The halibut and electric eel enter the LRT together
for some reason this headline did not print originally.
A pleasant and unexpected surprise today.
The Atlantic halibut (genus: Hippoglossus; Fig. 1) and the electric eel (genus: Electrophorus; Fig. 2) enter the large reptile tree (LRT, 1480 taxa) together with high Bootstrap values. Their skulls, other than the migration of the eyeball in the halibut, and being flat and rotated in vivo to lie upon the sea floor, are nearly identical.
Both of these specialized fish are derived
from a sister to the more primitive bowfin (genus: Amia calva).
Electrophorus (Linneaus 1766) is the extant electric eel. Not wide and flat, the ovate in cross-section murky water predator has likewise lost its cheek bones, narrowed the skull roof and came to rely on its toothy premaxilla for biting.
In traditional cladograms
these three taxa do not nest together except as bony fish in the clade Actinopterygii.
A bothersome conclusion is arising.
The LRT if recovering relationships that have been overlooked by prior academic workers, as it did in pterosaurs, birds, basal reptiles, basal tetrapods, whales, bats, snakes, caeids, mesosaurs, turtles and a long list of other taxa.
Amia calva (Linneaus 1766; up to 70cm in length) is the extant bowfin, a basal fish related to gars, able to breathe both water and air. Rather than two dorsal fins, an single elongate undulating fin is present. Hatchlings look like tadpoles or miniature placoderms. The squamosal an quadratojugal are absent. The postfrontal is fused to the fused frontal + parietal. In contrast, the lacrimal and jugal break apart into several bones.
Electrophorus electricus (originally Gymnotus electricus, Linneaus 1766; Gill 1864; up to 2m in length) is the extant electric eel, an obligate air breather nesting between Amia and Hippoglossus. The shape of the skull is like Amia, but the narrow dorsal bones and lack of lateral facial bones is like Hippoglossus. Electric organs that deliver shocks to enemies and prey make up 80% of the body.
Hippoglossus hippoglossus (Linneaus 1758; up to 4.7m in length) is the extant Atlantic halibut, one of the flounders, a fish that lives its life on its pale blind side. The lower eye migrates to the dark and camouflaged upper side as maturity approaches.
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
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)