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记述了在中国首次发现的采自辽宁黑山县八道壕矿区早白垩世晚期沙海组的一件“eu- pantotherian”(“真古兽类”)下颌骨化石。标本保存了最后两个前臼齿和4个臼齿,它以抬高的下颌角突,半臼齿化的最后一枚前臼齿,臼齿上面积增大但未发育成完整盆形的跟座,尚未形成的facet-5,及加长的最后臼齿等特点有别于所有已知的“eupantotherian”和具有雏形磨楔式臼齿的Kielantherium,被命名为一新属新种,Mozomus shikamai gen.et sp.nov.(鹿间明镇古兽),并由它而创建了一新科,Mozomuridae fam.nov. “Eupantotherian”是早期哺乳动物演化中的一个重要环节,是从无跟座的对齿兽(sym- metrodont)到具有磨楔式(tribosphenic)臼齿兽类的中间类型。早期兽类进化的成功模式是发育成具有磨楔式的臼齿,即在上臼齿上发育出原尖,而下臼齿的跟座形成由3个齿尖围成的盆状。这种结构扩大了牙齿的面积,使咀嚼切割能力更趋完善,今天的有袋类和真兽类均是如此。但在哺乳动物系统发育史上,“eupantotherian”类的化石发现不多,这给探讨具有磨楔式臼齿构造的两大门类(后兽类和真兽类)的起源带来不少困难和疑惑。而传统上的真古兽类形态分异又很大,并不是一个单系类群。其中有跟座发育较好者,如peramurans有可能更接近具有磨楔式臼齿兽类的基部位置,本文记述的Mozomus shikamai也应属于这一类型。具有雏形的被认为处于基干上的磨楔式臼齿类化石,迄今只有两种,即发现在英国早白垩世地层中的滨齿兽(Aegialodon)和蒙古早白垩世晚期Hoobor层的Kielantherium,前者仅有一颗下臼齿,后者由一枚下臼齿和一具有4颗臼齿的下牙床为代表。两种化石在分类上被归入单一的滨齿兽目(Order Aegialodontia Butler,1978),视为Boreosphenidans的基干(stem)。本文记述的Mozomus,其时代与Kielantherium的大体相当,在大小、齿式及臼齿形态上与后者也多有相近之处,但前者以其臼齿的facet-5尚未出现和跟盆发育不全等特点表明它较Kielantherium更为原始,不具备磨楔式臼齿的模式,因之不能归人Aegialodontia,而只能纳入”eupantotheri- ans”。但在后一类的组合中,Mozomus以它半臼齿化的最后前臼齿和面积增大但未发育成盆形的跟座等特点,又是组合中相当进步的类型。无论如何Mozomus的发现是在为数极少的向磨楔式臼齿模式进化的中间环节上增添了一件重要的化石标本,也增加了不少新的信息。它必会引起学者对这一进化过程的更加深入的反思和新的启示。
Describes an “eu- pantotherian” (“ancient beast”) mandible fossil that was first discovered in China from the Early Cretaceous Shahai Formation in the Badaohao mining area of Heishan County, Liaoning Province. The specimen preserved the last two premolar teeth and four molars, which elevated the mandibular angle, the last premolar teeth of the molars, the molars area increased but did not develop into a complete basin-shaped heel, has not yet formed Unlike other known “eupantotherian” and Kielantherium with rudimentary molars, the new facet-5 with longer lengthening molar is named as a new genus Mozomus shikamai gen.et sp.nov. (Cervus elaphus), and created a new family, Mozomuridae fam.nov. “Eupantotherian” is an important link in the evolution of early mammals from the sym-metrodont ) To an intermediate type with tribosphenic molars. The successful pattern of early evolution of mammals developed into wedged molars that developed apexes on the upper molars and the heel of the lower molars formed a basin shape surrounded by 3 tips. This structure expands the area of the teeth, making the ability to chew and cut more perfect today, both the bagged and real beasts. However, in the history of mammalian phylogeny, there are not many fossils found in the “eupantotherian” class, which brings many difficulties and doubts about the origins of the two major categories (after mammals and real beasts) with wedge-shaped molars. Traditionally, the morphological differentiation of ancient beasts is very large and not a monophyletic group. Among them, those with better development of the seat, such as peramurans may be closer to the wedge-shaped molars with the base of the beast position, the article described Mozomus shikamai should belong to this type. There are only two types of fossilized wedge-shaped molasse fossils believed to be on the base, namely, Aegialodon found in the Early Cretaceous strata in the UK and Kielantherium in the Hoobor layer in the late Early Cretaceous of Mongolia, with the former only There is a lower molars, the latter represented by a lower molars and a lower gum with 4 molars. Both fossils are classified as a single taxon Order Aegialodontia Butler (1978) as the stem of Boreosphenidans. The Mozomus described in this article has roughly the same age as the Kielantherium, and is similar in size, dentition and molars morphology to the latter. However, the former is characterized by the absence of facet-5 molars and incomplete hypoplasia It shows that it is more primitive than Kielantherium and does not have the wedged molars mode and therefore can not be classified as Aegialodontia but only as “eupantotherians.” However, in the latter group, Mozomus is also a fairly advanced type of combination due to its semi-molar final premolars and its enlarged but not conical shape. In any case, Mozomus’s findings add an important fossil specimen to the middle of the evolution of the very few wedge-shaped molars and add a lot of new information. It will certainly arouse scholars’ deeper reflection and new enlightenment on this evolutionary process.