ALBULIFORMES AND

Datovo, Aléssio & Vari, Richard P., 2014, The adductor mandibulae muscle complex in lower teleostean fishes (Osteichthyes: Actinopterygii): comparative anatomy, synonymy, and phylogenetic implications, Zoological Journal of the Linnean Society 171 (3), pp. 554-622 : 610

ALBULIFORMES AND NOTACANTHIFORMES

The morphological analyses of Forey (1973) and Forey et al. (1996) advanced a hypothesis that the Anguilliformes plus Notacanthiformes form a monophyletic group, which is, in turn, the sister clade to the Albuliformes ( Fig. 27A). This scheme of relationships was also arrived at in the molecular studies of Betancur-R et al. (2013) and Tang & Fielitz (2012). The sister-group relationship between the Anguilliformes and Notacanthiformes of Forey et al. (1996) is supported by several morphological characters, many of them representing losses of character acquired at the base of more inclusive clades ( Wiley & Johnson, 2010). This hypothesis of the Anguilliformes as the sister group of the Notacanthiformes , however, disagrees with the conclusions of the majority of morphological studies ( Nelson, 1973; Greenwood, 1977; Patterson & Rosen, 1977) and some molecular analyses ( Wang et al., 2002; Inoue et al., 2004; Johnson et al., 2011; Near et al., 2012) that alternatively propose a sister-group relationship between the Albuliformes and the Notacanthiformes ( Fig. 27B). Data from the adductor mandibulae are more congruent with this latter hypothesis. Based on the examined material and data from the literature, most albuliforms and notacanthiforms share two notable derived features of the adductor mandibulae. The first [1] is the presence of a conspicuous, well-differentiated endomaxillar ligament connecting the promalaris with the maxilla ( Figs 7 , 8 ; Greenwood, 1977). This condition, which is unique to the Albuliformes and the Notacanthiformes amongst lower teleosts ( Fig. 27), is paralleled elsewhere in the Teleostei only within the Neoteleostei. Elops also exhibits an endomaxillar tendon associated with the segmentum facialis, but the ligament in this genus disperses into the retrojugal lamina before reaching the maxilla. Furthermore, a promalaris cannot be differentiated from the remainder of the segmentum facialis in Elops . A second possible synapomorphy for the Albuliformes plus the Notacanthiformes is [2] the posterior expansion of the rear portion of the coronalis surpassing the limits of the lower jaw and becoming positioned dorsal to the region of insertion of the rictalis ( Figs 7 , 8 ; Greenwood, 1977). This condition is not found elsewhere in the Teleostei ( Fig. 27), albeit not universal within both the Albuliformes and Notacanthiformes . Notacanthids lack a segmentum mandibularis and consequently cannot exhibit the noted derived condition. Within the Halosauridae , the posteriorly expanded coronalis is apparently absent in Aldrovandia gracilis , albeit present in all other genera of the family ( Fig. 8 ; Greenwood, 1977). One major problem with the hypotheses that these two myological characters represent synapomorphies for the Albuliformes plus the Notacanthiformes is that according to the data in Greenwood (1977), both of these specializations are absent in the Pterothrissidae , an albuliform family that could not be examined in the present study. Characters 1 and 2 would, however, demonstrate a greater degree of homoplasy under the alternative hypothesis under which the Albuliformes is sister to the clade consisting of the Notacanthiformes plus Anguilliformes ( Fig. 26A ).

Figures

Figure 7. Adductor mandibulae and associated structures of Albula vulpes (Albuliformes: Albulidae), LIRP 7427 (189.3 mm standard length). Left side in (A) lateral and (B) medial views; ramus mandibularis trigeminus nerve removed. Abbreviations: AM, adductor mandibulae; IA, intersegmental aponeurosis.

Figure 8. Adductor mandibulae and associated structures of Halosaurus pectoralis (Notacanthiformes: Halosauridae), USNM 317567 (518 mm standard length). Left side in (A) lateral and (B) medial views. Abbreviations: AM, adductor mandibulae; BPM, buccopalatal membrane; IA, intersegmental aponeurosis; RMT, ramus mandibularis trigeminus nerve.

Figure 26. Adductor mandibulae and associated structures of Oncorhynchus mykiss (Salmoniformes: Salmonoidei: Salmonidae), MZUSP 85378 (106.4 mm standard length). Left side in (A) lateral and (B) medial views. Arrow indicates dorsal separation between the epistegalis and ricto-malaris. Anterodorsal tip of the dentary in B accidentally cut during dissection. Abbreviations: AM, adductor mandibulae; IA, intersegmental aponeurosis; RMT, ramus mandibularis trigeminus nerve.