A living fossil is an organism that has retained the same form over millions of years, has few or no living relatives, and represents a sole surviving lineage from an epoch long past.
Many living fossils alive today have bizarre, eccentric traits that make them seem more like aliens than anything from this world. They have often survived several mass extinctions, and many scientists consider them to be a rare glimpse at how life on Earth was long ago.
Here are 15 examples of these amazing creatures. Some are recognizable, but others look like nothing you've seen before. (Text: Bryan Nelson)