New interpretations of the skull of a primitive bony fish Erpetoichthys calabaricus (Actinopterygii: Cladistia)

Abstract

Polypterid fishes are considered the basalmost group of extant actinopterygians and may be a direct link to understanding the systematics and evolution of the first bony fishes. Several investigations have been conducted on one member genus, Polypterus; however, since the first specimens of its sister taxon Erpetoichthys calabaricus were described, remarkably little work has been done on the species. We review terminology critical to understanding cranial morphology in polypterids and present a new description of the skull of E. calabaricus as observed through classical methods of skeletal preparation, X-radiographic microfocus computed tomography, and 3D-digital reconstruction. Differences among E. calabaricus and at least three species of Polypterus (P. bichir, P. senegalus, and P. endlicheri), besides the gross variation in size, include an overall elongation of the skull roof observable in most elements of E. calabaricus with a shortening of most associated processes. In addition, several elements present in species of Polypterus are absent in E. calabaricus. As a result, Polypterus should not be used as a proxy for the family Polypteridae to the exclusion of E. calabaricus in phylogenetic studies, which examine early actinopterygians. Each should be treated separately, to resolve inter- and intrarelationships of Polypteridae.

Organization of the Serotonergic System in the Central Nervous System of Two Basal Actinopterygian Fishes: the Cladistians <b><i>Polypterus senegalus</i></b> and <b><i>Erpetoichthys calabaricus</i></b>

“…ganoid scales, cartilaginous skeleton, intestine with a spiral valve) and derived (e.g. highly modified dorsal fins, pectoral fins with a lobed base covered in scales, possession of only 4 gill arches) anatomical features [Patterson, 1982;Janvier, 1996;Britz and Johnson, 2003;Claeson et al, 2007;Takeuchi et al, 2009]. However, different molecular and phylogenomic approaches support that polypteriforms represent a relict of the basal actinopterygian lineage [Inoue et al, 2003;Kikugawa et al, 2004;Li et al, 2008;Suzuki et al, 2010;Takechi et al, 2011;Near et al, 2012;Faircloth et al, 2013].…”

“…E. calabaricus , with all of them inhabiting freshwater rivers and lakes of tropical Africa. E. calabaricus differs from Polypterus in terms of external morphology in several ways, most notably in relation to the elongation of the body, the lack of pelvic fins, and the extremely smaller size of the adult skull [Claeson et al, 2007]. They are usually considered an order, i.e.…”

Polypteridae (Actinopterygii: Cladistia) and DANA-SINEs insertions

“…With 16 recent species (Froese and Pauly, 2006), genus Polypterus shows a lower intraspecific diversification, while genus Erpetoichthys includes the only one living species, E. calabaricus (Daget and Desoutter, 1983;Gayet et al, 2001;Min and Schultze, 2001). In scientific literature, various molecular attempts to arrange the taxonomy of polypterids corresponding to recent systematic have been made (Zardoya et al, 1998; Meyer, 2001; Rasmussen and Arnason, 1999a,b;Venkatesh et al, 1999Venkatesh et al, , 2001Arnason et al, 2001;Kikugawa et al, 2004), also if phylogeny of sequences need not to be always the phylogeny of taxa, but currently they are considered the most primitive and monophyletic Actynopterygian fish group (Cloutier and Arratia, 2004;Gemballa et al, 2003;Britz and Bartsch, 2003;Chiu et al, 2006;Mallatt and Winchell, 2007;Egan et al, 2009), even if the inner relationships of the species actually belonging to this family remain poorly resolved (Otero et al, 2006;Claeson et al, 2007). Different studies (Kazazian, 2004;Britten, 2004; enlightened the role of Non-LTR retrotransposons as drivers of genome evolution, but the keystone to the value of SINEs as systematic characters (Ohshima et al, 1996;Hillis, 1999;Bowen and Jordan, 2002;Ogiwara et al, 2002) is their widely dispersed, irreversible and progressive re-integration into the hosts genome.…”

“…These interesting species shows both symplesiomophies with other basal actinonopterygian groups, than new synapomophies or convergent features (Zeiske et al, 2009). The systematic position of the species belonging to the Polypteriformes have been debated for a long time (Noack et al, 1996;Zardoya and Meyer, 1996;Daget et al, 2001;Ledje et al, 2002;Bagrosky et al, 2003;Britz and Johnson, 2003;Gardiner et al, 2005;Mallatt and Winchell, 2007;Morescalchi et al, 2007Morescalchi et al, , 2008, but currently they are considered to be the most basal Actinopterygyans, the Cladistia (Venkatesh et al, 1999(Venkatesh et al, , 2001Britz and Bartsch, 2003;Kikugawa et al, 2004;Claeson et al, 2007), also if still remain poorly understood the intraspecific diversification and the interrelationships among the ten extant African Polypterus species (Hanssens et al, 1995;Gayet et al, 2001;Daget et al, 2001;Britz, 2004;Otero et al, 2006). For these reasons, we amplified, cloned and sequenced the DANA elements in six species of Polypteridae (Polypterus palmas, P. senegalus, P. ornatipinnis, P. buettikoferi, P. delhezi and Erpetoichthys calabaricus) and two Dipnoans (Protopterus annectens and P. aethiopicus), used to compare a distantly related bony lungfish group, whose DNA was available in our laboratory.…”

Cytogenetic analysis in Polypterus ornatipinnis (Actinopterygii, Cladistia, Polypteridae) and 5S rDNA

“…These species represent a phyletical branch which became detached at a very early stage from the evolutionary trend of the Paleoniscoids, preserving the archaic morphological features of its members, and were then subjected to a sudden diversification and to the acquisition of numerous morphological and structural key-innovations (Patterson, 1982;Gardiner, 1984;Gosse, 1984;Greenwood, 1984;Arratia and Cloutier, 1996;Bartsch et al, 1997;Lund, 2000;Arnason et al, 2001;Gayet et al, 2002;Britz and Johnson, 2003;Otero et al, 2006;Claeson et al, 2007). Taxonomic research on recent Polypteridae in the last few decades has been limited to a revision of Polypterus palmas subspeciescomplex (Hanssens et al, 1995), to the description of Polypterus teugelsi (Britz, 2004) and Polypterus mokelembembe (Schlieven and Schafer, 2006).…”