Hurdia
Name: Hurdia.
Phonetic: Hur-de-ah.
Named By: Charles Doolittle Walcott - 1912.
Classification: Arthropoda, Dinocaridida,
Radiodonta, Anomalocarida, Hurdiidae.
Species: H. victoria
(type). H. triangulata ?
Diet: Uncertain, but fed upon other organisms,
refer to main text.
Size: Complete specimens commonly about 20
centimetres long, but isolated parts attributed to the genus suggest
an upper size of at least 50 centimetres long.
Known locations: Canada. China. USA.
Time period: Cambrian.
Fossil representation: Hundreds of specimens are
known, this genus is one of the best represented of all the
anomalocaridids.
Hurdia
is one of the best recognised of all the anomalocaridid
genera,
thanks mostly to the large number of specimens that have been found.
The feature that makes Hurdia really stand out is
the enlarged head
that has puzzled many researchers to its purpose. There is no need
for such a feature in terms of protection, there simply isn’t enough
within to protect. However wider studies in associated anomalocaridid
genera may yet yield new ideas about Hurdia,
which we’ll come to
later in the text.
Hurdia
has often been described as a predator in popular science, but really
this assumption is based more upon the familial link of Hurdia to the
famous Anomalocaris
which is usually dubbed ‘the’ apex predator of
the Cambrian oceans. Though both are anomalocaridids, Hurdia
actually has a very different body plant to that of Anomalocaris,
specifically the head. The main feeding appendages are also much
smaller than those of Anomalocaris as well as
proportionately weaker.
This leads to the conclusion that Hurdia simply
could not rip other
arthropods apart like Anomalocaris is often shown
to do.
A
clearer picture of the ecological adaptations of Hurdia
may actually
come about from the 2015 description of a new genus of
anomalocaridid named Aegirocassis.
Although much larger than Hurdia.
Aegirocassis has a very similar body form to Hurdia,
so much so that
the two genera are classified together into the same sub family of
anomalocaridid, the Hudiidae. Aegirocassis is
thought to have been
a filter feeder, and this raises the question, was Hurdia
also a
filter feeder? This would explain the relative weakness of the limbs
of Hurdia given that to filter feed an animal would
not need especially
strong appendages. Filter feeding would also mean that Hurdia
was not
competing with more actively predatory anomalocaridids, meaning that
it could live in the same ecosystems as them.
The
fact that two (and probably more to come) separate genera of
anomalocaridid can have greatly enlarged head shields would certainly
suggest familiar connection, but again to what purpose. A simple
answer could be that the head size and shape was an indicator for a
specific genus and species, allowing members of the same species to
recognise others of their own kind. Or perhaps as a filter feeder,
the shape of the head somehow allowed planktonic organisms to be
funnelled towards the appendages where they could catch a greater
concentration of organisms for easier feeding. Alternatively there
may be a combination of factors, some of which we simply do not know
about yet.
The
description of Aegirocassis made researchers of
Cambrian life,
particularly those who study anomalocaridids sit up because the most
ground breaking thing about it was that Aegirocassis
was proven to have
two rows of swimming flaps down the main body. Before this time
anomalocaridids were thought to have lost one row of flaps earlier on,
but this has caused a rethink in other anomalocaridid studies. The
describers of Aegirocassis also commented upon Hurdia
as well as the
genus Peytoia
and by comparison to the Aegirocassis specimens,
identified the presence of two rows of swimming flaps on both Hurdia
and Peytoia as well.
Further reading
- The Burgess Shale anomalocaridid Hurdia and its
significance for
early euarthropod evolution. - Science 323 (5921):
1597–1600. - Allison C. Daley, Graham E. Budd,
Jean-Bernard Caron, Gregory D. Edgecombe & Desmond
Collins - 2009.
- Morphology and systematics of the anomalocaridid arthropod Hurdia
from the Middle Cambrian of British Columbia and Utah. - Journal of
Vertebrate Paleontology vol 11, issue 7. - Allison C.
Daley, Graham E. Budd & Jean-Bernard Caron - 2013.
- Anomalocaridid trunk limb homology revealed by a giant
filter-feeder with paired flaps. - Nature. - Peter Van Roy,
Allison C. Daley & Derek E. G. Briggs - 2015.
Random favourites
 |
 |
 |