Growth interruptions in silicified conifer woods from the Upper Cretaceous Two Medicine Formation, Montana, USA: implications for palaeoclimate and dinosaur palaeoecology
Growth interruptions in silicified conifer woods from the Upper Cretaceous Two Medicine Formation, Montana, USA: implications for palaeoclimate and dinosaur palaeoecology
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DOI：
10.1016/s0031-0182(03)00539-x
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发表时间：
2003-10-25
影响因子：
3
通讯作者：
Falcon-Lang, HJ
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文献类型：
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作者：
Falcon-Lang, HJ
埋藏学研究表明，大多数恐龙骨骼组合在上白垩纪（坎帕尼亚）蒙大拿州的两个医学形成起源于干旱引起的大规模死亡的洪泛平原。这一假设进一步测试，通过研究在硅化木材的柏科/杉科针叶树在古纬度48 degreesN发现与恐龙骨骼材料的年内增长模式。真正的生长轮是完全没有的，但生长中断的特点是同心，持久的区域，1-8晚材细胞宽是常见的。中断不规则地间隔开，使得例如在一个样本中沿着仅25个细胞的半径可能出现沿着四个中断，而在另一个样本中超过650个细胞宽的半径可能完全没有中断。像这样的不规则的增长模式发生在上白垩纪的森林横跨一个广泛的纬度带在美国西部内陆表明，它们是由区域气候强迫，而不是本地化的现象。生长中断记录发生短期，非周期性干扰树木生长，在一个平稳的，megathermal气候，否则有利于连续的，全年的形成层活动。生长中断的唯一可能原因是干旱引起的地下水位波动和由此产生的水分胁迫。生长模式表明，足够的水不受抑制的增长是连续多年的时间，但当水分胁迫确实发生，它重复了几个月。与现在的东非相比，那里的树木显示出非常相似的生长模式，这意味着晚白垩世西部内陆的环境是稳定的，但不稳定的潮湿环境正是巨型动物大规模死亡的可能性。像东非一样，这种环境本来有足够的承载能力，允许大型动物群在正常条件下发展，但当干旱反复发生时，这些种群将非常脆弱。(C)2003 Elsevier B. V.保留所有权利。
Taphonomic studies suggest that most dinosaur bone assemblages in the Upper Cretaceous (Campanian) Two Medicine Formation of Montana originated from drought-induced mass mortalities on the floodplain. This hypothesis is tested further by studying intra-annual growth patterns in silicified woods of cupressaceous/taxodiaceous conifers found in association with dinosaur bone material at a palaeolatitude of 48degreesN. True growth rings are completely absent, but growth interruptions characterised by concentric, variably persistent zones, 1-8 latewood cells wide are common. Interruptions are irregularly spaced so that, for example, four interruptions may occur along a radius of only 25 cells in one specimen, whilst in another specimen a radius more than 650 cells wide may completely lack interruptions. Irregular growth patterns like this occur in Upper Cretaceous woods across a broad latitudinal belt in the US Western Interior demonstrating that they resulted from regional climatic forcing rather than localised phenomena. Growth interruptions record the occurrence of short-term, aperiodic disturbances to tree growth, under an equable, megathermal climate that was otherwise favourable for continuous, year-round cambial activity. The only probable cause of growth interruption formation were drought-induced fluctuations in the water table and resultant water stress. Growth patterns suggest that sufficient water for uninhibited growth was continuously available for years at a time, but when water stress did occur, it did so repeatedly over a very few months. Comparison with present-day East Africa, where trees show very similar growth patterns, implies that the equable, but erratically humid, environment of the Late Cretaceous Western Interior was exactly the kind of setting where mass mortalities amongst megafauna might be expected. Like East Africa, this environment would have had sufficient carrying capacity to permit large herds of megafauna to develop under normal conditions, but when repeated phases of droughts struck, such populations would have been highly vulnerable. (C) 2003 Elsevier B.V. All rights reserved.