在這段期間,小型、有冠的鴨嘴龍科化石都被描述成獨立的屬及種。最先被描述為亞冠龍的就是鵝龍(Cheneosaurus),牠的化石是從馬蹄鐵峽谷組發現的一個頭顱骨及一副四肢骨頭、脊椎及骨盆[14]。後來,威廉·狄勒·馬修(William Diller Matthew)將美國自然歷史博物館內的編號AMNH 5340化石命名為原鵝龍(Procheneosaurus),這個化石是從蒙大拿州的雙麥迪遜組發現的[15]。在1970年代前,這兩個分類單元都承認為有效的屬,直至彼得·達德森(Peter Dodson)證明了鵝龍很有可能是賴氏龍亞科的幼體為止。雖然他最關切的是屬於恐龍公園地層的冠龍及賴氏龍,但他仍指出鵝龍應該包含了現今高棘亞冠龍的幼體[16]。這個建議後來被接納[7],但卻沒有被正式地檢驗。發現於雙麥迪遜組的原鵝龍,與其他經達德森研究的標本不同,而有理由相信原鵝龍與直至1994年才命名的斯氏亞冠龍,兩者可能是同一物種[9]。
鼻甲是薄的骨頭或軟骨,可分為兩類,各自有其功能。嗅覺鼻甲在所有四足超綱都可以見到,具有嗅覺功能。呼吸鼻甲的功能是阻止水份從蒸發流失,只可以在鳥類及哺乳動物中發現,由於現今的溫血動物較冷血動物呼吸相對較多,以支撐較高的代謝,故牠們在呼吸時會失去大量的水份[23]。在1996年,J. A. Ruben與其他科學家的電腦斷層掃描研究,指出矮暴龍、似鳥龍及亞冠龍可能沒有呼吸鼻甲,所以沒有證據牠們是溫血動物[24]。
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