摘要
Previous reports on the morphological evolution of protoconodonts and paraconodonts are reviewed. The evolutionary trends exhibited by species of the protoconodont genus Gapparodus and the paraconodont genus Westergaadodina are discussed. Based on the present study on histology, genus Paibiconus is protoconodont, while genus Yongshunella is paraconodont (fig. 1 (a)). However, the nature of Huayuanodontus has not been fully understood so far. Recently, the transitional form New Gen. Sensu Miller, 1980 of late Late Cambrian has been found in Hunan Province, South China. It is considered as the Sister-Group of Proconodontus. Moreover, another kind of transitional form of middle Late Cambrian and late Late Cambrian between Prooneotodus notundatus and Pnoconodontus, which looks like Prooneotodus notundatus in gross morphology, but has anterior and posterior costae, has also been found in Hunan, South China. This kind of transitional form is believed to be probably the real intermediate link between Prooneotodus rotundatus and Pnoconodontus, and Prooneotodus rotundatus is most probably the ancestor of Proconodontus. The two transitional forms noted above are all euconodonts by the study of their histology. Unlike the euconodonts of Post-Cambrian, the evolutionary relationships among the species of protoconodonts, paraconodonts and the primitive euconodonts could not be made clear without the histological study on them.
Previous reports on the morphological evolution of protoconodonts and paracono-donts are reviewed. The evolutionary trends exhibited by species of the protoconodont genus Gapparodus and the paraconodont genus Westergaadodina are discussed. Based on the pre-sent study on histology, genus Paibiconus is protoconodont, while genus Yongshunella is para-conodont (fig. 1(a)). However, the nature of Huayuanodontus has not been fully understood so far. Recently, the transitional form New Gen. Sensu Miller, 1980 of late Late Cambrian has been found in Hunan Province, South China. It is considered as the Sister-Group of Proconodontus. Moreover, another kind of transitional form of middle Late Cambrian and late Late Cambrian between Prooneotodus rotundatus and Proconodontus, which looks like Prooneotodus rotunda-tus in gross morphology, but has anterior and posterior costae, has also been found in Hunan, South China. This kind of transitional form is believed to be probably the real intermediate link between Prooneotodus rotundatus and Proconodontus, and Prooneotodus rotundatus is most probably the ancestor of Proconodontus. The two transitional forms noted above are all eu-conodonts by the study of their histology. Unlike the euconodonts of Post-Cambrian, the evolu-tionary relationships among the species of protoconodonts, paraconodonts and the primitive euconodonts could not be made clear without the histological study on them.
基金
This work was supported by the National Natural Science Foundation of China (Grant Nos.40372001 and 40072007)
the Research Fund for Doctoral Program of Higher Education (Grant No. 2000000127)
by the Laboratory of Palaeobiology & Stratigraphy, Nanjing Institute of Geology and Palaeontology, the Chinese Academy of Sciences (Grant No. 021306).
