[D] Xiongguanlong baimoensis [sG] [T]
Describer
Li, Norell, Gao, Smith & Makovicky, 2009
Time
Cretaceous Early Aptian Albian
Classification
Saurischia Theropoda Tyrannosauria [Tyrannosauroidea]
Diet
Carnivore
Fossilsite
Xinminpu Group, Yujingzi Basin, Gansu, China
Info
Xiongguanlong baimoensis from the Aptian–Albian Xinminpu Group of western China that represents a phylogenetic, morphological, and temporal link between these disjunct portions of tyrannosauroid evolutionary history. Xiongguanlong is recovered in our phylogenetic analysis as the sister taxon to Tyrannosauridae plus Appalachiosaurus, and marks the appearance of several tyrannosaurid hallmark features, including a sharp parietal sagittal crest, a boxy basicranium, a quadratojugal with a flaring dorsal process and a flexed caudal edge, premaxillary teeth bearing a median lingual ridge, and an expanded axial neural spine surmounted by distinct processes at its corners.
Xiongguanlong is characterized by a narrow and elongate muzzle resembling that of Alioramus. The slender, unornamented nasals of Xiongguanlong are inconsistent with recent hypotheses of correlated progression in tyrannosauroid feeding mechanics, and suggest more complex patterns of character evolution in the integration of feeding adaptations in tyrannosaurids.
Body mass estimates for the fullgrown holotype specimen of Xiongguanlong fall between those of Late Cretaceous tyrannosaurids and Barremian tyrannosauroids, suggesting that the trend of increasing body size observed in North American Late Cretaceous Tyrannosauridae may extend through the Cretaceous history of Tyrannosauroidea though further phylogenetic work is required to corroborate this.
Etymology
Xiongguanlong—from the Mandarin Xiong Guan for Grand Pass, a historic name for the nearby city of Jiayuguan, and long for dragon; and baimoensis from Mandarin for White Ghost in reference to a prominent topographic feature in the field area dubbed the White Ghost Castle.
Holotype
FRDC-GS JB16-2-1 a complete skull without lower jaws, complete presacral vertebral series, partial right ilium.
Locality and horizon
White Ghost Castle field area, Yujingzi Basin, Gansu, China. The specimen derives from a grey mudstone near the bottom of the Early Cretaceous sedimentary series exposed in the basin. Other faunal elements from these strata include turtles, therizinosauroids (Li et al. 2007, 2008), ornithomimosaurs (Makovicky et al. in press), sauropods and ornithopods, whereas overlying redbed facies yield a fauna dominated by a small Neoceratopsian cf. Auroraceratops (You et al. 2005). Clear faunal similarities exist with the Xinminpu Group (Tang et al. 2001; Li et al. 2008) in the nearby Mazongshan and Suanjingzi basins, but some lithological and faunal differences at the species level indicate that these localities may not be completely correlative. These faunal similarities along with preliminary palynological examination indicate an Aptian–Albian age for the rocks that yielded the holotype of Xiongguanlong.
Diagnosis
Midsized tyrannosauroid (see electronic supplementary material 2 for measurements) with a uniquely elongate preorbital region reaching over two thirds of skull length. It can be distinguished from Late Cretaceous tyrannosaurids in lacking synapomorphies such as a rugose texture on the fused nasals, a distinct cornual process on the lacrimal, a pneumatic quadrate, and two pairs of cervical pleurocoels. It is more derived than Barremian tyrannosauroids in the possession of a basicranium that is wider than long, absence of pneumatic foramina along the lateral edge of the nasal, premaxillary teeth with a median lingual ridge, and lateral processes at the corners of the axial neural spine. Xiongguanlong differs from Dilong, Eotyrannus, Gorgosaurus and adult specimens of Tyrannosaurus in lacking serrations along the carinae of the premaxillary dentition. Our taxonomic usage of the terms tyrannosauroid and tyrannosaurid follows Sereno et al. (2005).
Li, Norell, Gao, Smith & Makovicky, 2009
Time
Cretaceous Early Aptian Albian
Classification
Saurischia Theropoda Tyrannosauria [Tyrannosauroidea]
Diet
Carnivore
Fossilsite
Xinminpu Group, Yujingzi Basin, Gansu, China
Info
Xiongguanlong baimoensis from the Aptian–Albian Xinminpu Group of western China that represents a phylogenetic, morphological, and temporal link between these disjunct portions of tyrannosauroid evolutionary history. Xiongguanlong is recovered in our phylogenetic analysis as the sister taxon to Tyrannosauridae plus Appalachiosaurus, and marks the appearance of several tyrannosaurid hallmark features, including a sharp parietal sagittal crest, a boxy basicranium, a quadratojugal with a flaring dorsal process and a flexed caudal edge, premaxillary teeth bearing a median lingual ridge, and an expanded axial neural spine surmounted by distinct processes at its corners.
Xiongguanlong is characterized by a narrow and elongate muzzle resembling that of Alioramus. The slender, unornamented nasals of Xiongguanlong are inconsistent with recent hypotheses of correlated progression in tyrannosauroid feeding mechanics, and suggest more complex patterns of character evolution in the integration of feeding adaptations in tyrannosaurids.
Body mass estimates for the fullgrown holotype specimen of Xiongguanlong fall between those of Late Cretaceous tyrannosaurids and Barremian tyrannosauroids, suggesting that the trend of increasing body size observed in North American Late Cretaceous Tyrannosauridae may extend through the Cretaceous history of Tyrannosauroidea though further phylogenetic work is required to corroborate this.
Etymology
Xiongguanlong—from the Mandarin Xiong Guan for Grand Pass, a historic name for the nearby city of Jiayuguan, and long for dragon; and baimoensis from Mandarin for White Ghost in reference to a prominent topographic feature in the field area dubbed the White Ghost Castle.
Holotype
FRDC-GS JB16-2-1 a complete skull without lower jaws, complete presacral vertebral series, partial right ilium.
Locality and horizon
White Ghost Castle field area, Yujingzi Basin, Gansu, China. The specimen derives from a grey mudstone near the bottom of the Early Cretaceous sedimentary series exposed in the basin. Other faunal elements from these strata include turtles, therizinosauroids (Li et al. 2007, 2008), ornithomimosaurs (Makovicky et al. in press), sauropods and ornithopods, whereas overlying redbed facies yield a fauna dominated by a small Neoceratopsian cf. Auroraceratops (You et al. 2005). Clear faunal similarities exist with the Xinminpu Group (Tang et al. 2001; Li et al. 2008) in the nearby Mazongshan and Suanjingzi basins, but some lithological and faunal differences at the species level indicate that these localities may not be completely correlative. These faunal similarities along with preliminary palynological examination indicate an Aptian–Albian age for the rocks that yielded the holotype of Xiongguanlong.
Diagnosis
Midsized tyrannosauroid (see electronic supplementary material 2 for measurements) with a uniquely elongate preorbital region reaching over two thirds of skull length. It can be distinguished from Late Cretaceous tyrannosaurids in lacking synapomorphies such as a rugose texture on the fused nasals, a distinct cornual process on the lacrimal, a pneumatic quadrate, and two pairs of cervical pleurocoels. It is more derived than Barremian tyrannosauroids in the possession of a basicranium that is wider than long, absence of pneumatic foramina along the lateral edge of the nasal, premaxillary teeth with a median lingual ridge, and lateral processes at the corners of the axial neural spine. Xiongguanlong differs from Dilong, Eotyrannus, Gorgosaurus and adult specimens of Tyrannosaurus in lacking serrations along the carinae of the premaxillary dentition. Our taxonomic usage of the terms tyrannosauroid and tyrannosaurid follows Sereno et al. (2005).