Skull-optics in ungulates, part 2

In part 1, we saw that the eyes of the pronghorn are both wider-set and proportionately bigger than those of the Balearic Islands cave goat. Now what about ungulates in which the eyes are extremely big but not particularly wide-set, and vice versa?

The common eland (Taurotragus oryx) and the grey rhebok (Pelea capreolus) rival the pronghorn in having exceptionally big eyes for ruminants. However, these eyes are not noticeably wide-set.

In the case of the common eland (the eyeballs of which I have myself measured), this is partly explained by a tendency for nocturnal activity. However, the grey rhebok is diurnal, apparently achieving some degree of rear vision without the protection of the orbits seen in the pronghorn.

Taurotragus oryx

https://www.alamy.com/stock-photo-eland-antelope-close-up-portrait-masai-mara-kenya-57613476.html
https://www.alamy.com/portrait-of-an-taurotragus-oryx-a-large-eland-antelope-also-known-as-southern-antelope-image348380230.html

https://www.alamy.com/stock-photo-common-eland-tragelaphus-oryx-rserve-de-bandia-senegal-31330477.html
https://www.iol.co.za/news/south-africa/kwazulu-natal/iconic-species-now-vulnerable-11250012

https://skullsandskinsforsale.com/product/eland-antelope-on-skull/
https://www.africancraftsmarket.com/products/african-animal-horns-skulls/Eland-skull.html
https://www.zoochat.com/community/media/education-building-common-eland-skull-taurotragus-oryx-2019-09-15.471708/
https://www.the-saleroom.com/en-gb/auction-catalogues/tennants-auctioneers/catalogue-id-2715248/lot-4459884

Pelea capreolus

https://www.shutterstock.com/nb/image-photo/closeup-female-grey-rhebok-southern-africa-446945287
http://blueduiker.com/product/rhebok-grey-vaal-xl-0003
https://www.facebook.com/craniatescuriosities/posts/1-day-auction-rare-vaal-rhebok-skulllast-up-for-auction-today-is-this-uncommon-v/2762723097308229/

The wapiti (Cervus canadensis), which does not seem to be strictly diurnal (https://bioone.org/journals/folia-zoologica/volume-66/issue-4/fozo.v66.i4.a4.2017/Activity-patterns-and-spatial-co-occurrence-of-sympatric-mammals-in/10.25225/fozo.v66.i4.a4.2017.full), presents the converse puzzle: extremely wide-set but not particularly big eyes.

https://www.dreamstime.com/stare-fight-elk-cherokee-north-carolina-stare-fight-elk-field-cherokee-north-carolina-spring-closeup-image220726388
https://www.pikist.com/free-photo-xcgyk

https://stock.adobe.com/fi/search?k=rehkopf&asset_id=179109544
https://www.alamy.com/wapiti-elk-deer-cervus-elaphus-canadensis-portrait-of-a-cow-germany-schleswig-holstein-district-steinburg-image281729692.html

https://www.hideandfur.com/inventory/5157.html
https://www.dinosaursrocksuperstore.com/products/american-elk-skull
https://www.skullsunlimited.com/products/replica-american-elk-skull-tq-191
https://www.skeletonsandskullssuperstore.com/product/american-elk-skull-replica/

Nobody seems to have measured the eyes of goats (genus Capra), either wild or domestic. It is obvious in photos that wild species of goats share wide-set eyes with the wapiti. The proportional size of the eyes of wild goats is harder to assess, but they seem big. If so, wild goats are similar to the pronghorn in a combination typical of open environments. And in this case there may be no adaptive anomaly, given that the incidence of carnivores in the last ten thousand years has been greater in Eurasia than in the Americas.

Capra nubiana:
https://www.alamy.com/stock-photo-nubian-ibex-young-male-portrait-82191245.html
https://www.alamy.com/stock-photo-israel-negev-outskirts-of-kibbutz-sde-boker-nubian-ibex-capra-ibex-18783208.html

Capra ibex:
https://www.alamy.com/stock-photo-portrait-of-a-young-alpine-ibex-capra-ibex-this-wild-goat-is-also-98082225.html
https://www.alamy.com/stock-image-alpine-ibex-capra-ibex-young-female-standing-on-meadow-niederhorn-160326155.html
https://www.alamy.com/stock-photo-alpine-ibex-capra-ibex-adult-female-close-up-of-head-niederhorn-swiss-52965984.html
https://www.alamy.com/stock-photo-mammal-brown-144551969.html
https://www.alamy.com/stock-photo-female-capricorn-frontal-144145144.html
https://www.alamy.com/female-pregnant-ibex-capra-ibex-on-the-rock-italian-alps-image69772970.html

Capra sibirica:
https://antlershornsandskulls.co.uk/product/siberian-ibex-horns-and-skull-ahs10/

Posted on August 24, 2021 04:16 AM by milewski