中国中生代鸟类的体重估计及其演化趋势

MASS ESTIMATE AND EVOLUTIONARY TREND IN CHINESE MESOZOIC FOSSIL BIRDS

体重是一项重要的生物学指标,生物的体重受到发育、繁殖和进化等诸多因素的影响。对于灭绝生物体重的估计有助于进一步恢复它们的各种生物学信息。本研究采用统计学的方法,对422件现生鸟类(分属于21目229种)的体重和18项骨骼量度指标分别进行一元回归分析,结果显示判定系数的分布范围在0.5～0.91之间,多数指标的判定系数均集中在0.8～0.9之间。采用另外64件测量有体重数据和骨骼量度的鸟样本对回归方程的估算准确率进行检验,发现前肢中肱骨长度和尺骨宽度以及后肢中胫跗骨宽度3项指标的估算准确率高于其他指标。分析结果还表明前肢两项指标对于估算鸣禽、猛禽和攀禽类等树栖鸟类的体重准确率较后肢显著;后肢指标对于估算陆禽类等地栖鸟类体重的准确率高于前肢指标。这一结果反映出与体重相关程度较高的骨骼量度指标在不同习性的鸟类当中存在着一定的差异。对于化石鸟类的体重估计,采用估算准确率较高并且便于测量的肱骨长度和胫跗骨宽度两项回归方程加以计算。通过对中国中生代鸟类的体重进行估算,结果显示中生代鸟类在系统发育过程中,反鸟类经历了体重逐渐减轻的过程,而今鸟类的体重开始不断增大并且出现显著的分异。

Body mass or weight is a crucial biological parameter for an organism.It is influenced by development,reproduction,physiology and evolution.Therefore,mass estimates for fossil species are important for many kinds of analyses.In this project,eighteen bivariate regression analyses of different measurements of the appendicular skeleton plotted against body weight in a data set of 422 individual birds,representing 229 species in 21 orders,revealed high correlations between several skeletal parameters and body mass.R-squared values of eighteen bivariate equations are ranged from 0.50 for tibiotarsal length,indicating a relative poor fit,to 0.91 for humeral diameter.To test the 18 equations empirically,they were used to predict the body weight of an additional 64 extant bird specimens,and the accuracies of various equations were compared.This predictive test showed that three parameters are generally most accurate as predictors of body mass：humerus length,ulna diameter,and tibiotarsal diameter.However,the humeral length and ulna diameter tended to give accurate results for particularly songbirds,raptors and climbing birds.The tibiotarsal diameter tended to give accurate results for terrestrial birds,such like chicken and doves.It is probable that humerus length and ulna diameters are the more accurate parameter for arboreal taxa,while tibiotarsal dia-meter is more accurate for terrestrial ones.Closer examination of the results showed that different measurements correlated best with body mass in different avian orders.This variation appeared to result from differences in habitat and functional morphology across the avian orders represented in the data set.The weights of some Chinese Mesozoic fossil birds were estimated using the equations generated for humeral length and tibiotarsal diameter,because ulnar diameter was frequently difficult to measure.Humeral length and tibiotarsal diameter yielded dramatically different mass estimates for some taxa,with estimates based on humerus length generally being lower.The result shows that these Early Cretaceous birds experienced a significant diversification in body weight during evolutionary process.