Abstract：
OBJECTIVE: The complexity of fossil forest ecosystems is difficult to reconstruct due to the fragmentary nature of the fossil record. However, detailed morpho-anatomical studies of well-preserved individual fossils can provide key information on tree growth and ecology, including in biomes with no modern analog such as the lush forests that developed in the polar regions during past greenhouse climatic episodes.
METHODS: We describe an unusual-looking stem from Middle Triassic (ca 240 Ma) deposits of Antarctica with over 100 very narrow growth-rings and conspicuous persistent vascular traces through the wood. Sections of the specimen were prepared using the cellulose acetate peel technique to determine its systematic affinities and analyse its growth.
RESULTS: The new fossil shows similarities with the form genus Woodworthia and with conifer stems from the Triassic of Antarctica, and is assigned to the conifers. Vascular traces are interpreted as those of small branches retained on the trunk. Growth-ring analyses reveal one of the slowest growth rates reported in the fossil record, with an average of 0.2 mm/season. While the tree was growing within the Triassic polar circle, sedimentological data and growth-ring information from other fossil trees, including from the same locality, support the presence of favorable conditions in the region.
CONCLUSIONS: The specimen is interpreted as a dwarf conifer tree that grew under a generally favorable regional climate but whose growth was suppressed due to stressful local site conditions. This is the first time that a tree with suppressed growth is identified as such in the fossil record, providing new insights on the structure of polar forests under greenhouse climates and, more generally, on the complexity of tree communities in deep time.
METHODS: We describe an unusual-looking stem from Middle Triassic (ca 240 Ma) deposits of Antarctica with over 100 very narrow growth-rings and conspicuous persistent vascular traces through the wood. Sections of the specimen were prepared using the cellulose acetate peel technique to determine its systematic affinities and analyse its growth.
RESULTS: The new fossil shows similarities with the form genus Woodworthia and with conifer stems from the Triassic of Antarctica, and is assigned to the conifers. Vascular traces are interpreted as those of small branches retained on the trunk. Growth-ring analyses reveal one of the slowest growth rates reported in the fossil record, with an average of 0.2 mm/season. While the tree was growing within the Triassic polar circle, sedimentological data and growth-ring information from other fossil trees, including from the same locality, support the presence of favorable conditions in the region.
CONCLUSIONS: The specimen is interpreted as a dwarf conifer tree that grew under a generally favorable regional climate but whose growth was suppressed due to stressful local site conditions. This is the first time that a tree with suppressed growth is identified as such in the fossil record, providing new insights on the structure of polar forests under greenhouse climates and, more generally, on the complexity of tree communities in deep time.
摘要：
目的：由于化石记录的零碎性质，化石森林生态系统的复杂性很难重建。然而,对保存完好的个体化石进行详细的形态解剖学研究可以提供有关树木生长和生态的关键信息，包括没有现代类似物的生物群落，例如在过去的温室气候事件中在极地地区发展的郁郁葱葱的森林。
方法：我们描述了来自南极洲中三叠纪（约240Ma）沉积物的不寻常的茎，具有超过100个非常狭窄的生长环和穿过木材的明显持久的血管痕迹。使用醋酸纤维素剥离技术制备样品的切片，以确定其系统亲和力并分析其生长。
结果：新化石显示出与伍德沃斯利亚属和南极洲三叠纪针叶树茎的相似之处，并被分配给针叶树。血管痕迹被解释为保留在躯干上的小分支的痕迹。生长环分析揭示了化石记录中报告的最慢的增长率之一，平均每季0.2毫米。当树在三叠纪极圆中生长时，来自其他化石树的沉积学数据和生长环信息，包括来自同一个地方的，支持该地区存在有利条件。
结论：该标本被解释为矮针叶树，在普遍有利的区域气候下生长，但由于当地条件恶劣，其生长受到抑制。这是第一次在化石记录中发现生长受到抑制的树，提供对温室气候下极地森林结构的新见解，更一般地说,深入了解树木群落的复杂性。
方法：我们描述了来自南极洲中三叠纪（约240Ma）沉积物的不寻常的茎，具有超过100个非常狭窄的生长环和穿过木材的明显持久的血管痕迹。使用醋酸纤维素剥离技术制备样品的切片，以确定其系统亲和力并分析其生长。
结果：新化石显示出与伍德沃斯利亚属和南极洲三叠纪针叶树茎的相似之处，并被分配给针叶树。血管痕迹被解释为保留在躯干上的小分支的痕迹。生长环分析揭示了化石记录中报告的最慢的增长率之一，平均每季0.2毫米。当树在三叠纪极圆中生长时，来自其他化石树的沉积学数据和生长环信息，包括来自同一个地方的，支持该地区存在有利条件。
结论：该标本被解释为矮针叶树，在普遍有利的区域气候下生长，但由于当地条件恶劣，其生长受到抑制。这是第一次在化石记录中发现生长受到抑制的树，提供对温室气候下极地森林结构的新见解，更一般地说,深入了解树木群落的复杂性。
