The mystery of these life-forms, known as Ediacarans Ee-dee-AK-arans , begins in the remote Flinders Ranges of South Australia, where a young geologist named Reginald Sprigg, on an assignment to reassess the derelict Ediacara Mines in , noticed some peculiar impressions in exposed sandstone beds. There were other shapes too, some of them bearing no clear resemblance to any known creature, living or extinct.
One figure looked like a fingerprint pressed into the sand. Scientists until then had believed that the Cambrian explosion was the point when life on Earth opened out, kaboom, like a starburst of wondrous beasts—elaborate and sizable beings we call them animals , many of whose descendants are still around. Primates order , Hominidae family , Homo genus , H. Then in a graduate student named S. Other beds nearby, sitting one upon another like layers of Precambrian cake, also proved to contain abundant and various fossils, preserved together as whole communities.
Many were still covered with thin crusts of fallen volcanic ash, like icing between each layer of cake. The ash, with its traces of radioactive uranium and the lead into which that decays, allowed for precise radiometric dating of the beds. The Mistaken Point fossils, going back million years, are the earliest evidence on Earth of large, biologically complex beings.
There are now more than 50 different Ediacaran forms known, from nearly 40 localities, on every continent except Antarctica. So what was it, after billions of years of only microbes populating the globe, that allowed the Ediacarans to get big and cover the Earth?
And what does their bigness suggest about their internal anatomies, their means of feeding, their ways of living? Before Ediacaran forms flourished on the planet, evolution worked on a mostly microscopic scale, kept in check by a shortage of oxygen, the element that fuels animal metabolism. Thanks to marine bacteria that generated oxygen as a product of photosynthesis, levels of the gas rose about two billion years ago but stayed relatively low for another billion years.
The great freeze ended as volcanic eruptions spewed carbon dioxide into the atmosphere, creating an early greenhouse effect that warmed the planet and thawed the oceans. Another brief glaciation around million years ago, known as the Gaskiers, may not have been global, but it put Newfoundland, among other places, in a deep freeze. These changes all preceded the earliest appearance of Ediacarans in the fossil record.
Were they the causes of what happened next? Did the end of the glaciers, an increase in available oxygen, and the evolution of more complex cells allow the Ediacarans to blossom, like the first crocuses of springtime? Defined by shared features such as tough exoskeletons and segmented bodies, the phylum includes well over a million named species, among them a snapping shrimp, a jungle nymph, an eastern lubber grasshopper, an Australian walking stick, a mantis shrimp, and a gaudy clown crab in the gallery below.
Millions more species are believed to be still unknown to science. Arthropods were the most diverse animal group in the Cambrian period and the Ordovician period that followed. The million-year-old limestone slab shown here captures an Ordovician menagerie, including various echinoderms and trilobites, such as Ceraurus, the turtle-like form on the left edge.
Equally enigmatic is their relationship to life today. Maybe the quilting, and the frondy shapes, also helped maximize surface area, so they could better absorb nutrients through their skin. Nutrition would have been problematic for the Ediacarans because, so far as fossil evidence reveals, almost none of them had a mouth.
They had no gut, no anus. No head, no eyes, no tail. In some cases there was a sort of anchoring knob or disk at one end, now known as a holdfast, which gripped the sea bottom and allowed the frond to waft upward in the water. Many sea-bottom areas at that time were coated with thick microbial mats, which helped stabilize the sediments like a layer of crusty soil.
One form, a sluglike thing called Kimberella, may have scratched up and swallowed this one did have a mouth, major advantage! But the leading hypothesis for most Ediacarans is osmotrophy, a fancy word for a very basic process: the uptake of dissolved nutrients by osmosis, or absorption through their outer membrane. It was good enough, maybe, in a simpler world at a simpler time, but it would have been meager sustenance.
Some scientists have focused on another fascinating aspect of many Ediacarans: their finer architecture. At a glance they look quilted, but close inspection reveals that their structure is fractal. That is, similar patterns repeat themselves at progressively smaller scales. A big frond was composed of smaller fronds, and those smaller fronds composed of still smaller fronds, all similar except for size.
The basic shape echoes itself at three or four scales. Possibly that fractal structuring helps explain how they were able to grow large. It provided some rigidity, it maximized surface area, and perhaps it reflected a genetic shortcut. A simple formula in the genome might have specified: Build a small frondy unit, then repeat that operation over and over, adding one upon another, to make me big. This sort of fractal structure showed in the snakelike creature Marc Laflamme and I saw in the purplish gray rock at Mistaken Point. It shows too in a number of other Ediacarans, collectively called rangeomorphs, named for a Namibian exemplar of the form, known as Rangea.
During our day on the Newfoundland rocks, Laflamme steered my eyes onto many more rangeomorphs, inconspicuous from 10 feet away but spooky when viewed closely. Here was Beothukis mistakensis, a paddle-shaped frond, named for its locale of discovery. Although the vast majority of books that have Lexile measures did not change, a small subset of books required updated Lexile measures. Many products and services offer Lexile measures for their books and reading materials. We are working with the hundreds of companies that partner with us to transition them to the more precise Lexile measures.
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Evolution recreates the billion-year story of life on Earth in stunning detail through vivid full-color illustrations and graphics, the latest scientific information. Illustrated by the brilliant duo Kevin Cannon and Zander Cannon, this volume is written by the noted comic author and professor of biology Jay Hosler. And in Hosler, Evolution has an award-winning biology teacher whose science comics have earned him a National Science Foundation.
Return to Book Page. Preview — Evolution by Douglas Palmer. Evolution recreates the 3. At the heart of the book is an astonishing, beautifully detailed panorama by renowned illustrator Peter Barrett that, in double-page site reconstructions, offers a freeze- Evolution recreates the 3. These groundbreaking artworks, based on the most recent findings at some of the most famous fossil sites around the world, are paired with an authoritative and highly informative text written for a wide audience of readers.
The volume includes an index of the hundreds of species shown in the illustrations, introductory articles on evolution, and many other features, making it a must-have reference for all homes, schools, and libraries. Get A Copy. Hardcover , pages. More Details Other Editions 2. Friend Reviews. To see what your friends thought of this book, please sign up.
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Showing Rating details. More filters. Sort order. Dec 11, Heather Shaw rated it it was amazing Shelves: science.