8 Animals With Surprisingly Common Ancestry  (4 of 5)

6. Echidnas and Platypus

One look at an echidna and you’d be convinced they’re simply a type of porcupine, but in reality they’re marsupials while porcupines are rodents. Instead, the echidna actually shares a kinship with the impossibly silly-looking duck-billed platypus! Echidnas are covered in spines and adapted to a terrestrial lifestyle, while platypus are semi-aquatic and have a duck-like bill for feeding on aquatic invertebrates. But nonetheless, both belong to the order Monotremata, characterized by egg-laying (they are the only two mammals that deliver babies that way), the presence of mammary glands for nursing their young, and a lack of nipples.

7. Horseshoe Crabs and Spiders

In an alternate universe, people decorate their houses with spooky horseshoe crabs on Halloween. But in our version of reality, we opt for spiders. What are we trying to get at? Why, the horseshoe crab and human garden spider are pretty much family! This is because both belong to the subphylum Chelicerata, a group of arthropods characterized by the presence of chelicerae, claw-like mouthparts, and the absence of jaws. Although they have evolved quite differently, they still retain other shared characteristics as well, including their eight legs, jointed limbs, and open circulatory systems.