Although rare, stomach contents are the only way to be absolutely certain about predator-prey relationships in extinct ecosystems.
I have described two specimens of Microraptor preserving ingested remains. One preserves the articulated remains of an enantiornithine bird; the other preserves the articulated remains of previously unknown species of lizard (named Indrasaurus wangi). These specimens together indicate that Microraptor was an agile, opportunistic predator that swallowed prey largely whole and head first, similar to most extant carnivorous birds and lizards.
Read more about the remains of the enantiornithine bird:
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Read more about the remains of the lizard: