A new genus and species of pachycormiform fish that lived 150 million years ago has been identified from fossils found in the Neuquén Basin of Argentina.
Pachycormiformes is a large order of extinct ray-finned fishes known from marine deposits of Eurasia, the Americas and Antarctica.
They inhabited the oceans of the Early Jurassic and the Late Cretaceous epochs, from 182 to 66 million years ago.
Pachycormiformes displayed great disparities in morphology, from streamlined open ocean tuna-like predators to large suspension-feeding fishes with blunt nose extensions, and billfish-like forms with large pointed nose extensions and serrated pectoral fins.
“As part of the transition from Holostei to Teleostei, Pachycormiformes represent a key group of fishes,” said Dr. Soledad Gouiric-Cavalli, a paleontologist with the Universidad Nacional de la Plata, the Museo de La Plata and CONICET, and Dr. Gloria Arratia, a paleontologist with the Biodiversity Institute and the Department of Ecology and Systematic Biology at the University of Kansas.
“However, the anatomy and phylogenetic relationships of the group in the context of the neopterygians are far from being understood.”
“Our study is the first in which several specimens are described for this group of fish, all very well preserved and some even in three dimensions,” Dr. Gouiric-Cavalli said.
The newly-identified pachycormiform species lived during the Upper Jurassic epoch, some 150 million years ago.
Scientifically named Kaykay lafken, the fish was a carnivore, more than 2 m (6.6 feet) in length.
“With scythe-shaped pectoral fins, very small and thin scales, Kaykay lafken was similar to living teleost fishes, such as tuna, sailfish or swordfish,” Dr. Gouiric-Cavalli said.
“The evidence also indicates that it was piscivorous, that is, it fed on other fish.”
“In fact, one of the specimens of Kaykay lafken had a prey inside its stomach cavity: the column of a teleost fish.”
The fossilized remains of the new species were found in the Neuquén Basin, Patagonia, Argentina.
“We made an exhaustive review of morphological characters of holostean and teleostean fishes and explore through a cladistic analysis the phylogenetic relationships of the new species,” the paleontologists said.
“Kaykay lafken is retrieved among Pachycormiformes as being the sister taxon of the macrocarnivorous clade composed of Orthocormus and Hypsocormus.”
“Among Pachycormiformes the pattern of relationships mostly agrees with previous hypotheses, although our study highlights the still poor knowledge of the anatomy of this group.”
The discovery is reported in a paper in the Journal of Systematic Palaeontology.
Soledad Gouiric-Cavalli & Gloria Arratia. 2021. A new Pachycormiformes (Actinopterygii) from the Upper Jurassic of Gondwana sheds light on the evolutionary history of the group. Journal of Systematic Palaeontology 19 (21): 1517-1550 ; doi: 10.1080/14772019.2022.2049382
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