Sclerorhynchoidea An extinct fish with a saw-like nose

[brontosauruschuck]

https://sarahzgibson.com/2017/11/02/the-slasher-ray-an-extinct-fish-with-a-saw-like-nose/
Jim Kirkland posted this blog post of someone else to his twitter a few days ago. Not sure why exactly, but it's really interesting. I've always found sawfish to be kind of inexplicable. They somehow have to use a snout with teeth around the edge to capture prey, and it looks like the sort of thing that a fish could wriggle off of very easily. They might still be mortally wounded, but unless the sawfish wants to swim after them, its still not getting its food. Kind of a lose lose situation really. Anyway, this article is cool and says that saw snouts actually developed convergently 5 different times that we know of, which just makes it even more baffling to me.

Also, does anyone know of Sarah Z. Gibson? I don't think I've come across that name before.

[Halichoeres]

Sarah Gibson finished her PhD at the University of Kansas just a couple of years ago. I knew her when she was a fossil preparator at the Field Museum in Chicago, back when I was working there. I've seen her speak at conferences and she's a really thorough, careful fish paleontologist. I think these days she's mostly working on Triassic actinopterygians; she recently revised some of the Redfieldiiformes. She's also one of the kindest paleontologists I've ever met. AND, last but not least, for years she ran the PLoS open access paleontology blog: https://blogs.plos.org/paleocomm/

[brontosauruschuck]

Woah! She sounds pretty cool. Does she have a Twitter?

[brontosauruschuck]

She does.  https://www.google.com/url?sa=t&source=web&rct=j&url=https://twitter.com/gombessagirl%3Flang%3Den&ved=2ahUKEwi8s7Hyg8vnAhXVJjQIHakUBdIQFjAAegQIBhAB&usg=AOvVaw1m2jK56HWLVyLUKrvdA4DD

[Halichoeres]

Glad you found it! Sorry I didn't reply earlier, these days it's really hard for me to steal a moment to goof around on the forum during the work week. Her Twitter handle is from the Comorian name for the coelacanth, gombessa.

[Ravonium]

Could someone inform me on the other two groups of chondrichthyan fish where saw-like snouts appeared?

[Halichoeres]

Could someone inform me on the other two groups of chondrichthyan fish where saw-like snouts appeared?

Besides the Sclerorhynchiformes, there's the related sawfishes and the saw sharks. The first two groups evolved from within batoids, so they would have ventral gills like rays and skates. Saw sharks have lateral gills like other true sharks, as well as sensory barbels. Saw sharks are also smaller on average than the other two groups.

[Ravonium]

Could someone inform me on the other two groups of chondrichthyan fish where saw-like snouts appeared?

Besides the Sclerorhynchiformes, there's the related sawfishes and the saw sharks. The first two groups evolved from within batoids, so they would have ventral gills like rays and skates. Saw sharks have lateral gills like other true sharks, as well as sensory barbels. Saw sharks are also smaller on average than the other two groups.

Apologies for not being clear enough; in the blogpost, it mentions saw-like rostrums convergently occuring 5 times. I'm aware of this occuring in Sclerorhynchiformes and the other two groups you mention, but (unless there's something major I'm unaware of) that only encompasses 3 of those times.

[Halichoeres]

Could someone inform me on the other two groups of chondrichthyan fish where saw-like snouts appeared?

Besides the Sclerorhynchiformes, there's the related sawfishes and the saw sharks. The first two groups evolved from within batoids, so they would have ventral gills like rays and skates. Saw sharks have lateral gills like other true sharks, as well as sensory barbels. Saw sharks are also smaller on average than the other two groups.

Apologies for not being clear enough; in the blogpost, it mentions saw-like rostrums convergently occuring 5 times. I'm aware of this occuring in Sclerorhynchiformes and the other two groups you mention, but (unless there's something major I'm unaware of) that only encompasses 3 of those times.

Oh, that's my mistake. Besides these groups, the other "two" groups referred to in Welten et al. 2015, cited in Gibson's blog post, are the spatula-snouted chimaera Squaloraja, the very strange chimaera Metopacanthus, which has a dental pick-shaped rostrum with enlarged denticles along one surface, and the Carboniferous shark Bandringa. You'll observe that that actually adds up to six. For some reason they're counting the chimaeras as a single instance. That's strange to me because the two chimaeras aren't each other's closest relatives and the morphology of their rostra is pretty different. Unless I'm quite mistaken, Bandringa has only ordinary denticles/placoid scales on its rostrum, not the big teeth of sawfishes and saw sharks. It is nevertheless frequently cited as an ecological analog to sawfishes because of its overall shape, its ventrally-oriented mouth, and the fact that the macro-arthropods found in some gut traces are similar to what you'd see in some saw-snouted chondrichthyans. If you're speaking more strictly about a long rostrum, composed of calcified cartilage and equipped with large laterally-facing teeth, there seem to be only three instances of that evolving. Welten et al. seem to be more liberally referring to chondrichthyans with oddly long snouts, which I would argue evolved a bunch of other times in Chondrichthyes, like some eugeneodontids and even the modern long-nosed chimaeras (Rhinochimaeridae).