The primitive arowana (Osteoglossum) enters the LRT

Osteoglossum formosum (Cuvier 1829; up to 2m in length; Figs. 1, 2) is the extant arowana or bonytongue. A facultive air breather, the slow-moving, heavily-scaled arowana feeds on prey just above the water. Fossils extend back to the Late Jurassic. The pelvic fins are reduced to strands. In the large reptile tree (LRT, 1516 taxa, Fig. 3), Osteoglossum nests with Early Jurassic Dapedium.

Figure 1. The arowana, an Amazon River predator, nests with Late Jurassic Dapedium in the LRT.

Figure 1. The arowana, an Amazon River predator, nests with Late Jurassic Dapedium in the LRT. The pink dot indicates the position of the pelvic fins, absent in the skeleton below, present in the specimen above.

I hope the DGS colors added to these fish skulls
make them more accessible for learning. Consider this a starting point on your own academic journey and learn as much as you can on your own.

FIgure 2. Osteoglossum skull with colors added to identify bones.

FIgure 2. Osteoglossum skull with colors added to identify bones.

And if you ever wanted to swim with a Jurassic fish,
you don’t have to start with a drop of blood from a mosquito. Just jump into the Amazon, the Nile or any of the rivers of Borneo and Western Australia. Prior to the split of these exclusively freshwater fish, all these areas were united at Pangaea and Gondwana.

For that matter
the walking catfish (Clarias) will take you back to the Silurian (430 mya), and it will get out of the water to walk with you! Or the headless lancelet (Amphioxous) will take you back to the Cambrian (550mya), about as far back as swimming chordates go.


References
Cuvier GCLD 1829. Le Règne Animal distribué d’apres son organisation, pour servir de base a l’histoire naturelle des animaux et d’introduction a l’anatomie comparée. Avec figures dessinées d’après nature. Nouvelle édition, revue et augmentée. Tome V. Suite et fin des Insectes. Par M. Latreille. Déterville & Crochard, Paris, i-xxiv + 556pp.

The reason the freshwater fish arowana live across the sea

wiki/Dapedium
wiki/Osteoglossum
wiki/Arowana

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