Earlier we looked at Falcatus, an Early Carboniferous ratfish with a diphycercal tail, like that of a teleost. Today, we look at another ratfish with a derived body plan, Belantsea (Figs. 1,2) as it enters the large reptile tree (LRT, 1500 taxa).
Figure 1. Belantsea from Lund 1989 (black and white) and from Long 1995, where the liver was misinterpreted as a pectoral fin (color). Be careful of the red one where the artist made a mistake on the liver.
Due to the anterior migration of the jaw joint
and several other traits, Belantsea nests with Chimaera, rather than Falcatus, with which it shares a diphycercal tail. I would not call Belantsea ‘transitional’ between the two morphologies because it has evolved away from that unknown or untested last common ancestor. Due to the small number of ratfish in the LRT, at present it is transitional.
FIgure 1. Belantsea in situ with DGS methods used to identify skull bones and a vestigial anal fin, as in Falcatus (Fig. 3). The premaxillalry beak is similar to the one in Chimaera (Fig. 4).
Using the pectoral fins for propulsion
is what modern ratfish do, a trait pioneered by a more primitive sister to Belantsea, a ratfish with the look and proportions of a frogfish.
Figure 3. Falcatus traced with DGS methods with reconstructed freehand image. Note the vestigial anal fin beneath the large tail fin.
Technical note:
MacClade tells me I can no longer add more taxa, now that I have reached the 1500 mark. No worries. Now that the structure is firm, smaller clades can be tested on their own.
References
Long JA 1995. The rise of fishes. The Johns Hopkins University Press, Baltimore and London.
Lund R 1989. New petalodonts (Chondrichthyes) from the Uppper Mississippian Bear Gulch limestone (Namurian E2b) of Montana. Journal of Vertebrate Paleontology 9(3):350–369.
