Once upon a time there lived a certain mammal named Necrolestes.  Its name means "Stealing the Dead," and that's exactly what it seems to have done in order to build its body type.  It was an odd assortment of characteristics from various animals, including some taken from other animals that had been extinct for tens of millions of years even before it came about.  Is it possible that this strange animal resulted from DNA exchange between species?  According to Asher et al,

Necrolestes has posed an enigma for multiple generations of paleontologists.  Despite the high quality of its osteological remains, making sense of its relationships within the framework of modern mammal diversity has proven difficult. 

So difficult, in fact, that six entirely different groups of animals have been listed as possibilities for its classification.  Its cheek teeth look like those of Gondwanatheres, a primitive mammal from the K-T Boundary 65 million years ago.  Its digital flexor tendon looks like that of a marsupial mole, but its mandibular angle is not like that of a marsupial.  Its incisors and fibula look metatherian.  In short, Necrolestes is a puzzling mix of various characteristics of its contemporaries, combined with characteristics from species that went extinct 20 million years before its time.[1]  It's as if the space alian angels, in order to invent this creature, mixed up DNA stir fry extracted from a bunch of different animals, and then threw in some 20 million year old DNA they had kept on ice.Click to read more about fossil frankensteins.