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."
Reefs gave the creatures access to nutrient-rich water currents amid
growing competition for food and living space. They attached to
fixed surfaces and to one another with a natural cement of calcium
carbonate to make rigid structures and aligned with a current to
filter out passing food particles.
Life on Earth emerged in the primordial oceans. These Cloudina reefs
were the earliest know animal-built structures. The earliest reefs
of any kind were built by microbes more than 3 billion years ago.
