Yangtzedonta是双壳类吗?

对Yangtzedonta pri mitivaYu模式标本(标本登记号:84430)的化石保存类型进行讨论,确认这应当是一枚单壳瓣实体标本,而非内模标本,由此判断,余汶(1985;Yu,2005)所描述的肌痕实际上是不存在的。所谓的"片状齿突"(余汶,1985)或"片状脊"(Yu,2005)很可能是外来的附加物,并非壳体的组成部分。无论如何,84430标本现有的形态证据尚不足于将它与双壳类联系在一起。

The Bivalve Yangtzedonta is not the Brachiopod Xianfengella

Abstract The alleged ＂holotype＂of the bivalve Yangtzedonta primitiva Yu.1985 figured by Qian （2001） is a broken and distorted specimen of the brachiopod Xianfengella prima He and Yang, 1982 and not the holotype of Y. primitiva. Qian contends that the oldest recognized monoplacophoran, Maikhanella pristinis （Jiang, 1980）, is neither a monoplacophoran nor the oldest molluscan fossil in the Meishucunian Stage of China. Furthermore, he considers that the oldest bivalve Xianfengoconcha eUiptica Zhang, 1980 is an inarticulate brachiopod, not a mollusc. WatsoneUa yunnanensis （He and Yang, 1982）, is associated with Yangtzedonta primitiva Yu but indicates no evolutionary relationship between the Classes Rostroconchia and Bivalvia in the Lower Cambrian Zhongyicun Member of the Yuhucun Formation. Qian＇s confusion in using non-molluscan fossils to discuss the early evolution of shelled molluscs also confuses the basic concepts of the respective groups.

Yangtzedonta is Undoubtedly a Junior Synonym of Xianfengella

With the verification of the type specimen by six experts from the Nanjing Institute of Geology and Palaeontology, the specimen of Xianfengella prima He and Yang, 1982 described by Qian （Qian, 2001, flge2： la-c） is confirmed to be the holotype specimen （NIGP. 84430） of Yangtzedonta primitiva Yu, 1985, and consequently, Yu Wen＇s view that they are not the same specimen is impractical. This fact demonstrates that Yangtzedonta primitiva Yu, 1985 is undoubtedly a junior synonym of Xianftngella prima He and Yang, 1982, and is invalid. Qian＇s conclusion （Qian, 2001 ） that no bivalve appeared in the early Meishucunian Stage of the Early Cambrian is rational.

Yangtzedonta and the early evolution of shelled molluscs

The holotype of Yangtzedonta Yu, 1985 and its type species, Y. primitiva Yu, 1985, is an incomplete specimen of Xianfengella prima He et Yang, 1982. Therefore, based on the principle of priority, the names Yangtzedonta and Y. primitiva Yu (1985) should be abandoned. The fact that ventral valve of Xianfengella is bilaterally symmetrical indicates that they are not the left valve of a bivalved mollusc, as originally proposed by Yu. At present, the oldest certain bivalve is Xianfengoconcha elliptica Zhang, which occurs in the Early Cambrian Qiongzhusi Stage in China. The oldest known rostroconch is Heraultipegma yunnanensis He et Yang, which first occurs in the third small shelly fossil assemblage zone of the Early Cambrian Meishucunian Stage. The oldest known monoplacophoran, Maikhanella pristinis (Jiang), first occurs in the first small shelly fossil assemblage zone (Meishucunian Stage). Evidence derived from analyses of shell morphology, mode of growth, histology, and stratigraphic occurrence suggests

关于“扬子蛤属是先锋贝属无疑”的质疑

2005年,地质学报(英文版,79卷第6期)同时刊出了余汶、钱逸关于扬子蛤(Yangtzedonta)与先锋贝(Xianfengella)是否为同一化石的争论文章。这一争论由来已久,引起多方关注。笔者详细观察了保存于中国科学院南京地质古生物研究所标本馆的余汶(1985)的Yangtzedonta primitivaYu正模标本(标本登记号:84430号)和钱逸(2001)的Xianfengella等模标本(登记号:125018-125022),认为84430号标本是一枚发育有特殊后接合缘构造、形态较为奇特的小壳化石。尽管钱逸(2001)称拥有与84430号标本相似的"更多、更精美的同类标本"和"完整个体",但他不仅从未展示具有与84430号标本相似后接合缘等形态构造的图影,还以与实际形态不相符的失真素描图等不实依据,混淆了84430号标本与Xianfengella在形态构造和壳体大小等方面的真实区别,断言84430号标本是一块Xianfengella的破碎标本,坚称"扬子蛤属是先锋贝属无疑"(地质学报(英文版),79卷第6期第777页)。对此,笔者提出质疑。