The Cambrian explosion has been associated scientific vagueness for several years. In a period of nearly 10 million years long, nearly all the modern phyla of animals appeared in the fossil record, including chordates. Anomalocaridids are some of the more controversial taxa in this era with their unusual morphology and complicated history of description. Now, newly discovered fossils, such as Anomalocaris, from the Cambrian era add to this mystery.
Anomalocaris, which means “meaning ‘abnormal shrimp, was first described in 1892. It is a 505 million year old animal from British Columbia’s Burgess Shale and has a complex history of description because parts of its body were described in isolation before it was realized they all belonged to the same animal.
Anomalocaris has been misidentified throughout history, due to its makeup of a mixture of mineralised and unmineralised body parts. Their mouth and feeding appendage were considerably harder and more easily fossilized than the body itself.
The pictures above both show pieces of the fossils. The picture on the right shows the mouth parts while the picture on the right shows the forelimbs. Trying to reassemble Anomalocaris fossils is described as “like trying to put together a jigsaw puzzle where no one has seen the picture on the box for 505 million years”.
The frontal appendage of Anomalocaris was first described as the body of a shrimp. The mouth parts were described as a jellyfish and a decomposed full body of the specimen was originally described as a sea cucumber. When Anomalocaris was studied in detail again, it was then incorrectly decided that it was actually a jellyfish on top of a sponge.
This picture shows the most complete specimen ever found was collected in 1991 by the Royal Ontario Museum. You can see from right to left, the pair of eyes, claws, lateral lobes along the body and the posterior fan.
Solving the mystery
Around the early 1980s, palaeontologist Harry Whittington was preparing a Burgess Shale fossil when he solved the mystery of Anomalocaris’s identity. Whittington found two Anomalocaris “shrimps” which were attached to the head region of a large body and it also had the jellyfish as its mouth. In the early 1990s, the specimens were collected by the Royal Ontario Museam and, here, complete specimens were reconstructed so Anomalocaris could be identified. Anomalocaris is now classified as a kind of primitive arthropod, which is a group that contains crustaceans, modern insects and arachnids,
But new evidence from 515 million years ago have been also studied again and this can also suggest new facts about this fossil. It suggests that Anomalocaris possessed very large compound eyes, giving the creature powers of vision that exceeds most living insects and crustaceans’s vision. Each eye could have measured up to three centimetres and have contained more than 16,000 separate hexagonal lenses. This new information shows that compound eyes evolved before hardened exoskeletons and also reinforces the fact that Anomalocaris may have been a close relative of arthropods.
The picture below illustrates an artist’s impression of Anomalocaris‘ compound eyes.
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