The Twitya Formation in Canada contains the oldest known megafossils, dating back 610-600 million years ago, predating the Cambrian Period. The fossils resemble cnidarians and include the iconic Charnia, which existed for 90 million years. The formation also includes simplistic fossils, and the Ediacaran fauna are considered the first experiments in multicellularity.
The oldest fossils of macroscopic bodies date from the ancient Ediacaran period, which spanned from 635 to 542 million years ago. The oldest known megafossil site is the Twitya Formation in the Mackenzie Mountains of northwestern Canada, with fossils dated to 610 to 600 million years ago. The extreme age of these fossils is truly remarkable: to put things into perspective, for over a hundred years, the Cambrian Period (starting 542 million years ago) was thought to contain the oldest multicellular fossils. It wasn’t until 1957 until it was realized that complex life could have existed a few dozen million years earlier.
The Twitya Formation fossils are older than the second oldest megafossil site by a factor of over 5 million years. The next oldest is the Drook Formation of southeast Newfoundland, with ages estimated to be between 595 and 565 million years old. The megafossils Twitya and Drook bear a resemblance to cnidarians – sea feathers – tufted, bilateral frond-like animals that are fern-like in appearance. Known as Charnia, these animals have only been tentatively classified as related to cnidarians because cnidarians are the oldest known metazoans (multicellular organisms) and most paleontologists fail to describe these enigmatic fossils.
Sometimes Charnia is cited as a “metazoan of cnidarian-level complexity”. It takes its name from Charnwood Forest in England where it was first discovered. Charnia is both the most iconic megafossil of the Ediacaran period and the longest-lived one: its fossils have been dated to 520 million years ago, 20 million years after the Ediacaran-Cambrian boundary. Thus the duration of Charnia’s existence was evidently 90 million years.
Another megafossil found at the Twitya Formation is Nimbia occlusa, a simplistic circular footprint sometimes excluded from the class “Ediacaran fauna” due to its simplicity. Sometimes confusion arises because it is debated whether such simple impressions are actually independent animals or rather just colonies of single-celled organisms.
The Twitya Formation is particularly unique among all fossil sites because it predates the Varangian-Marinoan glaciation, an ice age that occurred between 600 and 585 million years ago. This glaciation is often cited as a barrier that held back complex multicellular life from forming, although we can tell from the Twitya Formation that this is not true. It is true that the Twitya Formation includes only relatively simplistic fossils, but they are in fact macroscopic and most likely multicellular as well.
Post-Twitya fossils include a variety of immobile segmented worms, fronds, discs, and pouches, as well as probable still and trace fossils. These are collectively known as the Ediacaran fauna and are one of the most mysterious categories of life that ever lived. They are considered the first multicellularity experiments of life.
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