PART 4 of Burgess Shale Fossils:

This fourth part of my series about the Early Cambrian fossils of the Burgess Shale in British Columbia, Canada is about Opabinia regalia Walcott, 1912. Wallace found the original material (see first image shown below) and named it. At first glance, it looks like a worm, but the latest interpretation is that this fossil was a member of a “stem group” of phylum Arthropoda (arthro, joint; pod, foot), which is the largest phylum of living organisms. Some modern examples of arthropods are barnacles, crabs, insects, and spiders. Like annelids (worms), the arthropod body is segmented, but in arthropods, there is a fusion and specialization of segments, with two or three major body regions. Opabinia shows some degree of fusion of its segments, thereby indicating a relationship to an arthropod.

Side view of an actual imprint of O. regalia is from Walcott, 1912 (pl. 27, fig. 6). The fossil is about 5.5 cm in length. The original reference is Walcott, C.D. 1912. Middle Cambrian Branchiopoda, Malacostraca, Trilobita and Merostomata. Cambrian geology and paleontology, II. Smithsonian Miscellaneous Collection 57:146–228.  

In the images below, I used a plastic model to highlight the anatomical details of Opabinia. Many years ago, one of my graduate students visited a museum gift store, and came across a commercial “kit” with examples of Burgess Shale fossils. The plastic three-dimensional replicas are actually very good, and I used them for teaching purposes in my geology and paleontology classes. Their color schemes are certainly “made up,” but they help to show the dominant anatomical features. I believe that these kits were part of a “limited edition,” thus they are now hard to find. In my previous and subsequent write-ups about some other the Burgess Shale fossils, you will see that I used additional plastic models.

The following images show the dorsal, right side, and ventral views (in that order) of Opabinia regalis, and lastly, a closeup of its five compound (faceted) eyes. Notice the segmented body, numerous legs, tail, fins, and a single (very large) claw. The model shown here is 9.5 cm long, but, as mentioned earlier, the original specimens are up to approximately 5.5 cm in length.

Other Useful References:

Whittington, H.B. 1975. The enigmatic animal Opabinia regalis, Middle Cambrian, Burgess Shale. Philosophical Transactions of the Royal Society of London B, v. 271:1–43.

Briggs, D.E.G. 2015. Extraordinary fossils reveal the nature of Cambrian life: a commentary on Whittington (1975) “The enigmatic animal Opabinia regalis, Middle Cambrian, Burgess Shale, British Columbia. Philosophical Transactions Royal Society B, vol. 370. 

PART 3 of the Burgess Shale Fossils:

This post is part of a series of six posts dealing with “Middle Cambrian Life: Exceptional Fossils” (Lagerstätt) from the Burgess Shale Member of the Stephen Formation, British Columbia, Canada. Please see my previous two posts; the first of which serves as an introduction to this broad topic.

Wiwaxia corrugata (Matthew, 1899) (new combination) is shown below. There has been considerable controversy about what kind of animal group it represents. It was a soft-bodied, slug-like animal covered in carbonaceous scales and, along its dorsum, with two rows of 7 to 10 blade-like spines. Although some early workers believed that Wiwaxia might be an annelid (worm), that idea has fallen out of favor because Wiwaxia shows no evidence of segmentation. The general consensus is now that Wiwaxia represents a “stem group mollusk” that existed at the time when annelids and mollusks branched off from each other, in an evolutionary sense. Phylum Mollusca (mollusks) is a large group today and consists manily of chitons, scaphopods, bivalves, gastropods, and cephalopods.

The three views below show the bottom (mouth is the "v" shaped structure), top, and side of a plastic replica of Wiwaxia, in that order. The original size of this animal was about 5.5 cm in length.

Some researchers have classified Wiwaxia as a halkieriid, which is a group of Early to Middle Cambrian “small shelly fossils” that consisted of mineralized sclerites, or armored shell plates, which commonly disarticulate upon death. While alive, however, halkieriids looked like slugs in "chain mail."

On its ventral (basal) side, Wiwaxia has a small feeding apparatus consisting of two (rarely three) tooth plates, which are like a mollusk radula (a toothed ribbon of teeth) or the jaws of an annelid.

The name “Wiwaxia” is derived from the Stoney First Nation Nakota language, meaning “windy.” Although, Wiwaxia has been found (mostly as disarticulated scales) at various localities in the world (e.g., China), its principal locality is the Burgess Shale.