在这段期间,小型、有冠的鸭嘴龙科化石都被描述成独立的属及种。最先被描述为亚冠龙的就是鹅龙(Cheneosaurus),牠的化石是从马蹄铁峡谷组发现的一个头颅骨及一副四肢骨头、脊椎及骨盆[14]。后来,威廉·狄勒·马修(William Diller Matthew)将美国自然历史博物馆内的编号AMNH 5340化石命名为原鹅龙(Procheneosaurus),这个化石是从蒙大拿州的双麦迪逊组发现的[15]。在1970年代前,这两个分类单元都承认为有效的属,直至彼得·达德森(Peter Dodson)证明了鹅龙很有可能是赖氏龙亚科的幼体为止。虽然他最关切的是属于恐龙公园地层的冠龙及赖氏龙,但他仍指出鹅龙应该包含了现今高棘亚冠龙的幼体[16]。这个建议后来被接纳[7],但却没有被正式地检验。发现于双麦迪逊组的原鹅龙,与其他经达德森研究的标本不同,而有理由相信原鹅龙与直至1994年才命名的斯氏亚冠龙,两者可能是同一物种[9]。
鼻甲是薄的骨头或软骨,可分为两类,各自有其功能。嗅觉鼻甲在所有四足超纲都可以见到,具有嗅觉功能。呼吸鼻甲的功能是阻止水分从蒸发流失,只可以在鸟类及哺乳动物中发现,由于现今的温血动物较冷血动物呼吸相对较多,以支撑较高的代谢,故牠们在呼吸时会失去大量的水分[23]。在1996年,J. A. Ruben与其他科学家的电脑断层扫描研究,指出矮暴龙、似鸟龙及亚冠龙可能没有呼吸鼻甲,所以没有证据牠们是温血动物[24]。
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