A new filter-feeding giant that trolled the Cambrian seas has been
unearthed in Greenland.
The species, dubbed Tamisiocaris borealis, used
large, bristly appendages on its body to rake in tiny shrimplike
creatures from the sea, and likely evolved from the top predators
of the day to take advantage of a bloom in new foods in its
ecosystem, said study co-author Jakob Vinther, a paleobiologist at
the University of Bristol in England.
Explosion of life
The new creature was unearthed in sediments known as the Sirius
Passet formation. These shale-like deposits are teeming with
primeval organisms from the evolutionary "big bang' known as the
Cabrian explosion, a period between 540 million and 493 million
years ago when most complex life on Earth emerged.
Before then, most life forms were bacteria or microbiol
mat but during the Cambrian hard exoskeletons, jointed limbs,
compound eyes and antennae evolved.
Today, the Arctic region is so far north that the
excavation season lasts only during a six-week period of summer
when the sun never sets, but simply circles around in the sky. In
the Cambrian, however, the Arctic was a tropical ocean south of the
equator, Vinther said.
At that time Greenland and North America were part of a huge super
continent knows as Laurentia which was flipped on its side
relative to its current orientation.
Evolved giant
While on an excavation trip in 2009, the team unearthed fragments
of strange feeding appendages attached to a head shield from an
unknown creature. The appendages, which date to about 520 million
years ago, belonged to a group known as anomalocarids, the top
predators of their day.
These acient sea creatures grew to about 70 centimeters
(2.7 feet) long and "looked like something completely out of this
planet," with massive frontal appendages for grasping prey, huge
eyes on stalks, and a mouth shaped like a piece of canned
pineapple, Vinther told Live Science.
But the appendages from T. borealis were
different from those of other anomalocarids. Instead of large
grasping claws, the front pieces sported fine, delicate bristles,
much like the baleen found in the mouths of filter feeding
whales.
New food source
The strange-looking creature likely raked seawater for tiny
shrimplike organisms similar to krill, and evolved from predatory
anomalocarid ancestors. This shift from predation to filter feeding
echoes the evolutionary trajectory of baleen whales and whale
sharks, Vinther said.
"Every time you see these filter feeders — these gentle giants —
evolving, they evolved from the apex predators," Vinther said.
When predators evolve a filter-feeding strategy, they typically do
so because of a new bounty in available food. For instance, whales
evolved baleen when a water passage opened up between South America
and Antarctica, causing an upwelling of nutrient-rich deep water
and fueling a bloom of algae and krill, Vinther said. That suggests
a similar surge in sea life may have allowed these filter-feeding
giants to thrive in the ancient Cambrian oceans.
