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| Silutitan sinensis & Hamititan xinjiangensis Wang, Bandeira, Qiu, Jiang, Cheng, Ma & Kellner, 2021 |
Abstract
The Early Cretaceous Hami Pterosaur Fauna in Northwest China preserves a large number of specimens of the sexually dimorphic pteranodontoid pterosaur Hamipterus tianshanensis, including 3D eggs and embryos. During the last decade, several more fossils have been collected in this area, including three somphospondylan sauropod specimens. The first is Silutitan sinensis gen. et sp. nov., which consists of an articulated middle to posterior cervical vertebrae series. The second, Hamititan xinjiangensis gen. et sp. nov., consists of an incomplete articulated caudal sequence that could be assigned to lithostrotian titanosaurs based on the strongly procoelous caudal vertebrae with lateral concave surface, as well as marked ventrolateral ridges. The third specimen consists of four sacral vertebral elements, apparently unfused, with exposed camellate internal bone and regarded as somphospondylan. Cladistic analyses based on different datasets recovered Silutitan sinensis as an euhelopodid closely related to Euhelopus and Hamititan xinjiangensis as a titanosaur. Besides the pterosaur Hamipterus and one theropod tooth, these dinosaurs are the first vertebrates reported in this region, increasing the diversity of the fauna as well as the information on Chinese sauropods, further supporting a widespread diversification of somphospondylans during the Early Cretaceous of Asia.
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| All specimens described in this paper shown in one outline of a generic titanosaur: preserved cervical elements of Silutitan sinensis gen. et sp. nov. (IVPP V27874) (red), preserved caudal elements of Hamititan xinjiangensis gen. et sp. nov. (HM V22) (yellow) and the preserved sacral elements (IVPP V27875) (green). Image credit: Maurílio Oliveira. |
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| Map showing the fossil site where the new sauropod dinosaur specimens were collected (A,B), and the relative positions of these three specimens (C). |
Systematic paleontology
SAUROPODA Marsh, 1878
NEOSAUROPODA Bonaparte, 1986
TITANOSAURIFORMES Salgado et al., 1997
SOMPHOSPONDYLI Wilson & Sereno, 1998
EUHELOPODIDAE Romer, 1956 (sensu D’Emic, 2012)
Silutitan gen. nov.
Type species. Silutitan sinensis sp. nov., type by monotypy.
Etymology. “Silu” means the “Silk Road” in Chinese Mandarin pinyin, in memory the great trade routes which connected the East and West. “titan” means giant in Greek, symbolic of the large size of this genus.
Silutitan sinensis new species.
Etymology. "sinensis" refers to China, in Latin.
Holotype. An articulated series of six cervical vertebrae (IVPP V27874) with almost all cervical ribs, housed at IVPP (Figs. 2, 3; Table 1).
Locality and Horizon. Hami, Xinjiang, China; Lower Cretaceous Shengjinkou Formation (Tugulu Group).
Diagnosis. An euhelopodid sauropod exhibiting the following autapomorphies found in the cervical vertebrae: (1) ventrolaterally bifurcated postzygodiapophyseal laminae [PODL] in middle to posterior cervical vertebrae, (2) anteriorly bifurcated posterior centrodiapophyseal laminae [PCDL] on the four posterior-most cervical vertebrae, (3) parapodiapophyseal laminae [PPDL] forming developed ventral flanges, (4) contact surface of diapophysis and tuberculum in the middle and posterior cervical vertebrae constricted on anterior and posterior faces. It is further characterized by the following combination of characters: cervical vertebrae with developed epipophyses, prezygodiapophyseal laminae anteriorly projected, lateral pneumatic fossae on centra restricted anteriorly, neural arches with two fossae bordered by the epipophyseal-prezygapophyseal laminae, and the neural spines reduced anteroposteriorly.
SOMPHOSPONDYLI Wilson & Sereno, 1998
TITANOSAURIA Bonaparte & Coria, 1993
Hamititan gen. nov.
Type species. Hamititan xinjiangensis sp. nov., type by monotypy.
Etymology. “Hami” refers to Hami city where the specimen was found, “titan”, from the giants of the Greek myths and commonly used to name titanosaur taxa.
Hamititan xinjiangensis new species.
Etymology. “xinjiangensis”, refers to Xinjiang, China.
Holotype. An articulated series of seven anterior to middle caudal (HM V22), including the proximal portions of three chevrons, housed at Hami Museum (Figs. 2, 4; Table 2).
Locality and Horizon. Hami, Xinjiang, China; Lower Cretaceous Shengjinkou Formation (Tugulu Group).
Diagnosis. A titanosaur sauropod exhibiting the following autapomorphies: (1) tall neural arches with the neural arch higher than the height of the centrum, (2) neural arch on the anteriormost caudal sagittally expanded, (3) deep postzygapophyseal spinodiapophyseal fossa [POSDF] presenting inner open cavities on the anteriormost caudal vertebrae, (4) transverse processes on most anterior caudal vertebrae directed upwards, (5) abruptly change of orientation of the transverse processes from upward (see 3) to downwards. The new species is further characterized by the following combination of characters: prezygapophyses on the caudal vertebrae projecting mainly anterodorsally; and short transverse processes compressed anteroposteriorly and directed laterally.
Conclusions:
The discovery of Silutitan sinensis and Hamititan xinjiangensis increased the sauropod diversity of Asia, particularly from an area where these vertebrates are not common. Silutitan sinensis is closely related to Euhelopus. The existence of a more inclusive clade of similar sauropods (Euhelopodidae) is still a matter of debate and pends on more detailed description of some putative euhelopodid.
Hamititan xinjiangensis is one of the few titanosaurian sauropod recovered from Asia, which shows an unusual combination of sauropod features. The presence of two somphospondylan species in the Tugulu Group novel information on somphospondylan evolution and provides further support for a widespread diversification of these sauropods during the Early Cretaceous of Asia.
Xiaolin Wang, Kamila L. N. Bandeira, Rui Qiu, Shunxing Jiang, Xin Cheng, Yingxia Ma and Alexander W. A. Kellner. 2021. The First Dinosaurs from the Early Cretaceous Hami Pterosaur Fauna, China. Scientific Reports. 11, 14962. DOI: 10.1038/s41598-021-94273-7
Xiaolin Wang, Alexander W.A. Kellner, Shunxing Jiang, ... et Zhonghe Zhou. 2014. Sexually Dimorphic Tridimensionally Preserved Pterosaurs and Their Eggs from China. Current Biology. DOI: 10.1016/j.cub.2014.04.054
