Morphospace occupation in thalattosuchian crocodylomorphs: skull shape variation, species delineation and temporal patterns
Morphospace occupation in thalattosuchian crocodylomorphs: skull shape variation, species delineation and temporal patterns
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海鳄类鳄鱼形态的形态空间占据：头骨形状变化、物种划分和时间模式
DOI：
10.1111/j.1475-4983.2009.00904.x
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发表时间：
2009
期刊：
影响因子：
2.6
通讯作者：
E. Rayfield
中科院分区：
文献类型：
--
作者：
S. Pierce;K. Angielczyk;E. Rayfield
摘要：应用几何形态计量学技术研究了地中海藻 头骨形状的变异，以期区分物种，特别是关于卡洛纲物种的分类，并探索它们在进化历史上的差异模式。海龙头骨的形态多样性模式与现代鳄鱼非常相似：主要的变异来源是口鼻的长度和宽度，但这些广泛的变化与颞上窗和额骨的大小、鼻骨的长度、眼眶和上颌骨的大小以及鼻孔的位置有关。利用形状变化模式，结合离散状态形态以及地层和地理范围数据，区分了9种硬龙和14种甲龙，目前确认的4种卡洛龙被分成8种。研究发现，与硬龙相比，硬尾龙与形态空间的平均形状差异更大。然而，短吻甲龙和长鼻子硬龙在鼻子形态类型上表现出最大的差异，这表明每一组都倾向于探索形态空间的相反区域。系统发育对甲壳类的形态空间占据模式有适度的影响，但对硬龙的影响很小，这表明其他因素或限制因素控制着海龙的头骨形状变异模式。对海龙和恐龙/蛇龙的比较表明，海龙有一种独特的头骨形态，这意味着有多种方法来构建“长鼻子”。此外，有问题的物种Pelagosaurus typus的头骨几何形状被发现聚集在形态空间的硬龙区域。最后，海藻物种和地貌类型的时间分布与侏罗纪和早白垩世的海平面曲线和大规模灭绝事件具有明显的高度相关性。
Abstract: Skull shape variation in thalattosuchians is examined using geometric morphometric techniques in order to delineate species, especially with respect to the classification of Callovian species, and to explore patterns of disparity during their evolutionary history. The pattern of morphological diversity in thalattosuchian skulls was found to be very similar to modern crocodilians: the main sources of variation are the length and the width of the snout, but these broad changes are correlated with size of supratemporal fenestra and frontal bone, length of the nasal bone, size of the orbit and premaxilla and position of the narial opening. Patterns of shape variation, in combination with discrete‐state morphology and stratigraphic and geographic range data were used to distinguish nine species of teleosaurid and 14 species of metriorhynchid, with the four currently recognized Callovian species being split into eight. Metriorhynchids were found to be more disparate from the average shape of morphospace than teleosaurids. However, short‐snouted metriorhynchids and long‐snouted teleosaurids showed the greatest amount of disparity with respect to snout morphotypes, indicating that each group tended to explore opposite areas of morphospace. Phylogeny was found to have a moderate influence on the pattern of morphospace occupation in metriorhynchids, but little effect in teleosaurids suggesting that other factors or constraints control the pattern of skull shape variation in thalattosuchians. A comparison of thalattosuchians with dyrosaur/pholidosaurids shows that thalattosuchians have a unique skull morphology, implying that there are multiple ways to construct a ‘long snout’. Moreover, the skull geometry of the problematic species Pelagosaurus typus was found to converge on the teleosaurid area of morphospace. Finally, the temporal distribution of thalattosuchian species and morphotypes demonstrate a clear and highly correlated relationship with sea level curves and mass extinction events through the Jurassic and the Early Cretaceous.