Convergent Evolution and the Red Sea Rover: Emmelichthys marisrubri (Teleostei: Emmelichthyidae) Is a Species of Fusilier (Lutjanidae: Dipterygonotus)
Rovers, rubyfishes, and bonnetmouths (Emmelichthyidae) comprise a small family of fishes that can be distinguished from other perch-like fishes by their generally red, fusiform bodies, highly protrusible mouths, and large rostral cartilage. Their highly protrusible upper jaws have led ichthyologists to group morphologically similar but distantly related taxa within the Emmelichthyidae and is one of the stunning examples of morphological convergence within perch-like fishes. In 2014, the first and only emmelichthyid from the Red Sea, Emmelichthys marisrubri, was described. This species is diagnosed by 80–83 lateral-line scales, 8 dorsal-fin rays, and 4–5 isolated dorsal spines that are separated from membrane-bound dorsal-fin elements, among other features. While examining the osteology of E. marisrubri, I discovered several differences in the oral jaws, suspensorium, neurocranium, and dorsal fin when compared to other species of rovers. Based on these differences and the results of a phylogenetic analysis, I transfer this taxon to the genus Dipterygonotus within the Lutjanidae and among the fusiliers (formerly Caesionidae), an Indo-Pacific group of fishes that also have highly protrusible upper jaws.
Representative species of the Emmelichthyidae. (A) Plagiogeneion rubiginosum NMNZ P.061899. (B) Erythrocles schlegelii KAUM-I. 55963. (C) Emmelichthys struhsakeri KAUM-I. 106623. (D) Dipterygonotus marisrubri paratype HUJF 20199. (E) Emmelichthys nitidus NSMT 125978 with upper and lower jaws protruding. Scale bars = 1 cm.
Hypothesis of relationships from likelihood analysis of fusiliers based on morphological dataset. Morphological characters optimized unambiguously onto each branch are represented by a circle with the corresponding character number listed above and character state below. Circles with black fill are unique and unreversed character states. Circles with white fill are states that optimized multiple times in the phylogeny. Branch lengths and bootstrap support values for phylogeny are in the lower left-hand corner. See Data Accessibility for tree file.
Comparison of oral-jaw and suspensorial characters among (A) Emmelichthys nitidus NSMT 125987, (B) Dipterygonotus marisrubri paratype USNM 410584, and (C) D. balteatus USNM 388679. Arrows and numbers highlight characters being compared. (1) Ascending processes separate from each other. (1*) Ascending processes fused at midline. (2) Articular process fused to ascending process along majority of length. (2*) Articular and ascending processes as separate elements. (3) One postmaxillary process. (3*) Two postmaxillary processes. (4) Supramaxilla present. (4*) Supramaxilla absent. (5) Endopterygoid with ventral flange separating metapterygoid from quadrate. (5*) Endopterygoid without ventral flange. Scale bars = 1 mm.
Comparison of neurocranial characters among (A) Emmelichthys nitidus NSMT 125987, (B) Dipterygonotus marisrubri paratype USNM 410584, and (C) D. balteatus USNM 388679. Arrows and numbers highlight characters being compared. (1) Lateral ethmoid without posterior expansion. (1*) Lateral ethmoid with posterior expansion. (2) Pterosphenoids contact each other at midline. (2*) Pterosphenoids separate throughout length. (3) Apophysis of parasphenoid rudimentary. (3*) Apophysis of parasphenoid robust. (4) Prootic not ventrally expanded. (4*) Prootic with ventral extension covering pars jugularis. (5) Posterior margin of supraoccipital without indentation. (5*) Posterior margin of supraoccipital with indentation. (6) Basioccipital without ventral expansion. (6*) Basioccipital with horn-like ventral expansion. (7) Pterotic with flange that interacts with ventral arm of posttemporal. (7*) Pterotic with tube-like process that interacts with ventral arm of posttemporal. Scale bars = 1 mm.
Comparison of dorsal-fin characters among (A) Emmelichthys nitidus NSMT 125987, (B) Dipterygonotus marisrubri paratype HUJF 20199, and (C) D. balteatus USNM 388679. Arrows and numbers highlight characters being compared. (1) First of three rod-like supraneurals. (1*) First of two supraneurals, the first being “T”-shaped. (2) First of eight trisegmental pterygiophores. (2*) First of three trisegmental pterygiophores. (2**) First of two trisegmental pterygiophores. Comparison of vertebral characters between (D) Dipterygonotus marisrubri paratype HUJF 20199 and (E) D. balteatus USNM 388679. (3) First neural-arch prezygopophysis large and robust, extending far forward over the exoccipitals. (3*) First neural-arch prezygopophysis flat or strut-like, extending slightly over the exoccipitals. (4) First epipleural rib broad proximally, tapering distally. (4*) First epipleural rib uniform throughout length. Scale bars = 1 mm.
Contributor Notes
Associate Editor: W. L. Smith.