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Earliest animals with true body cavities found at 30 mya earlier than thought


Deuterostomes are animals with true body cavities, featuring a mouth and usually an anus.

Bag-like sea creature was humans' oldest known ancestor
artist’s reconstruction of Saccorhytus/S. Conway Morris, Jian Han

From Telegraph:

The 540 million-year-old “exquisite” fossil was unearthed during an excavation in China by led by University of Cambridge researchers, who say its discovery means humanity can now trace its roots back a further 30 million years.

The creature is now thought to be the most primitive example of the deuterostome, one of three “superphylum”, and the group from which human beings and countless other species evolved.

Most other early deuterostome groups date from about 510 to 520 million years ago, when they had already begun to diversify into vertebrates, as well sea squirts, as well as animals like starfish, sea urchins and acorn worms. More.

From Guardian:

“In effect what we are suggesting here is that this is the earliest, oldest, most primitive of the deuterostomes,” said Simon Conway Morris, professor of palaeobiology at the University of Cambridge, and a co-author of the research. “This is, if you like, the starting point of an evolution which led ultimately to things as different as a sea urchin, starfish and rabbit.” More.

Nothing like rushing evolution by shortening the time available. From a letter by the study authors to Nature:

Deuterostomes include the group we belong to (vertebrates) as well as an array of disparate forms that include echinoderms, hemichordates and more problematic groups such as vetulicolians and vetulocystids. The Cambrian fossil record is well-populated with representative examples, but possible intermediates are controversial and the nature of the original deuterostome remains idealized. Here we report millimetric fossils, Saccorhytus coronarius nov. gen., nov. sp., from an Orsten-like Lagerstätte from the earliest Cambrian period of South China, which stratigraphically are amongst the earliest of deuterostomes. The bag-like body bears a prominent mouth and associated folds, and behind them up to four conical openings on either side of the body as well as possible sensory structures. An anus may have been absent, and correspondingly the lateral openings probably served to expel water and waste material. This new form has similarities to both the vetulicolians4 and vetulocystids and collectively these findings suggest that a key step in deuterostome evolution was the development of lateral openings that subsequently were co-opted as pharyngeal gills. Depending on its exact phylogenetic position, the meiofaunal habit of Saccorhytus may help to explain the major gap between divergence times seen in the fossil record and estimates based on molecular clocks. – 00 MONTH 2017 | VOL 000 | NATURE | 1LETTERdoi:10.1038/nature21072Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China)Jian Han, Simon Conway Morris, Qiang Ou, Degan Shu & Hai HuangMore.

See also: How far back a lot of features of life forms actually go

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