First multicellularity (Evolution)

by David Turell , Thursday, March 31, 2016, 16:29 (3157 days ago) @ David Turell

About 555 million years ago strands of algae without any sense of complexity appeared in the Ediacaran period before the Cambrian:-https://www.sciencedaily.com/releases/2016/03/160322134110.htm-"But University of Wisconsin-Milwaukee paleontologist Stephen Dornbos and his research partners have discovered new clues in the quest. The team found fossils of two species of previously unknown ancient multicellular marine algae, what we now know as seaweed -- and they're among the oldest examples of multicellular life on Earth.-"Their age is estimated to be more than 555 million years old, placing the fossils in the last part of Precambrian times, called the Ediacaran Period. They provide a crucial view of Earth's earliest evolution of multicellular life, which scientists now think started millions of years earlier than previously thought.-***-"Certain kinds of sedimentary rocks, called Burgess Shale-type (BST) deposits, have the right characteristics to preserve soft-bodied organisms as thin carbon films. During the Cambrian Period, BST deposits are more common, and they preserve fossils of increasingly complex animals. But only a handful of Ediacaran BST deposits are known globally.-"Team members were searching for Ediacaran fossils in western Mongolia limestone when they uncovered a new BST deposit. That's where they found the seaweed fossils.-***-"BST fossils from the Ediacaran usually fall into two categories: multicellular algae, like seaweed, and fossils that are extremely difficult to classify, often the remains of extinct types of organisms. Consequently, Dornbos said, determining exactly what is preserved in Ediacaran fossil deposits can be hotly contested.-"'If you find a fossil from this time frame, you really need strong support for your interpretation of what it was," he said. "And the farther back you go in geologic time, the more contested the fossil interpretations are.'"-Comment: 'Hotly contested', but just simple plants, no animals.-********************-From the paper itself:-http://www.nature.com/articles/srep23438-"At this point, the Zuun-Arts biota is also similar to all other Ediacaran BST deposits in that it contains no unambiguous evidence for animals. Macroscopic animal-grade organisms are well known from other Ediacaran taphonomic windows, most notably in classical Ediacaran biota-style sandstone mold and cast preservational settings. With their sub-millimeter preservational capabilities, Ediacaran BST deposits should theoretically preserve animals relatively easily. This is certainly true of Cambrian BST deposits, which preserve a range of soft-bodied animal phyla in exquisite detail21. Although putative animal fossils have been described from Ediacaran BST deposits6, it remains unclear why they do not contain clear animal fossils. One possible explanation may be that the kind of animals that this preservational mode favors, such as ecdysozoans with their more preservable recalcitrant cuticle tissues22, simply did not exist yet."-Comment: BST refers to the Burgess Shale type deposits in Canada where the first Cambrian fossils sere found in the 1880's. The conclusion still must be there is a sharp distinction between the period of first simple plant (algae) multicellularity and the complex Cambrian animal multicellularity. The explosion that has no natural (Darwinian) explanation. No wonder Darwin was afraid of it.