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From reefs to riches

in Old Lost Sea by

In every sea, in every ocean,
Beasts of freakish locomotion
Prowl the substrate, seeking prey
To feast on in a monstrous way.

Dinner is served. On a plate before you: a delicious roast chicken. The bird, however, is larger than your head and you have no hands or teeth, let alone cutlery, you can break it up with. How are you going to eat it?

How about pushing one half of your stomach out through your mouth, dissolving the chicken in digestive juices, then hauling your belly back into place, full of nutritious bird-broth? No? Well you’re obviously not a starfish, then.

Asteroids, to give starfish their scientific name, are among the most familiar of all sea creatures; the five-fingered favourites of many a seaside publicity brochure. Yet even a cursory investigation of their biology, ecology and evolutionary history reveals this familiarity to be a deception. These icons of the intertidal are about as strange as life on Earth gets.

If their stomach-churning feeding habits weren’t weird enough, asteroids have a skeleton made of optical crystals, possess extraordinary powers of regeneration, and move around on a system of tiny hydraulic tentacles. And they don’t have a brain.

Spiny-skinned sea stars

Starfish are echinoderms, the ‘hedgehog-skinned’ group of marine animals that also includes sea urchins, brittle stars, sea lilies and sea cucumbers. Not content with being spiny, all living echinoderms are pentaradial, having five-fold body symmetry.

Sea lilies can have scores of feathery arms, but always in multiples of five, and though sea cucumbers and some sea urchins are bilaterally symmetrical, their quintupled body segments are still there if you look closely. Even strange, multi-rayed starfish, such as sun-stars, develop from a pentaradial template.

This five-ness is unique, but then echinoderms are a pretty special phylum. Their skeleton is made of uniquely porous calcite, with each little bone—an ossicle—functioning as a single crystal. Some brittle stars can literally see through their skin.

Then there are the regenerative powers. Echinoderms are truly otherworldly in this respect. If threatened by a predator, a sea cucumber can auto-eviscerate itself, spewing out its internal organs before crawling away to regrow them.

Some sea lilies can sacrifice their arms, regenerating them later. Starfish though, are perhaps the most amazing rejuvenators. Many species can cast off a limb and regrow it, but some are even able to develop a whole new starfish from a single, sacrificed ray. The thought of losing your arm in an industrial accident only to see that arm begin evolving into a twin brother is almost too bizarre to contemplate.

Huxley’s narrow star

As thoroughly strange as all this might sound, it unequivocally works. The echinoderms are a submarine success story, and perhaps none more so than the starfish. The fossil record tells us that asteroids have been doing their thing for about half-a-billion years, and their early history includes a Newfoundland chapter.

Composed of tiny ossicles held together by soft tissues, a dead starfish has a fairly low preservation potential. Most will not survive the ravages of tides and time. Thanks to the intermittent benevolence of the fossil record, though—particularly in regions where storms smother the seabed—asteroids do get fossilized occasionally.

In the mid-19th century, a beautiful, slender-rayed specimen was found by a Mr J. Richardson in the limestone beds of Point Riche, Port-aux-Choix. Elkanah Billings, a chap we’ve encountered before, named it Stenaster huxleyi, or Huxley’s narrow-star, presumably in honour of the eminent British biologist T. H. Huxley. What Mr. Richardson thought about being overlooked for immortalization isn’t recorded.

Billings described the starfish as Silurian, rocks of that age being the oldest then thought to yield fossils. We now know differently. There are pre-Silurian fossils galore: the Ediacaran, Cambrian and Ordovician periods all contain remains of complex creatures.

Mr. Richardson’s Point Riche starfish lived in the middle of the Ordovician period, about 470 to 460 million years ago. During this time, western Newfoundland was a tropical, shallow-water place, fringing the ancient North American continent of Laurentia.

Of trees and reefs

These were interesting times, ecologically. Though the preceding Cambrian period is well-known for its ‘explosion’ of animal life, the Ordovician is when biodiversification really got going. If the branches of the tree of life are Cambrian, the first crown of twigs and leaves was Ordovician.

Life at the time was almost exclusively marine. Shallow, tropical seas were the places of greatest abundance and variety and, much like the present-day, reefs were diversity hotspots.

Unlike the present day, reef-building in the Cambrian and early Ordovician wasn’t accomplished by animals, such as corals, but by simpler creatures, mostly microbes and sponges. Evidence for this is provided by reef limestones of this age in western Newfoundland and southern Labrador, such as the Forteau Formation and the thrombolites of Flower’s Cove.

Things were changing, though, and in the transition to animal-dominated reefs, the mid-Ordovician was a crucial phase, and the Point Riche starfish was at the heart of the Laurentian action.

Chazy, Chazy nights

In 1915, Huxley’s narrow-star was renamed. American palaeontologist Charles Schuchert decided Billings had gotten his genus wrong, and so the asteroid became Urasterella huxleyi, or ‘Huxley’s original little star’. Schuchert also described the beds it had been found in as being ‘of Chazy age’.

The Chazy Reefs are fossiliferous Ordovician limestones that crop out in much of eastern North America, from New York State, where the town of Chazy is found, up through Vermont and into Quebec. They represent the first major flourish of animal-built reefs in the geological record, the beginning of a Palaeozoic ecosystem that was to persist for millions of years.

What role were asteroids playing in these early carbonate mounds? Many living species are predators, but skeletal analysis of Ordovician starfish suggests they hadn’t yet acquired the body and mouth flexibility that enables them to capture and devour mobile prey.

It is more likely they were scavengers, or predators upon creatures that couldn’t escape. Nonetheless, the development of reefs provided plenty of new niches for them to exploit, and by the Silurian period, starfish had diversified significantly, including the first forms with more than five arms.

Asteroid impact

Ordovician starfish are scarce. Only one other specimen of Urasterella huxleyi has ever been found, in Ontario. For other clues of Ordovician asteroid activity, we are dependent on trace fossils such as starfish resting impressions.

But whilst Schuchert’s rebranding has stuck, it turns out that he was wrong about the age of Huxley’s original little star. More recent research shows that the Point Riche reefs are slightly older than the Chazy ones.

So on the limy Laurentian seabed of western Newfoundland, species as old as Huxley’s were pioneers of a brave new world, of habitats that are now vital to the flourishing of ocean life.

And if you’ve ever seen footage of crown-of-thorns starfish chomping their way across the Great Barrier Reef, you’ll appreciate just how successful the asteroids have been.


Editor’s note: If you would like to respond to this or any article on TheIndependent.ca, or if you would like to address an issue we haven’t yet covered, we welcome letters to the editor and consider each of them for publication in our Letters section. You can email yours to: justin at theindependent dot ca. Not all letters will be printed, but all will be read.

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