Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA.
Proc Biol Sci. 2009 Dec 22;276(1677):4303-8. doi: 10.1098/rspb.2009.1343. Epub 2009 Sep 30.
Sauropodomorph dinosaurs include the largest land animals to have ever lived, some reaching up to 10 times the mass of an African elephant. Despite their status defining the upper range for body size in land animals, it remains unknown whether sauropodomorphs evolved larger-sized genomes than non-avian theropods, their sister taxon, or whether a relationship exists between genome size and body size in dinosaurs, two questions critical for understanding broad patterns of genome evolution in dinosaurs. Here we report inferences of genome size for 10 sauropodomorph taxa. The estimates are derived from a Bayesian phylogenetic generalized least squares approach that generates posterior distributions of regression models relating genome size to osteocyte lacunae volume in extant tetrapods. We estimate that the average genome size of sauropodomorphs was 2.02 pg (range of species means: 1.77-2.21 pg), a value in the upper range of extant birds (mean = 1.42 pg, range: 0.97-2.16 pg) and near the average for extant non-avian reptiles (mean = 2.24 pg, range: 1.05-5.44 pg). The results suggest that the variation in size and architecture of genomes in extinct dinosaurs was lower than the variation found in mammals. A substantial difference in genome size separates the two major clades within dinosaurs, Ornithischia (large genomes) and Saurischia (moderate to small genomes). We find no relationship between body size and estimated genome size in extinct dinosaurs, which suggests that neutral forces did not dominate the evolution of genome size in this group.
蜥脚形亚目恐龙包括有史以来最大的陆地动物，有些恐龙的体重是非洲象的 10 倍。尽管蜥脚形亚目恐龙的体型定义了陆地动物体型的上限，但仍不清楚它们的基因组是否比它们的姐妹分类群——非鸟兽脚亚目恐龙——更大，或者恐龙的基因组大小与体型之间是否存在关系，这两个问题对于理解恐龙基因组进化的广泛模式至关重要。在这里，我们报告了 10 种蜥脚形亚目恐龙的基因组大小推断。这些估计值是从贝叶斯系统发育广义最小二乘方法得出的，该方法生成了与现存四足动物骨细胞腔体积相关的回归模型的后验分布。我们估计，蜥脚形亚目恐龙的平均基因组大小为 2.02pg（物种平均值范围：1.77-2.21pg），这一数值处于现存鸟类的上限范围内（平均值为 1.42pg，范围：0.97-2.16pg），接近现存非鸟类爬行动物的平均值（平均值为 2.24pg，范围：1.05-5.44pg）。研究结果表明，灭绝恐龙的基因组大小和结构的变异低于哺乳动物的变异。在恐龙的两个主要分支中，蜥脚形亚目（大基因组）和兽脚亚目（中等至小基因组）之间存在显著的基因组大小差异。我们在灭绝恐龙中没有发现体型和估计的基因组大小之间存在关系，这表明在这个群体中，中性力量并没有主导基因组大小的进化。
