Interpreting the buccal semet of the pronghorn

The pronghorn (Antilocapra americana) has an odd-looking mouth.

It also has an oddly graphic pattern of colouration at the mouth (see https://www.inaturalist.org/observations/74523202), which I suggest we call a buccal semet in view of its potential function of accentuating movements of the mouth as part of social communication within the species.

The mouth of the adult male is shown in https://www.featheredphotography.com/blog/2013/08/28/odd-growths-on-the-face-of-a-pronghorn/.

That of the adult female is shown in https://www.endangered.org/saving-the-sonoran-pronghorn-will-help-save-us/.

And https://www.zooborns.com/.a/6a010535647bf3970b01538fdcdd79970b-popup shows that this is the first feature of adult colouration to develop in the infant.

The fact that there is a crisp dark/pale pattern at the mouth can be explained in terms of the mutual monitoring of cud-chewing among group-members.

Many deer and bovids have comparable patterns although the precise design is unique to the pronghorn. Keeping an eye out for any interruption of rumination in companions could signify alarm, because any individual noticing potential danger immediately interrupts the 'white noise' of the chewing to listen up in the appropriate direction.

However, what remains odd about this species is that the pattern at the mouth is so black-and-white and so consistent regardless of age, sex, season, and individuality - which affect other features, both large- and small-scale, of the colouration of the pronghorn.

Most other ruminants have subtle, not stark, versions of the buccal semet (e.g. see https://www.gettyimages.com.au/detail/photo/chewing-buck-royalty-free-image/1252898190?adppopup=true, for Aepyceros melampus).

A possible explanation lies in a behavioural oddity of the pronghorn, which moves its lips in ways still poorly understood. Lip-smacking is certainly a social signal, given e.g. when the male is about to copulate.

However, compulsive lip-trembling is the really odd behaviour. Mueller-Schwarze and Mueller-Schwarze in 1972 wrote: "After sniffing materials such as crushed grass, rotten apples and the cud of deer, pronghorn of both sexes move their lips rhythmically at a rate of 150/minute for a long period, sometimes for longer than 20 minutes. During that period they may show interest in food...but are unable to eat. When put in the mouth the food falls out again".

Why would the pronghorn signify to group-members the discovery of bacterial odours in such an extreme way?

Publicado el domingo, 23 de mayo de 2021 a las 11:46 PM por milewski milewski

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Illustration of buccal semet in Raphicerus campestris:

https://www.inaturalist.org/observations/80251823

Anotado por milewski hace más de un año

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