For decades, paleontologists were limited to studying fossilized bones, which offered clues about skeletal structure but little else. Understanding the softer aspects of dinosaur life, such as their blood and metabolism, seemed impossible. This perception changed with discoveries that opened a new window into the deep past, providing a more detailed picture of how these animals lived.
Evidence of Blood in Fossils
While no liquid dinosaur blood has been found, researchers have discovered microscopic evidence of its components preserved within fossils. A key discovery was made by Dr. Mary Schweitzer in 2005, who found structures inside the femur of a 68-million-year-old Tyrannosaurus rex. After dissolving the bone’s mineral matrix in a weak acid, she observed flexible, branching structures that resembled blood vessels.
Within these vessel-like structures were smaller, reddish-brown dots that looked like red blood cells. Subsequent analysis also identified osteocytes, the cells that build and maintain bone. These are not living cells but mineralized fossils of the original organic material. The preservation was so complete that the three-dimensional shape of these cellular structures remained intact.
Further studies reinforced these findings. Chemical analyses detected the presence of iron, a component of hemoglobin, the protein that carries oxygen in the blood. Researchers also identified fragments of proteins consistent with those found in blood vessel walls, such as elastin and collagen. These discoveries are not limited to a single specimen, as similar structures have been found in other dinosaur fossils, suggesting this type of preservation may be more common than previously thought.
Insights into Dinosaur Metabolism
The discovery of blood-related structures provides clues in the debate about dinosaur metabolism. An animal’s circulatory system is directly linked to its metabolic rate—how it generates and uses energy. Warm-blooded animals (endotherms), like mammals and birds, have high metabolic rates and require an efficient circulatory system. In contrast, cold-blooded animals (ectotherms), like modern reptiles, have lower metabolic rates and less complex circulatory networks.
The evidence of dense blood vessel networks in dinosaur bones suggests a circulatory system capable of supporting a higher metabolic rate than that of a reptile. This anatomical data aligns with other evidence, such as rapid growth rates determined from bone histology. Dinosaurs grew much faster than modern reptiles, a trait associated with warm-blooded animals, which challenges the old view of them as slow, cold-blooded creatures.
Instead of a simple warm-blooded or cold-blooded classification, a leading theory proposes that many dinosaurs were mesotherms. Mesothermy is an intermediate metabolic strategy where an animal internally generates some heat but does not maintain a constant, high body temperature like a bird or mammal. This strategy would have allowed dinosaurs to be more active and grow faster than reptiles without the energetic cost of full endothermy, a model that fits the fossil evidence.
The Impossibility of Dinosaur Cloning
The discovery of blood-like structures raises the question of whether we could retrieve dinosaur DNA and clone them. However, this scenario is impossible due to the fragile nature of DNA. DNA is a molecule that begins to break down immediately after death as environmental factors and decay sever its chemical bonds.
Research establishes that DNA has a half-life of approximately 521 years. This means that after 521 years, half of the bonds in a DNA sample will have broken; after another 521 years, half of the remaining bonds will degrade, and so on. Even under ideal preservation conditions, scientists estimate no readable DNA strands would remain after about 1.5 million years.
The last non-avian dinosaurs died out 66 million years ago. Over this immense time, any DNA they possessed would have degraded completely, leaving no genetic blueprint to work from. While scientists have extracted DNA from more recent species like the woolly mammoth, the time scale for dinosaurs is vastly different. The structures found in fossils are the mineralized remnants of cells, not the viable genetic material needed for cloning.