Body Weight and Relative Brain Size (Encephalization) in Eocene Archaeoceti (Cetacea)
Body Weight and Relative Brain Size (Encephalization) in Eocene Archaeoceti (Cetacea)
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DOI：
10.1007/s10914-015-9304-y
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发表时间：
2016-03-01
影响因子：
1.9
通讯作者：
Gingerich, Philip D.
中科院分区：
文献类型：
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作者：
Gingerich, Philip D.
Felsenstein 布朗扩散模型的校准表明，系统发育可能对鲸目动物的体长和其他表型测量产生多达 10,000 代或约 180,000 年的影响，这在现存鲸目动物 3500 万年的历史中可以忽略不计。对当今鲸类物种表型特征的观察与系统发育和统计无关。比较了估计鲸类化石体重的四种方法：（1）中值序列回归，涉及一组对数体重对核心椎骨对数中心长度、宽度和高度的多元回归； (2)个体体重对数对体长对数的回归； (3) 物种平均值的对数全身重对对数体长的回归； (4)个体去脂体重对数对体长对数的回归。这些始新世古鲸 Dorudon atrox 的体重估计值分别为 1126、1118、1132 和 847 千克，其一致性和对部分骨骼的适用性有利于第一种方法。对于给定的体长 L-i（厘米），预期全身重 P-e（千克）由 log(10) P-e = 2.784 aEuro cent log(10) L-i -aEuro 千分之 4.429 给出。体重和体长的负异速生长（斜率 2.784 < 3.000）意味着小型鲸目动物比其体重预期更矮且更易于操作，而大型鲸目动物则比其体重预期更长且能量效率更高。脑化必须相对于参考样本进行量化，大多数哺乳动物是陆生哺乳动物，而陆生哺乳动物提供了逻辑基线。活陆生哺乳动物的脑化残差（ERTC）是观察到的 log(2) 脑重量（E-i，单位为 g）与预期 log(2) 脑重量（E-e，单位为 g）之间的差异，其中后者是根据体重（P-i，单位为 g）估计的，即 log(2) E-e = 0.740 aEuro cent log(2) P-i -aEuro 千分之 4.004。对于给定体型而言，对于大于预期的大脑，ERTC 呈正值；对于小于预期的大脑，ERTC 呈负值。以 2 为底的对数使 ERTC 标度更加直观，采用统一的减半或加倍单位。脑商 (EQ) 不适合进行比较，因为它们是不均匀比例的比例。始新世中期古生物的 ERTC 值接近-2（与预期相比减半），而始新世晚期古生物的 ERTC 值接近-1（与预期相比减半）。神秘鲸化石的 ERTC 并不为人所知，但活着的神秘鲸的 ERTC 值平均约为 -2。渐新世-近代齿鲸在整个时间范围内的 ERTC 值似乎平均约为 +1（比预期高一倍）。对鲸类脑化进化的明确解释需要更好的渐新世-近期须鲸类和齿鲸类的记录。
Calibration of the Brownian diffusion model of Felsenstein indicates that phylogeny may have an influence on body length and other phenotypic measures in Cetacea for as many as 10,000 generations or about 180,000 years, which is negligible in the 35 million year history of extant Cetacea. Observations of phenotypic traits in cetacean species living today are independent of phylogeny and independent statistically. Four methods for estimating body weight in fossil cetaceans are compared: (1) median serial regression involving a set of multiple regressions of log body weight on log centrum length, width, and height for core vertebrae; (2) regression of log whole body weight on log body length for individuals; (3) regression of log whole body weight on log body length for species means; and (4) regression of log lean body weight on log body length for individuals. These yield body weight estimates for the Eocene archaeocete Dorudon atrox of 1126, 1118, 1132, and 847 kg, respectively, with consistency and applicability to partial skeletons favoring the first approach. The whole-body weight expected, P-e (in kg), for a given body length, L-i (in cm), is given by log(10) P-e = 2.784 aEuro cent log(10) L-i -aEuro parts per thousand 4.429. Negative allometry of body weight and body length (slope 2.784 < 3.000) means that small cetaceans are shorter and more maneuverable than expected for their weight, while large cetaceans are longer and more efficient energetically than expected for their weight. Encephalization is necessarily quantified relative to a reference sample, most mammals are terrestrial, and terrestrial mammals provide a logical baseline. The encephalization residual for living terrestrial mammals as a class (ERTC), is the difference between observed log(2) brain weight (E-i in g) and expected log(2) brain weight (E-e in g), where the latter is estimated from body weight (P-i in g), as log(2) E-e = 0.740 aEuro cent log(2) P-i -aEuro parts per thousand 4.004. ERTC is positive for brains that are larger than expected for a given body size, and negative for brains that are smaller than expected. Base-2 logarithms make the ERTC scale intuitive, in uniform units of halving or doubling. Encephalization quotients (EQ) are unsuitable for comparison because they are proportions on a non-uniform scale. Middle Eocene archaeocetes have ERTC values close to -2 (two halvings compared to expectation), while late Eocene archaeocetes have ERTC values close to -1 (one halving compared to expectation). ERTC is not known for fossil mysticetes, but living mysticetes have ERTC values averaging about -2. Oligocene-Recent odontocetes appear to have ERTC values averaging about +1 (one doubling compared to expectation) through their temporal range. Definitive interpretation of the evolution of encephalization in Cetacea will require better documentation for Oligocene-Recent mysticetes and odontocetes.