What walks on four legs, then two, then three? A Musasaurus with a cane. First non-human animal to transition from 4 legs to two for walking.
https://news.google.com/articles/CBMiPmh0dHBzOi8vd3d3LmxpdmVzY2llbmNlLmNvbS82NTU2NC1kaW5vc2F1cnMtbGVncy1tb3ZlbWVudC5odG1s0gE-aHR0cHM6Ly9hbXAubGl2ZXNjaWVuY2UuY29tLzY1NTY0LWRpbm9zYXVycy1sZWdzLW1vdmVtZW50Lmh0bWw?hl=en-US&gl=US&ceid=US%3Aen