Taxonomy, Distribution and Evolution of Trisopterine Gadidae by Means of Otoliths and Other Characteristics

Abstract

In a greater study of the recent fossil Gadidae, the object of this paper is to better define the trisopterine species and their relationships. The taxonomy of the four recent species usually included in the genus Trisopterus is further elaborated by means of published and new data on their otoliths, by published data on general external features and meristics of the fishes, and their genetics. Fossil otoliths, from the beginning of the Oligocene up to the present, reveal much of their evolution and throw more light on their relationships. Several succeeding and partly overlapping lineages representing different genera are recognized during this time interval. The genus Neocolliolus Gaemers, 1976, for Trisopterus esmarkii (Nilsson, 1855), is more firmly based. A new genus, Allotrisopterus, is introduced for Trisopterus minutus (Linnaeus, 1758). The similarity with Trisopterus capelanus (Lacepède, 1800) is an example of convergent evolution. The tribe Trisopterini Endo (2002) should only contain Trisopterus, Allotrisopterus and Neocolliolus as recent genera. Correct identification of otoliths from fisheries research and from sea bottom samples extends the knowledge of the present day geographical distribution of T. capelanus and T. luscus (Linnaeus, 1758). T. capelanus is also living along the Atlantic coast of Portugal and at least up to and including the Ría de Arosa, Galicia, Spain. There it can easily be mistaken for A. minutus that is also living there. Otoliths of T. luscus have been identified from the Evvoïkós Channel between Euboia and the mainland of Greece, thus it must live also in the Aegean Sea. Otoliths prove to be a powerful tool in taxonomy, biogeography and evolution of teleosts.

Recognition and Distribution of Two North Atlantic Gadiculus Species, G. argenteus and G. thori (Gadidae), Based on Otolith Morphology, Larval Pigmentation, Molecular Evidence, Morphometrics and Meristics

“…Based on otoliths, meristic and some external characteristics, Trisopterus minutus is more closely related to Neocolliolus esmarkii than to Trisopterus luscus (Linnaeus, 1758) and T. capelanus (Lacepède, 1800). A new genus, Allotrisopterus, is therefore introduced by Gaemers [40] for Trisopterus minutus and is confirmed by the molecular data presented in this study (Figure 8).…”

“…It is interesting that the oldest trisopterine lineage known from the geological record also possesses a pseudocolliculum just like Gadiculus and Micromesistius [40]. This further confirmed the plesiomorphic character of collum and pseudocolliculum in the gadids.…”

“…Likewise, the otoliths of G. argenteus are relatively larger than those in G. thori. Gaemers [40] observed the same relationship between the relative size of the otoliths of Trisopterus capelanus (Lacepède, 1800) and the larger T. luscus (Linnaeus, 1758). In addition, Schmidt's [17] observations, that the post-larvae of G. thori are larger and slenderer compared with post-larvae of G. argenteus at the same stage of development, is in accordance with the difference in maximum size.…”

“…Otoliths are a powerful tool for distinguishing closely related species, reconstructing phylogenies, and estimating geological events [37,40]. Gadiculus otoliths show several plesiomorphic characters within the Gadidae.…”

“…Otolith and adult fish morphology, habitat and food preferences all show that Trisopterus esmarkii (Nilsson, 1855) is clearly different from the other Trisopterus species [40]. The genus Neocolliolus was erected for this taxon by Gaemers [36] based on its different otolith morphology.…”