Why do all vertebrates have very similar forms during development

They tend to show their evolutionary history or phylogeny

Explanation:

Vertebrates are animals that have backbone. During formation of zygote to foetus, they all pass through similar phase and look alike because their genes are similar. They share a particular trait and that is backbone. Generally, vertebrates all come from one family and their morphology is similar during pregnancy and only differ after towards 3/4 end of the pregnancy where each vertebrae have distinct characteristics of its species.

igneous rocks which formed by the crystallization of magma at the surface of the earth called extrusive rocks. they are characterized by fine-grained textures because the rapid cooling at or near the surface did not provide enough time for large crystals to grow.