Dinosaurs have fascinated and baffled paleontologists and evolutionary biologists for decades. How such gigantic animals, some of which weighed over ten tons and stood over 50 feet tall, could be so agile and energetic and how exactly did these creatures regulate their body temperature are some of the questions that remain under debate to this day.
Current studies of dinosaur fossils suggest that they were warm-blooded. While their leathery skin, skull shape, and counter-balancing tails are reptilian, their overall anatomy, suggests that they evolved from cold-blooded ancestors into a warm-blooded species. Unlike cold-blooded reptiles, whose legs are generally sprawled outwards, dinosaurs had legs that extended straight below the pelvis. They also had four-chambered hearts, a characteristic feature of warm-blooded animals that is almost never seen in modern reptilians.
The dinosaurs resembled both reptiles and mammals in their physiology. In fact, dinosaurs are often seen as the link between reptilian and mammalian species. Both mammals and dinosaurs have numerous tiny holes called “nutrient foramina” in their femoral bones. These foramina supply blood and nutrients to the living bone cells within. This is a feature of warm-blooded animals with a high metabolic rate and an active lifestyle. In dinosaurs, these foramina were found to be much larger and more numerous than those found in mammals, suggesting that dinosaurs were actually much more agile and active than mammals.
Several paleontologists also argue that dinosaurs must have been warm-blooded because standing erect requires the body to generate enough of its own heat and not rely on the ground for warmth (as lizards, snakes and alligators do). Moreover, a predator as large as some dinosaurs would have to be unusually nimble and quick in its movements. Such activity would require a high metabolic rate, which in turn suggests that dinosaurs were, indeed, warm-blooded.
Many have attempted to explain how dinosaurs became extinct. Some speculate that they were unable to adapt to the withdrawal of the second ice-age, some say they were wiped out by a meteorite, a few even argue that the extremely steep growth curve of dinosaurs might somehow have contributed to the end of this magnificent species. Each theory has its own shortcomings. The first one does not take into account the fact that dinosaurs had withstood the climatic changes brought about by the first ice age. The second theory seems unlikely because several contemporary species survived while the dinosaurs became extinct. The third one assumes that all types of dinosaurs grew at the same rate. Smaller dinosaurs, some of which grew only to a height of six inches, would have had a much slower rate of growth. Their extinction cannot be explained by this theory alone.