Is the fossil Allodesmus a seal or sea lion? Allodesmus lived in the Miocene period, about 10 million years ago. They were early pinnipeds (seals, sea lions and walruses) that shared the ocean with ancient whales and giant sharks. Since no one knows whether Allodesmus was a seal or sea lion, I will be comparing the fossilized skull and skeleton to those of modern day seals and sea lions to determine which it was.