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Taken from Lund, Richard, and Grogan, E.D., 2005, Bear Gulch web site, www.sju.edu/research/bear_gulch, 14/11/2016, page last updated 2/1/2006: "Heteropetalus elegantulus is an elegantly slim little euchondrocephalan with many different tooth shapes along its jaws. It ranges to only about 4 inches in length. Skull, jaws, and dentition place it close to Debeerius. It is common in the weedier shallow water areas. There are no scales, except for a small patch at the rear of the dorsal fin of males. Lateral line canals of the head are supported by rather large highly modified scales. Heteropetalus has an almost eel-like body, a protocercal tail, rounded and very flexible pectoral fins midway up the sides of the body, and a single long flexible undulatory dorsal fin (preceded by a small fin spine). All these features indicate a maneuverer in weedy or reef-like environments as well as along the bottom. Mature males have a distinctly strengthened, hooked and denticulated posterior end of the dorsal fin; the dorsal fin of males was significantly higher than that of females. This dorsal fin dimorphism is similar to that seen in the Gouramies, modern bony tropical fish available in any pet store. They have a very small mouth, with the teeth crowded to the front of the jaws, and a variety of plucking, nipping, and crunching teeth. The jaw suspension itself is rather flexible to give it a certain amount of both lateral and fore-and-aft motion. The bright yellow spots in the dorsal view of a head are the inner ears, and the yellow is from iron oxide particles that were bio-concentrated during the life of this fish. H. elegantulus was originally described as a petalodont, but subsequent discoveries proved it to be otherwise; it is closely related to Debeerius ellefseni." This fish is clearly a male as shown by the claspers. References: Lund, R. (1977). A new petalodont (Chondrichthyes, Bradyodonti) from the Upper Mississippian of Montana. Annals of Carnegie Museum, 46 (19): 129-155. Grogan E.D. & Lund, R. (2000). Debeerius ellefseni (Fam. Nov., Gen. Nov., Spec. Nov.), an autodiastylic chondrichthyan from the Mississippian Bear Gulch Limestone of Montana (USA), the relationships of the Chondrichthyes, and comments on gnathostome evolution. Journal of Morphology, 243 (3): 219-245.