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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