DISCOVERY OF NORDENSKIOLDIA(TROCHODENDRACEAE) FROM THE PALEOCENE OF ALTAI, XINJIANG AND ITS IMPLICATIONS
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Abstract:
Nordenskioldia borealis Heer, 1870, emend. Crane, Manchester et Dilcher, 1991, an extinct species of Trochodendraceae, is recognized and described from the Paleocene on the south of Ertix River of Altai city in Xinjiang. The key characteristics of these fruit specimens are that the infructescence axis has two braches with numerous sessile fruits. The axis is markedly expanded at the position where the two branches are given off. It rapidly tapers to the distal end. Fruits are subglobose or ovate in shape and schizocarpic at maturity. Each fruit is composed of 15 schizocarpic fruitlets arranged in a whorl around a central column. Specimens formerly described as seed scales of Ditaxoicladus planiphyllus Guo et Sun in Altai flora are reexamined and assigned to Nordenskioldia borealis. Based on the analysis of the geological distribution of Nordenskioldia in China, it is found that this genus occurred in four sites of China through geological time, namely, the Altai as mentioned in the present article, the Late Cretaceous Taipinglinchang Formation and Paleocene Wuyun Formation in Jiayin, Heilongjiang, and the Late Paleocene Changchang Formation in Qiongshan, Hainan. In consideration of the distribution of living species of Trochodendraceae, it is suggested that Nordenskioldia once widely distributed in China, and that it probably shrank back to the low latitude areas after Paleocene. In addition, it is concluded that Nordenskioldia has the advantage of Trochodendron in respect of adaptation to climate, and this confirms the opinion that Nordenskioldia is not the direct ancestral to Trochodendron although Nordenskioldia is currently the stratigraphically older known taxon.
