A bit on Jacks/Carangidae and Hyperostosis
I don't have too terribly much to say, other than to share some Carangidae tilly bone pictures and information I found in a fossil book and give a little appreciation to the family of the tilly bones I found!
First, some interesting facts from "Swollen bones in jacks and relatives (Teleostei: Acanthomorphata: Carangidae)" by Bruno Chanet (https://www.researchgate.net/publication/324224115_Swollen_bones_in_jacks_and_relatives_Teleostei_Acanthomorphata_Carangidae)
- Tilly bones are more frequent in Cutlassfish/Trichiuridae, Drums/Sciaenidae and Jacks/Carangidae, species, but are most frequent in Jacks
- The bone overgrowth in jacks appears "with increasing specimen size", and so is found in larger and older fish.
- No one really knows why Jacks have such frequent occurrence of tilly bones, or what function they serve.
Also wanted to share an interesting case of Jack hyperostosis being able to help distinguish different species and even help distinguish where an individual is from within the species Caranx hippos:
Review of the crevalle jacks, Caranx hippos complex (Teleostei: Carangidae), with a description of a new species from West Africa
And here is a Caranx hippos observation I've added to the project which displays hyperostosis on some of its vertebral spines:
https://www.inaturalist.org/observations/22355795
Now, here are the findings from The Fossil Vertebrates of Florida, edited by Richard C. Hulbert, Jr.:
And here are my tilly bones (https://www.inaturalist.org/observations/117684821), vertebra from an unidentified species of jack:
I find it interesting the hyperostosis is, until I cleaned them up in peroxide, more darkly colored than the rest of the vertebra. Reminds me of these observations, which I suspect might be jack as well:
https://www.inaturalist.org/observations/109648741
https://www.inaturalist.org/observations/109640167
In Chanet's "Swollen bones in jacks and relatives", it is mentioned that the hyperostosis in jack skeletons is a different material than the rest of the bone, specifically that "hyperostosic structures are truly scattered islands of cellular bone in a skeleton otherwise characterized by acellular bony tissue".
(A little bit on cellular vs acellular here: https://austhrutime.com/bone.htm)
Is that possibly why the coloration difference? They're different tissue? I certainly don't know enough about the nuances of these different type of bone structures to make any sort of educated guess, but I'm curious if that's a possible explanation.
See another jack observation with hyperostostis on the vertebral spines, albeit less obvious, this Silver Trevally:
https://www.inaturalist.org/observations/3750457
Apologies for any misinterpretations or inaccurate information, I am open to and grateful for any corrections. I like osteology a lot, but only as a hobby. I'm a complete amateur with no formal education in the subject, and most of my more dedicated exploration of the field is with comparative avian osteology. So I'm sure my ignorance shows here, I'm mostly just curious when it comes to tilly bones and I don't want to give the impression I'm knowledgeable on the subject, just casually interested.
