That must be some kind of tissue...to last millions of years. LOL!!
From other remains found in the same Park...
To the scientists’ astonishment, however, analysis with an electron microscope revealed what appeared to be red blood cells and collagen fibers that had remained intact over some 75 million years of fossilization.
Unlike bones and teeth, which can survive for hundreds of millions of years, soft tissues are among the first materials to disappear during the fossilization process. Even so, scientists have found intact soft tissue in dinosaur bones before. The most famous case dates to 2005, when Mary Schweitzer of North Carolina State University found collagen fibers in the fossilized leg bone of a Tyrannosaurus rex. But such discoveries are rare, and have previously occurred only with extremely well preserved fossils. The most extraordinary thing about the new find, which scientists from Imperial College London reported this week in the journal Nature Communications, is that the fossils they examined are of relatively poor condition (to put it kindly).
http://www.history.com/news/scientists-find-soft-tissue-in-75-million-year-old-dinosaur-bones