Aug. & Sept. 2017 Basal Atco Conglomerate Texas Fossil Hunt

[LSCHNELLE]

Got out for a brief 30 minute hunt in September at my favorite Basal Atco outcrop in Travis County for Ptychodus.  I found a couple of rare teeth - P. latissimus! Please see pics.  The largest is 26 mm tooth width (TW)) with 13 mm tooth height and 6 mm crown height.  The smaller fragmented tooth is >16 mm TW.

 

Also, at another location in August, I found a couple of nice teeth: a 23 mm TW P. mammilaris and a 16 mm TW P. mortoni. Both had complete roots for a change. 

 

Probably 90% of Atco locations around here have no or very few macro fossils except oyster/clam fragments.  But, this one has yielded about 45 Ptychodus teeth over two years plus many regular shark's teeth. Most of these teeth are absent most or all of the root mass.

 

Ptychodus finds have included:  1 P. atcoensis (15 mm TW), 1 P. mammilaris (9 mm TW), and the balance are P. mortoni up to 26 mm TW or unidentified species <8 mm TW.

 

I am especially pumped up with these two finds!

Edited September 11, 2017 by LSCHNELLE
Clarification about location

[Innocentx]

Cool! those are nice(shell crushing) teeth. What minerals replaced the original material? I don't know that much about Late Cretaceous fossils.

[Fossildude19]

Neat finds!

Thanks for posting them.  

[DPS Ammonite]

Having collected Ptychodus  and other teeth and bones from the Atco Fm in north Texas, I note that they are more or less the original phosphate (apatite) that are usually beige, brown or black on the outside.

[ynot]

Nice finds!

[LSCHNELLE]

Thanks, DPS Ammonite for answering Innocentx question.  I was not certain of the final replacement minerals. Phosphate based minerals make the most sense, because there are phosphate nodules located throughout the basal Atco Formation of the Austin Group.

 

Fossil colors here in the Austin, TX Atco Fmn are red, brown, and dark brown. Here is a discussion of basic color factors for Cenozoic Era shark teeth:   http://www.fossilguy.com/topics/shark-teeth-colors/index.htm

 

It may apply to the Mesozoic Era. 

 

I think the white fossil streaks are from a "leaching" of the mineral color in the fossil caused by roots or fractures that transmit surface water into the substrate near the fossil. While the yellow iron oxide colors may be a secondary mineralization of the conglomerate matrix caused by oxidation from phreatic (groundwater) or surface water.  

[jewelonly]

Gorgeous Ptychodus teeth, @LSCHNELLE! I love the coloring.  

 

Leah

[michele 1937]

They're wonderful