Cajado Alex Gabriel, de Oliveira Carlos Eduardo Maia, de Andrade Marco Brandalise, Nava William Roberto, Santucci Rodrigo Miloni
Instituto de Geociências, Universidade de Brasília, Campus Universitário Darcy Ribeiro, Brasilia, Distrito Federal, Brazil.
Federal Institute of Education, Science, and Technology, Votuporanga Campus, Votuporanga, São Paulo, Brazil.
J Anat. 2025 Sep-Oct;247(3-4):620-642. doi: 10.1111/joa.70012. Epub 2025 Jun 19.
A characteristic common to almost all crocodylomorphs, whether living or extinct, is the presence of a dermal skeleton. This covering is composed of bones known as osteoderms or dermal plates/scutes, which are interconnected by fibrous tissues. Osteoderms play essential roles in the biology of crocodylomorphs, and vary in size, shape, ornamentation pattern, and functions according to the species. This study analyzed the osteoderms of fossil species of four fossil crocodylomorphs taxa from the Upper Cretaceous of the Bauru Group and compared their morphological characteristics with other living and extinct lineages, including Candidodontidae and fossil Caimaninae. Sampling included osteoderms from different regions of the body and individuals of different ontogenetic stages. The osteoderms analyzed originate from distinct clades of crocodylomorphs (Peirosauridae, Baurusuchidae, Sphagesauridae, and the spaghesaurian Mariliasuchus), presenting distinct external morphologies at the macroscopic level. The histological analysis confirmed the similarities seen in distinct clades of crocodylomorphs (Peirosauridae, Baurusuchidae, Sphagesauridae, and Mariliasuchus), despite highly divergent macroscopic morphology. In all cases, the bony matrix is characterized by parallel and interwoven fibers, with secondary osteons much larger than the primary ones, indicating a process of bone resorption. Growth lines also provide information on the minimum age of the individuals at the time of death. Histological differences in the osteoderms of baurusuchid of different ontogenetic stages indicate a back-to-front progression in the reabsorption process, akin to the progressive ontogenetic fusion of neurocentral sutures seen in the vertebral spine of crocodylomorphs. A shift in the position of the parasagittal crest through ontogeny indicates that the growth process of the osteoderm is not symmetric at least in Baurusuchidae, and that individuals of different ages are expected to present meaningful macroscopic shifts in the morphology of their osteoderms. Peirosauridae ornamentation pattern also varies during ontogeny since pits present in early ontogenetic states are covered/obliterated by subsequent layers of bone that assume a more regular aspect.
几乎所有鳄形超目动物，无论现存的还是已灭绝的，都具有一个共同特征，即存在真皮骨骼。这种覆盖物由称为骨皮或真皮板/鳞片的骨头组成，它们通过纤维组织相互连接。骨皮在鳄形超目动物的生物学中起着重要作用，并根据物种的不同在大小、形状、纹饰图案和功能上有所差异。本研究分析了来自包鲁群上白垩统的四个化石鳄形超目分类单元的化石物种的骨皮，并将它们的形态特征与其他现存和已灭绝的谱系进行了比较，包括伪齿鳄科和化石凯门鳄亚科。采样包括来自身体不同部位以及不同个体发育阶段个体的骨皮。所分析的骨皮来自鳄形超目动物的不同分支（佩罗鳄科、包鲁鳄科、噬身龙科以及噬身龙类的马里利亚鳄），在宏观层面呈现出不同的外部形态。组织学分析证实了在鳄形超目动物的不同分支（佩罗鳄科、包鲁鳄科、噬身龙科和马里利亚鳄）中观察到的相似性，尽管宏观形态差异很大。在所有情况下，骨基质的特征是平行且交织的纤维，次生骨单位比初生骨单位大得多，这表明存在骨吸收过程。生长线也提供了个体死亡时的最小年龄信息。不同个体发育阶段的包鲁鳄科骨皮的组织学差异表明，重吸收过程是从后向前进行的，这类似于在鳄形超目动物脊椎中观察到的神经中央缝的渐进个体发育融合。通过个体发育，矢状嵴位置的变化表明，至少在包鲁鳄科中，骨皮的生长过程是不对称的，不同年龄的个体在其骨皮形态上预计会出现有意义的宏观变化。佩罗鳄科的纹饰图案在个体发育过程中也会发生变化，因为在个体发育早期出现的凹坑会被随后更规则的骨层覆盖/消除。
