Here\u2019s what you\u2019ll learn when you read this story:<\/p>\n
The discovery of a collection of about 700 fossils known as the Jiangchuan Biota gives scientists a better understanding of the transition between the Precambrian supereon and the Phanerozoic, our current geologic eon.<\/p>\n<\/li>\n
Because chordates and bilaterians were discovered in the Jiangchuan Biota, the Cambrian \u201cexplosion\u201d of complex life might be a misrepresentation caused by missing evidence in the fossil record.<\/p>\n<\/li>\n
Among the bilaterians found were deuterostomes, the ancestor of all vertebrates, including humans.<\/p>\n<\/li>\n<\/ul>\n
A very broad overview of the current scientific understanding of life\u2019s evolution goes something like this: Around four billion or so years ago, the first microbes<\/a>\u2014anaerobic, single-celled creatures\u2014appeared on the fiery ball of rock known as Earth. Next, about 3.5 billion more years of microbial development (along with the arrival of eukaryotes<\/a>) essentially filled up the period known as the Precambrian. But after that, things got interesting, as complex life-forms proliferated rapidly during what\u2019s known as the Cambrian Explosion<\/a>.<\/p>\n But scientists still don\u2019t know much about the transition between the Precambrian and the Phanerozoic, our current geologic eon. Now, however, a new fossil site<\/a> in southwest China known as the Jiangchuan Biota helps bridge the gap between the Cambrian period and the Ediacaran period<\/a>, which spans the 96 million years preceding the \u201cexplosion.\u201d In a new study published in the journal Science<\/a>, researchers from Yunnan University in China report that the 700 fossils at Jiangchuan are roughly 539 to 554 million years old. While some of the lifeforms were previously completely unknown, others were previously known to only exist in Cambrian rocks, so their presence among the Jiangchuan Biota seemingly pushes back the previously-accepted timeline of the origin of complex life.<\/p>\n Most of these fossilized animals are ancestors of modern invertebrates, including modern starfish, but a few among them count as ancient ancestors of humans\u2014though you\u2019d never know through resemblance alone. These worm-like creatures, known as bilaterians<\/a>, feature bodies that, when bisected, could be divided in two mirror-image halves. This is known as \u201cbilateral symmetry,\u201d and it stands in stark contrast to animals like cnidarians (coral) or ctenophores (comb jellies). Interestingly, the presence of these two latter phyla in the fossil record means that animals we thought only lived in the Cambrian might\u2019ve been around millions of years earlier.<\/p>\n \u201cOur discovery closes a major gap in the earliest phases of animal diversification,\u201d Oxford University\u2019s Gaorong Li, lead author of the study (he was at Yunnan University at the time), said in a press statement<\/a>. \u201cFor the first time, we demonstrate that many complex animals, normally only found in the Cambrian, were present in the Ediacaran period<\/a>, meaning that they evolved much earlier than previously demonstrated by fossil evidence.\u201d<\/p>\n Our distant ancestors, those wormy bilaterian critters known as deuterostomes, feature holdfasts that essentially secure the organism to the seabed as well as a feeding tube for grabbing grub. Eventually, this winning biological strategy gave rise to every vertebrate on Earth, and the Jiangchuan Biota now pushes their existence into the Ediacaran for the first time\u2014but that wasn\u2019t the only surprise discovery.<\/p>\n