华东白垩纪暴龙类恐龙蛋化石的新发现

New evidence on fossil eggs of Cretaceous Tyrannosaurs in eastern China

华东地区虽然迄今没有发现可靠的暴龙类恐龙骨骼化石,但近年在浙江天台白垩纪赤城山组地层中发现了白垩纪巨型暴龙类恐龙产的西峡巨型长形蛋(Macroelongatoolithus xixiaensis)化石。因暴龙类恐龙目前在系统分类上被归入兽足亚目(Theropoda)暴龙超科(Tyrannosauroidea)暴龙科(Tyrannosauridae),建议巨型长形蛋化石也可采用相应分类方法,归入长形蛋化石亚目(Elongatoolithineae)巨型长形蛋化石超科(Macroelongatoolithoidea)巨型长形蛋化石科(Macroelongatoolithidae),以便对应研究。这些蛋究竟是哪一种暴龙类恐龙所产?从目前掌握资料分析,在东亚的暴龙类恐龙属种中,冠龙和帝龙个体较小,成年体长分别仅约3m和1.6m,年代更早,分别为约160Ma和130Ma,基本上可以排除在外。鹰龙和分支龙成年体长5m^6m,还不能算巨型暴龙类恐龙。只有体长达10m,甚至更大的特暴龙,似乎最有可能产下这样的巨型长形蛋。但特暴龙迄今已知的化石层位时代为晚白垩世末期的Maastrichtian期(71Ma^65Ma),而浙江的巨型长形蛋的年代则是晚白垩世早期的Turonian期(约92Ma)。这样就存在两种可能,或许是特暴龙的生存年代要上溯到约92Ma,或许这种巨型长形蛋是另一种目前尚不为人知的,生存年代在约92Ma的巨型暴龙类恐龙所产。此外,根据这些蛋化石的外形特征及其在巢穴里的分布方式可以推测,这种暴龙类恐龙,具有功能双输卵管系统,每次产卵2枚,蛋在巢穴里呈2个一组放射状排列。其蛋壳并非刚性的硬壳,而是具有一定韧性的厚牛皮纸状外壳,在重力作用下变形呈扁的长椭球形。

The giant fossil eggs, Macroelongatoolithus xixiaensis, laid by huge tyrannosaurs were recently discovered from Late Cretaceous Chiehengshan Formation （ approximately 92Ma） in Tiantai County of Zhejiang Province, though some of their fossil skull or skeleton has not yet been found in eastern China so far. Based on the taxonomy of tyrannosaurs at present, the taxonomy of their fossil egg can be proposed accordingly, i. e. Suborder： Theropoda Marsh, 1881—— Elongatoolithineae oosubord, nov. Superfamily： Tyrannosauroidea Osborn, 1905 ——Macroelongatoolithoidea oosuperfam, nov. Family： Tyrannosauridae Osborn, 1905 ——Macroelongatoolithidae oofam, nov. Elongatoolithineae oosubord, nov. Diagnosis—— elliptic elongated eggs were laid in pairs and arranged abreast around a circle in a nest. Horizon ——The Triassic to Cretaceous Macroelongatoolithoidea oosuperfam, nov. Diagnosis—— giant flat and elliptic elongated eggs were laid in pairs and arranged abreast around a circle in a nest. Horizon ——Cretaceous Macroelongatoolithidae oofam, nov. Diagnosis and Horizon ——As for oosuperfamily. Oogenus Macroelongatoolithus Li et al. , 1995 Type oospeeies Macroelongatoolithus xixiaensis Li et al. , 1995 Synonymy. 2000 Macroelongatoolithus zhangi Fang et al. Which is the tyrannosaur laid the giant Macroelongatoolithus xixiaensis？ Of excavated fossil tyrannosaurs from eastern Asia, an adult Guanlong and an adult Dilong were apparently too small, only 3m and 1.6m long respectively, to lay giant eggs, and it was of old age, approximately 160Ma and 130Ma respectively. An adult Alectrosaurus and an adult Alioramus were 5 m - 6m long respectively, and perhaps not huge enough to lay such enormous eggs. No other than a Tarbosaurus, which an adult was more than 10 m long, was an imaginabale suspect laid these giant eggs. However all known Tarbosaurus were from terminal Cretaceous Maastrichtian （71Ma-65Ma）, and were not identical with Macroelongatoolithus from early Late Cretaceous Turonian （approximately 92Ma）. It is possible that the period of Tarbosaurus perhaps was extended to 92Ma, or other unknown huge tyrannosaurs laid these giant eggs in 92Ma. The binate Macroelongatoolithus xixiaensis presented in a nest indicated that the adult female tyrannosaur produced two eggs once in her nest as other theropod, i.e. they had a pair of functional oviducts. All of Macroelongatoolithus xixiaensis, furthermore, were flat oval and suggested that their eggshell were flexible as that of some modern reptiles. These eggs would be transmogrified by gravity, especially giant eggs as Macroelongatoolithus xixiaensis.