6ix Posted January 7, 2015 Share Posted January 7, 2015 Hi guys, need help for a newb with crab orientation.... So far I have been working on partially exposed crabs, but this is my first mystery. I have colour coded the "nick" in the concretion as a point of reference.. I have reread all the helpful posts here and Doctor Mud and I had a compare with my other crabs and we arent sure. Most of mine have pretty even hemispheres, except for the bigger Tumidocarcinus ones which the carapace is definitely the bigger part and the bottom is flatter. I suspect I am comparing two different species. To confuse things more, I have one where its left claw is the biggest! Anyway, I have taken a heap of photos - I have marked the nick in red when visible & blue when not. I was hoping the shape of the legs could be diagnostic. Link to comment Share on other sites More sharing options...
jpc Posted January 7, 2015 Share Posted January 7, 2015 CT scan Link to comment Share on other sites More sharing options...
Doctor Mud Posted January 7, 2015 Share Posted January 7, 2015 Great photos! I just noticed that these legs have flattened bottoms and rounded tops. There was another post on here looking at this feature. Presumable the legs get flattened by gravity on the underside. Does that mean the bottom would be the flattened side and our initial guess is correct? Link to comment Share on other sites More sharing options...
Doctor Mud Posted January 7, 2015 Share Posted January 7, 2015 CT scan I would love to see a CT scan of one of these crab concretions. I just recently saw a CT scan of a concretion in the same rock from north of here. The concretion contained pretty much an entire penguin and they CT scanned the skull in great detail. I guess you could 3D print the skull from the scan. Link to comment Share on other sites More sharing options...
6ix Posted January 8, 2015 Author Share Posted January 8, 2015 Hmm, that would make the top the bigger side, with the bottom the flatter... I have been focusing on the "( V )" in the leg... I'll take a couple of photos of others to show what I mean.. Conc.jpg Great photos! I just noticed that these legs have flattened bottoms and rounded tops. There was another post on here looking at this feature. Presumable the legs get flattened by gravity on the underside. Does that mean the bottom would be the flattened side and our initial guess is correct? Link to comment Share on other sites More sharing options...
6ix Posted January 8, 2015 Author Share Posted January 8, 2015 & Here's my big boy... Link to comment Share on other sites More sharing options...
Doctor Mud Posted January 8, 2015 Share Posted January 8, 2015 I see what you mean. You get those grooves on the top of the second segment of the legs of the Tumidos. Look at the most recent example I'm working on in a thread on TFF. I just took a look at a previous conc I have worked on and the flattening of the legs doesn't always work: Look at the bottom right image. The concretion is actually upside down. What I've found so far is that there is usually more material on the bottom than the top, so perhaps our original interpretation is best? Flatter side is top? Link to comment Share on other sites More sharing options...
Doctor Mud Posted January 8, 2015 Share Posted January 8, 2015 (edited) I think this was what we were considering before: This would be a view from the top and the large claw on the right forces the legs back on the right hand side. There is more room for the legs on the left hand side. This would fit with the general rule of more material on the underside of the concretion too. All the concs from here I have orientated so far have rounder bases with more material and slightly flatter tops. There is a guide to orientating crab concs from WA and the author figures that this is due to decomp. liquids making there way down in the sediment and encouraging conc. formation. Edited January 8, 2015 by Doctor Mud Link to comment Share on other sites More sharing options...
Doctor Mud Posted January 8, 2015 Share Posted January 8, 2015 CT scan Have you had a radiology department scan your concs before JPC? If so, how did you initially approach the radiology department. Did you write them a letter, call out of the blue or did you already have a contact. I was thinking it might be worth contacting the local radiology department. Thanks. Link to comment Share on other sites More sharing options...
CH4ShotCaller Posted January 8, 2015 Share Posted January 8, 2015 I have pretty good success with these old boys from here. I look for the 'more flat' side as being dorsal. Also, I was taught by another colleague that some are so hard to distinguish, that you must look edge-on and find where the angle starts for the opposite side. When found, the 'smaller' of the 2 sides usually has the dorsal. (from the micropterus101 school of crab). A fixed dactyl is a dead give away, but not always 100%. Let us know what ya git! Anyone who has never made a mistake has never tried anything new. -Albert Einstein Link to comment Share on other sites More sharing options...
6ix Posted January 8, 2015 Author Share Posted January 8, 2015 But.. the above example and my "Big Boy" which you have seen both have more material at the top. I'm just going to go for it.. Top of picture is ventral. I think this was what we were considering before: conc.jpg This would be a view from the top and the large claw on the right forces the legs back on the right hand side. There is more room for the legs on the left hand side. This would fit with the general rule of more material on the underside of the concretion too. All the concs from here I have orientated so far have rounder bases with more material and slightly flatter tops. There is a guide to orientating crab concs from WA and the author figures that this is due to decomp. liquids making there way down in the sediment and encouraging conc. formation. Link to comment Share on other sites More sharing options...
6ix Posted January 8, 2015 Author Share Posted January 8, 2015 Nuthing yet... about 10-12mm deep. Link to comment Share on other sites More sharing options...
Doctor Mud Posted January 8, 2015 Share Posted January 8, 2015 (edited) Nuthing yet... about 10-12mm deep. Nice one! I was writing a reply to your previous post and you answered my question with a picture. Hang on in there. Sometimes you have to widen the test hole a little if you can't get the scribe in there. Fingers crossed you expose a nice piece of crab shell in the not too distant future. The legs look like nice brown shell so I'm hoping for a good one for ya! Edited January 8, 2015 by Doctor Mud Link to comment Share on other sites More sharing options...
jpc Posted January 8, 2015 Share Posted January 8, 2015 Bring your concertion AND a prepped one to the local hospital and ask the ct folks if they would help you figure out which side is the top... When they have a spare minute. I halve had great results with this. My one concern is that the concs are so darn big, they may not be ctable. But it can't hurt to try. In general, ct techs love to play with their machines on something other than traumatized and sick humans. Link to comment Share on other sites More sharing options...
6ix Posted January 8, 2015 Author Share Posted January 8, 2015 Does X-Ray work? Link to comment Share on other sites More sharing options...
6ix Posted January 8, 2015 Author Share Posted January 8, 2015 Okay guys this is cool. Please dont beat me for being lazy but I can be impatient. http://vid158.photobucket.com/albums/t104/Hazara_NZ/CryingCrab.mp4 My guess: as the concretion has surfaced, it warmed up & separated a little from the host material. Then water has ingressed either via openings (legs) or via permeation. I think this is why I have heard of some crabs "popping" out when they are cracked. Link to comment Share on other sites More sharing options...
RJB Posted January 8, 2015 Share Posted January 8, 2015 This is a cool thread! I wish you the best 6ix. RB Link to comment Share on other sites More sharing options...
Auspex Posted January 8, 2015 Share Posted January 8, 2015 ... I just recently saw a CT scan of a concretion in the same rock from north of here. The concretion contained pretty much an entire penguin and they CT scanned the skull in great detail... !!! Is there any way to get a look at this? "There has been an alarming increase in the number of things I know nothing about." - Ashleigh Ellwood Brilliant “Try to learn something about everything and everything about something.” - Thomas Henry Huxley >Paleontology is an evolving science. >May your wonders never cease! Link to comment Share on other sites More sharing options...
jpc Posted January 8, 2015 Share Posted January 8, 2015 Does X-Ray work? Not really... even if the x-ray shows you what is inside, it cannot tell you which side is up.... unless... you put the rock up on its edge and xray it that way. Also put a piece of something next to one edge for reference as you have done with your colored spots. And bombard it with x-rays. Link to comment Share on other sites More sharing options...
Doctor Mud Posted January 8, 2015 Share Posted January 8, 2015 !!! Is there any way to get a look ate this? Hi Auspex, I'll see what I can do for ya. Our friends have a holiday house that they rent out near these sites. A family that stays in the holiday house found the penguin so I'll see if I can get in touch with them and rustle up some images. There was an information book that our friends made up for visitors to the house - info on history, geology, plants etc. and these images were in there. Link to comment Share on other sites More sharing options...
Doctor Mud Posted January 8, 2015 Share Posted January 8, 2015 Okay guys this is cool. Please dont beat me for being lazy but I can be impatient. http://vid158.photobucket.com/albums/t104/Hazara_NZ/CryingCrab.mp4 My guess: as the concretion has surfaced, it warmed up & separated a little from the host material. Then water has ingressed either via openings (legs) or via permeation. I think this is why I have heard of some crabs "popping" out when they are cracked. What the!! Bizzare! Looks like you have found the carapace o.k.! Crying statues, weeping crabs what next? 6ix's strange and mysterious world. All I can think of is that water has permeated into the concretion and started to dissolve rock at the crab, rock interface. I see this sometimes in the concretions I have prepped and it actually makes prepping much easier - the rock near the crab is softer (carbonates are leached) and easily flakes off the shell. The latest one I'm working on has evidence for this. As you approach the crab shell you see iron oxides or a rusty colour. The iron oxides would be transported in the ground water. The crab shell rock interface is obviously a point of weakness that will allow water to permeate the concretion. Over time a small gap may form between the crab shell and concretion and this may contain a tiny "aquifer". That's my theory anyway. I've never seen the Crying Crabs of Canterbury before though Link to comment Share on other sites More sharing options...
Auspex Posted January 8, 2015 Share Posted January 8, 2015 Hi Auspex, I'll see what I can do for ya. Our friends have a holiday house that they rent out near these sites. A family that stays in the holiday house found the penguin so I'll see if I can get in touch with them and rustle up some images. There was an information book that our friends made up for visitors to the house - info on history, geology, plants etc. and these images were in there. Thanks! I'll have to look into these accommodations the next time I'm in Kiwi Land "There has been an alarming increase in the number of things I know nothing about." - Ashleigh Ellwood Brilliant “Try to learn something about everything and everything about something.” - Thomas Henry Huxley >Paleontology is an evolving science. >May your wonders never cease! Link to comment Share on other sites More sharing options...
6ix Posted January 9, 2015 Author Share Posted January 9, 2015 Woot - yep I recon its the carapace too. Did a bit more work outside before it gets too hot in there. In some parts the boundary is mush.. I hit it with the air duster & 90psi.... that was enough to remove some concretion!! It is annoying to work with tho... all the dust gets stuck to wet surfaces so I have had to rinse it a couple of times. Before that tho, I used the air duster to blow a heap of water out & collected it - it froze like normal so I dont think its saline. Its amazing to work with compared to my "sticky" crab, This has been sitting in the sun for a half hour and is still crying.. You can see the steep drop to the carapace - thats because that .5mm either dissolves or breaks off. I'm very tempted to soak it in alcohol a few times, dry it out, fill it up with water again & freeze it. I dont know what will happen when that boundary dries.. will it turn back to concrete or remain softer? @Doctor Mud - your more than welcome to use my limited tools if you are getting itchy! Link to comment Share on other sites More sharing options...
Doctor Mud Posted January 11, 2015 Share Posted January 11, 2015 Hi 6ix, Made any more progress?? Thanks for the offer with the tools. I'll wait till I get home though since I know my tools really well now and I'll save these guys till I've finished my latest ones. Mmmmm what to do with your crab.... I'd probably just let it dry naturally it shouldn't take too long. You could even dry it in an oven a low temperature (60 - 80 degrees C). I don't think the rock will get significantly harder after drying. The calcium carbonate has probably been leached out of the crab-concretion interface and it is this that makes it hard. Good luck! Link to comment Share on other sites More sharing options...
6ix Posted January 11, 2015 Author Share Posted January 11, 2015 Well, funny you mention that. I was looking at my scribe this morning (and all the surface rust on it) & decided its salt water. I opened up the hole a bit, and when blowing the mud mix out with the airgun lost about a 1x2mm chunk of carapace. Decided to try & find a claw instead, then noticed a new line of wet... - put it outside to photograph but got distracted with the family, only to return a couple of hours later. It appears to be cracking (I'm guessing stress from salt crystals expanding and vibrations from engraver).. Have you checked yours for any degradation? it hit 32 degrees again here today! Link to comment Share on other sites More sharing options...
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