This is Haikouichthys. He's the size of your thumb nail, but he's an evolutionary giant. He's the first every fish, our earliest known ancestor.
— Allen, on Haikouichthys

Haikouichthys (name meaning "Haikou Fish") is a genus of prehistoric fish that originated during the Cambrian Era. Notable for being the very first fish, it is also the oldest and most primitive known backboned animal (vertebrate) on Earth, the forefather of reptiles, mammals, fish and humans.


Era & DiscoveryEdit

Haikouichthys lived in the seas during the Cambrian Period about 530 million years ago, living along side Trilobites and even the mighty Anomalocaris. It was formally described in China in 1999.

The holotype of Haikouichthys ercaicunensis was found in the Yuanshan member of the Qiongzhusi Formation in the 'Eoredlichia' Zone near Haikou at Ercaicun, Kunming City, Yunnan, China, hence its name "Haikou fish from Ercaicun". The fossil was recovered among the Chengjiang fauna, in one of a series of Lagerstätten sites where thousands of exquisitely preserved soft-bodied fossils have already been found. Following the discovery of the holotype, additional Lower Cambrian fossils of Haikouichthys ercaicunensis have been discovered.

Physical AttributesEdit

1000px-WWM1x1 Haikouichthys

Haikouichthys was one of the smallest, if not, arguably the smallest fish of all time and among the smallest creatures that ever lived. Measuring about 2.5 cm (1 inch) long, they grew to the size of a human's thumbnail. They also had a distinct head and tail; a segmented, streamlined body and a single dorsal fin that merged with the tail. Despite their tiny size, Haikouichthys was an evolutionary giant. As some of the first, if not, the very first fish ever to evolve, they are the earliest known ancestor of humans. They were unique because rather than having armor on the outside, they were tough inside. They evolved a primitive backbone, making them the very first vertebrate; forerunners of all future backbone animals from the reptiles, to mammals, to humans. Their flexible back-bone made them more maneuverable than spineless animals, like Anomalocaris. Haikouichthys could scavenge flesh and then dart away unharmed.

Along the side, the head of Haikouichthys had at least from six and perhaps to nine probable gills and multiple circular structures on his bottom that could be gonads or slime organs (as seen in modern hagfish). There are a number of segments (myomeres) with rear directed chevrons in the tail. There was also a notochord, although only a short segment is preserved in the single known specimen. There is a prominent dorsal fin with fin radials similar, but not comparable, to those of hagfish and lampreys. The fin radials seem to angle "forward" toward the end thought on the basis of internal structures to be the head. This happens with a few modern fish but is an uncommon arrangement. There are 13 circular structures along the bottom that may be gonads, slime organs, or something else entirely.

Behavior & TraitsEdit

Like many modern-day fish, Haikouichthys lived in large schools but was also most likely a scavenger.



  • Haikouichthys is the smallest fish brought to the park.
    • Additionally, it is also the smallest marine animal as well as the smallest prehistoric animal in general brought to the park.