Note: This is a mild deviation from my usual posts (on nature and conservation). Was writing a geology essay entitled “Bivalves and brachiopods: ships that passed in the night. Discuss…” and so I thought why not blog about it as well. I’m used to blogging my personal experiences rather than somewhat academic, informative posts, so bear with me!
Mention holidays and a picture of azure blue waters and pristine beaches usually jump into mind. Most people have been to a beach at least once in their life times – indeed some 44% of the world’s population live on the coast and some 12% rely on the sea for their livelihood. Beach combing and shell-collecting is a popular activity with most families and kids (not that I condone it because of naked hermit crabs), and shellfish is a highly demanded delicacy (though not in the past when some were considered to be ‘poor man’s food‘).
But what if we re-started time, would we still be delightfully picking up pretty shells with their nacre coating, slurping clam chowder and oysters, with assorted shells decorating the hotel we’re staying in? We might have been enjoying our pentamerid soup instead while gorging on productids like Giganteus productus (largest brachiopod ever).
During my schooling days (which wasn’t that long ago…), from research projects and shore trips, I thought I knew quite a bit about (intertidal) marine fauna. Then I came here and during the palaeontology aspects of the first year Earth Sciences course, I realised I knew close to nothing about fossil marine stuff (or fossil anything really). All I knew about brachiopods was that they are also known as lamp shells and are relatively rare, but I thought they were some kind of bivalve.
Turns out that brachiopods are in their own phylum, Brachiopoda, and though they look superficially like bivalves, they really aren’t that alike.
Not really going to go into depth the differences between bivalves and brachiopods, this blog has quite a good, easy-reading post on it if you’re interested. What I was interested in (and what I think was the focus of the set essay) was this:
Both taxa originated in the Cambrian, and diversified throughout the Palaeozoic. However, the brachiopods were dominant throughout the Palaeozoic (Cambrian to Permian), and the bivalves only came to dominate post-Palaeozoic (up to present). While it used to be thought that bivalves were generally superior to brachiopods and so out-competed them to become dominant post-Palaeozoic, it was suggested by Gould and Calloway in a 1980 paper that they might be ‘ships that pass in the night’. The Permian extinction is the worst (depending on your perspective I guess) known extinction in Earth’s history, with up to 96% of all marine species wiped out, including many brachiopods. The bivalves, on the other hand, seemed to have escaped relatively unscathed and for the first time in history, were more diverse than the brachiopods. They then went on to take over the marine world (subject to the terrors of the Mesozoic Marine Revolution, where predators abound), leaving the brachiopods to eat their dust.
If we could rewind time though, would things still turn out to be what they are now? If the Permian extinction had not occurred (seems to be a popular hypothetical discussion on many discussion boards), would the bivalves be as dominant as they are now? The emptying of the oceans during the extinction event would have freed up niches and promoted the appearance of novel forms, and eventually led to what we recognise as familiar marine creatures (I’m not saying that evolution is directional though).
And with our current plundering of the oceans and marine resources (90% of our major food fish stocks are depleted), we’re not too far off from another major extinction event. More people are starting to recognise a 6th (global) extinction, caused by us. It is a terrifying thought, that we could be wiping out so many species such that our living on this planet may no longer be viable (while technological advances are many and rapid, I’m not sure how technology as yet can generate the oxygen we breath, the food we eat, and the need for us to uitwaaien).
At the same time, I am wondering about the possibilities for other life forms to appear if we do manage to create such a huge void, and leave nature to its devices to repopulate the void. Unfortunately due to my limited imagination, unfueled by video games or sci-fi films, I really cannot fathom what it could be like.