Overview

Brief Summary

Anomalocaris is an extinct relative of modern arthropods that lived in the Cambrian Period, approximately 515 million years ago. It persisted up the Ordovician Period, 472 million years ago (1). Named “abnormal shrimp,” Anomalocaris is unlike any of its relatives still alive today. It had paired appendages at the front of its body, and a long segmented body with swimming lobes (fleshy boneless appendages used for swimming) on each segment (2). Anomalocaris was a large carnivore and specimens have been discovered with body lengths up to 2 m (3). It was a visual predator, gaining acute vision through compound eyes (4). 

  • 1. Van Roy, Peter, and Derek EG Briggs. "A giant Ordovician anomalocaridid." Nature 473.7348 (2011): 510-513.
  • 2. Chen, Jun-yuan, Lars Ramsköld, and Gui-qing Zhou. "Evidence for monophyly and arthropod affinity of Cambrian giant predators." Science 264.5163 (1994): 1304-1308.
  • 3. Conway Morris, Simon. The crucible of creation: the Burgess Shale and the rise of animals. Oxford; New York: Oxford University Press, 1998.
  • 4. Paterson, John R., et al. "Acute vision in the giant Cambrian predator Anomalocaris and the origin of compound eyes." Nature 480.7376 (2011): 237-240.
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Physical Description

Morphology

Eyes

Anomalocaris had acute vision. It had paired eyes, composed of at least 16,000 smaller lenses per eye. This is similar to the compound eyes seen in insects and other arthropods today, but the eyes of Anomalocaris were actually more complex. This finding is consistent with the notion that Anomalocaris was an active predator, and used vision to track prey (1).

The eyes of Anomalocaris represent an important discovery in understanding arthropod evolution. Anomalocaris is part of Dinocaridida, an extinct group of marine animals and an early relative to Arthropoda (2). The presence of compound eyes in Dinocaridida shows that this feature evolved earlier than previously thought. The compound eye evolved prior to the hardened exoskeleton seen in modern arthropods (1).

  • 1. Paterson, John R., et al. "Acute vision in the giant Cambrian predator Anomalocaris and the origin of compound eyes." Nature 480.7376 (2011): 237-240.
  • 2. Budd, Graham E. "The morphology of Opabinia regalis and the reconstruction of the arthropod stem‐group." Lethaia 29.1 (1996): 1-14.
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Ecology

Trophic Strategy

Feeding and Diet

Anomalocaris was a top predator in its oceanic environment. Paleontologists have long debated the nature of the prey of this ancient genus and whether it preyed upon soft-bodied or hard-bodied organisms. Bite marks matching Anomalocaris have been discovered on trilobite shells, and fossilized feces seeming to match Anomalocaris have been found containing ingested trilobite remains (1, 2). While this seems to support the notion that Anomalocaris fed on hard-bodied organisms, many questions yet remain. There is no concrete evidence that the feces were actually produced by Anomalocaris. They could have been produced by another organism living in the environment during this time period (2).

The jaws of Anomalocaris were not well-mineralized and therefore could not have been very hard. This raises questions on whether they would have been strong enough to crush trilobite shells. However, even if the jaws could not provide the force necessary to crack a trilobite shell, there are other strategies Anomalocaris may have used. They could have used their grasping appendages to hold a trilobite, rocking it back and forth until the stresses cracked the cuticle of their prey. This may have applied selective pressure for trilobites to evolve the ability to roll up and become more resistant to flexing (3). However, some recent analyses contest even this method of trilobite predation, indicating that the mouth plates of Anomalocaris would have cracked under the stress of eating a hard-shelled organism (4). Instead, it could have consumed softer prey through suction (5).

  • 1. Nedin, Christopher. "Anomalocaris predation on nonmineralized and mineralized trilobites." Geology 27.11 (1999): 987-990.
  • 2. Daley, Allison C., et al. "New anatomical information on Anomalocaris from the Cambrian Emu Bay Shale of South Australia and a reassessment of its inferred predatory habits." Palaeontology 56.5 (2013): 971-990.
  • 3. Nedin, Christopher. "Anomalocaris predation on nonmineralized and mineralized trilobites." Geology 27.11 (1999): 987-990.
  • 4. Witze, Alexandra. "Earth: Meeting notes: Fossil fangs not so fierce." Science News 178.11 (2010): 13-13.
  • 5. Daley, Allison C., and Jan Bergström. "The oral cone of Anomalocaris is not a classic ‘‘peytoia’’." Naturwissenschaften 99.6 (2012): 501-504.
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General Ecology

Anomalocaris lived in the Cambrian and Ordovician seas, becoming extinct approximately 472 million years ago (1). It is considered to have had a cosmopolitan distribution, meaning that it was globally distributed in appropriate marine habitats. Specimens of Anomalocaris have been discovered in a multitude of locations, including Australia, Utah, and China (2, 3, 4). One of the locations where it has been found is the Burgess Shale, a formation in British Columbia, Canada. This site is known for exceptional preservation of both soft and hard-bodied organisms, providing a wealth of information about this ancient ecosystem (5).

Most of the organisms found at the Burgess Shale Formation were benthic, or bottom-dwelling. Free-swimming organisms were rarely preserved here (6). Many of the taxa from the Burgess Shale do not belong to any known groups represented in modern times. Their dissimilarity from modern taxa often makes them difficult to classify. Specimens found here include the many-legged Hallucigenia, the hard-shelled Naroia, and Nectocaris, a particularly enigmatic taxon that may be related to modern cephalopods (7). This site is exceptional for the number of soft-bodied organisms preserved. Only 14% of genera present are shelled. Shelled organisms likely represented an even smaller proportion of the population when these organisms were alive, providing Anomalocaris with many soft-bodied potential prey (8).

  • 1. Van Roy, Peter, and Derek EG Briggs. "A giant Ordovician anomalocaridid." Nature 473.7348 (2011): 510-513.
  • 2. Briggs, Derek EG. "Giant predators from the Cambrian of China." Science 264.5163 (1994): 1283-1284.
  • 3. Briggs, Derek EG, et al. "Middle Cambrian arthropods from Utah." Journal Information 82.2 (2008).
  • 4. McHenry, B., and A. Yates. "First report of the enigmatic metazoan Anomalocaris from the southern hemisphere and a trilobite with preserved appendages from the Early Cambrian of Kangaroo Island, South Australia." Records of the South Australian Museum 26 (1993): 77-86.
  • 5. Butterfield, Nicholas J. "Hooking some stem‐group “worms”: fossil lophotrochozoans in the Burgess Shale." BioEssays 28.12 (2006): 1161-1166.
  • 6. Hall, Brian K. "Fossils of the Burgess Shale." Evolutionary Developmental Biology. Springer Netherlands, 1999. 39-54.
  • 7. Morris, S. Conway. "Burgess Shale faunas and the Cambrian explosion." Science 246.4928 (1989): 339-346.
  • 8. Morris, S. Conway. "The community structure of the Middle Cambrian phyllopod bed(Burgess Shale)." Palaeontology 29.3 (1986): 423-467.
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Life History and Behavior

Behavior

Swimming

Anomalocaris had a long segmented body with paired lateral lobes (fleshy appendages with no bones) upon each segment. These lobes functioned in locomotion for Anomalocaris. It swam by transmitting waves of motion along these appendages. By alternating direction of lobe undulation, Anomalocaris could have achieved a high degree of maneuverability (1). Recent computer analysis has determined that movement of all lobes as a single unit would have provided the most efficient swimming pattern for Anomalocaris. With separate lobes overlapping, this structure would operate similarly to a modern manta ray’s wing today (2).

  • 1. Whittington, Harry Blackmore, and Derek EG Briggs. "The largest Cambrian animal, Anomalocaris, Burgess Shale, British Columbia." Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences (1985): 569-609.
  • 2. Usami, Yoshiyuki. "Theoretical study on the body form and swimming pattern of Anomalocaris based on hydrodynamic simulation." Journal of Theoretical Biology 238.1 (2006): 11-17.
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Evolution and Systematics

Systematics or Phylogenetics

The evolutionary line containing Anomalocaris went extinct hundreds of millions of years ago, making classification with respect to modern groups difficult. Anomalocaris is considered to be either an early relative or a primitive member of the group Arthropoda, which contains living insects, spiders, and crustaceans. Anomalocaris is part of the extinct class Dinocarida and the order Radiodonta. Both these groupings contain only extinct organisms (1).

  • 1. Collins, Desmond. "The" evolution" of Anomalocaris and its classification in the arthropod class Dinocarida (nov.) and order Radiodonta (nov.)." Journal of Paleontology (1996): 280-293.
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