Postotic laterosensory canal and pterotic branch homology in catfishes

Abstract

Morphology of the postotic laterosensory canal was surveyed across loricarioid and outgroup catfishes in order to resolve conflicting statements regarding homology and phylogenetic significance of intrinsic character variation. A pterotic branch is widespread among catfishes and has been identified as a synapomorphy for siluriforms, but its presence in loricarioid catfishes has been disputed. In contrast to previous statements that absence of a pterotic branch is synapomorphic for loricarioids, we confirm the presence of a pterotic branch in Nematogenys inermis and other trichomycterids, callichthyids, and loricariids. The pterotic branch is secondarily absent in scoloplacids and astroblepids. We present criteria for establishing homology of the pterotic branch and review character state optimization schemes on the currently accepted phylogeny. The postotic region of loricariids is further specialized in having an expanded swimbladder capsule that incorporates the trunk lateral line canal and has a lateral opening covered by a greatly expanded pterotic complex. The trunk lateral line enters the swimbladder capsule mesial to the pterotic lateral wall and passes anteromedially as a fleshy tube before forming the postotic canal in the pterotic, a morphology reported previously for a single loricariid representative. Variation in the relative extent and topographic position of postotic canal branches and other morphologies is diagnostic of certain loricariid taxa, suggesting a rich character complex of potential utility in phylogeny reconstruction. J. Morphol. 246:212–227, 2000. © 2000 Wiley‐Liss, Inc.

Description of a new Pimelodella (Siluriformes: Heptapteridae) species with a discussion on the upper pectoral girdle homology of Siluriformes

“…However, an unexpected result from this survey was the discovery of a branch comparable with the pterotic branch in non‐siluriform Ostariophysi sampled for outgroup comparisons. In contrast to previous studies (Arratia & Gayet, ; Arratia & Huaquín, ; Schaefer & Aquino, ), representatives of all examined ostariophysan families exhibited a fleshy tubule and pore immediately posterior to the preopercular (po1) branch (Figure (b), (e)–(f)). This branch emerges from the main postotic canal, specifically from the region of contact between the pterotic and extrascapular bones, such as in P. bockmanni and many other siluriforms.…”

“…However, since this character dealt with the homology of the pectoral girdle elements and the lateral line was an additional piece of evidence used to argue in favour of their hypothesis, no further descriptions or anatomical illustration of the pterotic branch were provided by the authors. Nevertheless, all subsequent studies referring to the laterosensory system of the catfishes credited Fink and Fink () as the proponent of the pterotic branch homology, listing and repeatedly corroborating the presence of this branch as a synapomorphy for Siluriformes (Arratia & Gayet, , p. 500; Arratia & Huaquín, , p. 26; Schaefer & Aquino, , p. 212). Schaefer and Aquino () published a complete review of the pterotic branch occurrence across Siluriformes.…”

“…The so‐called pterotic branch (po2) is plesiomorphically present in Siluriformes (Arratia & Gayet, ; Arratia & Huaquín, ; Fink & Fink, , ). This particular branch emerges from the postotic canal associated with the pterotic (Arratia & Gayet, , figures 3–8; Arratia & Huaquín, , figure ; Schaefer & Aquino, , table ), or from the contact between pterotic and extrascapula ( e.g . Figures (d); Arratia & Gayet, , figure 9; Bockmann & Miquelarena, , figure 7; Slobodian & Bockmann, , figure ).…”

Description of a new Pimelodella (Siluriformes: Heptapteridae) species with a discussion on the upper pectoral girdle homology of Siluriformes

“…However, an unexpected result from this survey was the discovery of a branch comparable with the pterotic branch in non‐siluriform Ostariophysi sampled for outgroup comparisons. In contrast to previous studies (Arratia & Gayet, ; Arratia & Huaquín, ; Schaefer & Aquino, ), representatives of all examined ostariophysan families exhibited a fleshy tubule and pore immediately posterior to the preopercular (po1) branch (Figure (b), (e)–(f)). This branch emerges from the main postotic canal, specifically from the region of contact between the pterotic and extrascapular bones, such as in P. bockmanni and many other siluriforms.…”

“…However, since this character dealt with the homology of the pectoral girdle elements and the lateral line was an additional piece of evidence used to argue in favour of their hypothesis, no further descriptions or anatomical illustration of the pterotic branch were provided by the authors. Nevertheless, all subsequent studies referring to the laterosensory system of the catfishes credited Fink and Fink () as the proponent of the pterotic branch homology, listing and repeatedly corroborating the presence of this branch as a synapomorphy for Siluriformes (Arratia & Gayet, , p. 500; Arratia & Huaquín, , p. 26; Schaefer & Aquino, , p. 212). Schaefer and Aquino () published a complete review of the pterotic branch occurrence across Siluriformes.…”

“…The so‐called pterotic branch (po2) is plesiomorphically present in Siluriformes (Arratia & Gayet, ; Arratia & Huaquín, ; Fink & Fink, , ). This particular branch emerges from the postotic canal associated with the pterotic (Arratia & Gayet, , figures 3–8; Arratia & Huaquín, , figure ; Schaefer & Aquino, , table ), or from the contact between pterotic and extrascapula ( e.g . Figures (d); Arratia & Gayet, , figure 9; Bockmann & Miquelarena, , figure 7; Slobodian & Bockmann, , figure ).…”

Homology between the recessus lateralis and cephalic sensory canals, with the proposition of additional synapomorphies for the Clupeiformes and the Clupeoidei

“…It is equivalent to the pterotic branch of the frontal laterosensory canal of Weitzman & Fink (1983). Nevertheless, as the term pterotic branch was previously and most frequently applied to a nonhomologous structure of the postotic sensory system of siluriforms (Fink & Fink, 1981; Schaefer & Aquino, 2000), it will not be adopted here. Except in cases where there is no direct connection between the supraorbital and temporal canals, the postorbital branch of the supraorbital canal joins the infraorbital canal close to, but outside of the dermosphenotic or infraorbital 6 (when this bone is present) to form a single tube continuous with the anterior opening of the temporal canal bone.…”

The Laterosensory Canal System in Epigean and Subterranean Ituglanis (Siluriformes: Trichomycteridae), With Comments About Troglomorphism and the Phylogeny of the Genus

“…The anterior half‐pore opens at, or slightly caudal to, the dorsal contact between the pterotic and the sphenotic‐prootic‐pterosphenoid, being fused to the posterior pore of the otic canal; it represents the preoperculomandibular branch of the postotic canal ( sensu Schaeffer and Aquino, ). The posterior half‐pore opens at the dorsolateral contact between the pterotic and the posttemporo‐supracleithrum, is fused to the anterior half‐pore of the scapular canal, and represents the pterotic branch of the postotic canal ( sensu Schaeffer and Aquino, ). Externally, the anterior pore opens dorsomedially to the opercular patch of odontodes, and the posterior pore opens approximately on the line passing through the posterior portion of the interopercular patch of odontodes.…”

Description of a new Pimelodella (Siluriformes: Heptapteridae) species with a discussion on the upper pectoral girdle homology of Siluriformes

“…However, an unexpected result from this survey was the discovery of a branch comparable with the pterotic branch in non‐siluriform Ostariophysi sampled for outgroup comparisons. In contrast to previous studies (Arratia & Gayet, ; Arratia & Huaquín, ; Schaefer & Aquino, ), representatives of all examined ostariophysan families exhibited a fleshy tubule and pore immediately posterior to the preopercular (po1) branch (Figure (b), (e)–(f)). This branch emerges from the main postotic canal, specifically from the region of contact between the pterotic and extrascapular bones, such as in P. bockmanni and many other siluriforms.…”

“…However, since this character dealt with the homology of the pectoral girdle elements and the lateral line was an additional piece of evidence used to argue in favour of their hypothesis, no further descriptions or anatomical illustration of the pterotic branch were provided by the authors. Nevertheless, all subsequent studies referring to the laterosensory system of the catfishes credited Fink and Fink () as the proponent of the pterotic branch homology, listing and repeatedly corroborating the presence of this branch as a synapomorphy for Siluriformes (Arratia & Gayet, , p. 500; Arratia & Huaquín, , p. 26; Schaefer & Aquino, , p. 212). Schaefer and Aquino () published a complete review of the pterotic branch occurrence across Siluriformes.…”

“…The so‐called pterotic branch (po2) is plesiomorphically present in Siluriformes (Arratia & Gayet, ; Arratia & Huaquín, ; Fink & Fink, , ). This particular branch emerges from the postotic canal associated with the pterotic (Arratia & Gayet, , figures 3–8; Arratia & Huaquín, , figure ; Schaefer & Aquino, , table ), or from the contact between pterotic and extrascapula ( e.g . Figures (d); Arratia & Gayet, , figure 9; Bockmann & Miquelarena, , figure 7; Slobodian & Bockmann, , figure ).…”

Homology between the recessus lateralis and cephalic sensory canals, with the proposition of additional synapomorphies for the Clupeiformes and the Clupeoidei

“…It is equivalent to the pterotic branch of the frontal laterosensory canal of Weitzman & Fink (1983). Nevertheless, as the term pterotic branch was previously and most frequently applied to a nonhomologous structure of the postotic sensory system of siluriforms (Fink & Fink, 1981; Schaefer & Aquino, 2000), it will not be adopted here. Except in cases where there is no direct connection between the supraorbital and temporal canals, the postorbital branch of the supraorbital canal joins the infraorbital canal close to, but outside of the dermosphenotic or infraorbital 6 (when this bone is present) to form a single tube continuous with the anterior opening of the temporal canal bone.…”

The Laterosensory Canal System in Epigean and Subterranean Ituglanis (Siluriformes: Trichomycteridae), With Comments About Troglomorphism and the Phylogeny of the Genus

“…The anterior half‐pore opens at, or slightly caudal to, the dorsal contact between the pterotic and the sphenotic‐prootic‐pterosphenoid, being fused to the posterior pore of the otic canal; it represents the preoperculomandibular branch of the postotic canal ( sensu Schaeffer and Aquino, ). The posterior half‐pore opens at the dorsolateral contact between the pterotic and the posttemporo‐supracleithrum, is fused to the anterior half‐pore of the scapular canal, and represents the pterotic branch of the postotic canal ( sensu Schaeffer and Aquino, ). Externally, the anterior pore opens dorsomedially to the opercular patch of odontodes, and the posterior pore opens approximately on the line passing through the posterior portion of the interopercular patch of odontodes.…”

Description of a new Pimelodella (Siluriformes: Heptapteridae) species with a discussion on the upper pectoral girdle homology of Siluriformes

“…However, an unexpected result from this survey was the discovery of a branch comparable with the pterotic branch in non‐siluriform Ostariophysi sampled for outgroup comparisons. In contrast to previous studies (Arratia & Gayet, ; Arratia & Huaquín, ; Schaefer & Aquino, ), representatives of all examined ostariophysan families exhibited a fleshy tubule and pore immediately posterior to the preopercular (po1) branch (Figure (b), (e)–(f)). This branch emerges from the main postotic canal, specifically from the region of contact between the pterotic and extrascapular bones, such as in P. bockmanni and many other siluriforms.…”

“…However, since this character dealt with the homology of the pectoral girdle elements and the lateral line was an additional piece of evidence used to argue in favour of their hypothesis, no further descriptions or anatomical illustration of the pterotic branch were provided by the authors. Nevertheless, all subsequent studies referring to the laterosensory system of the catfishes credited Fink and Fink () as the proponent of the pterotic branch homology, listing and repeatedly corroborating the presence of this branch as a synapomorphy for Siluriformes (Arratia & Gayet, , p. 500; Arratia & Huaquín, , p. 26; Schaefer & Aquino, , p. 212). Schaefer and Aquino () published a complete review of the pterotic branch occurrence across Siluriformes.…”

“…The so‐called pterotic branch (po2) is plesiomorphically present in Siluriformes (Arratia & Gayet, ; Arratia & Huaquín, ; Fink & Fink, , ). This particular branch emerges from the postotic canal associated with the pterotic (Arratia & Gayet, , figures 3–8; Arratia & Huaquín, , figure ; Schaefer & Aquino, , table ), or from the contact between pterotic and extrascapula ( e.g . Figures (d); Arratia & Gayet, , figure 9; Bockmann & Miquelarena, , figure 7; Slobodian & Bockmann, , figure ).…”

Homology between the recessus lateralis and cephalic sensory canals, with the proposition of additional synapomorphies for the Clupeiformes and the Clupeoidei

“…It is equivalent to the pterotic branch of the frontal laterosensory canal of Weitzman & Fink (1983). Nevertheless, as the term pterotic branch was previously and most frequently applied to a nonhomologous structure of the postotic sensory system of siluriforms (Fink & Fink, 1981; Schaefer & Aquino, 2000), it will not be adopted here. Except in cases where there is no direct connection between the supraorbital and temporal canals, the postorbital branch of the supraorbital canal joins the infraorbital canal close to, but outside of the dermosphenotic or infraorbital 6 (when this bone is present) to form a single tube continuous with the anterior opening of the temporal canal bone.…”

The Laterosensory Canal System in Epigean and Subterranean Ituglanis (Siluriformes: Trichomycteridae), With Comments About Troglomorphism and the Phylogeny of the Genus

“…The anterior half‐pore opens at, or slightly caudal to, the dorsal contact between the pterotic and the sphenotic‐prootic‐pterosphenoid, being fused to the posterior pore of the otic canal; it represents the preoperculomandibular branch of the postotic canal ( sensu Schaeffer and Aquino, ). The posterior half‐pore opens at the dorsolateral contact between the pterotic and the posttemporo‐supracleithrum, is fused to the anterior half‐pore of the scapular canal, and represents the pterotic branch of the postotic canal ( sensu Schaeffer and Aquino, ). Externally, the anterior pore opens dorsomedially to the opercular patch of odontodes, and the posterior pore opens approximately on the line passing through the posterior portion of the interopercular patch of odontodes.…”