Huaxiagnathus

Huaxiagnathus Temporal range: Early Cretaceous,
Huaxiagnathus orientalis fossil displayed in Hong Kong Science Museum
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
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

Huaxiagnathus is a genus of theropod dinosaur from the Lower Cretaceous of China. It was a compsognathid, large for that group at about half a meter longer than Compsognathus and larger specimens of Sinosauropteryx, with the largest specimen about 1.8 meters (5.9 feet) in length.

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."

Description

Scale diagram of the two known specimens with a human (holotype in green)

Skeletal diagram

The holotype (CAGS-IG-02-301, Chinese Academy of Geological Sciences, Beijing) specimen was collected from the Yixian Formation (Jehol Group, Aptian) at Dabangou Village, Sihetun area, near Beipiao City, in western Liaoning Province. The holotype 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. Another, larger 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.

Cladistic analysis indicates that Huaxiagnathus is the basal most known compsognathid, as indicated by its unspecialized forearm.

Hwang et al. (2004, pp. 14–15) 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. In 2024, Andrea Cau published a study on the phylogenetics of compsognathids and immature theropods in general that called the assessment of Huaxiagnathus 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.

Phylogeny

Here is a simplified version of Cau (2024), which shows Huaxiagnathus in bold.

Tetanurae

Siamraptor Siamotyrannus Orionides Streptospondylus Xuanhanosaurus Poekilopleuron Piveteausaurus Piatnitzkysaurus Marshosaurus Leshansaurus Eustreptospondylus Condorraptor Asfaltovenator Sciurumimus Nedcolbertia Magnosaurus Duriavenator Afrovenator Compsognathus longipes Compsognathus corallestris Torvosaurus tanneri Torvosaurus gurneyi Megalosaurus Scipionyx Wiehenvenator Iberospinus Baryonychinae Spinosaurinae Avetheropoda Allosauroidea (Incl. Juravenator at an indeterminate position) Coelurosauria Sinosauropteryx Sinocalliopteryx Mirischia Huaxiagnathus Zuolong Tyrannoraptora Maniraptoromorpha NGMC 2124 Tanycolagreus Stokesosaurus Juratyrant Eutyrannosauria