Both species of Melvius were very large. A vertebral remain of M. thomasi would have belonged to a fish with standard length (length between tip of snout and the base of the caudal fin) of 161cm (5.28ft), and there are some specimens that exceed the height of that vertebra. Total length of this species would be at least 193–205cm (6.33–6.73ft). However, M. thomasi was dwarfed by M. chauliodous, as a specimen of M. chauliodous with abdominal centra which is 6.57cm (2.59in) wide would indicate a standard length of over 2m (6.6ft), and there is even larger abdominal centra which is 7.3cm (2.9in) wide.
↑K. M. Cantalice, A. M. Martinez-Melo, and V. A. Romero-Mayén. 2019. The paleoichthyofauna housed in the Colección Nacional de Paleontología of Universidad Nacional Autónoma de México. Zoosystematics and Evolution 95(2):429-452
12L. J. Bryant. 1987. A new genus and species of Amiidae (Holostei; Osteichthyes) from the Late Cretaceous of North America, with comments on the phylogeny of the Amiidae. Journal of Vertebrate Paleontology 7(4):349-361
↑L. Grande and W. E. Bemis. 1998. A comprehensive phylogenetic study of amiid fishes (Amiidae) based on comparative skeletal anatomy. An empirical search for interconnected patterns of natural history. Society of Vertebrate Paleontology Memoir 4. Journal of Vertebrate Paleontology 18(1, suppl.):1-690