dcsimg

Brief Summary

    Brief Summary
    provided by EOL authors

    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).

    license
    cc-by-3.0
    copyright
    Katherine Dzikiewicz
    partner site
    EOL authors
    ID
    29883006

Morphology

    Eyes
    provided by EOL authors

    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).

    license
    cc-by-3.0
    copyright
    Katherine Dzikiewicz
    partner site
    EOL authors
    ID
    29883014

Trophic Strategy

    Feeding and Diet
    provided by EOL authors

    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).

    license
    cc-by-3.0
    copyright
    Katherine Dzikiewicz
    partner site
    EOL authors
    ID
    29883270

General Ecology

    General Ecology
    provided by EOL authors

    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).

    license
    cc-by-3.0
    copyright
    Katherine Dzikiewicz
    partner site
    EOL authors
    ID
    29883276

Behavior

    Swimming
    provided by EOL authors

    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).

    license
    cc-by-3.0
    copyright
    Katherine Dzikiewicz
    partner site
    EOL authors
    ID
    29883023

Systematics or Phylogenetics

    Systematics or Phylogenetics
    provided by EOL authors

    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).

    license
    cc-by-3.0
    copyright
    Katherine Dzikiewicz
    partner site
    EOL authors
    ID
    29883026