What has 30 legs, 30 gills, 30 flippers, and a nose like an elephant’s trunk if an elephant’s trunk had a lobster like claw at the end of it? Let us not leave out the five oddly spaced eyes, mounted on little stalks and looking very much like a quintet of tiny mushrooms.
Did you answer, “Nothing on earth?” Well, you are exactly and precisely one hundred percent correct. There has not been a creature like Opabinia for 500 million years give or take a million or two, since the evolutionary boom times of the Middle Cambrian period.
The Cambrian Period is the first period of the Paleozoic Era. It began about 588 million years ago and lasted until approximately 488 million years ago. Although a glance at a Geologic time line chart reveals that evidence of life on earth exists in the fossil records of formations dating back as far as 3.5 million years, it is in the Cambrian period that life burgeoned, multiplied and diversified. The expansion of life forms was so dramatic that it has frequently been referred to as the “Cambrian Explosion”. Opabinia regalis was one by product of this explosion.
Oddity from the Burgess shale:
The Burgess Shale formation located in British Columbia is one of the premier sites for the recovery of Cambrian fossils. Located in northwest Canada today, 500 million years ago the area which now is British Columbia was part of the shallow seas surrounding the mega-island Laurentia, and was located south of the equator.
An aspect of the Burgess shale that makes it a particularly spectacular fossil repository is that it is formed of the residue of massive mudslides, characteristic of the Cambrian, which buried the marine flora and fauna en mass under layers of extremely fine mud. This allowed for extremely detailed preservation of animals that had no hard body parts, a rare event, with nearly photographic resolution. In some cases individual muscles, internal organs and even stomach contents are visible.
The Burgess fossil beds were first discovered in 1909 by a Dr. Charles Walcott, then with the Smithsonian Institute.
An amazing anatomy:
About thirty specimens of Opabinia regalis have been recovered from the shale beds, none exceeding 4” in length – including the decidedly odd proboscis. Fossils reveal an animal divided into 15 segments beginning behind the head, almost resembling those of a modern day shrimp although no close relationship to shrimp should be inferred from this. Each segment bears a pair of odd structures, part limb, and part gill which at first glance resembles the biramous limb common to crustaceans and arthropods. But Opabinias’ limbs lack the joints common to biramous limbs and the animal is not considered to be a true arthropod.
Opabinia probably used these limbs to crawl along the muddy floor of the Cambrian seas, and to propel itself through its waters.
The head resembles a small ball that has been slightly flattened top to bottom with the mouth located at the rear of the head. The mouth contains no hard biting or chewing parts and Opabinia must have fed upon small, soft bodied creatures; among them perhaps the annelid worms that were so prevalent at the time.
The trunk like proboscis tipped with its grasping claw would have been used to pluck this and other prey from the muck. The trunk is thought to be a hollow tube, flexible enough to convey food to Opabinias mouth.
Another fascinating feature are the five eyes mounted on their stubby stalks arranged so that two are on the sides of the head facing sideways and upwards, two pointing mostly forward and upwards, and a single eye located between the first pair mentioned, pointing upwards. The stalks would have allowed these organs to be trained with some degree of independence from the orientation of the head.
Attached to the posterior segments were three dual, paddle shaped rudders, arranged in a V shape much like the tail assembly of a Beech craft Bonanza V-35 light airplane. These rudders helped Opabinia to maneuver through its environment.
The appearance of this creature is so bizarre and so at odds with that of any other life form living or dead that when Harry Blackmore Whittington, an expert on Burgess Shale life forms presented his reconstruction and analysis of the creature to an audience in the 1970’s he was at first greeted with gales of laughter. It took a bit of explaining before the group realized that they were not the butt of a paleontologists joke.
What was Opabinia?
The simple answer is; a taxonomic embarrassment. The fossil record as yet reveals no recognizable predecessors of this remarkable creature, nor does the Opabinian line seem to lead anywhere. Regalis, the sole generally acknowledged species went extinct at the end of The Cambrian, giving rise to no descendents. Opabinia seems to be a one time only, ultimately unsuccessful collateral spin off from the Cambrian explosion.
Current thinking tentatively places Opabinia as an offshoot from an unknown ancestral form which also gave rise to the arthropods. Perhaps a fossil of this missing link even now awaits discovery deep with the Burgess Shale deposits of British Columbia.