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.一件产自美国新墨西哥州柯特兰组（Kirtland Formation）、保存极为完好的关节连接型梅尔维亚鱼（*Melvius chauliodous*）颅顶与脑颅标本，为梅尔维亚鱼属提供了详尽的骨骼学信息，揭示了此前未被记录的全新特征，借此可重新评估界定该属及其两个已确认物种——*M. chauliodous*与*M. thomasi*——的形态特征，以及该属在维达米亚鱼亚科（Vidalamiinae）内的系统发育关系。本次发现的全新特征包括膜翼耳骨鳍条（dermopterotic rays，俗称‘肋条’）与顶骨鳍束（parietal ray bundles），这两类结构此前在梅尔维亚鱼的两个物种中均未被发现。其中延长的膜翼耳骨鳍条曾被认为是扁颌鱼属（*Calamopleurus*）与卡拉姆普莱鲁族（Calamopleurini）的标志性特征，如今在梅尔维亚鱼中也得到了确认，但该类鳍条的起源点位于两块膜翼耳骨的后内侧角，与扁颌鱼属存在差异。此外，从顶骨后外侧角下方延伸出的短扇形鳍束，也在梅尔维亚鱼的两个物种中均有发现。梅尔维亚鱼此前被归入维达米亚鱼族（Vidalamiini），隶属于维达米亚鱼亚科，但本研究的系统发育分析显示，由于该属与卡拉姆普莱鲁族成员及扁颌鱼属共享部分独有特征，因此其归入维达米亚鱼族的分类地位，以及维达米亚鱼亚科内存在这两个独立演化支（族）的观点，均未得到支持。此前用于区分梅尔维亚鱼物种的形态特征，尤其是*M. chauliodous*与*M. thomasi*在眶后纹饰上的差异，被认为是存疑的。不过仍有其他特征可用于区分两物种间的种间变异。在获得更完整的*M. thomasi*标本以供正式描述之前，我们暂时保留这两个物种的分类地位。