What fossil evidence BEST supports the classification of animals into these two basic branches still recognized today?

The fossil evidence that best supports the classification of animals into the two basic branches—bilaterians and radiarians—includes the discovery of distinct body plans and symmetry in early fossils. For instance, the presence of Cambrian fossils, such as those of the trilobites (bilaterians) and various echinoderms (radiarians), showcases clear differences in body structure and organization. Additionally, the fossilized remains of early chordates provide critical insight into the development of complex body systems, further solidifying the bipartite classification of the animal kingdom.