what is the fate of notochord in vertebrates
Notochord Notochords are thought to be advantageous (both in an evolutionary and developmental context) because they provide(d) rigid structure for muscle attachment, but were still flexible. In some chordates, it persists throughout life as the main structural support of the body, while in most vertebrates it becomes the nucleus pulposus of the intervertebral disc.[1] The notochord plays a key role in signaling and coordinating development. Embryos of vertebrates still form transient notochord structures today during the gastrulation phase of development. The notochord is found ventral to the neural tube.
Evolution of mammalian auditory ossicles The evolution of mammalian auditory ossicles was an evolutionary event in which bones in the jaw of reptiles were co-opted to form part of the hearing apparatus in mammals. The event is well-documented[1] and important[2][3] as a demonstration of transitional forms and exaptation, the re-purposing of existing structures during evolution.[4]