■胃石是目的不确定的石头,通常在世界范围内的蛇颈龙化石的肋骨笼内发现。研究了来自四个艾伯塔省(加拿大)蛇颈龙的胃石,以确定它们的形状和质量,以及它们相对于体重的质量分数。一只动物的一组胃石是100%完整和完全可见的,但是其他人表现出不同程度的损失,损坏或模糊,所以需要估计他们的原始状态。
■研究的动物是:Albertonectesvanderveldei,斯洛文尼亚的Fluvionectessloanae,Nichollssauraborealis和Wapuskanectesbetsynichollsae。这些动物来自三种不同的古环境:开放的海洋,海岸附近的海洋,和河流。胃石形状被归类为剑突,圆柱形,基于观察和/或估计的尺寸的盘状或球形。尽管并非所有方法都适用于所有情况,对胃石的形状和质量进行了四种不同的估计:(1)直接测量和称重一个子集,并预测剩余的模糊和隐藏的石头的性质;(2)测量自由石的三轴椭球尺寸,以计算体积并乘以石的质量密度;(3)测量嵌入石的两个可见三轴尺寸,估计隐藏的第三维度三种不同的方式,然后通过计算确定体积和质量;(4)使用几何参数预测密集堆积的小胃石簇的密度和质量。
■任何蛇颈龙的总胃石质量从未超过体重的0.2%,并且与用蛇颈龙回收的胃石的数量作为压载物无效的想法一致。样本中最大的蛇颈龙具有最大的单个胃石,并且总胃石质量随体型的增加而增加。不同环境下胃石的形态特征不同,但从组成上讲,它们是由黑樱桃主导的。对于两个地理上接近且几乎同时代的Nichollssaura和Wapuskanectes,确定了胃石的可能共同来源。
UNASSIGNED: Gastroliths are stones of uncertain purpose that are commonly found inside the rib cages of plesiosaur fossils worldwide. Gastroliths from four Alberta (Canada) plesiosaurs were studied to determine both their shapes and masses, and their mass fractions relative to body mass. One animal\'s set of gastroliths was 100% complete and fully visible, but the others showed varying degrees of loss, damage or obscuration, so estimations of their original states were needed.
UNASSIGNED: The studied animals were: Albertonectes vanderveldei, Fluvionectes sloanae, Nichollssaura borealis and Wapuskanectes betsynichollsae. The animals come from three different palaeoenvironments: open marine, near shore marine, and fluvial. Gastrolith shapes were classified as either xiphoid, cylindrical, discoidal or spherical based on observed and/or estimated dimensions. Although not all methods could be applied in all cases, gastrolith shapes and masses were estimated four different ways: (1) direct measurement and weighing of a subset and predicting the properties of the remaining obscured and hidden stones; (2) measuring triaxial ellipsoid dimensions of free stones to calculate volumes and multiplying by the mass density of chert; (3) measuring two visible triaxial dimensions of embedded stones, estimating the hidden third dimension three different ways, and then determining volumes and masses by calculation; and (4) predicting the density and mass of a densely packed cluster of small gastroliths using geometrical arguments.
UNASSIGNED: Total gastrolith mass never exceeded 0.2% of body mass in any plesiosaur, and is consistent with the idea that the amounts of gastroliths recovered with plesiosaurs would be ineffective as ballast. The largest plesiosaur in the sample had the largest single gastrolith and total gastrolith mass increases with body size. The shape characteristics of the gastroliths were different for different environments, but compositionally they are dominated by black cherts. A possible common source for the gastroliths was identified for the two geographically close and near-contemporanous Nichollssaura and Wapuskanectes.