The oldest dryolestid mammal from the Middle Jurassic of Siberia

ABSTRACT—<i>Anthracolestes sergeii</i>, gen. et sp. nov., based on three isolated lower molars and several edentulous dentary fragments from the Middle Jurassic (Bathonian) Itat Formation at Berezovsk Quarry in Krasnoyarsk Territory, Russia, is the oldest and most basal representative of Dryolestidae. It shows four unambiguous synapomorphies of Dryolestidae: lower molars with unilaterally hypsodont crowns, unequal roots, and pronounced precingulid instead of cusp f, and dentary with unequal alveolar borders. The dental formula of the new taxon is i1–4, c (double-rooted), p1–4(?), and m1–4(?). <i>Anthracolestes sergeii</i>, gen. et sp. nov., is plesiomorphic relative to more derived and geologically younger dryolestids in having possibly fewer lower molars, less pronounced mesiodistal compression of lower molars, oblique protocristid, short mandibular symphysis, and shallow mandibular ramus of the dentary. Asia is most likely the place of origin for Dryolestidae, but this group is so far not known from that continent after the Middle Jurassic.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

摘要—安氏炭桩兽（*Anthracolestes sergeii*），新属新种（gen. et sp. nov.），其研究材料为产自俄罗斯克拉斯诺亚尔斯克边疆区别列佐夫斯克采石场中侏罗统（巴通阶）伊塔组的3枚孤立下臼齿与数件无齿齿骨碎片，是干兽科（Dryolestidae）已知最古老且最基干的代表类群。该类群具备干兽科4项明确的共源性状：下臼齿冠呈单侧高齿型，齿根不对称，具有显著的前齿带而非f尖，且齿骨的齿槽缘不对称。本新分类群的齿式为：门齿i1–4、犬齿c（双根）、前臼齿p1–4（？）以及臼齿m1–4（？）。相较于更衍化、地质年代更晚的干兽科类群，安氏炭桩兽保留更多祖征特征：其下臼齿数量可能更少，下臼齿的近中远中压缩程度更弱，下原脊呈倾斜状，下颌联合较短，且齿骨的下颌支较浅。干兽科最可能起源于亚洲，但目前该类群在中侏罗世之后的亚洲地层中尚无化石记录。补充数据—本文补充材料可于www.tandfonline.com/UJVP免费获取。