Toothy Calamopleurus enters the LRT with Amia

Updated January 16, 2021
with additional taxa and some score changes Calampleurus now nests with Amia.

Short one today.
If you like fish with big teeth,
you’ll like Calamopleurus (Agassiz 1841, Early Cretaceous; Figs. 1, 2), a taxon typically considered a relative of the bowfin, Amia.

Figure 1. The skull of Calamopleurus from Long 1995 and reconstructed using DGS methods.

Figure 1. The skull of Calamopleurus from Long 1995 and reconstructed using DGS methods.

When you add in a few more taxa,
Calamopleurus is derived from Trachinocephalus, the extant blunt-nosed lizardfish (Fig. 3) in the large reptile tree (subset Fig. x), with Amia.

Figure 2. Another specimen diagram of Calamopleurus.

Figure 2. Another specimen diagram of Calamopleurus. Looks like a bowfin, but it is closer to lizardfish.

Nesting where it does in the LRT,
(Fig. x) Calamopleurus is basal to virtually all other ray fin bony fish, but Trachinocephalus is close to our own direct ancestry… and also sea horses, sailfish, catfish, spiny sharks and placoderms. That means this fish and this clade of fish had its genesis and initial radiation 300 million years earlier, in the Silurian.

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

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

It should come as no surprise
that this clade of fish also includes several hyper-toothy taxa, including Chiasmodon (Fig. 4) and Malacosteus (Fig. 5).

Figure 2. Chiasmodon from Gregory 1938, here colorized. Compared to the lizardfish, Trachinocephalus, in figure 3.

Figure 4. Chiasmodon from Gregory 1938, here colorized.

Based on the preponderance of big teeth
at the base of the big bony fish split (Fig. x), evidently ‘long, sharp teeth’ was a primitive trait later sometimes lost in both lineages.

The LRT proposes a hypothesis of interrelationships
previously untested with extant and extinct taxa from several traditional clades here (Fig. x) tested together for the first time.

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

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

LRT change:
The enigmatic wide-mouth, big-eyed fish, Doliodus, now nests with the spiny sharks, Homalacanthus and Acanthoides. a few nodes apart from Xenacanthus, which also has twin-spiked teeth.


References
Agassiz L 1833-43. Recherches sur les poissons fossiles. Imprimerie de Petitpierre et Prince, Neuchâtel.

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