Open Paleo

Xunmenglong

Xing et al., 2020 shoon-MUNG-long

From Chinese xun ('swift'), meng ('fierce'), and long ('dragon'), meaning 'swift fierce dragon'

132.6–125.8 million years ago Hauterivian, Early Cretaceous
Early Cretaceous stages

Xunmenglong is a genus of compsognathid theropod dinosaur from the Huajiying Formation of Hebei Province, China. The type and only species is Xunmenglong yinliangis. The holotype material consists of a pelvis, tail base and hindlimbs that had previously been part of a chimera containing three different animals. The animal is described as being the smallest known member of Compsognathidae, being about the size of the sub-adult Scipionyx holotype specimen, or approximately 50 centimeters (1.6 ft) in length.

Under dispute

Xunmenglong was described as a small compsognathid in a polytomy with Compsognathus, Huaxiagnathus, and Juravenator, a placement Jones (2026) follows. Cau (2024) instead recovered it among the earliest-diverging branches of Tetanurae, outside Coelurosauria. It is retained in Compsognathidae; the basal-tetanuran hypothesis is reflected in the Compsognathidae clade dispute.

Diagnosis

  1. Penultimate pedal phalanx IV-4 markedly longer than IV-3
  2. Sacral and proximal caudal centra dorsoventrally taller than or as tall as anteroposteriorly long
  3. Vertical neural spines of proximal caudal vertebrae taller dorsoventrally than or as tall as centrum length
  4. Ilium with straight dorsal outline and rounded anterior margin in lateral view
  5. Tibia markedly longer than predicted by allometric trend among theropods (tibia/femur ratio 1.53)
  6. Three ossified distal tarsals II, III, and IV

Species

Xunmenglong yinliangis Xing et al., 2020

Type species

Named for the Yinliang Group of China, whose Yinliang Stone Natural History Museum houses the holotype.

Holotype
YLSNHM-00005 , Yinliang Stone Natural History Museum
Material
Sacrum, proximal caudal series, partial pelvis, and hindlimbs
Horizon
Sichakou Member, Huajiying Formation, Hauterivian, Early Cretaceous , 132.6–125.8 million years ago
Locality
Sichakou Basin, Hebei, China

References

  1. Xing, L.; Miyashita, T.; Wang, D.; Niu, K.; Currie, P. J. (2020). A new compsognathid theropod dinosaur from the oldest assemblage of the Jehol Biota in the Lower Cretaceous Huajiying Formation, northeastern China. Cretaceous Research 107. Elsevier BV. doi:10.1016/j.cretres.2019.104285 xing2020a
  2. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Theropods. Princeton University Press.

    Source of the mass and hip height estimates.

    jones2026c
  3. Cau, A. (2024). A Unified Framework for Predatory Dinosaur Macroevolution. Bollettino della Società Paleontologica Italiana 63(1): 1-19. doi:10.4435/BSPI.2024.08

    Recovered Xunmenglong among the earliest-diverging branches of Tetanurae, outside Coelurosauria.

    cau2024a