Hallucigenia
Name:
Hallucigenia
Phonetic: hal-lu-see-gen-ee-a.
Named By: Simon Conway Morris - 1977.
Synonyms: Canadia Sparsa.
Classification: Animalia, Onychophora,
Hallucigeniidae.
Species: H. sparsa (type),
H.
fortis.
Diet: Detritivore.
Size: 5 to 55 millimetres long.
Known locations: Canada, British Columbia -
Burgess Shale. China - Maotianshan Shale.
Time period: Early to Middle Cambrian.
Fossil representation: 109 specimens.
Hallucigenia
was first identified as the Cambrian aquatic worm Canadia
by Charles
Doolittle Walcott in 1911. However a study of the Canadia
fossils
by Simon Conway Morris in 1977 brought to light the discovery that
the fossils did not represent the same creature. Because of its
bizarre appearance of spikes and tentacles, Conway Morris gave the
different individuals the name Hallucigenia because
of their ‘bizarre
and dream-like quality’. However this realisation would be but the
beginning of even more confusion about how it Hallucigenia lived.
Fossils
of Hallucigenia appear worm like with seven spines
on one side, and
seven pincer tipped tentacles on the other. Six of the tentacles
match the spines for placement, the seventh however is forward.
There are also three much smaller tentacles further along. On the
ends of the main body were a blob on one end and a flexible tube on the
other. Such a creature would be enough to make many palaeontologists
give up and quit, but Morris persevered and worked out a conceivable
reconstruction of the living creature.
The
first and original interpretation of Hallucigenia
had it using its
spines for walking. The flexible tail would reach down to the sea
bottom and picking up morsels of food. The tail would then curl up
and pass the morsel onto the first tentacle which would then pass it on
to the next. The food morsel would then travel down the line of
tentacles towards the ‘blob’ that was interpreted as being the head.
There
are a few problems with this interpretaion the first of which is that
spikes, while possibly used for walking, would have been quite
cumbersome. The second is that this method requires a lot of physical
effort for feeding upon food sources that are possibly low in
nutrients. Usually animals put as short a distance as possible
between their mouths and their food source but in this reconstruction
the distance is at its potential maximum. The third problem is that
this method does not explain either the presence or function of the
smaller tentacles at the base of the tail.
A
possible alternative to the above is if the spines were indeed placed
at the bottom, could be that the spines were used to anchor
Hallucigenia amongst rocks in the path of oceanic,
or tidal
currents. The tentacles would then drift upwards with their pincers
catching food particles that were drifting in the current. The
tentacles could then pass the food onto the mouth whichever end that
may be, but if the mouth was on the tail and not the blob, then the
tail could arc around to pick up the food morsels from the tentacles.
Such a method would essentially see Hallucigenia
living like a
portable sea anemone.
The
second interpretation of Hallucigenia, and this
is the one that is
general accepted today, is to flip Hallucigenia
over so that the
spines point upwards and the tentacles are used for walking. This
interpretation was proposed by Lars Ramskold and Hou Xianguang in
1991, and is based upon fossils recovered from the Maotianshan
shales of China. Not only does this see the spines in a defensive
position, the tentacles are usually reconstructed to be in pairs.
The blob was also interpreted as a stain caused by preservation, the
claim based upon the observation that it is not present in all
specimens.
Although
this is the most often represented reconstruction today, paired
tentacles are not currently known in Hallucigenia
fossils. The spines
are also not considered by all to have been hard structures because
they are never found on their own like the hard parts of other soft
bodied creatures. The fossilised arrangement of the spines also only
covers the main body. While this could theoretically deter suction
feeders, other predators would have had quite a simple time avoiding
them.
The
phylogenetic position of Hallucigenia is also
strongly debated, and
while many entries of Hallucigenia place within the
Onychophora
(velvet worms), not everyone is convinced that Hallucigenia
belongs here. The possibility has even been raised that Hallucigenia
may in fact be part of a larger animal, like how another Cambrian
creature called Anomalocaris
was first identified as a small shrimp
until other body parts were pieced together to form the actual animal.
There also what appears to be robust and gracile morphs of
Hallucigenia which in 2002 were interpreted by
Desmond Collins to
represent male and female individuals.
Further reading
- A new metazoan from the Cambrian Burgess Shale of British Columbia. -
Palaeontology 20: 623–640. - S. Comway Morris - 1977.
- The second leg row of Hallucigenia discovered. -
Lethaia 25 (2):
221–4. - Lars - Ramsköld - 1992.
- A new species of Hallucigenia from the Cambrian
Stage 4 Wulongqing
Formation of Yunnan (South China) and the structure of sclerites in
lobopodians. - Bulletin of Geosciences 87: 107–124. - M. Steiner, S.
Hu, J. Liu & H. Keupp - 2012.
- Beyond the Burgess Shale: Cambrian microfossils track the rise and
fall of hallucigeniid lobopodians. - Proceedings of the Royal Society
B: Biological Sciences. 280 (1767): 20131613. - Jean-Bernard Caron,
Martin R. Smith & Thomas H. P. Harvey - 2013.
- Hallucigenia's onychophoran-like claws and the
case for Tactopoda. -
Nature. 514 (7522): 363–366. - M. R. Smith & J.
Ortega-Hernández - 2014.
- Hallucigenia's head and the pharyngeal armature
of early ecdysozoans.
- Nature. 523 (7558): 75–78. - Martin R. Smith & Jean-Bernard
Caron - 2015.
- A hypothetical reconstruction of Hallucigenia. - PeerJ Preprints. 7:
e27551v1 (1–10). - Christian McCall - 2019.
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