硅藻鼠科(哺乳纲,啮齿目)与亚洲中始新世啮齿类的双脊齿(英文)

THE DIATOMYIDAE(MAMMALIA,RODENTIA)AND BILOPHODONTY IN MIDDLE EOCENE ASIAN RODENTS

亚洲特有的啮齿类硅藻鼠科自渐新世以来分布于东亚和南亚。现生硅藻鼠类的分布只限于老挝的喀斯特地区。就目前所知,这些具有豪猪型头骨-松鼠型下颌的啮齿类的颊齿都是不同程度的横向双脊齿。时代最早的硅藻鼠类产于巴基斯坦渐新世地层中,其颊齿的双脊齿构造上仍保留齿尖残迹,基本符合双脊齿型牙齿结构。至渐新世末期,硅藻鼠科的牙齿出现分化。中新世及以后硅藻鼠类的化石记录相对较少。分子生物学证据将硅藻鼠类归入Ctenohystrica,这种归属也从始新世梳趾鼠类的臼齿形态上得到一定的支持。除此之外,有关硅藻鼠类的起源问题几乎一无所知。亚洲中始新世的Hydentomys臼齿表现出轻微的双脊型,然而其他方面却与硅藻鼠类不同。另一个具双脊齿的啮齿类Dolosimus(新属)产于江苏中始新世,其具有更为发育的双脊齿,特别是臼齿型下牙。新属的不完整记录及其形态不能解决如下问题:它是否与后来出现的像硅藻鼠类和跃兔类这些具有明显双脊齿型颊齿的啮齿类有亲缘关系,或者只是这种形态发育中没有留下后继者的早期试验品。

The Asian endemic rodent family Diatomyidae is known to have inhabited eastern and southern Asia since the Oligocene.Its current distribution is limited to karstic regions of Laos.So far as known these hystricomorphous-sciurognathous rodents have some degree of transverse bilophodonty of the cheek teeth.The earliest recognized diatomyids,which are from the Oligocene of Pakistan,retain some traces of cusps on the cheek teeth,overlying the basically bilophodont tooth structure.By the end of the Oligocene there is some dental diversity within the family.Miocene and later diatomyids are relatively rare in the fossil record.Molecular evidence unites the diatomyids in the Ctenohystrica,an assignment that receives some support from the molar morphology of Eocene ctenodactyloids.Other than this connection,little is clear regarding the origin of the diatomyids.The middle Eocene Asian Hydentomys exhibits a slight degree of bilophodonty,but is otherwise unlike diatomyids.Another taxon of bilophodont rodent,Dolosimus n.gen.from the middle Eocene of Jiangsu Province,has still more precocious development of bilophodonty,especially in the lower molariform teeth.The incomplete record of this new taxon as well as its morphology cannot answer the question of whether this taxon is allied to such later appearing,strongly bilophodont rodents as diatomyids and pedetids,or is an early experiment of this striking morphological development that left no successors.