Maiaspora: the hallmark of gleichenioid ferns (Gleicheniales) from the early Carboniferous

IF 2.3 2区 地球科学 Q1 PALEONTOLOGY
Dmitriy A. Mamontov, Duncan McLean, Olga A. Gavrilova
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Abstract

The Palaeozoic origin of gleichenioid ferns (Gleicheniales) has aroused curiosity for almost a century. The oldest definite sign of this ancient clade is the spore wall ultrastructure of Radiitheca dobranyana from the Moscovian of central Europe. However, familial assignment of this fern fossil is uncertain. A comparison of its in situ spores with those of the dispersed genus Maiaspora, from the Visean, suggests that they may represent the same group of leptosporangiates. Although these spores have a common metareticuloid sculpture, the ultra‐thin structure of the dispersed counterparts remained unknown. Study of the ultrastructure of Maiaspora concava and M. panopta from central Russia and Northumberland (UK) using transmission electron microscopy shows that the wall of Maiaspora has a middle exospore layer composed of foliated lamellae. These spread from the base of the aperture slit to the subequatorial margins of kyrtome areas. The lamellae do not overlap the aperture slit and terminate at between two‐thirds and three‐quarters of the slit height. The miospores have a three‐layered exospore in the interradial areas, while non‐apertural parts of the exospore consist of two layers. Such an ultrastructure is shared by extant Gleicheniales and fossil R. dobranyana. The combined evidence from the morphology, ultrastructure and spatiotemporal distribution of Maiaspora, as well as radioisotope dating and additional plant macrofossils, suggests that the origin of the Gleicheniales stem was related to closure of the Rheic Ocean. Apparently, the first Maiaspora‐producing gleichenioids emerged as neoendemic terrestrial ferns on the peri‐Gondwanan volcanic arcs.
Maiaspora:石炭纪早期蕨类植物(Gleicheniales)的标志
近一个世纪以来,古生代褶皱蕨类植物(Gleicheniales)的起源一直引起人们的好奇。这一古老支系最古老的明确迹象是来自中欧莫斯科期的 Radiitheca dobranyana 的孢子壁超微结构。然而,这一蕨类化石的科属还不确定。将它的原位孢子与维西纪分散的 Maiaspora 属的孢子进行比较后发现,它们可能代表同一类瘦孢子虫。虽然这些孢子具有共同的元孢子雕刻,但分散的同类孢子的超薄结构仍然未知。利用透射电子显微镜对俄罗斯中部和英国诺森伯兰的 Maiaspora concava 和 M. panopta 的超微结构进行的研究表明,Maiaspora 的壁有一个由叶状薄片组成的中间外孢子层。这些薄片从孔缝基部扩散到回旋体区域的近赤道边缘。薄片不与孔缝重叠,终止于孔缝高度的三分之二到四分之三处。米孢子在柱间区域有三层外胚层,而外胚层的非柱间部分由两层组成。这种超微结构为现生的 Gleicheniales 和化石 R. dobranyana 所共有。从 Maiaspora 的形态学、超微结构和时空分布,以及放射性同位素年代测定和其他植物大化石中获得的综合证据表明,Gleicheniales 茎的起源与莱茵洋的关闭有关。显然,第一批产马亚孢子囊的格列齐尼类植物是作为新特有的陆生蕨类植物出现在近冈瓦纳火山弧上的。
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来源期刊
Papers in Palaeontology
Papers in Palaeontology PALEONTOLOGY-
CiteScore
4.50
自引率
4.30%
发文量
55
期刊介绍: Papers in Palaeontology is the successor to Special Papers in Palaeontology and a journal of the Palaeontological Association (www.palass.org). The journal is devoted to the publication of papers that document the diversity of past life and its distribution in time and space. Papers in Palaeontology is devoted to the publication of papers that document the diversity of past life and its distribution in time and space. As a sister publication to Palaeontology its focus is on descriptive research, including the descriptions of new taxa, systematic revisions of higher taxa, detailed biostratigraphical and biogeographical documentation, and descriptions of floras and faunas from specific localities or regions. Most contributions are expected to be less than 30 pp long but longer contributions will be considered if the material merits it, including single topic parts. The journal publishes a wide variety of papers on palaeontological topics covering: palaeozoology, palaeobotany, systematic studies, palaeoecology, micropalaeontology, palaeobiogeography, functional morphology, stratigraphy, taxonomy, taphonomy, palaeoenvironmental reconstruction, palaeoclimate analysis, biomineralization studies.
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