New generic name for a small Triassic ray-finned fish from Perledo (Italy)

  1. Adriana López-Arbarello
  2. Rainer Brocke

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Abstract

Our new study of the species originally included in the genus Allolepidotus led to the taxonomic revision of the halecomorph species from the Triassic of Perledo, Italy. The morphological variation revealed by the analysis of the type material is sufficient to confirm four different taxa represented in the Perledo Formation. We correct the misunderstanding about the type species of Allolepidotus, which is A. ruppelii and not “A.” bellottii as considered in the literature over the past two decades. The latter species was originally placed in the genus Semionotus. Fossil material from the Kalkschieferzone of Besnasca/Ca' del Frate (Viggiù-Varese, Italy) and Meride (Ticino, Switzerland) which were referred to Allolepidotus, rather represent a species of Eoeugnathus. Therefore, we transfer the species Semionotus bellottii to that genus and propose the new combination E. bellottii. The second and only other species originally included in the genus Allolepidotus is transferred here to the new genus XXXX. The holotype of X. nothosomoides new comb. has been mechanically prepared, revealing additional anatomical information that allows to place this taxon in the halecomorph family Subortichthyidae. The other halecomorph species named from the Perledo Formation, Pholidophorus oblongus and Pholidophorus curionii, have been treated as junior synonyms of E. bellottii, but our analysis indicates that they represent distinct separate taxa. However, due to the loss of the type specimens, it is not possible to decide whether they might have been conspecific with other ray-finned fishes from the Middle Triassic of the Alps.

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  1. Peer Community in Paleontology

    Mesozoic fishes are extremely diverse. In fact, fishes are the most diverse group of vertebrates during the Mesozoic─just as during any other era. Yet, their study is severely underrepresented in comparison to other fossil groups. There are just too few palaeoichthyologists to deal with such a vast diversity of fishes. Nonetheless, thanks to the huge efforts they have made over the last few decades, we have come a long way in our understanding of Mesozoic ichthyofaunas. One of such devoted palaeoichthyologists is Dr. Adriana López-Arbarello, whose contributions have been crucial in elucidating the phylogenetic interrelationships and taxonomic diversity of Mesozoic actinopterygian fishes (e.g., López-Arbarello, 2012; López-Arbarello & Sferco, 2018; López-Arbarello & Ebert, 2023). In her most recent manuscript, Dr. López-Arbarello has joined forces with Dr. Rainer Brocke to tackle the taxonomy and systematics of the halecomorph fishes from one of the most relevant Triassic sites, the upper Ladinian Perledo locality from Italy (López-Arbarello & Brocke, 2024). 

    Fossil fishes were reported for the first time from Perledo in the first half of the 19th century (Balsamo-Crivelli, 1839), and up to 30 different species were described from the locality in the subsequent decades. Unfortunately, this is one of the multiple examples of fossil collections that suffered the effects of World War II, and most of the type material was lost. As a consequence, many of those 30 species that have been described over the years are in need of a revision. Based on the study of additional material that was transferred to Germany and is housed at the Senckenberg Research Institute and Natural History Museum, López-Arbarello & Brocke (2024) confirm the presence of four different species of halecomorph fishes in Perledo, which were previously put under synonymy (Lombardo, 2001). They provide new detailed information on the anatomy of two of those species, together with their respective diagnoses. But more importantly, they carry out a thorough exercise of taxonomy, rigorously applying the International Code of Zoological Nomenclature to disentangle the intricacies in the taxonomic story of the species placed in the genus Allolepidotus. As a result, they propose the presence of the species A. ruppelii, which they propose to be the type species for that genus (instead of A. bellottii, which they transfer to the genus Eoeugnathus). They also propose a new genus for the other species originally included in Allolepidotus, A. nothosomoides. Finally, they provide a set of measurements and ratios for Pholidophorus oblongus and Pholidophorus curionii, the other two species previously put in synonymy with A. bellottii, to demonstrate their validity as different species. However, due to the loss of the type material, the authors propose that these two species remain as nomina dubia. 

    In summary, apart from providing new detailed anatomical descriptions of two species and solving some long-standing issues with the taxonomy of the halecomorphs from the relevant Triassic Perledo locality, the paper by López-Arbarello & Rainer (2024) highlights three important topics for the study of the fossil record: 1) we should never forget that world-scale problems, such as World Wars, also affect our capacity to understand the natural world in which we live, and the whole society should be aware if this; 2) the importance of exhaustively following the International Code of Zoological Nomenclature when describing new species; and 3) we are in need of new palaeoichthyologists to, in Dr. López-Arbarello’s own words, “unveil the mysteries of those marvellous Mesozoic ichthyofaunas.”

    References

    Balsamo-Crivelli, G. (1839). Descrizione di un nuovo rettile fossile, della famiglia dei Paleosauri, e di due pesci fossili, trovati nel calcare nero, sopra Varenna sul lago di Como, dal nobile sig. Ludovico Trotti, con alcune riflessioni geologiche. Il politecnico repertorio mensile di studj applicati alla prosperita e coltura sociale, 1, 421–431.

    Lombardo, C. (2001). Actinopterygians from the Middle Triassic of northern Italy and Canton Ticino (Switzerland): Anatomical descriptions and nomenclatural problems. Rivista Italiana di Paleontologia e Stratigrafia, 107, 345–369. https://doi.org/10.13130/2039-4942/5439

    López-Arbarello, A. (2012). Phylogenetic interrelationships of ginglymodian fishes (Actinopterygii: Neopterygii). PLOS ONE, 7(7), e39370. https://doi.org/10.1371/journal.pone.0039370

    López-Arbarello, A., and Brocke, R. (2024). New generic name for a small Triassic ray-finned fish from Perledo (Italy). PaleorXiv, bxmg5, ver. 4, peer-reviewed by PCI Paleo. https://doi.org/10.31233/osf.io/bxmg5

    López-Arbarello, A., and Ebert, M. (2023). Taxonomic status of the caturid genera (Halecomorphi, Caturidae) and their Late Jurassic species. Royal Society Open Science, 10(1), 221318. https://doi.org/10.1098/rsos.221318

    López-Arbarello, A., and Sferco, E. (2018). Neopterygian phylogeny: The merger assay. Royal Society Open Science, 5(3), 172337. https://doi.org/10.1098/rsos.172337

  2. Version published to 10.31233/osf.io/bxmg5 on OSF Preprints