Paleontologists have examined the fossilized remains of Tujiaaspis vividus, a species of galeaspid that lived 436 million years ago (Silurian period) in China. Life reconstructions of Tujiaaspis vividus. Image credit: Qiuyang Zheng. Theories abound on the evolutionary beginnings of vertebrate fins and limbs — the evolutionary precursors of arms and legs — mostly based on comparative embryology. There is a rich fossil record, but early...
