Developmental regulation and morphological saltation in the heteromorph ammonite Nipponites
Developmental regulation and morphological saltation in the heteromorph ammonite Nipponites
复制标题
异形菊石 Nipponites 的发育调控和形态突变
作者：
T. Okamoto
新辉石是晚白垩世的一种新角石菊石，在中晚期表现为一种特殊的曲流壳生长。假定浮力为中性，相对于海底的孔径角为常数，用计算机模拟了该菊石的蜿蜒生长过程。在该模型中，曲折贝壳的生长受生命取向调节的控制。计算机模拟的样品与实际样品在卷曲方式和肋骨倾角模式上的惊人相似性，有力地表明了日本岩中具有接近中性浮力的自由生命模式。模拟还表明，由于生长方向上下限的微小变化，从简单的螺旋形形状如日本真螺旋体到曲折的贝壳形状如Nipponites的形态突变发生在没有任何中间形式的情况下。
Nipponites, a Late Cretaceous nostoceratid ammonite, shows a peculiar meandering shell growth in the middle-late stage. Assuming neutral buoyancy, and a constant aperture angle relative to the sea bottom, meandering growth of this ammonite was modeled by computer simulation. In this model, the meandering shell growth is controlled by regulation of life orientation. The remarkable similarity in the coiling modes and rib obliquity patterns between the computer-simulated and actual specimens strongly suggests a free living mode of life in Nipponites with an approximately neutral buoyancy. The simulation also suggests that morphological saltation from a simple helicoid form like Eubostrychoceras japonicum to a meandering shell form like Nipponites occurred abruptly without any intermediate form by minor change of the upper and lower limits of growth direction.