The origin of cephalopods inferred from shell structure, ontogeny and anatomy

我们的研究结果包括四个主要主题。(1)通过将“活化石”鹦鹉螺与其他头足类和软体动物的性状状态进行比较，确定了鹦鹉螺的半胚性或半胚性性状。(2)根据鹦鹉螺胚胎的个体发生资料，提出了头足类体形起源于原始针叶类的新假说。(3)通过对颌骨化石的详细检查，揭示了白垩纪现代型鞘翅目头足类动物的高度多样性。(4)推断白垩纪末期菊石灭绝的原因是海洋中初级生产者的减少。

The consequences of our research include four main topics. (1) Apomorphic or plesiomorphic characters were determined in "living fossil" Nautilus pompilius by comparing characters states of Nautilus with those of other cephalopods and molluscs. (2) Based on ontogenetic data on Nautilus embryo, a new hypothesis was proposed concerning the origin of cephalopod body plan from a primitive conchiferan stage. (3) High diversity of modern-type coleoidean cephalopods in the Cretaceous was revealed by detailed examinations of fossil jaws. (4) The cause of the end-Cretaceous extinction in ammonoids was inferred to be a decline of primary producers in the ocean.