Archaeornithoides by Moondawg

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 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.

Elzanowski & 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.

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).