Did the Cambrian fauna appear explosively in life-history?

  • Clarifying the question

    Question: The so-called Cambrian explosion was an event starting about 542 million years ago, where most all the major body types seem to appear in a geologic link of an eye.1 Is this a genuinely explosive appearance (rather than, say, an artifict of our incomplete sampling)?

    1. Encyclopædia Britannica '14:“The beginning of the Cambrian Period, now thought to date from 542 rather than 570 million years ago, witnessed an unparalleled explosion of life (see Paleozoic Era: Cambrian Period: Cambrian life). Many of the major phyla that characterize modern animal life—various researchers recognize between 20 and 35—appear to have evolved at that time, possibly over a period of only a few million years. [http://www.britannica.com/EBchecked/topic/129392/community-ecology/70649/The-Cambrian-explosion]

  • Experts agree

“Yes, after all…

  • Anomalocaris

    Anomalocaris (shrimp-like predator reaching over 6 feet long)1 appears explosively during the Cambrian explosion, without precurors, as do its innovations. (Notable are Anomalocaris's highly sophisticated eyes, which have 16,000+ lenses each, and a brain sophisticated enough to process the information).2

    1. Simon Conway Morris, The crucible of creation: the Burgess Shale and the rise of animals. (Oxford, 1998) 56–9.
    2. NewScientist: “The eyes were on stalks on the strange shrimp's head, and each was 2 to 3 centimetres across – about the size of an olive. They were covered with lenses, each 70 to 110 micrometres in diameter. That means each eye had at least 16,000 lenses. "Very few modern animals, particularly arthropods, have eyes as sophisticated as this," says Paterson. Houseflies, for instance, have a mere 3000 lenses. The only comparable species are some predatory dragonflies that have up to 28,000 lenses in each eye. Anomalocaris's acute eyesight probably allowed it to seek out its prey in the brightly lit upper layers of the ocean. The first arthropods – the group that includes insects, spiders and Anomalocaris – probably had compound eyes, says Graham Budd of Uppsala University in Sweden. "The arthropods have diversified spectacularly, but these inventions from the Cambrian have been retained all the way through." To make use of its eyes, Anomalocaris must have had a reasonable brain, Budd says. Indeed, molecular evidence suggests that key structures from the human brain date back to the first complex animals, alive at least 600 million years ago – long before Anomalocaris.” [“First top predator was giant shrimp with amazing eyes”, December 2011 by Michael Marshall]

  • [Waptia]

    [Brackets] mean “forthcoming.”

  • [Eldonia]

    [Brackets] mean “forthcoming.”