| Huadanosaurus | |
|---|---|
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| Photograph (a) and line drawing (b) of the holotype specimen | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Sinosauropterygidae |
| Genus: | †Huadanosaurus Qiu et al.,2025 |
| Species: | †H. sinensis |
| Binomial name | |
| †Huadanosaurus sinensis Qiu et al., 2025 | |
Huadanosaurus is anextinct genus ofcompsognathid-like theropod dinosaurs from theEarly CretaceousYixian Formation of China. The genus contains asingle species,H. sinensis, known from a nearly complete skeleton preserving feather-like structures.
TheHuadanosaurusholotype specimen,IVPP V14202, was discovered in outcrops of theYixian Formation (Dawangzhangzi bed) inLingyuan ofLiaoning Province, China. The specimen consists of a nearly complete skeleton preserved on aslab, missing the feet and the end of the tail.[1] Filamentous integument is preserved around the tail. Prior to its description, the specimen was attributed to the related genusSinosauropteryx.[2]
In 2025, Qiu et al.describedHuadanosaurus sinensis as a new genus and species of sinosauropterygid theropods based on these fossil remains. Thegeneric name,Huadanosaurus, combines "Huadan"—a Chinese word referring to the birthday of a great person or institution—with theAncient Greekσαῦρος (sauros), meaning "lizard". This honors the 70th anniversary of the founding of the Academic Divisions of theChinese Academy of Sciences (CASAD). Thespecific name,sinensis, is derived from theLatin wordsina, which refers to China.[1]
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Qiu et al. (2025) identified theHuadanosaurus holotype as belonging to a probable immature individual based on the unfused vertebral neurocentral sutures and scarred bone surfaces. Furthermore, its skull, measuring 10.1 cm (4.0 in) long, is fairly large in relation to the rest of the body.[1] The holotype individual is around 1 metre (3.3 ft) long.[3]
Compared to other compsognathid-like theropods, theHuadanosaurus holotype preserves several anatomical characteristics of the skull, teeth, andilium that are similar totyrannosauroids. Some of these may suggest thatHuadanosaurus had a stronger bite force than its relatives. For example, there is a prominentsurangular shelf on the lower jaw, indicating a strongadductor muscle for closing the jaws. The generally deep skull and mandible, as well as the fusednasal, are all adaptations towards resisting high levels of biting stress. However, Qiu et al. interpret these features as convergent with the tyrannosauroid lineage, rather than indicative of a placement within that clade.[1]
A later comment by paleontologist Christophe Hendrickx suggested additional careful research onHuadanosaurus and other Jehol 'compsognathids' may support their reidentification as juvenile forms of larger contemporary tyrannosauroids known from mature specimens, such asYutyrannus andSinotyrannus.[3]
In 2010, Fucheng Zhang and colleagues examined the fossilized feathers of several dinosaurs and early birds. They found evidence that the specimens preservedmelanosomes, a type of cellorganelle that stores biological pigments and give the feathers of modern birds their colour. The researchers further compared the observed melanosome structures to those of modern birds to determine a general range of colour. Among the specimens studied was theHuadanosaurus holotype (then provisionally referred toSinosauropteryx). They observed the presence of spherical phaeomelanosomes in this specimen, which can be correlated withchestnut torufous color tones, suggesting that at least parts of the animal were covered in reddish-brown feather-like filaments.[2]
Huadanosaurus is similar to several dinosaurs historically called theCompsognathidae. However, a 2024 analysis byAndrea Cau proposed that these taxa did not form a naturalmonophyletic clade and that some are juveniles of largertetanurans.[4] To test this hypothesis, Qiu et al. (2025) scoredHuadanosaurus in Cau's "Ontogenetic State Partitioning" (OSP) phylogenetic matrix and the more traditional "Theropod Working Group" (TWiG) matrix.[5] Bothphylogenetic analyses found support for a natural group of allJehol Biota (Early Cretaceous) compsognathid-like theropods (Sinosauropteryxspp.,Huaxiagnathus, andSinocalliopteryx) as well as the BrazilianMirischia. Using the OSP matrix,Huadanosaurus was recovered as thesister taxon toMirischia andSinocalliopteryx. SinceCompsognathus was recovered outside of this group, Qiu et al. opted to use the nameSinosauropterygidae for this group. These results are displayed inTopology A below. Using the TWiG matrix,Huadanosaurus was found to be the sister to the group formed byCompsognathus andSinosauropteryx spp., as shown inTopology B below.[1]
Several fragments of mammal bones, includingeutherians andeutriconodonts, were found in the abdominal cavity region ofHuadanosaurus. Based on the disarticulated but associated, well-preserved condition of the mammal remains, the individuals were likely swallowed whole. This further implies thatHuadanosaurus individuals were incapable of firmly grasping with their hands to tear or bite prey items. Most Mesozoic mammals were likelynocturnal, suggestingHuadanosaurus was as well.[1]
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