Oviraptorosauria

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Oviraptorosaurs Fossil range: Cretaceous
Nomingia by Michael Skrepnick.
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Sauropsida Order: Saurischia Suborder: Theropoda Infraorder: Oviraptorosauria Barsbold, 1976
Families
Avimimidae Caudipteridae Caenagnathidae Oviraptoridae

Oviraptorosaurs ("egg thief lizards") are a group of beaked, feathered dinosaurs from the Cretaceous Period of what are now Asia and North America. The group includes the Oviraptoridae, the Caenagnathidae and several species which do not belong to either of these families, including Avimimus, Caudipteryx, and Protarchaeopteryx. The group is close to the ancestry of birds and it has been suggested 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.

Contents 1 Feathers 2 Diet 3 True birds? 4 Taxonomy 4.1 Classification 4.2 Phylogeny 5 References

[edit] Feathers

Evidence for feathered oviraptorosaurs exists in several forms. Most directly, a few species of primitive oviraptorosaurs (Caudipteryx, Protarchaeopteryx) 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 one oviraptorosaur (Nomingia) was preserved with a pygostyle, a bony structure at the end of the tail that, in modern birds, is used to support a fan of feathers. 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 not have covered their eggs if they did not have wings and a substantial covering of feathers.

[edit] Diet

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.

[edit] True birds?

Even without direct evidence of feathers, most oviraptorosaurs are so bird-like that several scientists consider them to be true birds, more advanced than Archaeopteryx. Gregory S. Paul (1998, 2002) has written extensively on this possibility and Maryanska et al. published a technical paper, detailing this idea in 2002. Michael Benton (2004), in his widely-respected text Vertebrate Paleontology, also includes oviraptorosaurs as an order within the class Aves [1]. However, a number of researchers disagree with this classification, retaining oviraptorosaurs as non-avian maniraptorans slightly more primitive than the dromaeosaurs. For a detailed technical discussion of this debate, see Discussion of Maryanska et al. (2002) on EvoWiki.

[edit] Taxonomy

[edit] Classification

• Infraorder Oviraptorosauria
  • Incisivosaurus
  • Protarchaeopteryx
  •  ?Nomingia
  •  ?Shixinggia
  • Family Avimimidae
    • Avimimus
  • Family Caudipteridae
    • Caudipteryx
  • Superfamily Caenagnathoidea
    • Family Caenagnathidae
      • Caenagnathasia
      • Chirostenotes
      • Elmisaurus
      • Hagryphus
    • Family Oviraptoridae
      • Microvenator
      • Subfamily Ingeniinae
        • Conchoraptor
        • Heyuannia
        • "Ingenia"
        • Khaan
      • Subfamily Oviraptorinae
        • Citipati
        • Nemegtomaia
        • Oviraptor
        • Rinchenia

[edit] Phylogeny

Oviraptorosauria
 |--+--Incisivosaurus
 |  `-?Protarchaeopteryx
 `--+--Caudipteryx
       |--Avimimus
       |--Nomingia
       `--+--Shixinggia
             `--Caenagnathoidea
                    |--Caenagnathasia
                    |--Caenagnathidae
                    |  |-?Hagryphus
                    |  |--Chirostenotes
                    |  `--Elmisaurus
                    `--Oviraptoridae
                           |--Microvenator
                           |--Oviraptorinae
                           |      |--Oviraptor
                           |      |--Citipati
                           |      |--Rinchenia
                           |      `--Nemegtomaia
                           `--Ingeniinae
                                   |--Heyuannia
                                   |--"Ingenia" yanshini
                                   |--Conchoraptor
                                   `--Khaan

[edit] References

• Barsbold, R. (1983). "Carnivorous dinosaurs from the Cretaceous of Mongolia". Transactions of the Joint Soviet-Mongolian Paleontological Expedition 8: 39-44.
• Maryanska, T., Osmolska, H., & Wolsam, M. (2002). "Avialian status for Oviraptorosauria". Acta Palaeontologica Polonica 47(1): 97-116.
• Paul, G.S. (2002). Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Baltimore: Johns Hopkins University Press.
• Paul, G.S. (1988). Predatory Dinosaurs of the World. New York: Simon & Schuster.