Belonostomus longirostris ( Lambe, 1902 )

Sahni, Ashok, 1972, The vertebrate Fauna of the Judith River formation, Montana, Bulletin of the American Museum of Natural History 147 (6), pp. 319-416 : 345

Belonostomus longirostris ( Lambe, 1902)

Diphyodus longirostris LAMBE, 1902, p. 30.

Belonostomus longirostris : ESTES, 1964, p. 25.

A broken rostrum and a few scales that are referable to Belonostomus longirostris have been recovered during the present investigation. Although the genus does not occur commonly in the formation, it was first reported by Lambe (1902) from the Oldman Formation as Diphyodus longirostris . It was identified three years later (Stanton and Hatcher, 1905, p. 57) from the Judith River Formation of Montana. The genus Diphyodus was put in synonymy with Belonostomus by Estes (1964, p. 25) on the basis of the similarity of the rostrum and the fragmentary scales of the lateral line system. The fragment of the rostrum (AMNH 10111) from Clambank Hollow shows the presence of two rows of teeth along the outer margin. The width of the rostrum is about 3.6 mm. The dimensions compare closely with those of the type specimen described by Lambe (1902, p. 30) in which the anterior end of the dentary is 3.5 mm. wide and the posterior width is slightly larger (4.0 mm.).

The occurrence of this marine fish in these coastal plain deposits can only be attributed to the proximity of the sediments to the sea.