Saturday, January 2, 2010

Trilobites in Sheep's Wool

Enthusiasms have a ripple effect on people who come within your orbit. Mine for paleontology is no exception. Some of those effects can be very warming. My wife is a knitter who now knits trilobites. I am surviving in this currently harsh winter with a new cranberry colored wool cap adorned with trilobites, well, knitted images of same.

These knitted images are wonderfully true depictions of trilobites, capturing the general shape and some details of certain genera. Trilobites were arthropods – invertebrate animals with jointed legs such as insects and crustaceans. I like to think that the model for the pattern was an Elrathia kingi (Middle Cambrian – some 510 million years ago (mya)). I particularly like the eyes in the cephalon (head) and the segmented thorax. Spot on.
As for size, well not so accurate for Elrathia (the pictured fossil specimen is 1” in length), though size varied among trilobite genera, in some, the adults reached upwards of 30 inches in length. As for color, most members of the Trilobita class were sighted so I say bring on the color. I am encouraged in this speculation by Richard Fortey. In Trilobite: Eyewitness to Evolution (2000), he acknowledges that we cannot know whether trilobites came in different colors since fossils typically take on the color of the rock in which they fossilize. But, given that “sealife today is a symphony of hues,” why not believe trilobites wore flashy exoskeletons? As he writes, “The fossil world is a pallid world, which only imagination can revivify. . . . We can colour them up as we fancy.” (p. 28) So cranberry red may suit Elrathia kingi just fine.

Trilobites were a long lived class, surviving the entire Paleozoic (some 300 million years) until succumbing shortly before or in the Permian extinction, about 250 mya. They evolved over this period, diversifying to occupy different ecological niches. As Richard Dawkins would put it, they “made their living” in different ways, ranging from filter feeders to scavengers to predators. Over time, trilobites came in myriad shapes, some quite elaborate with eyes on long stalks, some seemingly just thoraxes bristling with wicked spines, others stretching out and still others shrinking to a miniature size. Eyes came and went for some genera. (Samuel Gon’s A Guide to the Orders of Trilobites is a great way to explore the world of trilobites.)

Sheep’s Wool
Of course, sheep and, more importantly for my purposes here, sheep’s wool are like trilobites – the products of evolution. For my limited understanding of sheep’s wool, I have to thank my wife’s enthusiasm for knitting. On a recent plane flight, my wife was engrossed in The Knitter’s Book of Wool: The Ultimate Guide to Understanding, Using, and Loving this Most Fabulous Fiber by Clara Parkes (2009) (have to love modest titles like that – unless otherwise noted, everything about sheep and wool in this post is derived from Parkes’ book). My wife looked up from her reading to comment, “It’s interesting. Did you know that textile traditions differ among different cultures and evolution might have played a part? Like with felting. Here.” She handed over the book, her knitting enthusiasm rippling into my paleontological one. (Disquieting how all of this has colored our conversations. Instead of something like “What do you think about remodeling the bathroom?”, it’s “Hey, what about that evolution?” Thank God.)

The wool in my cap came from sheep which were first domesticated possibly about 7,000 BCE, perhaps from the Asiatic mouflon (Ovis orientalis) (The Archaeology of Animals by Simon J. M. Davis, 1987). These ancestor sheep molted, shedding fleece periodically. Originally, shepherds gathered wool from their sheep by pulling the fibers from the molting animal, an activity known as “rooing.”

An aside: By now, Van Morrison’s song “I Wanna Roo You” is waltzing through my consciousness:

Twenty-third of December covered in snow.
You in the kitchen with the lights way down low,
I’m in the parlor playing my old guitar.
Speaking to you, darling, find out how you are.

I wanna roo you,
Wanna get through to you,
I wanna woo you,
Woo you tonight.

A bit of web searching was fruitless as to the derivation of the word “roo” the way Van Morrison uses it. Though, I do wonder if a sheep-based rural culture (after all, the full title of the song is “I Wanna Roo You (Scottish Derivative)”) may well have myriad positive connotations for rooing.

Selective breeding has produced breeds of sheep whose coats grow continuously. These breeds, such as the Merino, require periodic shearing. Of course, this human intervention in the evolution of the animal has had some of the expected unexpected consequences. Shrek, a Merino ram in New Zealand, reportedly “evaded” shearing until, finally, after six years, the shorn Shrek produced a fleece weighing 59 pounds. Not too shabby.

As for my wife’s comment in the plane, some different textile traditions indeed may have emerged from an intricate tangle of evolutionary roots. Parkes describes an intriguing example. Icelandic sheep’s wool differs markedly from wool from the Shetland Islands in its ability to be made into felt.

Felt can be produced when wool is immersed in warm water, a process enhanced if soap is added. The shafts of fiber swell and the scales that cover the exterior of each fiber open. Rubbing the wool together in this condition creates irreversible tangles. Knitted wool subjected to this process will shrink, generating felt. Though the Icelandic and Shetland Island sheep are genetically close, the fibers from Icelandic sheep felt readily (“in a heartbeat” according to Parkes) while that from sheep from the Shetland Islands does not. Not surprisingly, felt plays a prominent role in the Icelandic textile tradition, but not in the Shetland tradition. Though Parkes is agnostic on the exact interplay of evolution and tradition, I suspect that the original breeds in each geographic area started with a slightly different propensity to produce readily felting wool. A textile tradition began to take root in Iceland around that marginal felting predilection in its wool, and then came an intimate evolutionary dance with the selective breeding of Icelandic sheep.

Lots of wonderful natural history warming the top of my head.

Note: My wife followed a pattern posted on Kitty: Little Purls of Wisdom by a knitter whose husband is a paleontologist. ReBecca Hunt-Foster’s Dinochick Blogs put me on to this.


  1. I breed shetland sheep, lots of variation within this primitive and unimproved breed. Some of my fleeces felt well, others not so much. Always enjoy reading other's theories about the breed we are way too obsessive about to be objective! Nicely written and v. interesting!

  2. Jen and Rich: Thanks so much for your thoughtful comment from the sheep "front lines." Until I put together this posting, I had no clue about the rich variety of sheep and sheep's wool. Lots to learn. Clearly, there can be substantial variety within individual breeds, as well. Thanks again. Tony


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