Abstract: The hypothesis that conodonts are vertebrates has been supported by the evidence of the microstructural, topological and developmental homology of hard tissues between conodonts and vertebrates. However, this conclusion was based on the evidence from some highly derived euconodont taxa; the degree of their plesimophic to basal euconodonts still remains in question. By employing the oil-immension techniques, the authors observed tubular and atubular (parallel-and wavy-lamellar) dentine in the basal bodies of the most primitive euconodont Proconodontus tenuiserratus Miller, 1980 and Proconodontus muelleri Miller, 1969, respectively. The tubular dentine is also recognized from Granatodontus ani (Wang, 1985). Because these data represent the earliest euconodonts, these new histological data can be treated as the plesiomorphic feature of the basal euconodonts, strongly supporting that euconodonts have tight affinity with vertebrates.

Key words: euconodont, vertebrate, dentine, comparative histology

摘要： 牙形动物是脊椎动物的假说已经有牙形动物和脊椎动物之间微观构造的、拓扑学的以及发育学的同源性的证据。然而，这些结论是通过对高度进化的真牙形石属的研究获得的；它们在多大程度上代表了原始真牙形石还存在疑问。采用油浸法，在最早的真牙形石种Proconodontus tenuiserratus Miller, 1980基体中发现了管状牙本质；在Proconodontus muelleri Miller, 1969基体中识别出平行的层状、波层状等非管状牙本质；在真牙形石种Granatodontus ani (Wang, 1985)的基体中也发现了管状牙本质。这些组织学资料可以作为最原始真牙形石分子的近祖特征，为牙形石与脊椎动物的亲缘关系提供了新的证据。

关键词: 真牙形石, 脊椎动物, 牙本质, 比较组织学