Casque Anatomy

[mstocker]

Dear Chameleon friends,

Does anyone know about the anatomy of the casques in various species? In the veiled chameleon (and others) it is a bone arbor - sort of like a cage. What is it filled with? Is it a fatty lipid, or does it have good blood circulation?

I am asking not as a chameleon keeper, but as a naturalists looking at the possible function of this grand feature. Any ideas?

I have some ideas having to do with bio-acoustics, but the type of tissue would help clarify what it might be.

Thanks in advance for your thoughts!

Michael

 

[Chris Anderson]

Michael,

The structure of the casque is made up of bone. The center ridge is the parietal bone, the rear sides are the squamosal bones, and the base toward the eyes are the postorbitofrontal bones. The space between the bones is filled primarily with jaw adductor muscles (the muscles responsible for closing the mouth and bite force). The enlarged casque serves a sexual selection and specific recognition function, but also serves to increase the force they are able to bite with.

Chris

 

[ataraxia]

The space between the bones is filled primarily with jaw adductor muscles (the muscles responsible for closing the mouth and bite force). The enlarged casque serves a sexual selection and specific recognition function, but also serves to increase the force they are able to bite with.

Chris

I did not know that this is the area responsible for jaw strength. Very interesting.

Im glad this topic has come about as i have had questions about this also.

If you dont mind me asking another. With veileds, after good hydration sessions the casque becomes much thicker like the occipital flaps on a melleri. Is this space also "storage" for a lack of a better term or is the tissue itself being hydrated causing it to become thicker?

 

[Chris Anderson]

The enlarged casque serves a sexual selection and specific recognition function, but also serves to increase the force they are able to bite with.

Sorry, that should say "..sexual selection and species recognition...".

I did not know that this is the area responsible for jaw strength. Very interesting.

Im glad this topic has come about as i have had questions about this also.

If you dont mind me asking another. With veileds, after good hydration sessions the casque becomes much thicker like the occipital flaps on a melleri. Is this space also "storage" for a lack of a better term or is the tissue itself being hydrated causing it to become thicker?

Yeah, the increased surface for jaw adductor muscles to attach on the casque and the increased space to store the muscle bodies because of the increased space increases bite force. C. calyptratus has very high bite force for its size, for instance.

The casque and temporal region of the skull definitely gets sunken in, just like the eyes, with poor hydration and will fill back in with proper hydration. To the best of my knowledge this is just a hydration effect of the tissue, but I've not looked at it.

Chris

 

[Kmw]

Interesting indeed. If I didn't want to get bit by my veiled before, I sure don't now.

 

[Kent67]

Chris,

Michael emailed both Jared and myself about this and was wondering if we could point him towards any published resources. I haven't had a chance to look around yet so I'll just forward his email to you in case you have any further thoughts...

 

[absolutbill]

This is quite interesting to know, thanks for sharing your knowledge, Chris!

 

[Chris Anderson]

The best articles on the muscles of the casque is probably:

Rieppel, O. 1981. The skull and jaw adductor musculature in chamaeleons. Revue Suisse de Zoologie 88 (2): 433-445.
Rieppel, O. 1987. The phylogenetic relationships within the Chamaeleonidae, with comments on some aspects of cladistics analysis. Zoological Journal of the Linnean Society 89 (1): 41-62.

Chris

 

[mstocker]

Thanks Chris!

With all of that muscle mass these fellows must pack a nasty bite! I was initially speculating that the casque might provide some mass for the transmittal of substrate-borne tremulation - acoustical energy transmitted into the branches that they are perched on. But when I saw the cage-like form I had a second thought that it may include an acoustical lipid found in the hearing system of dolphins, elephants, and alligators.

That they do not have a a tympanic membrane or and oval window supports an acoustical lipid as a transmission path. What is the "free-floating end of the pterygoid bone" floating in?

It is quite possible that the dominant acoustical transmission path for these critters is through the substrate (hearing as well as communicating). This would support an acoustical lipid component to their hearing so any auditory threshold testing using exclusively air-borne acoustical stimulus would yield poor results.

Thanks for the reference papers, unfortunately I don't have subscriptions for these journals. Are any open-source?

Also is your UC Press chapter available to look at? If not, when will the book be published?

Thanks again for your direction on this.

Michael

 

[Chris Anderson]

A bunch of what Michael is responding to has to do with my email reply to him based on what he asked Kent (including some questions about whether the casque could have auditory function), so I'm posting my email to him below to make sure no one is left behind in what's going on as I think a bunch of you may find some of it interesting.

Hi Michael,

Kent forwarded me your email. I wanted to let you know that I answered some of your questions on the thread you posted on ChameleonForums (https://www.chameleonforums.com/casque-anatomy-92124/).

I just finished writing a book chapter on anatomy for University of California Press for a book on the biology of chameleons, so I'm pretty familiar with the anatomy of the casque, as well as the chameleon's sound perception abilities. Chameleons in general have pretty poor hearing. They lack a tympanic membrane with some species instead using a ligament attached to the membrane at the end of the free-floating end of the pterygoid bone (the pterygoid wing) in the temporal region of the skull as a substitute. They also lack traditional round windows making transduction of vibratory signals to the inner ear difficult and dampened.

Here are a few articles on the casque, casque musculature and ear of chameleons that may interest you:

Rieppel, O. 1981. The skull and jaw adductor musculature in chamaeleons. Revue Suisse de Zoologie 88 (2): 433-445.

Rieppel, O. 1987. The phylogenetic relationships within the Chamaeleonidae, with comments on some aspects of cladistics analysis. Zoological Journal of the Linnean Society 89 (1): 41-62.

Wever, E.G. 1968. The ear of the chameleon: Chamaeleo senegalensis and Chamaeleo quilensis. Journal of Experimental Zoology 168 (4): 423-436.

Wever, E.G. 1969a. The ear of the chameleon: the round window problem. Journal of Experimental Zoology 171: 1-5.

Wever, E.G. 1969b. The ear of the chameleon: Chamaeleo höhnelii and Chamaeleo jacksoni. Journal of Experimental Zoology 171 (3): 305-312.

Chris

As for your most recent post:

To the best of my knowledge the pterygoid wing and the membrane that continues off of it is surrounded by muscle, but I don't think anyone has looked at whether there could be an acoustical lipid presence in the area. Most of the auditory tests have focused on airborn sounds, although it is known that chameleons produce substrate vibrations. It has been much more recently that these vibrations that they produce were shown to be substrate vibrations used in copulation and intraspecific signaling, and possibly as a predator response. It has been presumed that these substrate vibrations are detected like snakes, however, through the jaw and quadrate. I wouldn't be surprised, however, if there were a means to amplify such signals.

The book chapter has gone through external review and revision but is now with the editors for final collection with the other chapters to send out to the publishers. It should be published some time next year.

Chris

 

[mstocker]

Substrate tremulations

The tremulation topic came up about ten years ago from work done by Kenneth Barnett:

Barnett, Kenneth E., Reginald B. Cocroft, and Leo J. Fleishman. “Possible Communication by Substrate Vibration in a Chameleon.” Herp Beat, May, 1999. Vol. 10, Issue 5,.

I noticed that the papers you've cited are a somewhat older, so the physiology would be informative, but if there was no discussion of tremulation at that time some of the features may have been overlooked.

Transmission of sound by way of acoustical lipids is also a more recent inquiry:

Heather Koopman, Suzanne Budge, Darlene Ketten, Sara Iverson “The Influence of Phylogeny, Ontogeny and Topography on the Lipid Composition of the Mandibular Fats of Toothed Whales: Implications for Hearing” 2003 Paper delivered at the Environmental Consequences of Underwater Sound conference, May 2003.

I am noticing this acoustical lipid system in a lot of animals and it would be interesting (and quite possible given the acoustical environment of the chameleon) that they may have some similar adaptation in their hearing

 

[zwhitman]

Do any species use the casque to direct rain/dew to the mouth? My veiled seems like he uses it for that when his misting system goes on.