Momipites的几个先驱种在我国下第三系的发现——兼评Carya的北美起源说

DISCOVERY OF SOME FORERUNNER SPECIES OF MOMIPITES FROM LOWER TERTIARY OF CHINA

我国早第三纪早期沉积中具孔类花粉相当普遍,除榆科和桦科花粉占有显著位置外,胡桃科的具三孔花粉也很常见,这类花粉的鉴定和对它在孢粉地层学上的意义尚未引起我国学者的重视。笔者近年来在我国古新统和下始新统发现的一些与胡桃科Engelhardia类花粉相似、可归于Momipites Wodehouse,

In the Early Tertiary of East China the occurrences of triporate pollen of Juglandaceae are quite common in addition to much more pollen belonging to Ulmaceae and Betulaceae. But little attention has yet been paid to their palynostratigraphic uses and morphological evolution. In recentyears, following the records of some species in North America, we have found some species assigned to the genus Momipites of Juglandaceae, which display a peculiar morphology and limited stratigraphic range. As the key species for both mainlands, they have a similar morphology and lasted a parallel period in history. Their earliest elements occurred in the upper Cretaceous, and then flourished in the Palaeocene, but most of them became rapidly extinct at the end of Palaeocene, with only a few species extending into the early Eocene. Palynologically the discovery of these fossils in China supports A. Graham's (1972) hypothesis that similar mixed mesophilic floras are developed both in Asia and in eastern North America during the Early Tertiary. The present paper is to describe several forerunner species of Momipites, viz., Momipites tenuipolus Anderson, M. amplus (Leffingwell) Nichols, 1973, M. triradiatus Nichols, 1973, M. triletipol-lenites (Rouse) Nichols, M. triangulus and M. polanulatus, which are correlated with those of North America in stratigraphic distribution (Text-table, 1). Comments are also made on Nichols's (1973) suggestion on North American origin of Carya. The morphogenetic trend as he pointed out, that Carya evolved from the basic triporate Juglandace(?)e pollen (exemplified by the coryloides group) was obvious and Momipites amplus (Leffingwell, 1971) Nichols, 1973 might be regarded as the ancestral form or an 'intermediate' between Momipites coryloides and Carya. However, since Momipites amplus has rarely been found from the Palaeocene of several localities in East China, the hypothesis on North American origin of Carya has not been justified.