Pikaia

Life image of pikaia gracilens

• North America ( Burgess Shale, Canada)

• Pikaia gracilens

Pikaia is an extinct representative of the acrania ( Cephalochordata ) and is generally regarded as the previously oldest known Chordatier. To date, the type species P. is only gracilens the genus assigned.

The first part of the two part Binomens of pikaia gracilens referred to the genus. Their name is derived from the Mount Pika in the vicinity of the site. So far as only one species was found, the genus is monotypic.

Fossil finds

The fossil remains of the only previously known species P. gracilens come from the approximately 525 million years old mittelkambrischen layers of the Burgess Shale, a world-famous fossil deposit in the Canadian Rocky Mountains.

Pikaia gracilens was discovered by Charles Walcott and described by him in 1911. He placed the Fund in the group of segmented worms ( Annelida ). 1971 saw the paleontologist Simon Conway Morris, the similarity of the four to five -inch-long fish-shaped fossil with the acrania, a sub- tribe of the chordates. With them pikaia shares some typical features ( synapomorphies ) in physique, including segmented into V-shaped myomeres skeletal muscle and one for rudder tail broadened notochord ( notochord ) at the rear end. So are his closest living relatives, the lancelet, the only extant representative of the acrania.

Phylogenetic position

Pikaia is the early chordates, which later became the first skull animals (vertebrates ), the jawless fishes, emerged, not anatomically close, but clearly show its derived features an already prolonged independent evolution runs on. This results in a separation between skull loose chordates and vertebrates leads to a time significantly from before the time Pikaias. From the Chinese province of Yunnan, 1999, the 530 million year old fossils of two species have been described, and Myllokunmingia Haikouichthys that were classified as early vertebrates due to their anatomical features. The hypothesis, this can therefore be also demonstrated by finds, as the oldest ever found remains of fossil vertebrates are therefore older than those of pikaia, bringing the genus to be the ancestor of the skull animals excretes.