Finally - first huge ptychodus. But what kind?

[zoocosmolina]

Went for a quick hunt this past Sunday and found this gem ('huge' is relative, it's huge in my books). My guess is P. Decurrens? If not, what gives away the correct ID?

 

Thank you!

Nicole

[JohnJ]

This topic has good images and references. 

[zoocosmolina]

Thank you. I previously worked my way through the quick guide and was trying to decide between decurrens and martini. I am tending towards the first but would love to get more input  

[siteseer]

22 hours ago, zoocosmolina said:

Thank you. I previously worked my way through the quick guide and was trying to decide between decurrens and martini. I am tending towards the first but would love to get more input  

 

Where did you find it?  What formation?  What else did you find with it?

[zoocosmolina]

It was found in Far North Dallas in what is considered Eagle Ford. I previously found P.whipplei teeth in that area as well as some x-fish verts. Last Sunday's finds were otherwise meager, a small whipplei and a worn, fish-y looking vert. 

 

[abyssunder]

I'm no expert here in this, but considering the reference link posted by John J and the description of the teeth characteristics of species, I think the tooth in question could be of P. decurrens.

 

Ptychodus decurrens

 

Diagnosis. Teeth with flat to gently rounded tooth crowns and tooth edges, short labial protuberance and shallow lingual sulcus. Medial files square in outline with ten to twelve transverse ridges; anterolateral teeth rectangular with multi-angled mesial and distal tooth edges with seven to ten ridges; posterior teeth have five to seven ridges; differs from other species by having ridges that extend and bifurcate completely at the lateral tooth edges. There are numerous fine ridges on the labial and lingual tooth edges perpendicular to the transverse ridges.

 

Description. The description here is based on an associated tooth set of P. decurrens (BMNH-12846) from the English Chalk Formation (Plate 5). Tooth shape square in anterior files with low, rounded and broad crowns with that gently slope and taper into the margin. The labial edge is rounded while the lingual tooth edge is weakly indented. The tooth crown overhangs a square root that is weakly bilobed. The lower medial file is mesio-distally elongate with between eight and ten straight to sinuous transverse ridges. At the margin, the ridges bifurcate and branch into numerous, finer anatomizing ridges that extend to the edge of the crown. The marginal area is ornamented with the thin anatomized ends of the transverse ridges. The anterior and posterior tooth margins bear fine bifurcating ridges oriented perpendicular to the crown. Anterolateral and posterior teeth are smaller and rectangular with crowns that are slightly inflated to flat.

 

Stratigraphic and Geographic occurrence. (...) and the Kamp Ranch Formation (Middle Turonian) of the Eagle Ford Group in Texas (Meyer, 1974; Welton and Farish, 1993; Hamm, 2003).

 

Ptychodus martini

 

Diagnosis. Medial teeth elongate and rectangular with a flat to gently raised occlusal surface crossed by nine to ten widely spaced, parallel transverse ridges; lateral teeth are square in outline with seven to nine ridges and the posteriors are elongate and rectangular with five to six ridges.
This species differs from others in that the crown is not elevated and has fine and parallel ridges that extend to a narrow margin area; marginal ornamentation consists of fine, bifurcating ridges oriented perpendicular to the crown face.

 

Description. The largest teeth in the type specimen of P. martini (KUVP- 55277) are from the lower medial file (Appendix III). There are eight teeth in the medial file; each are rectangular in outline with an extremely flat occlusal surface crossed (0.83 CH-TH ratio) by eight to nine parallel and slightly undulating ridges that extend fully to the lateral tooth edges. The ridges are closely spaced, thick at the base and thin at the apex, creating a sharp cutting edge. The ridges curve anteriorly at the mesial and distal edges and do not bifurcate at the lateral tooth margins.
The para-medial files are represented by eight teeth that are nearly rectangular with a gently raised (0.76 CH-TH ratio) and rounded occlusal surface with seven to eight transverse ridges that terminate at a narrow, shelf-like marginal area. Teeth of the anterolateral files have seven to eight parallel transverse ridges with a 0.72-0.77 CH-TH ratio. The tooth shape progressively becomes elongate and rectangular, having a 0.72-0.80 CW-TW ratio. The occlusal surfaces are flat, but are slightly elevated at the distal tooth edge. The posterior files have completely flat occlusal surfaces with an average of five transverse ridges that extend completely to the mesial and distal tooth margins. In each file, the pattern and arrangement of the transverse ridges are consistently parallel and uniform with a slight sinusoidal pattern. In some of the teeth from various tooth files, there are small spheroidal enameloid bumps in between several of the ridges. They are not consistent as to which ridges within the tooth they occur or among a particular tooth within a file, nor do they consistently occur among all tooth files. The marginal area is coarsely granulated, similar to the margin in P. latissimus. Ornamentation on the labial and lingual margins is composed of fine bifurcating ridges oriented perpendicular to the crown.

 

Stratigraphic and Geographic occurrence. (...) the basal Atco Formation (Early Coniacian) in Texas (Hamm, 2004); and a single tooth (SMU 69031) formerly known as P. connellyi from the Roxton Member of the Gober Chalk (Early Campanian) in Texas (Hamm and Shimada, 2004).

 

Excerpts from SYSTEMATIC, STRATIGRAPHIC, GEOGRAPHIC AND PALEOECOLOGICAL DISTRIBUTION OF THE LATE CRETACEOUS SHARK GENUS PTYCHODUS WITHIN THE WESTERN INTERIOR SEAWAY - Shawn Hamm. 2008.

 

 

 

 

 

 

[PFOOLEY]

Congrats on your tooth!

[zoocosmolina]

Thank you for everybody's responses =)

[JarrodB]

That's a nice tooth. Congrats

[siteseer]

On 10/27/2016 at 9:37 AM, zoocosmolina said:

It was found in Far North Dallas in what is considered Eagle Ford. I previously found P.whipplei teeth in that area as well as some x-fish verts. Last Sunday's finds were otherwise meager, a small whipplei and a worn, fish-y looking vert. 

 

 

It's pretty worn but it could be P. marginalis which seems like a better fit for the shape and age.  P. decurrens comes from older rocks, though without knowing the particular layer it came from, it can't be ruled out completely.  Most people seem to collect from members of the upper part of the Eagle Ford Group so I lean toward P. marginalis.

 

 

 

[zoocosmolina]

This is turning into a mystery. I ran it by the DPS folks at last week's Fossilmania and based on appearance, P. Decurrens is certainly the closest match but, as mentioned above, it just doesn't belong into my neck of the woods, it's not old enough (you are correct siteseer, I 'play' in the upper Eagle Ford  ). Let's see if I hear back from them. 

Thank you for your feedback!

[PFOOLEY]

More info for your search.  

 

Shawn Hamm's 2008 Masters thesis

[LSCHNELLE]

Congrats!  I think you were right from the start. I have found 18 to 20 mm wide P. Decurrens in the middle Eagle Ford.  P. Marginalis has a concentric pattern on a larger margin .  P.  Decurrens ridge pattern cuts across to the margin edges and can branch out like yours does.   Here is a modified chart of when Texas ptychodus are found.  The updated figure is more accurate on Central Texas formations.  It shows the Burditt/Sprinkle.  Please don't rely on the "draft" chart that doesn't have Atco in it.  These are modified from Shawn Hamm's thesis 2008.  I can't seem to delete the erroneous lowermost chart for some reason. Enjoy the geologic stage information and help to expand it if you finds something that doesn't match the apparent record.  That is what science is all about.  Also, P. Martini is too young for the Eagle Ford - only has been found in Austin Chalk - Atco.  Note that P. Decurrens is one of the oldest.

 

 

 

Edited November 4, 2016 by LSCHNELLE
updated chart and text discussion