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Pikaia gracilens is an extinct, primitive chordate marine animal known from the Middle Cambrian Burgess Shale of British Columbia.Described in 1911 by Charles Doolittle Walcott as an annelid, and in 1979 by Harry B. Whittington and Simon Conway Morris as a chordate, it became "the most famous early chordate fossil", [1] or "famously known as the earliest described Cambrian chordate". [2]
The Cambrian chordates are an extinct group of animals belonging to the phylum Chordata that lived during the Cambrian, between 538 and 485 million years ago.The first Cambrian chordate known is Pikaia gracilens, a lancelet-like animal from the Burgess Shale in British Columbia, Canada.
Pikaia was initially thought to be a worm, then was later upgraded to an early type of chordate, based on features such as shapes of certain muscles and the position of its anus.
A basal chordate described in 1911 by Walcott as an annelid worm, and in 1979 by Harry B. Whittington and Simon Conway Morris as a chordate. It became the "most famous early chordate fossil." Probably descended from an even earlier chordate based on fossil material from China, Pikaia swam through the Cambrian oceans like a modern fish ...
A chordate (/ ˈ k ɔːr d eɪ t / KOR-dayt) is a deuterostomal bilaterian animal belonging to the phylum Chordata (/ k ɔːr ˈ d eɪ t ə / kor-DAY-tə). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics ( synapomorphies ) that distinguish them from other taxa .
This article contains a list of all of the classes and orders that are located in the Phylum Chordata. The subphyla Tunicata and Vertebrata are in the unranked Olfactores clade, while the subphylum Cephalochordata is not. Animals in Olfactores are characterized as having a more advanced olfactory system than animals not in it.
Two other Cambrian Stage 3 (521-514 mya) species, Haikouichthys and Myllokunmingia from the Chengjiang biota, are the earliest body fossils of fish, [30] [31] whereas Pikaia, discovered much earlier but from the Mid Cambrian Burgess Shale, is now regarded as a primitive chordate. [32]
Pikaia. The increased amount of oxygen causes many eukaryotes, including most animals, to become obligate aerobes. The Chordata ancestor gave rise to the lancelets (Amphioxii) and Olfactores. Ancestral chordates evolved a post-anal tail, notochord, and endostyle (precursor of thyroid).