Fossil range: Cretaceous, 145–65 Ma
Fossil skeleton of Khaan mckennai
| Scientific classification
Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot - like skulls, with or without bony crests atop the head. The group includes the Oviraptoridae, the Caenagnathidae and several species which do not belong to either of these families, including Avimimus and Caudipteryx, and Incisivosaurus. They ranged in size from Caudipteryx, which was the size of a turkey, to the 8 meter long, 1.4 ton Gigantoraptor. The group (along with all maniraptoran dinosaurs) is close to the ancestry of birds. Analyses like those of Osmolska et al. (2004) suggest that they may in fact represent primitive flightless birds.
Paul Sereno, 2005 named the group Oviraptoriformes for all dinosaurs closer to Oviraptor than to modern birds. Therizinosaurs are usually considered members of this larger group, alongside the oviraptorosaurs.
Oviraptorosaurians are different from most other maniraptorans in the form of their skulls. They have shortened snouts, beak-like jaws with few or no teeth, and a large opening in the lower jaw bone. Some have bony crests atop the skull. The most primitive members have a few teeth in the front of the mouth; in Incisivosaurus, they are enlarged and form bizarrely prominent "bucktoothed" incisors. The arms and hands are generally long (though very reduced in some advanced species) and the shoulder girdle is large and massive, with flexed coracoid bones and prominent attachments for strong arm muscles.
Their tails are very short compared to other maniraptorans. In Nomingia and Similicaudipteryx, the tail ends in four fused vertebrae which Osmólska, He, and others have referred to as a "pygostyle", but which Witmer found was anatomically different and evolved separately from the pygostyle of birds (a bone which serves as the attachment point for a fan of tail feathers).
Evidence for feathered oviraptorosaurs exists in several forms. Most directly, two species of primitive oviraptorosaurs (Caudipteryx) have been found with impressions of well developed feathers, most notably on the wings and tail, suggesting that they functioned at least partially for display. Secondly, at least two oviraptorosaur specimens (Nomingia and Similicaudipteryx) preserved tails ending in something like a pygostyle, a bony structure at the end of the tail that, in modern birds, is used to support a fan of feathers. Similarly, quill knobs (anchor points for wing feathers on the ulna) have been reported in the oviraptorosaurian species Avimimus portentosus. Additionally, a number of oviraptorid specimens have famously been discovered in a nesting position similar to that of modern birds. The arms of these specimens are positioned in such a way that they could perfectly cover their eggs if they had small wings and a substantial covering of feathers.
The eating habits of these animals are not fully known: they have been suggested to have been either carnivorous, herbivorous, mollusk-eating or egg-eating (the latter is no longer considered valid); these options are not necessarily incompatible.
Some ate small vertebrates. Evidence for this comes from a lizard skeleton preserved in the body cavity of Oviraptor and two baby Troodontid skulls found in a Citipati nest. Evidence in favor of a herbivorous diet includes the presence of gastroliths preserved with Caudipteryx. There are also arguments for the inclusion of mollusks in their diet.
Originally these animals were thought to be egg raiders, based on a Mongolian find showing Oviraptor on top of a nest. Recent studies have shown that in fact the animal was on top of its own nest.
Relationship to birds Edit
The 2007 cladistic analysis of Turner an colleagues recovered the Oviraptorosauria as a maniraptoran clade (natural grouping) that branches off from the main lineage of maniraptorans far before birds. They found that the oviraptorosaurs are the sister group to the Therizinosauria and that the two, together, are more basal than any member of Paraves. However, a more recent study by Zanno and colleagues challenged that finding, showing therizinosaurs to be more primitive and not closely related to oviraptorosaurs.
Oviraptorosaurs, like dromaeosaurs, are so bird-like that several scientists consider them to be true birds, more advanced than Archaeopteryx. Gregory S. Paul has written extensively on this possibility and Teresa Maryańska and colleagues published a technical paper, detailing this idea in 2002. Michael Benton, in his widely-respected text Vertebrate Paleontology, also included oviraptorosaurs as an order within the class Aves. However, a number of researchers have disagreed with this classification, retaining oviraptorosaurs as non-avialan maniraptorans slightly more primitive than the dromaeosaurs.
- Infraorder Oviraptorosauria
- Family Avimimidae
- Family Caudipteridae
- Superfamily Caenagnathoidea
Oviraptorosaurians have shortened rostrums, massive, beaklike mandibles, and long parietals. The most primitive members have four pairs of teeth in the premaxillae, in Incisivosaurus they are enlarged and form bizarrely prominent bucktoothed incisors. The more advanced members have no teeth in the jaws. Pneumatization is extensive in the skulls and vertebrae of the more advanced members. Oviraptorosauria have thick, U - shaped furculae and a large sternal plates that are wider (together) than they are long, unlike in birds and dromaeosaurs. The arms are around half the length of the legs and over half the length of the presacral vertebral column. The Hands are long, and tridactyl, with a reduced third finger in Caudipteryx and Ingenia. There are between 5 and 8 sacral vertebrae. The pubis is vertical or subvertical. The tibia is 15%-25% longer than the femur. The tail is short, with the number of vertebrae reduced to 24 or so, and proximally very thick, with broad transverse processes.The ischium retains the primitive character of a prominent, triangular obturator process and lack the proximodorsal process that is found in birds. The pectoral girdle is also primitive; the scapula is a broad blade that is distally expanded, it lies on the lateral aspect of the thorax at an angle to the vertebral column, and the coracoid has the primitive coelurosaur shape with a proximal supracoracoidal nerve foramen and a moderate biceps tubercle.
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