| Archaeornithoides Temporal range: Late Cretaceous, 75 Ma |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | Dinosauria |
| Order: | Saurischia |
| Suborder: | Theropoda |
| (unranked): | Coelurosauria |
| Family: | Troodontidae? |
| Genus: | Archaeornithoides Elzanowksi & Wellnhofer, 1992 |
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Archaeornithoides is a genus of maniraptoriform theropod dinosaur. It was found in Late Cretaceous river sandstones of the Djadokhta Formation beds located in Bayn Dzak, Mongolia. The remains, consisting of a juvenile skull fragment comprehending paired maxillae and dentaries and also palate bones were described by Elzanowski and Wellnhofer in 1992[1] and 1993.[2]
The generic name (Archaeornithoides) means “shaped like an ancient bird” in ancient Greek. The specific descriptor (deinosauriscus) alludes to the animal's small size for a dinosaur.
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Elżanowski & Wellnhofer (1993) suggested that Archaeornithoides was the closest known relative to birds Avialae. This conclusion rested on key bird-like features; an interdigitated suture between the premaxilla and maxilla, broad palatal shelves, pneumatic sinuses, lack of interdental plates, and unserrated teeth. Since publication, though, all of these features have been discovered in new fossils of adult and/or juvenile troodonts and dromaeosaurs.[3]
Some scientists had suggested that the juvenile specimen of Archaeornithoides may belong to a previously known species of Mongolian troodontid, either Saurornithoides or Byronosaurus. However, studies of a juvenile Byronosaurus skull showed that theropod dinosaurs possess many distinctive adult characteristics even as hatchings or embryos, and that the lack of characters solidly linking Archaeornithoides to known adult specimens shows that it is probably a distinct species. Bever and Norell (in 2009) found no evidence to support the placement of Archaeornithoides close to Avialae, and only weak support for the idea that it is a juvenile troodontid.[4]
Elzanowski and Wellnhofer noted that the specimen has distinct bite marks, and suggested that its braincase was bitten off by a deltatheridiid (Deltatheridium) mammal the size of a weasel (adding that these are common in the Bayn Dzak assemblage). Clark and colleagues (2002) noted that it may have also passed through the digestive tract of the predator before fossilization. If true, this may be the first known evidence of Mesozoic mammals eating dinosaurs (see Repenomamus).