Is it a shrimp?! Is it a jellyfish?! No its Anomalocaris!

Science is not always static. Like any living species that has, currently or will exist it is constantly changing over time, with scientific theories evolving to fit the best available evidence. This phenomenon is prevalent throughout the scientific world but one area where it can be very clearly seen is in Palaeontology, where there are many instances of reconstructions of extinct life being very different in the past than they are today. One example of this is Megalosaurus, one of the first dinosaurs to be properly described by science. The original Victorian interpretation can be seen in a full scale model at the Crystal Palace in London. It is an impressive sculpture of a big hulking four legged lizard, portrayed as the Victorian scientists interpreted it, however it is nothing like the more graceful reconstruction nowadays. Another example, whose outdated model can be seen in the Sedgwick Museum in Cambridge, is the Carboniferous arthropod Megarachne (“Great Spider”). Once thought to be the largest spider that ever lived new research in 2005 found it to instead be a small to medium sized species of freshwater sea scorpion (though in my opinion this doesn’t make Megarachne any less unsettling to look at!)

However one of the most interesting cases of an extinct animal whose palaeontological reconstruction has changed greatly over time with new discoveries has to be Anomalocaris, whose name means “unusual shrimp”. Anomalocaris lived approximately 505 million years ago during the Early-Mid Cambrian. The Cambrian, from an evolutionary perspective, was prehistories equivalent of the European Renaissance of the 15th century. New body plans and weird evolutionary experiments were emerging during this period of earths history. Some animals from this time became extinct not long after they appeared. Some, like the trilobites, survived for an amazingly long period of time (trilobites appeared 520 million years ago in the Early Cambrian and went extinct during the Late Permian 250 million years ago – a longevity of 250 million years!) While others would eventually evolve and diversify into the main animal groups alive today; including the vertebrates which humans are a part of.

Anomalocaris is one of these weird wonders. It was discovered in 1892 by Joseph Frederick Whiteeves in the Burgess Shale formation, a fossil lagerstätten (which is a site where a high concentration of fossil material is preserved due to special environmental conditions) in Canada. The original fossil, named Anomalocaris canadensis, looked like a shrimp but with no clear headparts, hence its name of “unusual shrimp”. For a long time Anomalocaris was only known from this basic description and while it was definitely strange, its lifestyle was a complete mystery. Nineteen years later in 1911 the palaeontologist Charles Walcott, who is famous for his extensive work on the Burgess Shale, discovered a fossil of what seemed to be a primitive jellyfish. He gave it the name Peytoia nathorsti. Later, in 1928, Laggania cambria was discovered; the name given to a long bodied fossil that was interpreted as a relative of sea cucumbers.

Now you may be wondering “I thought you were going to be talking about Anomalocaris? Why have you wondered off topic to these random animals?” Well this is where the story gets interesting! In the early 1980s, nearly 90 years after Anomalocaris was first named, a palaeontologist working at the University of Cambridge by the name of Harry Whittington, an expert in Cambrian arthropods of the Burgess Shale, saw something that was truly astounding while preparing a fossil from the Burgess Shale. As he chipped away at the rock he saw two Anomalocaris “shrimps” attached to the head of a larger body not too dissimilar to Laggania. Not only that but a Peytoia fossilwas found to be attached to this same head. It soon became clear that Anomalocaris, Peytoia and Laggania were not separate species, but all part of one huge Cambrian animal, which was given the name Anomalocaris as that had been the original fossil part that had been found.

Anomalocaris was the top predator of its day. At around a metre in length it was the largest single animal the earth had ever seen at that point. After identifying its prey using large compound eyes, which gave it excellent eyesight comparable to modern day insects, it then used its prongs, once thought to be shrimps, to grab and hold its prey. Anomalocaris then held the prey close to its mouth-parts, once thought to be Peytonia, so the mouth parts could rip and break through the hard exoskeletons of trilobites and the soft bodies of other Cambrian arthropods that made up its prey. Anomalocaris swam via undulatory movements of their regularly arranged horizontal side flaps in the same manner that modern day soft bodied marine invertebrates do today. Anomalocarids as a group were widely successful, ranging across the globe from Canada to China and living from the Early to Middle Cambrian period. While most Anomalocarids were predators, another species has been described relatively recently in 2014 and named Tamisiocaris borealis (“sieve shrimp”). It had a very different lifestyle to Anomalocaris, possessing bristles on its prongs which it’s thought to have used in filter feeding, behaving rather like the baleen whales of today. This makes Tamisiocaris the earliest example of a large filter feeding animal known to science.

So Anomalocarids, the weird shrimps of the Cambrian, really are a fascinating group of arthropods. Once thought to be multiple separate animals, Anomalocaris and other Anomalocarids have instead been shown to be one of the weirdest of all Cambrian animals, and a true example of the evolutionary variety that has evolved on this planet.

The strange shrimp itself
Image credit: UNE photos,

EDIT: In this blog I state that Anomalocaris could “rip and break through the hard exoskeletons of trilobites”. This is actually wrong! A study in 2010, led by James Whitey Hagadorn from the the Denver Museum of Nature and Science, used 3-D models of Anomalocaris‘ mouth-parts to show that (a) it couldn’t close its mouth the whole way and (b) its mouth was too delicate to crush hard exoskeletons. As a result Anomalocaris would have fed mostly on soft bodied animals, and maybe even trilobites that had just moulted (and therefore had softer shells).

References/Further Reading

A blog, written by Ed Yong and published in Discover Magazine, about Anomalocaris

Yong, Ed, “The sharp eyes of Anomalocaris, a top predator that lived half a billion years ago”, Discover, Dec. 7, 2011,

The official Burgess Shale website page about Anomalocaris

“Anomalocaris canadensis”,

Vinther et. al. 2014 paper, published in the journal Nature, on the filter feeding Anomalocarid Tamisiocaris

Vinther, J., Stein, M., Longrich, N. et al. A suspension-feeding anomalocarid from the Early Cambrian. Nature 507, 496–499 (2014).

A wired article talking about the Hagadorn 2010 study that showed that Anomalocaris couldn’t eat hard bodied prey (USED FOR THE EDIT)

Mosher, Dave, “Giant Vicious-Looking Ancient Shrimp Was a Disappointing Wimp”, Wired, Mar. 11, 2010,

Original Hagadorn study: Hagadorn, J. (2010). Putting Anomalocaris on a soft-food diet. 2010 GSA Denver Annual Meeting.

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