Department of Biology, Slippery Rock University, Slippery Rock, Pennsylvania, USA.
Louisiana Department of Wildlife and Fisheries, Baton Rouge, Louisiana, USA.
J Morphol. 2022 Jun;283(6):805-814. doi: 10.1002/jmor.21472. Epub 2022 Apr 14.
Variation in vertebrate cranial morphology is both extensive and functionally significant. Morphometric analysis attempts to explain such variation in form in evolutionary and functional contexts. Developmental morphometric analyses of vertebrate crania are less common, and many taxa are underrepresented. For example, the published morphometric studies of crocodilian cranial development focus mainly on posthatchling head development, with few, incomplete morphometric analyses of prehatchling heads. To further explore ontogenetic changes in the alligator head, we recorded and analyzed six linear cranial measurements in 77 preserved embryonic and hatchling American alligators (Alligator mississippiensis) representing 20 different stages. Examination of individual measurements revealed nonlinear changes in growth rate during development, suggesting a level of dynamic complexity worthy of further analysis. Using principal components analysis, we identified three distinct phases in prenatal alligator head growth. The second (intermediate) phase disrupts an otherwise monotonic developmental trajectory and represents a phase of reduced snout growth. Although this is a detailed description of prehatchling ontogenetic trajectory of the alligator head, further studies in other crocodilians are needed to assess evolutionary patterns among crocodilians.
脊椎动物颅形态的变异既广泛又具有重要的功能意义。形态计量分析试图在进化和功能背景下解释形态的这种变异。脊椎动物颅骨的发育形态计量分析则较少见，许多类群的研究也不足。例如，已发表的鳄形目颅骨发育的形态计量研究主要集中在后孵化期的头部发育，而对孵化前的头部进行的形态计量分析很少且不完整。为了进一步探索短吻鳄头部的发育变化，我们记录并分析了 77 只保存完好的胚胎和孵化期的美洲短吻鳄（Alligator mississippiensis）的 6 个线性颅骨测量值，这些短吻鳄代表 20 个不同的发育阶段。对单个测量值的检查显示，在发育过程中生长速度呈非线性变化，表明存在值得进一步分析的动态复杂性水平。通过主成分分析，我们确定了短吻鳄头部生长的三个不同阶段。第二（中间）阶段打破了 otherwise monotonic 的发育轨迹，代表了一个鼻子生长减缓的阶段。尽管这是对短吻鳄头部孵化前发育轨迹的详细描述，但需要在其他鳄形目动物中进一步研究，以评估鳄形目动物之间的进化模式。
