Sawfish Ptychotrygon triangularis rostral teeth? Anyone ever find one?

[JamieLynn]

I realized that I have a LOT of ptychotrygon oral teeth, but no rostral teeth....I think.  From the little bit of research I've done (Elasmo.com, Farish's Texas Sharks and Rays book, google search) all I see are the oral teeth and no indication of rostrals.  In the same formation the Ptychotrygon teeth are coming from, also finding rostrals that I see labeled as Ischyrhiza.

 

Has anyone found what they can positively (or mostly) ID as pytchotrygon rostrals?  @Al Dente @Mikrogeophagus @Jared C and anyone else who might know?

[Mikrogeophagus]

That's a topic of debate that has gone many ways over the past decades. The most recent and important development were specimens to a new species (Ptychotrygon rostrispatulata) from the Turonian of Morocco. They have excellent preservation and the presence of Ptychotrygon-esque oral teeth lead the team to their identification. Importantly, these fossils had no rostral teeth associated with their rostrums! Seems that if the orals were preserved, there is no fossilization-related reason for the rostrals to not be as well. This coincides with one school of thought that suggests the family Ptychotrygonidae (Ptychotrygon + Texatrygon + potentially others) as a whole lacked rostral teeth, having lost them evolutionarily. It is difficult, however, to be totally sure that P. rostrispatulata isn't just an outlier in the family (though I am leaning towards the idea that Ptychotrygonidae as a whole lacked rostrals).

 

In your searching for micros, you have most certainly found some rostral teeth that are commonly referred to as "Ischyrhiza avonicola". I. avonicola-like rostrals are present in the Texas record from the Cenomanian all the way to the Maastrichtian (I've found them and will discuss them in my guide. They exist in the Woodbine, Kamp Ranch, Atco, Ozan, and Kemp Clay). Some have considered these to represent rostral teeth to the various species of Ptychotrygon that often co-occur, but this is usually impossible to do with confidence because members of Onchopristis, Ischyrhiza, etc. are also present most of the time (though there is a Kirkland article I saw that claimed to have I. avonicola-like teeth present exclusively with Ptychotrygon orals).

 

A popular alternative for the source of I. avonicola-like teeth is that they derive from proximal/nasal positions on the rostrums of genera like Onchopristis, Ischyrhiza, etc. Take a look at this Sclerorhynchus atavus rostrum and notice the I. avonicola-like denticles that are present closer to the head (proximal). See how they differ from the bigger rostrals distally:

 

 

 

Obviously I am not an authority on the issue, but I think the evidence pretty strongly suggests that I. avonicola-like teeth are not associated with Ptychotrygonidae and they are instead smooth-billed sawskates. A similar fish nowadays is the paddlefish, so perhaps they were doing something similar. It was once thought the paddlefish's bill was used for scooping mud, but the modern consensus is that it is for electroreception to hunt. 

 

 

I'm guessing the formation you are referring to is the Atco in which case you could be conservative and keep those rostrals labeled as I. avonicola or more ambitiously label them as Ischyrhiza schneideri. Sclerorhynchus cf. S. priscus does also occur in the Atco and could contribute to the I. avonicola-like teeth, but for North TX they seem to be kinda rare. Down in the Austin Atco, Sclerorhynchus cf. S. priscus is more common though in my experience. Sclerorhynchoidei indet. would include both Ischyrhiza and Sclerorhynchus if you prefer that .

[JamieLynn]

THANK YOU!! Smooth billed sawfish...interesting! 

[Al Dente]

Here's a photo of one of the Ptychotrygon fossils.