Haikouichthys

Haikouichthys is an extinct, small fishlike chordate from the Cambrian period, known from fossils in China and often classified among the earliest vertebrates.

Chordate: An animal that has a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail at some life stage. Haikouichthys displays the defining body plan of this broader animal group.
Chengjiang Biota: A diverse assemblage of exceptionally preserved Cambrian fossils from Yunnan, China. Haikouichthys fossils come from this celebrated fossil assemblage.
Cambrian: The geological period from about 539 to 485 million years ago, marked by major diversification of animal life. Haikouichthys lived during this early interval of animal diversification.
Vertebrate origins: The evolutionary emergence of vertebrates from earlier chordate ancestors. Haikouichthys is often used to investigate how early vertebrate features arose.
Notochord: A flexible, rodlike support running along the body axis of chordates. A notochord is among the internal structures attributed to Haikouichthys.
Maotianshan Shales: Cambrian sedimentary deposits in Yunnan, China, known for exceptionally preserved fossils. These deposits preserve the specimens used to describe Haikouichthys.
Cambrian explosion: A geologically brief interval of rapid diversification in animal forms early in the Cambrian Period. Haikouichthys contributes to evidence for early diversity among chordate body plans.
Fossil preservation: The physical and chemical processes that determine which organisms and structures survive in the fossil record. Preservation quality limits which anatomical traits can be assessed in Haikouichthys.
Vertebrate: An animal in the chordate lineage characterized by a vertebral column or its evolutionary precursors. Haikouichthys is often placed near the base of this lineage.
Myllokunmingia: An early Cambrian fishlike fossil from China, often discussed alongside Haikouichthys as a possible vertebrate. Its close resemblance makes the two fossils central to comparisons of early vertebrate anatomy.

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