Cambrian Explosion: first jawed animal found (Introduction)

by David Turell , Friday, April 28, 2017, 15:34 (2766 days ago) @ David Turell

This animal had pincers and a mandible with a highly complex body plan, from 507 million years ago, found in Canadian shale:

https://www.sciencedaily.com/releases/2017/04/170426131024.htm

"The creature, named Tokummia katalepsis by the researchers, is a new and exceptionally well-preserved fossilized arthropod -- a ubiquitous group of invertebrate animals with segmented limbs and hardened exoskeletons. Tokummia documents for the first time in detail the anatomy of early "mandibulates," a hyperdiverse sub-group of arthropods which possess a pair of specialized appendages known as mandibles, used to grasp, crush and cut their food. Mandibulates include millions of species and represent one of the greatest evolutionary and ecological success stories of life on Earth.

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"Analysis of several fossil specimens, following careful mechanical preparation and photographic work at the ROM, showed that Tokummia sported broad serrated mandibles as well as large but specialized anterior claws, called maxillipeds, which are typical features of modern mandibulates.

"'The pincers of Tokummia are large, yet also delicate and complex, reminding us of the shape of a can opener, with their couple of terminal teeth on one claw, and the other claw being curved towards them," said Aria. "But we think they might have been too fragile to be handling shelly animals, and might have been better adapted to the capture of sizable soft prey items, perhaps hiding away in mud. Once torn apart by the spiny limb bases under the trunk, the mandibles would have served as a revolutionary tool to cut the flesh into small, easily digestible pieces."

"The body of Tokummia is made of more than 50 small segments covered by a broad two-piece shell-like structure called a bivalved carapace. Importantly, the animal bears subdivided limb bases with tiny projections called endites, which can be found in the larvae of certain crustaceans and are now thought to have been critical innovations for the evolution of the various legs of mandibulates, and even for the mandibles themselves.

"The many-segmented body is otherwise reminiscent of myriapods, a group that includes centipedes, millipedes, and their relatives. "Tokummia also lacks the typical second antenna found in crustaceans, which illustrates a very surprising convergence with such terrestrial mandibulates," said Aria."

Comment: this highly complex predator appears, as all Cambrian animals do, with no predecessors in earlier layers. The Cambrian Explosion is the basis of all existing phyla of animals today, with no clear explanation of the driving evolutionary force creating such a complex diversity of forms. As Darwin knew, it still presents the main challenge to his step-by-step theory. It is true that oxygen levels rose as this occurred, but the higher oxygen levels allowed this to happen, but cannot be identified as a cause of the sudden inventiveness of the evolutionary process. Only a designing mind can accomplish this type of change in form. Preceding forms were simple bags of cells, nothing slightly complex.