Department of Anthropology, University of Toronto Scarborough, Toronto, Ontario, Canada.
Institute of Biotechnology, Helsinki Institute of Life Science, University of Helsinki, Helsinki, Finland.
Anat Rec (Hoboken). 2023 Oct;306(10):2443-2465. doi: 10.1002/ar.25142. Epub 2023 Jan 5.
Vertebrate endocasts are widely used in the fields of paleoneurology and comparative neuroanatomy. The validity of endocranial studies is dependent upon the extent to which an endocast reflects brain morphology. Due to the variable neuroanatomical resolution of vertebrate endocasts, direct information about the brain morphology can be sometimes difficult to assess and needs to be investigated across lineages. Here, we employ X-ray computed tomography (CT), including diffusible iodine-based contrast-enhanced CT, to qualitatively compare brains and endocasts in different species of squamates. The relative position of the squamate brain within the skull, as well as the variability that may exist in such spatial relationships, was examined to help clarify the neurological regions evidence on their endocasts. Our results indicate that squamate endocasts provide variable representation of the brain, depending on species and neuroanatomical regions. The olfactory bulbs and peduncles, cerebral hemispheres, as well as the medulla oblongata represent the most easily discernable brain regions from squamate endocasts. In contrast, the position of the optic lobes, the ventral diencephalon and the pituitary may be difficult to determine depending on species. Finally, squamate endocasts provide very limited or no information about the cerebellum. The spatial relationships revealed here between the brain and the surrounding bones may help to identify each of the endocranial region. However, as one-to-one correspondences between a bone and a specific region appear limited, the exact delimitation of these regions may remain challenging according to species. This study provides a basis for further examination and interpretation of squamate endocast disparity.
脊椎动物的内颅骨广泛应用于古神经学和比较神经解剖学领域。内颅骨研究的有效性取决于内颅骨反映脑形态的程度。由于脊椎动物内颅骨的神经解剖分辨率不同，因此有时很难直接评估有关脑形态的信息，需要在不同的谱系中进行研究。在这里，我们使用 X 射线计算机断层扫描（CT），包括可扩散碘基对比增强 CT，对内颅骨在不同蜥蜴类物种中的脑形态进行定性比较。研究了蜥蜴类脑在颅骨内的相对位置，以及这种空间关系中可能存在的可变性，以帮助澄清其内颅骨上的神经区域证据。我们的结果表明，蜥蜴类内颅骨根据物种和神经解剖区域的不同，提供了可变的脑代表。嗅球和嗅束、大脑半球以及延髓是最容易从蜥蜴类内颅骨中分辨出来的脑区。相比之下，视叶、腹侧间脑和垂体的位置可能因物种而异而难以确定。最后，蜥蜴类内颅骨几乎无法提供小脑的信息。脑与周围骨骼之间揭示的空间关系可能有助于识别每个内颅骨区域。然而，由于骨头和特定区域之间的一一对应似乎有限，因此根据物种，这些区域的确切划分可能仍然具有挑战性。本研究为进一步检查和解释蜥蜴类内颅骨差异提供了基础。
