Yohoia

Name: Yohoia.
Phonetic: Yo-ho-e-ah.
Named By: Charles Doolittle Walcott‭ ‬-‭ ‬1912.
Classification: Arthropoda,‭ ‬Megacheira,‭ ‬Yohoiidae.
Species: Y.‭ ‬tenuis‭ (‬type‭)‬.
Diet: Carnivore‭?‬/Detritivore‭?
Size: Individuals range between‭ ‬7‭ ‬and‭ ‬23‭ ‬millimetres long.
Known locations: Canada,‭ ‬British Columbia‭ ‬-‭ ‬Burgess Shale.
Time period: Mid Cambrian.
Fossil representation: Literally hundreds of individuals.

       Yohoia is an interesting little creature that‭ ‬was‭ ‬first discovered in the Canadian Burgess Shale where it is one of the more common creatures so far found.‭ ‬The body of Yohoia begins with a cephalon‭ (‬head shield‭) ‬that is followed by thirteen more body segments which end in a paddle-like tail.‭ ‬Three pairs of leg like appendages grew down from the cephalon,‭ ‬and these almost certainly supported the‭ ‬animals‭’‬ body when resting on the sea floor.‭ ‬Flat,‭ ‬flap like appendages grew down from the body segments that were behind the head,‭ ‬and these supported stiff bristle like structures.‭ ‬These may have been gills for extracting oxygen out of the water.
       The key features that raise the most questions about Yohoia are the arm-like appendages that grow from the front of the base of the head.‭ ‬These are more robust than the leg appendages,‭ ‬and quickly make a sharp bend,‭ ‬dividing the appendage into‭ ‘‬upper‭’ ‬and‭ ‘‬lower‭’‬ portions.‭ ‬At the end of the lower portion a cluster of four large spines grew forward and it is here that the main question about the lifestyle of Yohoia begins.‭ ‬Some chose to interpret these spikes as being a predatory adaptation,‭ ‬used to grasp smaller creatures which could then be eaten.‭ ‬Others however prefer an alternate theory where the spiked ends of these appendages where pushed through the soft sediment of the sea floor,‭ ‬filtering and trapping small bits of organic matter that were otherwise hidden.
       One further argument for the predatory Yohoia theory is the eyes.‭ ‬At the front of the head bulbuos structures may have been eyes and the key thing here is that they were more forward facing eyes,‭ ‬a common feature for animals that live predatory lifestyles because this gives them much greater visual ability when hunting‭ (‬e.g.‭ ‬the ability to judge distances‭)‬.‭ ‬Ultimately however we are still uncertain as to which interpretation is correct.

Further reading
-‭ ‬Taphonomy of the Greater Phyllopod Bed community,‭ ‬Burgess Shale‭‬.‭ ‬PALAIOS‭ ‬21‭ (‬5‭)‬:‭ ‬451‭–‬65.‭ ‬-‭ ‬Jean-Bernard Caron‭ & ‬Donald A.‭ ‬Jackson.‭ ‬-‭ ‬2006.



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