Caenagnathinae

Caenagnathids Temporal range: Late Cretaceous, PreЄ Є O S D C P T J K Pg N
Reconstructed skull of Anzu wyliei
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Order:	Saurischia
Suborder:	Theropoda
Superfamily:	†Caenagnathoidea
Family:	†Caenagnathidae Sternberg, 1940
Type species
Caenagnathus collinsi Sternberg, 1940
Genera
†Anzu †Caenagnathus †Epichirostenotes †Gigantoraptor †Hagryphus †Microvenator †Ojoraptorsaurus †Elmisaurinae †Apatoraptor †Caenagnathasia †Chirostenotes †Elmisaurus †Leptorhynchos
Synonyms
Elmisauridae Osmólska, 1981

Caenagnathidae is a family of bird-like maniraptoran theropod dinosaurs from the Late Cretaceous of North America and Asia. They are a member of the Oviraptorosauria, and close relatives of the Oviraptoridae. Like other oviraptorosaurs, caenagnathids had specialized beaks, long necks, and short tails, and would have been covered in feathers. The relationships of caenagnathids were long a puzzle. The family was originally named by Charles Hazelius Sternberg in 1940 as a family of flightless birds. The discovery of skeletons of the related oviraptorids revealed that they were in fact non-avian theropods, and the discovery of more complete caenagnathid remains revealed that Chirostenotes pergracilis, originally named on the basis of a pair of hands, and "Ornithomimus" elegans, named from a foot, were caenagnathids as well.

Overall, the anatomy of the caenagnathids is similar to that of the closely related Oviraptoridae, but there are a number of differences. In particular, caenagnathid jaws exhibited a distinct suite of specializations not seen in other oviraptorosaurs. Compared to the oviraptorids, the jaws tended to be relatively long and shallow, suggesting that the bite was not as powerful. The inside of the lower jaws also bore a complex series of ridges and toothlike processes, as well as a pair of horizontal, shelf-like structures. Furthermore, the jaws were unusual in being hollow and air filled, apparently being connected to the air sac system. Caenagnathids also tended to be more lightly built than the oviraptorids. They had slender arms and long, gracile legs, although they lacked the extreme cursorial specializations seen in avimimids and Caudipteryx.

The name Caenagnathus (and hence Caenagnathidae) means "recent jaws"—when first discovered, it was thought that caenagnathids were close relatives of paleognath birds (such as the ostrich) based on features of the lower jaw. Since it would be unusual to find a recent group of birds in the Cretaceous, the name "recent jaws" was applied. Most paleontologists, however, now think that the birdlike features of the jaw were acquired convergently with modern birds.

The earliest known caenagnathid is Caenagnathasia martinsoni, from the Turonian Bissekty Formation of Uzbekistan. The jaw of Caenagnathasia already has the specialized ridges and crushing surfaces seen in later forms. This suggests that caenagnathids originated well before the Turonian, but currently, there are no Early Cretaceous caenagnathid fossils. Caenagnathids later appeared in western North America, during the Campanian, suggesting that they may have originated in Asia, then migrated into western North America. Caenagnathids showed considerable variation in form. The tiny jaws of Caenagnathasia suggest a small animal, perhaps the size of a turkey. An unnamed species from the Hell Creek Formation indicates a much larger animal, considerably larger than a human. If Gigantoraptor erlianensis is a caenagnathid, then it would represent far and away the largest member of the group, measuring up to 8 meters in length and weighing up to 1.4 tons. Their beaks also show considerable variation; that of Caenagnathasia is relatively short and deep, while that of Caenagnathus is long and shovel-shaped. This variation in size and beak shape suggests that caenagnathids evolved to exploit a range of ecological niches. Caenagnathids persisted up until the end of the Cretaceous period, as shown by the presence of at least two species in the late Maastrichtian Hell Creek Formation, before vanishing at the end of the Cretaceous along with all other non-avian dinosaurs.

...
Wikipedia