The second titanosaurian (Dinosauria: Sauropoda) from the middle Cretaceous Galula Formation, southwestern Tanzania, with remarks on African titanosaurian diversity

The paleobiogeographic significance of continental Africa during the middle and Late Cretaceous is not well understood, in part due to incomplete sampling from large portions of the landmass during these intervals. Intensified field efforts in the Galula Formation exposed in southwestern Tanzania have revealed a diverse vertebrate fauna, including the novel titanosaurian <i>Shingopana songwensis</i>, gen. et sp. nov., described herein. Based on a left angular, cervical vertebrae, cervical and dorsal ribs, a left humerus, and a partial left pubis, <i>Shingopana</i> exhibits morphology indicating affinities with the Late Cretaceous aeolosaurine titanosaurians of South America. The bulbous expansion of the cervical vertebral neural spine is similar to the condition in <i>Bonitasaura salgadoi, Overosaurus paradasorum</i>, and <i>Trigonosaurus pricei</i>. The dorsal ribs of <i>Shingopana</i> also present proximal anterior and posterior flanges that previously were proposed to be unique to <i>Overosaurus</i>. Furthermore, <i>Shingopana</i> is diagnosed by a divided spinoprezygapophyseal lamina in the middle-to-posterior cervical vertebrae. Parsimony and both uncalibrated and tip-dated Bayesian phylogenetic approaches support <i>Shingopana</i> as the first African titanosaurian that is closely related to aeolosaurines. Comparisons with other African titanosaurians, such as the co-occurring <i>Rukwatitan bisepultus</i> and geographically proximate <i>Malawisaurus dixeyi</i>, suggest that southern African forms represent diverse taxa rather than forming a monophyletic group. Moreover, southern African forms exhibit stronger affinities with South American clades than with representative northern African form, suggesting that tectonically driven separation of the two landmasses may have influenced the development of progressively isolated southern African faunas throughout the Cretaceous.

白垩纪中晚期非洲大陆的古生物地理学意义尚未得到充分阐明，部分原因在于该时期非洲大陆广袤区域的化石采样仍存在大量空白。针对坦桑尼亚西南部出露的加拉鲁组（Galula Formation）开展的强化野外调查，发现了种类丰富的脊椎动物群，其中包括本文记述的新型泰坦龙类（titanosaurian）新属新种*Shingopana songwensis*（gen. et sp. nov.）。该物种的化石标本包括一块左隅骨、多节颈椎、颈椎肋与背肋、一块左肱骨以及部分左耻骨。*Shingopana*的形态特征显示其与南美洲白垩纪晚期的风神龙亚科（aeolosaurine）泰坦龙类存在密切亲缘关系：其颈椎神经棘的球状膨大结构，与*Bonitasaura salgadoi*、*Overosaurus paradasorum*以及*Trigonosaurus pricei*的相关特征高度相似；其背肋还具有近端前、后突——该特征此前被认为仅存在于*Overosaurus*中。此外，*Shingopana*以中至后部颈椎具有分裂的前棘前关节板（divided spinoprezygapophyseal lamina）作为鉴别诊断特征。简约法（Parsimony）、未校准贝叶斯系统发育分析以及末端定年贝叶斯系统发育分析均支持，*Shingopana*是首个被证实与风神龙亚科亲缘关系紧密的非洲泰坦龙类。通过与同期的*Rukwatitan bisepultus*以及地理上邻近的*Malawisaurus dixeyi*等其他非洲泰坦龙类进行对比，研究结果表明，南部非洲的泰坦龙类类群并非单系群（monophyletic group），而是包含多样的分类单元。进一步来看，南部非洲的泰坦龙类与南美洲演化支的亲缘关系较北非代表类群更为密切，这暗示白垩纪期间构造运动驱动的两大陆块分离，可能促成了南部非洲动物群的逐步隔离分化。