Science2014-06-16 3:03 PM

恐龙的代谢率--不很快,也不很慢 Evidence for mesothermy in dinosaurs

论文摘要 

据一项新的研究报道,恐龙的代谢率曾被认为是缓慢的,使得这些现已灭绝的动物在大地上行走的步伐笨重缓慢。恐龙的代谢率不能被定性为缓慢且变温的(它反映了一种从外部进行调节的体温)或者是高度活动及恒温的(其体温是从内部进行调节的);相反,它们的代谢率处于两者之间的某个水平。恐龙可能是第一个广泛展示这种产能特征的分类学中的群体,但这种情况的存在提示恒温相对于变温的双歧性可能没有准确地代表动物世界中代谢状态的多样性。已灭绝分类群体的代谢率,尤其是恐龙的代谢率,让科学家们产生了广泛的兴趣,但要确定它们并不容易。在这项研究中,John M. Grady等人提出了一种分析该已灭绝分类群体代谢的新方法,这种方法不仅观察化石中以生长年轮体现的生长速度,而且还根据个体发育生长的模式(某动物从出生至成年过程中的体型变化)来估测代谢率。为了在许多动物中仔细分析生长与代谢率之间的关系,研究人员使用了一个大型的比较数据集,它涵盖了一个范围广泛的包括了已灭绝及现在仍然存在的各种脊椎动物。他们的最终结论是,恐龙代谢处于变温动物与恒温动物之间的某个水平,它最接近现有的如金枪鱼、鼠鲨及棱皮龟等的中温动物。尽管它们不算完全的恒温动物,但这些动物有时依赖于体内产生的代谢热量来维持体温,而在其它时候则受到外部温度的制约。Grady及其同事的研究可帮助科学家们更好地理解远古中生代的生态系统,并或可用来估测来自这一时期的其它生物能量学还不清楚的动物的代谢率。

Abstract 

Were dinosaurs ectotherms or fast-metabolizing endotherms whose activities were unconstrained by temperature? To date, some of the strongest evidence for endothermy comes from the rapid growth rates derived from the analysis of fossil bones. However, these studies are constrained by a lack of comparative data and an appropriate energetic framework. Here we compile data on ontogenetic growth for extant and fossil vertebrates, including all major dinosaur clades. Using a metabolic scaling approach, we find that growth and metabolic rates follow theoretical predictions across clades, although some groups deviate. Moreover, when the effects of size and temperature are considered, dinosaur metabolic rates were intermediate to those of endotherms and ectotherms and closest to those of extant mesotherms. Our results suggest that the modern dichotomy of endothermic versus ectothermic is overly simplistic.

Editor's Summary

Not too fast, not too slow, somewhere in between

In early depictions, dinosaurs lumbered slowly, dragging their tails. More recently, we have imagined them lifting their tails and running. The question boils down to whether dinosaurs had energetic systems closer to those of rapidly metabolizing mammals and birds, or to those of slower reptiles that do not internally regulate their body temperature. However, determining the metabolic rate of extinct organisms is no easy task. Grady et al. analyzed a huge data set on growth rate in both extinct and living species, using a method that considers body temperature and body size. Dinosaur metabolism seems to have been neither fast nor slow, but somewhere in the middle—so, dinosaurs did not fully regulate their internal temperature but they were also not entirely at the whim of the environment; neither slow goliaths nor supercharged reptiles.

Science, this issue p. 1268
( http://www.sciencemag.org/content/344/6189/1268 )

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