Ray and shark Dermal Denticals

[TroyB]

Here are the variety of dermal denticals from various ray and shark type creatures from the Martin Marietta cement quarry.  They date around 90 million years ago and were found in the contact between the Austin chalk and Eagle Ford shale.

[ynot]

Nice pieces.

I have been told that most shark denticles are less than 1 millimeter, any larger than that, then it is a ray or skate. There are a few sharks that defy this rule (bramble shark).

 

What size are these?

@TroyB Have You seen this thread?

 

Or this one...

 

[Tidgy's Dad]

Very interesting. 

Thanks for sharing. 

[Heteromorph]

Nice denticles! I have yet to find one from the quarry myself, but that might change when I go through all the matrix I brought home. 

[MarcoSr]

1 hour ago, ynot said:

Nice pieces.

I have been told that most shark denticles are less than 1 millimeter, any larger than that, then it is a ray or skate. There are a few sharks that defy this rule (bramble shark).

 

What size are these?

@TroyB Have You seen this thread?

 

 

 

Tony

 

Placoid scales are less than 1 millimeter.  Sharks and rays both have placoid scales.  Rays also have dermal denticles usually along their mid-line.  Dermal denticles can be much larger than 1 millimeter. The problem arises when  researchers use the terms interchangeably.

 

Marco Sr.

[ynot]

3 minutes ago, MarcoSr said:

The problem arises when  researchers use the terms interchangeably.

And being dyslexic makes it real hard for Me to keep them seperate.

[MarcoSr]

21 minutes ago, ynot said:

And being dyslexic makes it real hard for Me to keep them seperate.

 

Tony

 

Placoid scales and dermal denticles have different purposes.  Placoid scales that cover a shark's body are designed to lessen water resistance and help the shark glide through the water.  Dermal denticles on rays (usually along the mid-line) are more a form of armor to protect the ray from attack.  Rays also have sparse placoid scales that help somewhat with water resistance.

 

Marco Sr.

[TroyB]

11 hours ago, ynot said:

Nice pieces.

I have been told that most shark denticles are less than 1 millimeter, any larger than that, then it is a ray or skate. There are a few sharks that defy this rule (bramble shark).

 

What size are these?

@TroyB Have You seen this thread?

 

Or this one...

 

The smallest ones are about 0.7mm across and the largest ones are about 5mm.