棘龙下颌骨 相关原文

mandibular rami were laterally displaced when the mandible was depressed. Two types of theropods show this morphology of the mandibular articulation, namely the weakly and fast biting carnivores with an elongated skull, and sometimes a sigmoid alveolar margin of the upper jaw (i.e., Tawa, Dilophosaurus, Eustreptospondylus, Guanlong, Tsaagan, Bambiraptor), and the massive predators with powerful and robust skulls that were able to swallow large chunks of meat (Acrocanthosaurus, Shaochilong). Spinosauridae were recovered in the first type of theropods, yet they differ from dilophosaurids, Eustreptospondylus, proceratosaurids and dromaeosaurids by having a much larger body size and a strongly elongated crocodile-like skull. Such a transformation of the skull also affected the mandibular articulation which shows a derived morphology among theropods. The presence of a narrow and posteriorly displaced ectocondyle displaying a large concave surface on the anterior face first implies a very strong and particularly stable articulation between the mandibular condyles of the quadrate and the glenoid fossa of the articular. In Baryonyx and Irritator, the dorsal margin of the articular bone shows a deep glenoid fossa formed by two depressions separated by a faint interglenoid ridge (Fig 14B; Sues et al. [87]; n.b., the left articular of Baryonyx was identified as the right atlantal neural arch by Charig and Milner [89]
and the central body of the left pterygoid by Sereno et al. [25], whereas the right articular was interpreted as the left postorbital by Charig and Milner [89] and the posterior portion of the right surangular by Sereno et al. [25]; Matt Carrano pers. comm.). A similar morphology most likely existed in Spinosaurus, and Morphotype 2 probably had one of the most stable mandibular articulations among all theropods. Indeed, based on the morphology of the mandibular articulation, the articular of MHNM.KK376 was deeply excavated by a narrow glenoid fossa. It also had two well-defined lateral and medial glenoid depressions divided by an acute interglenoid ridge. The articulation must also have been stabilized by a smooth and prominent convexity delimiting the anterior surface of the lateral glenoid depression. Evolution towards a particularly stable mandibular articulation in Spinosauridae was probably the result of two independent factors: an important lateral displacement of the two rami of the mandible, and the swift movement of the jaw opening. As soon as the mandible was depressed, the interglenoid ridge of the articular slid along the lateromedially oriented intercondylar sulcus of the quadrate, forcing the articular, and consequently the two mandibular rami, to be displaced laterally (Fig 15A–15D, 15F and 15G). This lateral displacement was increased by the fact that the interglenoid fossa could carry on its movement along the ventrodorsally high posterior articular surface of the ectocondyle, especially in Morphotype 2. A strong lateral displacement of the two rami allowed the pharynx of Spinosauridae to be significantly enlarged, therefore favoring the deglutition of whole prey or large chunks of food. A similar lateral displacement of the lower jaw was also observed in pterosaurs and living pelecanids, which share an elongated and narrow skull and a piscivorous diet with spinosaurids [127–130].

其中A、B、F为棘龙嘴部闭合状态，C、D、G为开合状态，论文叙述，棘龙的下颌骨向下旋转70°是有可能的，其活动方式与翼龙的旋转关节类似，棘龙科的螺旋关节也提供了更好的抵抗内侧位移的能力。