CAJ | 학술논문

描述了哺乳纲柱齿兽目柱齿兽科(Docodontidae,Docodonta,Mammalia)一新属种--孙氏尖钝齿兽(Acuodulodon sunae gen.et sp.nov.).标本产于新疆东北部准噶尔盆地五彩湾地区上侏罗统牛津阶石树沟组上部(159～161 Ma),为一不完整左下颌骨及齿列.新属下臼齿具柱齿兽类典型特征:齿尖b位于齿尖a前方;齿尖c位于齿尖a后舌侧;齿尖a前舌侧发育有齿尖g.不同于其他柱齿兽,新属下臼齿无齿尖e和齿脊b-e.齿尖g和齿脊b-g很快被磨蚀掉而齿尖a和c却能保持尖锐状态,表明该动物的臼齿在生活中具备并保持切割和碾压双重功能.基于下臼齿性状特征的系统发育分析表明,柱齿兽目作为一单系类群具有显著的鉴定特征.其中尖钝齿兽和Itatodon+(Simpsonodon,Castorocauda+(Tegotherium+Sibirotherium))形成一单系子类群;但tegotheriids各分子未形成独立于柱齿兽科的单系类群.尖钝齿兽的下颌齿骨亦为典型的柱齿兽类型.齿骨内侧下部近腹缘有浅的齿后骨槽和宽大的内侧脊,但两者未延伸到下颌关节髁的基柄部.这表明尖钝齿兽的齿后骨与齿骨的连接比摩根齿兽类更为松散,其中耳在进化上更接近真正意义上的哺乳动物中耳.
묘술료포유강주치수목주치수과(Docodontidae,Docodonta,Mammalia)일신속충--손씨첨둔치수(Acuodulodon sunae gen.et sp.nov.).표본산우신강동북부준갈이분지오채만지구상주라통우진계석수구조상부(159～161 Ma),위일불완정좌하합골급치렬.신속하구치구주치수류전형특정:치첨b위우치첨a전방;치첨c위우치첨a후설측;치첨a전설측발육유치첨g.불동우기타주치수,신속하구치무치첨e화치척b-e.치첨g화치척b-g흔쾌피마식도이치첨a화c각능보지첨예상태,표명해동물적구치재생활중구비병보지절할화년압쌍중공능.기우하구치성상특정적계통발육분석표명,주치수목작위일단계류군구유현저적감정특정.기중첨둔치수화Itatodon+(Simpsonodon,Castorocauda+(Tegotherium+Sibirotherium))형성일단계자류군;단tegotheriids각분자미형성독립우주치수과적단계류군.첨둔치수적하합치골역위전형적주치수류형.치골내측하부근복연유천적치후골조화관대적내측척,단량자미연신도하합관절과적기병부.저표명첨둔치수적치후골여치골적련접비마근치수류경위송산,기중이재진화상경접근진정의의상적포유동물중이.
A new genus and species of docodontid(Docodonta,Mammalia),Acuodulodon sunae,represented by a partial left lower jaw and dentition,is described.It is from the upper part of the Shishugou Formation in the Wucaiwan area of the Junggar Basin in northeastern Xinjiang,China,with an estimated age of 159～161 Ma(Oxfordian,early Late Jurassic).The new mammal is typical of docodonts in having a cusp b in front of cusp a,a cusp c distolingual to cusp a and a cusp g mesiolingual to cusp a on lower molariforms.Differing from other docodonts,it has no cusp e or crest b-e developed on lower molariforms.Unique among docodonts.cusps a and c of the new animal maintained their sharpness while cusp g and crest b-g wore away fast,indicating that both shearing and crushing/grinding occurred in the chewing cycle and probably last for most of the life span of the animal.Phylogenetic analysis of a data matrix with 24 lower molariform characters across 15 taxa recovers a monophyletic Docodonta,which has distinct diagnostic characters in lower molariforms.Within docodonts,Docodon and Borealestes are successively basal to other docodonts;Acuodulodon and Itatodon +(Simpsonodon,Castorocauda+(Tegotherium+Sibirotherium))form a monophyletic clade.Tegotheriid genera are nested within Docodontidae,but a monophyletic tegotheriid clade composed of Tegotherium,Sibirotherium,hatodon,and Tashkumyrodon is not recovered.The dentary of Acuodulodon is typical of docodonts.It has a shallow postdentary trough and a wide and sharp medial ridge,both of which do not extend onto the medial side of the condylar peduncle,indicating looser contact between postdentary bones and the dentary than in morganucodontids,a more derived condition in the evolution toward the definitive mammalian middle ear.