The salamanderfish and the lizardfish enter the LRT together

Updated December 16, 2019
with updates on Trachinocephalus, Lepidogalaxias and the fish subset of the LRT.

Earlier we looked at a new extant deep sea sister for the Devonian basal ray fin fish, Cheirolepis (Fig. 1). Today, we add two more overlooked extant cousins (Figs. 2,3) to the Cheirolepis branch of the the LRT.

Figure 1a. Cheirolepis fossils.

Figure 1a. Cheirolepis fossils from Devonian strata. Note the upper one leans toward acanthodians (spiny sharks).

An overlooked extant saltwater shoreline taxon
Trachinocephalus myops (Fig. 2), the blunt-nosed lizardfish, nests with Cheirolepis in the large reptile tree (LRT, 1527 taxa). A variety of living lizardfish are known. Some are deep sea denizens.

Figure 3. The extant blunt-nosed lizardfish, Trachinocephalus, nests with Calamopleurus in the LRT.

Figure 2. The extant blunt-nosed lizardfish, Trachinocephalus, nests with Calamopleurus in the LRT.

Trachinocephalus myops (originally Salmo myops and Saurus myops Forster 1801; 40 cm) is the extant blunt-nosed lizardfish. Traditionally it nests in the clade Synodontidae.

Figure 3. Lepidogalaxias, the salamander fish, with bones stained and colorized.

Figure 3. Lepidogalaxias, the salamander fish, with bones stained and colorized.

Figure 4. The salamander fish, Lepidogalaxias, in vivo. Note the bendable neck, odd for any fish.

Figure 4. The salamander fish, Lepidogalaxias, in vivo. Note the bendable neck, odd for any fish.

The salamander fish
Lepidogalaxias salamandroides (Mees 1961, 7cm in length) is the extant salamanderfish, the only fish with a neck capable of turning the head nearly at right angles to the torso. Like lungfish, the freshwater salamanderfish is capable of surviving dry seasons by burrowing into the sand.

Molecular studies
consistently recover Lepidogalaxias close to the base of the Telostei where Cheirolepis also nests (when fossils and traits are tested), but the connection has never been made until now (let me know if there is a prior citation I missed).

It is so important to use extant and extinct taxa.
For that reason alone, avoid genetic tests. The second reason is: genetic tests don’t match trait tests over deep time in this and other major clades. The third reason: lots of extant taxa go way, way back phylogenetically.

Figure x. Subset of the LRT, focusing on fish for July 2020.

Figure x. Subset of the LRT, focusing on fish for July 2020.

According to tolweb.org
“Fink (1984) referred to Lepidogalaxias as a ‘potpouri of contradictory and reductive characters’ and placed it in an unresolved trichotomy with the Salmonidae as the sister group of the Neoteleostei. The phylogenetic affinity of this bizarre little fish has been enigmatic since Mees (1961) described it as a galaxiid.”

With about 390 million years between them
it is no wonder that the lizardfish and salamander fish developed traits not seen in Cheirolepis… so did all the other fish that are derived from Cheirolepis! The wonder is, why so few traits evolved to distinguish the extant taxa from the overlooked Devonian sister?


References
Forster JR 1801. in Bloch, ME and Schneider JG editors, Systema Ichthyologiae Iconibus cx Ilustratum. Post obitum auctoris opus inchoatum absolvit, correxit, interpolavit Jo. Gottlob Schneider, Saxo. Berolini. Sumtibus Auctoris Impressum et Bibliopolio Sanderiano Commissum. i-lx + 1-584.
Mees GF 1961. Description of a new fish of the family Galaxiidae from Western Australia. J. Roy. Soc. West. Aust. 44: 33-38.

wiki/Cheirolepis
wiki/Trachinocephalus
wiki/Lepidogalaxias

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