Who has closest DNA to dinosaurs?

Could you please explain, in a concise manner, who possesses the closest DNA to dinosaurs among the current living organisms? I'm intrigued to know if scientists have discovered any modern-day species that share a remarkable genetic similarity with these ancient reptiles. Furthermore, how do researchers determine such closeness in DNA, and what are the implications of this discovery, if any, for our understanding of evolution and the interconnectedness of life on Earth?