Cenozoic extinctions account for the low diversity of extant gymnosperms compared with angiosperms
Cenozoic extinctions account for the low diversity of extant gymnosperms compared with angiosperms
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DOI：
10.1111/j.1469-8137.2011.03862.x
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发表时间：
2011-12-01
期刊：
影响因子：
9.4
通讯作者：
Cook, Lyn G.
中科院分区：
文献类型：
--
作者：
Crisp, Michael D.;Cook, Lyn G.
通过将裸子植物与被子植物进行比较，我们验证了人们普遍认为的裸子植物是“古老的”和“活化石”的观点。这种看法部分源于一些中生代裸子植物化石与其现存近亲（如银杏、苏铁和黎明红木）之间缺乏明显的形态差异，这表明裸子植物的进化速度一直很缓慢。基于对21个化石的matK叶绿体DNA （cpDNA）和26S核糖体DNA （nrDNA）序列的系统发育分析，我们使用贝叶斯松弛分子钟定年方法估计了裸子植物谱系的年龄和多样化率，并将这些结果与已发表的被子植物的估计结果进行了比较。新生代裸子植物的冠群明显比被子植物的冠群年轻（中位年龄：32 Ma vs 50 Ma），并且具有长而不分枝的茎，这表明与被子植物相比，裸子植物在新生代发生了主要的灭绝。在新近纪幸存的裸子植物比被子植物的多样性更慢，因为它们的灭绝率更高。与被子植物相比，现存的裸子植物群并不古老。化石记录还表明，裸子植物在渐新世和中新世的气候变化中遭受了大规模的灭绝。现存的裸子植物群体占据着不同的栖息地，其中一些可能是在进行适应性转变后幸存下来的。
We test the widely held notion that living gymnosperms are 'ancient' and 'living fossils' by comparing them with their sister group, the angiosperms. This perception derives partly from the lack of gross morphological differences between some Mesozoic gymnosperm fossils and their living relatives (e.g. Ginkgo, cycads and dawn redwood), suggesting that the rate of evolution of gymnosperms has been slow.We estimated the ages and diversification rates of gymnosperm lineages using Bayesian relaxed molecular clock dating calibrated with 21 fossils, based on the phylogenetic analysis of alignments of matK chloroplast DNA (cpDNA) and 26S nuclear ribosomal DNA (nrDNA) sequences, and compared these with published estimates for angiosperms.Gymnosperm crown groups of Cenozoic age are significantly younger than their angiosperm counterparts (median age: 32 Ma vs 50 Ma) and have long unbranched stems, indicating major extinctions in the Cenozoic, in contrast with angiosperms. Surviving gymnosperm genera have diversified more slowly than angiosperms during the Neogene as a result of their higher extinction rate.Compared with angiosperms, living gymnosperm groups are not ancient. The fossil record also indicates that gymnosperms suffered major extinctions when climate changed in the Oligocene and Miocene. Extant gymnosperm groups occupy diverse habitats and some probably survived after making adaptive shifts.