra (Fig. 5), associated with a large epidermal, papilla-like structure surrounded by a deep groove that has its deep internal portion lodged in the dentary fenestra. The external surface of this papilla bears several exposed neuromasts. The ventral face of the dentary bone, posterior to the fenestra, is concave (ch. 5 in Malabarba, 1998: 216, and ch. 16 in Weitzman &amp; Malabarba, 1999: 128, fig. 12). Infraorbital bones are reduced in number and possibly fused. <i>Amazonspinther dalmata</i> has the first and second infraorbitals fused and slightly bifurcated anteriorly, and the third infraorbital reduced (Fig. 11). Fourth to sixth infraorbitals are absent, as observed for <i>Spintherobolus</i> (see discussion under ch. 9 in Malabarba, 1998: 216, and ch. 18 in Weitzman &amp; Malabarba, 1999: 128, fig. 13). There is a small number of pelvic-fin rays, not exceeding six branched rays (see ch. 14 in Malabarba, 1998: 216, and discussion under ch. 19 in Weitzman &amp; Malabarba, 1999: 129, fig. 14). <i>Amazonspinther dalmata</i> has i,5,i and <i>Spintherobolus</i> species i,4,i; i,5; i,5,i or i,6, while remaining cheirodontines show i,7-8 branched rays. The anal fin has a small number of 9-16 branched rays. This number varies among the species of this clade, with the highest range observed in <i>S. broccae</i> (13-16 branched rays; state 1), an intermediate range in <i>S. ankoseion</i> and <i>S. leptoura</i> (11-14; state 2), and the smallest number found in <i>A. dalmata</i> and <i>S. papilliferus</i> (8-9 and 9-10, respectively; state 3). State 0 corresponds to 16 to 24 branched rays, following Weitzman &amp; Malabarba (1999: character 20; figs. 9 and 15). Reduction in the number of branched anal-fin rays is a synapomorphy of <i>A. dalmata</i> + <i>Spintherobolus</i>. The remarkably reduced number of branched anal-fin rays in <i>A. dalmata</i> and <i>S. papilliferus</i> is the lowest observed in Cheirodontinae but it is most parsimoniously accepted as basal in the clade <i>Amazonspinther</i> + <i>Spintherobolus</i>. An anterior pseudotympanum lies anterior to the first pleural rib (Fig. 1) (ch. 2 in Malabarba, 1998: 216, and ch. 21 in Weitzman &amp; Malabarba, 1999: 130). The symphyseal dentary joint surfaces are smooth oval articulations lacking the intercalated and folded bony surfaces found in outgroup characids. The articulation is supported by tough ligamentous tissue (ch. 4 in Malabarba, 1998: 216 and ch. 24 in Weitzman &amp; Malabarba, 1999: 131). Lateral line is reduced to 2-6 perforated scales (see ch. 60 in Malabarba, 1998: 216, and discussion under ch. 25 in Weitzman &amp; Malabarba, 1999: 131). <i>Amazonspinther dalmata</i> has 4-5 scales, averaging 4.8, similar to that of <i>S. papilliferus</i> (4.6). The coracoid bone of the pectoral girdle (Fig. 12) is reduced in length, and more or less discoid in shape (ch. 13 in Malabarba, 1998: 216, and ch. 26 in Weitzman &amp; Malabarba, 1999: 131, fig. 18). The pectoral-fin is relatively short. Weitzman &amp; Malabarba (1999: 132; ch. 28) found this character to be ambiguous, supporting two equally parsimonious hypotheses: the acquisition in a common ancestor to <i>Spintherobolus</i> and a reversal in <i>S. ankoseion</i>, or the independent acquisition in <i>S. papilliferus</i> and in the clade <i>S. broccae</i> + <i>S. leptoura</i>. The presence of a short pectoral fin in <i>A. dalmata</i> (13.82-16.30 % of SL, mean 15.19) supports this character as a synapomorphy of <i>Amazonspinther</i> + <i>Spintherobolus</i>, and the longer pectoral fin of <i>S. ankoseion</i> as autapomorphic and a reversal. New characters added herein are as follows: The teeth are conical to tricuspid (ch. 36, Fig. 5). We treat the conical or tricuspid teeth separately and independent of teeth pedunculation (ch. 3). The conical to tricuspid teeth are proposed as a synapomorphy of <i>A. dalmata</i> + <i>Spintherobolus</i> (<i>vs</i>. multicuspid teeth of remaining cheirodontines - except the compsurin <i>Macropsobrycon uruguayanae</i>). The antorbital of <i>A. dalmata</i> and <i>Spintherobolus</i> species is short and rounded to oval (ch. 38, Fig. 11), instead of elongate, slender and ventrally expanded, as observed in the remaining Cheirodontinae. It resembles that of <i>Carnegiella</i>, Gasteropelecidae (adnasal in Weitzman, 1954). Not checked in <i>S. leptoura</i>. The gill rakers are short and conical, instead of elongate and lanceolate (ch. 40, Fig. 6). The gill rakers on the lower branch of the first gill arch are absent or only the posteriormost gill raker at the junction of the ceratobranchial and the epibranchial is present (ch. 41, Fig. 6). Gill rakers on the lower branch of the first gill arch are always present on remaining cheirodontines. First branchial arches of the four known <i>Spintherobolus</i> species were checked for comparisons with <i>A. dalmata</i>. All the species lack gill rakers or have only one gill raker (the posteriormost) on lower branchial branch, and the gill rakers are conical and the shortest among cheirodontines (Figs. 6 a-d). <i>Amazonspinther dalmata</i> has 3 upper gill rakers and none on the lower branch (two c&amp;s specimens) (Fig. 6a). <i>Spintherobolus papilliferus</i> has none (1), 5(4), 6(6), 7(2) upper gill rakers, and one (13) lower gill raker (the posteriormost). The anteriormost gill rakers on upper branch are very short in the specimen photographed (Fig. 6b). <i>Spintherobolus broccae</i> has 1(2), 2(4) on upper gill rakers, and none (2) or 1(4) lower gill rakers (Fig. 6c). <i>Spintherobolus ankoseion</i> has 1(4), 2(2), 3(2), 4(1), 5(2) upper gill rakers and one (11) lower gill raker (the posteriormost, in photographed specimen not visible, damaged) (Fig. 6d). In contrast, <i>Spintherobolus leptoura</i> has 2-3 upper gill rakers, and one lower gill raker (two alcohol specimens examined). For comparison, <i>Cheirodon ibicuhiensis</i> has 7 gill rakers on upper branch and 11 on lower branch, and <i>Serrapinnus heterodon</i> has 5 on upper branch and 13 on lower branch (Fig. 6 e-f). The maxillary shape is irregular, not bearing a smooth dorsal border. Instead, there are two concave sections in the dorsal border of the maxilla separated by a dorsal short projection in the bearing tooth region of the bone (ch. 42, Fig. 5). The anterior arm of the maxilla that articulates to the premaxilla is thicker than usual in the Characidae. Remaining cheirodontines have a smooth dorsal border in the maxilla. <b>Monophyly of <i>Spintherobolus</i></b> Most characters previously used to diagnose <i>Spintherobolus</i> by either Malabarba (1998) or Weitzman &amp; Malabarba (1999) are herein proposed as synapomorphies of <i>Amazonspinther</i> + <i>Spintherobolus</i>. Two characters remain synapomorphic for <i>Spintherobolus</i>: the lack of an adipose fin (Weitzman &amp; Malabarba, 1999: 131, ch. 17), and the relatively small eye. The eyes of <i>Spintherobolus</i> species are remarkably small compared to that of remaining cheirodontines (see discussion in Weitzman &amp; Malabarba, 1999: 131, ch. 27). <i>Amazonspinther dalmata</i> has large horizontal eye diameter 33.0-39.4% of head length compared to 21.3-28.7% observed in <i>Spintherobolus</i>. The hypothesis of relationships among <i>Spintherobolus</i> species proposed herein (Fig. 10) agrees with that proposed by Weitzman &amp; Malabarba (1999), in which <i>S. papilliferus</i> is the sister species of one clade formed by the other three species of the genus. Additionally, the polytomy formed by <i>S. broccae</i>, <i>S. leptoura</i>, and <i>S. ankoseion</i> (Weitzman &amp; Malabarba, 1999) was resolved in the present study. The low number of gill rakers on the upper branch of the first gill arch (1-3, ch. 39) supports a hypothesis of sister group relationship between <i>S. broccae</i> and <i>S. leptoura</i> (Fig. 10), a character that independently appears in <i>A. dalmata</i>. The higher number of gill rakers observed in <i>S. ankoseion</i> and <i>S. papilliferus</i> is suggested as plesiomorphic. <b>Remarks on <i>Amazonspinther</i> apomorphic characters</b> A high number of ventral procurrent caudal-fin rays (11- 28) is a synapomorphy for the Cheirodontini, and the small number (7-9) observed in <i>Amazonspinther</i> (Fig. 3) is a reversal (Malabarba, 1998; Bührnheim, 2006). Similarly, the ventral procurrent caudal-fin rays articulating with the hemal spines of at least the four posterior caudal vertebrae is a synapomorphy of the tribe Cheirodontini, and the reduced articulation observed in <i>Amazonspinther</i> (Fig. 3) is a reversal (Weitzman &amp; Malabarba, 1999: 9, ch. 9; fig. 8). <b>The phylogenetic position of † <i>Megacheirodon unicus</i></b> † <i>Megacheirodon unicus</i> (Travassos &amp; Santos, 1955) is an extinct cheirodontine, previously proposed as sister-group to <i>Spintherobolus</i> by M. C. Malabarba (1998a,b). The species is known only through two fossilized specimens, a female and a highly sexually dimorphic male. Support for its inclusion in the tribe Cheirodontini is given by the apomorphic traits found in both anal and caudal fins of the male specimen. The inclusion of the fossil in the analysis and the most parsimonious resulting tree allowed the recognition of † <i>Megacheirodon</i> as sister group to <i>Spintherobolus</i> + <i>Amazonspinther</i> (Fig. 13), but we have reservations about these results. Three apomorphic traits are shared by † <i>M</i>. <i>unicus</i> and <i>Spintherobolus</i> species and are absent in <i>Amazonspinther</i>, and six synapomorphies are shared by <i>Spintherobolus</i> species and <i>Amazonspinther</i>, and are absent in † <i>M</i>. <i>unicus</i>. Sixteen characters, however, are missing in the fossilized remains of this fish (1, 2, 15, 16, 17, 21, 24, 28, 31, 34, 35, 38, 39, 40, 41, and 43). Further complications are related to the lack of mature males of <i>Amazonspinther dalmata</i> that resulted in coding 13 characters as missing in this species (6, 7, 8, 9, 10, 11, 12, 13, 14, 22, 23, 32 and 37). Although monophyly of the Clade † <i>Megacheirodon</i> + <i>Spintherobolus</i> + <i>Amazonspinther</i>, seems to be strongly supported, the internal relationships among the three genera may change with the addition of the missing information. So far, characters supporting a close relationship between <i>Spintherobolus</i> and <i>Amazonspinther</i> and that are absent in † <i>Megacheirodon unicus</i> (see M. C. Malabarba, 1998 for characters description in † <i>M</i>. <i>unicus</i>) are, infraorbital bones reduced or fused (ch. 18); one unbranched and five or six branched pelvic-fin rays (ch. 19); anal fin with iii unbranched and 8-16 branched rays (ch. 20); lateral line with 2 to 6 perforated scales (ch. 25), the coracoid bone of the pectoral girdle discoid in shape (ch. 26), and the teeth conical or with three cusps (ch. 36). Two synapomorphies are shared by all <i>Spintherobolus</i> species and † <i>Megacheirodon unicus</i>, but these are observed only in mature males, and mature males of <i>A. dalmata</i> were unavailable for comparisons. Both characters, however, are related to the fusion and reduced proximal portion of the anteriormost ventral procurrent caudal-fin rays. Since <i>A. dalmata</i> has a small number of ventral procurrent caudal-fin rays, located posteriorly and in the usual position found in other characids (Fig. 3), we expect the following characters are unlikely to occur in <i>A. dalmata</i>: the anterior ventral procurrent caudal-fin rays in adult males, those that have their proximal ends inserted anterior to the hemal spine of the antepenultimate vertebrae, are proximally fused to one another (Weitzman &amp; Malabarba, 1999: 130, ch. 22; fig. 8); and the anterior ventral procurrent caudal-fin rays of males have reduced proximal portions, not rising above the area of fusion between the rays, while the posterior dorsal portions of these rays are fused into a flat compressed plate that inserts between the hemal spine of the antepenultimate vertebra and the hemal spines of the anterior vertebrae (Weitzman &amp; Malabarba, 1999: 131, ch. 23; fig. 8). One additional apomorphic trait present in † <i>Megacheirodon unicus</i>, clearly discernible in the male specimen (M. C. Malabarba, 1998: 195, fig. 3), is the pterygiophore of the sixth branched anal-fin ray, directed dorsally, away from the fifth which is directed anteriorly and in parallel with the pterygiophores anterior to it (Sarraf, 1997: Fig. 6; Weitzman &amp; Malabarba, 1999: character 33; fig. 9). Such character is shared with <i>S. ankoseion</i>, <i>S. leptoura</i> and <i>S. broccae</i>, again suggesting a close relationship of † <i>Megacheirodon unicus</i> to <i>Spintherobolus</i>.
description: Published as part of <i>Bührnheim, Cristina M., Carvalho, Tiago P., Malabarba, Luiz R. &amp; Weitzman, Stanley H., 2008, A new genus and species of characid fish from the Amazon basin - the recognition of a relictual lineage of characid fishes (Ostariophysi: Cheirodontinae: Cheirodontini), pp. 663-678 in Neotropical Ichthyology 6 (4)</i> on pages 669-673, DOI: 10.1590/S1679-62252008000400016, http://zenodo.org/record/4567159
description: {"references": ["Weitzman, S. H. 1954. The osteology and relationships of the South American characid fishes of the subfamily Gasteropelecinae. Stanford Ichthyological Bulletin, 4 (4): 213 - 263.", "Malabarba, M. C. S. L. 1998 a. Megacheirodon, a new fossil genus of characiform fish (Ostariophysi: Characidae) from Tremembe Formation, Tertiary of Sao Paulo, Brazil. Ichthyological Exploration of Freshwaters, 8 (3): 193 - 200.", "Sarraf, A. 1997. Redescription and distribution of Spintherobolus broccae Myers (Characiformes: Characidae). Revue francaise d' Aquariologie Herpetologie, 24: 27 - 30."]}