Blue Diamond Ruins Inhabitants are animals shown to be located within the Blue Diamond Ruins. most of these are prehistoric creatures and are only seen in the episode "Wild Blue Yonder".
Coelacanth[]
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This is an Equestrian Coelacanth that the Mane Six followed to the ruins.
Coelacanths are medium to large-sized fish known to inhabit both Equus and Earth. Both fish are considered ancient in both worlds, though the Earth counterpart is described as larger in size and duller in color compared to the equestrian coelacanth. They're found in shoals much like other fish.
- The Equestrian Coelacanth is shown to be an ambush predator, and able to beach itself much like killer whales hunting seals on shore, shown when it was hunting seagulls.
- The Earth Coelacanth is able to hunt more similarly to a Great White Shark, able to breach the surface of the water to catch prey, shown when it caught Steven Universe's Surfboard.
Plesiosaur[]
A Plesiosaur is shown as the Mane Six arrived in the ruins. It is described as a long-necked plesiosaur, and possibly the largest inhabitant within the ruins. It doesn't show much fear in the presence of ponies, as it brought its head right to their submarine, and peacefully allowing them to pass it.
It is unclear if the prehistoric beast is from Earth or Equus, however.
Diplocaulus[]
Diplocaulus is briefly described when the Mane six, Lapis Lazuli, Steven Universe, and Jade as one of the few animal inhabitants able to go around on the surface rather than fully stay underwater.
Like the Plesiosaur, it's unclear if this animal is from Equus or Earth.
Hybodus[]
Hybodus are a distinguishable species of prehistoric Shark with large spikes on its dorsal fins. It is described as an Earth prehistoric fish, and one of many that the Mane Six see swimming around upon arrival.
Dwarf Sea Serpent[]
The Dwarf Sea Serpent is presumably a prehistoric species of Equestrian Sea Serpent, as one of the fish swimming around when the Mane Six arrived.