Fakultät für Geowissenschaften, Geotechnik und Bergbau, TU Bergakademie Freiberg, Freiberg, Germany.
FRM II and Physics E21, Technische Universität München, Garching, Germany.
J Morphol. 2023 Sep;284(9):e21621. doi: 10.1002/jmor.21621.
The nasal region of the fossorial anomodont Kawingasaurus fossilis was virtually reconstructed from neutron-computed tomographic data and compared with the terrestrial species Pristerodon mackayi and other nonmammalian synapsids. The tomography of the Kawingasaurus skull reveals a pattern of maxillo-, naso-, fronto- and ethmoturbinal ridges that strongly resemble the mammalian condition. On both sides of the nasal cavity, remains of scrolled maxilloturbinals were preserved that were still partially articulated with maxilloturbinal ridges. Furthermore, possible remains of the lamina semicircularis as well as fronto- or ethmoturbinals were found. In Kawingasaurus, the maxilloturbinal ridges were longer and stronger than in Pristerodon. Except for the nasoturbinal ridges, no other ridges in the olfactory region and no remains of turbinates were recognized. This supports the hypothesis that naso-, fronto-, ethmo- and maxilloturbinals were a plesiomorphic feature of synapsids, but due to their cartilaginous nature in most taxa were, in almost all cases, not preserved. The well-developed maxilloturbinals in Kawingasaurus were probably an adaptation to hypoxia-induced hyperventilation in the fossorial habitat, maintaining the high oxygen demands of Kawingasaurus' large brain. The surface area of the respiratory turbinates in Kawingasaurus falls into the mammalian range, which suggests that they functioned as a countercurrent exchange system for thermoregulation and conditioning of the respiratory airflow. Our results suggest that the environmental conditions of the fossorial habitat led to specific sensory adaptations, accompanied by a pulse in brain evolution and of endothermy in cistecephalids, ~50 million years before the origin of endothermy in the mammalian stem line. This supports the Nocturnal Bottleneck Theory, in that we found evidence for a similar evolutionary scenario in cistecephalids as proposed for early mammals.
挖掘兽类的 Kawingasaurus fossilis 的鼻部区域是根据中子计算机断层扫描数据进行的虚拟重建，并与陆生物种 Pristerodon mackayi 和其他非哺乳动物合弓类动物进行了比较。Kawingasaurus 头骨的断层扫描显示出一种上颌骨、鼻甲骨、额骨和筛骨嵴的模式，强烈类似于哺乳动物的状态。在鼻腔的两侧，保存了仍然与筛骨嵴部分连接的卷曲上颌骨的痕迹。此外，还发现了可能的半规管瓣以及额骨或筛骨的痕迹。在 Kawingasaurus 中，上颌骨嵴比 Pristerodon 更长、更强。除了鼻甲骨嵴外，嗅觉区域没有其他嵴，也没有鼻甲的痕迹。这支持了这样的假说，即鼻骨、额骨、筛骨和上颌骨是合弓类动物的一个原始特征，但由于它们在大多数分类群中的软骨性质，几乎在所有情况下都没有保存下来。在 Kawingasaurus 中，高度发达的上颌骨可能是对挖掘栖息地缺氧诱导的过度通气的一种适应，维持了 Kawingasaurus 大脑对高氧气的需求。Kawingasaurus 的呼吸鼻甲的表面积落入哺乳动物的范围内，这表明它们作为逆流交换系统，用于调节体温和呼吸气流的条件。我们的研究结果表明，挖掘栖息地的环境条件导致了特定的感觉适应，伴随着脑进化的脉冲和合弓类动物的温血现象，这发生在温血现象在哺乳动物谱系中的起源之前约 5000 万年。这支持了夜行性瓶颈理论，因为我们在合弓类动物中发现了类似于早期哺乳动物所提出的类似进化情景的证据。
