Sinornithosaurus
A small, feathered dromaeosaurid from early Cretaceous China.
Sinornithosaurus, whose name combines Latin and Greek for "Chinese bird-lizard," belonged to the feathered dromaeosaurid group and lived during the early Cretaceous Period (late Barremian) in what is now China. By 1999, it was the fifth non-avian feathered dinosaur genus ever identified. The first specimen came from the Sihetun locality in western Liaoning, within the Jianshangou beds of the Yixian Formation, dated to 124.5 million years ago. Later finds occurred in the younger Dawangzhangzi bed, around 122 million years old.
Xu Xing described the genus and conducted a phylogenetic analysis showing it was a basal, or primitive, dromaeosaur. He also found that its skull and shoulder features closely resembled those of *Archaeopteryx* and other avialans. Together, these points indicate that early dromaeosaurs were more bird-like than later ones. *Sinornithosaurus* was among the smallest dromaeosaurids: the holotype measured 1.2 meters (3.9 feet) long and weighed 3–5 kilograms (6.6–11.0 pounds).
Fossil impressions show feathers covering its entire body and forming wings, indistinguishable in structure from bird feathers in the same deposits. Body feathers were 3–4.5 centimeters long and came in two types: tufts of several filaments like modern down, and feathers with barbs joined along a central shaft (rachis), similar to modern bird feathers. However, unlike flight feathers of flying birds, they lacked barbules—tiny hooks that create a continuous vane. Some scientists suggest these feathers might have allowed *Sinornithosaurus* to glide short distances after leaping from trees. A 2010 study, based on microscopic cell structures, indicated its feathers likely varied in color across the body, with rod and spherical melanosomes suggesting black and rufous hues.
In 2009, a team led by Empu Gong examined a well-preserved skull and proposed *Sinornithosaurus* was the first venomous dinosaur. They noted long, fang-like maxillary teeth with prominent grooves running down the outer surface toward the rear, a feature seen only in venomous animals. They also interpreted a cavity in the jaw above these teeth as a possible venom gland site. Gong suggested these adaptations helped it hunt small prey like birds, using its fangs to penetrate feathers and envenomate prey, while short, forward-pointing teeth at the jaw tip might have stripped feathers. However, in 2010, a te
- lived
- Early Cretaceous (late Barremian), about 124.5–122 million years ago
- field
- Paleontology
- known_for
- Being a basal, feathered dromaeosaurid with bird-like skull and shoulder features; among the smallest dromaeosaurids
- type_species
- Sinornithosaurus millenii (described 1999)
- length
- 1.2 meters (3.9 ft) for the holotype
- weight
- 3–5 kilograms (6.6–11.0 lb)
Quick Facts
- Taxon
- Sinornithosaurus
- Type Species
- Sinornithosaurus millenii
- Type Species Authority
- Xu, Wang, & Wu, 1999
- Subdivision
- S. millenii / Xu, Wang, & Wu, 1999 · S. haoiana? / Liu, Ji, Tang & Gao, 2004
Facts from the source article.
Lore & Background
Sinornithosaurus was described by Xu Xing, whose phylogenetic analysis demonstrated that it is basal, or primitive, among the dromaeosaurs. He also showed that features of the skull and shoulder are very similar to Archaeopteryx and other avialans, indicating that the earliest dromaeosaurs were more like birds than later dromaeosaurs. Specimens have preserved impressions of feathers covering the entire body and forming wings, indistinguishable in form from bird feathers from the same deposits. The body feathers were 3–4.5 cm long and included tuft-like down feathers and vaned feathers with a central shaft, though lacking barbules for a continuous vane.
Reader's Guide
Sinornithosaurus is significant as an early feathered dinosaur that helps clarify the evolutionary transition from non-avian dinosaurs to birds. Its basal position among dromaeosaurs and its bird-like skull and shoulder features support the idea that the earliest members of this group were more avian than later forms. The presence of vaned feathers, similar to those of contemporary birds, suggests that such plumage was widespread among early dromaeosaurs. A 2010 study indicated that Sinornithosaurus may have had feathers varying in color across the body, with black and rufous hues based on melanosome analysis. The possibility of a venomous bite was proposed in 2009 but disputed in 2010, with critics noting grooved teeth are common in other theropods and that the supposed venom gland chambers could not be independently verified. Comparisons of scleral rings suggest it may have been cathemeral, active throughout the day and night. Its ability to glide has been debated, with some studies suggesting aerodynamic potential and others arguing it was too heavy for flight.
Did You Know?
- Sinornithosaurus means 'Chinese bird-lizard' in a combination of Latin and Greek.
- It was the fifth non-avian feathered dinosaur genus discovered by 1999.
- A 2010 study suggested Sinornithosaurus had black and rufous feathers based on melanosome analysis.
- The possibility of a venomous bite was proposed in 2009 but disputed in 2010 due to grooved teeth being common in other theropods.
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