Weiss Bailey M, Dollman Kathleen N, Choiniere Jonah N, Browning Claire, Botha Jennifer
Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa.
School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa.
J Anat. 2025 Sep-Oct;247(3-4):587-607. doi: 10.1111/joa.14166. Epub 2024 Oct 27.
Orthosuchus stormbergi was a small-bodied crocodyliform, representative of a diverse assemblage of Early Jurassic, early branching crocodylomorph taxa from the upper Elliot Formation of South Africa. The life history of these early branching taxa remains poorly understood, with only sparse investigations into their osteohistology, yet species like Orthosuchus have potential to inform about the macroevolution of growth strategies on the stem leading to crown crocodilians. In order to elucidate the growth patterns of Orthosuchus, we used propagation phase contrast X-ray synchrotron micro-computed tomography to virtually image the osteohistology of the postcrania of two specimens, including multiple elements from the type (SAM-PK-K409), and the femur of a referred specimen (BP/1/4242). In total, we scanned nine mid-diaphyseal sections of the humerus, radius, ulna, radiale, femur, tibia, fibula, and a rib. We then compared our results to osteohistological sections of crocodylomorph taxa from the published literature. Our results show that the most predominant bone tissue type in Orthosuchus is lamellar, with a few patches of woven and parallel-fibred bone. The type specimen contains four to five lines of arrested growth and the hindlimb elements present outer circumferential lamellae, whereas the referred specimen contains six to seven. Both specimens grew at similar rates, reaching adult skeletal body size at year four or five. The sectioned bones, most notably the radius and ulna, are comparatively thick walled and compact. Our virtual osteohistological sections are one of the first for an early branching crocodyliform, and the broad sample of skeletal elements makes Orthosuchus a key anchor point for understanding the plesiomorphic life history traits of the clade.
斯托姆伯格鳄是一种小型鳄形类动物，代表了来自南非上艾略特组的早侏罗世早期分支鳄形类群的多样化组合。这些早期分支类群的生活史仍知之甚少，对其骨组织学的研究也很稀少，但像斯托姆伯格鳄这样的物种有潜力为通向现代鳄鱼的主干上生长策略的宏观演化提供信息。为了阐明斯托姆伯格鳄的生长模式，我们使用传播相位对比X射线同步加速器微计算机断层扫描技术对两个标本的后颅骨骨组织学进行了虚拟成像，包括模式标本（SAM-PK-K409）的多个骨骼元素，以及一个参考标本（BP/1/4242）的股骨。我们总共扫描了肱骨、桡骨、尺骨、桡侧腕骨、股骨、胫骨、腓骨和一根肋骨的九个骨干中段切片。然后，我们将结果与已发表文献中鳄形类群的骨组织学切片进行了比较。我们的结果表明，斯托姆伯格鳄中最主要的骨组织类型是板层骨，有一些编织骨和平行纤维骨斑块。模式标本包含四到五条生长停滞线，后肢骨骼元素有外周板层骨，而参考标本包含六到七条。两个标本的生长速度相似，在第四或五年达到成年骨骼体型。切片的骨骼，最明显的是桡骨和尺骨，壁相对较厚且致密。我们的虚拟骨组织学切片是早期分支鳄形类动物的首批切片之一，广泛的骨骼元素样本使斯托姆伯格鳄成为理解该类群原始生活史特征的关键锚点。
