Pinnixa crabs from Carmel Valley

[KOI]

Hi! I did search for pea crabs from Carmel Valley and did not find any topics on The Fossil Forum.

So, I decided to fill the gap with few links hoping that others will also share the experience.

 

 

 

 

[Mark Kmiecik]

Thank you.

[caldigger]

I have an outcrop of the Monterey Shale near by with the Pinnexia represented, but have yet to ever find a whole crab imprint.

[Nimravis]

Just now, caldigger said:

I have an outcrop of the Monterey Shale near by with the Pinnixia represented, but have yet to ever find a whole crab imprint.

I am surprised that there are any left with you collecting them- LOL

[KOI]

We visit the area once a year (my birthday or father's day) and usually find 1-3 good crabs each time leaving most of the pieces to local school kids who do field trips to the location. The video combines finds from over a decade. As mentioned in the video, we do not waste time breaking slabs - its not productive. You just have to focus and scan the rocks with your eyes. Every one who finds a crab gets ice cream!

[Scylla]

Nice crabs!

[Fossil-Hound]

That's awesome. Thank you for sharing.

[siteseer]

On 7/6/2019 at 11:10 AM, KOI said:

We visit the area once a year (my birthday or father's day) and usually find 1-3 good crabs each time leaving most of the pieces to local school kids who do field trips to the location. The video combines finds from over a decade. As mentioned in the video, we do not waste time breaking slabs - its not productive. You just have to focus and scan the rocks with your eyes. Every one who finds a crab gets ice cream!

 

 

I first collected those pea crabs back in the early 90's, and like you, checked the area maybe 1-2 times per year, skipping a year a couple of times.  I've scouted different sites around Carmel Valley and have seen them from as far south as Ventura County (finds by the late great Bruno Benson) and as far north as the Point Reyes area (Galloway, 1977: p. 27).  I haven't been out there in a couple of years.

 

Yeah, it's easier to surface collect but splitting sizable pieces is not a waste of time.  It's true it's not super-productive (and maybe you don't want kids using a hammer and chisel) but you will find more than three crabs if you do some splitting.  I would say you could find maybe another 5-10 crabs that way in an hour or two.  You need a hammer and a sharp-edged chisel.  I once found a nice chunk, split it and found a nice positive and negative of three crabs.  It might be the best piece I've ever found but I traded it to Gery (Nala) so he could have something really good from California.  A piece I have kept is from my first trip.  It's a little chunk that must have split after eroding out of the cliff and rolling onto the road.  The positive and negative of a nicely-colored orange crab is nicely displayed (much like the crab showing on the image in the first video).  i thought fossil collecting was super-easy at that point.

 

I have seen the crabs in different colors including the same color as the rock.  You can tint them later with clear shellac which actually dries a little darker to bring contrast to the crab.  I have seen them yellow, orange, and black - colors from whatever minerals are present.  It's tough to find a crab with all the legs visible and you often need a scribe to expose the legs that are there.  Sometimes, you can see that at least one of the legs or the claws is tucked under the body.

 

The layer is actually shale.  A geologist told me it was the Aguajito Shale Member of the Monterey Shale.  it splits nicely sometimes but it also breaks weirdly sometimes and that might have to do with transitions in rock type.  As I understand it, the crabs tend to be found in only a couple of layers - somewhere high in the cliff and near the base - perhaps representing episodes of die-off due to some local disturbance.  And yes, it's easier and safer just to surface collect and split whatever is on the ground and away from the road yet not up against the cliff (watch for falling rocks).  In the spring-summer watch for ticks especially if you venture up and down grassy slopes.  I agree that checking areas in the spring is the best time (more fresh stuff on the ground).

 

I've also found partial leaves, shell impressions (mainly Arca), worm tubes, fish vertebrae (even an essentially-complete fish), and an essentially-complete larger species of crab.  An article was recently written about the worm tubes because the form is only otherwise known from a site in Turkey or that region.  I've seen a Hexanchus tooth from there and an older collector told once me someone found a tiger shark tooth in the 70's or 80's.

 

Perhaps the nicest specimen I've ever seen from there is a small branch with leaves along with a crab that a friend found.  Another friend once split out a slab larger than a dinner plate and the surface was covered with crabs (I didn't get to see that one).   Another of my personal finds is a crab with seaweed around it.  I used a colored shellac to preserve it then and it looks unnaturally dark so I'm thinking of diluting it to a lighter shade.  A few years ago, I found a smaller piece with a bunch of crabs on it but it had sat exposed for a while and the crabs are weathered.

 

I have been told that all the crabs are Pinnixa galliheri and the other names are junior synonyms.  That seems to be the prevailing opinion, but remember, all scientific names are official proposals - not the final words.

 

Jess 

 

Galloway, A.J.  1977.

Geology of the Point Reyes Peninsula, Marin County, California.  Bulletin 202.  California Division of Mines and Geology.  Sacamento, CA.

[KOI]

On 7/11/2019 at 10:13 PM, siteseer said:

 

 

I first collected those pea crabs back in the early 90's, and like you, checked the area maybe 1-2 times per year, skipping a year a couple of times.  I've scouted different sites around Carmel Valley and have seen them from as far south as Ventura County (finds by the late great Bruno Benson) and as far north as the Point Reyes area (Galloway, 1977: p. 27).  I haven't been out there in a couple of years.

 

Yeah, it's easier to surface collect but splitting sizable pieces is not a waste of time.  It's true it's not super-productive (and maybe you don't want kids using a hammer and chisel) but you will find more than three crabs if you do some splitting.  I would say you could find maybe another 5-10 crabs that way in an hour or two.  You need a hammer and a sharp-edged chisel.  I once found a nice chunk, split it and found a nice positive and negative of three crabs.  It might be the best piece I've ever found but I traded it to Gery (Nala) so he could have something really good from California.  A piece I have kept is from my first trip.  It's a little chunk that must have split after eroding out of the cliff and rolling onto the road.  The positive and negative of a nicely-colored orange crab is nicely displayed (much like the crab showing on the image in the first video).  i thought fossil collecting was super-easy at that point.

 

I have seen the crabs in different colors including the same color as the rock.  You can tint them later with clear shellac which actually dries a little darker to bring contrast to the crab.  I have seen them yellow, orange, and black - colors from whatever minerals are present.  It's tough to find a crab with all the legs visible and you often need a scribe to expose the legs that are there.  Sometimes, you can see that at least one of the legs or the claws is tucked under the body.

 

The layer is actually shale.  A geologist told me it was the Aguajito Shale Member of the Monterey Shale.  it splits nicely sometimes but it also breaks weirdly sometimes and that might have to do with transitions in rock type.  As I understand it, the crabs tend to be found in only a couple of layers - somewhere high in the cliff and near the base - perhaps representing episodes of die-off due to some local disturbance.  And yes, it's easier and safer just to surface collect and split whatever is on the ground and away from the road yet not up against the cliff (watch for falling rocks).  In the spring-summer watch for ticks especially if you venture up and down grassy slopes.  I agree that checking areas in the spring is the best time (more fresh stuff on the ground).

 

I've also found partial leaves, shell impressions (mainly Arca), worm tubes, fish vertebrae (even an essentially-complete fish), and an essentially-complete larger species of crab.  An article was recently written about the worm tubes because the form is only otherwise known from a site in Turkey or that region.  I've seen a Hexanchus tooth from there and an older collector told once me someone found a tiger shark tooth in the 70's or 80's.

 

Perhaps the nicest specimen I've ever seen from there is a small branch with leaves along with a crab that a friend found.  Another friend once split out a slab larger than a dinner plate and the surface was covered with crabs (I didn't get to see that one).   Another of my personal finds is a crab with seaweed around it.  I used a colored shellac to preserve it then and it looks unnaturally dark so I'm thinking of diluting it to a lighter shade.  A few years ago, I found a smaller piece with a bunch of crabs on it but it had sat exposed for a while and the crabs are weathered.

 

I have been told that all the crabs are Pinnixa galliheri and the other names are junior synonyms.  That seems to be the prevailing opinion, but remember, all scientific names are official proposals - not the final words.

 

Jess 

 

Galloway, A.J.  1977.

Geology of the Point Reyes Peninsula, Marin County, California.  Bulletin 202.  California Division of Mines and Geology.  Sacamento, CA.

Many thanks to siteseer for detailed comments! Lots of interesting information.

By the way, there is an interesting article about worm tubes found with crabs.

FORAMINIFERA USED IN THE CONSTRUCTION OF MIOCENE POLYCHAETE WORM TUBES, MONTEREY FORMATION, CALIFORNIA, USA

by KENNETH L. FINGER, MEGAN M. FLENNIKEN, JERE H. LIPPS

published in Journal of Foraminiferal Research, v. 38, no. 4, p. 277–291, October 2008.

It was quite a surprise for us when we realized that the "fish eggs" were actually worm tubes made of forams.

Considering information about cool finds shared by siteseer , it's not just about crabs, there may be more things to discover! 

Thanks again!

 

 

 

[Mark Kmiecik]

On 7/6/2019 at 1:10 PM, KOI said:

Every one who finds a crab gets ice cream!

Chocolate ice cream? I'm in. I'm 68, entering my second childhood. Maybe third -- I lost track.

[siteseer]

On 7/14/2019 at 12:00 AM, KOI said:

Many thanks to siteseer for detailed comments! Lots of interesting information.

By the way, there is an interesting article about worm tubes found with crabs.

FORAMINIFERA USED IN THE CONSTRUCTION OF MIOCENE POLYCHAETE WORM TUBES, MONTEREY FORMATION, CALIFORNIA, USA

by KENNETH L. FINGER, MEGAN M. FLENNIKEN, JERE H. LIPPS

published in Journal of Foraminiferal Research, v. 38, no. 4, p. 277–291, October 2008.

It was quite a surprise for us when we realized that the "fish eggs" were actually worm tubes made of forams.

Considering information about cool finds shared by siteseer , it's not just about crabs, there may be more things to discover! 

Thanks again!

 

 

 

 

Yes, I think that's the article. 

 

I should clarify that the Pinnixa species that are junior synonyms are all names for that pea crab.  Whether one is a little rounder or more oval might just be some distortion from the fossilization process.  There are at least two other genera of crabs present.  One friend found what appear to be parts of a very large spider crab.

 

Yeah, fish eggs wouldn't fossilize in a layer like that.  We would've found other soft-bodied animal impressions as well.