Last week I gave you this guest mystery object, courtesy of Joseph van Sambeek:
The bony struts reinforcing thin plates of bone show it’s from something that lives in water all the time and which lacks lungs – you can tell this because this structure is what you get when you’re dealing with forces moving in a variety of directions, rather than mainly dealing with the constant force of gravity or compensating for buoyancy that is unavoidable when you live in water, but have lungs.
This means that many of you recognised it as being the neurocranium (that’s the bit of the skull that surrounds the brain) from a fish – more specifically from Sarah Gibson:
The first image is the skull roof, showing the elongated frontals and parietals (front of snout is left in first three images). Second image is a left lateral view, showing the internal parasphenoid that would pass between the two eye sockets. Third image is a ventral view, showing the bottom of the parasphenoid. And obviously last image is posterior view, showing the foramen magnum where the spinal cord would pass through, over the occipital condyle. It just may not look like a skull to some because it’s missing the eye sclera bones, jaws, cheek bones, pretty much anything that is not the skull roof or braincase.
However, as we all know, there are a LOT of different sorts of fish – around 33,600 described species and counting. This can make fish a nightmare to identify. However, there are some great resources out there, like Osteobase which has a very useful identification guide for various elements of a range of fish.
Alas, Osteobase didn’t have anything that fits this mystery specimen, so narrowing down to a species is rather difficult. I had the advantage of knowing that the specimen was collected in Baja California, although that was of little help in trying to get in an approximate area of the fishy family tree based on morphology, and there are still a ridiculous number of fish species is the area.
Sarah Gibson suggested that it may be a Barracuda, and it certainly fits in many aspects, but the shape of the frontals and parietals and details of the point of connection between the parasphenoid (that’s the bottom bar bit you see in the side view) don’t quite fit.
I had almost given up hope, when it occurred to me to concentrate on understanding the unusually large occipital condyle that Allen Hazen noticed, which suggested that it might be a taxon with an extremely extended rostrum (like the paddlefish or swordfish that Jennifer Macaire suggested) but with a weedier body and defined neck region since there would be no need for such a large articulation in a fusiform fish (they’re the muscular type that taper at both ends and have no neck, so don’t move their heads).
With this bizarre sounding fish in mind I was able to fairly rapidly narrow down the possibilities to one of the three species of cornetfish that live in the Pacific. I was delighted to find some great images of the skull of a Red Cornetfish, which matches the morphology very well.
However, the Red Cornetfish doesn’t really occur in the eastern Pacific, so it’s very unlikely to be that species. The Reef Cornetfish does occur in the eastern Pacific, but has only been reported in Californian coastal waters since November 2015 and this mystery specimen was collected back in January 2000 (which doesn’t make it impossible to be a Reef Cornetfish, just very unlikely). Which leaves us with the most likely identification (although by no means confirmed) of Deepwater Cornetfish Fistularia corneta Gilbert & Starks, 1904.
These long, thin fish can reach up to 2m, but they have tiny mouths that limit them to eating crustaceans, marine worms and smaller fish that they pick up from near the surface of reefs and the sea bed – presumably being harder to spot as a predator thanks to their very small frontal projected area.
I’ve asked Joe to check his specimen against the images of the cornetfish, since there’s nothing better than having a specimen in your hand when attempting an identification.
I hope you enjoyed the challenge!
I am glad I didn’t try too hard.
Do chodricthyes skulls get preserved in this way too (paddlefish etc) or were you, when saying “fish”, referring specifically to the teleosts, or even the actinopterygeans?
As my history of posting might show, I am far more fascinated by models of categorisation than the actual category labels themselves. For example, it is wonderful to know that marsupials have holes in their palates, but I could still not tell a thylacine skull from a Tasmanian Devil skull. (Well, thanks to Zygoma, I probably could, now, but the point is that I prefer to be able to know what distinguishes marsupials from placental or monotremes, to knowing specifically which species of drop bear is being referred to.)
well not to rain on the parade, but in comparing my specimen to the photos…. i’m not convinced.
the posterior of the skull is shaped differently, and since skull is symmetrical i don’t believe more bone has chipped away so evenly on both sides.
also the foramen magnum seems to protrude farther back on the skull than is shown in the photos.
that said… i don’t have a better guess. ?
Don’t forget that were talking about a different species to the one in the image. I’ve not found a good image of the Reef Cornetfish neurocranium for comparison, so there’s no chance of a definite identification – it’s always uncertain!
What you’ll tend to find with vatiation between species is differences in extent and relative proportion rather than absence and presence of structures, so although the shape is somewhat different, it has the same characteristics.
To be sure we’d need a neurocranium from the Reef Cornetfish for comparison, which we’re lacking.
Chondrychthyan skulls are of a very different structure. I don’t think they HAVE occipital condyles: looking up the BONES subsection of the VERTEBRATE section of Palaeos.com, it looks as if instead they have a pit where the front end of the notochord inserts into the base of the skull. (Though from the wording at Palaeos.com, this may describe only some, basal, Chondrichthyans. I really don’t know my fish anatomy very well.)
As Allen says. Check this for a clear example https://c1.staticflickr.com/8/7297/12518507975_b52d44a876_b.jpg