Appearing some 530 million years ago, vertebrate animals are distinguished from other animals by, among other things, the presence of an internal skeleton made of bone or cartilage.(104 kb)
Soon a vetebral column took from and became the primary distinctive characteristic of vertebrates. In their primitive years, vertebrates were one small group among many that struggled to get by in Cambrian seas. But at the beginning of the Devonian, about 115 million years later, they became highly successful and much more mobile with their paired fins and post-anal tail, dominating aquatic food chains around the world.
Other features specific to vertebrates are the highly differentiated brain, special paired sensory organs, and a closed circulatory system with a ventral heart.
All vertebrates at the beginning of the Devonian were fish and as such were restricted to the aquatic domain. One could even say that the terms fish and vertebrates were synonyms. But during the 57 million years of the Devonian Period, fish diversified, new groups appeared, others became extinct, and some even evolved into tetrapods that went on to colonize land.
Two thirds of the animals that inhabited the ancient Miguasha estuary and its shorelines were vertebrates.