Excellent eyesight is essential if you are a top predator, like the prehistoric sea creature Anomalocaris, an early arthropod relative that patrolled the oceans over 500 million years ago. However, finding proof that a long-extinct animal had super vision has been difficult, until now.
Illustration of Anomalocaris, the ancient top sea predator in Cambrian times over 500 million years ago. Its compound eyes had at least 16,000 lenses each, making its sight rival many arthropods living today. © Katrina Kenny
A team of scientists led by University of New England, Australia, and including those at the Natural History Museum, have uncovered the first direct evidence that Anomalocaris had compound eyes, each with more than 16,000 lenses. This means that Anomalocaris’ vision was as good 500 million years ago as that of other arthropods today, such as flies and crabs.
This research is published today in the journal Nature and is on this week's cover.
Museum scientist Dr Greg Edgecombe who worked on the research says, ‘This find is significant because having direct evidence of compound eyes confirms that Anomalocaris is a close relative of arthropods. These huge, sophisticated eyes would give animals a tremendous advantage at locating prey.’
The team examined fossils uncovered from Kangaroo Island, South Australia, which were about 515 million years old. Using scanning electronic microscopy (SEM) they could detect imprints of thousands of individual lenses in the 2 large eyes of Anomalocaris. They found at least 16,700 lenses. In comparison, the creatures alive today with the most powerful compound eyes are dragonflies, with as many as 28,000 lenses.
Compound eyes give an animal a pixelated view of the world. The resolution isn't as good as a human would see, but compound eyes have a much wider view angle and they are particularly good for detecting movement, perfect for a predator like Anomalocaris.
Close up of eyes of a dragonfly. They have the most powerful compound eyes with 28,000 lenses. © Alexis Tindall
Anomalocaris, meaning ‘abnormal shrimp’, was up to 1-metre-long and had a large body, spiny grasping claws at the front of the head and teeth-like serrations in its mouth. Its eyes were 2-3cm wide and set on stalks.
It was the top predator in the sea and there were no land animals around at this time in Earth's history. Anomalocaris managed to eat trilobites (extinct marine arthropods) that were at least 10cm long. Scientists know this because their broken remains appear in the fossilised poo, or coprolites of Anomalocaris.
This research also suggests that compound eyes evolved earlier than was previously known. Edgecombe explains, ‘We know from this find that eyes first evolved and developed very early during arthropod evolution, originating before other anatomical characteristics of this group, such as a hardened exoskeleton and walking legs.’
Having excellent eyesight as well as being a top predator may have had an even larger effect on other Cambrian creatures. This was a time of when most major groups of life went through rapid diversification, known as the Cambrian explosion. Dr John Paterson from the University of New England explains, ‘Highly visual hunters in Cambrian marine communities would have placed considerable selective pressures on their prey. This would have influenced the “arms race” at this important phase in early animal evolution, over half a billion years ago.’