The Major Groups of Coelurosaurs
Extremely bird-like theropod dinosaurs
Warning: You are entering an area of taxonomic research that is constantly changing. The phylogeny of this group of theropods is debated by paleontologists involved in its study, and new classifications are proposed several times a year! We will attempt to keep this site updated, but for now, as you warily maneuver through the shadowy byways of this theropod exhibit, remember that the relationships of this diverse group are not yet understood fully. It is both a frustrating and exciting area of research. So tread carefully from here on and watch the shadows! Hungry beasts lurk ahead!
Current coelurosaur classification
Coelurosauria is defined as the clade containing all theropods more closely related to birds than to carnosaurs. Some diagnostic characteristics of coelurosaurs include elongated arms and well- developed hinge-like ankles (possible rotation of the ankle is reduced, which is helpful during locomotion). These features may be lost or modified by later coelurosaurs (birds, for example).
All coelurosaurs show a great number of morphological similarities with birds, but different coelurosaurs lack different bird-like characteristics, so this complicates the matter of resolving the phylogeny of the group.
Two examples of this problem are the very bird-like Compsognathus longipes (shown at right) and Ornitholestes hermanni, small theropods known from good specimens, but whose phylogenetic affinities have not been well resolved yet, because they share some features that might closely unite them with a group, but then lack some features that are considered diagnostic for that group. At this point they are considered incertae sedis;in other words, we know that they are theropods; and probably coelurosaurs; but we don't know who they are related to or how they fit into the big picture of theropod phylogeny.
Major coelurosaurian groups: