Why are manes fully-developed at birth in giraffids?

Giraffids look odd compared to deer and bovids, with their long necks, long tongues, skin-covered horns, and extreme colouration (https://www.dreamstime.com/royalty-free-stock-images-giraffe-butt-image14173949 and https://es.123rf.com/photo_97882739_okapi-close-up-detail.html). However, an unremarked oddness of giraffids is the precociality of their manes.

Manes occur on the nuchal region (i.e. the dorsal surface of the neck) in various mammals including Carnivora (http://diversityofanimalsandplants.weebly.com/maned-wolf.html), suids (https://safarihuntingafrica.com/project/warthog/), tapirs (https://www.stockfreeimages.com/10352184/Funny-tapir.html), equids (https://es.123rf.com/photo_16460957_zebra-mane-close-up.html), and various ruminants (https://www.greatbigcanvas.com/view/male-black-wildebeest-calling-mountain-zebra-national-park-south-africa,2403179/).

Various adaptive functions of manes remain to be studied, but an obvious one is to exaggerate body size, particularly in masculine display. Those ruminants in which both sexes have horns also tend to have nuchal manes, consistent with an antagonistic theme.

In the few ungulates in which hornless/antlerless females possess manes, these are raised in defensive anger (https://www.alamy.com/stock-photo-cow-moose-defends-her-newly-born-calf-from-the-grant-creek-wolf-pack-75290283.html), again consistent with a theme of antagonistic exaggeration of body size.

These patterns do not apply to giraffes, in which the nuchal mane is proportionately largest at birth, smaller in adult females, and smallest in mature males.

Let us examine Giraffa giraffa giraffa for example:

infants:
https://es.123rf.com/photo_85501756_a-very-young-baby-southern-south-african-giraffe.html
https://es.123rf.com/photo_85501759_a-very-young-baby-southern-south-african-giraffe.html
https://www.robertharding.com/preview/764-6139/baby-cape-giraffe-giraffa-camelopardalis-giraffa-kruger-national/

adult females:
http://www.africanreferencephotos.com/photo/3952/Giraffe-Female-in-Profile.html

juvenile males:
https://www.istockphoto.com/photo/young-male-giraffe-walking-savute-chobe-np-botswana-gm176053405-10245077

mature males:
https://www.alamy.com/stock-photo-cape-giraffe-adult-kruger-nationalpark-south-africa-africa-giraffa-98140864.html
https://www.independent.co.uk/news/world/africa/giraffe-headbutt-death-carlos-carvalho-filmmaker-south-africa-glen-afric-broederstroom-a8339616.html

Turning to Giraffa tippelskirchi tippelskirchi, the following shows the differences between infants and adult females. Note that the mane becomes proportionately smaller with age but the occipital horn-tufts (see https://www.inaturalist.org/journal/milewski/59906-occipital-horn-tufts-a-previously-overlooked-feature-of-certain-giraffes#) show the opposite trend, being proportionately smaller in infants than in adults: https://www.istockphoto.com/photo/giraffe-mother-and-calf-serengeti-national-park-tanzania-africa-gm618728448-107737387?utm_source=unsplash&utm_medium=affiliate&utm_campaign=srp_photos_top&utm_content=https%3A%2F%2Funsplash.com%2Fs%2Fphotos%2Fbaby-giraffe&utm_term=baby%20giraffe%3A%3A%3A.

Two other tracts of dorsal pelage are also proportionately largest at birth in giraffes.

The first is the main horn-tufts. The following show that, for example in Giraffa tippelskirchi, the main horn-tufts are proportionately larger in infants than in adult females:
https://www.dreamstime.com/stock-illustration-female-giraffe-baby-savannah-kenya-tanzania-east-africa-excellent-illustration-image78918560 and https://fineartamerica.com/featured/close-up-of-a-baby-giraffe-giraffa-animal-images.html and https://www.dreamstime.com/stock-photo-adorable-baby-giraffe-looking-silly-tufts-surrounded-foliage-kenya-s-masai-mara-image80848245 and https://www.dreamstime.com/stock-photography-african-giraffe-image3991832.

The following show Giraffa giraffa: https://www.dreamstime.com/stock-photography-baby-giraffe-image17651562 and https://www.dreamstime.com/giraffe-baby-kruger-national-park-giraffe-baby-kruger-national-park-south-africa-image180808850.

The second is a caudal mane. Giraffa tippelskirchi and Giraffa giraffa possess a slight mane on the tail-stalk, which is most noticeable at birth, when the tail-tassel is still small:
https://www.inaturalist.org/observations/102135119 and https://www.dreamstime.com/stock-photo-masai-giraffe-calf-walking-young-across-savanna-nairobi-national-park-kenya-nairobi-skyline-background-image83751771 and https://www.dreamstime.com/stock-photo-mother-baby-giraffe-going-walk-camelopardalis-than-weeks-old-as-still-has-its-umbilical-cord-attached-image68333446 and https://www.dreamstime.com/stock-images-standing-tall-image622554.

The following shows, in summary, that in newborns of Giraffa tippelskirchi the nuchal and caudal manes are proportionately large, in keeping with the main horn-tufts but not in keeping with the tail-tassel: https://fineartamerica.com/featured/newborn-masai-giraffe-harold-garrard.html.

It remains unknown why, in adaptive terms, manes are precocial - as well as why the main horn-tufts are precocial whereas the occipital horn-tufts are not. However, it is noteworthy that none of these feature of the pelage, other than the tail-tassel, remains noticeable in mature males.

The okapi (Okapi johnstoni, https://en.wikipedia.org/wiki/Okapi) has a hardly-noticeable mane. However, in this species again the nuchal mane is fully developed at birth, disappearing in juveniles (https://www.zooborns.com/.a/6a010535647bf3970b0240a48578ab200d-popup).

I can summarise the main puzzle pointed out in this Post by means of the following two photos. Please compare the relative sizes of the mane in this infant https://sciencing.com/baby-giraffes-8632947.html and this mature male https://www.alamy.com/stock-photo-giraffe-in-etosha-namibias-largest-game-park-in-africa-19177272.html.

Lähettänyt milewski milewski, 22. marraskuuta 2021 23:37

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Lähettänyt milewski noin 2 kuukautta sitten (Lippu)

To see an individual infant of Giraffa tippelskirchi with particularly well-developed main horn-tufts, please scroll down to the fifth photo in https://www.biologicaldiversity.org/publications/earthonline/endangered-earth-online-no993.html. These are likely to be larger than in adults not only relative to the sizes of the body and head, but also in absolute terms.

Lähettänyt milewski noin 1 kuukausi sitten (Lippu)

the following shows how small the tail-tassel can be in infants: https://www.gettyimages.ie/detail/photo/giraffe-legs-royalty-free-image/126239269?adppopup=true.

Lähettänyt milewski noin 1 kuukausi sitten (Lippu)
Lähettänyt milewski noin 1 kuukausi sitten (Lippu)

one of the best illustrations of the caudal mane: https://www.inaturalist.org/observations/54688347

Lähettänyt milewski noin 1 kuukausi sitten (Lippu)

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