The first jawless fish (Agnathan Ostracodermi). Fish gradually evolved, in the water, to develop various characteristics and behaviors that would later become typical of terrestrial animals: they were gregarious, even among different species; they developed a sense of hearing (experiments on various fish species have shown that they can recognize different types of music), eyes, and later jaws, the ability to recognize objects and living beings, memory, and strategic planning skills. All of this would later be used by different species in completely different contexts.
