Unusual Finger-Like Marine Mold Fossil, What is it?

[Bronzviking]

I found this unusual finger-like fossil on a Tampa Bay beach in Florida. It's about 3 inches long by 1 1/4 inch wide. It has an oval indention with swirls on the end, that looks like an external bivalve mold. The finger-like piece has corallite markings on it. Is this a mold of a shell or a fossilized coral finger? Thanks!

[Johannes]

Its a cast of a bivalve boring hole (Gastrochaenolites isp.) in a coral colony, recent examples can be seen here.

The inner hole is the impression of the bivalve (Pholas-relative)

[Plantguy]

Yep I agree with Johannes that its a cast of a bore hole in a coral. Nice find! 

 

For comparison here's a photo of a heavily bioturbated section of Septastrea I have from our local Tamiami formation showing several of those finger shaped boring tubes and a bivalve (marked by the red arrow) in the end of one of them. 

 

Regards, Chris 

[Bronzviking]

5 hours ago, Johannes said:

Its a cast of a bivalve boring hole (Gastrochaenolites isp.) in a coral colony, recent examples can be seen here.

The inner hole is the impression of the bivalve (Pholas-relative)

Nature is pretty amazing. Thanks for the ID and links.

[Bronzviking]

On 1/5/2019 at 8:06 PM, Plantguy said:

Yep I agree with Johannes that its a cast of a bore hole in a coral. Nice find! 

 

For comparison here's a photo of a heavily bioturbated section of Septastrea I have from our local Tamiami formation showing several of those finger shaped boring tubes and a bivalve (marked by the red arrow) in the end of one of them. 

   

Regards, Chris 

Thanks Chris for the examples. It helped me understand the process that Johannes quoted.

[Plantguy]

12 hours ago, Bronzviking said:

Thanks Chris for the examples. It helped me understand the process that Johannes quoted.

Glad to help...lots of folks here on the forum have helped me with all of the various traces we can around find here...

Continued hunting success!

Regards, Chris 

[Bronzviking]

On 1/5/2019 at 8:06 PM, Plantguy said:

Yep I agree with Johannes that its a cast of a bore hole in a coral. Nice find! 

 

For comparison here's a photo of a heavily bioturbated section of Septastrea I have from our local Tamiami formation showing several of those finger shaped boring tubes and a bivalve (marked by the red arrow) in the end of one of them. 

 

 

Regards, Chris 

Chris, Do the boring bivalves bore holes in live or dead coral?

[Plantguy]

17 hours ago, Bronzviking said:

Chris, Do the boring bivalves bore holes in live or dead coral?

Great question. I didnt know the answer for sure but thought some might just be just looking for a hard surface to drill into. Sure enough on page 12 of the article "Environment and Mode of deposition of a Pliocene Coral Bed: Coral Thickets and Storms in the Fossil Record" by Ketcher and Allmon,  Palaios, 1993, V8 P3-17.

https://eurekamag.com/research/008/612/008612385.php

that Ive been reading about my specimen it does state that Lithophagid types prefer dead substrates but are occasionally found in living coral (Soliman, 1969).

 

My particular piece is probably from Bed 11 APAC Sarasota which is thought to have included broken parts of a coral thicket knocked down in a storm/storms and was bioeroded for maybe 20-25 years and then subsequently buried. Here's a picture of the some of the smoothing/sand blasting of areas of the corallites. Some recessed areas are almost uneffected. Apparently there were also at least 2 different generations of lithophagid borings. 

Glad you presented your find as it caused me to do some more reading and learn something new. 

 

Regards, Chris