First multicellularity: new find disputed (Evolution)

by David Turell , Tuesday, May 17, 2016, 22:42 (2894 days ago) @ David Turell

Mats of cells have been found in China dated 1.5 billion years ago. Whether they are eukaryotes is strongly debated:-http://phys.org/news/2016-05-complex-life-billion-years-earlier.html-"Researchers said Tuesday they had uncovered fossils showing that complex life on Earth began more than 1.5 billion years ago, nearly a billion years earlier than previously thought.-"But the evidence, published in Nature Communications, immediately provoked debate, with some scientists hailing it as rock solid, and others saying they were wholly unconvinced.-***- "The fossils were uncovered in Hebei Province's Yanshan region, where Mao Zedong and his communist army hunkered down during World War II before coming to power.-"Zhu and colleagues found 167 measurable fossils, a third of them in one of four regular shapes—an indication of complexity.-"The largest measured 30 by eight centimetres (12 by three inches).-"Taken together, they are "compelling evidence for the early evolution of organisms large enough to be visible with the naked eye," said Zhu.-***-"Up to now, eukaryotes of comparable size have not shown up in the fossil record until about 600 million years ago, when a multitude of soft-bodied creatures inhabited the world's oceans. ( my comment: early Cambrian)-"Phil Donoghue, a professor of palaeobiology at the University of Bristol, described the discovery as a "big deal".-"'They are not the oldest eukaryotes, but they are certainly the oldest demonstrably multicellular eukaryotes," he told AFP. -"Their very existence 1.56 billion years ago would mean that "oxygen levels were sufficiently high to allow for such large organisms to subsist."-"But other experts were more sceptical.-"'There is nothing here to suggest that the specimens are eukaryotic, as opposed to bacterial," said Jonathan Antcliffe, a senior researcher in the University of Oxford's department of zoology.-"Bacteria are, by definition, unicellular, and do not have distinct nuclei containing genetic material.-"Antcliffe suggested the fossils more likely corresponded to colonies of bacterial cells, rather than a single complex organism.-"Truly multicellular creatures display three-dimensional form in which only some cells are in direct contact with the environment.-"This is "critically important for function because it introduces transport problems for oxygen, nutrients, and signalling molecules" needed by the internal cells, Andrew Knoll of Harvard University explained in an article reviewing scientific literature on the origins of complex life.-"Another researcher, Abderrazak El Albani of the University of Poitiers in France, said there simply wasn't enough detail in the study to back up the claim.-"'The morphological measures, on their own, are absolutely insufficient to tell us if these organisms were multicellular, eukaryotes or complex," he told AFP when asked to comment.-Comment: Early unicellular life clumped together as stromatolites 3.5 billion years ago, so clumping may not be much of an issue. But real complexity in the Cambrian is of much more importance