This is book number 1 in the Boundary series.
Paradigms Shift, Worlds Collide
A daring and resourceful paleontologist uncovers something at the infamous K-T boundary marking the end of dinosaurs in the fossil record--something big, dangerous, and absolutely, categorically impossible. It's a find that will catapult her to the Martian moon Phobos, then down to the crater-pocked desert of the Red Planet itself. For this mild-mannered fossil hunter may just have become Earth's first practicing xenobiologist
A new hard SF thriller from bestselling alternate history master Eric Flint and ace game designer Ryk E. Spoor.