Cambrian Explosion: early tiny forms (Introduction)

by David Turell , Sunday, December 24, 2017, 15:33 (2526 days ago) @ David Turell

In the northern tip of Greenland microscopic soft forms from the early Cambrian have been found. Makes the explosion larger:

https://www.sciencedaily.com/releases/2017/12/171219093415.htm

"A team of researchers from Uppsala University have uncovered a hidden diversity of microscopic animal fossils from over half a billion years ago lurking in rocks from the northern tip of Greenland.

"The 'Cambrian explosion' of animal diversity beginning ~541 million years ago is a defining episode in the history of life. This was a time when the seas first teemed with animal life, and the first recognisably 'modern' ecosystems began to take shape.

"Current accounts of this explosion in animal diversity rely heavily on records from fossilised shells and other hard parts, since these structures are the most likely to survive as fossils.

"However, since most marine animals are 'soft-bodied' this represents only a small fraction of the total diversity.

***

"Most of the fossils were less than a millimetre long and had to be studied under the microscope. Fossils at the nearby Sirius Passet site typically preserve much larger animals, so the new finds fill an important gap in our knowledge of the small-scale animals that probably made up the majority of these ecosystems. Among the discoveries were the tiny spines and teeth of priapulid worms -- small hook shaped structures that allowed these worms to efficiently burrow through the sediments and capture prey. Other finds included the tough outer cuticles and defensive spines of various arthropods, and perhaps most surprisingly, microscopic fragments of the oldest known pterobranch hemichordates -- an obscure group of tube-dwelling filter feeders that are distant relatives of the vertebrates. This group became very diverse after the Cambrian Period and are among some of the most commonly found fossils in rocks from younger deposits, but were entirely unknown from the early Cambrian. This new source of fossils will also help palaeontologists to better understand the famously difficult to interpret fossils at the nearby Sirius Passet site, where the flattened animal fossils are usually complete, but missing crucial microscopic details.

"The sheer abundance of these miniature animal fossils means that we have only begun to scratch the surface of this overlooked resource, but it is already clear that this discovery will help to reshape our view of the non-shelly animals that crawled and swam among the early Cambrian seas more than half a billion years ago,' says Sebastian Willman, researcher at the Department of Earth Sciences, Uppsala University."

Comment: This new study makes the gap between the pre-Cambrian and the actual Cambrian animals much bigger. Where are the intermediate forms, if any? Darwin's fear continues.