Argyriou and Romano 2019
study an Early Triassic fish, Perleidus woodwardi (Fig. 1).
From the abstract:
“Despite decades of research, the deep-time origins and ancestral morphologies of crown actinopterygian evolutionary lineages remain obscure, with the membership of late Paleozoic-Triassic taxa being particularly fluid with respect to the actinopterygian crown group. Lack of data on the endoskeleton of important fossil groups, and a disjunction among phylogenetic matrices aimed at resolving different branches of the actinopterygian tree of life, are the major causes of this gap of knowledge.”
The large reptile tree (LRT, 1592 taxa) solved this problem over the last few months by including more taxa than in prior studies without much data from the endoskeleton of fish.
The abstract continues:
“The Triassic ‘perleidids’ have been historically viewed as early members of Neopterygii, the most successful group of modern actinopterygians.”
That is confirmed in the LRT.
“Yet, recent research has cast doubts not only on their evolutionary affinities, but also their monophyly, though no stable phylogenetic alternatives have been provided. Based on previously undescribed material in museum collections in Paris and Zurich, we reappraise ‘Perleidus’ woodwardi, from the early Olenekian (Early Triassic) of Spitsbergen. Exquisitely preserved exoskeletons provide novel data on the osseus constituents of the ethmoid region, and the anatomy of the tail fin, which is now shown to lack obvious epaxial rays. In addition, using μCT, we studied a recently collected, three-dimensionally preserved cranium and pectoral girdle, which revealed a wealth of phylogenetically important information.”
“The braincase and endocast of ‘P’. woodwardi broadly resemble those of Australosomus, with the presence of a posteriorly elongate parasphenoid in the former being a notable difference between the two.”
Australosomus is another Early Triassic ray-fin fish. The rest of the abstract provides various skeletal traits of interest without making additional comparisons.
In the LRT
Perleidus nests between the tuna-like Triassic ray-fin, Pholidophorus (Fig. 2) and the derived extant bronze featherback, Notopterus, taxa not mentioned in the Arygriou and Romano abstract.
the LRT was able to nest Pholidophorus with the distinctively different Notopterus. Perleidus provides the perfect transitional taxon. In fact, it is so midway between the two sister taxa that there is complete loss of resolution between the three.
Arygriou T and Romano C 2019. New fins or old fins? Skull and pectoral girdle of Early Triassic ‘Perleidus’ woodwardi revisited using µCT. Journal of Vertebrate Paleontology abstract.