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Euan's Paleo Blog

Fish + Medieval battle armour = Osteostracans

Posted on May 9, 2015 at 5:05 PM

WARNING: If your afraid of big scary latin names, turn back now.

 

the following article is rated L for Latin.

Hey Guys. I'm finally back and writing again. So who's up for some fossil chit chat?

Ever heard about Osteostracans? well your about to. It might sound like some kind of painful bone infection, but this group of fairly- obscure early fishes (they might be less obscure if those high and mighty PhD professors decided on a latin name that could be pronounced in lay terms :/) were  long- lived and widely- distributed creatures. They were most common in the early Devonian, but they ranged in age from the early Silurian until the Late Devonian- which is when they perished in the devastating late devonian extinctions.

 

Let's explain the fish fauna of the Devonian with a quick thought experiment.

Imagine going to a fish market (e.g at morrisons- they may have overpriced bread, but they have a great fish market) and taking a look at what's in the cold ice. You see the usual selection of fish- Salmon fillets from Scotland, trout, snapper, herring, haddock, plaice, and (if your in China) Shark steaks.

but imagine you could have a fish counter from the Early Devonian. What would you see?

well, you might still see shark, but like no shark you've ever seen. smaller. more primive, and bonier- sharks of this age were less cartilaginous than modern sharks. However, the other fish you might see bear absolutely no resemblance to the fish counter of today. There are the Crossopterygians (yes, sorry people, the dreaded scientific latin is in full force today), the major group of lobe- finned fish that the living 'fossil' Coelacanth belongs to, as well as the four living species of Lungfishes, and...guess what? YOU! yes, the Tetrapods form part of this group too. So, if you boil it down, you, me, (definately my sisters) and every other person on the planet IS NOTHING BUT A FISH WITH LEGS! we can thank those hard- working fish that came ashore during the devonian for that little fact. Anyway, wandering of todays topic. Back to our Devonian fish store....

There were the Thelodonts. A bizarre group of small fish without jaws and with no pectoral or pelvic fins. Then there's the Placoderms (meaning plated skin), fish covered in thick scales and particularly- thick trunk armour.You might see the Heterostracans, another group of fish without jaws and often equipped with thick armour. In fact, most of the fish for sale on this fish counter have no jaws. And this is true of the Osteostracan fish as well. Today, we've come to the fish store looking for an Osteostracan out of all the devonian weirdos. So we buy one. Good, this way we get a good look at one. And it's definately weird. They had a long, flexible torso and body protected by overlapping scales and plates. At the front, this is exchanged for an impressive headsheild which covers the entire head and neck, terminating in large spines (called Cornua's) that are characteristic for each species (The shape of the headsheild also varies between species). One each side of the creatures headsheild are areas of super-sensitivity. These organs are thought to have been used to detect movements, possibly for detecting prey on the ocean floor (as they are thought to have been fairly slow swimmers who fed on small bottom- dwelling organisms). And the more advanced species in the group also developed paired fins behind the headsheild. Most likely not for use in swimming, but perhaps for steering.

The early history of fish with jaws is extremely complex, and if you're interested or curious enough to dabble in the academic literature, then I respect you. Because it is SCARY. This is one of the hottest topics in palaeontology, and there are literally thousands of articles to do with it. To save you the pain, I'll do my best to be brief but thorough- but remember, anything in the next paragraph will probably be proved wrong within six months of my writing this article (palaeontology is one of the fastest growing sciences. For instance, an average of 1 new dinosaur species is found every month?!):

Fish with jaws evolved, not so surprisingly, from fish without them. Simple enough, except that all earlier fishes had no jaws. Scientists have spent the last 50 years picking apart the complicated lines of evolutionary descent of these early fish, and we now have a pretty good idea of what was going on (but like I said, 1 find can change everything, so I'll say no more). The Osteostracans, according to these studies, is the sister group to the fish with jaws. Basically, they were the most closely related to the jawed fish than any of the other weird devonian jawless types- so they were the most advanced of the fish without jaws of this time.

But why have I just ranted about Osteostracans, a group you may (or may not) have ever heard of, out of the blue? Well, there is logic.

A few years ago, I managed to drag my parents halfway down the country for the sake of fossils yet again (hey, it was the day before my birthday, so I got away with it). We went down to the Wren's Nest Nature reserve in Dudley, and wasted the best part of an hour of nice july weather trying to find the site- which we did, after we realised that the reason we couldn't find it was because it was hiding dead centre in the middle of crappiest housing estate I've ever seen (so far; apologies to anyone from Dudley reading this- nothing personal. And anyway, who cares? You've got world- class fossils. Much better than anything I've got here in Manchester). Where's this going?

 

Well, we got into the Nature reserve, had a spot of lunch, and fanned-out heads to the ground in usual fossil- hunter fashion. After a few minutes, I spotted something shiny embedded in a badly- weathered chunk of limestone. I grabbed it, and inspected the weird pits and bumps on the surface of whatever it was. At the time, I didn't have a clue. But since then, I've spent more time looking and cleaning the specimen up, and I can say that in my opinion, it is an Osteostracan. But I'm also consulting a few experts on these animals because it could be more than this. I have corresponded with Dean Lomax- who you probably know about, either from his damn good books, or in person if you were there on the Doncaster plant hunt earlier this year (or was it last- my memory is shoking). He believes the specimen is worth taking to an expert on fossil fish. If the specimen really is an Osteostracan, then not only would it be the first of its kind found at this location, but it may be a new species. But it's too early to tell, so there will be no big claims. I only ask that if anyone knows any other scientists who might like a look at it, then could you message me how to contact them.

So, the moral here is :

KEEP FOSSIL HUNTING - AND GO FIND A NEW SPECIES. THE FOSSIL RECORD IS SO POROUS THAT ONLY 1% OF THE CREATURES THAT HAVE EVER EXISTED HAVE BEEN FOUND AND NAMED. JUST THINK OF THE WEIRD CRITTERS OUT THERE TO FIND. 8)

 

 

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