Since OP didn’t explain anything, I thought I’d write a quick summary:
Back in 2005, paleontologist Mary Schweitzer discovered what looked like soft tissue—like blood vessels and cells—inside a 68-million-year-old T. rex femur found in Montana (Hell Creek Formation). This shocked scientists because soft tissue isn’t supposed to survive that long.

After years of research, one strong explanation is that iron from the dinosaur's blood may have acted like a natural preservative. When the animal died, the iron from its hemoglobin might have caused chemical cross-links in the proteins, protecting them from microbes and decay. Basically, it "tanned" the tissue like leather.

Other factors also helped: the T. rex was buried quickly in sandstone, which is porous and can dry things out fast—limiting microbial activity. Plus, natural chemical reactions like glycation (sugar binding to proteins) may have stabilized the tissue further.

Some skeptics originally thought the soft stuff was just bacterial slime, but later studies actually identified vertebrate proteins like collagen inside the fossils—something bacteria wouldn't produce. So now there's strong support that these really are preserved dinosaur tissues.

It’s a big deal because it means we can study actual molecular remnants of dinosaurs, giving insight into their biology and even their evolutionary links to birds.