Delphyodontos: a young petalodont, not a finless cannibal embryo with an enlarged abdomen

These three new identifications
reduce the possibility that Delphyodontos was a cannibal embryo.

Delphyodontus dacriformes
(Lund 1980; Bear Gulch, Late Carbonferous; second specimen, 2.9cm) was named earlier than Obrechevodus, but considered a finless embryo with a teardrop-shaped body capable of oophagy (eating siblings within the womb). The ‘abdominal enlargement’ is actually a pair of pectoral fins, as in Obruchevodus (Fig. 3) and Belantsea (Fig. 5).

Belantsea montana
(Fig. 5, Lund 1989; Early Mississipian, Early Carboniferous; 25 cm in length) is a mid-sized petalodont ratfish with typically giant, fan-like pectoral fins and a small diphycercal tail. The dark spot on the torso is the liver and other internal organs.

Petalodonts of the Carboniferous
were convergent with extant queen triggerfish (Fig. 5) in their morphology and dentition. The procumbent premaxillary dentition of triggerfish evolved to feed on coral.

I did not have firsthand access to this specimen
yet was better able to identify elements overlooked by Lund 1980 by using DGS methods and comparable specimens unavailable in 1980. Those other petalodonts (above) certainly helped.

References
Grogan ED, Lund R and Fath M 2014. A new petalodont chondrichthyan from the bear gulch limestone of montana, USA, with reassessment of Netsepoye hawesi and comments on the morphology of holomorphic petalodonts. Paleontological Journal 48 (9): 1003–1014.
Lund R 1980. Viviparity and Intrauterine Feeding in a New Holocephalan Fish from the Lower Carboniferous of Montana. Science, New Series 209(4457):687–699.
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.