晚古生代的科达科——起源和演化的研究

中国科学院大学学报

晚古生代的科达科——起源和演化的研究

王士俊

收稿日期:1900-01-01 修回日期:1900-01-01 出版日期:1997-07-10 发布日期:1997-07-10
通讯作者: 王士俊

A Study on Origin and Evolution of Cordaitaceae in Late Paleozoic

Wang Shi-jun

Received:1900-01-01 Revised:1900-01-01 Online:1997-07-10 Published:1997-07-10
Contact: Wang Shi-jun

摘要/Abstract

摘要：

科达科Cordaitaceae植物广泛分布于晚古生代的欧美植物区和华夏植物区，目前包括3个自然属：Mesoxylon、Pennsylvanioxylon和Shanxioxylon。根据目前资料，欧美植物区只见有前两个属，而在华夏植物区这3个属则都有分布。本文详细讨论了这3个属的茎的初生构造、雄性球果穗及胚珠，认为在这3个属中Mesoxylon最原始，Pennsylvanioxylon较进化，Shanxioxylon的茎的初生构造虽具一定的原始性(如具中始式叶迹)，但其生殖器官却相当进化。因此，本文提出Shanxioxylon是一种可塑性较强的科达植物，能够适应环境的变化，最终有可能演化为新的植物类群，如某种早期的松杉类；Pennsylvanioxylon则是一种较为特化的植物，其结局是走向绝灭。结合地层中科达科化石的分布情况，本文认为最早出现的科达植物应是Mesoxylon，它可能是由某种前裸子植物演化而来，再由其演化至Shanxioxylon和Pennsylvanioxylon。由于气候和地理环境的不同，华夏植物区和欧美植物区的科达植物各自沿着不同的路线进行演化。其中，欧美植物区科达科的演化路线可能为：某种前裸子植物→Mesoxylon的较原始类型(如M．multirame，Mitrospermum bulbosum)→Mesoxylon的较进化的类型(如M．thompsonii)→Pennsylvanioxylon的较原始类型(如P．iowense)→Pennsylvanioxylon的较进化类型(如P．nauertianum，P．birame)→绝灭。华夏植物区科达植物的可能的演化路线则为：某种前裸子植物→Mesoxylon→Shanxioxylon→Pennsylvanioxylon→绝灭，或某种前裸子植物→Mesoxylon→Shanxioxylon→绝灭或演化为某种新的植物，如某种早期的松杉类。

关键词: 科达科, 晚古生代, 华夏植物区, 欧美植物区, 起源演化

Abstract:

The Cordaitaceae was widely distributed throughout the Euramerican Flora and Cathaysian Flora in the Carboniferous and Permian of the Late Paleozoic. It consists of three natural genera: Mesoxylon, Shanxioxylon and Pennsylvanioxylon. All of them can be found in the Cathaysian Flora, While in Euramerican Flora only Mesoxylon and Pennsy lvanioxylon were discovered.

The isolated organs of Mesosxylon have been identified as different organ genera:

Stem: Mesoxylon Scott et Maslen 1910. leaf: Cordaites Unger 1850. male strobilus: Gothania Hirmer 1933. female strobilus: CordaitanthusFeistmantel 1876. ovule: Mitrospermum Arber 1910. pollen: Sullisaccites Millay et Taylor 1974, Felixipollenites Millay et Tayllor 1974.

And those of Pennsylvanioxylon are:

Stem: Pennsylvanioxylon Vogenellhner 1965. leaf: Cordaites Unger 1850. male and female strobilus: Cordaitanthus Feistmantel 1876. ovule: Cardiocarpus Brongniart 1881. pollen: Florinites sensu strictu Millay et Taylor 1974.

The isolated organs of Shanxioxylon are put into the same genera as those of Pennsylvanioxylon respectively, except for the stem( named as Shanxioxylon Tian et Wang 1987). Since its stem, leaf, male strobilus and ovule are quite different from those of Mesoxylon and Pennsylvanioxylon, Shanxioxylon is considered as the third natural genus of the Cordaitaceae, which is found only in the Cathaysian Flora at present.

The stem and reproductive organs of Mesoxylon are rather primitive. Its stem is similar to that of pteridophytes. The stem of Pennsylvanioxylon is rather advanced and quite similar to that of modern conifers, but its reproductive organs are quite primitive. The stem of Shanxioxylon lies between Mesoxylon and Pennsylvaniomylon, but its reproductive organs have advanced characteristics. It is supposed that Shanxioxylon is probably a kind of plant

with great evolutionary plasticity, from which more advanced cordaites or even conifers might have been derived. In fact, stems of one species of Shanxioxylon are quite advanced. For example, it is of typical sympodial vasculature with sympodia undulate along the longitudinal direction, the same as that of modern conifers. Shanxioxylon is probably a kind of cordaites which possesses a great evolutionary potential and is a transitional type linking primitive cordaites and some primitive conifers.

In the Euramerican Flora, the earliest fossil record of cordaites is probably at Tournaisian stage of the Early Carboniferous. The appearence of cordaites, especialy the anatomical features, in this time is not clear. The only known organ with internal amatomical structures is an ovule Mitrospermum bulbosum Long. It is inferred that the cordaites in this time probably belong to Mesoxylon. At the Westphalian stage, cordaites become common, but mainly Mesoxylon,such as M. sutcliffii, M. hultirame etc., in the Lower Coal Measures, England. Later, M. sp. (cf. M. multirame or M. sutcliffii ) also occurred in early Middle Pennsylvanian, America. Pennsylvanioxylon came to appear in this time. In the Middle Pennsylvanian, cordaites in North America reached its evolutionary peak. In addition to Pennsylvanioxylon, more advanced species of Mesoxylon (i. e. M. thompsonii )appeared. At the Stephanian stage(late Later Carboniferous) cordaites began to decrease. In the Permian, cordaites became rare except a few leaf impressions. An evolutionary line of cordaites in the Euramerican Flora is proposed based on the fossil record of the Late Paleozoic:

Progymnosperm→primitive Mesoxylon (such as Mitrospermum bulbosum , Mesoxylon

sutcliffii etc. )→more advanced Mesoxylon (such as M. thompsonii )→Pennsylvan-

ioxylon→extinct.

The earliest Cathaysian cordaites were living in the age of Early Carboniferous(Visean Stage). They were all impressions of leaves. The earlist anotomically preserved cordaitean fossils are the stem of Mesoxylon sp. in coal balls of the Hongtuwa Formation(early Late Carboniferous in age), Gansu Province. Lately, in coal balls of the Taiyuan Formation(early Early Permian in age), the advanced cordaites, such as Shanxioxylon and Pennsylvanioxylon, appeared. The fossils of cordaites in China are very abundant throughout the whole Permian beds, so it is convenient for us to study the late evolution of cordaites. Based on the available information, there probably existed two evolutionary lines in the Cathaysian Flora cordaites:

1. Progymnosperm→Mesoxylon→Shanxioxylon→Pennsylvanioxylon→extinct.

2. Progymnosperm→Mesoxylon→Shanxioxylon→extinct or evolved into some

new plants(such as early primitive conifers).

Key words: Cordaitaceae, Late Paleozoic, Cathaysian Flora, Euramerican Flora, Origin, Evolution

王士俊. 晚古生代的科达科——起源和演化的研究[J]. 中国科学院大学学报.

Wang Shi-jun. A Study on Origin and Evolution of Cordaitaceae in Late Paleozoic[J]. .