Strange Egg Shaped Rock With Grooves On It.

[Torrio888]

I have found this rock on the beach in Croatia, it looks like other round white limestone pebbles on the beach but has strange lines/grooves on it.

More pictures here:

https://imgur.com/a/autqj

Edited April 8, 2015 by Torrio888

[jpc]

strange....

[pinkus]

My best guess is a coral rounded by wave action. It is really cool.

[Darktooth]

Interesting indeed.

[fossilized6s]

Welcome.

That looks to be a water worn and polished mushroom coral.

[Agos1221]

Definitely coral

[Taogan]

Looks interesting, is it rock? It has an unusual sheen that makes me think ceramic. If it is rock then some sort of coral, but the eroded band around it makes me suspicious.

[Fossildude19]

I was thinking manmade on this as a possibility on this as well.

The band in the center has a seam-like look to it.

Regards,

[Fossildude19]

The rest of the photos for those of you who do not wish to leave the site to view them.

Regards,

[fossilized6s]

Check this out guys.

http://en.m.wikipedia.org/wiki/Fungia

Now imagine the protruding ribs being sanded down (pun intended). The OP is the end result. I think Digit (Ken) may know about these.

[abyssunder]

I have one in my collection,maybe could help.

[Fossildude19]

Sorry guys, but I am not convinced. The pictures provided look much flatter than this item.

I'd be interested to know if this item fizzes when exposed to vinegar, as limestone would

Regards,

[Torrio888]

Sorry guys, but I am not convinced. The pictures provided look much flatter than this item.

I'd be interested to know if this item fizzes when exposed to vinegar, as limestone would

Regards,

Yes it does.

[Auspex]

I found an image of a polished Caninia coral (TX Pennsylvanian)

This is just for comparison; I still do not see how wave-tumbling could have caused the equatorial groove in the mystery object.

[Carl]

I, too, vote away from coral. But I don't have a good alternative.

[digit]

While reading down through this topic I often try to form an opinion. Then reading further I get to see what others are saying and use that as a gauge to see if it supports my ideas or if I'm way off base with my initial ideas.

This one has me stumped. When people suggested a coral I started thinking Fungia (as Charlie had predicted) but this would be a really weird mushroom coral from the ones I am familiar with. For your one minute micro-lesson on corals here is a bit of info on Fungia:

<lesson>

They are called 'mushroom corals' because newly settled recruits grow on a stem before widening out into a mushroom-like "cap". Eventually, the coral gets too big from its tiny base and it breaks off (leaving a scar at its base for some time). These corals then become 'free living' and live unattached for the rest of their lives. Storms, currents and wave surge will tend to transport these along the reef but most tend to settle into an area where they live for some time. Many have long enough tentacles that they can flip themselves if they become overturned. Many don't seem to have this capability (I occasionally right a flipped over one if I come across it). Several species divide so that they have multiple mouths and actually form free living colonies but some just grow larger as a single polyp. They tend to have a large number of septal plates (the radial ridges) and can grow to sizes many orders of magnitude larger than the often tiny polyps in colonial corals.

Here is a very colorful (fluorescent) Fungia coral that is a single polyp and about 10cm in length. The tissue is violet and the tiny tentacles are a light green. The elongated mouth is visible in the center.

Some fungiids (like this Heliofungia actiniformis) have extremely well developed tentacles and would could easily be mistaken for anemones by those unfamiliar with them. The fact that they are unattached and have the heavy calcium carbonate skeleton at the base easily distinguishes them from their anemone kin. Several species of pipefishes, crabs, and shrimps associate with this species. Can you spot the tiny Periclimenes kororensis shrimp in this one?

</lesson>

I can see the resemblance of the mystery fossil to a worn down fungiid with an smooth area where the supposed mouth would be. I kinda got that vibe as well (maybe because I just returned from the Indian Ocean and saw lots of fungiids recently). It would seem too large and to solitary for any other kind of coral that I know (though I am by no means an expert in the ancient forms of corals). It's the longitudinal ridge running around the equator and ridges on the "bottom" on this item that throws me. Not what I would expect to see on any fungiid which tend to have a transition from a ridged upper surface (the septal plates) to a smooth under surface. The edge is usually thin and never concave as with this oddity.

It's obviously biological--too fantastic for me to believe this could be geological. I had to consider something man-made as well (some sort of grinding stone for a ball mill) but that seems far fetched.

You got a real top-shelf mystery there. My first impulse would be to go back to the beach and spend a lot of time trying to find a second one. Additional examples may provide the clue to unlocking this mystery.

I'm truly intrigued.

Cheers.

-Ken

[Auspex]

I am thinking in terms of something that has been 'cobbled' by wave-wear.

Not that that line of thought has born fruit...

[digit]

Hmmm...fruit you say? Nah, still haven't a clue. Googling for similar items through a variety of descriptive adjectives haven't turned up anything even vaguely similar. My money is on the first positive proof of alien visitation.

-Ken

[Auspex]

Nessie egg?

[abyssunder]

Maybe it is not an individual, but two united mushroom corals.

[digit]

Believe me. I considered even this far fetched possibility. In life mushroom corals (fungiids) would never be found this way. If this was a chance burial of two that were somehow fused as fossils I'd call that incredible luck to have them line up perfectly like that.Though I can see the resemblance to fungiids I have to believe this is a case of seeing elephants in cloud formations--an artifact of our mind's incredible capacity for seeing similarities in things as part of our innate search image software.

I'm still with Auspex--Nessie egg is as plausible as any explanation at the moment.

Would love to know if Torrio888 can locate more of these where this one was found. I think more clues will be necessary before this nut is cracked. I wouldn't be at all surprised though is some TFF member with an arcane knowledge of this mystery steps up and provides the answer. I've seen it happen before with other mysteries.

Writing this from the lounge at the Doha, Qatar airport during my 8 hour delay heading back to Male, Maldives enroute to the second leg of a survey of the reefs of the Chagos Archipelago.

Cheers.

-Ken

[TqB]

I think it's a worn piece of coral. The horizontal band would be a growth constriction with some remaining outer wall so the septa remain more or less hidden in that bit.

I don't know what type but a bit of Thecosmilia for example could produce that effect.

[abyssunder]

What do you propose I think is a good possibility...

Edit: for example

Edited April 11, 2015 by abyssunder

[Taogan]

I have been looking for a while and am even less convinced about this being coral, we need more data on the collection site, whether it is mineralised etc.

[digit]

Coral is as good of a guess as any at this point. I am reasonably familiar with most forms of extant coral but I'm a complete noob as to what archaic coral might have left their traces in the fossil record. The semi-spherical shape still nags at me with "septal" type lines on both hemispheres. I guess I could believe it more if the rounded shape was a result of weathering that have smoothed this into its current cobble-like form that might not have been apparent in its living state.

If these were more common and we had a number of samples to work with, I'd sure love to see one of these split cleanly on a slab saw along the equatorial valley to see what structure is revealed within.

Hoping for a resolution to this but enjoying the mystery.

-Ken