Departamento de Paleobiología, Museo Nacional de Ciencias Naturales-CSIC, Madrid, Spain.
PLoS One. 2012;7(1):e30060. doi: 10.1371/journal.pone.0030060. Epub 2012 Jan 17.
Sauropod dinosaurs were the largest animals ever to walk on land, and, as a result, the evolution of their remarkable adaptations has been of great interest. The braincase is of particular interest because it houses the brain and inner ear. However, only a few studies of these structures in sauropods are available to date. Because of the phylogenetic position of Spinophorosaurus nigerensis as a basal eusauropod, the braincase has the potential to provide key evidence on the evolutionary transition relative to other dinosaurs.
METHODOLOGY/PRINCIPAL FINDINGS: The only known braincase of Spinophorosaurus ('Argiles de l'Irhazer', Irhazer Group; Agadez region, Niger) differs significantly from those of the Jurassic sauropods examined, except potentially for Atlasaurus imelakei (Tilougguit Formation, Morocco). The basisphenoids of Spinophorosaurus and Atlasaurus bear basipterygoid processes that are comparable in being directed strongly caudally. The Spinophorosaurus specimen was CT scanned, and 3D renderings of the cranial endocast and inner-ear system were generated. The endocast resembles that of most other sauropods in having well-marked pontine and cerebral flexures, a large and oblong pituitary fossa, and in having the brain structure obscured by the former existence of relatively thick meninges and dural venous sinuses. The labyrinth is characterized by long and proportionally slender semicircular canals. This condition recalls, in particular, that of the basal non-sauropod sauropodomorph Massospondylus and the basal titanosauriform Giraffatitan.
CONCLUSIONS/SIGNIFICANCE: Spinophorosaurus has a moderately derived paleoneuroanatomical pattern. In contrast to what might be expected early within a lineage leading to plant-eating graviportal quadrupeds, Spinophorosaurus and other (but not all) sauropodomorphs show no reduction of the vestibular apparatus of the inner ear. This character-state is possibly a primitive retention in Spinophorosaurus, but due the scarcity of data it remains unclear whether it is also the case in the various later sauropods in which it is present or whether it has developed homoplastically in these taxa. Any interpretations remain tentative pending the more comprehensive quantitative analysis underway, but the size and morphology of the labyrinth of sauropodomorphs may be related to neck length and mobility, among other factors.
蜥脚类恐龙是有史以来在陆地上行走的最大动物，因此，它们非凡适应能力的进化一直是人们关注的焦点。脑壳特别有趣，因为它容纳了大脑和内耳。然而，迄今为止，只有少数关于蜥脚类恐龙这些结构的研究。由于尼日尔的尼日尔棘龙是基础eusauropod 的种属位置，因此脑壳有可能提供相对于其他恐龙进化过渡的关键证据。
方法/主要发现：唯一已知的尼日尔棘龙脑壳（“Irhazer 组的 Argiles de l'Irhazer”；尼日尔阿加德兹地区）与所检查的侏罗纪蜥脚类恐龙有很大的不同，除了可能与 Atlasaurus imelakei（摩洛哥的 Tilougguit 组）有关。尼日尔棘龙和 Atlasaurus 的基蝶骨具有强烈指向尾侧的基翼突，这两者相似。尼日尔棘龙标本进行了 CT 扫描，并生成了颅腔内部和内耳系统的 3D 渲染。脑腔与大多数其他蜥脚类恐龙相似，具有明显的脑桥和大脑褶皱、大而长圆形的垂体窝，并且由于前存在相对较厚的脑膜和硬脑膜静脉窦，大脑结构被遮挡。迷路的特点是长而比例细长的半规管。这种情况特别让人联想到基础的非蜥脚类蜥脚形亚目恐龙和基础的泰坦巨龙。
结论/意义：尼日尔棘龙具有中等衍生的古神经解剖模式。与在导致食草重力四足动物的谱系中可能预期的早期情况相反，尼日尔棘龙和其他（但不是全部）蜥脚形亚目恐龙没有减少内耳的前庭器官。这种特征状态在尼日尔棘龙中可能是原始保留，但由于数据稀缺，尚不清楚它是否也存在于存在这种状态的各种后来的蜥脚类恐龙中，或者它是否在这些分类单元中具有同源发生。在正在进行的更全面的定量分析之前，任何解释仍然是暂定的，但蜥脚形亚目动物的迷路的大小和形态可能与颈部长度和活动性等因素有关。
