División Paleontología Vertebrados, Museo de La Plata, Unidades de Investigación Anexo II Museo, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata, Buenos Aires, Argentina.
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Ciudad Autónoma de Buenos Aires, Argentina.
PeerJ. 2023 Jul 12;11:e15548. doi: 10.7717/peerj.15548. eCollection 2023.
Shape ontogenetic changes of the lower jaw in crocodylians are poorly understood. In order to answer some questions related to the inter- and intraspecific morphological variation of the mandible of two extant species, we performed a three-dimensional geometric morphometric approach. For this purpose, we used landmarks and semilandmarks on two ontogenetic mandibular series of 48 and 15 post-hatching specimens of and , respectively. We have also examined the relationship between these anatomical transformations and ontogenetic shifts in diet. We performed a principal component analysis (PCA) for the two species, and regression and partial least squares (PLS) analyses for each species, separately. As a result, species were segregated along the PC1 with specimens of showing more gracile mandibles, and specimens of more robust ones. The PC2 and regression analyses showed an age gradient and represented ontogenetic shape changes. Adult caiman mandibles are higher and wider than juvenile ones, and shape changes are more conspicuous in . The PLS analyses showed a significant relationship between shape and diet. Morphological changes of the PLS1 of block-1 match with those of the regression analysis for both species. We have detected morphological transformations in areas where the musculature in charge of mandibular movements is attached. Common morphological changes occurring during ontogeny seem to reflect the same mechanical properties required for crushing and killing in both species, driven by an ontogenetic shift in the diet from invertebrates to vertebrates. Additionally, interspecific differences were also found to be correlated to ontogenetic changes in diet and could be related to dissimilar feeding mechanical requirements (., stiffness and toughness of the item consumed), and to different habitat preferences. Robust mandibles would be more suitable for shallow and fully vegetated environments, as it can be seen in , whereas slender jaws seem to be more suitable for more aquatic species such as .
鳄形目动物的下颌骨形态发生变化的情况了解甚少。为了回答与两种现存物种的下颌骨形态在种内和种间的变异相关的一些问题，我们采用了三维几何形态测量法。为此，我们使用了 48 个孵化后阶段的和 15 个孵化后阶段的个体的两个下颌骨连续系列的标志点和半标志点。我们还检查了这些解剖结构变化与饮食的种间和种内变化之间的关系。我们针对两个物种进行了主成分分析（PCA），并针对每个物种分别进行了回归和偏最小二乘法（PLS）分析。结果表明，物种沿 PC1 分离，其中的个体具有更纤细的下颌骨，而 的个体具有更粗壮的下颌骨。PC2 和回归分析显示出年龄梯度，并代表了形态发生的变化。成年凯门鳄的下颌骨比幼年的更高更宽，而 的变化更为明显。PLS 分析表明，形状与饮食之间存在显著的关系。块 1 的 PLS1 的形态变化与两个物种的回归分析相匹配。我们已经检测到负责下颌运动的肌肉附着处的形态变化。在种内和种间，形态发生过程中的共同变化似乎反映了两种物种在从无脊椎动物到脊椎动物的饮食转变过程中所需的相同机械性能，这种变化是由种间和种内的饮食变化驱动的。此外，还发现种间差异与饮食的种间变化相关，这可能与不同的摄食机械需求（例如，所消耗物品的硬度和韧性）以及不同的栖息地偏好有关。粗壮的下颌骨更适合于浅而完全植被的环境，这在 中可以看到，而细长的下颚似乎更适合于像 这样的水生物种。
