Science, Tech, Math › Animals & Nature Haikouichthys Share Flipboard Email Print Haikouichthys (Wikimedia Commons). Animals & Nature Dinosaurs Basics Paleontologists Carnivores Dinosaurs & Birds Herbivores Marine Reptiles Prehistoric Mammals Amphibians Birds Habitat Profiles Mammals Reptiles Wildlife Conservation Insects Marine Life Forestry Evolution View More By Bob Strauss Science Writer B.S., Cornell University Bob Strauss is a science writer and the author of several books, including "The Big Book of What, How and Why" and "A Field Guide to the Dinosaurs of North America." our editorial process Bob Strauss Updated March 17, 2017 Name: Haikouichthys (Greek for "fish from Haikou"); pronounced HIGH-koo-ICK-thiss Habitat: Shallow seas of Asia Historical Period: Early Cambrian (530 million years ago) Size and Weight: About one inch long and less than an ounce Diet: Small marine organisms Distinguishing Characteristics: Tiny size; fin along length of back About Haikouichthys The Cambrian period is famous for its "explosion" of bizarre invertebrate life forms, but this span of time also saw the evolution of the earliest almost-vertebrates--marine organisms like Haikouichthys, Pikaia and Myllokunmingia that bore the faintest outlines of backbones and had a noticeably fish-like shape. As with these other genera, whether or not Haikouichthys was technically a prehistoric fish is still a subject of debate. This was certainly one of the earliest craniates (i.e., organisms with skulls), but lacking any definitive fossil evidence, it may have had a primitive "notochord" running down its back rather than a true backbone. Haikouichthys and its companions did, however, introduce some features that are so commonplace now as to be completely unremarkable. For example, this creature's head was distinct from its tail, it was bilaterally symmetric (that is, its right side matched up with its left side), and it had two eyes and a mouth on its "head" end. By Cambrian standards, it may have been the most advanced life form of its day!