A reappraisal of the pectoral skeleton of lantern sharks (Elasmobranchii: Squaliformes: Etmopteridae)

Abstract

The morphology of the articular region of the pectoral girdle and associated basals in Etmopteridae is revised in light of new evidence provided by taxa unavailable for previous studies. Such studies considered that etmopterids plesiomorphically had a single pectoral articular condyle, and only Etmopterus had two separate ones. Our reanalysis indicates that the possession of two separate condyles, one for the articulation of the propterygium and the second for the meso‐ and metapterygium, is the most widespread condition in this group. However, the presence of two separate articular condyles is not recovered as a synapomorphy for Etmopteridae. Previous studies also proposed that etmopterids lack a hook‐like process on the anteroproximal margin of the anteriormost pectoral basal. We document that the hook‐like process is plesiomorphically present in Etmopteridae, thus corroborating the hypothesis of closer relationships between this family and the other squaliforms that also share this process, namely Centrophoridae, Dalatiidae, Oxynotidae, and Somniosidae.

Untangling the systematic dilemma behind the roughskin spurdog Cirrhigaleus asper (Merrett, 1973) (Chondrichthyes: Squaliformes), with phylogeny of Squalidae and a key to Cirrhigaleus species

“…Presence of a facet on the pectoral articular region for propterygium was proposed as synapomorphy of Squalidae in [32] and again in [49,51] which is in contrast to our current analysis. Cirrhigaleus share a condition similar to those observed for Etmopteridae (as described in [51]): a condyle for the propterygium and a condyle for the mesopterygium and metapterygium. Some synapomorphies, however, require revision as other members within Squaliformes that were left out of the present analysis.…”

“…Out of the 18 synapomorphies for the clade, only one was previously proposed: dignathic homodonty in [ 22 ]. Presence of a facet on the pectoral articular region for propterygium was proposed as synapomorphy of Squalidae in [ 32 ] and again in [ 49 , 51 ] which is in contrast to our current analysis. Cirrhigaleus share a condition similar to those observed for Etmopteridae (as described in [ 51 ]): a condyle for the propterygium and a condyle for the mesopterygium and metapterygium.…”

“…Character polarity was made by outgroup comparison following [46]. Data for D. licha and I. brasiliensis were obtained from literature review if available (including [22,32,34,[47][48][49][50][51][52]) and/or examination of specimens (see comparative material). Character matrix was divided into two datasets: S1 Phylogenetic analysis was performed under parsimony using TNT 1.1 [53,54] and the 'Traditional Search' option, using the TBR (Tree Bisection Reconnection) algorithm.…”

“…Dalatias and Isistius have crown diamond-shaped (51,0). Cirrhigaleus, S. mitsukurii, S. montalbani and S. japonicus have heartshaped dermal denticles (51,1). Squalus acanthias and S. suckleyi present dermal denticles arrow-shaped (51,2) whereas S. megalops, S. brevirostris, S. albifrons have club-shaped dermal denticles (51,3).…”

A redescription of the appendicular skeleton of Squalus acanthias (Elasmobranchii: Squaliformes: Squalidae)

“…megalops ; Figures 2a, b, 4c, 5d and 6a). A similar condition is present in Aculeola , Etmopterus and Centroscyllium (Etmopteridae; Silva & Carvalho, 2015; Silva & Datovo, 2021). A single articular region for the pectoral basals is observed in other members of Squaliformes representing different families: Isistius , Dalatias , Euprotomicrus , Squaliolus , Trigonognathus (Dalatiidae), Deania , Centrophorus (Centrophoriidae), Centroscymnus , Centroselachus , Zameus , Scymnodon , Somniosus , Scymnodalatias (Somniosidae) and Oxynotus (Oxynotidae) (Figure 12; see also Silva & Carvalho, 2015).…”