Fossils Show Anatomy Of Ancient Fuxianhuiid Arthropod
February 28, 2013

New Fossils Reveal Anatomy Of One Of Earth’s Earliest Creatures

April Flowers for - Your Universe Online

An international group of scientists led by researchers at the University of Cambridge has made an extraordinary find in South China. For the first time, scientists are able to see through the head of the "fuxianhuiid" arthropod, revealing one of the earliest evolutionary examples of limbs used for feeding along with the oldest nervous system to stretch beyond the head in fossil record.

Prior to this find, heads covered by a wide shell, or carapace, characterized all the known fossils of this extremely soft-bodied animal. This carapace obscured underlying contents from detailed study.

A new fossil-rich site in South China, however, contains arthropod samples where the carapace has literally been "flipped" over before fossilization occurred. This allowed the scientists an unprecedented look at the fuxianhuiid head.

Published recently in the journal Nature, the study findings highlight the discovery of previously controversial limbs under the head. Millions of years before creatures emerged from the oceans, these limbs were used to shovel sediment into the mouth as the fuxianhuiid crawled across the seabed.

The research team, which also included scientists from Yunnan University in Kunming, South China, claims this could be the earliest and simplest example of manipulative limbs used for feeding purposes. This hints at the adaptive ability that made arthropods so successful and abundant as they evolved into the insects, spiders and crustaceans we know today.

Fuxianhuiids developed the limbs to push seafloor sediment into their mouth in order to filter it for organic matter — such as traces of decomposed seaweed — which constituted the creatures' food, using a feeding technique scientist's call "detritus sweep-feeding."

The new fuxianhuiid fossils revealed the oldest nervous system on record that is post-cephalic, or beyond the head. This nervous system consists of only a single stark string in what was a very basic form of early life compared to modern life.

"Since biologists rely heavily on organization of head appendages to classify arthropod groups, such as insects and spiders, our study provides a crucial reference point for reconstructing the evolutionary history and relationships of the most diverse and abundant animals on Earth," said Javier Ortega-Hernández, from Cambridge's Department of Earth Sciences. "This is as early as we can currently see into arthropod limb development."

Fuxianhuiids lived around 520 million years ago. One of the first examples of complex animal life, they emerged roughly 50 million years before primordial land creatures crawled from the sea and were likely to have evolved from creatures resembling worms with legs. Arthropods were the first animals with joints that enabled them to crawl.

Most of the fuxianhuiid´s time would have been spent grazing the sea floor shoveling sediment into their mouths with their feeding limbs. They might also have been able to swim short distances using their bodies like tadpole shrimp.

The fossils at the new site date to the early part of the Cambrian explosion event when life on Earth changed from the multi-cellular organisms to a sudden and widespread abundance of marine species. This was the first major evolutionary step toward the animal kingdom we know today.

"These fossils are our best window to see the most primitive state of animals as we know them — including us," said Ortega-Hernández. "Before that there is no clear indication in the fossil record of whether something was an animal or a plant — but we are still filling in the details, of which this is an important one."

The Cambrian explosion is still a mystery, but theories abound. Examples of such theories include possible correlations with oxygen rises, spikes in oceanic nutrient concentration, and genetic complexity reaching critical mass.

The South China site could prove to be a key in uncovering more information about this pivotal moment in evolutionary history. The collection of all organisms preserved in this location, known as the Xiaoshiba biota, is similar to the world-famous Chengjiang biota, which provided many of the best arthropod fossil records to date.

"The Xiaoshiba biota is amazingly rich in such extraordinary fossils of early organisms," explained Ortega-Hernández. "Over 50 specimens of fuxianhuiids have been found in just over a year, whereas previous areas considered fossil rich such as Chengjiang it took years — even decades — to build up such a collection."

"So much material is so well preserved. There's massive potential for Xiaoshiba to become a huge deal for new discoveries in early animal evolution."