Chubutensis or Angustiden

[Maxsg]

So I have posted a picture of this tooth before but I was recently showing it to a buddy and he said it looked like a chub but the cusps make me think angustidens. I want to know what you all think. I found this in an area that the formation is exposed in spots. The clay is a thick white clay speckled with tiny pebbles and other fossils. my geological maps that i used to find the location say that it is of Miocene age in the hawthorn group. However I am starting to think that there might be older clays exposed in the area. Please help me figure out what kind of tooth I have here, thank you. 

[digit]

Down in South Florida we generally only see megs (Carcharocles megalodon) and so that is where most of my experience lies. A while back I enjoyed a diving trip off North Carolina where there were some big megs but also some C. chubutensis which was a treat for me because the only big shark teeth that I'm used to seeing with side cusps are the unrelated Sand Tiger (Carcharias taurus).

 

The taxonomy and evolution of the mega toothed sharks attracts some research attention and is periodically in flux.  Others can correct me if I'm wrong (a reasonable likelihood there ) but I believe the current concept is that the genus Carcharocles evolved from the genus Otodus. There has been a steady progression of the teeth becoming larger (as well as the shark which made use of these larger teeth ) while the cusps slowly diminished till they disappeared completely in the megs. The lineage looks something like this:

 

 

Carcharocles aksuaticus
(alternatively Otodus aksuaticus)

|

V

Carcharocles auriculatus

|

V

Carcharocles angustidens

|

V

Carcharocles chubutensis

|

V

Carcharocles megalodon

 

 

A friend of mine, Victor Perez, recently published an interesting paper on the transition between these last two chronospecies (species that evolved into each other over time). You can find that paper here:

 

https://doi.org/10.1080/02724634.2018.1546732

 

It is not uncommon for juveniles of a species to show some characteristics of previous steps along the evolutionary process. These ancestral traits are called atavisms and occasional cusps on juvenile meg teeth are thought to be such an atavism.

 

https://en.wikipedia.org/wiki/Atavism

 

Having not seen a lot of cusped Carcharocles teeth first hand (other than some nice C. chubutensis that I picked up while diving for megs off North Carolina), it is difficult for me to spot the delineations between the very cusped C. auriculatus as it blends into the more cusp-attached C. angustidens and nearly disappears with C. chubutensis. Even doing internet image searches for each of these species doesn't always help as search results often return images of related species in queries. The cusps on your tooth above seem to have more prominent cusps than the few C. chubutensis that I have in my collection and do look more like C. angustidens to me. The further north in Florida you found that item the better chance that it dates from older formations. I know that @Shellseeker has found a few nice cusped teeth and has researched their identity so hopefully Jack will be able to weigh in on what he has learned.

 

Definitely a cool tooth to be found in Florida.

 

 

Cheers.

 

-Ken

[Harry Pristis]

There is no flawless scheme for putting a fine label on an individual otodontid tooth based on morphology alone.  As I read the Perez et al. paper, the most reliable basis for labeling such a tooth is geochronological - the age of the surrounding sediments.  "There might be older clays exposed in the area" is not the sort of data that is useful for this purpose.

 

Maxsg is asking for a morphological identification based on features that are variable over long periods of time and, most critically, are variable in individual sharks, perhaps ontogenetically.  And this ask is not accompanied the crucial geological clues.

 

Most of us amateurs are accustomed to biochronological dating of our float finds.  If we find and identify a Holmesina floridanus fossil, we assume with some confidence that the fossil dates to the Early Pleistocene.  We do something similar with mega-shark teeth, but without the same confidence.  But, we must have labels, so we adopt models of typical chronomorphs that allow us to put a name to a fossil tooth. 

 

 

[Shellseeker]

Max,

I have found numerous small Megalodons (About the size of your tooth) in the Peace River (Arcadia to Bartow) that have cusps  - I believe regressive cusps.  These are Megalodons because that identification "fits" the geological Peace River formation (Miocene). No Chubs, Rics, or Angys here. I believe I am in basic agreement with @Harry Pristis.  Copy to @digit

 

[hemipristis]

On 8/7/2019 at 9:35 PM, Shellseeker said:

Max,

I have found numerous small Megalodons (About the size of your tooth) in the Peace River (Arcadia to Bartow) that have cusps  - I believe regressive cusps.  These are Megalodons because that identification "fits" the geological Peace River formation (Miocene). No Chubs, Rics, or Angys here. I believe I am in basic agreement with @Harry Pristis.  Copy to @digit

 

 

 

Point of note: C. chubutensis is considered by many authors as the Miocene member of the megalodon lineage.