Australian Trilobites: Wonders Down Under

It sounds like a locale drawn straight out of a classic adventure novel, a swashbuckling action flick, or at least a Disney theme park… Kangaroo Island. It is an exciting name, one seemingly cloaked in mystery and intrigue, designed to make the mind's eye instantly wander towards visions of exotic ports and far-away destinations. And in many ways this distant, rather isolated spot off the coast of South Australia more than lives up to its colorful moniker. Indeed, Kangaroo Island would be the ideal setting for any Hollywood blockbuster seeking rugged terrain, picturesque landscapes, an abundance of wildlife and a decidedly non-21st Century ambiance. Being 93 miles long, with a population barely topping 4,000, KI—as the locals call it—has long been one of Australia's favorite vacation spots, with its miles of sandy white beaches, dense semi-tropical forests and acclaimed nature preserves serving to provide this oceanic oasis with a laid-back aura and a definite National Geographic vibe. 

There's even a thriving art community on the island—sort of a high-brow retreat for those seeking to escape the Big City “marsupial race” found in Sydney, Melbourne or nearby Adelaide—which is situated 70 miles to the northwest. Clearly, Kangaroo Island has a rhythm, and a look, all its own. Lying only 8 miles off the Aussie mainland across the Gulf of St. Vincent, in many ways this is a place light years removed from the rest of Oz in terms of tone, temperament and manner. And the fact is that KI has had quite a lengthy time during which to develop its unique charms at its own unhurried pace. First separated from the Australian continental mass some 9,000 years ago by a rise in surrounding sea levels, stone tools dating back 11,000 years have been found in a number of sites throughout the island. Yet it is believed that all First Nations life ceased to exist on KI over 2,000 years ago due to reasons that are still not fully understood, though some scientists presume this disappearance may have been caused by dramatic climate changes which saw all of the island's native inhabitants either flee back to the mainland…or be wiped out.

Aside from its natural beauty, rich history and thriving art scene, there is another reason that Kangaroo Island has risen to prominence in the minds of some, especially those within the paleontological community—it just-so-happens to be the site of one of the most significant Lower Cambrian trilobite formations in the world. Along the island's North Coast, among the rugged cliffs that outline the beautiful blue waters of Emu Bay on an isthmus known as Cape D'Estaing, lies the aptly named Emu Bay Shale Formation. It is one of the few spots on the globe—along with the likes of Canada's famed Burgess Shale and China's Chengjaing Formation—which presents a rich biota of soft-bodied Cambrian organisms right along-side its hard-shelled trilobite fauna, with some of the latter also displaying perfectly preserved antennae. 

The formation's trilobites include Estangia bilobata and Holyoakia simpsoni, along with large examples of Redlichia takooensis (occasionally over six inches in length), which closely resemble Redlichia types found in various Chinese sedimentary layers of roughly the same age. KI's soft-bodied material features the likes of the enigmatic Tuzoia, the worm-like Palaeoscolex and the legendary “trilobite eater,” Anomolocaris, the giant predator also known from fossils found in both the Middle Cambrian Burgess and Lower Cambrian Chengjaing outcroppings. 

In addition to the rarity, beauty and scientific significance of these aforementioned specimens, what the Emu Bay Shale is perhaps best known for among trilobite collectors are the primitive species, Emuella polymera and Balocoracania dailyi, diminutive trilo-types (usually less than an half-an-inch long) indigenous only to these formations, both of which feature an average of 60 segments within their elongated opistothorax. Some scientists have recently come to view an extended opistothorax—the extension of the trilobite's main body, culminating in a comparatively tiny pygidium—as a probable indicator of the trilobite line's more primitive origins. Lower Cambrian Olenellid trilobites found in other parts of the world (including California and Nevada) also present prominent, but comparatively much smaller opistothorax'. Yet no trilobites yet found anywhere else on earth can rival either Emuella or Balocoracania in terms of their sheer segmented majesty, with their elongated thoraxes constituting nearly 50 percent of their total mass.

Expansive view of the hills surrounding Emu Bay, on Kangaroo Island, Australia.

“The material coming out of the Emu Bay Shale is truly unique,” said Dave Simpson, based in South Australia, who has emerged as one of the world's experts on the formation's fauna. “Many of the species—especially Emuella and Balocoracania—are known only from here, and some of the trilobites, mostly Redlichia, have soft body parts preserved. The different types of Emuella and Balocoracania that are found on Kangaroo Island have drawn considerable interest because they are the most segmented trilobites yet found.”

While there are numerous Cambrian-age locations on Planet Earth that feature a more diverse array of trilobite species, few paleontological hotspots have drawn more recent interest than the formations of Kangaroo Island. The reason behind this growing fascination is based to a great extent upon the fact that the sedimentary layers of the Emu Bay Formation appear to be somewhat older than the approximately 500 million year old Burgess Shale material and somewhat younger than the 520 million year old Chengjaing material. Thus the Australian specimens provide a unique looking glass upon a primitive world where early life was still struggling to grasp a solid foothold, experimenting with countless strange shapes, sizes and body configurations in its efforts to survive. 

Similarly exciting paleontological stories are revealed in the fossils of the Burgess Shale, the legendary formation in British Columbia that has generated more scientific study—as well as whimsical mainstream media analysis-- than any other invertebrate locale in the world. And though the trilobite material emanating out of the Emu Bay Formation seems most closely aligned with the less renowned Chengjaing layers— with Redlichia dominating both outcroppings—a number of the soft body species found on KI appear more similar to the specimens drawn from the oft-studied Burgess biota. 

The similarities, as well as the differences, between the specimens found in these various locations have drawn particular interest among those scientists who specialize in studying fossilized soft body preservation. What fascinates these paleontologists is the concept that back in the primordial past Burgess and Chengjaing were both apparently cool, deep water environments, located off of the continental shelf. In contrast, during the Cambrian, the area surrounding what is now the Emu Bay Shale was a shallow, warm water costal estuary, located close to the equator. The fact that such apparently divergent climates managed to nurture similar fauna-- as well as present an environment that would eventually allow for soft body preservation-- provides new and fascinating information to those studying this phenomenon. That is especially true since it has been a long-held, and widely accepted hypothesis that only shelf environments-- where unexpected mudslides and sudden shelf collapses could quickly bury the area's invertebrate inhabitants-- were suited for preserving soft body parts in fossilized remains.

“That has always been the accepted picture of Burgess,” said one noted trilobite expert. “You'd have these amazing, alien-looking creatures living in an environment where a mudslide could wipe them out at any second. Of course, it probably didn't happen very often. But over the course of millions of years it happened often enough to provide us with an amazingly rich source of fossil material. Chengjaing is roughly similar. But we still need to do more study to properly understand the forces at work at Emu Bay, which provided a very different environment in a number of important ways.”

Photo courtesy of Dan Cooper: All specimens were surface collected from scree

Click here for the Gallery of Emu Bay Shale Trilobites