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Gymnura sp

A Fossil Megachasma Shark Tooth From The California Pliocene

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Gymnura sp

What a thrill it was to come across this excellent Megachasma pelagios shark tooth in a California Pliocene fossil bed!

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Over the Thanksgiving weekend my wife and I were searching our favorite Pliocene locality for GW shark teeth when she came upon this little gem. Although we had never before found a Megachasma tooth (here or elsewhere) it's unique morphology made it's ID instantly certain.

The only CA Megachasma record I'm aware of is for the lower Miocene teeth (of very different form) from the Pyramid Hill area of Kern County. The above tooth measures in at 0.722 inches and appears to me to be a dead-ringer for M. pelagios.

For your info, other elasmobranch fossils we find in these Pliocene beds include Carcharodon carcharias, Isurus planus, other Isurus forms which seem to include I. hastalis and another smaller, narrower form (I. paucus?) as well as Carcharhinus sp. and Negaprion sp. Meg was here as well but examples are very rare. Characteristic Pliocene inverts we find are Ostrea vespertina, Pecten sp. and Patinopecten sp.

We would appreciate any hearing additional information on west coast Megachasma finds. Thanks!

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RickNC

Very nice!

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Boesse

What formation is this from? There's an early Miocene record of "Megachasma" from Mendocino Co., the same morphotype as is known from Pyramid Hill. As far as what has been published, there are no published records of Megachasma from the Pacific coast of the US.

Bobby

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Gymnura sp

Hi Bobby,

I figured this might pique your interest. We found the tooth in what I like to refer to as the Fernando formation. I realize that designation may be outdated but for lack of a better term I use it based on Woodring (1930). He refers to it as an outright formation, others have referred to the "Fernando group" for certain Ventura Basin Pliocene beds.

Thanks for confirming that there have been no published west coast records for fossil megamouths. I figured that to be the case.

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cowsharks

Have you read the info on elasmo.com regarding the STH Megachasma teeth? If not, got to elasmo.com, click on fauna's, select Shark Tooth Hill, and scroll down to the Megachasma tooth/description and click on it; see pic below...

vr,

Daryl.

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Gymnura sp

Hi Daryl,

Thanks! We checked out the elamso website per your recommendation and the extant Megachasma tooth pictured there looks very similar to the CA fossil tooth we found.

Since we found the mega-mouth tooth last month we have been sifting more sand with a finer mesh screen. Hopefully we'll find another specimen!

Gymnura

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Boesse

Hey Gymnura,

To be quite honest there haven't really been any marine vertebrate remains described from the Fernando Fm., but I think some scraps are in LACM collections. What else have you found, out of curiosity - other sharks? Anything in the way of birds or marine mammals (e.g. pinniped teeth or dolphin earbones)? Feel free to PM me if you prefer.

I'm interested in getting more Pliocene marine vertebrates written up and published for California, since so few studies have been published to date.

Bobby

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siteseer

Hey Bobby,

Yes, here's the title of the article noting that occurrence:

http://techplace.datapages.com/data/pac_sepm/017/017001/pdfs/137.htm

I don't know of any fossil occurrences of the megamouth from the west coast of North America either - not even any informal claims.

Jess

There's an early Miocene record of "Megachasma" from Mendocino Co., the same morphotype as is known from Pyramid Hill. As far as what has been published, there are no published records of Megachasma from the Pacific coast of the US.

Bobby

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siteseer

Hi Gymnura,

I think I have read that the Fernando Formation is called something else now or at least a name change has been proposed. I might have at least one article that discusses the formation but I'm away on business at the moment - will try to get back to you on that next week.

I have one great white collected in the 80's from that formation.

You might find some 1-2mm shark and ray teeth if your screen is fine enough for them.

I don't think that Pyramid Hill form is going to end up being named as a species of Megachasma (similar but different root) but it appears to be at least a close relative of its ancestor. I know a few people have considered naming it, but now that Bruce Welton has retired, he might be the one who ends up doing it.

Thanks for the interesting report.

Jess

Hi Bobby,

I figured this might pique your interest. We found the tooth in what I like to refer to as the Fernando formation. I realize that designation may be outdated but for lack of a better term I use it based on Woodring (1930). He refers to it as an outright formation, others have referred to the "Fernando group" for certain Ventura Basin Pliocene beds.

Thanks for confirming that there have been no published west coast records for fossil megamouths. I figured that to be the case.

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Boesse

I forgot to mention that Pieter de Schutter (2009) has figured and discussed the Pyramid Hill taxon, which he referred to as Megachasma sp. Here's a link to the article: www.vliz.be/imisdocs/publications/225843.pdf

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Gymnura sp

Hey guys,

Here's a brief list of elasmobranch material I've found in the same beds arranged in order of relative abundance:

Carcharodon carcharias

Isurus planus

Isurus paucus?

Carcharhinus sp

Isurus hastalis

Carcharocles megalodon

Physogaleus contortus

Negaprion sp.

Myliobatis sp.

Megachasma pelagios

I'll post pics over the weekend.

None of these fossils are very plentiful and it takes a lot of work/luck to find much here.

In the outcrop (Fernando fm?) there are a series of altertnating sand and conglomerate beds. Teeth can be found in either facies. As you can imagine examples in the conglomerate have been pretty well beat up. The sand however yields an occasional gem!

I do find fragments of whale bone... And once in a while a dolphin periotic pops up. I'll post a pics of those too.

Gymnura sp

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siteseer

I just ran across this thread while goggling something else.  I think at least part of what used to be called the Fernando Formation back in the 70's-80's is now called the Repetto Formation.

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