Coelurosauria
Clade of hollow-tailed dinosaurs that includes all birds.
Coelurosauria, meaning "hollow-tailed lizards," is a major clade within theropod dinosaurs, defined as all theropods more closely related to birds than to carnosaurs. This group includes compsognathids, tyrannosauroids, ornithomimosaurs, maniraptorans, and, more recently, megaraptorans, though the placement of the latter remains uncertain. Maniraptora itself encompasses birds, the only dinosaur lineage still living today. Historically, the term was used for all small theropods, but that classification has since been revised. Anatomically, coelurosaurs are distinguished by a sacrum longer than in other dinosaurs, a tail stiffened toward the tip, a bowed ulna, and a tibia longer than the femur. The last common ancestor of the group likely evolved the ability to digest plant matter, adapting to an omnivorous diet, a trait thought to contribute to the clade’s success; later lineages specialized into insectivorous, herbivorous, and carnivorous forms. The clade includes both the largest known carnivorous dinosaurs, such as *Tyrannosaurus*, and some of the smallest, like *Microraptor* and *Parvicursor*. Most feathered dinosaurs discovered are coelurosaurs, and it is considered probable that all coelurosaurs were feathered, though skin impressions from some members show pebbly, scaly skin, indicating feathers did not completely replace scales. Fossil traces of feathers have been found in most major coelurosaurian lineages, and scales are retained on portions of the body, particularly the feet. The oldest unambiguous coelurosaurs are proceratosaurid tyrannosauroids from the late Middle Jurassic, and by the Late Jurassic, coelurosaurian differentiation was virtually complete. A superb range of early Cretaceous fossils, including avians, comes from the Yixian Formation in Liaoning, where all known theropods are coelurosaurs. Most coelurosaur groups went extinct in the Cretaceous–Paleogene event, with only modern birds surviving. Under modern cladistics, birds are considered the only living lineage of coelurosaurs, classified within the subgroup Maniraptora.
- field
- Paleontology
- known_for
- Clade of theropod dinosaurs that includes birds and feathered dinosaurs
- time_range
- Late Triassic to present (birds)
- key_fossil_sites
- Yixian Formation (Liaoning), Morrison Formation (Wyoming), Daohugou Beds (China), Bavaria
- oldest_unambiguous_members
- Proceratosaurus and Kileskus from the late Middle Jurassic
Quick Facts
- Taxon
- Coelurosauria
Facts from the source article.
Lore & Background
Coelurosauria, meaning "hollow-tailed lizards," is the clade of theropod dinosaurs more closely related to birds than to carnosaurs. This group includes compsognathids, tyrannosauroids, ornithomimosaurs, maniraptorans, and possibly megaraptorans, though the latter's placement remains uncertain. Maniraptora itself contains birds, the only dinosaur lineage still living. Historically, the term was applied to all small theropods, but that usage has been revised. Anatomically, coelurosaurs are distinguished by a sacrum longer than in other dinosaurs, a stiffened tail tip, a bowed ulna, and a tibia longer than the femur. The last common ancestor likely evolved an omnivorous diet, a trait that may have fueled the group's success; later lineages specialized into insectivores (Alvarezsauridae), herbivores (Therizinosauridae), and carnivores (Tyrannosauroidea, Dromaeosauridae). The clade includes both the largest carnivorous dinosaurs, such as *Tyrannosaurus*, and the smallest, like *Microraptor* and *Parvicursor*. Most feathered dinosaurs discovered are coelurosaurs, and it is considered probable that all coelurosaurs were feathered, though some skin impressions show pebbly, scaly skin, indicating feathers did not entirely replace scales. Fossil traces of feathers appear in most major coelurosaurian lineages, while scales and scutes are retained on feet and, in some primitive species, on upper legs and tail portions. Feather-like structures are also known in some ornithischians and pterosaurs, but these may have evolved independently. Brain casts show that an increase in cerebrum size began with Coelurosauria and continued through maniraptoran and early bird evolution. The oldest unambiguous coelurosaurs are proceratosaurid tyrannosauroids from the late Middle Jurassic. By the Late Jurassic, coelurosaurian differentiation was virtually complete, as shown by fossils like *Archaeopteryx* from Bavaria and *Ornitholestes* from the Morrison Formation. The Early Cretaceous Yixian Formation in Liaoning yields a superb range of coelurosaurian fossils, including avians. Most coelurosaur groups perished in the Cretaceous–Paleogene extinction event, with only Neornithes (modern birds) surviving and diversifying. Under cladistic definitions, birds are considered the only living coelurosaurs. A juvenile coelurosaur tail fragment was found encased in amber in 2015.
Reader's Guide
Coelurosauria is a pivotal clade in dinosaur evolution because it includes birds, the only dinosaur lineage that survives today. The study of coelurosaurian anatomy, particularly the brain and sensory systems, helps document the neurological transition from reptiles to modern birds. The discovery of feathered coelurosaurs has revolutionized understanding of dinosaur integument and the origin of feathers. Although feathers were once thought exclusive to coelurosaurs, similar structures in ornithischians and pterosaurs suggest either common ancestry or convergent evolution. The clade's classification has undergone extensive revision, moving from a 'dumping ground' for small theropods to a precisely defined group that includes both tiny feathered dinosaurs and giant predators like Tyrannosaurus. The group's ability to adapt to diverse diets—from herbivory to insectivory to carnivory—likely contributed to its long-term success and eventual survival through birds.
Did You Know?
- Most feathered dinosaurs discovered so far have been coelurosaurs.
- The group includes both the largest (Tyrannosaurus) and smallest (Microraptor, Parvicursor) carnivorous dinosaurs ever discovered.
- The oldest unambiguous coelurosaurs are the proceratosaurid tyrannosauroids Proceratosaurus and Kileskus from the late Middle Jurassic.
Frequently Asked Questions
Who is Coelurosauria?
Coelurosauria is a clade of theropod dinosaurs whose name means 'hollow-tailed lizards,' uniting every theropod that is more closely related to modern birds than to carnosaurs. The group spans an enormous diversity of forms, from tiny compsognathids up through tyrannosauroids, ornithomimosaurs, maniraptorans, and megaraptorans.
What are Coelurosauria's powers/role?
This clade is the one most strongly linked to feathers, as the overwhelming majority of all known feathered dinosaurs ever recovered turn out to be coelurosaurs. It also holds the record for the widest size range among carnivorous dinosaurs, packing both some of the smallest and some of the largest meat-eaters ever found.
How does Coelurosauria's story end?
Rather than vanishing at the end of the Cretaceous, Coelurosauria's lineage persists to this day through its surviving branch: birds. The clade's overall time range therefore stretches from the Late Triassic all the way to the present, making it the only dinosaur group still alive.
Why is Coelurosauria important?
It is the sole known dinosaur group with living descendants, creating a direct evolutionary bridge from the Mesozoic to the animals we encounter today. Its members also include some of the most iconic theropods—tyrannosaurs, ornithomimosaurs, and the ancestors of every bird species—placing it at the heart of dinosaur-evolution research.
What's Coelurosauria's origin story?
The earliest unambiguous coelurosaur fossils, Proceratosaurus and Kileskus, come from the late Middle Jurassic, marking the group's first clear appearance in the record. Since then, its descendants have been uncovered in key sites like the Yixian Formation in Liaoning, the Morrison Formation in Wyoming, the Daohugou Beds in China, and localities in Bavaria.
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