Analysis of Compound Eye Fossil Indicates that Apex Predator had Fantastic Vision
Scientists
have revealed that Anomalocaris, an ancient marine invertebrate that
lived more than 500 million years ago was equipped with sophisticated
compound eyes. These eyes gave this metre long creature superb vision
enabling it to be a formidable hunter. This remarkable research has been
undertaken by South Australian Museum and University of Adelaide
scientists working on fossils of compound eyes dating from more than 500
million years ago. The fossils from the Emu Bay area of Kangaroo Island
show that by the Mid Cambrian some invertebrates had evolved very
sophisticated vision, much better than many types of extant insects and
crustaceans and perhaps at least as good as those aerial masters the
dragonflies.
This research has already got palaeontologists very
excited as it sheds light on how the first food chains may have evolved,
with the evolution of sophisticated vision helping some types of
Arthropod to thrive at the expense of others. The research team are
confident that the compound eyes belonged to - the world's first apex
predator - Anomalocaris.
An International Team of Scientists Led the Research
The
international team behind this study includes two Adelaide researchers
Associate Professor Michael Lee (South Australia Museum and University
of Adelaide) and Dr. Jim Jago (South Australia Museum). From our
understanding of the fossil evidence, the advanced compound eye probably
belonged to the largest predator known from strata dating from the same
geological period - Anomalocaris. This invertebrate, a member of the
Arthropoda, the largest phylum of animals is distantly related to
crustaceans such as lobsters and shrimps. At up to a metre in length,
this is the largest animal known from Cambrian strata. Fossils ascribed
to Anomalocaris have been found in Southern China as well as these from
Australia that the scientists studied, but perhaps most famously, this
fierce predator is associated with the Burgess Shale deposits of British
Columbia (Canada).
The Burgess Shale location in British Columbia
is one of the most important fossil sites in the world. The rock
formations were formed from mud-slips that fell onto a shallow seabed,
burying an entire ecosystem. Over hundreds of thousands of years a
number of major mudslides occurred, each time burying the fauna of the
area, some of which was preserved as exquisite fossils.
Anomalocaris - Nightmarish Beast of the Cambrian Geological Period
Anomalocaris
is the stuff of nightmares and sci-fi movies. It is considered to be at
the top of the earliest food chains because of its large body size,
formidable grasping claws armed with sharp spikes and a circular mouth
positioned under the head with its razor-sharp serrations.
Fossils
of Trilobites contemporaneous to Anomalocaris fossil material are
testament to this fearsome predator. Some of the Trilobite fossils show
signs of severe damage and there has even been some five hundred million
year old fossilised poo (coprolite) containing crushed and smashed
pieces of Trilobite exoskeleton - the remains of an Amomalocaris meal
perhaps?
The discovery of superbly preserved eye fossils, the
remains of the calcite based compound eyes that were supported on the
end of a stiff stalk each side of the head, show astonishing detail of
the optical design. Having excellent vision, far better than its prey
would have given animals like Anomalocaris a huge advantage when
hunting. Bio-mechanical studies have shown that Anomalocaris was
nektonic (free-swimming), but not a very fast swimmer. However, with
much more advanced eyesight than most of its prey, this armoured giant
of the Cambrian seas would have been a very effective hunter.
The Powerful Eyes of a Hunter
The
fossils represent compound eyes - the multi-faceted variety seen in
Arthropods such as flies, crabs and such like. However, the fossils
represent compound eyes that are up to three centimetres in diameter.
They are amongst the largest compound eyes ever to have evolved. Each
eye contains up to 16,000 individual lenses, that is like having two
16-kilo pixel cameras perched on stalks either side of the head. This
would have given this predator excellent almost 300 degree vision.
Whilst Trilobites and other marine invertebrates may have been able to
discern shapes and distinguish between light and dark, the
super-developed eyes of the Anomalocaris would have given this predator a
huge advantage over potential prey species.
The number of lenses
and other aspects of their optical design suggest that Anomalocaris
would have seen its world with exceptional clarity whilst hunting in
well-lit waters. Only a few Arthropods, such as modern predatory
dragonflies, have similar resolution.
A Predator/Prey "Arms Race"
The
international research team conclude that the existence of highly
sophisticated, visual hunters within Cambrian communities would have
accelerated the predator/prey "arms race" that began during this
important phase in early animal evolution over half a billion years ago.
Such a predator/prey relationship would have helped to speed up
evolution, perhaps helping to explain the rapid diversification of
marine animal forms during this geological period.
The discovery
of powerful compound eyes in Anomalocaris confirms it is a close
relative of Arthropods, and has other far-reaching evolutionary
implications. It demonstrates that this particular type of visual organ
appeared and was elaborated upon very early during Arthropod evolution,
originating before other characteristic anatomical structures of this
group, such as a hardened exoskeleton and walking legs.
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