about the same size as a ostirch
An oviraptor
Oviraptors did, but scientists found a fossil of one sitting on a clutch of eggs which looked like the eggs from Protoceratops . They were actually Oviraptor eggs. The scientists thought that Oviraptor died when it found the eggs
No
Oviraptor, by scientific guess, lived around 3 years, maybe 5 if there are few predators. Oviraptor could well defend itself, though. It is probable they could live longer, but we may never know, due to the fact that Oviraptor is extinct.
Oviraptor was a small dinosaur, measuring about 6 feet long and a little over 3 feet tall. Gigantoraptor was a close relative, but, as its name suggests, it was big, at 26 feet in length and weighing more than a ton.
on earth
Tyrannosaurs like Tarbosaurus and Alioramus, and dromaeosaurs like Velociraptor could have been natural predators of Oviraptor.
The dinosaur name oviraptor originally meant "egg thief", because of the fact that an oviraptor skeleton was discovered "stealing" eggs from another dinosaur's nest. But recent evidence actually shows that the oviraptor was just being a good mother and protecting her nest from egg thiefs, but most likely a sand storm.
Oviraptor probably would have run from predators. If it was desperate, it could have attacked by biting them with its beak or attacking with its claws.
The Maiasaura and the Oviraptor did.
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The closest living relatives of Oviraptor are birds. Birds are the only type of dinosaurs that still exist. Therefor, not only are birds the closest living relatives of the Oviraptor, they are also the closest living relatives of any other extinct dinosaur.