Saurichthys: a Triassic needlefish

Updated September 1, 2021
with new identifications of the skull bones in Saurichthys based on homology with the needlefish, Tylosurus. The errors in Gregory 1938 are corrected here (Fig. 1).

Saurichthys (Fig. 1) looks like a Triassic barracuda, but here in the large reptile tree (LRT, 1535 then, 1918 now taxa, subset Fig. 5) nests with the needlefish, Tylosurus (Fig. 2), which it greatly resembles overall. That was thought to be by convergence, but it is now considered by homology after reidentifying several facial bones.

Figure 1. Saurichthys, shaped like a barracuda, sister to the tuna. Note: the diagram, from Gregory 1938, lacks teeth. More complete specimens have teeth.

Figure 1. Saurichthys, shaped like a barracuda, sister to the tuna. Note: the diagram, from Gregory 1938, lacks teeth. More complete specimens have teeth.

Saurichthys sp. (Agassiz 1843; up to 1m in length; Early Triassic to Mid Jurassic) is a predatory needlefish sister with a long pointed snout and a long, barracuda-like body. Traditionally considered a member of the Saurichthyformes, that clade now appears to be a junior synonym for the previously named Belonidae and Scomberosocoidea. More than 30 species are known. Several taxa are junior synonyms.

Figure 5. Tylosurus, the needlefish, in several views. This taxon nests with Esox in the LRT.

Figure 2. Tylosurus, the needlefish, in several views. This taxon nests with Esox in the LRT.

Tylosurus acus
(Lacépéde 1803; Fig. 2) is the extant needlefish, a long-snouted, toothy sister to the Triassic needlefish, Saurichthys and the extant muskellunge, Esox (Fig. 3). Note the divided naris and new bone identities compared to the Gregory 1938 drawing.

Figure 2. The muskie (Esox masquinongy) in vivo.

Figure 3. The muskie (Esox masquinongy) in vivo.

This appears to be a novel hypothesis of interrelationships
that links previously unlinked taxa. If I missed a citation that predates this one that supports this hypothesis of interrelationships, please send me the citation.

The LRT continues to bring diverse clades of fish together,
reducing the number of clades and illuminating interrelationships.


References
Agassiz L 1832. Untersuchungen über die fossilen Fische der Lias-Formation. Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefaktenkunde, 3, 139–149.
Agassiz JLR 1835. Recherches sur les Poissons fossiles, 5 volumes. Imprimerie de Petitpierre et Prince, Neuchaatel, 1420 pp.
Agassiz JLR 1835. On the fossil fishes of Scotland. Report of the British Association for the Advancement of Science, British Association for the Advancement of Science, Edinburgh.
Gross W 1933 1936 Die Fische des baltischen Devons, Palcteontographica A 79:1-74.
Jessen 1966. in Piveteau (Ed.). Traite de paleontologie. Tome 4. L’origine des Vertebres, leur expansion dans les eaux douces et le milieu marin. Vol. 3. Actinopterygiens, Crossopterygiens, Dipneustes. Masson & Cie, Paris
Wu F-X, Sun Y-L and Fang G-Y 2018. A new species of Saurichthys from the Middle Triassic (Anisian) of Southwestern China. Vertebrata PalAsiatica 56(4):287–294. pdf

wiki/Saurichthys
wiki/Tylosurus

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