Phylogenetic Relationships of the Triassic Archaeosemionotus Deecke (Halecomorphi, Ionoscopiformes) from the ‘Perledo Fauna’

Abstract

The lagerstätten in the Monte San Giorgio have provided excellent fossils representing one of the most important windows to the marine life during the Triassic. Among these fossils, fishes are abundant and extraordinarily well preserved. Most of these fishes represent extinct lineages and were difficult to understand and classify during the early years after discovery. These difficulties usually led to a mixture of species under the same taxonomic name. This is the case of fishes referred to the genus Archaeosemionotus. The name bearing type of A. connectens, the type species of this genus, represents a basal halecomorph, but most other fishes referred to this genus represent basal ginglymodians. Therefore, we conducted this study to clarify the taxonomic status and phylogenetic relationships of A. connectens, which is a member of the family Furidae (Halecomorphi, Ionoscopiformes) representing the second cladistically supported evidence of ionoscopiforms in the Triassic and it is thus one of the two oldest reliable records of this group. Ionoscopiforms have a long stratigraphic range, though their fossil record is rather patchy. In our analysis, the sister taxon of Archaeosemionotus is Robustichthys from the Anisian of China, and they together form a clade with Furo, which is known from several localities ranging from the Early to the Late Jurassic. Other ionoscopiforms are so far known from the Kimmeridgian to the Albian and it is thus evident that recent efforts have concentrated on the later history of the group (Late Jurassic to Cretaceous). The phylogenetic relationships obtained for the Ionoscopiformes do not show a clear palaeobiogeographic pattern, but give important new insights into the origin, divergence date and early history of this clade.

New holostean fishes (Actinopterygii: Neopterygii) from the Middle Triassic of the Monte San Giorgio (Canton Ticino, Switzerland)

“…Remarks . The specimens here referred to the new genus Ticinolepis have previously been erroneously identified in the genus Archaeosemionotus , the taxonomy and phylogenetic relationships of which have been revised by López-Arbarello, Stockar & Bürgin ( 2014 ). Very different from Ticinolepis , Archaeosemionotus presents three very large infraorbital bones forming the ventral margin of the orbit, with the first and third of them being the largest bones in the circumborbital series; there are no anterior infraorbitals; the cheek is covered with only two large suborbital bones, with a little third suborbital between them at their posterior margins; the maxilla is much longer, reaching the level of the posterior border of the orbit; and there is a large gular plate.…”

“…The systematic nomenclature follows López-Arbarello ( 2012 ) for Ginglymodi, López-Arbarello, Stockar & Bürgin ( 2014 ) for Halecomorphi, and Sferco, López-Arbarello & Báez ( 2015 ) for Teleostei. Accordingly, the informal term ‘gars’ correspond to the Lepisosteoidei of López-Arbarello ( 2012 ), which is equivalent to the Lepisosteiformes of Grande ( 2010 ), and the term ‘teleosts’ correspond to the total clade Teleostei as defined by De Pinna ( 1996 ).…”

“…During the last decades, an increasing number of crown neopterygians have been described from Middle Triassic sediments of China (e.g., Tintori et al , 2007 ; Tintori et al , 2010 ; López-Arbarello et al , 2011 ; Wen et al , 2012 ; Xu & Wu , 2012 ; Chen et al , 2014 ; Xu, Zhao & Coates , 2014 ; Xu & Shen , 2015 ) and the Southern and Eastern Alps (e.g., Herzog , 2003 ; Bürgin , 2004 ; Herzog & Bürgin , 2005 ; Arratia & Herzog , 2007 ; Tintori & Lombardo , 2007 ; Tintori et al , 2007 ; Lombardo & Tintori , 2008 ; Lombardo, Tintori & Tona , 2012 ; López-Arbarello, Stockar & Bürgin , 2014 ), and several of these taxa are closely related to typical Jurassic neopterygians in Europe, indicating that the development of the Tethys played a very important role for the diversification of this group. The fossil assemblages from the Besano Formation and the Meride Limestone represent exceptional opportunities to study the evolution of life during the Middle Triassic, in particular for the time span between the latest Anisian and early late Ladinian.…”

“…The specimens described here were previously identified as Archaeosemionotus sp., based on an erroneous concept of this genus, which was long considered to be a semionotid. The taxonomic status and phylogenetic relationships of the halecomorph Archaeosemionotus (Furidae) has recently been clarified ( López-Arbarello, Stockar & Bürgin , 2014 ). This study is thus aimed to solve the taxonomy of the more than hundred specimens that have been excavated by the University of Zurich on the Swiss part of the Monte San Giorgio since 1924, and provisionally referred to that genus ( Bürgin , 1998 ).…”

Redescription and Phylogenetic Placement of †Hemicalypterus weiri Schaeffer, 1967 (Actinopterygii, Neopterygii) from the Triassic Chinle Formation, Southwestern United States: New Insights into Morphology, Ecological Niche, and Phylogeny

“…As † Hemicalypterus has been hypothesized to be related to semionotids within Holostei, five additional holostean fishes were included to further resolve the relationships of holostean fishes: the ionoscopid fish † Archaeosemionotus connectens ; ginglymodian fishes † Lepidotes elvensis , † Camerichthys lunae , and † Kyphosichthys grandei ; and the archaeomaenid fish † Aetheolepis mirabilis . Scores for † Archaeosemionotus connectens are based on [ 35 ]; scores for † Lepidotes elvensis are based on [ 36 ]; scores for † Camerichthys are based on [ 33 ]; scores for † Kyphosichthys are based on [ 37 ]; scores for † Aetheolepis mirabilis are based on [ 38 ] and examination of photographs of specimens.…”