Skeletal morphology of <i>Kritosaurus navajovius</i> (Dinosauria: Hadrosauridae) from the Late Cretaceous of the North American south-west, with an evaluation of the phylogenetic systematics and biogeography of Kritosaurini
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The osteology of the hadrosaurid dinosaur <i>Kritosaurus navajovius</i> (late Campanian of southern North America) is documented in detail, and the taxonomy and phylogenetic relationships of the genus are revised. <i>Kritosaurus</i> is rediagnosed based on the extensive length of the dorsolateral margin of the maxilla and a unique combination of characters that includes a jugal with orbital constriction deeper than infratemporal one, infratemporal fenestra greater than orbit and with dorsal margin greatly elevated above dorsal orbital margin in adults, frontal participating in orbital margin, and paired caudal parasagittal processes of nasals resting over frontals. The taxonomy of numerous hadrosaurid specimens previously referred to <i>Kritosaurus</i> is reassessed; the vast majority of these cannot be positively referred to <i>Kritosaurus</i>. One exception is a specimen collected from the Cerro del Pueblo Formation that extends the geographical range of <i>K. navajovius</i> further south in Laramidia, to present-day northern Mexico. <i>Anasazisaurus</i> is regarded a junior synonym of <i>Kritosaurus</i>; their holotypes are indistinguishable from each other when considering the overlapping elements. However, many characters support distinction of <i>Naashoibitosaurus ostromi</i> as a valid taxon. <i>Kritosaurus</i>, consisting of the sister species <i>K. navajovius</i> and <i>K. horneri</i>, is deeply nested within Saurolophinae as a member of Kritosaurini. The latter clade includes also <i>Naashoibitosaurus</i>, <i>Gryposaurus</i>, and the South American <i>Secernosaurus</i>. Kritosaurini is characterized by a rostral nasal dorsal process not reaching the rostral margin of the narial foramen, frontal with triangular rostrolateral projection ending in a narrow apex (convergent in Brachylophosaurini), and a subrectangular dorsal region of infratemporal fenestra, among other characters. Kritosaurin hadrosaurids are hypothesized to have originated in southern Laramidia no later than the early Campanian. Subsequently, members of the clade reached northern Laramidia and South America via dispersal no later than the early and late Campanian, respectively.
本研究对鸭嘴龙类（hadrosaurid）恐龙纳瓦霍克里托龙（*Kritosaurus navajovius*，北美南部晚坎潘期）的骨骼解剖学特征进行了详细记述，并修订了该属的分类学与系统发育关系。基于上颌骨背外侧缘的极长延伸，以及如下独特特征组合，本研究重新诊断了克里托龙属：颧骨的眼窝收缩深度大于颞下收缩；成体个体的颞下孔大于眼窝，且其上缘显著高于眼窝背缘；额骨参与构成眼窝边缘；成对的鼻骨尾侧矢状突架于额骨之上。此前被归入克里托龙属的大量鸭嘴龙类标本的分类学地位得到重新评估；其中绝大多数无法被可靠地归属于克里托龙属。唯一例外是一件采自塞罗德尔普埃博组的标本，该标本将纳瓦霍克里托龙的地理分布范围向南拓展至拉腊米迪亚古陆现今的北墨西哥境内。阿纳萨齐龙（*Anasazisaurus*）被视为克里托龙属的次同物异名；对比二者的重叠骨骼部分时，其正模标本无法被明确区分。然而，诸多形态特征支持奥斯特罗姆纳修比托龙（*Naashoibitosaurus ostromi*）作为独立有效分类单元的地位。克里托龙属包含姐妹种纳瓦霍克里托龙与霍纳克里托龙（*K. horneri*），其在赖氏龙亚科（Saurolophinae）中处于较深的嵌套位置，隶属于克里托龙族（Kritosaurini）。该演化支还包含纳修比托龙、格里波龙（*Gryposaurus*）以及南美类群秘龙（*Secernosaurus*）。克里托龙族的鉴别特征包括：鼻骨吻侧背突未延伸至鼻孔孔的吻侧边缘；额骨具三角形吻侧外侧突起，末端收窄为尖状（该特征在短冠龙族（Brachylophosaurini）中存在趋同演化）；颞下孔的背侧区域呈亚矩形等诸多形态特征。研究推测克里托龙族鸭嘴龙类最早起源于拉腊米迪亚古陆南部，时间不早于早坎潘期。随后该演化支的类群分别不晚于早坎潘期与晚坎潘期，通过扩散抵达拉腊米迪亚北部与南美地区。
