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Huaxiagnathus

Last updated August 14, 2025
Extinct genus of dinosaurs

Huaxiagnathus
Temporal range: Early Cretaceous, 125  Ma
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Huaxiagnathus orientalis.JPG
Huaxiagnathus fossil displayed in Hong Kong Science Museum
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family:† Compsognathidae
Genus:† Huaxiagnathus
Hwang et al., 2004
Species:
†H. orientalis
Binomial name
†Huaxiagnathus orientalis
Hwang et al., 2004
Synonyms
  • Sinotyrannus?
    Ji et al., 2009

Huaxiagnathus is an extinct genus of coelurosaurian theropod dinosaur from the Lower Cretaceous of China. The genus contains a single species, Huaxiagnathus orientalis, known from two immature individuals from the Yixian Formation. Huaxiagnathus may represent an earlier ontogenetic stage of the tyrannosauroid Sinotyrannus from the younger Jiufotang Formation.

Contents

  • Etymology
  • Description
  • Phylogeny
  • References

Etymology

The name Huaxiagnathus is derived from the Chinese Hua Xia , 華夏, a traditional word for "China", and from the Greek gnathos, Latinised into gnathus, meaning "jaw." [1]

Description

Scale diagram of the two known specimens with a human (holotype in green) Huaxiagnathus Size Comparison by PaleoGeek.svg
Scale diagram of the two known specimens with a human (holotype in green)
Skeletal diagram Huaxiagnathus skeletal.jpg
Skeletal diagram

The holotype (CAGS-IG-02-301, Chinese Academy of Geological Sciences, Beijing) specimen was collected from the Yixian Formation (Barremian stage, 125  million years ago) at Dabangou Village, Sihetun area, near Beipiao City, in western Liaoning Province. The holotype is a subadult and consists of an essentially complete skeleton, lacking only the end of the tail, preserved on five large slabs. Partially digested bones of an unidentified vertebrate were found within the holotype specimen. A larger, ontogenetically older specimen of Huaxiagnathus was discovered earlier in the Yixian Formation of the Sihetun area (NGMC 98-5-003, National Geological Museum of China, Beijing), but damage and mistakes made during its preparation rendered it unsuitable as a holotype. [1]

The known Huaxiagnathus specimens are larger than the related Sinosauropteryx , with the largest specimen about 1.8 meters (5.9 feet) in length. [1]

Hwang et al. diagnosed this genus as follows: differing from all other known compsognathids in having a very long posterior process of the premaxilla that overlaps the antorbital fossa, a manus equal to the combined lengths of the humerus and radius, large manual unguals I and II which are subequal in length and 167% the length of manual ungual III, a first metacarpal which has a smaller proximal transverse width than the second metacarpal, and the presence of a reduced olecranon process on the ulna. [1]

Phylogeny

In their 2004 description of Huaxiagnathus, Hwang et al. recovered it as the basalmost known compsognathid, as indicated by its unspecialized forearm. [1]

In 2024, Andrea Cau published a study on the phylogenetics of compsognathids and immature theropods in general that called the assessment of Huaxiagnathus—known only from immature specimens—within Compsognathidae into question. The paper recovered the taxon, along with four other proposed compsognathids in a polytomy within basal Coelurosauria. This polytomy notably did not include Composognathus proper, which would make none of these species compsognathids. [2]

Reconstructed skeleton of Sinotyrannus, a possible mature form and junior synonym of Huaxiagnathus Sinotyrannus kazuoensis skeletal.png
Reconstructed skeleton of Sinotyrannus, a possible mature form and junior synonym of Huaxiagnathus

Using an updated version of this matrix, Cau and Paterna (2025) determined that Sinotyrannus , a large coeval tyrannosauroid known from a specimen of an adult individual, was a mature form of Huaxiagnathus. Both species share a dorsally convex ilium with a short preacetabular process without an anteroventral hook. Other differences observed between the two species are likely the result of differences in body size and ontogenetic stage, consistent with the more established growth series of other tyrannosauroids like Tyrannosaurus. Since Huaxiagnathus was named before Sinotyrannus, this genus name holds priority, making Sinotyrannus a junior synonym of the former. [3]

Qiu et al. (2025) also argued against the monophyly of Compsognathidae using Cau's dataset and revised the definition of the monophyletic Sinosauropterygidae within Coelurosauria as a family containing all compsognathid-like theropods from the Jehol Biota of China: Sinosauropteryx , Huadanosaurus , Huaxiagnathus and Sinocalliopteryx , in addition to the Brazilian Mirischia . Their phylogenetic analyses are reproduced below: [4]

Topology A: OSP dataset [2]
Sinosauropterygidae

Sinosauropteryx lingyuanensis

Sinosauropteryx prima

Huaxiagnathus orientalis

Huadanosaurus sinensis

Mirischia asymmetrica

Sinocalliopteryx gigas

Tyrannosauroidea

Other maniraptoriforms

Topology B: TWiG dataset [5]

Tyrannosauroidea

Sinosauropterygidae

Mirischia asymmetrica

Huaxiagnathus orientalis

Sinocalliopteryx gigas

Juravenator starki

Huadanosaurus sinensis

Compsognathus longipes

Sinosauropteryx lingyuanensis

Sinosauropteryx prima

Other maniraptoriforms

References

  1. 1 2 3 4 5 Hwang, S.H.; Norell, M.A.; Ji, Q.; Gao, K. (2004). "A large compsognathid from the Early Cretaceous Yixian Formation of China". Journal of Systematic Palaeontology. 2 (1): 13–30. doi:10.1017/S1477201903001081.
  2. 1 2 Cau, Andrea (2024). "A Unified Framework for Predatory Dinosaur Macroevolution" (PDF). Bollettino della Società Paleontologica Italiana. 63 (1): 1–19. doi:10.4435/BSPI.2024.08 (inactive 12 July 2025). Archived from the original (PDF) on 2024-04-27. Retrieved 2024-04-22.{{cite journal}}: CS1 maint: DOI inactive as of July 2025 (link)
  3. ↑ Cau, Andrea; Paterna, Alessandro (May 2025). "Beyond the Stromer's Riddle: the impact of lumping and splitting hypotheses on the systematics of the giant predatory dinosaurs from northern Africa" . Italian Journal of Geosciences. 144 (2): 162–185. doi:10.3301/IJG.2025.10.
  4. ↑ Qiu, Rui; Wang, Xiaolin; Jiang, Shunxing; Meng, Jin; Zhou, Zhonghe (2025-02-22). "Two new compsognathid-like theropods show diversified predation strategies in theropod dinosaurs". National Science Review. 12 (5). doi: 10.1093/nsr/nwaf068 . ISSN   2095-5138. PMC   11970238 .
  5. ↑ Brusatte, Stephen L.; Lloyd, Graeme T.; Wang, Steve C.; Norell, Mark A. (2014-10-20). "Gradual Assembly of Avian Body Plan Culminated in Rapid Rates of Evolution across the Dinosaur-Bird Transition". Current Biology . 24 (20): 2386–2392. doi: 10.1016/j.cub.2014.08.034 .
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Taxon identifiers
Huaxiagnathus
  • Wikidata: Q1056138
  • EoL: 4433883
  • GBIF: 4822714
  • Open Tree of Life: 4126508
  • Paleobiology Database: 68220
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