The first articulated skull roof and braincase of <i>Melvius chauliodous</i> (Amiidae, Vidalamiinae) from the Upper Cretaceous Kirtland Formation, San Juan Basin, New Mexico

A new, exceptionally well-preserved articulated skull roof and braincase of <i>Melvius chauliodous</i>, from the Kirtland Formation of New Mexico, reveals new features that provide detailed osteological information for <i>Melvius</i>, thus allowing for a reassessment of characters that defines the genus, its two recognized species <i>M</i>. <i>chauliodous</i> and <i>M</i>. <i>thomasi</i>, and its phylogenetic relationships within Vidalamiinae. The new features include the presence of dermopterotic rays (‘ribs’) and parietal ray bundles, previously unknown for both species of <i>Melvius</i>. The presence of elongated dermopterotic rays, a feature previously considered to be distinctive for the genus <i>Calamopleurus</i>, and tribe Calamopleurini, is now documented in <i>Melvius</i>, but these rays differ in their point of origination at the posteromedial corners of both dermopterotics. Bundles of short fan-shaped rays emanating from below the posterolateral corners of the parietals are also documented in both species of <i>Melvius</i>. <i>Melvius</i> was previously placed in the tribe Vidalamiini (Subfamily Vidalamiinae), but because it shares some unique features with members of the tribe Calamopleurini and the genus <i>Calamopleurus</i>, its placement within Vidalamiini, and the recognition of these two distinct clades (tribes) within Vidalamiinae, are not supported in our phylogenetic analysis. Previous characters distinguishing <i>Melvius</i> species, particularly differences in postinfraorbital ornamentation between <i>M</i>. <i>chauliodous</i> and <i>M</i>. <i>thomasi</i>, are considered dubious. However, other features may serve to determine interspecific variation or differences. For the present, we retain both species until more definitive material of <i>M. thomasi</i> is described.