Vendian Gallery
Here are a few of the known Vendian fossils. Because these are so rare, it is almost
impossible to acquire these for private collections.
Cyclomedusa
Cyclomedusa is probably the most common and widespread Vendian fossil. It is considered by some to have been a benthic (bottom-dwelling)
polyp, somewhat like a sea anemone.
Charnia
Charnia is one of the largest Vendian fossils, with some specimens reaching one meter in length. The flat, leafy body
of Charnia was attached to a disk-shaped holdfast that attached the organism to the bottom
(not seen on this fossil).
Here's an artist's rendering:
Drawing from Meg at www.formsmostbeautiful.net
Researchers place Charnia closest to the living
"sea pens" or pennatulaceans, a group of
colonial cnidarians distantly related to the corals.
Sea pens are actually colonies of
polyps.
Eoporpita
Eoporpita is one of the most striking Vendian fossils, noted
for its thick tentacles surrounding a central body. Some researchers consider
it to have been a benthic polyp rather like a sea anemone.
Other researches feel that Eoporpita was a chondrophorine.
Chondrophorines are cnidarians in the class Hydrozoa;
although they look somewhat like individual jellyfish, with a round body from
which tentacles hang, they are actually colonies of individual polyps, each one specialized for a function like feeding or
reproduction. The whole colony floats with an internal disc-shaped float that
may or may not have a sail attached. Living chondrophorines are known as "sailors-by-the-wind" and may wash up on beaches in huge
numbers at certain times of the year. They are probably relatives of the Siphonophora, an order of colonial cnidarians that includes
the venomous "Portuguese man-o-war".
Nemiana
Nemiana is one of the simplest of all Vendian fossils, and is
difficult to interpret. It seems to be an impression of a saclike body. Similar
impressions in later rocks and in modern sediments are attributed to sea
anemones; however, unlike most sea anemones, Nemiana has no tentacles,
although occasionally central markings are found that could represent a mouth.
Other researchers have speculated that Nemiana might be some sort of large protist,
or possibly an alga.
We do know that Nemiana was gregarious; it is rare to find isolated
specimens. Nemiana could reproduce by splitting in
two. There is also a tendency to find abundant Nemiana in rock layers that were
formed during or just after some kind of local environmental disturbance. It
seems plausible that Nemiana,
whatever it was, was a "Vendian weed" —
able to colonize disturbed habitats and reproduce rapidly thanks to its very
simple anatomy.
Pteridinium
Pteridinium has been found in Russia, Australia, Namibia, and North Carolina. Unfortunately,
exactly what it was, or how it lived, is open to question.
Some feel that if
it was a cnidarian (Jellyfish, coral, or other
stinger), it was not closely related to living cnidarians; it may belong to a
group that is now extinct.
Whatever it was, Pteridinium had an elongated, ribbed body that is usually
found squashed flat. By examination of numerous specimens we can tell that it
was composed of three ribbed "leaflets" which met along the central
mid line.
It probably lay on the bottom, but we do not know whether it
fed on small particles, took up dissolved nutrients from the water, depended on
symbiotic microorganisms in its tissues, or perhaps used some combination of
these ways of life.
Arkarua
The name "Arkarua" comes from a mythical giant snake of the
Aboriginal peoples who live where the fossil was discovered — the Flinders
Ranges of south Australia, near Adelaide. Arkarua occurs
alongside Dickinsonia, Tribrachidium, Cyclomedusa,
and other familiar Ediacaran animals as well as many
new and as yet undescribed species.
Arkarua is a small disc-like fossil, and was described as an echinoderm (from starfish
to sea cucumbers).
If this is correct, then Arkarua is the oldest known
echinoderm.
The fossils preserve what appears to be a five-lobed central
region that is interpreted as five ambulacral grooves,
which are characteristic of echinoderms.
Unfortunately, the fossils found in sandstone thus far do
not preserve any details of the internal organs, so the identification is still
inconclusive.
Dickinsonia
Dickinsonia is often considered to be an annelid worm because of its apparent similarity to
one genus of extant polychaete, Spinther.
However, in the opinion of some, it may in fact be a cnidarian polyp, like a soft-bodied version of the "banana coral."
Sprigginida
The striking Vendian fossil Spriggina (shown here) and its close relative Marywadea make up the Sprigginida,
a clade of soft-bodied organisms that are restricted
to the Precambrian.
Spriggina is known largely from the Ediacara Hills of south Australia, near Adelaide. The organism had a
crescent-shaped head and numerous segments tapering to the posterior end; it is
only about three centimeters long.
Spriggina was described as an annelid (segmented worm), but it now appears to be related
to the arthropods, although Spriggina had no hard
parts, and it is unclear exactly what kind of appendages it had. Compare it to
our pictures of trilobites and see what you think!
Tribrachidium
Few fossils of Ediacaran animals
are so compellingly bizarre as this unusual
disc-shaped form with three-part (triradial)
symmetry. Named Tribrachidium heraldicum,
its affinities are still mysterious, although distant relationships have been
proposed with either the Cnidaria (corals and
anemones) or Echinodermata (urchins and sea stars).
Kimberella
Some researchers have reasoned that Kimberella probably had a tough shell-like covering
that rigidly stood up into the sediment when the animals were buried. Kimberella appears to be somewhat like a mollusk. Nevertheless, it is still uncertain
which group of modern animals is most closely related to this interesting
animal.
Here's an artist's drawing of Kimberella.
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