Cambrian Explosion: best illustrated guide (Introduction)

by David Turell , Sunday, April 17, 2016, 14:53 (3142 days ago) @ David Turell

A wonderful article with great illustrations of some of the wacky forms, and a clear representation of the time lines:-http://nautil.us/issue/17/big-bangs/the-greatest-animal-war-" Then, within 54 million years (a relative blink but still, 270 times the duration of humans' existence thus far), most of the main animal groups around today originated. This rapid rate of increase in animal architectures has never since been repeated.-***-"Most of today's 30 to 40 animal phyla originated in the Cambrian, and have persisted through time with hundreds of variations on a theme (see Explosion). Where the Cambrian Explosion saw a proliferation of architectures (picture igloos, cabins, skyscrapers, suburban houses, and grass huts), the rest of time has mainly been about remodeling existing forms (add a Jacuzzi, a deck, or a tin roof). The explosion of animal phyla in the Cambrian includes the category, the chordates, to which humans, reptiles, sloths, and fish belong. Chordates are united by a central bundle of nerve fibers running down our backs, supported by a stiff rod. -***-"Why did it take so long for the explosion to happen? After all, life arose 3.5 billion years ago, and the first eukaryotic cells (the kind within our bodies) occurred a billion and a half years later. Beneath the surface, a lot was probably going on: DNA had to work just right for organisms with multiple cells to evolve, and then enable a diversity of forms for natural selection to play with. In the Cambrian, “[animals] got large, and biomineralized, and they started doing stuff they never did before,” says Nick Butterfield, a paleontologist at the University of Cambridge in the United Kingdom. “Suddenly,” he says, “it just started to click.”-"Certainly, the environment around the time of the Cambrian encouraged the explosion as well. Oxygen had accumulated in the oceans after extreme ice ages occurred between 800 and 550 million years ago. With plentiful oxygen, animals could grow large and absorb the air they needed to breathe through their skin. (Lungs evolved later in time.) -***- "Finally, other changes in dissolved oceanic gases helped. Calcium levels increased, which made possible the skeletons and shells of Cambrian marine life.-***-"However, had the conditions been right but life passive, we might not be alive today. As soon as moving animals with mouths, nerves, and guts formed, they began to eat other animals—and their prey reacted. So ensued a biological arms race like the offensive and defensive escalation that occurs between warring nations (see Radiation). As predators gobbled up smaller prey, vulnerable animals landed on various means of protection: thick shells, spikes, and sophisticated methods of hiding. Their aggressors followed suit with specialized ways to track specific prey. Claws to smash shells, for example, or keen eyes to spot camouflaged prey."-Comment: Certainly enough time had passed for preparation of an Earth with the proper concentration of elements and soil, 3.5 million years, but the drive to complexity is not explained by the article, only a Darwinian appeal to survival. The author's note that soft-bodied predecessors are hard to find is not true with very recent discoveries. The article is from 2014 and based on earlier references.