Post‐hatching early life history of Cretaceous Ammonoidea
Post‐hatching early life history of Cretaceous Ammonoidea
复制标题
白垩纪菊总科孵化后早期生活史
DOI：
10.1111/j.1502-3931.1993.tb01804.x
复制
发表时间：
1993
期刊：
影响因子：
--
通讯作者：
Y. Shigeta
中科院分区：
文献类型：
--
作者：
Y. Shigeta
本文通过对白垩纪4个亚目71个种的壳密度计算，讨论了其孵化后的早期生活史。计算是在假设一个新孵化的菊石有一个充满气体的腔室和一个随后的充满身体的螺旋终止于主缢痕的情况下进行的。结果表明，在孵化阶段，所检查的物种的密度几乎是恒定的，相对小于海水中的密度，即动物是正浮力的。这一事实有力地表明了一种节俭的生活方式。在所有种类中，密度随着生长而逐渐增加，并在壳直径为2.C ~ 2.5mm时达到中性浮力。因此，大多数菊石可能改变了他们的生活方式，从南极到nektoprotictic或nektobenthic在这个关键点。新孵化的标本（ammontellas）在许多菊石组合中的罕见发生也可能支持这一解释。一个新孵化的菊石浮游持续时间可能会调节动物的密度在孵化，壳生长模式，cameral体积（或孵化大小），cameralliquid去除率（或siphuncle直径）。后两者似乎是决定物种生物地理框架的非常重要的因素，正如四方花科所证明的那样。□白垩纪，阿蒙诺总科，密度计算，早期生活史。
Post-hatching early life histories in Cretaceous Ammonoidea are discussed on the basis of density calculations of the shells in 71 species belonging to four separate suborders. The calculation was made under the assumption that a newly hatched ammonoid had a gas-filled chamber and a succeeding body-filled whorl terminating at the primary constriction. The results show that the density of the species examined at the hatching stage is almost constant and is relatively smaller than that of seawater, i.e. the animals are positively buoyant. This fact strongly suggests a planktic mode of life. In all species, the density increases gradually with growth and attains neutral buoyancy at 2.C2.5 mm in shell diameter. Thus, most ammonoids probably changed their mode of life from planktic to nektoplanktic or nektobenthic at this critical point. The rare occurrence of newly hatched specimens (ammonitellas) in many ammonoid assemblages may also support this interpretation. Planktic duration of a newly hatched ammonoid might be regulated by the animal's density at hatching, shell growth pattern, cameral volume (or hatching size), and rate of cameralliquid removal (or siphuncle diameter). The latter two seem to be very important factors in determining the biogeographical framework of species, as demonstrated in the Tetragonitaceae.□Cretaceous, Ammonoidea, density calculation, early life history.