在1856年,古生物學家約瑟夫·萊迪將發現於美國蒙大拿州的兩顆暴龍科前上頜骨牙齒,命名為恐齒龍;這些牙齒大而粗壯,年代屬於上白堊紀[9]。在1922年,馬修與布朗認為這些牙齒有可能是屬於蛇髮女怪龍,但由於缺乏恐齒龍的身體化石,無法確定兩者是否為同種動物,因此暫時列名為「?Deinodon libratus」[10]。不過,單靠牙齒特徵是很難去分辨不同的暴龍科,故恐齒龍今天仍被認為是疑名[7][8]。蒙大拿州的朱迪斯河組(英语:Judith River Formation)曾發現數具暴龍科骨骼,可能屬於蛇髮女怪龍,但無法確定是否為平衡蛇髮女怪龍,或是否可成立新的種[4]。蒙大拿州的一個標本(編號TCMI 2001.89.1)被發現有數個病徵,例如:受傷後癒合過的後肢、肋骨、脊椎,下頜前端患有骨髓炎,造成明顯的牙齒脫落,以及腦瘤[11][12]。
蛇髮女怪龍與艾伯塔龍非常類似,因此許多科學家曾將牠們歸類於同一屬。艾伯塔龍是在1905年被敘述、命名,而蛇髮女怪龍是在1914年被敘述、命名,若兩者屬於同一屬,艾伯塔龍將具有優先權,蛇髮女怪龍將成為艾伯塔龍的次異名。早在1922年,威廉·狄勒·馬修(英语:William Diller Matthew)與巴納姆·布朗(Barnum Brown)就曾提出蛇髮女怪龍與艾伯塔龍可能是相同動物[10]。在1970年,戴爾·羅素(英语:Dale Russell)重新研究暴龍科時,正式將蛇髮女怪龍歸類於艾伯塔龍屬的一個種[7],之後也得到很多學者的支持[24][25]。這種歸類使艾伯塔龍的地理分布與生存時期擴張。但是霍茨卻認為蛇髮女怪龍與艾伯塔龍的物種有足夠的差異,可確立牠們是獨立屬[6]。柯里認為蛇髮女怪龍、艾伯塔龍有足夠的差異,如同懼龍、暴龍,若後兩者是個別的獨立屬,蛇髮女怪龍與艾伯塔龍也可以維持個別的獨立屬狀態。柯爾更提出,在阿拉斯加州、新墨西哥州、與北美其他地點發現的未命名暴龍科化石,有助於解決這些分類爭議[4]。
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^ 2.02.1Lambe, Lawrence M. Lambe. On a new genus and species of carnivorous dinosaur from the Belly River Formation of Alberta, with a description of Stephanosaurus marginatus from the same horizon. Ottawa Naturalist. 1914, 28: 13–20.
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