My name is Andrew Simpson and I am a gallery volunteer at the Sedgwick Museum of Earth Sciences and a recent MGeol graduate in Geology with Paleobiology from the University of Leicester. My main interest is in vertebrate palaeontology, however, I like writing about all facets of palaeontology, from evolutionary history to fossil lagerstätten.

Science, like any organism, is constantly changing over time with scientific theories evolving to fit the best available evidence. This phenomenon is prevalent throughout the scientific world but can be very clearly seen in Palaeontology. There are many instances of reconstructions of extinct life being different in the past than they are today. One example, represented in the Sedgwick Museum, is the Carboniferous arthropod Megarachne ("Great Spider"). Once thought to be the largest spider ever, further research in 2005 found it to instead be a medium sized species of freshwater sea scorpion (though I don’t think this makes Megarachne less unsettling to look at!)

However one of the most interesting cases of an extinct animal whose palaeontological reconstruction has changed with new discoveries is the Cambrian arthropod Anomalocaris ("strange shrimp"). The Cambrian, from an evolutionary perspective, was a renaissance. New body plans and weird evolutionary experiments were emerging. Some animals became extinct soon after they appeared. Some, like the trilobites, survived for an amazingly long period of time. While others would evolve into the main animal groups alive today.
Anomalocaris is one of these weird wonders. It was discovered in 1892 by Joseph Whiteeves in the Burgess Shale formation in Canada. The original fossil looked shrimp-like but with no clear headparts. For a long time this was the only known description, its lifestyle a complete mystery. Later in 1911 the palaeontologist Charles Walcott, who also worked on the Burgess Shale, discovered a fossil which looked like a primitive jellyfish. He gave it the name Peytoia nathorsti.
Now you may be wondering "I thought you were going to be talking about Anomalocaris? Why have you wondered off topic?" Well this is where it gets interesting! In the early 1980s, Cambridge University palaeontologist, Harry Whittington, saw something astounding whilst preparing another Burgess Shale fossil. As he chipped away at the rock he noticed two Anomalocaris "shrimps" attached to the head of a larger body of another creature. Not only that, but a Peytoia fossil was attached to this same head. It became clear that the Anomalocaris shrimp and the Peytoia jellyfish were not separate species, but all part of one large Cambrian animal.

Anomalocaris was the top predator of its day. At around a metre long it was the largest animal the earth had seen to that point. After identifying its prey using large compound eyes, it then used its prongs to grab its prey. Anomalocaris then held its prey close to its mouth-parts so they could break through the hard exoskeleton. anomalocarids were widely successful, ranging across the globe from Canada to China and living from the Early to Middle Cambrian. While most anomalocarids were predators, a filter feeding species was described in 2014 and named Tamisiocaris borealis ("sieve shrimp").
So anomalocarids, the strange shrimps of the Cambrian, really are one of the most fascinating group of arthropods known. They are a great example of the evolutionary variety that has evolved on this planet.

Andrew Simpson