Dinosaurs and the ancestors of mammals evolved during almost the same time toward the end of the Triassic Period. But why did the dinosaurs become predominate?
The ancestors of mammals developed a number of adaptations such as specialized front, canine and cheek teeth. They also had a closed palate, which enabled them to breathe while chewing.
Megazostrodon, one of the early mammals.
Photo: John Cummings
They developed specialized spinal vertebrae and a diaphragm in the chest cavity which made their breathing more efficient. Also, their limbs were placed directly under their bodies, which enabled them to run faster than their ancestors.
But the dinosaurs developed nearly all of the same features and, in combination with their much larger size, became superior to mammals. The early mammals that lived in the shadow of the dinosaurs were small and nocturnal.
The oldest known predatory dinosaur is Coelophysis, which lived at the end of the Triassic Period. More than 100 fossil skeletons of that species have been found in present-day New Mexico. Their bodies varied in length from 80 centimetres to over three metres (tails included).One of the largest specimens had eaten up one of the smaller – an example of cannibalism from over 200 million years ago!
Coelophysis, predatory dinosaur – and cannibal.
Image: Simon Stålenhag