You know how many modern mammals like cats and ferrets occasionally adopt their prey? Well, it makes sense that Mesozoic mammals also did this. In this case, a Gobiconodon took a fancy to an enantiornithean bird and is shoving it down her pouch. This is incredibly painful for both parties - the mammal gets a violently thrashing dinosaur ripping her pouch while the bird is being suffocated by the synapsid's pouch.
