Burgess Shale Extravaganza: Aysheaia

20 05 2010

Good tidings and well-wishes!

Although many self-described “hard-core” scientists refuse to acknowledge it, popular culture exerts an appreciable influence upon virtually every discipline of science imaginable. Dinosaurian afficionados are well aware of Gary Larson’s “The Far Side” leading to the anatomical term “thagomizer” (which, for those ill-versed in paleo-jargon, describes the unique  spike arrangements on the tails of stegosaurs), guitarist Mark Knopfler’s namesake theropod Masiakasaurus knopfleri, and, of course, the “Harry Potter”-inspired pachycephalosaur Dracorex hogwartsia.

Dinosaurs, however popular, are far from the sole examples of this trend, as evidenced by the Burgess Shale denizen Aysheaia sp. whose genus name derives from the Ayesha mountain peak which, in turn, was named for Aysha: a sorceress and the “title” character of Rider Haggard’s 1905 novel “She: A History Of Adventure”. As is the case with its literary namesake, the simultaneously “alien” and “familiar” appearance of the two-inch Aysheaia is, as with many Burgess Shale residents, quite spell-binding (how’s that for a labored segue?).

According to Stephen Jay Gould’s “Wonderful Life”:

Aysheaia has an annulated, cylindrical trunk, with ten pairs of annulated limbs attached at the sides near the lower surface and pointing down, presumably for use in locomotion. The anterior end is not separated as a distinct head. It bears a single pair of appendages, much like the others in form and annulation but attatched higher on the sides and pointing laterally. The terminal mouth (smack in the middle of the front surface) is surrounded by six or seven papillae. The head appendages bear three spinelike branches at their tip, and three additional spines along the anterior margin. The body limbs end in a blunt tip carrying a group of up to seven tiny, curved claws. Larger spines emerge from the limbs themselves. These spines are absent on the first pair, point forward on pairs 2-8, and backward on 9-10.”

It should be noted that the limb-like appendages of Aysheaia are not true legs but can best be termed “lobopods”. Despite the fact that each lobopod is divided into a series of transverse rings, these are not to be mistaken for the series of joints which compose the legs of arthropods. In life, these lobopods would have contained a thick, muscular core surrounded by a fluid-filled cavity. This setup would have served as a hydraulic pump of sorts designed to enable locomotion.

Interestingly, a large percentage of Aysheaia specimens are found in association with the remains of sponges–an essentially nonexistent occurence elsewhere within the Burgess faunal roster. This has given rise to the well-accepted hypothesis that Aysheaia may have fed and dwelt upon these most primitive of animals. The idea is granted additional credibility when one considers the uselessness that the animal’s many claws would have likely served on the muddy floor of the basin. However, these spikes could have easily been employed for the purposes of scaling sponge colonies. Furthermore, it’s logical to conclude that Aysheaia‘s preserved anatomy insinuates no recognizable form of defense: a dire predicament which could have easily been averted were the creature to seek refuge within its (theoretical) spongy home.

As for Aysheaia‘s phylogenetic relationships, most paleontologists acknowledge that the beast bears a strong overall resemblance to the modern velvet worms (phylum Onychophora), although whether or not the genera should be considered a member of their phylum remains the subject of debate.

May the fossil record continue to enchant us all!




5 responses

20 05 2010
Zach Miller

Heh. I was about to ask whether this animal was thought to be related to velvet worms. The fossil looks very similar. I love how the reconstructions make it look like some demonic D&D beast (apart from the last one), and give MUCH more detail that you actually see in the shadow-like fossil. 🙂

20 05 2010

I’ve always thought that many of the Burgess shale critters (including Aysheaia here) would make for excellent sci-fi aliens!

21 05 2010
chris y

I’ve always thought that many of the Burgess shale critters (including Amiskwia here) would make for excellent sci-fi aliens!

You’d have to scale them up a bit! Two inches is not scary.

21 05 2010


25 10 2010
An explosion in diversity | David Attenborough's First Life

[…] with seven pairs of legs and spines, which was first wrongly interpreted as walking on its spines Aysheaia – A lobopod worm which lived on and fed on sponges Pikaia – A small worm-like creature with a […]

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

%d bloggers like this: