Sindacharax (Stewart, 1997)

Zanata, Angela M. & Vari, Richard P., 2005, The family Alestidae (Ostariophysi, Characiformes): a phylogenetic analysis of a trans-Atlantic clade, Zoological Journal of the Linnean Society 145 (1), pp. 1-144 : 124-126

RELATIONSHIPS OF SINDACHARAX

The fossil characiform genus, Sindacharax , has been the subject of considerable discussion in the literature ( Greenwood, 1972, 1976; Greenwood & Howes, 1975; Stewart, 1997a, b). Although the age of the specimens identified as Sindacharax (Pliocene–Miocene) is too recent to be informative as to the timing of higher level cladogenic events within the Alestidae , some biogeographically interesting hypotheses have been advanced as to the possible phylogenetic relationships of this genus.

The first description of fossil material later assigned to Sindacharax was by Greenwood (1972) who described it as Alestes deserti . The form of the first dentary tooth in A. deserti , with a deep indentation along its posterior margin (his fig. 6b) and cusps (his figs 2-4), is comparable to that in the cleared and stained specimens of Alestes , Brycinus and Bryconaethiops examined in our study.

Soon thereafter, Greenwood & Howes (1975: 99) proposed Sindacharax to include A. deserti of Greenwood (1972) along with S. lepersonnei , a species that was first described in the same publication. They compared the dentition of Sindacharax to that of the genus Colossoma of the Neotropical subfamily Serrasalminae and posed the question of whether Sindacharax might be ‘the last traces of an Old World Serrasalmine lineage.’ Subsequently, Greenwood (1976: 2) described additional material of Sindacharax , this time based on jaw bones.

Perceived similarities of the dentition of Sindacharax to that of various Neotropical serrasalmines were, in turn, the basis for a hypothesized occurrence of the Serrasalminae , a subfamily known only from South America among Recent species, in both South American and Africa prior to the separation of the two continents as a consequence of continental drift ( Ortí & Meyer, 1997: 95). More recently Stewart (2003: 94) reiterated the proposed relationship of Sindacharax with the Serrasalminae based on Greenwood & Howes (1975). A necessary corollary of the hypothesized presence of a serrasalmine clade in both Africa and South America in the past was the subsequent extirpation within Africa of the clade of characiforms which included the Serrasalminae following the separation from South America.

Our analysis raises questions as to the association of Sindacharax with the Serrasalminae . The morphology of the posterior portion of the premaxilla in Sindacharax (see Greenwood, 1976: 2–3, fig. 1A, D), in particular the presence of a premaxillary pedicle, is comparable to that in all members of the African members of the Alestidae (Figs 2, 13, 15; see also Greenwood, 1976: fig. 2C, D) with exception of the basal genus Arnoldichthys and the more derived Lepidarchus . The latter genus is a diminutive form that demonstrates a number of reductive attributes and the lack of a premaxillary pedicle may be correlated with its reduced body size (see also discussion under ‘Miniaturization and Gigantism in the Alestidae’, above).

Such an occurrence of the premaxillary pedicle in both the Recent members of the Alestidae and Sindacharax and the geographical overlap of the geographical distribution of those taxa brings to the fore the question of association, i.e. that Sindacharax might lie with the Alestidae rather than with members of the Neotropical Serrasalminae . It is noteworthy that a pedicle is present in the Serrasalminae in Colossoma macropomum ( Machado-Allison, 1982: fig. 22B; but not C. bidens, Greenwood, 1976 : fig. 2A), Piaractus ( Machado-Allison, 1982: fig. 22A) and Mylesinus , all of which are components of one of the major subclades of that family ( Machado-Allison, 1983: fig. 1).

It is, however, absent in Acnodon ( Jégu & Santos, 1990: fig. 10), Myleus (Jégu & Santos 2002: fig. 5), Ossubtus ( Jégu, 1992: fig. 7C), Tometes ( Jégu et al., 2002a: fig. 6; Jégu et al., 2002b: fig. 6) and Utiarichthys ( Machado-Allison, 1983: fig. 4C), other components of the same clade within the Serrasalminae . It is also absent in Pristobrycon ( Machado-Allison, 1983: fig. 5; 1985: fig. 3) and Pygopristes and Serrasalmus ( Machado-Allison, 1985: fig. 3), all of which are members of the second major lineage within the Serrasalminae for which information on the morphology of the upper jaw is available in the literature.

Further analysis demonstrates that the overall form of the premaxilla of Sindacharax is, when viewed ventrally, comparable to that of cleared and stained specimens of Bryconaethiops . The latter genus typically has, however, one tooth or an area of attachment for such a tooth between the two rows of premaxillary teeth shown by Greenwood (1976: fig. 1A) for Sindacharax . We found that this tooth is absent on one premaxilla in one of the five cleared and stained specimens of Bryconaethiops examined in this study. Furthermore, that specimen lacks any apparent scar in the expected area of attachment of such a tooth, a condition comparable to that in the illustrated premaxilla of Sindacharax ( Greenwood, 1976: fig. 1A).

Finally, and most importantly, the pattern of cusps in the dentition of Sindacharax ( Greenwood, 1972: figs 2-4; Greenwood & Howes, 1975: fig. 22C) has the ‘included cusps’ that are present in Alestes , Brycinus and Bryconaethiops (see character 64), but absent in the members of the subclade of the Serrasalminae with a posterior pedicle on the premaxilla. As a consequence, it is most parsimonious to hypothesize that the phylogenetic relationships of Sindacharax lie with a component of the Alestidae , in particular the clade consisting of Alestes , Brycinus and Bryconaethiops , rather than with the subunit of the Serrasalminae where the pedicle arises homoplastically.

Stewart (1997a) described another species, S. greenwoodi , and suggested that it might be most closely related to Alestes stuhlmanni , a Recent East African species. The overall form of the premaxilla and arrangement of the dentition on that bone in S. greenwoodi is from a ventral view ( Stewart, 1997a: fig. 1) comparable to these osteological systems in Bryconaethiops boulengeri . This situation parallels that for other nominal species of Sindacharax . Although it is difficult to evaluate the reported similarities in form of the dentition of S. greenwoodi vs. A. stuhlmanni based on available data, it is noteworthy that the distribution of the oral teeth differ dramatically in those two species (compare Stewart, 1997a: fig. 1 for S. greenwoodi with Paugy, 1986: fig. 18, for A. stuhlmanni , respectively) raising doubts about the suggested close relationship between those two species.

The suggestion that A. stuhlmanni should possibly be transferred to Sindacharax ( Stewart, 1997a: 38) is untenable. The shift of a species that Brewster (1986: 190) assigned to ‘ Alestes sensu stricto ’, the Alestes of this study, on the basis of two very distinctive synapomorphies (her synapomorphies 19 and 20), would undoubtedly render Alestes nonmonophyletic and is thus an inappropriate course of action.