Burgess Shale Extravaganza: Amiskwia

20 05 2010

Good tidings and well-wishes!

NOTE: Contrary to the assertions of WordPress, this article was in fact posted on the 19th.

The soft bodied and rather delicately-built Amiskwia sagittiformis is a superb example of the conflict which often arises when a fossil is subjected to exceptional preservation and a debatable amount of deformity. The soft composition and meager proportions of Amiskwia and its kin prevent their fossil record from becoming remotely extensive. Hence, we may never know the degree to which geologic forces have altered the appearance of this superficially worm-like animal. Nonetheless, enough information has been gathered to make a few tentative educated guesses concerning its lifestyle and possible taxonomic affiliations.

Though the statement may sound comical, at a full inch in length, Amiskwia was a comparatively large inhabitant of the Burgess Shale and the elder Maotianshan Shales . This considerable size appears to have come at the expense of abundance, with a mere eighteen specimens of this peculiar genus having been found in the former deposit as of this writing.

Amiskwia‘s entire body is dorso-ventrally compressed. Its head sports a pair of ventrally-situated tentacles, just behind and between which lies an ovular mouth. Though the creature’s “trunk” is unsegmented, it does contain a pair of lateral fins which are unsupported by any sort of stiffening device: the same is true for the caudal fin which comprises the beast’s tail. The trunk and caudal regions of Amiskwia‘s anatomy appear to have been quite muscular: a piece of evidence which supports the hypothesis that Amiskwia may have been a pelagic (free-swimming) organism, which would also help to explain its aforementioned rarity in the formerly muddy Burgess basin.

Intriguingly, the internal anatomy of Amiskwia is also relatively well preserved, as partially displayed by the following fossil specimen:

According to the Smithsonian Institution’s official page on the species:

“Note that in the fossil preparation the head shows a highly reflective area (cerebral ganglia? [aka: the bilobed ‘brain’ of many modern worms and arthropods])… The broad light area running along the trunk is the gut, while the narrow linear structures along the trunk may be traces of blood vessels and a nerve cord.”


Note the rather conspicuous pair of bulb-like organs in the head of this Amiskwia reconstruction: this is the artist's depiction of its cerebral ganglia.

The phylogenetic relationships of Amiskwia are a matter of some debate. However, the general consensus amongst Cambrian paleontologists is that while the genus exhibits characteristics akin to those of the chaetognatha and nemertea. it cannot be scientifically accomodated by either group.

May the fossil record continue to enchant us all!




2 responses

20 05 2010

Opabinia was also a giant, at a mighty one inch long! But Amiskwia is one of the Burgess critters who really strikes me as alien. Maybe one day my museum could have a big walk through of the Cambrian with the animals blown up to our scale. This guy would certainly get a place of honor.

20 05 2010

Both Amiskwia and Opabinia would have quivered in fear at the sight of a meter-long Anomalocaris!! It just goes to show that size exists only by way of comparison.

That exhibit sounds awesome! Have you ever seen the Chicago Field Museum’s Burgess display? If not, I think you’d greatly appreciate it: the wall contains a perpetually-moving animated diorama depicting dozens of the shale’s residents interacting and roaming about.

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