Do all of the largest-bodied ungulates have disproportionate mouthparts?

Ungulates (https://en.wikipedia.org/wiki/Ungulate) range in body size from 1.5 kilograms (https://en.wikipedia.org/wiki/Java_mouse-deer) to perhaps 15 tonnes (https://en.wikipedia.org/wiki/Paraceratherium).

This is an astonishing range of ten thousand-fold, for mammals sharing unguligrade locomotion, in which the animals have

hooves (including Hippopotamidae, https://www.shutterstock.com/it/image-photo/detailed-front-view-hippo-foot-over-1052002556 and https://www.pinterest.com.au/pin/304907837245600064/ and https://www.flickr.com/photos/laimafideal/3327153962), and/or
only two digits on each foot (as in Camelidae, https://www.gettyimages.in/detail/photo/camel-toes-royalty-free-image/137784743?adppopup=true and https://www.istockphoto.com/photo/camel-hooves-gm1331638964-414720291?phrase=camel+hoof and https://www.gettyimages.in/detail/photo/camels-hoof-close-up-royalty-free-image/1069841060?adppopup=true and https://www.gettyimages.in/detail/news-photo/emiratis-are-seen-behind-the-feet-of-camels-competing-in-a-news-photo/502463822?adppopup=true and https://www.gettyimages.in/detail/photo/foot-of-camel-royalty-free-image/a0148-000292?adppopup=true and scroll in https://stichtingdalel.org/en/the-camel/).

Please consider the allometry of the mouthparts of herbivores (https://research.wur.nl/en/publications/why-elephant-have-trunks-and-giraffe-long-tongues-how-plants-shap and https://www.researchgate.net/publication/272239184_Why_elephant_have_trunks_and_giraffe_long_tongues_How_plants_shape_large_herbivore_mouth_morphology and https://www.wur.nl/en/Publication-details.htm?publicationId=publication-way-343836393733 and https://www.semanticscholar.org/paper/Why-elephant-have-trunks-and-giraffe-long-tongues%3A-PretoriusBoer/bccd09c31c16d355369bff0aeb4911aaa8c7237a).

Also please see https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1749-4877.2012.00315.x and https://www.researchgate.net/publication/236183185_Structural_and_functional_comparison_of_the_proboscis_between_tapirs_and_other_extant_and_extinct_vertebrates.

Allometry is basically the study of variable proportionality (https://en.wikipedia.org/wiki/Allometry). As animals evolve from small to large, their proportions must change, in order to remain biologically viable.

This is because of the laws of physics - beginning with the principle that, as objects get bigger, their volume rapidly outpaces their surface-area (https://en.wikipedia.org/wiki/Surface-area-to-volume_ratio#:~:text=The%20surface%2Darea%2Dto%2D,object%20or%20collection%20of%20objects.).

In this Post, I explore the idea that, as the body size of ungulates increases evolutionarily, a threshold is reached at a body mass of about 500 kg in adult females.

Beyond this body mass, herbivores may become subject to a profound disadvantage in foraging. This is theoretically compensated for by means of various modifications, combining

extension of the mouthparts or neck, and
anatomical 'baffles' that discriminate against fibrous items.

The basic problem is that large items in the vegetation - which are a natural fit for large mouths - tend to be indigestible and nutrient-poor. An elephant-size ungulate, if 'normal' in shape, would tend to be relegated to a diet of wood and straw, which are not fit to eat in the first place.

As ungulates are scaled up, the mouth is, by default, correspondingly scaled up. The trouble with this is that large items in the vegetation tend to be too fibrous, nutrient-poor, and poor in digestible energy to sustain any ungulate.

If a megaherbivore was merely 'a small herbivore writ large', it would have a mouth too gross, clumsy, and slow-moving to select, at a sufficient rate, the palatable items in the vegetation, which tend to be small items.

Therefore, the foraging anatomy must theoretically be 'boggled', to maintain the rate at which suitably small and rich items can be procured.

This allometric principle leads to the predictions that

most ungulates weighing more than 500 kg will have mouthparts modified in ways not seen in small to medium-size ungulates, and
those small ungulates possessing aberrant mouthparts will prove to use these mainly for purposes other than foraging.

THE RELEVANCE OF ELEPHANTS

Proboscideans, the largest extant herbivores, are not ungulates.

However, they set an extreme in anatomical modification for foraging rapidly and selectively for relatively rich items such as shoots.

The proboscidean proboscis is derived from a seamless union of nose and upper lip. This proboscis combines extreme extension, flexibility, and dexterity, partly substituting for shortness of the neck in elephants.

The tip of the proboscis is, effectively, a pair of lips, mounted on a 'neck' so mobile that there is a virtually 'chimaeric' effect: a gross animal has a fine mechanism for the procurement of food, attached to its face.

The incisors and canine teeth of elephants are unrecognisably modified, or lost altogether.

Extant elephants are also surprisingly capable of bipedal standing (https://www.treehugger.com/worlds-tallest-land-animals-4869723), allowing them to reach even higher into the crowns of trees than their extended proboscides would suggest.

No ungulate, extant or extinct, rivals proboscideans in the extent and degree of modification of the anatomy relevant to foraging. However, I attempt, as follows, to assess the various allometric modifications that the largest-bodied ungulates do exhibit.

RHINOCEROTIDAE (https://en.wikipedia.org/wiki/Rhinoceros)

Ceratotherium: broadened lips and loss of incisors and canine teeth
Diceros: prehensile upper lip and loss of incisors and canine teeth
Rhinoceros: less modified than the above, in association with...

TAPIRIDAE

Tapirus indicus is marginal to this topic, because females average less than 500 kg. However, it possesses a small proboscis, of a type different from that of proboscideans. The anterior dentition is hardly reduced (https://upload.wikimedia.org/wikipedia/commons/f/fb/Tapirus_indicus_02_MWNH_374.jpg and https://upload.wikimedia.org/wikipedia/commons/0/05/Skulls_of_a_Malayan_tapir_%28Tapirus_indicus%29_and_a_Sumatran_rhinoceros_%28Dicerorhinus_sumatrensis%29%2C_Lee_Kong_Chian_Natural_History_Museum%2C_Singapore_-_20150808.jpg and https://www.skullsunlimited.com/products/replica-malayan-tapir-skull-tq-96).

HIPPOPOTAMIDAE

Hippopotamus: broadened lips and extreme modification of incisors and canine teeth in ways that make these teeth superfluous in foraging

https://www.sciencedirect.com/science/article/abs/pii/S0304380003003053

https://onlinelibrary.wiley.com/doi/10.1111/mam.12056

https://www.semanticscholar.org/paper/Aquatic-foraging-by-Hippopotamus-in-Za%C3%AFre%3A-Response-Mugangu-M.-HUNTER/65e1b4ae82296e5600e513f646cbd7f8d8e4689c and https://www.degruyter.com/document/doi/10.1515/mamm.1992.56.3.345/html?lang=en

GIRAFFIDAE

Extant species of Giraffa qualify, because body mass of adult females about 800 kg

Giraffa:

extremely long neck,
extremely extensile, semi-prehensile tongue, and
extremely tight mouth

CAMELIDAE

Camelus: body mass of adult females approaches 500 kg.

The mouthparts are somewhat modified for foraging, mainly in the form of

large, flexible lips (https://www.alamy.com/stock-photo-read-my-lips-camel-head-close-up-97792901.html?imageid=8609C1D7-40D3-42B3-8F2F-F543758F0183&p=289162&pn=1&searchId=e186aae61ba59c89d1650e85d6883dc5&searchtype=0 and https://www.usatoday.com/story/news/nation/2018/01/24/camels-disqualified-saudi-arabia-beauty-pageant-using-botox/1060842001/ and https://www.freeimages.com/photo/smiling-camel-1385079) and
an extremely developed philtrum, separating the left from the right upper lip (https://www.asergeev.com/pictures/archives/zb.htm and https://www.dreamstime.com/stock-photo-closeup-camel-tooth-mouth-face-front-focusing-which-jumps-out-image73304655 and https://www.dreamstime.com/camel-israel-desert-funny-close-up-camel-israel-desert-funny-image176757292 and https://www.dreamstime.com/camel-israel-desert-funny-close-up-image176753911).

The neck is also unusually long for ungulates, allowing wide scope from side to side and from ground-level to ?4 m high (https://www.researchgate.net/figure/Browse-line-at-camel-height-observed-on-Santalum-acuminatum-in-the-survey-area-in-2003_fig4_272493512 and https://www.researchgate.net/figure/Browse-line-at-camel-height-observed-on-Brachychiton-gregorii-along-the-Anne-Beadell_fig3_272493512).

BOVIDAE

Bovini (https://www.inaturalist.org/observations?place_id=any&taxon_id=846321&view=species):

The only extant forms of bovin bovids that, on average, surpass 500 kg in adult females are Bubalus arnee (https://www.inaturalist.org/taxa/74125-Bubalus-arnee) and Bos gaurus (https://www.inaturalist.org/taxa/74111-Bos-gaurus), both of which live on the Indian subcontinent.

In the case of Bison, no extant species qualifies. The closest is Bison bison athabascae, in which the average body mass for adult females approaches 500 kg.

However, several extinct species of Bison were more massive than the extant species, and thus qualify.

The situation is similar in the case of genus Syncerus. The extant species, Syncerus caffer, fails to qualify, because the mean body mass for adult females is somewhat less than 500 kg. However, the extinct Syncerus antiquus qualified (https://en.wikipedia.org/wiki/Syncerus_antiquus).

The lips and teeth of the largest-bodied bovins seem unremarkable, relative to less massive bovids.

The lips are noticeably broader in Bubalus than in Bison or Bos gaurus. However, this is not extreme.

It is possible that, in Bubalus, the tongue is as important as in Bos taurus, or more so, in being extensile and raspy, thus routinely sweeping grass into the mouth (https://www.shutterstock.com/it/video/clip-1098214151-thai-buffalo-grazing-green-grass).

If so, it may be the case that the tongue is extreme relative to all other bovids, as well as cervids.

The foraging methods of B. gaurus do not seem to have been documented.

The mouth of B. gaurus seems unremarkable (https://www.pond5.com/stock-footage/item/111939767-gaur-faces-camera-tadoba-andhari-tiger and https://www.pond5.com/stock-footage/item/145383265-close-face-indian-bison-gaur-gimbal-shot and https://www.pond5.com/stock-footage/item/74671091-close-portrait-indian-gaur-bison and https://www.pond5.com/stock-footage/item/73798916-close-female-indian-gaur-bison-standing-and-chewing-food and https://www.pond5.com/stock-footage/item/72928780-close-portrait-indian-gaur-bison-male and https://www.shutterstock.com/it/video/clip-26765767-indian-gaur-bison-female-jawing-bright-painted).

However, the following show that, even when B. taurus grazes short, green grass, the tongue is used (https://www.shutterstock.com/it/video/clip-1054995428-many-gaur-on-hill-natural-forest-khao and https://www.shutterstock.com/it/video/clip-1055819996-gaurs-eating-grass-on-mountains-khao-yai and https://www.shutterstock.com/it/video/clip-1054995176-gaur-herd-on-hill-natural-forest-khao).

Bison is remarkable for the extreme elevation of the withers (https://www.gettyimages.in/detail/news-photo/photo-shows-a-reproduction-of-a-seven-feet-tall-bison-who-news-photo/51660123?adppopup=true
), plus an outsize head. This may be crucial for foraging in snow, when the large head acts as a sweep for snow, efficiently uncovering the grass below.

However, this disproportionality of the head is a feature of males, more than females.

In summary, if there is something extraordinary about the foraging anatomy of the largest-bodied bovins, it is probably the extensile, raspy tongue, which van be used for grazing 'bulk-and-roughage' as well as fairly short grass.

CERVIDAE

Alces:

falls short of the criterion, because the greatest body mass recorded for females is 490 kg (https://en.wikipedia.org/wiki/Moose)

However, deserves consideration because it is the largest extant member of a major family of artiodactyls

The only species of deer in which adult females certainly weighed more, in average, than 500 kg is Cervalces latifrons (https://en.wikipedia.org/wiki/Cervalces_latifrons).

Would it be far-fetched to suggest that perhaps the females lf Cervalces possessed antlers, and that these were used to break branches while foraging?

Madoqua:

Saiga:

Litocranius:

Posted on Μάιος 07, 2023 0133 ΜΜ by

milewski

Do all of the largest-bodied ungulates have disproportionate mouthparts?

Σχόλια

Προσθήκη σχόλιου