Department of Zoology, Swedish Museum of Natural History, Box 50007, SE-10405 Stockholm, Sweden.
BMC Evol Biol. 2014 Jan 15;14:8. doi: 10.1186/1471-2148-14-8.
The avian Order Passeriformes is an enormously species-rich group, which comprises almost 60% of all living bird species. This diverse order is believed to have originated before the break-up of Gondwana in the late Cretaceous. However, previous molecular dating studies have relied heavily on the geological split between New Zealand and Antarctica, assumed to have occurred 85-82 Mya, for calibrating the molecular clock and might thus be circular in their argument.
This study provides a time-scale for the evolution of the major clades of passerines using seven nuclear markers, five taxonomically well-determined passerine fossils, and an updated interpretation of the New Zealand split from Antarctica 85-52 Mya in a Bayesian relaxed-clock approach. We also assess how different interpretations of the New Zealand-Antarctica vicariance event influence our age estimates. Our results suggest that the diversification of Passeriformes began in the late Cretaceous or early Cenozoic. Removing the root calibration for the New Zealand-Antarctica vicariance event (85-52 Mya) dramatically increases the 95% credibility intervals and leads to unrealistically old age estimates. We assess the individual characteristics of the seven nuclear genes analyzed in our study. Our analyses provide estimates of divergence times for the major groups of passerines, which can be used as secondary calibration points in future molecular studies.
Our analysis takes recent paleontological and geological findings into account and provides the best estimate of the passerine evolutionary time-scale currently available. This time-scale provides a temporal framework for further biogeographical, ecological, and co-evolutionary studies of the largest bird radiation, and adds to the growing support for a Cretaceous origin of Passeriformes.
雀形目是一个物种极其丰富的鸟类目，约占现存鸟类物种的 60%。这个多样化的目被认为起源于白垩纪末期冈瓦纳大陆解体之前。然而，以前的分子定年研究严重依赖于新西兰和南极洲之间的地质分裂，该分裂被认为发生在 85-8200 万年前，用于校准分子钟，因此它们的论点可能是循环的。
本研究利用 7 个核标记、5 个分类学上确定的雀形目化石以及对新西兰与南极洲 85-5200 万年前分裂的更新解释，为主要雀形目类群的进化提供了一个时间尺度。我们还评估了对新西兰-南极洲隔离事件的不同解释如何影响我们的年龄估计。我们的研究结果表明，雀形目的多样化始于白垩纪晚期或新生代早期。去除新西兰-南极洲隔离事件的根校准（85-5200 万年前）会极大地增加 95%置信区间，并导致不切实际的古老年龄估计。我们评估了我们研究中分析的 7 个核基因的个体特征。我们的分析为雀形目主要类群的分化时间提供了估计值，可作为未来分子研究的二级校准点。
我们的分析考虑了最近的古生物学和地质学发现，并提供了目前可用的雀形目进化时间尺度的最佳估计。这个时间尺度为对最大的鸟类辐射的进一步生物地理学、生态学和协同进化研究提供了一个时间框架，并为雀形目起源于白垩纪的观点提供了更多支持。
