寒武纪早期帽状动物壳体Lathamellids类的微细构造及其系统分类

帽状动物壳体 lathamellids 类化石包括 Lathamella caeca, Lathamella sp. nov. 以及 Lathamella symmetrica sp. nov. 三种,目前仅发现于四川峨嵋麦地坪下寒武统麦地坪组上段地层,它们皆以磷质内核方式保存.通过内核化石表面所复制的原始壳体微细构造印痕的研究表明,易漏螺类壳体为双层结构:内层——纤晶层,外层——棱柱层;其壳体原始成分可能为文石质.据上述现象推断,lathamellids 并非为磷质无绞纲腕足类,相反,而与软体动物更为接近,但其在壳腔内具—纵向中突,主要位于壳顶附近,很难与已知的任何一类软体动物直接对比,可能为一类独特的、已经绝灭了的软体动物的1个早期分支.

EARLY CAMBRIAN CAP-SHAPED LATHAMELLIDS: THEIR MICROSTRUCTURES AND SYSTEMATICS

Although original aragonitic skeleton might be rather common in the early Cambrian small shelly biota, it is scarcely found in the fossil record because of the thermodynamically unstable aragonite. However, broadly occurring syndiagenetic phosphatization has been well documented, which may have replicated the original microstructures of the calcareous skeletons through secondary apatite fillings and coats (Runnegar, 1985b). Therefore, the study of phosphatereplicated microstructures may provide an effective method to study the original microstructures and mineral composition.