#cloudina

*Amelia M. Penny1, Rachel Wood1, Andrew Curtis1, Frederick Bowyer1, Rosalie Tostevin2 and Karl-Heinz Hoffman3

1University of Edinburgh 2University College London 3Geological Survey of Namibia

The oldest known calcified metazoans are from the Ediacaran Period, around 550Ma. These metazoans are the first known adopters of the skeleton-building strategy which became widespread among metazoan taxa during the Cambrian. Three Ediacaran taxa, Cloudina,Namacalathus and Namapoikia, are locally abundant in shallow and mid-ramp settings of the Nama Group of southern Namibia, a mixed carbonate and clastic succession extending from around 552-541Ma.

New fossil material from the Nama Group permits new insights into the palaeoecology of these calcified metazoans. In particular, the Nama Group contains extensive microbial-metazoan reefs, where the presence of free-growing, reef-building Cloudina, as well as thrombolite-associated Cloudina and Namacalathus and fissure-dwelling Namapoikia, indicates a differentiation of metazoans into the distinct open surface and cryptic biotas characteristic of Phanerozoic reefs, with accompanying complex ecological interactions.

Ongoing work on the calcified metazoans of the Nama Group seeks to further investigate their palaeoecology, adding to the picture of ecological complexity in the early skeletonised metazoan communities of the Nama Group.

Until now, the oldest known reefs made of metazoans (multicellular animals) have been dated to about 530 million years. Scientists thought that many defensive strategies and ecological innovation -- like forming hard skeletons and building reefs -- emerged as a response to the Cambrian explosion when many major animal groups rapidly started appearing on Earth. Suddenly the oceans became a dangerous place, filled with competition for food and living space. 

But according to University of Edinburgh’s Amelia Penny and colleagues, reef building happened before that great speciation event. This newly discovered, older reef in Namibia (now located on dry land) is comprised of tiny, filter-feeding animals, called Cloudina, that were attached to each other and cemented together. These widely studied organisms are the oldest known skeletal animals; up until the emergence of Cloudina in the Ediacaran right before the Cambrian, animals had soft bodies. "We found them in life position, forming a reef," Penny tells the Los Angeles Times. Cloudina formed these rigid structures by producing a natural cement made of calcium carbonate. 

WASHINGTON (Reuters) - A sea creature that looked like a stack of tiny ice cream cones is providing quite a treat for scientists studying the dawn of animal life on Earth.

Researchers said on Thursday they found fossils of the oldest-known animal-made reef in Namibia, built by a small, filter-feeding seabed creature called Cloudina 548 million years ago.

The discovery indicates that important evolutionary developments were unfolding millions of years before the so-called Cambrian explosion when many of the major animal groups first appeared. It also showed that reef building by marine invertebrates, akin to today's coral reefs, began 18 million years earlier than previously known.

Cloudina, one of Earth's earliest-known animals, was the first one with a hard skeleton, in this case an outer shell.

Its fossils have been found in Europe, North and South America, Asia and Africa but it had not been known that it built reefs - a collective activity that helps gain protection from predators and improves food gathering.

The reefs - now on dry land in southern Namibia - were small, about three to six feet across (1 to 2 meters), and stood alongside larger ones made by microbes. Cloudina, perhaps related to jellyfish, corals and sea anemones, was up to six inches long (15 cm) with a diameter of about three-tenths of an inch (8 mm).

"Cloudina's key innovation was the skeleton – it is the first animal known to have produced any kind of biomineralized skeleton. Skeletons have been especially important in the history of animal evolution, providing support, protection and mineral storage," University of Edinburgh geoscientist Amelia Penny said.

"The skeleton is made up of a series of long, nested conical structures which fit one inside another, a bit like a stack of ice cream cones."

Scientists think the animal itself occupied only the top cone of the stack so that - like some modern corals - a small living animal was supported by a larger, unoccupied skeleton that grew over time.

It lived during the Ediacaran Period, a remote time in Earth's history that preceded the torrent of animal evolution seen in the Cambrian Period that followed. The oldest animal fossils date from the Ediacaran.

"Traditionally, the Ediacaran period has been viewed as a time when animal ecologies were quite simple," University of Edinburgh geoscientist Rachel Wood said.

"It's becoming clear that some of the evolutionary innovations of the Cambrian had precursors in the Precambrian. The discovery of reef-building animals in the Ediacaran adds to that picture of early animals dealing with a wider, more complex range of ecological pressures than we expect for the Ediacaran."

Read more here.

(via Science Daily)

The Cloudina (1972)

Phylum : Incertae sedis Family : Cloudinidae Genus : Cloudina Species : C. hartmannae, C. riemkeae, C. lucianoi, C. sinensis, C. carinata

Ediacaran (560 - 530 Ma)

15 mm high (size)

America (map)

Cloudina varies in size from a diameter of 0.3 to 6.5 mm, and 8 to 150 mm in length. Fossils consist of a series of stacked vase-like calcite tubes, whose original mineral composition is unknown. Each cone traps a significant pore space beneath it, and stacks eccentrically in the one below. This results in a ridged external appearance. The overall tube is curved or sinuous, and occasionally branches. The tube walls are 8 to 50 micrometers thick, usually lying in the range 10 to 25 μm. Although it used to be thought that the tubes had test-tube like bases, detailed three-dimensional reconstruction has shown that the tubes had an open base. There is evidence that the tube was flexible.

Cloudina is usually found in association with microbial stromatolites, which are limited to shallow water; their isotopic composition suggests that water temperatures were relatively cool. They have also been found in normal sea-floor sediments, suggesting that they were not only restricted to dwelling on microbial mounds. On the other hand Cloudina has never been found in the same layers as the soft-bodied Ediacara biota, but Cloudina and Ediacara biota have been found in alternating layers. This suggests that the two groups of organisms had different environmental preferences.