Early Jurassic Ohmdenia and Strongylosteus enter the LRT

Updated December 17, 2020
with a new tracing of Strongylosteus that reveals it was nearly identical to Chondrosteus.

We’re talking about large Early Jurassic bony fish
with small teeth (or no teeth) today, one mistakenly nested by prior workers due to taxon exclusion.

Friedman 2011
reexamined Ohmdenia, who mistakenly reported, “the enigmatic actinopterygian Ohmdenia, from the Lower Jurassic (Toarcian) Posidonia Shale of Germany (Hauff 1953), is the immediate sister group of edentulous †pachycormiforms.”

Figure 1. From bottom to top: Ohmdenia in situ, as reconstructed by Friedman 2011, as traced by Friedman 2011 (colors added) and as reconstructed here.

Figure 1. From bottom to top: Ohmdenia in situ, as reconstructed by Friedman 2011, as traced by Friedman 2011 (colors added) and as reconstructed here. Note the bundling of rays to produce a pectoral fin spine here.

By contrast,
with a more accurate reconstruction and by including a wider gamut of taxa, the large reptile tree (LRT, 1685+ taxa (then, 1779 taxa now), subset Fig. 9) nests long-jawed Ohmdenia with the extant long-jawed arowana, Osteoglossum, which is not a suspension feeder (contra Friedman 2011), but an opportunistic freshwater predator and a facultative air-breather.

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

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

Osteoglossum formosum (Cuvier 1829; up to 2m in length) is the extant arowana or bonytongue. This taxon is among the most primitive of ray fin fish. The manus rays are robust. Note the long dorsal area. The pelvic fins are reduced to strands. Fossils extend back to the Late Jurassic.

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

Figure 3. The arowana, an Amazon River predator, nests with Late Jurassic Dapedium in the LRT.

The other large fish entering the LRT might be a suspension feeder
or just a predator with a large mouth lacking teeth.

New figure of Strongylosteus in lateral view.

New figure of Strongylosteus in lateral view.

Figure 1. Chondrosteus animation (2 frames) in situ and reconstructed in lateral view. This is the transitional taxon linking sturgeons to bony fish + sharks.

Figure 1. Chondrosteus animation (2 frames) in situ and reconstructed in lateral view. This is the transitional taxon linking sturgeons to bony fish + sharks.

Strongylosteus hindernburgi (originally Chondrosteus hindenburgi Pompeckj 1914; Hauff 1921; Henning 1925; Early Toarcian, Early Jurassic; 3-4.5m) is traditionally considered “related to modern sturgeons, but with a different kind of mouth.” Here Strongylosteus is little different from ChondrosteusStrongylosteus was a giant open predator cruising opens waters with a wide mouth, similar to a whale shark (Rhincodon) by homolog.

How closely is Pachycormus related to these two?
Pachycormus (Fig. 8) is just a few nodes away from Ohmdenia, in the stem bony fish portion of the LRT (Fig. 9). That’s why these phylogenetic errors popped up. More closely related taxa were omitted and reconstructions were drawn without the use of DGS.


References
Cope ED 1873. On two new species of Saurodontidae. Proceedings of the Academy of Natural Sciences of Philadelphia 25:337-339.
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.
Friedman M 2011, 2012. Parallel evolutionary trajectories underlie the origin of giant suspension-feeding whales and bony fishes. Proceedings of the Royal Society B 279, 944–951. doi:10.1098/rspb.2011.1381
Friedman M, Shimada K, Martin LD, Everhart MJ, Liston JJ, Maltese A and Triebold M 2010. 100-million-year dynasty of giant planktivorous bony fishes in the Mesozoic seas. Science 327(5968):990-993.
Hauff B 1921.Untersuchung der Fossilfundstätten von Holzmaden im Posidonienschiefer des oberen Lias Württembergs. Palaeontographica. 1921;64(1–3):1–42.
Hauff B 1953. Ohmdenia multidentata nov. gen. et nov. sp. Ein neuer grober Fischfund aus den Posidonienschiefern des Lias e von Ohmden/Holzmaden in Wü rttemburg. Neues Jahrb. Geol. P.-A. 97, 39–50.
Hennig E 1925. Chondrosteus Hindenburgi Pompeckj 1914.—Ein «Stör» des württembergischen Ölschiefers (Lias\epsilon). Palaeontographica (1846-1933), 115-134.
Linneaus C von 1766. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio duodecima, reformata. pp. 1–532. Holmiæ. (Salvius)

wiki/Bonnerichthys
wiki/Ohmdenia
wiki/Strongylosteus
wiki/Pachycormiformes

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